Advances in 3D Culture Models to Study Exosomes in Triple-Negative Breast Cancer

Breast cancer, a leading cause of cancer-related deaths globally, exhibits distinct subtypes with varying pathological, genetic, and clinical characteristics. Despite advancements in breast cancer treatments, its histological and molecular heterogeneity pose a significant clinical challenge. Triple-negative breast cancer (TNBC), a highly aggressive subtype lacking targeted therapeutics, adds to the complexity of breast cancer treatment. Recent years have witnessed the development of advanced 3D culture technologies, such as organoids and spheroids, providing more representative models of healthy human tissue and various malignancies. These structures, resembling organs in structure and function, are generated from stem cells or organ-specific progenitor cells via self-organizing processes. Notably, 3D culture systems bridge the gap between 2D cultures and in vivo studies, offering a more accurate representation of in vivo tumors' characteristics. Exosomes, small nano-sized molecules secreted by breast cancer and stromal/cancer-associated fibroblast cells, have garnered significant attention. They play a crucial role in cell-to-cell communication, influencing tumor progression, invasion, and metastasis. The 3D culture environment enhances exosome efficiency compared to traditional 2D cultures, impacting the transfer of specific cargoes and therapeutic effects. Furthermore, 3D exosomes have shown promise in improving therapeutic outcomes, acting as potential vehicles for cancer treatment administration. Studies have demonstrated their role in pro-angiogenesis and their innate therapeutic potential in mimicking cellular therapies without side effects. The 3D exosome model holds potential for addressing challenges associated with drug resistance, offering insights into the mechanisms underlying multidrug resistance and serving as a platform for drug screening. This review seeks to emphasize the crucial role of 3D culture systems in studying breast cancer, especially in understanding the involvement of exosomes in cancer pathology.

Kindlin-2 Regulates the Oncogenic Activities of Integrins and TGF-β In Triple Negative Breast Cancer Progression and Metastasis

Background

Kindlin-2, an adaptor protein, is dysregulated in various human cancers, including triple negative breast cancer (TNBC), where it drives tumor progression and metastasis by influencing several cancer hallmarks. One well-established role of Kindlin-2 involves the regulation of integrin signaling, achieved by directly binding to the cytoplasmic tail of the integrin β subunit. In this study, we present novel insights into Kindlin-2's involvement in stabilizing the β1-Integrin:TGF-β type 1 receptor (TβRI) complexes, acting as a physical bridge that links β1-Integrin to TβRI. The loss of Kindlin-2 results in the degradation of this protein complex, leading to the inhibition of downstream oncogenic pathways.

Methods

Our methodology encompassed a diverse range of in vitro assays, including CRISPR/Cas9 gene editing, cell migration, 3D tumorsphere formation and invasion, solid binding, co-immunoprecipitation, cell adhesion and spreading assays, as well as western blot and flow cytometry analyses, utilizing MDA-MB-231 and 4T1 TNBC cell lines. Additionally, preclinical in vivo mouse models of TNBC tumor progression and metastasis were employed to substantiate our findings.

Results

The investigation revealed that the direct interaction between Kindlin-2 and β1-Integrin is mediated through the C-terminal F3 domain of Kindlin-2, while the interaction between Kindlin-2 and TβRI is facilitated through the F2 domain of Kindlin-2. Disruption of this bridge, achieved via CRISPR/Cas9-mediated knockout of Kindlin-2, led to the degradation of β1-Integrin and TβRI, resulting in the inhibition of oncogenic pathways downstream of both proteins, subsequently hindering tumor growth and metastasis. Treatment of Kindlin-2-deficient cells with the proteasome inhibitor MG-132 restored the expression of both β1-Integrin and TβRI. Furthermore, the rescue of Kindlin-2 expression reinstated their oncogenic activities both in vitro and in vivo.

Conclusions

This study identifies a novel function of Kindlin-2 in stabilizing the β1-Integrin:TβR1 complexes and regulating their downstream oncogenic signaling. The translational implications of these findings are substantial, potentially unveiling new therapeutically targeted pathways crucial for the treatment of TNBC tumors.

Time-resolved live-cell spectroscopy reveals EphA2 multimeric assembly

Ephrin type-A receptor 2 (EphA2) is a receptor tyrosine kinase that initiates both ligand-dependent tumor-suppressive and ligand-independent oncogenic signaling. We used time-resolved, live-cell fluorescence spectroscopy to show that the ligand-free EphA2 assembles into multimers driven by two types of intermolecular interactions in the ectodomain. The first type entails extended symmetric interactions required for ligand-induced receptor clustering and tumor-suppressive signaling that inhibits activity of the oncogenic extracellular signal-regulated kinase (ERK) and protein kinase B (AKT) protein kinases and suppresses cell migration. The second type is an asymmetric interaction between the amino terminus and the membrane proximal domain of the neighboring receptors, which supports oncogenic signaling and promotes migration in vitro and tumor invasiveness in vivo. Our results identify the molecular interactions that drive the formation of the EphA2 multimeric signaling clusters and reveal the pivotal role of EphA2 assembly in dictating its opposing functions in oncogenesis.

Alginate-based hydrogel platform embedding silver nanoparticles and cisplatin: characterization of the synergistic effect on a breast cancer cell line

Introduction: Breast cancer is a significant cause of mortality in women globally, and current treatment approaches face challenges due to side effects and drug resistance. Nanotechnology offers promising solutions by enabling targeted drug delivery and minimizing toxicity to normal tissues. Methods: In this study, we developed a composite platform called (Alg-AgNPs-CisPt), consisting of silver nanoparticles coated with an alginate hydrogel embedding cisplatin. We examined the effectiveness of this nanocomplex in induce synergistic cytotoxic effects on breast cancer cells. Results and Discussion: Characterization using various analytical techniques confirmed the composition of the nanocomplex and the distribution of its components. Cytotoxicity assays and apoptosis analysis demonstrated that the nanocomplex exhibited greater efficacy against breast cancer cells compared to AgNPs or cisplatin as standalone treatments. Moreover, the nanocomplex was found to enhance intracellular reactive oxygen species levels, further validating its efficacy. The synergistic action of the nanocomplex constituents offers potential advantages in reducing side effects associated with higher doses of cisplatin as a standalone treatment. Overall, this study highlights the potential of the (Alg-AgNPs-CisPt) nanocomplex as a promising platform embedding components with synergistic action against breast cancer cells.

PARKIN UBIQUITINATION OF KINDLIN-2 ENABLES MITOCHONDRIA-ASSOCIATED METASTASIS SUPPRESSION

Mitochondria are signaling organelles implicated in cancer, but the mechanisms are elusive. Here, we show that Parkin, an E3 ubiquitin ligase altered in Parkinson's Disease (PD), forms a complex with the regulator of cell motility, Kindlin-2 (K2) at mitochondria of tumor cells. In turn, Parkin ubiquitinates Lys581 and Lys582 using Lys48 linkages, resulting in proteasomal degradation of K2 and shortened half-life from ∼5 h to ∼1.5 h. Loss of K2 inhibits focal adhesion turnover and β1 integrin activation, impairs membrane lamellipodia size and frequency, and inhibits mitochondrial dynamics, altogether suppressing tumor cell-ECM interactions, migration, and invasion. Conversely, Parkin does not affect tumor cell proliferation, cell cycle transitions or apoptosis. Expression of a Parkin ubiquitination-resistant K2 Lys581Ala/Lys582Ala double mutant is sufficient to restore membrane lamellipodia dynamics, correct mitochondrial fusion/fission, and preserve single-cell migration and invasion. In a 3D model of mammary gland developmental morphogenesis, impaired K2 ubiquitination drives multiple oncogenic traits of EMT, increased cell proliferation, reduced apoptosis and disrupted basal-apical polarity. Therefore, deregulated K2 is a potent oncogene and its ubiquitination by Parkin enables mitochondria-associated metastasis suppression.

Abstract 620: Regulation of anti-tumor immune response by EphA2 receptor tyrosine kinase

Eph receptors are the largest family of receptor tyrosine kinases. Overexpression of EphA2 is common across many types of human cancer, particularly in the late stage malignant diseases. We report here that EphA2 knock-out causes delayed tumor growth in several syngeneic mouse caner models, such as breast, colon, lung, and prostate cancer as well as melanoma. However, such effects are missing in immune deficient mice, which suggests the involvement of immune components. Immunophenotyping of the tumors shows elevated T cell infiltration and accompanied by reduced MDSC population in the EphA2 KO tumors. Single cell transcriptomic analysis and cytokine measurements support these results showing increased production of CCL5, CXCL9 and IFNg in the EphA2 KO tumors. Analysis on tumors at very early time points reveals elevated levels of CXCL1 and CXCL2 which recruits suppressive MDSCs. Consistently, larger population of MDSCs was found in PBMCs from the control tumor bearing mice than those bearing EphA2 KO tumors. These results suggest that EphA2 in cancer cells drive the production of CXCL1 and CXCL2 to recruit suppressive MDSCs to the tumor site, thus subvert the host anti-tumor immune surveillance. Targeting the overexpressed EphA2 in cancer can help reshape the tumor micro- environment towards type I anti-tumor immune response.

Citation Format: Roger Xiaojun Shi, Ryan Lingerak, So-Yeon Kim, Wei Wang, Khalid Sossey-Alaoui, Bingcheng Wang. Regulation of anti-tumor immune response by EphA2 receptor tyrosine kinase [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 620.

Neighborhood and racial influences on triple negative breast cancer: evidence from Northeast Ohio

PURPOSE

Triple negative breast cancer (TNBC) is an aggressive subtype of breast cancer (BC) with higher recurrence rates and poorer prognoses and most prevalent among non-Hispanic Black women. Studies of multiple health conditions and care processes suggest that neighborhood socioeconomic position is a key driver of health disparities. We examined roles of patients' neighborhood-level characteristics and race on prevalence, stage at diagnosis, and mortality among patients diagnosed with BC at a large safety-net healthcare system in Northeast Ohio.

METHODS

We used tumor registry to identify BC cases from 2007 to 2020 and electronic health records and American Community Survey for individual- and area-level factors. We performed multivariable regression analyses to estimate associations between neighborhood-level characteristics, measured by the Area Deprivation Index (ADI), race and comparative TNBC prevalence, stage at diagnosis, and total mortality.

RESULTS

TNBC was more common among non-Hispanic Black (53.7%) vs. non-Hispanic white patients (46.4%). Race and ADI were individually significant predictors of TNBC prevalence, stage at diagnosis, and total mortality. Race remained significantly associated with TNBC subtype, adjusting for covariates. Accounting for TNBC status, a more disadvantaged neighborhood was significantly associated with a worse stage at diagnosis and higher death rates.

