Abstract 2393: Characterization and validation of a Smad3/TGFb pathway reporter mouse for analysis of TGFβ signaling in normal homeostasis and cancer

TGFβs play a central regulatory role in maintaining homeostasis in the adult animal, and dysregulation of TGFβ signaling occurs in many cancers. Consequently, TGFβ pathway antagonists are now in early phase clinical oncology trials, but surprisingly little is known about when and where the TGFβ pathway is activated in the adult animal. We recently generated a TGFβ pathway reporter mouse in which expression of eGFP is driven by an enhancer consisting of 6 repeats of a strong Smad3 binding element (S3x6>GFP reporter), knocked into the ROSA26 locus. Here we present further characterization of the founder line (“Lime” mouse). Whole body fluorescent imaging of an adult mouse highlighted Smad3 activation in the expected tissues, such as the gastrointestinal tract, costal cartilage, and brown adipose tissue among others. Unexpectedly, intercrossing the Lime mouse with a Smad3 germline knockout mouse did not reveal a significant reduction in signal. However, since Smad3 knockout mice survive to adulthood despite having no Smad3, the persistence of signal could reflect compensatory signaling through other Smads, such as Smad1/5 or the Smad3-like Smad2 splice variant, Smad2DelEx3. Alternatively, the reporter may not report with fidelity in the chromatin context of the ROSA26 locus. To address these alternatives, Lime mice were intercrossed with the MMTV-PyVT model of mammary tumorigenesis. Mammary tumors showed high reporter activity, and a mammary tumor cell line (“LimePyVT”) was derived for characterization. Reporter activity in LimePyVT cells was enhanced by TGFβ and reduced by TGFβ receptor kinase inhibitors, but not by a BMP kinase inhibitor, as expected. Reduction in reporter signal with TGFβ receptor kinase inhibitors was only seen with prolonged treatment and 2x daily redosing, likely reflecting both the long half-life of the GFP (1-2 days), and the high sensitivity of the reporter to breakthrough signaling. siRNA knockdown in LimePyVT cells ex vivo confirmed that GFP reporter expression is dependent on Smad3 and Smad4. In other validation experiments, multicolor immunofluorescence showed heterogeneous reporter activity in the normal mammary epithelium, with highest activity in ER+ cells, where TGFβ is most active. Normal mammary epithelial cells were FACS-sorted into GFP-high and GFP-low fractions. RNASeq and pathway analysis showed TGFβ to be the top upstream regulator of the GFP-high cell transcriptome, consistent with the reporter reflecting TGFβ pathway activation. Overall, we believe that the high sensitivity of the reporter and the long GFP half-life likely mean that it will not report accurately on the impact of TGFβ antagonists in vivo. However, this reporter mouse should be a useful tool to assess the cellular location and extent of TGFβ/activin pathway activation during tumor progression, and the transcriptomic consequences.

Citation Format: Yuan Yang, Zachary Millman, Christina Stuelten, Madhu Gargesha, Mark Simpson, Howard Yang, Maxwell Lee, Lalage M. Wakefield. Characterization and validation of a Smad3/TGFb pathway reporter mouse for analysis of TGFβ signaling in normal homeostasis and cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2393.

Live tumor imaging shows macrophage induction and TMEM-mediated enrichment of cancer stem cells during metastatic dissemination

Cancer stem cells (CSCs) play an important role during metastasis, but the dynamic behavior and induction mechanisms of CSCs are not well understood. Here, we employ high-resolution intravital microscopy using a CSC biosensor to directly observe CSCs in live mice with mammary tumors. CSCs display the slow-migratory, invadopod-rich phenotype that is the hallmark of disseminating tumor cells. CSCs are enriched near macrophages, particularly near macrophage-containing intravasation sites called Tumor Microenvironment of Metastasis (TMEM) doorways. Substantial enrichment of CSCs occurs on association with TMEM doorways, contributing to the finding that CSCs represent >60% of circulating tumor cells. Mechanistically, stemness is induced in non-stem cancer cells upon their direct contact with macrophages via Notch-Jagged signaling. In breast cancers from patients, the density of TMEM doorways correlates with the proportion of cancer cells expressing stem cell markers, indicating that in human breast cancer TMEM doorways are not only cancer cell intravasation portals but also CSC programming sites.

Aging and CNS Myeloid Cell Depletion Attenuate Breast Cancer Brain Metastasis

PURPOSE

Breast cancer diagnosed in young patients is often aggressive. Because primary breast tumors from young and older patients have similar mutational patterns, we hypothesized that the young host microenvironment promotes more aggressive metastatic disease.

EXPERIMENTAL DESIGN

Triple-negative or luminal B breast cancer cell lines were injected into young and older mice side-by-side to quantify lung, liver, and brain metastases. Young and older mouse brains, metastatic and naïve, were analyzed by flow cytometry. Immune populations were depleted using antibodies or a colony-stimulating factor-1 receptor (CSF-1R) inhibitor, and brain metastasis assays were conducted. Effects on myeloid populations, astrogliosis, and the neuroinflammatory response were determined.

RESULTS

Brain metastases were 2- to 4-fold higher in young as compared with older mouse hosts in four models of triple-negative or luminal B breast cancer; no age effect was observed on liver or lung metastases. Aged brains, naïve or metastatic, contained fewer resident CNS myeloid cells. Use of a CSF-1R inhibitor to deplete myeloid cells, including both microglia and infiltrating macrophages, preferentially reduced brain metastasis burden in young mice. Downstream effects of CSF-1R inhibition in young mice resembled that of an aged brain in terms of myeloid numbers, induction of astrogliosis, and Semaphorin 3A secretion within the neuroinflammatory response.

CONCLUSIONS

Host microenvironmental factors contribute to the aggressiveness of triple-negative and luminal B breast cancer brain metastasis. CSF-1R inhibitors may hold promise for young brain metastasis patients.

Abstract 1645: A new TGF-b pathway reporter mouse for analysis of TGF-β signaling in normal homeostasis and cancer

TGF-βs play a central regulatory role in maintaining homeostasis and coordinating response to injury in the adult animal. Consequently, dysregulation of TGF-β signaling has been implicated in many pathological states, including cancer. Several TGF-β pathway antagonists are now in early phase clinical oncology trials. However, surprisingly little is known about when and where the TGF-β pathway is activated in the adult animal. To address this need, we have generated a TGF-β pathway reporter mouse in which the expression of eGFP is driven by an artificial enhancer element consisting of 6 repeats of a strong Smad3 binding element from the distal region of the JunB promoter (S3 × 6>GFP reporter). This reporter was >10x more sensitive in vitro than the commonly used CAGA12-based reporter. The reporter construct was knocked into the mouse ROSA26 locus using CRISPR technology and a founder line was derived. Whole body fluorescent imaging of an adult female mouse highlighted TGF-β pathway activation in the gastrointestinal tract, lymph nodes, costal cartilage, brown adipose tissue, brain ventricles and choroid plexi, among other tissues. Since high dose pharmacologic inhibition of the TGF-β pathway has previously been associated with cardiac valvulopathy in preclinical toxicology studies, we immunostained heart sections from the reporter mouse for GFP and observed high endogenous TGF-β pathway activation in the atrioventricular valve leaflets. Quantitative IVIS fluorescent imaging of isolated organs confirmed TGF-β pathway activation in many different tissues in the normal adult mouse, with the pancreas showing the highest level of endogenous activation. Interestingly, the level of TGF-β pathway activation in different tissues was highly correlated with the frequency of inactivating mutations in TGF-β pathway components in tumors from the corresponding tissue in humans. This observation suggests that a high level of TGF-β pathway activation in normal tissues may reflect a non-redundant tumor suppressor role for the TGF-β pathway in maintaining homeostasis in those tissues. To specifically address the activation state of the TGF-β pathway during tumorigenesis, we intercrossed the S3 × 6>GFP reporter mouse with the MMTV-PyVT mouse model of metastatic breast cancer. Reporter activity was strongly upregulated in mammary tumors when compared with the surrounding mammary gland. Using cells cultured from the primary tumors, we confirmed that the reporter signal in the tumor cells can be blocked by small molecule antagonists of the TGF-β pathway. This reporter mouse should be a useful tool to assess the cellular location and extent of TGF-β pathway activation during tumor development, and the impact of TGF-β antagonists on TGF-β signaling in tumors and normal tissues.

Citation Format: Yu-an Yang, Christina Stuelten, Youngjae Bahn, Ji-Hyeon Lee, Madhu Gargesha, Hibret Adissu, Mark Simpson, Caroline S. Hill, Sushil G. Rane, Lalage M. Wakefield. A new TGF-b pathway reporter mouse for analysis of TGF-β signaling in normal homeostasis and cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1645.

Abstract 372: Macrophage contact-dependent stemness induction and progressive CSC enrichment during metastatic dissemination in breast cancer

Background: Cancer stem cells (CSCs) play an important role during metastatic progression of breast cancer. However, little is known, at the single cell level, about the process of stemness induction in non-stem cells or the dynamic behavior of CSCs during hematogenous dissemination.

Methods: Here, we employed high-resolution intravital multiphoton microscopy with a SOX2/OCT4 responsive fluorescent biosensor for stemness to directly observe the induction of stemness in single non-stem cells and their evolution through the metastatic cascade in living animals using orthotopic breast cancer xenograft model. We confirmed our findings in vitro using tumor cell-macrophage co-culture assays.

Results: We report that, both in vitro and in vivo, direct physical contact with macrophages induces stemness in non-stem cancer cells via juxtacrine Notch-Jagged1 signaling. In vivo, macrophage depletion with clodronate treatment showed a significant decrease in stem cells. In vitro, using either the fate mapping of non-stem cells with or without macrophage contact, or the origin-mapping of stem cells to find whether they originated from non-stem cells or pre-existing stem cells, we found that there was four-fold increase in new CSC induction after direct macrophage contact. In contrast, we did not see any role of macrophages in the expansion of pre-existing CSCs, both in vivo and in vitro, indicating that macrophage contact-dependent stem induction is the primary mechanism of CSC generation.

Using immunohistochemical staining in fixed tissue and live imaging of primary tumors and lungs in mice using optical windows, we found that during the course of dissemination of tumor cells from the primary site, CSCs become progressively enriched in the tumor cell population as they approach dissemination doorways (known as TMEM, Tumor MicroEnvironment of Metastasis), intravasate, circulate and arrive at the lung. Association with and passage through TMEM doorways is the step that generates the greatest enrichment in CSCs (~ 60-fold). On arrival in the lung, CSCs represent more than 75% of the disseminated tumor cell population, greatly enriched compared with their representation in the bulk primary tumor of ~ 1%.

