Expression-Based Diagnosis, Treatment Selection, and Drug Development for Breast Cancer

There is currently no gene expression assay that can assess if premalignant lesions will develop into invasive breast cancer. This study sought to identify biomarkers for selecting patients with a high potential for developing invasive carcinoma in the breast with normal histology, benign lesions, or premalignant lesions. A set of 26-gene mRNA expression profiles were used to identify invasive ductal carcinomas from histologically normal tissue and benign lesions and to select those with a higher potential for future cancer development (ADHC) in the breast associated with atypical ductal hyperplasia (ADH). The expression-defined model achieved an overall accuracy of 94.05% (AUC = 0.96) in classifying invasive ductal carcinomas from histologically normal tissue and benign lesions (n = 185). This gene signature classified cancer development in ADH tissues with an overall accuracy of 100% (n = 8). The mRNA expression patterns of these 26 genes were validated using RT-PCR analyses of independent tissue samples (n = 77) and blood samples (n = 48). The protein expression of PBX2 and RAD52 assessed with immunohistochemistry were prognostic of breast cancer survival outcomes. This signature provided significant prognostic stratification in The Cancer Genome Atlas breast cancer patients (n = 1100), as well as basal-like and luminal A subtypes, and was associated with distinct immune infiltration and activities. The mRNA and protein expression of the 26 genes was associated with sensitivity or resistance to 18 NCCN-recommended drugs for treating breast cancer. Eleven genes had significant proliferative potential in CRISPR-Cas9/RNAi screening. Based on this gene expression signature, the VEGFR inhibitor ZM-306416 was discovered as a new drug for treating breast cancer.

Abstract 1296: Targeting nuclear AURKA and hypoxia signaling pathway attenuates metastatic burden in triple negative breast cancer

Despite remarkable progress in diagnosis and treatment, metastasis from the primary tumor to distant organs is responsible for over 90% of cancer deaths. Therefore, there is a need to understand the drivers of the process to detect, target, and develop therapeutics to treat metastases better and extend their lifespan. Aurora-A Kinase (AURKA) is a serine/threonine kinase that typically localizes in the cytoplasm. However, the nuclear localization of AURKA (N-AURKA) has been reported in multiple cancers and correlates with poor survival and the advanced/metastatic stage of the disease. AURKA is often present in the nucleus of metastatic Triple Negative Breast Cancer (TNBC) cells and patient biopsies compared to non-metastatic cells. Moreover, induced translocation of AURKA to the nucleus in experimental models of TNBC results in a 5-fold increase in metastases to the bones, lungs, and liver compared to AURKA in the cytoplasm. We have previously shown that N-AURKA under normoxic conditions binds to HIF1A/1B and leads to induction of hypoxia signaling via transactivation of Hypoxia Inducible Factors (HIFs)-dependent genes, including migration/invasion, survival/death, and stemness, promoting early cancer dissemination. Transactivation of HIF1-genes requires cofactor p300/CBP. It is currently unknown if N-AURKA/HIF1 transcription is p300 dependent. In this study, we used the small molecular inhibitor Chetomin to disrupt the interaction of HIF1A and co-activator CBP/p300 in experimental TNBC and animal models combined with AURKA inhibitor Alisertib. Disruption of the hypoxia signaling pathway significantly decreases the transactivation of HIF-dependent genes, including migration/invasion, survival/death, and stemness in N-AURKA cells. Moreover, in mouse models, inhibition of HIF1 activity via treatment with Chetomin in combination with AURKA inhibitor Alisertib significantly decreased metastatic burden suggesting that p300 binding to AURKA/HIF complex is critical for gene expression and enabling metastatic dissemination/colonization. Our studies show the mechanistic relationship between N-AURKA and hypoxia signaling and lay the foundation for developing novel combination treatment strategies to improve patient outcomes.

Citation Format: Abha Maskey, Kristina Marinak Whately, Elena N. Pugacheva. Targeting nuclear AURKA and hypoxia signaling pathway attenuates metastatic burden in triple negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1296.

NEDD9 Overexpression Causes Hyperproliferation of Luminal Cells and Cooperates with HER2 Oncogene in Tumor Initiation: A Novel Prognostic Marker in Breast Cancer

HER2 overexpression occurs in 10-20% of breast cancer patients. HER2+ tumors are characterized by an increase in Ki67, early relapse, and increased metastasis. Little is known about the factors influencing early stages of HER2- tumorigenesis and diagnostic markers. Previously, it was shown that the deletion of NEDD9 in mouse models of HER2 cancer interferes with tumor growth, but the role of NEDD9 upregulation is currently unexplored. We report that NEDD9 is overexpressed in a significant subset of HER2+ breast cancers and correlates with a limited response to anti-HER2 therapy. To investigate the mechanisms through which NEDD9 influences HER2-dependent tumorigenesis, we generated MMTV-Cre-NEDD9 transgenic mice. The analysis of mammary glands shows extensive ductal epithelium hyperplasia, increased branching, and terminal end bud expansion. The addition of oncogene Erbb2 (neu) leads to the earlier development of early hyperplastic benign lesions (~16 weeks), with a significantly shorter latency than the control mice. Similarly, NEDD9 upregulation in MCF10A-derived acini leads to hyperplasia-like DCIS. This phenotype is associated with activation of ERK1/2 and AURKA kinases, leading to an increased proliferation of luminal cells. These findings indicate that NEDD9 is setting permissive conditions for HER2-induced tumorigenesis, thus identifying this protein as a potential diagnostic marker for early detection.

Nuclear Aurora-A kinase-induced hypoxia signaling drives early dissemination and metastasis in breast cancer: implications for detection of metastatic tumors

Metastatic breast cancer causes most breast cancer-associated deaths, especially in triple negative breast cancers (TNBC). The metastatic drivers of TNBCs are still poorly understood, and effective treatment non-existent. Here we reveal that the presence of Aurora-A Kinase (AURKA) in the nucleus and metastatic dissemination are molecularly connected through HIF1 (Hypoxia-Inducible Factor-1) signaling. Nuclear AURKA activates transcription of "hypoxia-induced genes" under normoxic conditions (pseudohypoxia) and without upregulation of oxygen-sensitive HIF1A subunit. We uncover that AURKA preferentially binds to HIF1B and co-localizes with the HIF complex on DNA. The mass-spectrometry analysis of the AURKA complex further confirmed the presence of CBP and p300 along with other TFIIB/RNApol II components. Importantly, the expression of multiple HIF-dependent genes induced by nuclear AURKA (N-AURKA), including migration/invasion, survival/death, and stemness, promote early cancer dissemination. These results indicate that nuclear, but not cytoplasmic, AURKA is a novel driver of early metastasis. Analysis of clinical tumor specimens revealed a correlation between N-AURKA presence and decreased patient survival. Our results establish a mechanistic link between two critical pathways in cancer metastasis, identifying nuclear AURKA as a crucial upstream regulator of the HIF1 transcription complex and a target for anti-metastatic therapy.