CONCLUSION

Our findings suggest that both neighborhood socioeconomic position and race are strongly associated with TNBC vs. other BC subtypes. The burden of TNBC appears to be highest among Black women in the most socioeconomically disadvantaged neighborhoods. Our study suggests a complex interplay of social conditions and biological disease characteristics contributing to racial disparities in BC outcomes.

The WAVE3/β-catenin oncogenic signaling regulates chemoresistance in triple negative breast cancer

BACKGROUND

Metastatic breast cancer is responsible for the death of the majority of breast cancer patients. In fact, metastatic BC is the 2nd leading cause of cancer-related deaths in women in the USA and worldwide. Triple negative breast cancer (TNBC), which lacks expression of hormone receptors (ER-α and PR) and ErbB2/HER2, is especially lethal due to its highly metastatic behavior, propensity to recur rapidly, and for its resistance to standard of care therapies, through mechanisms that remain incompletely understood. WAVE3 has been established as a promoter of TNBC development and metastatic progression. In this study, we investigated the molecular mechanisms whereby WAVE3 promotes therapy-resistance and cancer stemness in TNBC, through the regulation of β-catenin stabilization.

METHODS

The Cancer Genome Atlas dataset was used to assess the expression of WAVE3 and β-catenin in breast cancer tumors. Kaplan-Meier Plotter analysis was used to correlate expression of WAVE3 and β-catenin with breast cancer patients' survival probability. MTT assay was used to quantify cell survival. CRISPR/Cas9-mediated gene editing, 2D and 3D tumorsphere growth and invasion assays, Immunofluorescence, Western blotting, Semi-quantitative and real-time quantitative PCR analyses were applied to study the WAVE3/β-catenin oncogenic signaling in TNBC. Tumor xenograft assays were used to study the role of WAVE3 in mediating chemotherapy resistance of TNBC tumors.

RESULTS

Genetic inactivation of WAVE3 in combination of chemotherapy resulted in inhibition of 2D growth and 3D tumorsphere formation and invasion of TNBC cells in vitro, as well as tumor growth and metastasis in vivo. In addition, while re-expression of phospho-active WAVE3 in the WAVE3-deficient TNBC cells restored the oncogenic activity of WAVE3, re-expression of phospho-mutant WAVE3 did not. Further studies revealed that dual blocking of WAVE3 expression or phosphorylation in combination with chemotherapy treatment inhibited the activity and expression and stabilization of β-catenin. Most importantly, the combination of WAVE3-deficiency or WAVE3-phospho-deficiency and chemotherapy suppressed the oncogenic behavior of chemoresistant TNBC cells, both in vitro and in vivo.

CONCLUSION

We identified a novel WAVE3/β-catenin oncogenic signaling axis that modulates chemoresistance of TNBC. This study suggests that a targeted therapeutic strategy against WAVE3 could be effective for the treatment of chemoresistant TNBC tumors.

Inducible Nitric Oxide Synthase Embedded in Alginate/Polyethyleneimine Hydrogel as a New Platform to Explore NO-Driven Modulation of Biological Function

Nitric oxide (NO), a small free radical molecule, turned out to be pervasive in biology and was shown to have a substantial influence on a range of biological activities, including cell growth and apoptosis. This molecule is involved in signaling and affects a number of physiologic functions. In recent decades, several processes related to cancer, such as angiogenesis, programmed cell death, infiltration, cell cycle progression, and metastasis, have been linked with nitric oxide. In addition, other parallel work showed that NO also has the potential to operate as an anti-cancer agent. As a result, it has gained attention in cancer-related therapeutics. The nitric oxide synthase enzyme family (NOS) is required for the biosynthesis of nitric oxide. It is becoming increasingly popular to develop NO-releasing materials as strong tumoricidal therapies that can deliver sustained high concentrations of nitric oxide to tumor sites. In this paper, we developed NO-releasing materials based on sodium alginate hydrogel. In this regard, alginate hydrogel discs were modified by adsorbing layers of polyethyleneimine and iNOS-oxygenase. These NO-releasing hydrogel discs were prepared using the layer-by-layer film building technique. The iNOS-oxygenase is adsorbed on the positively charged polyethyleneimine (PEI) matrix layer, which was formed on a negatively charged sodium alginate hydrogel. We show that nitric oxide is produced by enzymes contained within the hydrogel material when it is exposed to a solution containing all the components necessary for the NOS reaction. The electrostatic chemical adsorption of the layer-by-layer process was confirmed by FTIR measurements as well as scanning electron microscopy. We then tested the biocompatibility of the resulting modified sodium alginate hydrogel discs. We showed that this NOS-PEI-modified hydrogel is overall compatible with cell growth. We characterized the NOS/hydrogel films and examined their functional features in terms of NO release profiles. However, during the first 24 h of activity, these films show an increase in NO release flux, followed by a gradual drop and then a period of stable NO release. These findings show the inherent potential of using this system as a platform for NO-driven modulation of biological functions, including carcinogenesis.

The WAVE2/miR-29/Integrin-β1 Oncogenic Signaling Axis Promotes Tumor Growth and Metastasis in Triple-negative Breast Cancer

Breast cancer is the most frequently diagnosed malignancy in women and the major cause of death because of its invasion, metastasis, and resistance to therapies capabilities. The most aggressive subtype of breast cancer is triple-negative breast cancer (TNBC) due to invasive and metastatic properties along with early age of diagnosis and poor prognosis. TNBC tumors do not express estrogen, progesterone, and HER2 receptors, which limits their treatment with targeted therapies. Cancer invasiveness and metastasis are known to be promoted by increased cell motility and upregulation of the WAVE proteins. While the contribution of WAVE2 to cancer progression is well documented, the WAVE2-mediated regulation of TNBC oncogenic properties is still under investigated, as does the molecular mechanisms by which WAVE2 regulates such oncogenic pathways. In this study, we show that WAVE2 plays a significant role in TNBC development, progression, and metastasis, through the regulation of miR-29 expression, which in turn targets Integrin-β1 (ITGB1) and its downstream oncogenic activities. Conversely, we found WAVE2 expression to be regulated by miR-29 in a negative regulatory feedback loop. Reexpression of exogenous WAVE2 in the WAVE2-deficient TNBC cells resulted in reactivation of ITGB1 expression and activity, further confirming the specificity of WAVE2 in regulating Integrin-β1. Together, our data identify a novel WAVE2/miR-29/ITGB1 signaling axis, which is essential for the regulation of the invasion-metastasis cascade in TNBC. Our findings offer new therapeutic strategies for the treatment of TNBC by targeting WAVE2 and/or its downstream effectors.

Significance

Identification of a novel WAVE2/miR-29/ITGB1 signaling axis may provide new insights on how WAVE2 regulates the invasion-metastasis cascade of TNBC tumors through the modulation of ITGB1 and miR-29.

The NOGO receptor NgR2, a novel αVβ3 integrin effector, induces neuroendocrine differentiation in prostate cancer

Androgen deprivation therapies aimed to target prostate cancer (PrCa) are only partially successful given the occurrence of neuroendocrine PrCa (NEPrCa), a highly aggressive and highly metastatic form of PrCa, for which there is no effective therapeutic approach. Our group has demonstrated that while absent in prostate adenocarcinoma, the αVβ3 integrin expression is increased during PrCa progression toward NEPrCa. Here, we show a novel pathway activated by αVβ3 that promotes NE differentiation (NED). This novel pathway requires the expression of a GPI-linked surface molecule, NgR2, also known as Nogo-66 receptor homolog 1. We show here that NgR2 is upregulated by αVβ3, to which it associates; we also show that it promotes NED and anchorage-independent growth, as well as a motile phenotype of PrCa cells. Given our observations that high levels of αVβ3 and, as shown here, of NgR2 are detected in human and mouse NEPrCa, our findings appear to be highly relevant to this aggressive and metastatic subtype of PrCa. This study is novel because NgR2 role has only minimally been investigated in cancer and has instead predominantly been analyzed in neurons. These data thus pave new avenues toward a comprehensive mechanistic understanding of integrin-directed signaling during PrCa progression toward a NE phenotype.

Abstract 5986: WAVE2/EGF signaling and miR29 regulates WAVE2 to promote tumor growth and metastasis in triple negative breast cancer

Breast cancer is the most frequently diagnosed malignancy in women and is one of the leading causes of death due to cancer invasion, metastasis, and resistance to therapies. Among its variants, triple-negative breast cancer (TNBC) is considered the most aggressive due to its early age of diagnosis, invasive and metastatic properties with poor prognosis. TNBC is a type of breast cancer that lacks expression of the receptors that are commonly found in this type of cancer (estrogen, progesterone, and HER2), which makes it a more difficult target for treatment. Cancer invasiveness and metastasis are known to be promoted by increased cell motility and upregulation of the Wiskott-Aldrich syndrome protein (WASP) and WASP family verprolin-homologous protein (WAVE) - WAVE1, WAVE2, and WAVE3. While the contribution of WAVE2 to cancer progression is well documented, the WAVE2-mediated regulation of TNBC oncogenic properties is still under investigated. In this study, we show that WAVE2 plays a significant role in TNBC development, progression, and metastasis. To investigate this notion, we used CRISPR/Cas9 gene editing to successfully inhibit WAVE2 expression in several TNBC cell lines. In vitro, loss of WAVE2 expression inhibited 3D tumorsphere formation and invasion of TNBC cells. In vivo, in mouse models for TNBC, loss of WAVE2 inhibited tumor growth and metastasis. Mechanistically, we show that the WAVE2-mediated modulation of the oncogenic behavior of TNBC cells is in part due to its phosphorylation downstream of EGF. At the post transcriptional level, we found WAVE2 expression to be regulated by miR29. Together, our findings identify a novel post-translational WAVE2/EGF oncogenic signaling axis, along with a post-transcriptional regulatory axis downstream of miR29, which together regulate the oncogenic activity of WAVE2 in TNBC and open a new therapeutic strategy for the treatment of TNBC.

Citation Format: Priyanka S. Rana, Wei Wang, Akram Alkrekshi, Vesna Markovic, Khalid Sossey-Alaoui. WAVE2/EGF signaling and miR29 regulates WAVE2 to promote tumor growth and metastasis in triple negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5986.