Conclusion: Overall, these data indicate, for the first time, that macrophages associated with TMEM induce CSCs and promote TMEM-mediated CSC intravasation and early metastatic seeding. Our results are consistent with the dramatic enrichment of cancer stem cell markers in association with TMEM in breast cancer patients (Kim et al 2020 AACR abstract) and support a strategy for anti-metastatic therapy.

Citation Format: Ved P. Sharma, Yarong Wang, Binwu Tang, George S. Karagiannis, Emily A. Xue, David Entenberg, Lucia Borriello, Anouchka Coste, Joan G. Jones, Chinmay R. Surve, Dominic Esposito, Maja H. Oktay, Lalage M. Wakefield, John S. Condeelis. Macrophage contact-dependent stemness induction and progressive CSC enrichment during metastatic dissemination in breast cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 372.

Peptidylarginine Deiminase IV Regulates Breast Cancer Stem Cells via a Novel Tumor Cell-Autonomous Suppressor Role

Peptidylarginine deiminases (PADI) catalyze posttranslational modification of many target proteins and have been suggested to play a role in carcinogenesis. Citrullination of histones by PADI4 was recently implicated in regulating embryonic stem and hematopoietic progenitor cells. Here, we investigated a possible role for PADI4 in regulating breast cancer stem cells. PADI4 activity limited the number of cancer stem cells (CSC) in multiple breast cancer models in vitro and in vivo. Mechanistically, PADI4 inhibition resulted in a widespread redistribution of histone H3, with increased accumulation around transcriptional start sites. Interestingly, epigenetic effects of PADI4 on the bulk tumor cell population did not explain the CSC phenotype. However, in sorted tumor cell populations, PADI4 downregulated expression of master transcription factors of stemness, NANOG and OCT4, specifically in the cancer stem cell compartment, by reducing the transcriptionally activating H3R17me2a histone mark at those loci; this effect was not seen in the non-stem cells. A gene signature reflecting tumor cell-autonomous PADI4 inhibition was associated with poor outcome in human breast cancer datasets, consistent with a tumor-suppressive role for PADI4 in estrogen receptor-positive tumors. These results contrast with known tumor-promoting effects of PADI4 on the tumor stroma and suggest that the balance between opposing tumor cell-autonomous and stromal effects may determine net outcome. Our findings reveal a novel role for PADI4 as a tumor suppressor in regulating breast cancer stem cells and provide insight into context-specific effects of PADI4 in epigenetic modulation. SIGNIFICANCE: These findings demonstrate a novel activity of the citrullinating enzyme PADI4 in suppressing breast cancer stem cells through epigenetic repression of stemness master transcription factors NANOG and OCT4.

SOD2 acetylation on lysine 68 promotes stem cell reprogramming in breast cancer

Mitochondrial superoxide dismutase (SOD2) suppresses tumor initiation but promotes invasion and dissemination of tumor cells at later stages of the disease. The mechanism of this functional switch remains poorly defined. Our results indicate that as SOD2 expression increases acetylation of lysine 68 ensues. Acetylated SOD2 promotes hypoxic signaling via increased mitochondrial reactive oxygen species (mtROS). mtROS, in turn, stabilize hypoxia-induced factor 2α (HIF2α), a transcription factor upstream of "stemness" genes such as Oct4, Sox2, and Nanog. In this sense, our findings indicate that SOD2K68Ac and mtROS are linked to stemness reprogramming in breast cancer cells via HIF2α signaling. Based on these findings we propose that, as tumors evolve, the accumulation of SOD2K68Ac turns on a mitochondrial pathway to stemness that depends on HIF2α and may be relevant for the progression of breast cancer toward poor outcomes.

The Outcome of TGFβ Antagonism in Metastatic Breast Cancer Models In Vivo Reflects a Complex Balance between Tumor-Suppressive and Proprogression Activities of TGFβ

PURPOSE

TGFβs are overexpressed in many advanced cancers and promote cancer progression through mechanisms that include suppression of immunosurveillance. Multiple strategies to antagonize the TGFβ pathway are in early-phase oncology trials. However, TGFβs also have tumor-suppressive activities early in tumorigenesis, and the extent to which these might be retained in advanced disease has not been fully explored.

EXPERIMENTAL DESIGN

A panel of 12 immunocompetent mouse allograft models of metastatic breast cancer was tested for the effect of neutralizing anti-TGFβ antibodies on lung metastatic burden. Extensive correlative biology analyses were performed to assess potential predictive biomarkers and probe underlying mechanisms.

RESULTS

Heterogeneous responses to anti-TGFβ treatment were observed, with 5 of 12 models (42%) showing suppression of metastasis, 4 of 12 (33%) showing no response, and 3 of 12 (25%) showing an undesirable stimulation (up to 9-fold) of metastasis. Inhibition of metastasis was immune-dependent, whereas stimulation of metastasis was immune-independent and targeted the tumor cell compartment, potentially affecting the cancer stem cell. Thus, the integrated outcome of TGFβ antagonism depends on a complex balance between enhancing effective antitumor immunity and disrupting persistent tumor-suppressive effects of TGFβ on the tumor cell. Applying transcriptomic signatures derived from treatment-naïve mouse primary tumors to human breast cancer datasets suggested that patients with breast cancer with high-grade, estrogen receptor-negative disease are most likely to benefit from anti-TGFβ therapy.

CONCLUSIONS

Contrary to dogma, tumor-suppressive responses to TGFβ are retained in some advanced metastatic tumors. Safe deployment of TGFβ antagonists in the clinic will require good predictive biomarkers.

Epigenetic re-wiring of breast cancer by pharmacological targeting of C-terminal binding protein

The C-terminal binding protein (CtBP) is an NADH-dependent dimeric family of nuclear proteins that scaffold interactions between transcriptional regulators and chromatin-modifying complexes. Its association with poor survival in several cancers implicates CtBP as a promising target for pharmacological intervention. We employed computer-assisted drug design to search for CtBP inhibitors, using quantitative structure-activity relationship (QSAR) modeling and docking. Functional screening of these drugs identified 4 compounds with low toxicity and high water solubility. Micro molar concentrations of these CtBP inhibitors produces significant de-repression of epigenetically silenced pro-epithelial genes, preferentially in the triple-negative breast cancer cell line MDA-MB-231. This epigenetic reprogramming occurs through eviction of CtBP from gene promoters; disrupted recruitment of chromatin-modifying protein complexes containing LSD1, and HDAC1; and re-wiring of activating histone marks at targeted genes. In functional assays, CtBP inhibition disrupts CtBP dimerization, decreases cell migration, abolishes cellular invasion, and improves DNA repair. Combinatorial use of CtBP inhibitors with the LSD1 inhibitor pargyline has synergistic influence. Finally, integrated correlation of gene expression in breast cancer patients with nuclear levels of CtBP1 and LSD1, reveals new potential therapeutic vulnerabilities. These findings implicate a broad role for this class of compounds in strategies for epigenetically targeted therapeutic intervention.

Abstract 972: Direct observation in living tumors shows macrophage-dependent induction and dissemination of cancer stem cells in breast cancer

Cancer stem cells (CSCs) play an important role during metastatic progression of breast cancer. However, the in vivo properties and dynamic behavior of CSCs are not well understood. Here, we employed high-resolution intravital multiphoton microscopy using a SOX2/OCT4 responsive fluorescent stem cell biosensor to directly observe CSC dynamics in the living animal using an orthotopic breast cancer xenograft model. We report that CSCs constitute a minority population (1-3%) in the primary tumors, and display the slow-migratory, invasive phenotype that is specifically associated with disseminating tumor cell population. We also report, for the first time, that CSCs are preferentially localized in direct contact with macrophages near and in tumor microenvironment of metastasis (TMEM) sites, the macrophage-containing intravasation doorway for tumor cells and that CSCs metastasize to lung and are strikingly enriched in early lung metastatic colonies. This is explained by our observation that, in vitro and in vivo, direct physical contact with macrophages induces stemness in non-stem cancer cells via juxtacrine Notch-Jagged1 signaling. These data indicate for the first time that macrophages play an actively inductive role in the CSC niche and promote TMEM-mediated CSC intravasation and early metastatic seeding.

Citation Format: Ved P. Sharma, Yarong Wang, Binwu Tang, George S. Karagiannis, Emily A. Xue, David Entenberg, Lucia Borriello, Anouchka Coste, Chinmay R. Surve, Dominic Esposito, Maja H. Oktay, Lalage M. Wakefield, John S. Condeelis. Direct observation in living tumors shows macrophage-dependent induction and dissemination of cancer stem cells in breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 972.

Abstract 3676: Novel tumor suppressive role of Peptidylarginine deiminase IV involving cancer stem cell regulation in breast cancer models

Breast cancer accounts for >500,000 deaths annually worldwide. Despite therapeutic advances, treated patients often relapse with metastases. Emerging research indicates that relapse may be driven by a subpopulation of tumor cells termed cancer stem cells (CSCs), that are uniquely capable of self-renewal and have enhanced drug resistance. Understanding the properties of these CSCs is critical for development of more effective therapies. Peptidyl arginine deiminase 4 (PADI4) is an enzyme that catalyzes deimination of arginine to citrulline. Citrullination of histones modulates expression of key stem cell transcription factors in embryonic stem cells (Christophorou, et al., 2014, Nature 507:104), so we hypothesized that PADI4 could be involved in CSC regulation. We showed that PADI4 mRNA and protein are expressed at varying levels across a panel of breast cancer cell lines, and we knocked down PADI4 in two high expressing lines, MCF10Ca1h and MDAMB231-LM2. PADI4 knockdown did not alter tumor cell proliferation in vitro, but it enhanced migration and invasion and increased cell survival. Importantly, PADI4 knockdown increased clonogenicity and enhanced tumorsphere formation, suggesting that it specifically increases the CSC population. In vivo studies showed higher tumor initiation efficiency following PADI4 knockdown, and increased lung metastasis. PADI4 is predicted to have multiple isoforms with unknown biological activity that complicate PADI4 expression-based analysis in patient data sets. We circumvented this issue by pharmacologically inhibiting PADI4 in MCF10Ca1h to generate a transcriptomic signature reflecting PADI4 gene activity. This PADI4 gene activity signature was shown to correlate with lower tumor grade and better disease outcome in transcriptomic datasets from human ER+ breast cancers. In conclusion, our findings suggest that PADI4 functions as a tumor suppressor in breast cancer, in part through effects on the CSC.

Citation Format: Humberto J. Ochoa, Nellie Moshkovich, Binwu Tang, Howard H. Yang, Maxwell P. Lee, Lalage M. Wakefield. Novel tumor suppressive role of Peptidylarginine deiminase IV involving cancer stem cell regulation in breast cancer models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3676.