Primary Cilium Is Involved in Stem Cell Differentiation and Renewal through the Regulation of Multiple Signaling Pathways

Signaling networks guide stem cells during their lineage specification and terminal differentiation. Primary cilium, an antenna-like protrusion, directly or indirectly plays a significant role in this guidance. All stem cells characterized so far have primary cilia. They serve as entry- or check-points for various signaling events by controlling the signal transduction and stability. Thus, defects in the primary cilia formation or dynamics cause developmental and health problems, including but not limited to obesity, cardiovascular and renal anomalies, hearing and vision loss, and even cancers. In this review, we focus on the recent findings of how primary cilium controls various signaling pathways during stem cell differentiation and identify potential gaps in the field for future research.

Functional Hierarchy and Cooperation of EMT Master Transcription Factors in Breast Cancer Metastasis

Several master transcription factors (TF) can activate the epithelial-to-mesenchymal transition (EMT). However, their individual and combinatorial contributions to EMT in breast cancer are not defined. We show that overexpression of EMT-TFs individually in epithelial cells upregulated endogenous SNAI2, ZEB1/2, TCF4, and TWIST1/2 as a result of positive feedback mediated in part by suppression of their negative regulator miRNAs miR200s/203/205. We identified TCF4 as a potential new target of miR200s. Expression of ZEB1/2 strongly correlated with the mesenchymal phenotype in breast cancer cells, with the CD24^-/CD44⁺ stemness profile, and with lower expression of core epithelial genes in human breast tumors. Knockdown of EMT-TFs identified the key role of ZEB1 and its functional cooperation with other EMT-TFs in the maintenance of the mesenchymal state. Inducible ZEB1+2 knockdown in xenograft models inhibited pulmonary metastasis, emphasizing their critical role in dissemination from primary site and in extravasation. However, ZEB1+2 depletion one-week after intravenous injection did not inhibit lung colonization, suggesting that ZEB1/2 and EMT are not essential for macrometastatic outgrowth. These results provide strong evidence that EMT is orchestrated by coordinated expression of several EMT-TFs and establish ZEB1 as a key master regulator of EMT and metastasis in breast cancer. IMPLICATIONS: The EMT program is orchestrated by coordinated expression of multiple EMT transcription factors, whereas ZEB1 integrates the EMT master regulatory network and plays the major role in promoting EMT and metastasis.

Skeletal muscle reprogramming by breast cancer regardless of treatment history or tumor molecular subtype

Increased susceptibility to fatigue is a negative predictor of survival commonly experienced by women with breast cancer (BC). Here, we sought to identify molecular changes induced in human skeletal muscle by BC regardless of treatment history or tumor molecular subtype using RNA-sequencing (RNA-seq) and proteomic analyses. Mitochondrial dysfunction was apparent across all molecular subtypes, with the greatest degree of transcriptomic changes occurring in women with HER2/neu-overexpressing tumors, though muscle from patients of all subtypes exhibited similar pathway-level dysregulation. Interestingly, we found no relationship between anticancer treatments and muscle gene expression, suggesting that fatigue is a product of BC per se rather than clinical history. In vitro and in vivo experimentation confirmed the ability of BC cells to alter mitochondrial function and ATP content in muscle. These data suggest that interventions supporting muscle in the presence of BC-induced mitochondrial dysfunction may alleviate fatigue and improve the lives of women with BC.

Mutations in ARL2BP, a protein required for ciliary microtubule structure, cause syndromic male infertility in humans and mice

Cilia are evolutionarily conserved hair-like structures with a wide spectrum of key biological roles, and their dysfunction has been linked to a growing class of genetic disorders, known collectively as ciliopathies. Many strides have been made towards deciphering the molecular causes for these diseases, which have in turn expanded the understanding of cilia and their functional roles. One recently-identified ciliary gene is ARL2BP, encoding the ADP-Ribosylation Factor Like 2 Binding Protein. In this study, we have identified multiple ciliopathy phenotypes associated with mutations in ARL2BP in human patients and in a mouse knockout model. Our research demonstrates that spermiogenesis is impaired, resulting in abnormally shaped heads, shortened and mis-assembled sperm tails, as well as in loss of axonemal doublets. Additional phenotypes in the mouse included enlarged ventricles of the brain and situs inversus. Mouse embryonic fibroblasts derived from knockout animals revealed delayed depolymerization of primary cilia. Our results suggest that ARL2BP is required for the structural maintenance of cilia as well as of the sperm flagellum, and that its deficiency leads to syndromic ciliopathy.

The flagellated tails of sperm cells require a stringent developmental process that is essential for motility and fertility. The components that comprise the sperm tail assemble in regulated steps with protein processing, transport, and structural assembly dependent on each other for sperm tail maturity. In this work, we have identified ARL2BP, a previously retinal-associated protein, to be essential for sperm tail development and assembly. We show that without functional ARL2BP in humans or mice, sperm tails fail to develop, starting with the assembly of the core microtubular structure within the tail. Loss of ARL2BP also effects other ciliated cells, indicating a unique role for ARL2BP in ciliary microtubule formation. This research on ARL2BP provides further understanding on the links between vision and fertility. This work also demonstrates how genomic studies for human patients and murine models can coincide to provide greater insight into disease.

Human Breast Cancer Xenograft Model Implicates Peroxisome Proliferator-activated Receptor Signaling as Driver of Cancer-induced Muscle Fatigue

PURPOSE

This study tested the hypothesis that a patient-derived orthotopic xenograft (PDOX) model would recapitulate the common clinical phenomenon of breast cancer-induced skeletal muscle (SkM) fatigue in the absence of muscle wasting. This study additionally sought to identify drivers of this condition to facilitate the development of therapeutic agents for patients with breast cancer experiencing muscle fatigue.

EXPERIMENTAL DESIGN

Eight female BC-PDOX-bearing mice were produced via transplantation of tumor tissue from 8 female patients with breast cancer. Individual hind limb muscles from BC-PDOX mice were isolated at euthanasia for RNA-sequencing, gene and protein analyses, and an ex vivo muscle contraction protocol to quantify tumor-induced aberrations in SkM function. Differentially expressed genes (DEG) in the BC-PDOX mice relative to control mice were identified using DESeq2, and multiple bioinformatics platforms were employed to contextualize the DEGs.

RESULTS

We found that SkM from BC-PDOX-bearing mice showed greater fatigability than control mice, despite no differences in absolute muscle mass. PPAR, mTOR, IL6, IL1, and several other signaling pathways were implicated in the transcriptional changes observed in the BC-PDOX SkM. Moreover, 3 independent in silico analyses identified PPAR signaling as highly dysregulated in the SkM of both BC-PDOX-bearing mice and human patients with early-stage nonmetastatic breast cancer.

CONCLUSIONS

Collectively, these data demonstrate that the BC-PDOX model recapitulates the expected breast cancer-induced SkM fatigue and further identify aberrant PPAR signaling as an integral factor in the pathology of this condition.