Abstract 5346: WAVE3 phosphorylation promotes chemoresistance and cancer stemness in triple negative breast cancer through downstream of β-catenin oncogenic signaling

Acquisition of the metastatic phenotype is responsible for the death of ~90% of breast cancer (BC) patients. Metastatic BC is the 2nd leading cause of cancer-related deaths in women in the United States, annually accounting for more than 40,100 deaths and 266,000 new cases of invasive BC. Amongst individual BC subtypes, those classified as TNBCs are especially lethal due to their highly metastatic behavior and propensity to recur rapidly. As a group, TNBCs lack expression of hormone receptors (ER-α and PR) and ErbB2/HER2, which has prevented the development of FDA-approved targeted drug therapies that are effective against this BC subtype. Likewise, recurrent TNBCs frequently acquire resistance to standard-of-care chemotherapeutic agents (e.g., doxorubicin, cyclophosphamides, and taxanes) through mechanisms that remain incompletely understood. We established Wiskott-Aldrich Syndrome Protein-3 (WAVE3) as a novel promoter of TNBC development and metastatic progression. Our recently published studies have shown that WAVE3 phosphorylation regulates the interplay between PI3K, TGF-β, and EGF signaling pathways. In this study, we show that WAVE3 phosphorylation promotes chemotherapy-resistance and cancer stemness in TNBC, both in vitro and in in vivo mouse models. CRISPR/Cas9-mediated inactivation of WAVE3 resulted in inhibition of 2D growth and 3D tumorspheres’ invasion of TNBC cells in vitro, as well as tumor growth and metastasis in vivo. In addition, while re-expression of phospho-active WAVE3 in the WAVE3-deficient TNBC cells restored the oncogenic activity of WAVE3, re-expression of phospho-mutant WAVE3 or the pharmacologic inhibition of WAVE3 phosphorylation did not. Further studies revealed that dual blocking WAVE3 expression or phosphorylation with chemotherapy treatment inhibited the activity and expression of β-catenin. Importantly, a combination of WAVE3-deficiency and chemotherapy suppressed the oncogenic behavior of chemo-resistant TNBC cells, both in vitro and in vivo. This study suggests that a targeted therapeutic strategy against WAVE3 could be effective for the treatment of chemoresistant TNBC tumors.

Citation Format: Wei Wang, Priyanka Rana, Akram Alkrekshi, Vesna Markovic, Khalid Sossey-Alaoui. WAVE3 phosphorylation promotes chemoresistance and cancer stemness in triple negative breast cancer through downstream of β-catenin oncogenic signaling [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5346.

Abstract P1-06-02: Targeted deletion of Kindlin-2 in mouse mammary glands inhibits tumor growth, invasion and metastasis downstream of TGF-β/EGF oncogenic signaling pathway

Cancer metastasis is a complex process by which cancer cells migrate through the blood and the lymphatic systems to lodge and proliferate in distant sites and organs in the body. Metastasis is the main cause of death in patients suffering from cancer, including those patients with breast cancer. Breast cancer (BC) is the most frequently diagnosed malignancy in women and is one of the leading causes of death due to cancer invasion, metastasis, and resistance to therapies. Among its variants, triple-negative breast cancer (TNBC) is considered the most aggressive due to its early invasive and metastatic properties with poor prognosis. Kindlin-2, which is encoded by Fermitin family homolog 2 gene (FERMT2) has been associated with pathogenesis of several types of cancers of epithelial origin. Our previous studies have addressed the role of Kindlin-2 as a major regulator of the invasion-metastasis cascade in breast cancer by controlling several hallmarks of cancer in tumor cells. The contribution of mammary epithelial cell Kindlin-2 in the mammary glands to the process of tumor progression and metastasis has, however, not been investigated. Accordingly, we generated a floxed mouse strain by targeting the FREMT2 (K2lox/lox) locus using a CRISPR/Cas9-based editing strategy, followed by tissue-specific deletion of the Kindlin-2 in the basal subtype of the mammary epithelial cells (MECs) in the mouse mammary glands by crossing the K2lox/lox mice with K14-cre mice. Loss of Kindlin-2 in the basal MECs had no deleterious effects on mammary glands development, mouse development and fertility and lactation in mice bearing the Kindlin 2-deletetion phenotype and their progeny. However, in a syngeneic mouse model of BC, the loss of Kindlin-2 in MECs inhibited tumor growth and metastasis in mice inoculated with the aggressive murine TNBC E0771 cells when implanted directly in their mammary fat pads. Injecting the E0771 cells via the tail vein of Kindlin-2-deleted mice had, however, no effect on tumor colonization in the lungs, when compared to wild-type mice, clearly supporting a critical role of MECs Kindlin-2 in BC tumor growth and metastasis. Mechanistically, we found the MECs Kindlin-2-mediated inhibition of tumor growth and metastasis is through the regulation of the TGF-β/ERK MAP. kinase signaling axis, in a similar manner that our published studies showed that Kindlin-2 regulates this oncogenic pathway in the BC cells. Thus, our findings strongly suggest that Kindlin-2 supports BC oncogenesis in both the tumor cells and the MECs in the mammary glands, through the regulation of the TGF-β/EGF oncogenic signaling pathway. Therefore, therapeutic strategies targeting Kindlin-2 in both the cancer cells and the mammary glands may be necessary for a successful inhibition of BC tumors.

Citation Format: Priyanka Rana, Wei Wang, Akram Alkrekchi, Katarzyna Bialkowska, Vesna Markovic, Edward F Plow, Elzbieta Pluskota, Khalid Sossey-Alaoui. Targeted deletion of Kindlin-2 in mouse mammary glands inhibits tumor growth, invasion and metastasis downstream of TGF-β/EGF oncogenic signaling pathway [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P1-06-02.

Targeted Deletion of Kindlin-2 in Mouse Mammary Glands Inhibits Tumor Growth, Invasion, and Metastasis Downstream of a TGF-β/EGF Oncogenic Signaling Pathway

Breast cancer (BC) is one of the leading causes of cancer-related deaths due in part to its invasive and metastatic properties. Kindlin-2 (FERMT2) is associated with the pathogenesis of several cancers. Although the role of Kindlin-2 in regulating the invasion-metastasis cascade in BC is widely documented, its function in BC initiation and progression remains to be fully elucidated. Accordingly, we generated a floxed mouse strain by targeting the Fermt2 (K2^lox/lox) locus, followed by tissue-specific deletion of Kindlin-2 in the myoepithelial compartment of the mammary glands by crossing the K2^lox/lox mice with K14-Cre mice. Loss of Kindlin-2 in mammary epithelial cells (MECs) showed no deleterious effects on mammary gland development, fertility, and lactation in mice bearing Kindlin-2-deletion. However, in a syngeneic mouse model of BC, mammary gland, specific knockout of Kindlin-2 inhibited the growth and metastasis of murine E0771 BC cells inoculated into the mammary fat pads. However, injecting the E0771 cells into the lateral tail vein of Kindlin-2-deleted mice had no effect on tumor colonization in the lungs, thereby establishing a critical role of MEC Kindlin-2 in supporting BC tumor growth and metastasis. Mechanistically, we found the MEC Kindlin-2-mediated inhibition of tumor growth and metastasis is accomplished through its regulation of the TGF-β/ERK MAP kinase signaling axis. Thus, Kindlin-2 within the mammary gland microenvironment facilitates the progression and metastasis of BC.

A comprehensive review of the functions of YB-1 in cancer stemness, metastasis and drug resistance

The Y Box binding protein 1 (YB-1) is a member of the highly conserved Cold Shock Domain protein family with multifunctional properties both in the cytoplasm and inside the nucleus. YB-1 is also involved in various cellular functions, including regulation of transcription, mRNA stability, and splicing. Recent studies have associated YB-1 with the regulation of the malignant phenotypes in several tumor types. In this review article, we provide an in-depth and expansive review of the literature pertaining to the multiple physiological functions of YB-1. We will also review the role of YB-1 in cancer development, progression, metastasis, and drug resistance in various malignancies, with more weight on literature published in the last decade. The methodology included querying databases PubMed, Embase, and Google Scholar for Y box binding protein 1, YB-1, YBX1, and Y-box-1.

Phosphorylation of the proline-rich domain of WAVE3 drives its oncogenic activity in breast cancer

Post-translational modification of proteins, such as tyrosine phosphorylation, plays a major role in driving the oncogenic activity of oncogenes. WAVE3 (WASF3), an adaptor and actin cytoskeleton remodeling protein, contributes to cell migration, cancer cell invasion, and metastasis. WAVE3 plays a vital role in the progression and metastasis of triple negative breast cancer (TNBC), in part through the regulation of cancer stem cells (CSCs). Several studies have shown that WAVE3 tyrosine phosphorylation is required for its oncogenic activity. Moreover, our recent study showed that the proline rich domain (PRD) of WAVE3 is required for maintenance of the CSC niche in breast cancer by regulating the nuclear translocation of the CSC-specific nuclear transcription factor YB1. Here, we show that the PRD domain of WAVE3 and its phosphorylation are essential for driving the oncogenic activity of WAVE3. We show that phosphorylation of WAVE3 PRD is essential for migration and invasion of breast cancer cells in vitro, as well as tumor growth and metastasis in vivo. Mechanistically, we show that phosphorylation of the WAVE3 PRD is essential for interaction between WAVE3 and YB1. Loss of PRD phosphorylation inhibits such interaction and the YB1-mediated activation of expression of CSC markers, as well as the WAVE3 mediated activation of EMT. Together, our study identifies a novel role of WAVE3 and its PRD domain in the regulation of the invasion metastasis cascade in BC that is independent of the known function of WAVE3 as an actin cytoskeleton remodeling protein through the WAVE regulatory complex (WRC).

WAVE3 phosphorylation regulates the interplay between PI3K, TGF-β, and EGF signaling pathways in breast cancer

Both TGF-β and the PI3K-AKT signaling pathways are known activators of various intracellular pathways that regulate critical cellular functions, including cancer cell survival and proliferation. The interplay between these two oncogenic pathways plays a major role in promoting the initiation, growth, and progression of tumors, including breast cancers. The molecular underpinning of the inter-relationship between these pathways is, however, not fully understood, as is the role of WAVE3 phosphorylation in the regulation of tumor growth and progression. WAVE3 has been established as a major driver of the invasion–metastasis cascade in breast cancer and other tumors of epithelial origin. WAVE3 phosphorylation downstream of PI3K was also shown to regulate cell migration. Here we show that, in addition to PI3K, WAVE3 tyrosine phosphorylation can also be achieved downstream of TGF-β and EGF and that WAVE3 tyrosine phosphorylation is required for its oncogenic activity. Our in vitro analyses found loss of WAVE3 phosphorylation to significantly inhibit cell migration, as well as tumorsphere growth and invasion. In mouse models for breast cancer, loss of WAVE3 phosphorylation inhibited tumor growth of two aggressive breast cancer cell lines of triple-negative subtype. More importantly, we found that WAVE3 phosphorylation is also required for the activation of PI3K, TGF-β, and EGF signaling and their respective downstream effectors. Therefore, our study identified a novel function for WAVE3 in the regulation of breast cancer development and progression through the modulation of a positive feedback loop between WAVE3 and PI3K-TGF-β-EGF signaling pathways.