The transcription factor CBFB suppresses breast cancer through orchestrating translation and transcription

Translation and transcription are frequently dysregulated in cancer. These two processes are generally regulated by distinct sets of factors. The CBFB gene, which encodes a transcription factor, has recently emerged as a highly mutated driver in a variety of human cancers including breast cancer. Here we report a noncanonical role of CBFB in translation regulation. RNA immunoprecipitation followed by deep sequencing (RIP-seq) reveals that cytoplasmic CBFB binds to hundreds of transcripts and regulates their translation. CBFB binds to mRNAs via hnRNPK and enhances translation through eIF4B, a general translation initiation factor. Interestingly, the RUNX1 mRNA, which encodes the transcriptional partner of CBFB, is bound and translationally regulated by CBFB. Furthermore, nuclear CBFB/RUNX1 complex transcriptionally represses the oncogenic NOTCH signaling pathway in breast cancer. Thus, our data reveal an unexpected function of CBFB in translation regulation and propose that breast cancer cells evade translation and transcription surveillance simultaneously through downregulating CBFB.

CBFB is highly mutated in breast cancers and is known to interact with RUNX proteins to regulate transcription. Here, the authors describe a non-canonical role of CBFB in translation regulation in which it binds to mRNAs through hnRNPK, facilitating translation by eIF4B.

Abstract 1768: An anti-TGF-β1/2 antibody that spares TGF-β3 retains full anti-tumor efficacy and generates an improved metabolic profile

TGF-β family members are overexpressed in many advanced cancers and correlate with metastasis and poor prognosis. Based on encouraging preclinical data, therapeutics that target the TGF-β pathway are now in early phase clinical trials in oncology. While the three isoforms of TGF-β have essentially identical activities in vitro, there is relatively little known about how they might differ in vivo. Using a panel of twelve mouse allograft models of metastatic breast cancer, we showed that while TGF-β1 protein was consistently up-regulated in mammary tumors compared with normal mammary gland, the opposite was true for TGF-β3. Furthermore, in human breast cancer high TGF-β3 mRNA or protein expression was associated with better outcome, particularly in estrogen-receptor positive breast cancers. Collectively the data suggest that TGF-β1 and TGF-β3 may have opposing effects on breast cancer progression. Using an antibody that selectively neutralizes only TGF-β1 and TGF-β2, we explored the effect of sparing TGF-β3 on therapeutic outcome in the 4T1 and TSAE1 models of metastatic breast cancer. While the TGFβ1,2 antibody and two pan-TGF-β antibodies had similar efficacy against the metastasis endpoint in these very aggressive models, transcriptomic analysis of primary tumors after two weeks of antibody therapy suggested that sparing TGF-β3 might have positive effects on the metabolic profile of treated animals. To address this issue directly, we showed that mice without tumors had a significantly improved glucose tolerance following treatment with anti-TGF-β1/2 antibodies for 2-3 weeks when compared with mice treated with pan-TGF-β antibodies. Addressing potential human relevance, we showed that high expression of transcripts that were selectively upregulated in the primary tumors when TGF-β3 was spared correlated with good outcome in human breast cancer. The data suggest that use of isoform-selective TGF-β antagonists may offer advantages over the use of pan-TGF-β blocking agents for the treatment of breast cancer.

Citation Format: Yu-an Yang, Srividya Vasu, Howard Yang, Maxwell P. Lee, Sushil Rane, Amer M. Mirza, Lalage M. Wakefield. An anti-TGF-β1/2 antibody that spares TGF-β3 retains full anti-tumor efficacy and generates an improved metabolic profile [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1768.

Quantitation of TGF-β proteins in mouse tissues shows reciprocal changes in TGF-β1 and TGF-β3 in normal vs neoplastic mammary epithelium

Transforming growth factor-βs (TGF-βs) regulate tissue homeostasis, and their expression is perturbed in many diseases. The three isoforms (TGF-β1, -β2, and -β3) have similar bioactivities in vitro but show distinct activities in vivo. Little quantitative information exists for expression of TGF-β isoform proteins in physiology or disease. We developed an optimized method to quantitate protein levels of the three isoforms, using a Luminex® xMAP®-based multianalyte assay following acid-ethanol extraction of tissues. Analysis of multiple tissues and plasma from four strains of adult mice showed that TGF-β1 is the predominant isoform with TGF-β2 being ~10-fold lower. There were no sex-specific differences in isoform expression, but some tissues showed inter-strain variation, particularly for TGF-β2. The only adult tissue expressing appreciable TGF-β3 was the mammary gland, where its levels were comparable to TGF-β1. In situ hybridization showed the luminal epithelium as the major source of all TGF-β isoforms in the normal mammary gland. TGF-β1 protein was 3-8-fold higher in three murine mammary tumor models than in normal mammary gland, while TGF-β3 protein was 2-3-fold lower in tumors than normal tissue, suggesting reciprocal regulation of these isoforms in mammary tumorigenesis.

Abstract 1846: Immunocompetent mouse allograft models for development of therapies to target breast cancer metastasis therapies to target breast cancer metastasis

Effective drug development to combat metastatic disease in breast cancer would be aided by the availability of well-characterized preclinical animal models that (a) metastasize with high efficiency, (b) metastasize in a reasonable time-frame, (c) have an intact immune system, and (d) capture some of the heterogeneity of the human disease. To address these issues, we have assembled a panel of twelve mouse mammary cancer cell lines that can metastasize efficiently on implantation into syngeneic immunocompetent hosts. Genomic characterization shows that more than half of the 30 most commonly mutated genes in human breast cancer are represented within the panel. Transcriptomically, most of the models fall into the luminal A or B intrinsic molecular subtypes, despite the predominance of an aggressive, poorly-differentiated or spindled histopathology in all models. Patterns of immune cell infiltration, proliferation rates, apoptosis and angiogenesis differed significantly among models. Inherent within-model variability of the metastatic phenotype mandates large cohort sizes for intervention studies but may also capture some relevant non-genetic sources of variability. The varied molecular and phenotypic characteristics of this expanded panel of models should aid in model selection for development of anti-metastatic therapies in vivo, and serve as a useful platform for predictive biomarker identification.

Citation Format: Yu-an Yang, Howard Yang, Ying Hu, Peter Watson, Huaitian Liu, Thomas R. Geiger, Miriam R. Anver, Diana Haines, Philip Martin, Maxwell P. Lee, Kent W. Hunter, Lalage M. Wakefield. Immunocompetent mouse allograft models for development of therapies to target breast cancer metastasis therapies to target breast cancer metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1846. doi:10.1158/1538-7445.AM2017-1846

Prosurvival long noncoding RNA PINCR regulates a subset of p53 targets in human colorectal cancer cells by binding to Matrin 3

Thousands of long noncoding RNAs (lncRNAs) have been discovered, yet the function of the vast majority remains unclear. Here, we show that a p53-regulated lncRNA which we named PINCR (p53-induced noncoding RNA), is induced ~100-fold after DNA damage and exerts a prosurvival function in human colorectal cancer cells (CRC) in vitro and tumor growth in vivo. Targeted deletion of PINCR in CRC cells significantly impaired G1 arrest and induced hypersensitivity to chemotherapeutic drugs. PINCR regulates the induction of a subset of p53 targets involved in G1 arrest and apoptosis, including BTG2, RRM2B and GPX1. Using a novel RNA pulldown approach that utilized endogenous S1-tagged PINCR, we show that PINCR associates with the enhancer region of these genes by binding to RNA-binding protein Matrin 3 that, in turn, associates with p53. Our findings uncover a critical prosurvival function of a p53/PINCR/Matrin 3 axis in response to DNA damage in CRC cells.

DOI:http://dx.doi.org/10.7554/eLife.23244.001

Though DNA contains the information needed to build the proteins that keep cells alive, only 2% of the DNA in a human cell codes for proteins. The remaining 98% is referred to as non-coding DNA. The information in some of these non-coding regions can still be copied into molecules of RNA, including long molecules called lncRNAs. Little is known about what lncRNAs actually do, but growing evidence suggests that these molecules are important for a number of vital processes including cell growth and survival.

When the DNA in an animal cell gets damaged, the cell needs to decide whether to pause growth and repair the damage, or to kill itself if the harm is too great. One of the best-studied proteins guiding this decision is the p53 protein, which increases the number of protein-coding genes needed to carry out either option in this decision. That is to say that, p53 regulates the genes needed to kill the cell and the genes needed to temporarily pause its growth and repair the damage, which instead keeps the cell alive. So, how does the p53 protein guide the decision, and are lncRNA molecules involved?

Using human colon cancer cells, Chaudhary et al. now report that when DNA is damaged, the levels of a specific lncRNA increase 100-fold. Further experiments showed that this lncRNA – named PINCR, which refers to p53-induced noncoding RNA – promotes the survival of cells. Chaudhary et al. showed that PINCR molecules do this by recruiting a protein called Matrin 3 to a certain region in the DNA called an enhancer and then links it to promoter region in the DNA of specific genes that temporarily pause cell growth but keep the cell alive. This in turn activates these ‘pro-survival genes’. In further experiments, when the PINCR molecules were essentially deleted, p53 was not able to fully activate these genes and as a result more of the cells died.

Together these findings increase our knowledge of how lncRNAs can work, especially in the context of DNA damage in cancer cells. A next important step will be to uncover other roles for the PINCR molecule in both cancer and healthy cells.

DOI:http://dx.doi.org/10.7554/eLife.23244.002

Immunocompetent mouse allograft models for development of therapies to target breast cancer metastasis

Effective drug development to combat metastatic disease in breast cancer would be aided by the availability of well-characterized preclinical animal models that (a) metastasize with high efficiency, (b) metastasize in a reasonable time-frame, (c) have an intact immune system, and (d) capture some of the heterogeneity of the human disease. To address these issues, we have assembled a panel of twelve mouse mammary cancer cell lines that can metastasize efficiently on implantation into syngeneic immunocompetent hosts. Genomic characterization shows that more than half of the 30 most commonly mutated genes in human breast cancer are represented within the panel. Transcriptomically, most of the models fall into the luminal A or B intrinsic molecular subtypes, despite the predominance of an aggressive, poorly-differentiated or spindled histopathology in all models. Patterns of immune cell infiltration, proliferation rates, apoptosis and angiogenesis differed significantly among models. Inherent within-model variability of the metastatic phenotype mandates large cohort sizes for intervention studies but may also capture some relevant non-genetic sources of variability. The varied molecular and phenotypic characteristics of this expanded panel of models should aid in model selection for development of antimetastatic therapies in vivo, and serve as a useful platform for predictive biomarker identification.