LPA signaling is regulated through the primary cilium: a novel target in glioblastoma

The primary cilium is a ubiquitous organelle presented on most human cells. It is a crucial signaling hub for multiple pathways including growth factor and G-protein coupled receptors. Loss of primary cilia, observed in various cancers, has been shown to affect cell proliferation. Primary cilia formation is drastically decreased in glioblastoma (GBM), however, the role of cilia in normal astrocyte or glioblastoma proliferation has not been explored. Here we report that loss of primary cilia in human astrocytes stimulates growth rate in a lysophosphatidic acid (LPA)-dependent manner. We show that lysophosphatidic acid receptor 1 (LPAR1) is accumulated in primary cilia. LPAR1 signaling through Gα12/Gαq was previously reported to be responsible for cancer cell proliferation. We found that in ciliated cells, Gα12 and Gαq are excluded from the cilium, creating a barrier against unlimited proliferation, one of the hallmarks of cancer. Upon loss of primary cilia, LPAR1 redistributes to the plasma membrane with a concomitant increase in LPAR1 association with Gα12 and Gαq. Inhibition of LPA signaling with the small molecule compound Ki16425 in deciliated highly proliferative astrocytes or glioblastoma patient-derived cells/xenografts drastically suppresses their growth both in vitro and in vivo. Moreover, Ki16425 brain delivery via PEG-PLGA nanoparticles inhibited tumor progression in an intracranial glioblastoma PDX model. Overall, our findings establish a novel mechanism by which primary cilium restricts proliferation and indicate that loss of primary cilia is sufficient to increase mitogenic signaling, and is important for the maintenance of a highly proliferative phenotype. Clinical application of LPA inhibitors may prove beneficial to restrict glioblastoma growth and ensure local control of disease.

Abstract 1084: Combination of eribulin and AURKA inhibitor prevents metastatic colonization and eradicates established metastases in breast cancer

The majority of cancer-related deaths (90%) are happened due to metastasis from the primary tumor site to distant organs. MLN8237 is a small, highly selective molecule inhibitor of Aurora A kinase (AURKA), which results in disruption of the mitotic spindle, chromosome segregation collapse, and inhibition of cell proliferation. Numerous studies have showed that levels of AURKA are elevated in many types of cancer, including breast cancer. Our previous studies indicated that MLN8237 is extremely potent against pulmonary metastasis, but not the primary tumor in orthotropic xenograft model. To further enhance MLN8237 based regiment, its combination with other therapeutic compounds can be used. As a potential partner we chose eribulin - fully synthetic macrocyclic analogue of the marine natural product halichondrin B. Eribulin belong to the class of non-taxane microtubule destabilizing molecules, currently used in clinic to treat taxol resistant metastatic breast cancer. In present study we have investigated the effect of MLN8237 and eribulin against breast cancer in vivo and in vitro. The results showed that combination of drugs possess a synergistic effect on both primary tumor and metastases, through inducing cytotoxic autophagy and apoptosis. This data clearly indicate great potential behind the MLN8237 based therapies and introduce a new hope for the eradication of metastatic breast cancer.

Citation Format: Elena N. Pugacheva, Varvara Kozyreva, Anna Kiseleva, Ryan Ice, Brandon Jones, Yuriy Loskutov. Combination of eribulin and AURKA inhibitor prevents metastatic colonization and eradicates established metastases in breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1084. doi:10.1158/1538-7445.AM2017-1084

Dual Targeting of Mesenchymal and Amoeboid Motility Hinders Metastatic Behavior

Commonly upregulated in human cancers, the scaffolding protein NEDD9/HEF1 is a known regulator of mesenchymal migration and cancer cell plasticity. However, the functional role of NEDD9 as a regulator of different migration/invasion modes in the context of breast cancer metastasis is currently unknown. Here, it is reported that NEDD9 is necessary for both mesenchymal and amoeboid individual cell migration/invasion in triple-negative breast cancer (TNBC). NEDD9 deficiency results in acquisition of the amoeboid morphology, but severely limits all types of cell motility. Mechanistically, NEDD9 promotes mesenchymal migration via VAV2-dependent Rac1 activation, and depletion of VAV2 impairs the ability of NEDD9 to activate Rac1. In addition, NEDD9 supports a mesenchymal phenotype through stimulating polymerization of actin via promoting CTTN phosphorylation in an AURKA-dependent manner. Interestingly, an increase in RhoA activity in NEDD9-depleted cells does not facilitate a switch to functional amoeboid motility, indicating a role of NEDD9 in the regulation of downstream RhoA signaling effectors. Simultaneous depletion of NEDD9 or inhibition of AURKA in combination with inhibition of the amoeboid driver ROCK results in an additional decrease in cancer cell migration/invasion. Finally, we confirmed that a dual targeting strategy is a viable and efficient therapeutic approach to hinder the metastasis of breast cancer in xenograft models, showcasing the important need for further clinical evaluation of this regimen to impede the spread of disease and improve patient survival.Implications: This study provides new insight into the therapeutic benefit of combining NEDD9 depletion with ROCK inhibition to reduce tumor cell dissemination and discovers a new regulatory role of NEDD9 in the modulation of VAV2-dependent activation of Rac1 and actin polymerization. Mol Cancer Res; 15(6); 670-82. ©2017 AACR.

Combination of Eribulin and Aurora A Inhibitor MLN8237 Prevents Metastatic Colonization and Induces Cytotoxic Autophagy in Breast Cancer

Recent findings suggest that the inhibition of Aurora A (AURKA) kinase may offer a novel treatment strategy against metastatic cancers. In the current study, we determined the effects of AURKA inhibition by the small molecule inhibitor MLN8237 both as a monotherapy and in combination with the microtubule-targeting drug eribulin on different stages of metastasis in triple-negative breast cancer (TNBC) and defined the potential mechanism of its action. MLN8237 as a single agent and in combination with eribulin affected multiple steps in the metastatic process, including migration, attachment, and proliferation in distant organs, resulting in suppression of metastatic colonization and recurrence of cancer. Eribulin application induces accumulation of active AURKA in TNBC cells, providing foundation for the combination therapy. Mechanistically, AURKA inhibition induces cytotoxic autophagy via activation of the LC3B/p62 axis and inhibition of pAKT, leading to eradication of metastases, but has no effect on growth of mammary tumor. Combination of MLN8237 with eribulin leads to a synergistic increase in apoptosis in mammary tumors, as well as cytotoxic autophagy in metastases. These preclinical data provide a new understanding of the mechanisms by which MLN8237 mediates its antimetastatic effects and advocates for its combination with eribulin in future clinical trials for metastatic breast cancer and early-stage solid tumors. Mol Cancer Ther; 15(8); 1809-22. ©2016 AACR.

KAP1 promotes proliferation and metastatic progression of breast cancer cells

KAP1 (TRIM28) is a transcriptional regulator in embryonic development that controls stem cell self-renewal, chromatin organization, and the DNA damage response, acting as an essential corepressor for KRAB family zinc finger proteins (KRAB-ZNF). To gain insight into the function of this large gene family, we developed an antibody that recognizes the conserved zinc fingers linker region (ZnFL) in multiple KRAB-ZNF. Here, we report that the expression of many KRAB-ZNF along with active SUMOlyated KAP1 is elevated widely in human breast cancers. KAP1 silencing in breast cancer cells reduced proliferation and inhibited the growth and metastasis of tumor xenografts. Conversely, KAP1 overexpression stimulated cell proliferation and tumor growth. In cells where KAP1 was silenced, we identified multiple downregulated genes linked to tumor progression and metastasis, including EREG/epiregulin, PTGS2/COX2, MMP1, MMP2, and CD44, along with downregulation of multiple KRAB-ZNF proteins. KAP1-dependent stabilization of KRAB-ZNF required direct interactions with KAP1. Together, our results show that KAP1-mediated stimulation of multiple KRAB-ZNF contributes to the growth and metastasis of breast cancer.