Abstract 6084: Wave3 tyrosine phosphorylation activates the invasion-metastasis cascade of triple negative breast cancer tumors through the maintenance of the cancer stem cell niche

The acquisition of metastatic phenotypes is responsible for the death of ~90% of breast cancer (BC) patients. In fact, metastatic BC is the 2nd leading cause of cancer-related deaths in women in the United States, annually accounting for more than 40,100 deaths and 266,000 new cases of invasive BC. Typically, metastases are incurable and result in a median survival of only 1.5 to 3 years for BC patients. Clinically, ~30% of BC patients diagnosed with early-stage, noninvasive disease will ultimately progress to late-stage, metastatic disease, an event that severely limits treatment options and associates with dismal clinical outcomes. This problem is exacerbated by the fact the BCs are heterogeneous and comprised of at least 5 genetically distinct subtypes. Amongst individual BC subtypes, those classified as TNBCs are especially lethal due to their highly metastatic behavior and propensity to recur rapidly. As a group, TNBCs lack expression of hormone receptors (ER-α and PR) and ErbB2/HER2, which has prevented the development of FDA-approved targeted drug therapies effective against this BC subtype. Likewise, recurrent TNBCs frequently acquire resistance to standard-of-care chemotherapeutic agents (e.g., doxorubicin, cyclophosphamides, and taxanes) through mechanisms that remain incompletely understood. We established Wiskott-Aldrich Syndrome Protein-3 (WAVE3) as a novel promoter of TNBC development and metastatic progression. Our previously published studies have shown that phosphorylation of WAVE3 at specific tyrosine residues by c-Abl non-receptor tyrosine kinase is required for cancer cell migration and invasion. In this study, we show that WAVE3 phosphorylation is required for the activation of the invasion-metastasis cascade of TNBCs, both in vitro and in in vivo mouse models. Genetic inactivation of WAVE3 via CRISPR/Cas9 gene editing suppressed migration, invasion and the formation of 3D tumorspheres of TNBC cells, in vitro, as well as tumor growth and metastasis in vivo. While re-expression of phospho-active WAVE3 in the WAVE3-deficient TNBC cells restored the oncogenic activity of WAVE3, re-expression of phospho-mutant WAVE3 or the pharmacologic inhibition of WAVE3 phosphorylation did not. Further studies revealed that phosphorylation of WAVE3 was required for the activation of several hallmarks of cancer through the upregulation of survival signaling pathways. Blocking WAVE3 expression or phosphorylation inhibited epithelial-mesenchymal transition (EMT) as well as disrupted the breast cancer stem cell (BCSC) niche by inhibiting expression of BCSC-specific markers. Finally, loss of WAVE3 phosphorylation was sufficient to resensitize TNBC cells to standard of care chemotherapy-induced apoptosis and cell death through the targeting of the BCSCs. Together, our data support the targeting of WAVE3 as a novel therapeutic strategy to treat metastasis in patients with TNBC tumors by specifically targeting BCSCs.

Citation Format: Wei Wang, Urna Kansakar, Vesna Markovic, Khalid Sossey-Alaoui. Wave3 tyrosine phosphorylation activates the invasion-metastasis cascade of triple negative breast cancer tumors through the maintenance of the cancer stem cell niche [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 6084.

Elucidating the molecular signaling pathways of WAVE3

Cancer metastasis is a complex, multistep process that requires tumor cells to evade from the original site and form new tumors at a distant site or a different organ, often via bloodstream or the lymphatic system. Metastasis is responsible for more than 90% of cancer-related deaths. WAVE3 belongs to the Wiskott-Aldrich syndrome protein (WASP) family, which regulate actin cytoskeleton remodeling as well as several aspects of cell migration, invasion, and metastasis. In fact, WAVE3 has been established as a driver of tumor progression and metastasis in cancers from several origins, including triple negative breast cancers (TNBCs), which are classified as the most lethal subtype of breast cancer, due to their resistance to standard of care therapy and highly metastatic behavior. In this review, we will attempt to summarize the recent advances that have been made to understand how WAVE3 contributes to the molecular mechanisms that control cancer progression and metastasis. We will also review the signaling pathways that are involved in the regulation of WAVE3 expression and function to identify potential therapeutic options targeted against WAVE3 for the treatment of patients with metastatic tumors.

Role of Kindlin-2 in cancer progression and metastasis

Cancer metastasis is a complex and multistep process whereby cancer cells escape the confines of the primary site to establish a new residency at distant sites. This multistep process is also known as the invasion-metastasis cascade. The biological and molecular mechanisms that control the invasion-metastasis cascade, which ultimately leads to the spread of cancer cells into distant sites, remain poorly understood. Kindlin-2 (K2) belongs to the 4.1-ezrin-ridixin-moesin (FERM) domain family of proteins, which interact with the cytoplasmic tails of β-integrin subunits, leading to the activation of extensive biological functions. These biological functions include cell migration, differentiation, cancer initiation, development, and invasion. In this review, we will discuss the various molecular signaling pathways that are regulated by K2 during the invasion-metastasis cascade of cancer tumors. These signaling pathways include TGFβ, Wnt/β-Catenin, Hedgehog, p53 and senescence, and cancer stem cell (CSC) maintenance. We will also discuss the molecular signaling pathways that regulate K2 function both at the transcriptional and the posttranslational levels. Finally, we will consider molecular mechanisms to specifically target K2 as novel therapeutic options for cancer treatment.

Site-specific phosphorylation regulates the functions of kindlin-3 in a variety of cells

Studies of isolated cells, mice, and humans have demonstrated the vital role of the FERM domain protein kindlin-3 in integrin activation in certain hematopoietic and non-hematopoietic cells, consequent to binding to integrin β-subunits. To explore regulatory mechanisms, we developed a monoclonal antibody that selectively recognizes the phosphorylated form of Ser⁴⁸⁴ (pS⁴⁸⁴) in kindlin-3. Activation of platelets, HEL megakaryocytic-like cells and BT549 breast cancer cells led to enhanced expression of pS⁴⁸⁴ as assessed by immunofluorescence or Western blotting. In platelets, pS⁴⁸⁴ rose rapidly and transiently upon stimulation. When a mutant form of kindlin-3, T⁴⁸²S⁴⁸⁴/AA kindlin-3, was transduced into mouse megakaryocytes, it failed to support activation of integrin α_IIbβ₃, whereas wild-type kindlin-3 did. In MDA-MB231 breast cancer cells, expression of T⁴⁸²S⁴⁸⁴/AA kindlin-3 suppressed cell spreading, migration, invasion, and VEGF production. Wild-type kindlin-3 expressing cells markedly increased tumor growth in vivo, whereas T⁴⁸²S⁴⁸⁴/AA kindlin-3 significantly blunted tumor progression. Thus, our data establish that a unique phosphorylation event in kindlin-3 regulates its cellular functions.

The Kindlin2-p53-SerpinB2 signaling axis is required for cellular senescence in breast cancer

In cancer, cellular senescence is a complex process that leads to inhibition of proliferation of cells that may develop a neoplastic phenotype. A plethora of signaling pathways, when dysregulated, have been shown to elicit a senescence response. Two well-known tumor suppressor pathways, controlled by the p53 and retinoblastoma proteins, have been implicated in maintaining the cellular senescence phenotype. Kindlin-2, a member of an actin cytoskeleton organizing and integrin activator proteins, has been shown to play a key role in the regulation of several hallmarks of several cancers, including breast cancer (BC). The molecular mechanisms whereby Kindlin-2 regulates cellular senescence in BC tumors remains largely unknown. Here we show that Kindlin-2 regulates cellular senescence in part through its interaction with p53, whereby it regulates the expression of the p53-responsive genes; i.e., SerpinB2 and p21, during the induction of senescence. Our data show that knockout of Kindlin-2 via CRISPR/Cas9 in several BC cell lines significantly increases expression levels of both SerpinB2 and p21 resulting in the activation of hallmarks of cellular senescence. Mechanistically, interaction between Kindlin-2 and p53 at the promotor level is critical for the regulated expression of SerpinB2 and p21. These findings identify a previously unknown Kindlin-2/p53/SerpinB2 signaling axis that regulates cellular senescence and intervention in this axis may serve as a new therapeutic window for BCs treatment.

Abstract LB-082: The Kindlin2-p53-SerpinB2 signaling axis is required for the regulation of cellular senescence in breast cancer

Physiological cellular senescence is defined as the irreversible arrest of cell proliferation. However, in cancer, pathological aberrations of signaling pathways that regulate specific oncogenes and tumor suppressor genes, can also lead to senescence in cancer cells. In both physiological and pathological settings, senescence is regulated by at least two well-defined pathways; i.e. the p53/p21 and p16INK4a/pRB pathways. In cancer, it is now well established that senescence is a driver of hyperplastic pathology. Kindlin-2 (FERMT2) belongs to the FERM domain-containing family of intracellular proteins that have been established as playing a key role in the activation of integrins. Several recent studies, including those from our group, have associated Kindlin-2 with the pathology of cancers originating from different organs, including breast cancer (BC). For example, we have shown that Kindlin-2 is involved in the regulation of the tumor microenvironment in BC by recruiting macrophages to the tumor site and their polarization to a pro-tumorigenic state. We have also established Kindlin-2 as a major regulator of the EMT process in BC. The role of Kindlin-2 in senescence in BC is, however, not well understood. Our RNA-Seq analyses determined that loss of Kindlin-2 expression in several BC cell lines resulted in a significant increase (at least 30-fold) in SerpinB2 and p21 expression levels, both known associated with cancer cell senescence, compared to the control cells, using RT-PCR, western blot analyses, and by immunostaining of mouse tumors xenografts derived from Kindlin-2-deficient MDA-MB-231 and 4T1 BC cells. Concomitant with the increase of SerpinB2 and p21 expression, we observed a significant increase of β-galactosidase staining, a marker for senescence, in both the Kindlin-2-defficient cells as well as senescent cells, clearly implicating Kindlin-2 in cancer cell senescence via the regulation of expression of senescence-specific genes. Further investigations revealed that Kindlin-2 can be found in nuclear immunocomplexes that also contain p53 in non-senescent cells; and to a much lesser extent in senescent cells. This latest observation led us to hypothesize that binding of Kindlin-2 to p53 may have an inhibitory effect on the function of p53 as a senescence-inducer gene by inhibiting the binding of p53 to the promoter of SerpinB2 and p21. This hypothesis was confirmed by chromatin immunoprecipitation analyses which showed that Kindlin-2, like p53, can bind to the promoters of both SerpinB2 and p21. The binding of Kindlin-2 to SerpinB2 and p21 promoters was, however, weakened in senescent cells. More importantly, in the Kindlin-2-deficient cancer cells, the binding of p53 to the promoters of both SerpinB2 and p21 was significantly much stronger, further supporting our hypothesis that Kindlin-2, by being present in the same immunocomplexes as p53, inhibits the binding of p53 to SerpinB2 and promoters to induce their expression and, therefore, cancer cell senescence. Collectively, our data provide the underpinnings of a new signaling axis (Kindlin-2/p53/SerpinB2-p21), in which Kindlin-2 regulates cancer cell senescence through its binding to p53 and modulating the p53-mediated regulation of expression of senescence-specific genes, thereby identifying a novel role of Kindlin-2 in the regulation of BC progression and metastasis.