Regulation of Head and Neck Squamous Cancer Stem Cells by PI3K and SOX2

Background

We have an incomplete understanding of the differences between cancer stem cells (CSCs) in human papillomavirus-positive (HPV-positive) and -negative (HPV-negative) head and neck squamous cell cancer (HNSCC). The PI3K pathway has the most frequent activating genetic events in HNSCC (especially HPV-positive driven), but the differential signaling between CSCs and non-CSCs is also unknown.

Methods

We addressed these unresolved questions using CSCs identified from 10 HNSCC patient-derived xenografts (PDXs). Sored populations were serially passaged in nude mice to evaluate tumorigenicity and tumor recapitulation. The transcription profile of HNSCC CSCs was characterized by mRNA sequencing, and the susceptibility of CSCs to therapy was investigated using an in vivo model. SOX2 transcriptional activity was used to follow the asymmetric division of PDX-derived CSCs. All statistical tests were two-sided.

Results

CSCs were enriched by high aldehyde dehydrogenase (ALDH) activity and CD44 expression and were similar between HPV-positive and HPV-negative cases (percent tumor formation injecting ≤ 1x10(3) cells: ALDH(+)CD44(high) = 65.8%, ALDH(-)CD44(high) = 33.1%, ALDH(+)CD44(high) = 20.0%; and injecting 1x10(5) cells: ALDH(-)CD44(low) = 4.4%). CSCs were resistant to conventional therapy and had PI3K/mTOR pathway overexpression (GSEA pathway enrichment, P < .001), and PI3K inhibition in vivo decreased their tumorigenicity (40.0%-100.0% across cases). PI3K/mTOR directly regulated SOX2 protein levels, and SOX2 in turn activated ALDH1A1 (P < .001 013C and 067C) expression and ALDH activity (ALDH(+) [%] empty-control vs SOX2, 0.4% ± 0.4% vs 14.5% ± 9.8%, P = .03 for 013C and 1.7% ± 1.3% vs 3.6% ± 3.4%, P = .04 for 067C) in 013C and 067 cells. SOX2 enhanced sphere and tumor growth (spheres/well, 013C P < .001 and 067C P = .04) and therapy resistance. SOX2 expression prompted mesenchymal-to-epithelial transition (MET) by inducing CDH1 (013C P = .002, 067C P = .01), followed by asymmetric division and proliferation, which contributed to tumor formation.

Conclusions

The molecular link between PI3K activation and CSC properties found in this study provides insights into therapeutic strategies for HNSCC. Constitutive expression of SOX2 in HNSCC cells generates a CSC-like population that enables CSC studies.

Immune-mediated pathology in Duchenne muscular dystrophy

Immunological and inflammatory processes downstream of dystrophin deficiency as well as metabolic abnormalities, defective autophagy, and loss of regenerative capacity all contribute to muscle pathology in Duchenne muscular dystrophy (DMD). These downstream cascades offer potential avenues for pharmacological intervention. Modulating the inflammatory response and inducing immunological tolerance to de novo dystrophin expression will be critical to the success of dystrophin-replacement therapies. This Review focuses on the role of the inflammatory response in DMD pathogenesis and opportunities for clinical intervention.

Abstract B13: Targeting the TGF-β pathway in breast cancer: Insights from preclinical studies

Overexpression of transforming growth factor-βs (TGF-βs) correlates with metastasis and poor prognosis in many advanced cancers, and TGF-βs have pro-oncogenic effects on nearly every cell type in the ecosystem of advanced tumors. Based on these observations and encouraging results in preclinical models, strategies to block TGF-β signaling are in early phase clinical oncology trials. To date however, preclinical studies supporting the development of anti-TGF-β therapeutics in cancer have focused around a few well-characterized mouse models which do not capture the heterogeneity of the human disease. To address this issue for breast cancer, we have assembled a panel of transplantable mouse models of metastatic mammary cancer that can be used in fully immunocompetent hosts, so as to preserve any immune contributions to therapeutic efficacy. Hormone receptor status, histopathological characteristics and intrinsic subtype of the models were assessed. Using this panel of models, we tested the efficacy of a pan-TGF-β neutralizing antibody (1D11) in inhibiting lung metastasis. We observed therapeutic efficacy or trend to efficacy in 5 models (InhibMet), no effect in 2 models (NoEff) and an undesirable stimulation or trend to stimulation of metastasis in 4 models (StimMet). This heterogeneity in therapeutic responses suggests that it will be critical to develop good predictive biomarkers for patient selection in clinical trials using TGF-β antagonists. Since the model panel provides an excellent platform for biomarker discovery, we have performed transcriptomics on untreated primary tumors across the panel, as well as completing full exome gDNA sequencing and copy number variant analysis on the tumor cell lines. The relationship between response-to-therapy and mutation load will be presented. Analyses of the untreated primary tumors show that the tumor transcriptomes segregate by response to anti-TGF-β therapy in principal component analysis, after removal of mouse strain as a confounding factor. Encouragingly for biomarker development, this observation suggests that there are major pre-existing differences in the biology of InhibMet and StimMet primary tumors before they are treated. A gene signature generated from the differentially expressed gene list was strongly associated with outcome in a metaanalysis of human breast cancer datasets, suggesting human relevance. Ingenuity Pathway Analysis of differentially-expressed genes indicates that InhibMet models are characterized by higher TGF-β pathway activation, higher angiogenesis, poor immune cell infiltration/activation, and other markers of tumor aggressiveness such as higher tumor cell proliferation and survival. Interestingly, the higher TGF-β pathway activation that was strongly predicted in the InhibMet tumors by the transcriptomic analyses (p=5.8e-25) was not evident from a multipronged quantitative proteomics assessment of activation of canonical Smad signaling, or non-canonical signaling through Akt, Erk, Jnk or p38MAPK pathways. Thus steady-state signaling by TGF-β in tumors in vivo may represent the integrated sum of the activities of more downstream signaling pathways than were captured in this analysis, or additional information about the intracellular localization of the phospho-forms of the signaling proteins and/or the identity of interacting proteins may be necessary to fully assess the activation state of the pathway. Despite these caveats, the data suggest that TGF-β antagonists will have therapeutic efficacy in more aggressive, poor prognosis breast cancers, and suggest that it will be possible to generate molecular signatures that predict the therapeutic response.

Citation Format: Yu-an Yang, Kathleen Flanders, Jin-qui Chen, Anand S. Merchant, Howard Yang, Maxwell P. Lee, Lalage M. Wakefield. Targeting the TGF-β pathway in breast cancer: Insights from preclinical studies. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Breast Cancer Research; Oct 17-20, 2015; Bellevue, WA. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(2_Suppl):Abstract nr B13.

Growth differentiation factor-15 encodes a novel microRNA 3189 that functions as a potent regulator of cell death

According to the latest version of miRBase, approximately 30% of microRNAs (miRNAs) are unique to primates, but the physiological function of the vast majority remains unknown. In this study, we identified miR-3189 as a novel, p53-regulated, primate-specific miRNA embedded in the intron of the p53-target gene GDF15. Antagonizing miR-3189 increased proliferation and sensitized cells to DNA damage-induced apoptosis, suggesting a tumor suppressor function for endogenous miR-3189. Identification of genome-wide miR-3189 targets revealed that miR-3189 directly inhibits the expression of a large number of genes involved in cell cycle control and cell survival. In addition, miR-3189 downregulated the expression of multiple p53 inhibitors resulting in elevated p53 levels and upregulation of several p53 targets including p21 (CDKN1A), GADD45A and the miR-3189 host gene GDF15, suggesting miR-3189 auto-regulation. Surprisingly, miR-3189 overexpression in p53-/- cells upregulated a subset of p53-targets including GDF15, GADD45A, and NOXA, but not CDKN1A. Consistent with these results, overexpression of miR-3189 potently induced apoptosis and inhibited tumorigenicity in vivo in a p53-independent manner. Collectively, our study identified miR-3189 as a novel, primate-specific miRNA whose effects are mediated by both p53-dependent and p53-independent mechanisms. miR-3189 may, therefore, represent a novel tool that can be utilized therapeutically to induce a potent proapoptotic effect even in p53-deficient tumors.

Abstract 2221: Transforming Growth Factor-beta (TGF-β) directly regulates breast cancer stem cell dynamics in vitro and in vivo

Many tumors consist of a hierarchy of cells with different proliferative and developmental potentials. A small number of cancer stem cells (CSCs) give rise to a larger population of highly proliferative, committed progenitor cells, which may then undergo limited differentiation. Importantly CSCs are uniquely capable of initiating and sustaining tumorigenesis, and they have been implicated in driving disease recurrence after cancer therapy. In order to be able to assess stem cell behavior in real-time at a single cell rather than a population level, we have developed and validated a novel lentiviral-based reporter system for direct visualization, quantitation and isolation of cells with CSC properties. The construct consists of a tandemly-repeated composite SOX2-OCT4 response element (“SORE6”) driving expression of a destabilized green fluorescent protein reporter. Using the human MCF10CA1h breast cancer cell line, we have shown that SORE6-GFP+ cells within the cell population are relatively undifferentiated and enriched for stem cell markers. These cells can self-renew and regenerate SORE6-GFP- cells, show enhanced asymmetric division, and are enriched for tumorigenesis and resistance to chemotherapeutics in vivo. We and others have previously suggested that TGF-β can regulate the CSC population with stimulatory or inhibitory effects depending on model. In the MCF10Ca1h breast cancer model, which retains tumor suppressor responses to TGF-β, we hypothesized that endogenous TGF-β suppresses tumorigenesis by direct effects on the CSCs. Using our reporter, we show TGF-β reduces the size of the CSC population and the frequency of asymmetric self-renewing divisions in the MCF10Ca1h model. Although TGF-β had relatively little effect on invasion and migration of the bulk MCF10Ca1h population, it clearly inhibited migration and invasion of the CSCs, suggesting that biological responses to TGF-β can vary depending on the position of the cell in the differentiation hierarchy. Combining our stem cell reporter with a TGF-β pathway reporter, we show that CSCs have higher endogenous activation of the TGF-β pathway than do the bulk cells, and by time-lapse video microscopy we find that CSCs with active TGF-β signaling are relatively quiescent. Furthermore, neutralization of TGF-β in vivo, leads to an increased representation of CSCs in the MCF10Ca1h tumors. Thus our preliminary results suggest that in breast cancer models where TGF-β acts as a tumor suppressor, TGF-β signaling is preferentially activated in the CSC compartment and may keep a subpopulation of CSCs in a proliferatively quiescent and stationary state.