Role for chondroitin sulfate glycosaminoglycan in NEDD9-mediated breast cancer cell growth

There are lines of evidence demonstrating that NEDD9 (Cas-L, HEF-1) plays a key role in the development, progression, and metastasis of breast cancer cells. We previously reported that NEDD9 plays a critical role for promoting migration and growth of MDA-MB-231. In order to further characterize the mechanisms of NEDD9-mediated cancer migration and growth, stable cells overexpressing NEDD9 were generated using HCC38 as a parental cell line which expresses low level of endogenous NEDD9. Microarray studies demonstrated that core proteins of CD44 and Serglycin were markedly upregulated in HCC38(NEDD9) cells compared to HCC38(Vector) cells, while those of Syndecan-1, Syndecan-2, and Versican were downregulated in HCC38(NEDD9). Importantly, enzymes generating chondroitin sulfate glycosaminoglycans (CS) such as CHST11, CHST15, and CSGALNACT1 were upregulated in HCC38(NEDD9) compared to HCC38(Vector). Immunofluorescence studies using specific antibody, GD3G7, confirmed the enhanced expression of CS-E subunit in HCC38(NEDD9). Immunoprecipitation and western blotting analysis demonstrated that CS-E was attached to CD44 core protein. We demonstrated that removing CS by chondroitinase ABC significantly inhibited anchorage-independent colony formation of HCC38(NEDD9) in methylcellulose. Importantly, the fact that GD3G7 significantly inhibited colony formation of HCC38(NEDD9) cells suggests that CS-E subunit plays a key role in this process. Furthermore, treatment of HCC38(NEDD9) cells with chondroitinase ABC or GD3G7 significantly inhibited mammosphere formation. Exogenous addition of CS-E enhanced colony formation and mammosphere formation of HCC38 parental and HCC38(Vector) cells. These results suggest that NEDD9 regulates the synthesis and expression of tumor associated glycocalyx structures including CS-E, which plays a key role in promoting and regulating breast cancer progression and metastasis and possibly stem cell phenotypes.

Prometastatic NEDD9 Regulates Individual Cell Migration via Caveolin-1-Dependent Trafficking of Integrins

The dissemination of tumor cells relies on efficient cell adhesion and migration, which in turn depends upon endocytic trafficking of integrins. In the current work, it was found that depletion of the prometastatic protein, NEDD9, in breast cancer cells results in a significant decrease in individual cell migration due to impaired trafficking of ligand-bound integrins. NEDD9 deficiency does not affect the expression or internalization of integrins but heightens caveolae-dependent trafficking of ligand-bound integrins to early endosomes. Increase in mobility of ligand-bound integrins is concomitant with an increase in tyrosine phosphorylation of caveolin-1 (CAV1) and volume of CAV1-vesicles. NEDD9 directly binds to CAV1 and colocalizes within CAV1 vesicles. In the absence of NEDD9, the trafficking of ligand-bound integrins from early to late endosomes is impaired, resulting in a significant decrease in degradation of ligand-integrin complexes and an increase in recycling of ligand-bound integrins from early endosomes back to the plasma membrane without ligand disengagement, thus leading to low adhesion and migration. Reexpression of NEDD9 or decrease in the amount of active, tyrosine 14 phosphorylated (Tyr14) CAV1 in NEDD9-depleted cells rescues the integrin trafficking deficiency and restores cellular adhesion and migration capacity. Collectively, these findings indicate that NEDD9 orchestrates trafficking of ligand-bound integrins through the attenuation of CAV1 activity.

IMPLICATIONS

This study provides valuable new insight into the potential therapeutic benefit of NEDD9 depletion to reduce dissemination of tumor cells and discovers a new regulatory role of NEDD9 in promoting migration through modulation of CAV1-dependent trafficking of integrins.

Abstract 2013: NEDD9 depletion leads to MMP14 inactivation by TIMP2 and prevents invasion and metastasis

The scaffolding protein NEDD9 is an established pro-metastatic marker in several cancers. Nevertheless, the molecular mechanisms of NEDD9 driven metastasis in cancers remain ill defined. Here, using a comprehensive breast cancer (BCa) tissue microarray, we show that increased levels of NEDD9 protein significantly correlated with the transition from carcinoma in situ to invasive carcinoma. NEDD9 expression is crucial for the mesenchymal invasion of cancer cells at the primary site but not at the metastatic site. Depletion of NEDD9 is sufficient to suppress invasion, leading to decrease in circulating tumor cells (CTCs) and lung metastases in xenograft models. Mechanistically, NEDD9 localizes to invasive pseudopods and is required for local matrix degradation via regulation of MMP14 trafficking. Depletion of NEDD9 impaired invasion of cancer cells through inactivation of MMP14 by excess TIMP2 on the cell surface. Re-expression of NEDD9 is sufficient to restore the activity of MMP14 and the invasive properties of BCa cells. Collectively, these findings uncover critical steps in invasion of BCa cells with potential strategy to target metastasis through manipulation of NEDD9.

Citation Format: Elena N. Pugacheva, Sarah McLaughlin, Ryan Ice, Anuradha Rajulapati, Polina Kozyulina, Ryan Livengood, Varvara Kozyreva, Yuriy Loskutov, Alexey Ivanov, Scott Weed. NEDD9 depletion leads to MMP14 inactivation by TIMP2 and prevents invasion and metastasis. [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 2013. doi:10.1158/1538-7445.AM2014-2013

NEDD9/Arf6-dependent endocytic trafficking of matrix metalloproteinase 14: a novel mechanism for blocking mesenchymal cell invasion and metastasis of breast cancer

NEDD9 is an established marker of invasive and metastatic cancers. NEDD9 downregulation has been shown to dramatically reduce cell invasion and metastasis in multiple tumors. The mechanisms by which NEDD9 regulates invasion are largely unknown. In the current study, we have found that NEDD9 is required for MMP14 enzymatic recovery/recycling through the late endosomes to enable disengagement of tissue inhibitor of matrix metalloproteinase 2 (TIMP2) and tumor invasion. Depletion of NEDD9 decreases targeting of the MMP14/TIMP2 complex to late endosomes and increases trafficking of MMP14 from early/sorting endosomes back to the surface in a small GTPase Arf6-dependent manner. NEDD9 directly binds to Arf6-GAP, ARAP3, and Arf6 effector GGA3 thereby facilitating the Arf6 inactivation required for MMP14/TIMP2 targeting to late endosomes. Re-expression of NEDD9 or a decrease in Arf6 activity is sufficient to restore MMP14 activity and the invasive properties of tumor cells. Importantly, NEDD9 inhibition by Vivo-Morpholinos, an antisense therapy, decreases primary tumor growth and metastasis in xenograft models of breast cancer. Collectively, our findings uncover a novel mechanism to control tumor cells dissemination through NEDD9/Arf6-dependent regulation of MMP14/TIMP2 trafficking, and validates NEDD9 as a clinically relevant therapeutic target to treat metastatic cancer.