Citation Format: Khalid Sossey-Alaoui, Elzbieta Pluskota, Dorota Szpak, Edward F. Plow. The Kindlin2-p53-SerpinB2 signaling axis is required for the regulation of cellular senescence 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 LB-082.

The Kindlin-2 regulation of epithelial-to-mesenchymal transition in breast cancer metastasis is mediated through miR-200b

Metastasis is the main cause of death in cancer patients, including breast cancer (BC). Despite recent progress in understanding the biological and molecular determinants of BC metastasis, effective therapeutic treatments are yet to be developed. Among the multitude of molecular mechanisms that regulate cancer metastasis, the epithelial-to-mesenchymal transition (EMT) program plays a key role in the activation of the biological steps leading to the metastatic phenotype. Kindlin-2 has been associated with the pathogenesis of several types of cancers, including BC. The role of Kindlin-2 in the regulation of BC metastasis, and to a lesser extent in EMT is not well understood. In this study, we show that Kindlin-2 is closely associated with the development of the metastatic phenotype in BC. We report that knockout of Kindlin-2 in either human or mouse BC cells, significantly inhibits metastasis in both human and mouse models of BC metastasis. We also report that the Kindlin-2-mediated inhibition of metastasis is the result of inhibition of expression of key molecular markers of the EMT program. Mechanistically, we show that miR-200b, a master regulator of EMT, directly targets and inhibits the expression of Kindlin-2, leading to the subsequent inhibition of EMT and metastasis. Together, our data support the targeting of Kindlin-2 as a therapeutic strategy against BC metastasis.

The WAVE3-YB1 interaction regulates cancer stem cells activity in breast cancer

Resistance to therapy is the main cause of tumor recurrence and metastasis and cancer stem cells (CSCs) play a crucial role in this process, especially in triple-negative breast cancers (TNBCs). Unfortunately, no FDA-approved treatment is currently available for this subtype of BC, which explains the high rate of mortality in patients with TNBC tumors. WAVE3, a member of the WASP/WAVE actin-cytoskeleton remodeling family of protein, has been established as a major driver of tumor progression and metastasis of several solid tumors, including those originating in the breast. Our recently published studies found WAVE3 to mediate the process of chemoresistance in TNBCs. The molecular mechanisms whereby WAVE3 regulates chemoresistance in TNBC tumors remains largely unknown, as does the role of WAVE3 in CSC maintenance. Here we show that WAVE3 promotes CSC self-renewal and regulates transcription of CSC-specific genes, which, in part, provides a mechanistic explanation for the function of WAVE3 in chemoresistance in TNBCs. Our data show that WAVE3 is enriched in the CSC-subpopulation of TNBC cell lines. Knockout of WAVE3 via CRISPR/Cas9 significantly attenuates the CSC-subpopulation and inhibits transcription of CSC transcription factors. Mechanistically, we established a link between WAVE3 and the Y-box-binding protein-1 (YB1), a transcription factor and CSC-maintenance gene. Indeed, the interaction of WAVE3 with YB1 is required for YB1 translocation to the nucleus of cancer cells, and activation of transcription of CSC-specific genes. Our findings identify a new WAVE3/YB1 signaling axis that regulates the CSC-mediated resistance to therapy and opens a new therapeutic window for TNBCs treatment.

Kindlin-2 Regulates the Growth of Breast Cancer Tumors by Activating CSF-1-Mediated Macrophage Infiltration

Interplay between tumor cells and host cells in the tumor microenvironment dictates the development of all cancers. In breast cancer, malignant cells educate host macrophages to adopt a protumorigenic phenotype. In this study, we show how the integrin-regulatory protein kindlin-2 (FERMT2) promotes metastatic progression of breast cancer through the recruitment and subversion of host macrophages. Kindlin-2 expression was elevated in breast cancer biopsy tissues where its levels correlated with reduced patient survival. On the basis of these observations, we used CRISPR/Cas9 technology to ablate Kindlin-2 expression in human MDA-MB-231 and murine 4T1 breast cancer cells. Kindlin-2 deficiency inhibited invasive and migratory properties in vitro without affecting proliferation rates. However, in vivo tumor outgrowth was inhibited by >80% in a manner associated with reduced macrophage infiltration and secretion of the macrophage attractant and growth factor colony-stimulating factor-1 (CSF-1). The observed loss of CSF-1 appeared to be caused by a more proximal deficiency in TGFβ-dependent signaling in Kindlin-2-deficient cells. Collectively, our results illuminate a Kindlin-2/TGFβ/CSF-1 signaling axis employed by breast cancer cells to capture host macrophage functions that drive tumor progression. Cancer Res; 77(18); 5129-41. ©2017 AACR.

Of Kindlins and Cancer

Kindlins are 4.1-ezrin-ridixin-moesin (FERM) domain containing proteins. There are three kindlins in mammals, which share high sequence identity. Kindlin-1 is expressed primarily in epithelial cells, kindlin-2 is widely distributed and is particularly abundant in adherent cells, and kindlin-3 is expressed primarily in hematopoietic cells. These distributions are not exclusive; some cells express multiple kindlins, and transformed cells often exhibit aberrant expression, both in the isoforms and the levels of kindlins. Great interest in the kindlins has emerged from the recognition that they play major roles in controlling integrin function. In vitro studies, in vivo studies of mice deficient in kindlins, and studies of patients with genetic deficiencies of kindlins have clearly established that they regulate the capacity of integrins to mediate their functions. Kindlins are adaptor proteins; their function emanate from their interaction with binding partners, including the cytoplasmic tails of integrins and components of the actin cytoskeleton. The purpose of this review is to provide a brief overview of kindlin structure and function, a consideration of their binding partners, and then to focus on the relationship of each kindlin family member with cancer. In view of many correlations of kindlin expression levels and neoplasia and the known association of integrins with tumor progression and metastasis, we consider whether regulation of kindlins or their function would be attractive targets for treatment of cancer.

Kindlin-2 directly binds actin and regulates integrin outside-in signaling

Bledzka et al. show that kindlin-2 binds actin via its F0 domain, and mutation of this site diminishes cell spreading, revealing a new mechanism by which kindlin-2 regulates cellular responses.

Reduced levels of kindlin-2 (K2) in endothelial cells derived from K2^+/− mice or C2C12 myoblastoid cells treated with K2 siRNA showed disorganization of their actin cytoskeleton and decreased spreading. These marked changes led us to examine direct binding between K2 and actin. Purified K2 interacts with F-actin in cosedimentation and surface plasmon resonance analyses and induces actin aggregation. We further find that the F0 domain of K2 binds actin. A mutation, LK⁴⁷/AA, within a predicted actin binding site (ABS) of F0 diminishes its interaction with actin by approximately fivefold. Wild-type K2 and K2 bearing the LK⁴⁷/AA mutation were equivalent in their ability to coactivate integrin αIIbβ3 in a CHO cell system when coexpressed with talin. However, K2-LK⁴⁷/AA exhibited a diminished ability to support cell spreading and actin organization compared with wild-type K2. The presence of an ABS in F0 of K2 that influences outside-in signaling across integrins establishes a new foundation for considering how kindlins might regulate cellular responses.

Abstract A49: WAVE3 modulates sensitivity of TNBCs to chemotherapeutics by inhibiting the STAT-HIF-1α-mediated angiogenesis

Chemoresistance allows for disease to recur and ultimately causes the death of most breast cancer patients. This scenario is particularly relevant in patients harboring triple-negative breast cancer (TNBC) tumors for which there are no effective FDA-approved drugs. However, a recent study determined that TNBCs can be segregated into 6 genetically distinct subtypes that do in fact exhibit differential rates of pathological complete response (pCR) to standard-of-care chemotherapies. Of these, the mesenchymal and mesenchymal stem-like subtypes of TNBCs exhibit the lowest rates of pCR when treated with standard-of-care chemotherapies. WAVE3 is an actin-cytoskeleton remodeling protein, and recent studies have highlighted a potential role for WAVE3 in promoting tumor progression and metastasis in TNBC. However, whether WAVE3 activity is involved in the development of chemoresistance in TNBCs remains unclear. Here we show that loss of WAVE3 expression resensitizes human TNBC cells to doxorubicin and docetaxel, as measured by increased apoptosis and cell death. We also show that WAVE3 knockdown in the chemotherapy-treated TNBC cells results in inhibition of STAT1 phosphorylation, as well as a significant decrease in expression levels of its downstream effector HIF-1α. Since HIF-1α is a major activator of VEGF-A production, and therefore a stimulator of tumor angiogenesis, loss of HIF-1α in the WAVE3-knockdown cells resulted in the inhibition the chemotherapy-mediated VEGF-A secretion and the downstream activation of angiogenesis, a phenomenon that often accompanies chemoresistance. Our data identify a critical role of WAVE3 in sensitizing TNBC to chemotherapy by inhibiting the STAT1/HIF-1α/VEGF-A signaling axis, and support the possibility that WAVE3 inhibition may be a promising target for TNBC cancer therapy.

Citation Format: Gangarao Davuluri, William P. Schiemann, Edward F. Plow, Khalid Sossey-Alaoui. WAVE3 modulates sensitivity of TNBCs to chemotherapeutics by inhibiting the STAT-HIF-1α-mediated angiogenesis. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Metastasis; 2015 Nov 30-Dec 3; Austin, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(7 Suppl):Abstract nr A49.