Citation Format: Binwu Tang, Asaf Raviv, Dominic Esposito, Catherine Daniel, Kathleen C. Flanders, Yu-an Yang, Lalage M. Wakefield. Transforming Growth Factor-beta (TGF-β) directly regulates breast cancer stem cell dynamics in vitro and in vivo. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2221. doi:10.1158/1538-7445.AM2015-2221

Abstract 4094: Neutralizing anti-TGF-β antibodies elicit heterogeneous therapeutic responses in a panel of murine metastatic breast cancer models

Overexpression of transforming growth factor-βs (TGF-βs) correlates with metastasis and poor prognosis in many advanced cancers, and TGF-βs have pro-oncogenic effects on nearly every cell type in the ecosystem of advanced tumors. Based on these observations and encouraging results in preclinical models, strategies to block TGF-β signaling are in early phase clinical oncology trials. To date however, preclinical studies supporting the development of anti-TGF-β therapeutics in cancer have focused around a few well-characterized mouse models which do not capture the heterogeneity of the human disease. To assess the generalizability of these findings within a given tumor type, we have assembled a panel of transplantable mouse models of metastatic breast cancer. Using this panel of models, we tested the efficacy of a pan-TGF-β neutralizing antibody (1D11), against the metastatic endpoint using fully immunocompetent mouse hosts to capture the contribution of anti-tumor immune responses. We observed therapeutic efficacy or trend to efficacy in 5 models (InhibMet), no effect in 2 models (NoEff) and an undesirable stimulation or trend to stimulation of metastasis in 4 models (StimMet). This heterogeneity in therapeutic responses suggests that it will be critical to develop good predictive biomarkers for patient selection in clinical trials using TGF-β antagonists. Plausible candidate biomarkers suggested by the existing literature, such as p53 mutation status, claudin-low status, or TGF-β protein expression, did not correlate with therapeutic response, so we applied integrated genomic discovery approaches to the panel. We find significant differences in patterns of gene expression, gene polymorphism/mutation and copy number variation between the StimMet and InhibMet models. Notably, transcriptomic analyses of the untreated primary tumors show that these segregate by response to therapy in principal component analysis, after removal of mouse strain and tumor origin (spontaneous vs genetically-engineered) as factors. Analysis of differentially-expressed genes suggests that InhibMet models are characterized by higher TGF-β pathway activation, higher angiogenesis, poor immune cell infiltration/activation, and other markers of tumor aggressiveness such as higher tumor cell proliferation and survival. The data point to fundamental differences in tumor biology between the two classes of model and suggest that it will be possible to generate biomarkers that predict therapeutic response to TGF-β pathway antagonists.

Citation Format: Yu-an Yang, Kathleen C. Flanders, Binwu Tang, Miriam R. Anver, Anand Merchant, Howard Yang, Maxwell Lee, Scott Lonning, John M. McPherson, Lalage M. Wakefield. Neutralizing anti-TGF-β antibodies elicit heterogeneous therapeutic responses in a panel of murine metastatic breast cancer models. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4094. doi:10.1158/1538-7445.AM2015-4094

Abstract 2244: Functional interactions between estrogen-related-receptor β (ESRRB) and transforming growth factor-beta (TGF-β) in the regulation of breast cancer stem cell dynamics

Breast cancer is a worldwide problem that accounts for almost a quarter of all cancers in women; however, better therapeutic approaches are required since it is estimated that one to three deaths from overtreatment occur for every one death avoided. Our lab is interested in transforming growth factor beta (TGF-β) signaling and its dual role as tumor suppressor/promoter in breast cancer and its therapeutic applications. We previously performed genome-wide ChIP/Chip analysis to identify TGF-β-activated Smad3 target genes in a model of breast cancer progression. We discovered that the estrogen-related-receptor β (ESRRB) transcription factor binding motif was significantly enriched in Smad3 binding regions in breast cancer cell lines. The data suggested that functional interactions between ESRRB and the TGF-β pathway may influence breast cancer progression. ESRRs (α, β, γ) are members of the nuclear orphan receptor family that share significant homology with the estrogen receptors but are not activated by natural estrogens. Additionally, ESRRB maintains pluripotency in embryonic stem cells (ESCs) and is activated by Wnt signaling to promote self-renewal in ESCs. Thus we hypothesized that mechanistically ESRRB/TGF-β may affect breast cancer progression through effects on cancer stem cell (CSC) dynamics and cancer cell differentiation. We showed that ESRRB protein is overexpressed in human breast cancer compared with matched normal breast tissue, and that high expression of ESRRB colocalizes with the stem cell master regulator OCT4 in human breast cancer xenografts. We performed ESRRB knockdown in the MCF10Ca1h, MCF10Ca1a and MDAMB231 breast cancer cell lines and our data demonstrate that ESRRB opposes the inhibitory effects of TGF-β on CSCs as measured by tumorsphere formation assay, while having little or no effect on proliferation of the bulk tumor cell culture in vitro. More importantly, knockdown of ESRRB reduced the in vivo tumorigenicity of all three breast cancer lines and enhanced their histologic differentiation. Extreme limiting dilution assays in vivo showed that knockdown of ESRRB in MDAMB231 cells caused a 78-fold decrease in the relative number of CSCs. In conclusion, our preliminary findings suggest that ESRRB antagonizes the inhibitory effects of TGF-β on CSCs and breast cancer progression, making ESRRB an attractive therapeutic target whose inhibition can restore the tumor suppressive effects of TGF-β and reduce the tumorigenic breast CSC population.

Citation Format: Nellie Moshkovich, Misako Sato, Binwu Tang, Yu-an Yang, Kathleen C. Flanders, Mitsutaka Kadota, Howard Yang, Maxwell P. Lee, Lalage M. Wakefield. Functional interactions between estrogen-related-receptor β (ESRRB) and transforming growth factor-beta (TGF-β) in the regulation of breast cancer stem cell dynamics. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2244. doi:10.1158/1538-7445.AM2015-2244

Abstract 4940: Role of Smad3 linker phosphorylation in breast cancer progression

Smad3 plays an important role in inhibiting cell proliferation and promoting apoptosis in multiple tissues, including the breast tissue. At late stages, Smad3 promotes breast cancer progression and metastasis. We previously showed that the proline-rich linker region of Smad3 is phosphorylated by several kinases, such as by CDKs and MAP kinases. We have mapped these phosphorylation sites. We show that mutation of the phosphorylation sites in the Smad3 linker region increases the ability of Smad3 to inhibit cell proliferation and promote apoptosis. Interestingly, mutation of the Smad3 linker phosphorylation sites also increases the ability of Smad3 to activate genes that promote metastasis. Accordingly, mutation of the Smad3 linker phosphorylation sites markedly inhibits tumorigenicity but promotes metastasis of breast cancer cell lines. Using human breast cancer tissue microarrays, we further show that Smad3 linker phosphorylation is progressively reduced along breast cancer progression. Taken together, our findings strongly suggest that Smad3 linker phosphorylation promotes tumorigenesis but inhibits metastasis. Our findings have important implications for cancer therapy.

Citation Format: Fang Liu, Wen Xie, Zhengxue Liu, Tanima Roy, Eunjin Bae, Lalage M. Wakefield, Seong-Jin Kim, Akira Ooshima, Michael Reiss, Isao Matsuura. Role of Smad3 linker phosphorylation in breast cancer progression. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4940. doi:10.1158/1538-7445.AM2015-4940

Capillary nano-immunoassays: advancing quantitative proteomics analysis, biomarker assessment, and molecular diagnostics

There is an emerging demand for the use of molecular profiling to facilitate biomarker identification and development, and to stratify patients for more efficient treatment decisions with reduced adverse effects. In the past decade, great strides have been made to advance genomic, transcriptomic and proteomic approaches to address these demands. While there has been much progress with these large scale approaches, profiling at the protein level still faces challenges due to limitations in clinical sample size, poor reproducibility, unreliable quantitation, and lack of assay robustness. A novel automated capillary nano-immunoassay (CNIA) technology has been developed. This technology offers precise and accurate measurement of proteins and their post-translational modifications using either charge-based or size-based separation formats. The system not only uses ultralow nanogram levels of protein but also allows multi-analyte analysis using a parallel single-analyte format for increased sensitivity and specificity. The high sensitivity and excellent reproducibility of this technology make it particularly powerful for analysis of clinical samples. Furthermore, the system can distinguish and detect specific protein post-translational modifications that conventional Western blot and other immunoassays cannot easily capture. This review will summarize and evaluate the latest progress to optimize the CNIA system for comprehensive, quantitative protein and signaling event characterization. It will also discuss how the technology has been successfully applied in both discovery research and clinical studies, for signaling pathway dissection, proteomic biomarker assessment, targeted treatment evaluation and quantitative proteomic analysis. Lastly, a comparison of this novel system with other conventional immuno-assay platforms is performed.

Differential Proteome Analysis Identifies TGF-β-Related Pro-Metastatic Proteins in a 4T1 Murine Breast Cancer Model

Transforming growth factor-β (TGF-β) has a dual role in tumorigenesis, acting as either a tumor suppressor or as a pro-oncogenic factor in a context-dependent manner. Although TGF-β antagonists have been proposed as anti-metastatic therapies for patients with advanced stage cancer, how TGF-β mediates metastasis-promoting effects is poorly understood. Establishment of TGF-β-related protein expression signatures at the metastatic site could provide new mechanistic information and potentially allow identification of novel biomarkers for clinical intervention to discriminate TGF-β oncogenic effects from tumor suppressive effects. In the present study, we found that systemic administration of the TGF-β receptor kinase inhibitor, SB-431542, significantly inhibited lung metastasis from transplanted 4T1 mammary tumors in Balb/c mice. The differentially expressed proteins in the comparison of lung metastases from SB-431542 treated and control vehicle-treated groups were analyzed by a quantitative LTQ Orbitrap Velos system coupled with stable isotope dimethyl labeling. A total of 36,239 peptides from 6,694 proteins were identified, out of which 4,531 proteins were characterized as differentially expressed. A subset of upregulated proteins in the control group was validated by western blotting and immunohistochemistry. The eukaryotic initiation factor (eIF) family members constituted the most enriched protein pathway in vehicle-treated compared with SB-43512-treated lung metastases, suggesting that increased protein expression of specific eIF family members, especially eIF4A1 and eEF2, is related to the metastatic phenotype of advanced breast cancer and can be down-regulated by TGF-β pathway inhibitors. Thus our proteomic approach identified eIF pathway proteins as novel potential mediators of TGF-β tumor-promoting activity.