NEDD9 regulates actin dynamics through cortactin deacetylation in an AURKA/HDAC6-dependent manner

The prometastatic protein NEDD9 (neural precursor cell expressed, developmentally downregulated 9) is highly expressed in many cancers and is required for mesenchymal individual cell migration and progression to the invasive stage. Nevertheless, the molecular mechanisms of NEDD9-driven migration and the downstream targets effecting metastasis are not well defined. In the current study, knockdown of NEDD9 in highly metastatic tumor cells drastically reduces their migratory capacity due to disruption of actin dynamics at the leading edge. Specifically, NEDD9 deficiency leads to a decrease in the persistence and stability of lamellipodial protrusions similar to knockdown of cortactin (CTTN). Mechanistically, it was shown that NEDD9 binds to and regulates acetylation of CTTN in an Aurora A kinase (AURKA)/HDAC6-dependent manner. The knockdown of NEDD9 or AURKA results in an increase in the amount of acetylated CTTN and a decrease in the binding of CTTN to F-actin. Overexpression of the deacetylation mimicking (9KR) mutant of CTTN is sufficient to restore actin dynamics at the leading edge and migration proficiency of the tumor cells. Inhibition of AURKA and HDAC6 activity by alisertib and Tubastatin A in xenograft models of breast cancer leads to a decrease in the number of pulmonary metastases. Collectively, these findings identify CTTN as the key downstream component of NEDD9-driven migration and metastatic phenotypes.

IMPLICATIONS

This study provides a mechanistic platform for therapeutic interventions based on AURKA and HDAC6 inhibition for patients with metastatic breast cancer to prevent and/or eradicate metastases.

NEDD9 depletion leads to MMP14 inactivation by TIMP2 and prevents invasion and metastasis

The scaffolding protein NEDD9 is an established prometastatic marker in several cancers. Nevertheless, the molecular mechanisms of NEDD9-driven metastasis in cancers remain ill-defined. Here, using a comprehensive breast cancer tissue microarray, it was shown that increased levels of NEDD9 protein significantly correlated with the transition from carcinoma in situ to invasive carcinoma. Similarly, it was shown that NEDD9 overexpression is a hallmark of highly invasive breast cancer cells. Moreover, NEDD9 expression is crucial for the protease-dependent mesenchymal invasion of cancer cells at the primary site but not at the metastatic site. Depletion of NEDD9 is sufficient to suppress invasion of tumor cells in vitro and in vivo, leading to decreased circulating tumor cells and lung metastases in xenograft models. Mechanistically, NEDD9 localized to invasive pseudopods and was required for local matrix degradation. Depletion of NEDD9 impaired invasion of cancer cells through inactivation of membrane-bound matrix metalloproteinase MMP14 by excess TIMP2 on the cell surface. Inactivation of MMP14 is accompanied by reduced collagenolytic activity of soluble metalloproteinases MMP2 and MMP9. Reexpression of NEDD9 is sufficient to restore the activity of MMP14 and the invasive properties of breast cancer cells in vitro and in vivo. Collectively, these findings uncover critical steps in NEDD9-dependent invasion of breast cancer cells.

IMPLICATIONS

This study provides a mechanistic basis for potential therapeutic interventions to prevent metastasis.

Abstract A094: The influence of pro-metastatic protein NEDD9 expression in supporting distant breast cancer metastasis

Although advances in treating early stage breast cancer have increased the overall survival rate, once the disease has metastasized treatment options become severely limited. Neural precursor cell expressed developmentally downregulated 9, NEDD9, is a pro-metastatic protein known to play a role during invasion and is increased in many tumor types including ductal breast carcinomas. The purpose of our study is to understand how NEDD9 contributes to the survival of metastatic disease and to establish via therapeutically relevant means the impact of reducing NEDD9 in metastatic breast cancer. Utilizing breast tumor xenograft models and in situ Zymography we were able to conclude that the reduction of NEDD9 led to a decrease in matrix metalloproteinase activity in the tumor cells in the primary site and distant lung metastasis thus reducing the number of invading cells. Additionally our study shows, via fluorescent immunohistochemistry analysis of lung metastasis, that by reducing the levels of NEDD9 in vivo the levels of active caspase 3 increased, along with decreasing Ki67 and phosphorylated Akt levels. These changes led to decreased proliferation and survival and increased cell death at distant metastatic sites and dramatically reduced number and size of lung metastasis. Finally, we have demonstrated that the application of NEDD9 Vivo-morpholinos is a valid method for targeting NEDD9 in a clinically relevant setting to reduce the levels of NEDD9 for treatment of metastatic breast cancer. Taken together our data suggests that not only does NEDD9 play a role in primary tumor invasion but is necessary for sustaining metastatic disease and can be reduced in a clinically viable manner resulting in less metastasis.

Citation Format: Ryan J. Ice, Sricharan A. Mahavadi, Elena N. Pugacheva. The influence of pro-metastatic protein NEDD9 expression in supporting distant breast cancer metastasis. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Breast Cancer Research: Genetics, Biology, and Clinical Applications; Oct 3-6, 2013; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2013;11(10 Suppl):Abstract nr A094.

Abstract 3125: KAP1 promotes malignant properties of breast cancer cells and regulates the expression of multiple KRAB-ZNFs

Background and Objective: Chromatin remodeling is fundamental for normal development and is universally affected in cancer cells. The largest family of human transcription factors, KRAB-ZNF repressors, and their essential cofactor KAP1 play important roles in chromatin organization and regulate multiple cellular processes such as cell differentiation, pluripotency, apoptosis, DNA repair and imprinting. Here, we explored the role of KAP1 and KRAB-ZNFs in breast cancer.

Methods: Using cancer patient samples, in vitro and animal xenograft model we analyzed KAP1 role in cancer cell proliferation and primary tumor formation.

Results: Patient sample analysis showed KAP1 and KRAB-ZNFs overexpression in significant proportion of breast tumors. KAP1 depletion in a panel of breast cancer cell lines inhibited cancer cell proliferation, while KAP1 overexpression stimulated cell growth. Concordantly, KAP1 knockdown in MDA-MB-231LN human breast cancer cells inhibited primary tumor growth in orthotopic xenograft mouse model, while KAP1 overexpression had an opposite, growth stimulatory effect. KAP1 depletion resulted in decreased expression of a number of cancer-associated genes. Functional in vitro studies provided evidence that KAP1 positively regulates expression of multiple KRAB-ZNFs.

Discussion and Conclusions: These results thus establish KAP1 as an oncogenic factor in breast cancer. Grant support: NIH NCRR grant P20 RR16440 and Susan G. Komen for the Cure grant KG110350.

Citation Format: Joseph B. Addison, Renata Galeeva, Dongquan Chen, Elena N. Pugacheva, Alexey V. Ivanov. KAP1 promotes malignant properties of breast cancer cells and regulates the expression of multiple KRAB-ZNFs. [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 3125. doi:10.1158/1538-7445.AM2013-3125

Abstract 4934: The role of Aurora A kinase-dependent phosphorylation of cortactin in invadopodia formation

Aurora A kinase (AURKA) is a serine/threonine kinase known for its critical role in regulation of cell cycle progression. Overexpression and activation of AURKA is implicated in development of multiple types of human cancer. AURKA upregulation is considered as independent prognostic marker for breast cancer patients and associated with poor survival outcome. Recent work by our laboratory and others suggests a new role for AURKA in promotion of tumor cells migration and invasion through regulation of actin dynamics. However, the specific manner in which AURKA regulates actin-based machinery of migrating cancer cells is unknown. In our current work we show that phosphorylation of cortactin (CTTN) by AURKA directly regulates actin dynamics in breast cancer cells. CTTN is known to be regulated by oncogenic Src kinase. This phosphorylation is pivotal for formation of free barbed ends and further actin polymerization. Dynamic polymerization/depolimerization is required for invasion of cancer cells. Thus inhibition of Src-dependant phosphorylation of CTTN is critical for invadopodia maturation. In our current work we identify the phosphorylation site on CTTN targeted by AURKA and show that phosphorylation of CTTN by AURKA could potentially inhibit further phosphorylation of CTTN by Src leading to stabilization of invadopodia. Inhibition of AURKA activity or depletion of AURKA in cancer cells led to decrease in invasion and invadopodia maturation. In addition, we showed that adaptor protein NEDD9 which is known to bind both AURKA and Src also binds to CTTN and therefore potentially can mediate Src-CTTN-AURKA complex formation that regulates the sequential phosphorylation events necessary for invadopodia genesis. It is our expectation that AURKA-phosphorylated CTTN will inhibit Src-driven tyrosine-phosphorylation of CTTN, regulating a mechanistic switch between complementary actin polymerization and actin stabilization programs.