Deptor enhances triple-negative breast cancer metastasis and chemoresistance through coupling to survivin expression

Transforming growth factor-β (TGF-β) functions to suppress tumorigenesis in normal mammary tissues and early-stage breast cancers and, paradoxically, acts to promote the metastasis and chemoresistance in late-stage breast cancers, particularly triple-negative breast cancers (TNBCs). Precisely how TGF-β acquires oncogenic characteristics in late-stage breast cancers remains unknown, as does the role of the endogenous mammalian target of rapamycin (mTOR) inhibitor, Dep domain-containing mTOR-interacting protein (Deptor), in coupling TGF-β to TNBC development and metastatic progression. Here we demonstrate that Deptor expression was downregulated in basal-like/TNBCs relative to their luminal counterparts. Additionally, Deptor expression was 1) inversely correlated with the metastatic ability of human (MCF10A) and mouse (4T1) TNBC progression series and 2) robustly repressed by several inducers of epithelial-mesenchymal transition programs. Functional disruption of Deptor expression in 4T07 cells significantly inhibited their proliferation and organoid growth in vitro, as well as prevented their colonization and tumor formation in the lungs of mice. In stark contrast, elevated Deptor expression was significantly associated with poorer overall survival of patients harboring estrogen receptor α-negative breast cancers. Accordingly, enforced Deptor expression in MDA-MB-231 cells dramatically enhanced their 1) organoid growth in vitro, 2) pulmonary outgrowth in mice, and 3) resistance to chemotherapies, an event dependent on the coupling of Deptor to survivin expression. Collectively, our findings highlight the dichotomous functions of Deptor in modulating the proliferation and survival of TNBCs during metastasis; they also implicate Deptor and its stimulation of survivin as essential components of TNBC resistance to chemotherapies and apoptotic stimuli.

miR-138-Mediated Regulation of KINDLIN-2 Expression Modulates Sensitivity to Chemotherapeutics

Prostate cancer is the second leading cause of cancer-related death in men, second only to lung cancer, mainly due to disease reoccurrence as a result to lack of response to androgen deprivation therapies (ADT) after castration. Patients with metastatic castration-resistant prostate cancer (mCRPC) have very limited treatment options, with docetaxel as the first-line standard of care, for which resistance to this chemotherapeutic ultimately develops. Therefore, finding ways to sensitize tumors to chemotherapies and to limit chemoresistance provides a viable strategy to extend the survival of mCRPC patients. This study investigated the role of Kindlin-2 (FERMT2/K2), a member of the Kindlin family of FERM domain proteins and key regulators of the adhesive functions mediated by integrin, in the sensitization of mCRPC to chemotherapeutics. Loss of K2, which is overexpressed in prostate cancer cells derived from mCRPC tumors, compared with those cells derived from androgen-dependent tumors, significantly enhanced apoptosis and cell death of docetaxel-treated PC3 cells. Furthermore, it was determined that K2-mediated sensitization to docetaxel treatment is the result of inhibition of β1-integrin signaling. Finally, miR-138 specifically targeted K2 and inhibited its expression, thereby regulating a miR-138/K2/β1-integrin signaling axis in mCRPC that is critical for the modulation of sensitivity to chemotherapeutics. Thus, these data identify a novel signaling axis where K2 in combination with chemotherapeutics provides a new target for the treatment of mCRPC.

IMPLICATIONS

Targeted inhibition of Kindlin-2 in combination with chemotherapy represents an effective treatment option for mCRPC.

Abstract 2925: WAVE3 is associated with chemoresistance in TNBC by activating tumor angiogenesis downstream of the STAT1/Hif-1α/VEGF-A signaling axis

Chemoresistance is the main cause of disease recurrence and eventual death of breast cancer patients, particularly those harboring triple-negative breast cancer (TNBC) tumors for which effective FDA-approved drugs currently do not exist. However, a recent study determined that TNBCs can be segregated into 6 genetically distinct subtypes that do in fact exhibit differential rates of pathological complete response (pCR) to standard-of-care chemotherapies. Interestingly, the mesenchymal and mesenchymal stem-like subtypes of TNBCs exhibit the lowest rates of pCR when treated with standard-of-care chemotherapies. WAVE3 is an actin-cytoskeleton remodeling protein, and recent studies have highlighted a potential role for WAVE3 in promoting tumor progression and metastasis in TNBC. However, whether WAVE3 activity is involved in the development of chemoresistance in TNBCs, remains unclear. Here we show that loss of WAVE3 expression resensitizes human TNBC cells to Doxorubicin and Docetaxel, as measured by increased apoptosis and cell death. We also show that WAVE3 knockdown in the chemotherapy-treated TNBC cells results in inhibition of STAT1 phosphorylation, as well as a significant decrease in expression levels of its downstream effector Hif-1α. Since Hif-1α is a major activator of VEGF-A production, and therefore, a stimulator of tumor angiogenesis, loss of Hif-1α in the WAVE3-knocdown cells resulted in the inhibition the chemotherapy-mediated VEGF-A secretion and the downstream activation of angiogenesis, a phenomenon that often accompanies chemoresistance. Our data identify a critical role of WAVE3 in sensitizing TNBC to chemotherapy by inhibiting the STAT1⌠Hif-1α⌠VEGF-A signaling axis, and support the possibility of WAVE3 inhibition as a promising approach for TNBC cancer therapy.

Citation Format: Gangarao Davuluri, Edward F. Plow, William P. Schiemann, Khalid Sossey-Alaoui. WAVE3 is associated with chemoresistance in TNBC by activating tumor angiogenesis downstream of the STAT1/Hif-1α/VEGF-A signaling axis. [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 2925. doi:10.1158/1538-7445.AM2015-2925

Abstract 405: Kindlin-2 regulates integrin function and sensitivity to docetaxel in prostate cancer cells

Over the past decade, many lines of evidence have emerged to implicate the three members of the kindlin family of FERM domain proteins as important regulators of integrin adhesion receptors. Specifically, kindlins appear to cooperate with talin to be essential regulators of the ligand binding function of integrins and thereby enhance the adhesive and migratory responses of cells. Kindlin-2 (FERMT2) is the most broadly distributed of the kindlins. To explore the relationship between integrin activation and kindlin-2, prostate cancer cell lines were screened and LNCaP prostate cancer cells were found to express relatively low levels of kindlin-2 and endogenous levels of beta-1 integrin on their surface. A portion of this integrin was expressed in an activated state as detected with an activation specific antibody, HUTS-4. These cells were transfected with vectors for kindlin-2, with or without talin-head domain, a combination that leads to activation of β3 integrins in model cells. Transfections with kindlin-2 suppressed β1 integrin activation on the surface of the LNCaP cells. This inhibitory effect was abolished by mutation of kindlin-2 that prevented its binding to integrin cytoplasmic tail. This inhibitory response to kindlin-2 on β1 integrin was in stark contract to the effects of kindlin-2 plus talin-head expression on β3 function, where co-expression of the same constructs enhanced integrin activation. A mutation in kindlin-2, deletion of its last 15 amino acids, that blocks activation of β3 integrins without preventing its binding to the integrin, also prevents its inhibition of β1 function. We next looked at the effects of kindlin-2 on docetaxel induced apoptosis as monitored with Annexin V staining and cell death as monitored by propidium iodide staining (both by flow cytometry). Compared to LNCaP cells expressing EGFP alone, cells overexpressing EGFP-kindlin-2 were protected against apoptosis and cell death. This effect was dependent upon binding of kindlin-2 to the cytoplasmic tail of integrins. Hence, the capacity of kindlin-2 to influence integrin function depends upon the integrin subfamily and can range from activation to suppression of function. Kindlin-2, which is often overexpressed in transformed cells, may desensitize cells towards chemotherapeutic agents.

Citation Format: Edward F. Plow, Mitali Das, Jamila Hirbawi, Khalid Sossey-Alaoui. Kindlin-2 regulates integrin function and sensitivity to docetaxel in prostate cancer cells. [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 405. doi:10.1158/1538-7445.AM2015-405

Loss of WAVE3 sensitizes triple-negative breast cancers to chemotherapeutics by inhibiting the STAT-HIF-1α-mediated angiogenesis

Chemoresistance allows for disease to recur and ultimately causes the death of most breast cancer patients. This scenario is particularly relevant in patients harboring triple-negative breast cancer (TNBC) tumors for which there are no effective FDA-approved drugs. However, a recent study determined that TNBCs can be segregated into 6 genetically distinct subtypes that do in fact exhibit differential rates of pathological complete response (pCR) to standard-of-care chemotherapies. Of these, the mesenchymal and mesenchymal stem-like subtypes of TNBCs exhibit the lowest rates of pCR when treated with standard-of-care chemotherapies. WAVE3 is an actin-cytoskeleton remodeling protein, and recent studies have highlighted a potential role for WAVE3 in promoting tumor progression and metastasis in TNBC. However, whether WAVE3 activity is involved in the development of chemoresistance in TNBCs remains unclear. Here we show that loss of WAVE3 expression resensitizes human TNBC cells to doxorubicin and docetaxel, as measured by increased apoptosis and cell death. We also show that WAVE3 knockdown in the chemotherapy-treated TNBC cells results in inhibition of STAT1 phosphorylation, as well as a significant decrease in expression levels of its downstream effector HIF-1α. Since HIF-1α is a major activator of VEGF-A production, and therefore a stimulator of tumor angiogenesis, loss of HIF-1α in the WAVE3-knockdown cells resulted in the inhibition the chemotherapy-mediated VEGF-A secretion and the downstream activation of angiogenesis, a phenomenon that often accompanies chemoresistance. Our data identify a critical role of WAVE3 in sensitizing TNBC to chemotherapy by inhibiting the STAT1→HIF-1α→VEGF-A signaling axis, and support the possibility that WAVE3 inhibition may be a promising target for TNBC cancer therapy.

WAVE3-NFκB interplay is essential for the survival and invasion of cancer cells

The WAVE3 cytoskeletal protein promotes cancer invasion and metastasis. We have shown that the WAVE3-mediated activation of cancer cell invasion is due, in part, to its regulation of expression and activity of key metalloproteinases (MMPs), including MMP9, which is centrally involved in invadopodia-mediated degradation of the extracellular matrix (ECM). MMP9 is also a major NFκB target gene, suggesting a potential linkage of WAVE3 to this pathway, which we sought to investigate. Mechanistically, we found that loss of WAVE3 in cancer cells leads to inhibition of NFκB signaling as a result of a decrease in the nuclear translocation of NFκB and therefore loss of activation of NFκB target genes. Conversely, overexpression of WAVE3 was sufficient to enhance NFκB activity. Both pharmacologic and genetic manipulations of NFκB effector molecules show that the biological consequence of loss of WAVE3 function in the NFκB pathway result the inhibition of invadopodia formation and ECM degradation by cancer cells, and these changes are a consequence of decreased MMP9 expression and activity. Loss of WAVE3 also sensitized cancer cells to apoptosis and cell death driven by TNFα, through the inhibition of the AKT pro-survival pathway. Our results identify a novel function of WAVE3 in NFκB signaling, where its activity is essential for the regulation of invadopodia and ECM degradation. Therefore, targeted therapeutic inhibition of WAVE3 will sensitize cancer cells to apoptosis and cell death, and suppress cancer invasion and metastasis.