A flexible reporter system for direct observation and isolation of cancer stem cells

Many tumors are hierarchically organized with a minority cell population that has stem-like properties and enhanced ability to initiate tumorigenesis and drive therapeutic relapse. These cancer stem cells (CSCs) are typically identified by complex combinations of cell-surface markers that differ among tumor types. Here, we developed a flexible lentiviral-based reporter system that allows direct visualization of CSCs based on functional properties. The reporter responds to the core stem cell transcription factors OCT4 and SOX2, with further selectivity and kinetic resolution coming from use of a proteasome-targeting degron. Cancer cells marked by this reporter have the expected properties of self-renewal, generation of heterogeneous offspring, high tumor- and metastasis-initiating activity, and resistance to chemotherapeutics. With this approach, the spatial distribution of CSCs can be assessed in settings that retain microenvironmental and structural cues, and CSC plasticity and response to therapeutics can be monitored in real time.

Definition of smad3 phosphorylation events that affect malignant and metastatic behaviors in breast cancer cells

Smad3, a major intracellular mediator of TGFβ signaling, functions as both a positive and negative regulator in carcinogenesis. In response to TGFβ, the TGFβ receptor phosphorylates serine residues at the Smad3 C-tail. Cancer cells often contain high levels of the MAPK and CDK activities, which can lead to the Smad3 linker region becoming highly phosphorylated. Here, we report, for the first time, that mutation of the Smad3 linker phosphorylation sites markedly inhibited primary tumor growth, but significantly increased lung metastasis of breast cancer cell lines. In contrast, mutation of the Smad3 C-tail phosphorylation sites had the opposite effect. We show that mutation of the Smad3 linker phosphorylation sites greatly intensifies all TGFβ-induced responses, including growth arrest, apoptosis, reduction in the size of putative cancer stem cell population, epithelial-mesenchymal transition, and invasive activity. Moreover, all TGFβ responses were completely lost on mutation of the Smad3 C-tail phosphorylation sites. Our results demonstrate a critical role of the counterbalance between the Smad3 C-tail and linker phosphorylation in tumorigenesis and metastasis. Our findings have important implications for therapeutic intervention of breast cancer.

Brightfield proximity ligation assay reveals both canonical and mixed transforming growth factor-β/bone morphogenetic protein Smad signaling complexes in tissue sections

Transforming growth factor-β (TGF-β) is an important regulator of cellular homeostasis and disease pathogenesis. Canonical TGF-β signaling occurs through Smad2/3–Smad4 complexes; however, recent in vitro studies suggest that elevated levels of TGF-β may activate a novel mixed Smad complex (Smad2/3-Smad1/5/9), which is required for some of the pro-oncogenic activities of TGF-β. To determine if mixed Smad complexes are evident in vivo, we developed antibodies that can be used with a proximity ligation assay to detect either canonical or mixed Smad complexes in formalin-fixed paraffin-embedded sections. We demonstrate high expression of mixed Smad complexes in the tissues from mice genetically engineered to express high levels of TGF-β1. Mixed Smad complexes were also prominent in 15–16 day gestation mouse embryos and in breast cancer xenografts, suggesting important roles in embryonic development and tumorigenesis. In contrast, mixed Smad complexes were expressed at extremely low levels in normal adult mouse tissue, where canonical complexes were correspondingly higher. We show that this methodology can be used in archival patient samples and tissue microarrays, and we have developed an algorithm to quantitate the brightfield read-out. These methods will allow quantitative analysis of cell type-specific Smad signaling pathways in physiological and pathological processes.

An integrated genomic approach identifies persistent tumor suppressive effects of transforming growth factor-β in human breast cancer

Introduction

Transforming growth factor-βs (TGF-βs) play a dual role in breast cancer, with context-dependent tumor-suppressive or pro-oncogenic effects. TGF-β antagonists are showing promise in early-phase clinical oncology trials to neutralize the pro-oncogenic effects. However, there is currently no way to determine whether the tumor-suppressive effects of TGF-β are still active in human breast tumors at the time of surgery and treatment, a situation that could lead to adverse therapeutic responses.

Methods

Using a breast cancer progression model that exemplifies the dual role of TGF-β, promoter-wide chromatin immunoprecipitation and transcriptomic approaches were applied to identify a core set of TGF-β-regulated genes that specifically reflect only the tumor-suppressor arm of the pathway. The clinical significance of this signature and the underlying biology were investigated using bioinformatic analyses in clinical breast cancer datasets, and knockdown validation approaches in tumor xenografts.

Results

TGF-β-driven tumor suppression was highly dependent on Smad3, and Smad3 target genes that were specifically enriched for involvement in tumor suppression were identified. Patterns of Smad3 binding reflected the preexisting active chromatin landscape, and target genes were frequently regulated in opposite directions in vitro and in vivo, highlighting the strong contextuality of TGF-β action. An in vivo-weighted TGF-β/Smad3 tumor-suppressor signature was associated with good outcome in estrogen receptor-positive breast cancer cohorts. TGF-β/Smad3 effects on cell proliferation, differentiation and ephrin signaling contributed to the observed tumor suppression.

Conclusions

Tumor-suppressive effects of TGF-β persist in some breast cancer patients at the time of surgery and affect clinical outcome. Carefully tailored in vitro/in vivo genomic approaches can identify such patients for exclusion from treatment with TGF-β antagonists.

Synergistic antitumor effects of a TGFβ inhibitor and cyclophosphamide

In a mouse model of breast carcinoma, the combination of cyclophosphamide and transforming growth factor β1,2,3 (TGFβ1,2,3)-targeting antibody achieved superior antineoplastic effects. This novel paradigm of synergistic chemoimmunotherapy promises to improve the clinical outcome of cancer patients with micrometastases, and thus deserves further investigation.

A mutant p53/let-7i-axis-regulated gene network drives cell migration, invasion and metastasis

Most p53 mutations in human cancers are missense mutations resulting in a full-length mutant p53 protein. Besides losing tumor suppressor activity, some hotspot p53 mutants gain oncogenic functions. This effect is mediated in part, through gene expression changes due to inhibition of p63 and p73 by mutant p53 at their target gene promoters. Here, we report that the tumor suppressor microRNA let-7i is downregulated by mutant p53 in multiple cell lines expressing endogenous mutant p53. In breast cancer patients, significantly decreased let-7i levels were associated with missense mutations in p53. Chromatin immunoprecipitation and promoter luciferase assays established let-7i as a transcriptional target of mutant p53 through p63. Introduction of let-7i to mutant p53 cells significantly inhibited migration, invasion and metastasis by repressing a network of oncogenes including E2F5, LIN28B, MYC and NRAS. Our findings demonstrate that repression of let-7i expression by mutant p53 has a key role in enhancing migration, invasion and metastasis.

Effective chemoimmunotherapy with anti-TGFβ antibody and cyclophosphamide in a mouse model of breast cancer

TGFβ is reportedly responsible for accumulation of CD4⁺Foxp3⁺ regulatory T cells (Tregs) in tumor. Thus, we treated mouse 4T1 mammary carcinoma with 1D11, a neutralizing anti-TGFβ (1,2,3) antibody. The treatment delayed tumor growth, but unexpectedly increased the proportion of Tregs in tumor. In vitro, 1D11 enhanced while TGFβ potently inhibited the proliferation of Tregs. To enhance the anti-tumor effects, 1D11 was administered with cyclophosphamide which was reported to eliminate intratumoral Tregs. This combination resulted in long term tumor-free survival of up to 80% of mice, and the tumor-free mice were more resistant to re-challenge with tumor. To examine the phenotype of tumor infiltrating immune cells, 4T1-tumor bearing mice were treated with 1D11 and a lower dose of cyclophosphamide. This treatment markedly inhibited tumor growth, and was accompanied by massive infiltration of IFNγ-producing T cells. Furthermore, this combination markedly decreased the number of splenic CD11b⁺Gr1⁺ cells, and increased their expression levels of MHC II and CD80. In a spontaneous 4T1 lung metastasis model with resection of primary tumor, this combination therapy markedly increased the survival of mice, indicating it was effective in reducing lethal metastasis burden. Taken together, our data show that anti-TGFβ antibody and cyclophosphamide represents an effective chemoimmunotherapeutic combination.

Genetic background may contribute to PAM50 gene expression breast cancer subtype assignments

Recent advances in genome wide transcriptional analysis have provided greater insights into the etiology and heterogeneity of breast cancer. Molecular signatures have been developed that stratify the conventional estrogen receptor positive or negative categories into subtypes that are associated with differing clinical outcomes. It is thought that the expression patterns of the molecular subtypes primarily reflect cell-of-origin or tumor driver mutations. In this study however, using a genetically engineered mouse mammary tumor model we demonstrate that the PAM50 subtype signature of tumors driven by a common oncogenic event can be significantly influenced by the genetic background on which the tumor arises. These results have important implications for interpretation of "snapshot" expression profiles, as well as suggesting that incorporation of genetic background effects may allow investigation into phenotypes not initially anticipated in individual mouse models of cancer.

Beyond TGFβ: roles of other TGFβ superfamily members in cancer

Much of the focus on the transforming growth factor-β (TGFβ) superfamily in cancer has revolved around the TGFβ ligands themselves. However, it is now becoming apparent that deregulated signalling by many of the other superfamily members also has crucial roles in both the development of tumours and metastasis. Furthermore, these signalling pathways are emerging as plausible therapeutic targets. Their roles in tumorigenesis frequently reflect their function in embryonic development or in adult tissue homeostasis, and their influence extends beyond the tumours themselves, to the tumour microenvironment and more widely to complications of cancer such as cachexia and bone loss.