Citation Format: Varvara K. Kozyreva, Laura Kelley, Sarah L. McLaughlin, Elena N. Pugacheva. The role of Aurora A kinase-dependent phosphorylation of cortactin in invadopodia formation. [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 4934. doi:10.1158/1538-7445.AM2013-4934

NEDD9 depletion destabilizes Aurora A kinase and heightens the efficacy of Aurora A inhibitors: implications for treatment of metastatic solid tumors

Aurora A kinase (AURKA) is overexpressed in 96% of human cancers and is considered an independent marker of poor prognosis. While the majority of tumors have elevated levels of AURKA protein, few have AURKA gene amplification, implying that posttranscriptional mechanisms regulating AURKA protein levels are significant. Here, we show that NEDD9, a known activator of AURKA, is directly involved in AURKA stability. Analysis of a comprehensive breast cancer tissue microarray revealed a tight correlation between the expression of both proteins, significantly corresponding with increased prognostic value. A decrease in AURKA, concomitant with increased ubiquitination and proteasome-dependent degradation, occurs due to depletion or knockout of NEDD9. Reexpression of wild-type NEDD9 was sufficient to rescue the observed phenomenon. Binding of NEDD9 to AURKA is critical for AURKA stabilization, as mutation of S296E was sufficient to disrupt binding and led to reduced AURKA protein levels. NEDD9 confers AURKA stability by limiting the binding of the cdh1-substrate recognition subunit of APC/C ubiquitin ligase to AURKA. Depletion of NEDD9 in tumor cells increases sensitivity to AURKA inhibitors. Combination therapy with NEDD9 short hairpin RNAs and AURKA inhibitors impairs tumor growth and distant metastasis in mice harboring xenografts of breast tumors. Collectively, our findings provide rationale for the use of AURKA inhibitors in treatment of metastatic tumors and predict the sensitivity of the patients to AURKA inhibitors based on NEDD9 expression.

Abstract A66: NEDD9 promotes cell invasion through modulation of ARF6 activity and endocytic recycling

The adhesion scaffolding protein NEDD9 was identified as potential pro-metastatic gene in several cancers. The molecular mechanisms of NEDD9-driven metastasis are still unknown. In this study, we show that expression of NEDD9 positively correlates with the invasive stage of breast cancer. We show that NEDD9 localizes to invadopodia and endosomes. Notably, NEDD9 depleted cells have increased levels of inactive surface receptors due to increase in fast recycling of Rab4 and Rab5 positive vesicles. Mechanistically, we found that NEDD9 binds to and scaffolds the Arf6 specific GAP - ASAP3, decreasing Arf6 activity. Thus, depletion of NEDD9 leads to activation of Arf6. Inhibition of Arf6 or re-expression of NEDD9 in shNEDD9 cells was sufficient to restore recycling rates, decrease the number of Rab4 and 5 positive vesicles and the invasive properties of tumor cells. Thus, in this work, we uncover the mechanistic basis of NEDD9-driven invasion and identify a new role for NEDD9 in Arf6-dependant endocytosis.

Citation Format: Elena N. Pugacheva, Yuriy Loskutov, Sarah McLaughlin, Polina Kozyulina, Varvara Kozyreva, Ryan Ice, Mark Culp, Robert Wysolmerski, Scott Weed, Alexey Ivanov. NEDD9 promotes cell invasion through modulation of ARF6 activity and endocytic recycling. [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 A66.

Calmodulin activation of Aurora-A kinase (AURKA) is required during ciliary disassembly and in mitosis

This study demonstrates for the first time that binding of calcium-activated calmodulin to a minimal interaction site within the disordered N-terminal domain is required for the essential Aurora-A activity in mitosis and in regulation of ciliary disassembly.

The centrosomal Aurora-A kinase (AURKA) regulates mitotic progression, and overexpression and hyperactivation of AURKA commonly promotes genomic instability in many tumors. Although most studies of AURKA focus on its role in mitosis, some recent work identified unexpected nonmitotic activities of AURKA. Among these, a role for basal body–localized AURKA in regulating ciliary disassembly in interphase cells has highlighted a role in regulating cellular responsiveness to growth factors and mechanical cues. The mechanism of AURKA activation involves interactions with multiple partner proteins and is not well understood, particularly in interphase cells. We show here that AURKA activation at the basal body in ciliary disassembly requires interactions with Ca²⁺ and calmodulin (CaM) and that Ca²⁺/CaM are important mediators of the ciliary disassembly process. We also show that Ca²⁺/CaM binding is required for AURKA activation in mitosis and that inhibition of CaM activity reduces interaction between AURKA and its activator, NEDD9. Finally, mutated derivatives of AURKA impaired for CaM binding and/or CaM-dependent activation cause defects in mitotic progression, cytokinesis, and ciliary resorption. These results define Ca²⁺/CaM as important regulators of AURKA activation in mitotic and nonmitotic signaling.

Aurora A kinase activity influences calcium signaling in kidney cells

Aurora A is abnormally expressed and activated in cells lining cysts associated with polycystic kidney disease and can phosphorylate and inactivate polycystin 2.

Most studies of Aurora A (AurA) describe it as a mitotic centrosomal kinase. However, we and others have recently identified AurA functions as diverse as control of ciliary resorption, cell differentiation, and cell polarity control in interphase cells. In these activities, AurA is transiently activated by noncanonical signals, including Ca²⁺-dependent calmodulin binding. These and other observations suggested that AurA might be involved in pathological conditions, such as polycystic kidney disease (PKD). In this paper, we show that AurA is abundant in normal kidney tissue but is also abnormally expressed and activated in cells lining PKD-associated renal cysts. PKD arises from mutations in the PKD1 or PKD2 genes, encoding polycystins 1 and 2 (PC1 and PC2). AurA binds, phosphorylates, and reduces the activity of PC2, a Ca²⁺-permeable nonselective cation channel and, thus, limits the amplitude of Ca²⁺ release from the endoplasmic reticulum. These and other findings suggest AurA may be a relevant new biomarker or target in the therapy of PKD.