Abstract 2088: Kindlin-3 enhances breast cancer metastasis through upregulation of Twist-mediated tumor angiogenesis

The FERM domain containing protein, Kindlin-3, has been recognized as a major regulator of integrin function in hematopoietic cells but its role in neoplasia is totally unknown. We have examined the relationship between Kindlin-3 and breast cancer in mouse models and human tissues. Human breast tumors showed a ∼7-fold elevation in kindlin-3 mRNA compared to non-neoplastic tissue by quantitative polymerize chain reaction. At the protein level, Kindlin-3 was found to be expressed abundantly in breast cancer tissue, and its expression increases with the advancing stage of tumor development. Mining of the Oncomine database (www.oncomine.com) confirmed this association: Kindlin-3 was in the top 3 % of gene products elevated in breast cancer (p< 10-12). When Kindlin-3 was over-expressed in a breast cancer cell line, primary tumor growth and lung metastasis increased by 2.5- and 3-fold, respectively when implanted into mice compared to cells expressing vector alone. Mechanistically, the Kindlin-cells displayed a 2.2-fold increase in Vascular Endothelial Growth Factor (VEGF) secretion and B1 integrin activation. Increased VEGF secretion resulted from enhanced production of Twist, a transcription factor which promotes tumor angiogenesis. Knockdown of Twist diminished VEGF production and knockdown of B1 integrins diminished Twist and VEGF production by Kindlin-3 cells while non-targeting si-RNA had no effect on expression of these gene products. The activation of this signaling cascade resulted in the enhancement of breast cancer cell invasion, and tumor angiogenesis and metastasis. Hence, our studies established the pathway in which cross-talk between Kindlin-3 and B1 integrins activates the nuclear translocation of TWIST, which leads to enhanced VEGF-A production and secretion, macrophage infiltration as well as activation of the Epithelial-to-mesenchymal-transition (EMT) program. The activation of this signaling cascade culminates in enhanced breast cancer cell migration, invasion and tumor angiogenesis, all of which are required for tumor progression and metastasis.

In summary, by analysis of human tissue samples and in vitro and in vivo studies, we have identified a novel role for Kindlin-3 in the progression of breast cancer. To our knowledge, this is the first demonstration of the presence and implication of Kindlin-3 in breast cancer or any cancer.

Citation Format: Khalid Sossey-Alaoui, Elzbieta Pluskota, Gangarao Davuluri, Katarzyna Bialkowska, Mitali Das, Daniel Lindner, Edward F. Plow. Kindlin-3 enhances breast cancer metastasis through upregulation of Twist-mediated tumor angiogenesis. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2088. doi:10.1158/1538-7445.AM2014-2088

Fibroblast growth factor receptor splice variants are stable markers of oncogenic transforming growth factor β1 signaling in metastatic breast cancers

Introduction

Epithelial–mesenchymal transition (EMT) and mesenchymal–epithelial transition (MET) facilitate breast cancer (BC) metastasis; however, stable molecular changes that result as a consequence of these processes remain poorly defined. Therefore, with the hope of targeting unique aspects of metastatic tumor outgrowth, we sought to identify molecular markers that could identify tumor cells that had completed the EMT:MET cycle.

Methods

An in vivo reporter system for epithelial cadherin (E-cad) expression was used to quantify its regulation in metastatic BC cells during primary and metastatic tumor growth. Exogenous addition of transforming growth factor β1 (TGF-β1) was used to induce EMT in an in situ model of BC. Microarray analysis was employed to examine gene expression changes in cells chronically treated with and withdrawn from TGF-β1, thus completing one full EMT:MET cycle. Changes in fibroblast growth factor receptor type 1 (FGFR1) isoform expression were validated using PCR analyses of patient-derived tumor tissues versus matched normal tissues. FGFR1 gene expression was manipulated using short hairpin RNA depletion and cDNA rescue. Preclinical pharmacological inhibition of FGFR kinase was employed using the orally available compound BGJ-398.

Results

Metastatic BC cells undergo spontaneous downregulation of E-cad during primary tumor growth, and its expression subsequently returns following initiation of metastatic outgrowth. Exogenous exposure to TGF-β1 was sufficient to drive the metastasis of an otherwise in situ model of BC and was similarly associated with a depletion and return of E-cad expression during metastatic progression. BC cells treated and withdrawn from TGF-β stably upregulate a truncated FGFR1-β splice variant that lacks the outermost extracellular immunoglobulin domain. Identification of this FGFR1 splice variant was verified in metastatic human BC cell lines and patient-derived tumor samples. Expression of FGFR1-β was also dominant in a model of metastatic outgrowth where depletion of FGFR1 and pharmacologic inhibition of FGFR kinase activity both inhibited pulmonary tumor outgrowth. Highlighting the dichotomous nature of FGFR splice variants and recombinant expression of full-length FGFR1-α also blocked pulmonary tumor outgrowth.

Conclusion

The results of our study strongly suggest that FGFR1-β is required for the pulmonary outgrowth of metastatic BC. Moreover, FGFR1 isoform expression can be used as a predictive biomarker for therapeutic application of its kinase inhibitors.

Kindlin-3 enhances breast cancer progression and metastasis by activating Twist-mediated angiogenesis

The FERM domain containing protein Kindlin-3 has been recognized as a major regulator of integrin function in hematopoietic cells, but its role in neoplasia is totally unknown. We have examined the relationship between Kindlin-3 and breast cancer in mouse models and human tissues. Human breast tumors showed a ∼7-fold elevation in Kindlin-3 mRNA compared with nonneoplastic tissue by quantitative polymerase chain reaction. Kindlin-3 overexpression in a breast cancer cell line increased primary tumor growth and lung metastasis by 2.5- and 3-fold, respectively, when implanted into mice compared with cells expressing vector alone. Mechanistically, the Kindlin-3-overexpressing cells displayed a 2.2-fold increase in vascular endothelial growth factor (VEGF) secretion and enhanced β1 integrin activation. Increased VEGF secretion resulted from enhanced production of Twist, a transcription factor that promotes tumor angiogenesis. Knockdown of Twist diminished VEGF production, and knockdown of β1 integrins diminished Twist and VEGF production by Kindlin-3-overexpressing cells, while nontargeting small interfering RNA had no effect on expression of these gene products. Thus, Kindlin-3 influences breast cancer progression by influencing the crosstalk between β1 integrins and Twist to increase VEGF production. This signaling cascade enhances breast cancer cell invasion and tumor angiogenesis and metastasis.

Upregulated WAVE3 expression is essential for TGF-β-mediated EMT and metastasis of triple-negative breast cancer cells

Breast cancer is the second leading cause of cancer death in women in the United States. Metastasis accounts for the death of ~90 % of these patients, yet the mechanisms underlying this event remain poorly defined. WAVE3 belongs to the WASP/WAVE family of actin-binding proteins that play essential roles in regulating cell morphology, actin polymerization, cytoskeleton remodeling, cell motility, and invasion. Accordingly, we demonstrated previously that WAVE3 promotes the acquisition of invasive and metastatic phenotypes by human breast cancers. Herein, we show that transforming growth factor-β (TGF-β) selectively and robustly induced the expression of WAVE3 in metastatic breast cancer cells, but not in their nonmetastatic counterparts. Moreover, the induction of WAVE3 expression in human and mouse triple-negative breast cancer cells (TNBCs) by TGF-β likely reflects its coupling to microRNA expression via a Smad2- and β3 integrin-dependent mechanism. We further demonstrate the requirement for WAVE3 expression in mediating the initiation of epithelial-mesenchymal transition (EMT) programs stimulated by TGF-β. Indeed, stable depletion of WAVE3 expression in human TNBC cells prevented TGF-β from inducing EMT programs and from stimulating the proliferation, migration, and the formation of lamellipodia in metastatic TNBC cells. Lastly, we observed WAVE3 deficiency to abrogate the outgrowth of TNBC cell organoids in 3-dimensional organotypic cultures as well as to decrease the growth and metastasis of 4T1 tumors produced in syngeneic Balb/C mice. Indeed, WAVE3 deficiency significantly reduced the presence of sarcomatoid morphologies indicative of EMT phenotypes in pulmonary TNBC tumors as compared to those detected in their parental counterparts. Collectively, these findings indicate the necessity for WAVE3 expression and activity during EMT programs stimulated by TGF-β; they also suggest that measures capable of inactivating WAVE3 may play a role in alleviating metastasis stimulated by TGF-β.

miRNA-548c: a specific signature in circulating PBMCs from dilated cardiomyopathy patients

High fidelity genome-wide expression analysis has strengthened the idea that microRNA (miRNA) signatures in peripheral blood mononuclear cells (PBMCs) can be potentially used to predict the pathology when anatomical samples are inaccessible like the heart. PBMCs from 48 non-failing controls and 44 patients with relatively stable chronic heart failure (ejection fraction of ≤ 40%) associated with dilated cardiomyopathy (DCM) were used for miRNA analysis. Genome-wide miRNA-microarray on PBMCs from chronic heart failure patients identified miRNA signature uniquely characterized by the downregulation of miRNA-548 family members. We have also independently validated downregulation of miRNA-548 family members (miRNA-548c & 548i) using real time-PCR in a large cohort of independent patient samples. Independent in silico Ingenuity Pathway Analysis (IPA) of miRNA-548 targets shows unique enrichment of signaling molecules and pathways associated with cardiovascular disease and hypertrophy. Consistent with specificity of miRNA changes with pathology, PBMCs from breast cancer patients showed no alterations in miRNA-548c expression compared to healthy controls. These studies suggest that miRNA-548 family signature in PBMCs can therefore be used to detect early heart failure. Our studies show that cognate networking of predicted miRNA-548 targets in heart failure can be used as a powerful ancillary tool to predict the ongoing pathology.

Abstract 2702: WAVE3 regulates NFκB signaling and sensitizes cancer cells to apoptosis and cell death driven by TNFα

ABSTRACT

WAVE3, a member of actin nucleation proteins promotes cancer invasion and metastasis, in part through regulation of expression and activity of key matrix metalloproteinases (MMPs) MMP9, which is centrally involved in invadopodia-mediated degradation of the extracellular matrix (ECM). MMP9 is also a major NFκB target gene, suggesting a potentially important role of WAVE3 in this pathway. Mechanistically, we found that loss of WAVE3 in cancer cells leads to significant inhibition of TNFα-induced NFκB activation as a result of de-stabilization of the IκBα-NFκB complex. Conversely, overexpression of WAVE3 was sufficient to enhance NFκB activity by stabilizing the IκBα-NFκB complex. We used both pharmacological and genetic manipulations of NFκB effector molecules and identified IKKβ but not IKKα as the primary upstream target for WAVE3-mediated regulation of NFκB activity. We also showed that loss of WAVE3 resulted in a significant inhibition of TNFα-mediated MMP9 expression and activity. Loss of WAVE3 also sensitized cancer cells to TNFα-driven apoptosis and cell death. Finally, we showed that either the basic rich (BR) or the proline rich (PR) domain of WAVE3 is sufficient to modulate NFkB signaling. Our results identify a novel function of WAVE3 in NFκB signaling, where its activity is essential for the stabilization of NFκB complex that promotes the metastatic phenotype of cancer cells. Therefore, therapeutic targeting of WAVE3 may prove beneficial for preventing or reducing the metastatic burden in cancer patients.