Abstract 5484: Heterogeneity of response to anti-TGF-β antibody therapy in preclinical models

TGF-βs are pleiotropic growth factors with complex roles in tumorigenesis. Overexpression of TGF-β1 in many advanced human tumors correlates with metastasis and poor prognosis, and TGF-β antagonists are being developed for cancer therapy. Using a panel of syngeneic mouse transplant models of metastatic breast cancer, we found that an anti-TGF-β neutralizing antibody suppresses metastasis in several models, including the widely-used 4T1 model. However, as expected from the complexity of TGF-β action, responses were heterogeneous and anti-TGF-β antibody treatment had no effect or even stimulated metastasis in other models. This panel of models provides a powerful platform to identify candidate biomarkers for their ability predict therapeutic response to TGF-β antibodies. Previously we have shown that therapeutic outcome does not correlate with the expression of TGF-β ligands, the growth inhibitory response of the tumor model to TGF-β in vitro, the level of Six-1 expression, or the activation of non-canonical TGF-β signaling through formation of mixed Smad complexes. We next performed extensive histopathologic and immunohistochemical characterization of the tumor models to look for features that might correlate with therapeutic response. We found no obvious correlations between therapeutic response and a variety of markers, including estrogen receptor status, cytokeratin expression profile (luminal vs basal differentiation), p63 expression (basal marker), p53 expression or mutation status, smooth muscle actin expression or desmoplasia. There was also no correlation of response with tumor cell proliferation as assessed by quantitation of mitotic figures and Ki67, tumor cell apoptosis, extent of necrosis or histomorphology of the tumor cells (spindled vs polygonal). We then focused on mechanistic analysis of the undesirable stimulatory effect of anti-TGF-β antibodies in the Mvt-1 model in an attempt to generate new leads for biomarker analysis. We showed that the stimulatory effect of anti-TGF-β antibody treatment in the Mvt-1 model is still seen in SCID mice, suggesting that it does not involve T-cell mediated immune responses. Comparison of treated and untreated Mvt-1 tumors showed no effect of anti-TGF-β antibodies on tumor cell apoptosis, or infiltration by F480+ or CD11b+ immune cells. Tumor cell proliferation was actually decreased by the antibody treatment. In vitro assays showed that TGF-β had similar stimulatory effects on migration and invasion in both the 4T1 and Mvt-1 models, suggesting that the stimulatory effect of antibody therapy in the Mvt-1 model could not be explained by an anomalous invasion response to TGF-β. Thus the mechanism by which anti-TGF-β antibodies can stimulate metastasis in this model are unclear. Transcriptomic analyses of treated and untreated tumors are ongoing and results will be presented.

Citation Format: Yu-an Yang, Jia Weng, Michael Welsh, Nancy Guan, Josh Webster, Kathy Flanders, Scott M. Lonning, John McPherson, Lalage M. Wakefield. Heterogeneity of response to anti-TGF-β antibody therapy in preclinical models. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5484. doi:10.1158/1538-7445.AM2013-5484

Abstract 5331: A novel function of p21 in inhibition of epithelial-mesenchymal transition through microRNAs

The tumor suppressor p21 inhibits cell proliferation during the stress response. However, p21 can also directly regulate gene expression by repressing specific transcription factors. Here, we identified p21-regulated miRNAs by sequencing small RNAs from HCT116-p21+/+ and HCT116-p21-/- cells. Three abundant clusters, miR-200b-200a-429, miR-200c-141 and miR-183-96-182 were down-regulated in p21-depleted HCT116 and MCF10A cells. Loss of p21 induced epithelial-mesenchymal transition (EMT) and enhanced migration and invasion in multiple model systems. Identification of genome-wide targets of the miR-183-96-182 cluster indicated that miR-183 and miR-96 repressed common targets, including SLUG, ZEB1, ITGB1 and KLF4, to inhibit EMT, migration and invasion. In turn, elevated ZEB1 levels in HCT116-p21-/- cells directly repressed miR-183-96-182 cluster transcription, revealing a feedback loop. Re-introduction of miR-200, miR-183 or miR-96 in HCT116-p21-/- cells inhibited migration and invasion. These novel findings suggest that coordinated down-regulation of three miRNA clusters upon loss of p21 in unstressed cells promotes EMT, migration and invasion.

Citation Format: Xiao L. Li, Toshifumi Hara, Youngeun Choi, Murugan Subramanian, Princy Francis, Sven Bilke, Robert L. Walker, Marbin Pineda, Yu-an Yang, Ji Luo, Lalage M. Wakefield, Ben H. Park, Thomas Brabletz, Dipanjan Chowdhury, Paul S. Meltzer, Ashish Lal. A novel function of p21 in inhibition of epithelial-mesenchymal transition through microRNAs. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5331. doi:10.1158/1538-7445.AM2013-5331

Abstract 4310: An integrated genomic approach specifically dissects out the tumor suppressor aspect of TGF-β in breast cancer

Transforming growth factor-βs (TGF-βs) have complex roles in tumorigenesis, with context-dependent effects that can either suppress or promote tumor progression. The dogma is that tumor suppressive effects are active in the early stages of carcinogenesis, but that later pro-progression effects come to dominate. Since TGF-β antagonists of various types are in early phase clinical trials in cancer, it is important to know whether the tumor suppressive effects of TGF-β are still intact in any tumors at the time of diagnosis and treatment. Existing TGF-β-related gene expression signatures were not designed a priori to discriminate the tumor suppressive from the tumor promoting activities. To address this question, we applied integrated ChIP-chip and transcriptomic approaches in the MCF10A-based model of breast cancer progression. We have previously shown that TGF-β has tumor suppressor activity in the less malignant cell lines of the series (MCF10A, MCF10AT1k, MCF10Ca1h), but that this effect is lost in the most malignant cell line (MCF10Ca1a). The tumor suppressor activity is dependent on the downstream signaling component Smad3. Using promoter-wide ChIP-chip, we found that the genomic landscape of TGF-β induced Smad3 binding differed dramatically between the four cell lines, despite their close genetic relatedness. Interestingly, TGF-β induced Smad3 binding only at genetic loci that were already transcriptionally active, suggesting that TGF-βs may primarily play a modulator rather than an instigator role in regulating transcription. This feature probably contributes significantly to the known contextuality of TGF-β activity. By focusing on the two malignant cell lines (MCF10CA1h and MCF10CA1a), we identified a core signature of 26 TGF-β/Smad3 regulated genes that were specifically associated with the tumor suppressor activity of TGF-β. Unexpectedly, the direction of regulation of 25% of these genes by TGF-β differed in vitro and in vivo, highlighting a further novel contribution to TGF-β contextuality, and emphasizing the importance of including in vivo data in this type of analysis. The in vivo weighted form of the TGF-β/Smad3 tumor suppressor signature was associated with good outcome in estrogen-receptor positive breast cancer patients, suggesting that TGF-β tumor suppressive pathways are still active and influencing disease outcome in a subset of patients’ tumors at the time of surgery. TGF-β is a potent growth inhibitor for most epithelial cells, but anti-proliferative effects made only a minor contribution to the tumor suppressor activity in the breast cancer cohorts. Instead, novel tumor suppressor effects of TGF-β captured by this approach included the restoration of tumor suppressive EphrinA signaling, leading to increased tumor cell differentiation. The results have important implications for patient stratification in ongoing clinical trials with TGF-β antagonists.

Citation Format: Misako Sato, Mitsutaka Kadota, Binwu Tang, Yu-an Yang, Mengge Shan, Jia Weng, Michael Welsh, Aleksandra Michalowski, Howard Yang, Robert Clifford, Maxwell Lee, Lalage M. Wakefield. An integrated genomic approach specifically dissects out the tumor suppressor aspect of TGF-β in breast cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4310. doi:10.1158/1538-7445.AM2013-4310

TGF-β-SMAD3 signaling mediates hepatic bile acid and phospholipid metabolism following lithocholic acid-induced liver injury

Transforming growth factor-β (TGFβ) is activated as a result of liver injury, such as cholestasis. However, its influence on endogenous metabolism is not known. This study demonstrated that TGFβ regulates hepatic phospholipid and bile acid homeostasis through MAD homolog 3 (SMAD3) activation as revealed by lithocholic acid-induced experimental intrahepatic cholestasis. Lithocholic acid (LCA) induced expression of TGFB1 and the receptors TGFBR1 and TGFBR2 in the liver. In addition, immunohistochemistry revealed higher TGFβ expression around the portal vein after LCA exposure and diminished SMAD3 phosphorylation in hepatocytes from Smad3-null mice. Serum metabolomics indicated increased bile acids and decreased lysophosphatidylcholine (LPC) after LCA exposure. Interestingly, in Smad3-null mice, the metabolic alteration was attenuated. LCA-induced lysophosphatidylcholine acyltransferase 4 (LPCAT4) and organic solute transporter β (OSTβ) expression were markedly decreased in Smad3-null mice, whereas TGFβ induced LPCAT4 and OSTβ expression in primary mouse hepatocytes. In addition, introduction of SMAD3 enhanced the TGFβ-induced LPCAT4 and OSTβ expression in the human hepatocellular carcinoma cell line HepG2. In conclusion, considering that Smad3-null mice showed attenuated serum ALP activity, a diagnostic indicator of cholangiocyte injury, these results strongly support the view that TGFβ-SMAD3 signaling mediates an alteration in phospholipid and bile acid metabolism following hepatic inflammation with the biliary injury.

Biological responses to TGF-β in the mammary epithelium show a complex dependency on Smad3 gene dosage with important implications for tumor progression

TGF-β plays a dual role in epithelial carcinogenesis with the potential to either suppress or promote tumor progression. We found that levels of Smad3 mRNA, a critical mediator of TGF-β signaling, are reduced by approximately 60% in human breast cancer. We therefore used conditionally immortalized mammary epithelial cells (IMEC) of differing Smad3 genotypes to quantitatively address the Smad3 requirement for different biologic responses to TGF-β. We found that a two-fold reduction in Smad3 gene dosage led to complex effects on TGF-β responses; the growth-inhibitory response was retained, the pro-apoptotic response was lost, the migratory response was reduced, and the invasion response was enhanced. Loss of the pro-apoptotic response in the Smad3(+/-) IMECs correlated with loss of Smad3 binding to the Bcl-2 locus, whereas retention of the growth-inhibitory response in Smad3 IMECs correlated with retention of Smad3 binding to the c-Myc locus. Addressing the integrated outcome of these changes in vivo, we showed that reduced Smad3 levels enhanced metastasis in two independent models of metastatic breast cancer. Our results suggest that different biologic responses to TGF-β in the mammary epithelium are differentially affected by Smad3 dosage and that a mere two-fold reduction in Smad3 is sufficient to promote metastasis.

Abstract A7: Roles of miRNAs in the switch of TGF-β from tumor suppressor to pro-oncogenic factor in cancer progression

TGF-β is a widely expressed pleiotropic growth factor that plays complex roles in tumorigenesis. TGF-β switches from tumor suppressor to pro-oncogenic factor during breast cancer progression. Our goal is to identify molecular determinants of the TGF-β switch. Since miRNA expression is deregulated in cancer, and TGF-β is reported to regulate expression and biogenesis of miRNAs, we hypothesize that miRNAs may contribute to this switch. To model the TGF-β switch, we used a series of human breast cancer cell lines derived from the spontaneously immortalized MCF10A human breast epithelial cell line. The model consists of 4 cell lines. In the MCF10A (M-I; normal), MCF10AT (M-II; premalignant) and MCF10CA1hcl4 (M-IIIcl4; low-grade tumor) lines, TGF-β is a tumor suppressor. In contrast, in the MCF10CA1a cell line (M-IV), which gives rise to aggressive metastatic tumors, the tumor suppressor activity is lost and TGF-β promotes metastasis. To test the possible involvement of miRNAs in the TGF-β switch, we compared expression profiles of miRNAs by Next Gen miRNA sequencing 1) basally in cultures of all four cell lines and 2) in M-IIIcl4 and M-IV with and without TGF-β treatment. A variety of patterns of change in basal miRNA expression with malignant progression were seen. We focused on miRNAs whose expression level differs basally between M-IIIcl4 and M-IV, since the switch occurs between these two cell lines. 46 miRNAs were expressed &gt; 1.5 fold higher in M-IIIcl4 than in M-IV, whereas 29 miRNAs were expressed &gt; 1.5 fold higher in M-IV than in M-IIIcl4. We selected several miRNAs whose expression was most different between the two cell lines, and examined whether these miRNAs regulate cellular responses to TGF-β. As an example, let-7i and let-7g were expressed higher in M-IV than in M-IIIcl4. Forced expression of these miRNAs partially reversed TGF-β-induced growth inhibition in M-IIIcl4. A similar strategy was applied to miRNAs whose regulation by TGF-β is different between M-IIIcl4 and M-IV. The results of these experiments will be discussed.