Abstract B61: HEF1-dependent Aurora A kinase phosphorylation activates HDAC6

Histone deacetylase 6 (HDAC6) is known to be important participant of many tumorgenesis processes including cytoskeleton rearrangement, cell migration and invasion. Activation of HDAC6 promotes cell motility and proteolytic degradation of the extracellular matrix which thereby facilitates invasion and metastasis of cancer cells. But precise mechanisms of HDAC6 regulation are still unknown. Human enhancer of filamentation 1 (HEF1/Cas-L/Nedd9) is scaffolding protein implicated in essential normal cell functions like cell division as well as pathologic conditions such as in cancer progression. It has been shown that HEF1 is over-expressed in multiple tumor types and is well known marker of malignancy. HEF1 possesses a key role in cancer development by acting as a signaling hub to coordinate tumor associated signaling. Among numerous targets which are regulated by HEF1 one of the most important is Aurora A kinase (AurA). It is known that up-regulation of AurA launches a cascade of reactions promoting oncogenic cell transformation. In our experiments, we demonstrated that HEF1 knockdown leads to impairment of cell capability to invade into extracellular matrix. We hypothesize that invasion deficiency in HEF1 depleted cells is directly linked to inability of AurA to phosphorylate/activate HDAC6. We have shown previously that depletion of HEF1 decreases AurA activity and demonstrated that HDAC6 is a substrate of AurA kinase. In this work we have determined AurA phosphorylation sites in HDAC6 using site-directed mutagenesis and in vitro kinase assay with wild-type HDAC6 and HDAC6 phospho-mutants. We revealed that AurA phosphorylates HDAC6 at Ser479/Thr481. We will test the effect of this AurA phosphorylation event on HDAC6 activation. Biological effect of such regulation will be explored in breast cancer cell lines. Our observation allows us to establish a mechanistic pathway that describes the convergent roles of HDAC6, AurA and HEF1 in tumor progression.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the Second AACR International Conference on Frontiers in Basic Cancer Research; 2011 Sep 14-18; San Francisco, CA. Philadelphia (PA): AACR; Cancer Res 2011;71(18 Suppl):Abstract nr B61.

Rapid calcium-dependent activation of Aurora-A kinase

Oncogenic hyperactivation of the mitotic kinase Aurora-A (AurA) in cancer is associated with genomic instability. Increasing evidence indicates that AurA also regulates critical processes in normal interphase cells, but the source of such activity has been obscure. We report here that multiple stimuli causing release of Ca²⁺ from intracellular endoplasmic reticulum stores rapidly and transiently activate AurA, without requirement for second messengers. This activation is mediated by direct Ca²⁺-dependent calmodulin (CaM) binding to multiple motifs on AurA. On the basis of structure–function analysis and molecular modelling, we map two primary regions of CaM-AurA interaction to unfolded sequences in the AurA N- and C-termini. This unexpected mechanism for AurA activation provides a new context for evaluating the function of AurA and its inhibitors in normal and cancerous cells.

Aurora-A kinase localizes to centrosomes, is involved in the progression through mitosis and is overexpressed in certain cancers. Here, calcium is shown to induce Aurora-A auto-phosphorylation in a calmodulin-dependent manner, suggesting a novel role for Aurora-A in non-mitotic cells.

Abstract 1086: The role of HEF1 protein in stabilization and activation of AurA kinase in metastatic breast cancer

AurA kinase expression is linked to human disease since the extent of AurA up-regulation was significantly associated with advanced tumor stage and the occurrence of metastasis. AurA inhibitors have recently entered phase II clinical trials for cancer treatment, but application of these inhibitors for treatment of advanced human cancers has demonstrated limited efficacy. The reasons why potent in vitro inhibitors of AurA are inefficient under these conditions are unknown. In our current study, we define the mechanisms by which AurA is upregulated in breast tumor cells and what impact HEF1 expression has on AurA-associated occurrence of metastasis. Our hypothesis is that over-expression of HEF1 protein in breast cancer cells will protect AurA from proteolytic degradation, resulting in activation of AurA kinase. Here we demonstrate that direct binding of HEF1 stabilizes AurA by blocking the cdh1 binding site and limiting AurA ubiquitination. HEF1 binding decreases the efficacy of AurA inhibitors in cell culture. Deletion of HEF1 by gene knockout and depletion by siRNA in cell lines cause dramatic decreases in AurA protein level and kinase activity - indicating HEF1 is the major AurA regulator in vivo. We further show that deletion of HEF1 reduces tumor cell proliferation and invasion in mouse mammary tumor models. These data provide insights into the potential development of small molecule inhibitors that could be used therapeutically to target the HEF1/AurA pathway and thereby inhibit tumor formation.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1086.

NEDD9 promotes oncogenic signaling in mammary tumor development

In the past 3 years, altered expression of the HEF1/CAS-L/NEDD9 scaffolding protein has emerged as contributing to cancer metastasis in multiple cancer types. However, whereas some studies have identified elevated NEDD9 expression as prometastatic, other work has suggested a negative role in tumor progression. We here show that the Nedd9-null genetic background significantly limits mammary tumor initiation in the MMTV-polyoma virus middle T genetic model. Action of NEDD9 is tumor cell intrinsic, with immune cell infiltration, stroma, and angiogenesis unaffected. The majority of the late-appearing mammary tumors of MMTV-polyoma virus middle T;Nedd9(-/-) mice are characterized by depressed activation of proteins including AKT, Src, FAK, and extracellular signal-regulated kinase, emphasizing an important role of NEDD9 as a scaffolding protein for these prooncogenic proteins. Analysis of cells derived from primary Nedd9(+/+) and Nedd9(-/-) tumors showed persistently reduced FAK activation, attachment, and migration, consistent with a role for NEDD9 activation of FAK in promoting tumor aggressiveness. This study provides the first in vivo evidence of a role for NEDD9 in breast cancer progression and suggests that NEDD9 expression may provide a biomarker for tumor aggressiveness.

Cell cycle-dependent ciliogenesis and cancer

In mammals, most cell types have primary cilia, protruding structures involved in sensing mechanical and chemical signals from the extracellular environment that act as major communication hubs for signaling controlling cell differentiation and polarity. The list of clinical disorders associated with ciliary dysfunction has expanded from polycystic kidney disease to include many others. Transformed cells commonly lack cilia, but whether this lack is cause or consequence of transformation is not well understood. Here we discuss work addressing recently identified actions of the cancer-promoting proteins Aurora A and HEF1/NEDD9/CAS-L at cilia. Together with older studies, this work suggests that loss of cilia in cancer may contribute to the insensitivity of cancer cells to environmental repressive signals, based in part on derangement of cell cycle checkpoints governed by cilia and centrosomes.

HEF1-dependent Aurora A activation induces disassembly of the primary cilium

The mammalian cilium protrudes from the apical/lumenal surface of polarized cells and acts as a sensor of environmental cues. Numerous developmental disorders and pathological conditions have been shown to arise from defects in cilia-associated signaling proteins. Despite mounting evidence that cilia are essential sites for coordination of cell signaling, little is known about the cellular mechanisms controlling their formation and disassembly. Here, we show that interactions between the prometastatic scaffolding protein HEF1/Cas-L/NEDD9 and the oncogenic Aurora A (AurA) kinase at the basal body of cilia causes phosphorylation and activation of HDAC6, a tubulin deacetylase, promoting ciliary disassembly. We show that this pathway is both necessary and sufficient for ciliary resorption and that it constitutes an unexpected nonmitotic activity of AurA in vertebrates. Moreover, we demonstrate that small molecule inhibitors of AurA and HDAC6 selectively stabilize cilia from regulated resorption cues, suggesting a novel mode of action for these clinical agents.