Citation Format: Gangarao Davuluri, Khalid Sossey-Alaoui, Edward Plow. WAVE3 regulates NFκB signaling and sensitizes cancer cells to apoptosis and cell death driven by TNFα. [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 2702. doi:10.1158/1538-7445.AM2013-2702

Surfing the big WAVE: Insights into the role of WAVE3 as a driving force in cancer progression and metastasis

WAVE3 belongs to the WASP/WAVE family of actin cytoskeleton remodeling proteins. These proteins are known to be involved in several biological functions ranging from controlling cell shape and movement, to being closely associated with pathological conditions such as cancer progression and metastasis. Last decade has seen an explosion in the literature reporting significant scientific advances on the molecular mechanisms whereby the WASP/WAVE proteins are regulated both in normal physiological as well as pathological conditions. The purpose of this review is to present the major findings pertaining to how WAVE3 has become a critical player in the regulation of signaling pathways involved in cancer progression and metastasis. The review will conclude with suggesting options for the potential use of WAVE3 as a therapeutic target to prevent the progression of cancer to the lethal stage that is the metastatic disease.

Abstract C34: WAVE3 is required for TGF-β-mediated EMT

Breast cancer (BC) is the second leading cause of cancer death in women in the United States. Metastasis accounts for the death of ~90% of these patients, yet the mechanisms underlying this event remain poorly defined. WAVE3 belongs to the WASP/WAVE family of actin-binding proteins that mediate essential roles in regulating cell shape/morphology, actin polymerization and cytoskeleton remodeling, and cell motility and invasion. Accordingly, we have shown that WAVE3 promotes the acquisition of invasive and metastatic phenotypes by human BCs. Along these lines, we also established that members of the miR-200 family, together with miR-31 suppress WAVE3 expression, thereby limiting its prometastatic behavior. We show here that Transforming Growth Factor-beta (TGFβ;) robustly decreases miR-31 expression and induces WAVE3 expression through a Smad2 and β3-integrin dependent mechanism. Moreover, WAVE3 expression is required for BC cells to undergo epithelial-mesenchymal transition (EMT) in response to TGF-β;. Accordingly, stable depletion of WAVE3 expression in metastatic MDA-MB-231 or 4T1 BC cells prevented TGF-β; from inducing the EMT as determined by monitoring changes in the actin cytoskeleton and expression of EMT markers by real-time PCR. Along these lines, WAVE3 depletion significantly inhibited the ability of 4T1 cells to migrate and proliferate in response to TGF-β;. Moreover, WAVE3 deficiency abrogated the outgrowth of MDA-MB-231 and 4T1 cell organoids in 3D organotypic cultures. In vivo bioluminescent imaging indicated that WAVE3 knockdown also decreased tumor growth and metastasis in 4T1 tumors that possess enhanced autocrine TGF-β; signaling. Collectively, these findings indicate that WAVE3 activity is required for TGF-β;-mediated EMT and suggest that measures capable of inactivating WAVE3 may alleviate BC metastasis stimulated by TGF-β;.

Citation Format: Molly A. Taylor, Gangarao Davuluri, Brian McCue, Edward F. Plow, William P. Schiemann, Khalid Sossey-Alaoui. WAVE3 is required for TGF-β-mediated EMT. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Invasion and Metastasis; Jan 20-23, 2013; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2013;73(3 Suppl):Abstract nr C34.

TGF-β upregulates miR-181a expression to promote breast cancer metastasis

Late-stage breast cancer metastasis is driven by dysregulated TGF-β signaling, but the underlying molecular mechanisms have not been fully elucidated. We attempted to recapitulate tumor and metastatic microenvironments via the use of biomechanically compliant or rigid 3D organotypic cultures and combined them with global microRNA (miR) profiling analyses to identify miRs that were upregulated in metastatic breast cancer cells by TGF-β. Here we establish miR-181a as a TGF-β-regulated "metastamir" that enhanced the metastatic potential of breast cancers by promoting epithelial-mesenchymal transition, migratory, and invasive phenotypes. Mechanistically, inactivation of miR-181a elevated the expression of the proapoptotic molecule Bim, which sensitized metastatic cells to anoikis. Along these lines, miR-181a expression was essential in driving pulmonary micrometastatic outgrowth and enhancing the lethality of late-stage mammary tumors in mice. Finally, miR-181a expression was dramatically and selectively upregulated in metastatic breast tumors, particularly triple-negative breast cancers, and was highly predictive for decreased overall survival in human breast cancer patients. Collectively, our findings strongly implicate miR-181a as a predictive biomarker for breast cancer metastasis and patient survival, and consequently, as a potential therapeutic target in metastatic breast cancer.

Increased expression levels of WAVE3 are associated with the progression and metastasis of triple negative breast cancer

Background

Breast Cancer (BC) is a heterogeneous disease comprised of at least five genetically distinct subtypes, which together form the second leading cause of cancer death in women in the United States. Within BC subtypes, those classified as Triple Negative BCs (TNBCs) exhibit dismal survival rates due to their propensity to develop distant metastases. We have identified the WAVE3 protein, which is a critical regulator of actin cytoskeleton dynamics that are required for the motility and invasion of cancer cells through its activation of the Arp2/3 complex, as a key regulator of the different steps of the invasion-metastasis cascade in BC, especially in the more aggressive TNBCs. Our published studies have also shown that elevated expression levels of WAVE3 in the TNBC cell lines directly contribute to their increased invasion and metastasis potentials both in vitro and in vivo in murine models of BC metastasis.

Methodology/Principal Findings

Herein, we utilized both immunohistochemistry (IHC) of primary human BC tumors as well as quantitative real-time RT-PCR of WAVE3 in the peripheral blood of BC patients to clearly establish that WAVE3 is a predictive marker of overall BC patients’ survival. High levels of WAVE3 were predictive for reduced distant recurrence-free survival as well as for decreased disease-specific mortality. Our analysis of WAVE3 expression levels in the peripheral blood of BC patients showed that WAVE3 is highly expressed in the blood of patients who developed metastatic breast cancer compared to those who did not. WAVE3 expression was also highly upregulated in the blood of BC patients with the more aggressive TNBC subtype.

Conclusions

Together, these findings establish WAVE3 as a novel marker for increased risk of breast-cancer-specific mortality and for the metastatic potential of the TNBCs, and also identify WAVE3 as an attractive therapeutic target for the treatment of metastatic BC.

Abstract 5315: WAVE3 modulates the invasion-metastasis cascade by regulating invadopodia structures, MMP activity and ECM degradation

Invadopodia are dynamic membrane structures enriched in actin that form on the ventral side of invasive cancer cells and are required for the degradation of the extracellular matrix (ECM), therefore, allowing the invasion of the tumor-surrounding tissue and subsequent colonization and metastasis. Invadopodia are the site of assembly of a multitude of proteins, including the actin regulators cortactin and members of WASP/WAVE proteins family. In our previously published studies we have identified WAVE3 as a key player in modulating the invasion-metastasis cascade in breast cancer (BC), where WAVE3 expression levels are significantly increased in metastatic BC cell lines and tumors. We have also shown that the metastasis-promoting activity of WAVE3 is achieved in part by affecting the activity of several matrix metalloproteinases (MMPs), including MMP1, MMP3 and MMP9. These MMPs, which are integral constituents of invadopodia, are required for the degradation of the ECM. More importantly, we have shown that phosphorylation of WAVE3 by Abl tyrosine kinase at specific tyrosine residues is required for the WAVE3-mediated modulation of BC metastasis. Here we present evidence that WAVE3 phosphorylation regulates the metastatic phenotype of BC by affecting the formation of invadopodia, MMPs activity and ECM degradation. First we show that loss of WAVE3 in the metastatic MDA-MB-231 BC cells results in a significant reduction in the number of invadopodia. Loss of WAVE3 expression also results in a significant decrease in MMP expression and activity in the zymography assay, loss of the ability of MDA-MB-231 cells to degrade gelatin in the ECM degradation assay, and consequently, a dramatic decrease in the invasive potential of these cells. Mechanistically, our data have now established a new link between WAVE3 and invadopodia, where WAVE3 phosphorylation downstream of Abl is critical for the formation of invadopodia structures as well as for MMP activity and for the degradation of the ECM. Loss of WAVE3 phosphorylation either by site directed mutagenesis or by pharmacological inhibition of Abl kinase activity leads to a significant decrease in invadopodia formation, MMP2 and MMP9 activity as well as ECM degradation, as a direct result of the inability of phospho-mutant WAVE3 to localize to invadopodia. In an independent study, we have found that WAVE3 is involved in a different molecular pathway, where WAVE3 phosphorylation is also required for the nuclear translocation of NFkB and the activation of MMP9, downstream of TNFα. The WAVE3-mediated NFkB nuclear translocation to activate MMP9 is facilitated through a WAVE3-Importin interaction, either directly or within a protein complex. Together, our data indentify two independent pathways whereby WAVE3 modulates the cancer invasion-metastasis cascade through its regulation of invadopodia structures and the NFkB-mediated activation of MMPs.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5315. doi:1538-7445.AM2012-5315

miR-31 and its host gene lncRNA LOC554202 are regulated by promoter hypermethylation in triple-negative breast cancer

Background

microRNAs have been established as powerful regulators of gene expression in normal physiological as well as in pathological conditions, including cancer progression and metastasis. Recent studies have demonstrated a key role of miR-31 in the progression and metastasis of breast cancer. Downregulation of miR-31 enhances several steps of the invasion-metastasis cascade in breast cancer, i.e., local invasion, extravasation and survival in the circulation system, and metastatic colonization of distant sites. miR-31 exerts its metastasis-suppressor activity by targeting a cohort of pro-metastatic genes, including RhoA and WAVE3. The molecular mechanisms that lead to the loss of miR-31 and the activation of its pro-metastatic target genes during these specific steps of the invasion-metastasis cascade are however unknown.

Results

In the present report, we identify promoter hypermethylation as one of the major mechanisms for silencing miR-31 in breast cancer, and in the triple-negative breast cancer (TNBC) cell lines of basal subtype, in particular. miR-31 maps to the intronic sequence of a novel long non-coding (lnc)RNA, LOC554202 and the regulation of its transcriptional activity is under control of LOC554202. Both miR-31 and the host gene LOC554202 are down-regulated in the TNBC cell lines of basal subtype and over-expressed in the luminal counterparts. Treatment of the TNBC cell lines with either a de-methylating agent alone or in combination with a de-acetylating agent resulted in a significant increase of both miR-31 and its host gene, suggesting an epigenetic mechanism for the silencing of these two genes by promoter hypermethylation. Finally, both methylation-specific PCR and sequencing of bisulfite-converted DNA demonstrated that the LOC554202 promoter-associated CpG island is heavily methylated in the TNBC cell lines and hypomethylated in the luminal subtypes.

Conclusion

Loss of miR-31 expression in TNBC cell lines is attributed to hypermethylation of its promoter-associated CpG island. Together, our results provide the initial evidence for a mechanism by which miR-31, an important determinant of the invasion metastasis cascade, is regulated in breast cancer.