Citation Format: Yoshiko Nagano, Maxwell P. Lee, Lalage M. Wakefield. Roles of miRNAs in the switch of TGF-β from tumor suppressor to pro-oncogenic factor in cancer progression [abstract]. In: Proceedings of the AACR Special Conference on Noncoding RNAs and Cancer; 2012 Jan 8-11; Miami Beach, FL. Philadelphia (PA): AACR; Cancer Res 2012;72(2 Suppl):Abstract nr A7.

A novel approach for the generation of genetically modified mammary epithelial cell cultures yields new insights into TGFβ signaling in the mammary gland

INTRODUCTION

Molecular dissection of the signaling pathways that underlie complex biological responses in the mammary epithelium is limited by the difficulty of propagating large numbers of mouse mammary epithelial cells, and by the inability of ribonucleic acid interference (RNAi)-based knockdown approaches to fully ablate gene function. Here we describe a method for the generation of conditionally immortalized mammary epithelial cells with defined genetic defects, and we show how such cells can be used to investigate complex signal transduction processes using the transforming growth factor beta (TGFβ/Smad pathway as an example.

METHODS

We intercrossed the previously described H-2Kb-tsA58 transgenic mouse (Immortomouse) which expresses a temperature-sensitive mutant of the simian virus-40 large T-antigen (tsTAg), with mice of differing Smad genotypes. A panel of conditionally immortalized mammary epithelial cell (IMEC) cultures were derived from the virgin mammary glands of offspring of these crosses and used to assess the Smad dependency of different biological responses to TGFβ.

RESULTS

IMECs could be propagated indefinitely at permissive temperatures and had a stable epithelial phenotype, resembling primary mammary epithelial cells with respect to several criteria, including responsiveness to TGFβ. Using this panel of cells, we demonstrated that Smad3, but not Smad2, is necessary for TGFβ-induced apoptotic, growth inhibitory and EMT responses, whereas either Smad can support TGFβ-induced invasion as long as a threshold level of total Smad is exceeded.

CONCLUSIONS

This work demonstrates the practicality and utility of generating conditionally immortalized mammary epithelial cell lines from genetically modified Immortomice for detailed investigation of complex signaling pathways in the mammary epithelium.

Modeling metastasis biology and therapy in real time in the mouse lung

Pulmonary metastasis remains the leading ca use of death for cancer patients. Opportunities to improve treatment outcomes for patients require new methods to study and view the biology of metastatic progression. Here, we describe an ex vivo pulmonary metastasis assay (PuMA) in which the metastatic progression of GFP-expressing cancer cells, from a single cell to the formation of multicellular colonies, in the mouse lung microenvironment was assessed in real time for up to 21 days. The biological validity of this assay was confirmed by its prediction of the in vivo behavior of a variety of high- and low-metastatic human and mouse cancer cell lines and the discrimination of tumor microenvironments in the lung that were most permissive to metastasis. Using this approach, we provide what we believe to be new insights into the importance of tumor cell interactions with the stromal components of the lung microenvironment. Finally, the translational utility of this assay was demonstrated through its use in the evaluation of therapeutics at discrete time points during metastatic progression. We believe that this assay system is uniquely capable of advancing our understanding of both metastasis biology and therapeutic strategies.

Transient tumor-fibroblast interactions increase tumor cell malignancy by a TGF-Beta mediated mechanism in a mouse xenograft model of breast cancer

Carcinoma are complex societies of mutually interacting cells in which there is a progressive failure of normal homeostatic mechanisms, causing the parenchymal component to expand inappropriately and ultimately to disseminate to distant sites. When a cancer cell metastasizes, it first will be exposed to cancer associated fibroblasts in the immediate tumor microenvironment and then to normal fibroblasts as it traverses the underlying connective tissue towards the bloodstream. The interaction of tumor cells with stromal fibroblasts influences tumor biology by mechanisms that are not yet fully understood. Here, we report a role for normal stroma fibroblasts in the progression of invasive tumors to metastatic tumors. Using a coculture system of human metastatic breast cancer cells (MCF10CA1a) and normal murine dermal fibroblasts, we found that medium conditioned by cocultures of the two cell types (CoCM) increased migration and scattering of MCF10CA1a cells in vitro, whereas medium conditioned by homotypic cultures had little effect. Transient treatment of MCF10CA1a cells with CoCM in vitro accelerated tumor growth at orthotopic sites in vivo, and resulted in an expanded pattern of metastatic engraftment. The effects of CoCM on MCF10CA1a cells were dependent on small amounts of active TGF-β1 secreted by fibroblasts under the influence of the tumor cells, and required intact ALK5-, p38-, and JNK signaling in the tumor cells. In conclusion, these results demonstrate that transient interactions between tumor cells and normal fibroblasts can modify the acellular component of the local microenvironment such that it induces long-lasting increases in tumorigenicity and alters the metastatic pattern of the cancer cells in vivo. TGF-β appears to be a key player in this process, providing further rationale for the development of anti-cancer therapeutics that target the TGF-β pathway.

Delineating genetic alterations for tumor progression in the MCF10A series of breast cancer cell lines

To gain insight into the role of genomic alterations in breast cancer progression, we conducted a comprehensive genetic characterization of a series of four cell lines derived from MCF10A. MCF10A is an immortalized mammary epithelial cell line (MEC); MCF10AT is a premalignant cell line generated from MCF10A by transformation with an activated HRAS gene; MCF10CA1h and MCF10CA1a, both derived from MCF10AT xenografts, form well-differentiated and poorly-differentiated malignant tumors in the xenograft models, respectively. We analyzed DNA copy number variation using the Affymetrix 500 K SNP arrays with the goal of identifying gene-specific amplification and deletion events. In addition to a previously noted deletion in the CDKN2A locus, our studies identified MYC amplification in all four cell lines. Additionally, we found intragenic deletions in several genes, including LRP1B in MCF10CA1h and MCF10CA1a, FHIT and CDH13 in MCF10CA1h, and RUNX1 in MCF10CA1a. We confirmed the deletion of RUNX1 in MCF10CA1a by DNA and RNA analyses, as well as the absence of the RUNX1 protein in that cell line. Furthermore, we found that RUNX1 expression was reduced in high-grade primary breast tumors compared to low/mid-grade tumors. Mutational analysis identified an activating PIK3CA mutation, H1047R, in MCF10CA1h and MCF10CA1a, which correlates with an increase of AKT1 phosphorylation at Ser473 and Thr308. Furthermore, we showed increased expression levels for genes located in the genomic regions with copy number gain. Thus, our genetic analyses have uncovered sequential molecular events that delineate breast tumor progression. These events include CDKN2A deletion and MYC amplification in immortalization, HRAS activation in transformation, PIK3CA activation in the formation of malignant tumors, and RUNX1 deletion associated with poorly-differentiated malignant tumors.

Identification of novel gene amplifications in breast cancer and coexistence of gene amplification with an activating mutation of PIK3CA

To identify genetic events that characterize cancer progression, we conducted a comprehensive genetic evaluation of 161 primary breast tumors. Similar to the "mountain-and-hill" view of mutations, gene amplification also shows high- and low-frequency alterations in breast cancers. The frequently amplified genes include the well-known oncogenes ERBB2, FGFR1, MYC, CCND1, and PIK3CA, whereas other known oncogenes that are amplified, although less frequently, include CCND2, EGFR, FGFR2, and NOTCH3. More importantly, by honing in on minimally amplified regions containing three or fewer genes, we identified six new amplified genes: POLD3, IRAK4, IRX2, TBL1XR1, ASPH, and BRD4. We found that both the IRX2 and TBL1XR1 proteins showed higher expression in the malignant cell lines MCF10CA1h and MCF10CA1a than in their precursor, MCF10A, a normal immortalized mammary epithelial cell line. To study oncogenic roles of TBL1XR1, we performed knockdown experiments using a short hairpin RNA approach and found that depletion of TBL1XR1 in MCF10CA1h cells resulted in reduction of cell migration and invasion as well as suppression of tumorigenesis in mouse xenografts. Intriguingly, our mutation analysis showed the presence of activation mutations in the PIK3CA gene in a subset of tumors that also had DNA copy number increases in the PIK3CA locus, suggesting an additive effect of coexisting activating amino acid substitution and dosage increase from amplification. Our gene amplification and somatic mutation analysis of breast primary tumors provides a coherent picture of genetic events, both corroborating and novel, offering insight into the genetic underpinnings of breast cancer progression.

TGF-beta3 and cancer: a review

With the development of growth factors and growth factor modulators as therapeutics for a range of disorders, it is prudent to consider whether modulating the growth factor profile in a tissue can influence tumour initiation or progression. As recombinant human TGF-beta3 (avotermin) is being developed for the improvement of scarring in the skin it is important to understand the role, if any, of this cytokine in tumour progression. Elevated levels of TGF-beta3 expression detected in late-stage tumours have linked this cytokine with tumourigenesis, although functional data to support a causative role are lacking. While it has proved tempting for researchers to interpret a 'correlation' as a 'cause' of disease, what has often been overlooked is the normal biological role of TGF-beta3 in processes that are often subverted in tumourigenesis. Clarifying the role of this cytokine is complicated by inappropriate extrapolation of the data relating to TGF-beta1 in tumourigenesis, despite marked differences in biology between the TGF-beta isoforms. Indeed, published studies have indicated that TGF-beta3 may actually play a protective role against tumourigenesis in a range of tissues including the skin, breast, oral and gastric mucosa. Based on currently available data it is reasonable to hypothesize that administration of acute low doses of exogenous TGF-beta3 is unlikely to influence tumour initiation or progression.