GST Pull-down

INTRODUCTIONGlutathione-S-transferase (GST) fusion proteins have had a wide range of applications since their introduction as tools for synthesis of recombinant proteins in bacteria. One of these applications is their use as probes for the identification of protein-protein interactions. The pull-down method described in this protocol is fundamentally similar to immunoprecipitation. Immunoprecipitation is based on the ability of an antibody to bind to its antigen in solution, and the subsequent purification of the immunocomplex by collection on protein A- or G-coupled beads. Similarly, the GST pull-down is an affinity capture of one or more proteins (either defined or unknown) in solution by its interaction with the GST fusion probe protein and subsequent isolation of the complex by collection of the interacting proteins through the binding of GST to glutathione-coupled beads.

Identification of Protein-Protein Interactions with Glutathione-S-Transferase (GST) Fusion Proteins

INTRODUCTIONGlutathione-S-transferase (GST) fusion proteins have had a wide range of applications since their introduction as tools for synthesis of recombinant proteins in bacteria. GST was originally selected as a fusion moiety because of several desirable properties. First and foremost, when expressed in bacteria alone, or as a fusion, GST is not sequestered in inclusion bodies (in contrast to previous fusion protein systems). Second, GST can be affinity-purified without denaturation because it binds to immobilized glutathione, which provides the basis for simple purification. Consequently, GST fusion proteins are routinely used for antibody generation and purification, protein-protein interaction studies, and biochemical analysis. This article describes the use of GST fusion proteins as probes for the identification of protein-protein interactions.

Far Western: Labeling GST Fusion Proteins

INTRODUCTIONA far-Western blot (also known as an overlay assay) is used to detect the interaction of a recombinant GST fusion protein (produced and purified from bacteria) with a target protein on a membrane. Three methods are generally used to detect an interaction: radioactive labeling of the fusion protein, biotinylation of the fusion protein, and detection by anti-GST antibodies. This protocol describes the radioactive labeling of GST fusion proteins using a phosphorylation site that has been integrated into the fusion protein. This is rapid, easy, and because the phosphorylation site is in the fusion portion of the protein, labeling the fusion protein generally has little impact on subsequent activity. The fusion protein consists of a GST moiety, a protease cleavage site, and the phosphorylation target site for a known kinase, which are translated in-frame with the protein of interest. The purified protein is bound to glutathione beads and is radioactively labeled with (32)P using a commercially available kinase. Unincorporated nucleotides are removed from the solution by washing, and the radioactively labeled protein is cleaved with protease (e.g., factor X or thrombin) or eluted with glutathione to remove the GST moiety, which eliminates the possibility of detecting proteins bound to GST during membrane probing.

Preparation of GST Fusion Proteins

INTRODUCTIONThis protocol describes the preparation of glutathione-S-transferase (GST) fusion proteins, which have had a wide range of applications since their introduction as tools for synthesis of recombinant proteins in bacteria. GST was originally selected as a fusion moiety because of several desirable properties. First and foremost, when expressed in bacteria alone, or as a fusion, GST is not sequestered in inclusion bodies (in contrast to previous fusion protein systems). Second, GST can be affinity-purified without denaturation because it binds to immobilized glutathione, which provides the basis for simple purification. Consequently, GST fusion proteins are routinely used for antibody generation and purification, protein-protein interaction studies, and biochemical analysis.

Interdependence of cell attachment and cell cycle signaling

Adult metazoans represent the culmination of an intricate developmental process involving the temporally and spatially orchestrated division, migration, differentiation, attachment, polarization and death of individual cells. An elaborate infrastructure connecting the cell cycle and cell attachment machinery is essential for such exquisite integration of developmental processes. Integrin-, cadherin-, Merlin- and planar cell polarity (PCP)-dependent signaling cascades quantitatively and qualitatively program cell division during development. Proteins in this signaling infrastructure may represent an important source of cancer vulnerability in metazoans, as their dysfunction can pleiotropically promote the oncogenic process.

HEF1 is a necessary and specific downstream effector of FAK that promotes the migration of glioblastoma cells

The highly invasive behavior of glioblastoma cells contributes to the morbidity and mortality associated with these tumors. The integrin-mediated adhesion and migration of glioblastoma cells on brain matrix proteins is enhanced by stimulation with growth factors, including platelet-derived growth factor (PDGF). As focal adhesion kinase (FAK), a nonreceptor cytoplasmic tyrosine kinase, has been shown to promote cell migration in various other cell types, we analysed its role in glioblastoma cell migration. Forced overexpression of FAK in serum-starved glioblastoma cells plated on recombinant (rec)-osteopontin resulted in a twofold enhancement of basal migration and a ninefold enhancement of PDGF-BB-stimulated migration. Both expression of mutant FAK(397F) and the downregulation of FAK with small interfering (si) RNA inhibited basal and PDGF-stimulated migration. FAK overexpression and PDGF stimulation was found to increase the phosphorylation of the Crk-associated substrate (CAS) family member human enhancer of filamentation 1 (HEF1), but not p130CAS or Src-interacting protein (Sin)/Efs, although the levels of expression of these proteins was similar. Moreover downregulation of HEF1 with siRNA, but not p130CAS, inhibited basal and PDGF-stimulated migration. The phosphorylated HEF1 colocalized with vinculin and was associated almost exclusively with 0.1% Triton X-100 insoluble material, consistent with its signaling at focal adhesions. FAK overexpression promoted invasion through normal brain homogenate and siHEF1 inhibited this invasion. Results presented here suggest that HEF1 acts as a necessary and specific downstream effector of FAK in the invasive behavior of glioblastoma cells and may be an effective target for treatment of these tumors.

HEF1-aurora A interactions: points of dialog between the cell cycle and cell attachment signaling networks

Regulated timing of cell division cycles, and geometrical precision in the planar orientation of cell division, are critical during organismal development and remain important for the maintenance of polarized structures in adults. Mounting evidence suggests that these processes are coordinated at the centrosome through the action of proteins that mediate both cell cycle and cell attachment. Our recent work identifying HEF1 as an activator of the Aurora A kinase suggests a novel hub for such integrated signaling. We suggest that defects in components of the machinery specifying the temporal and spatial integration of cell division may induce cancer and other diseases through pleiotropic effects on cell migration, proliferation, apoptosis, and genomic stability.

Deregulation of HEF1 impairs M-phase progression by disrupting the RhoA activation cycle

The focal adhesion-associated signaling protein HEF1 undergoes a striking relocalization to the spindle at mitosis, but a function for HEF1 in mitotic signaling has not been demonstrated. We here report that overexpression of HEF1 leads to failure of cells to progress through cytokinesis, whereas depletion of HEF1 by small interfering RNA (siRNA) leads to defects earlier in M phase before cleavage furrow formation. These defects can be explained mechanistically by our determination that HEF1 regulates the activation cycle of RhoA. Inactivation of RhoA has long been known to be required for cytokinesis, whereas it has recently been determined that activation of RhoA at the entry to M phase is required for cellular rounding. We find that increased HEF1 sustains RhoA activation, whereas depleted HEF1 by siRNA reduces RhoA activation. Furthermore, we demonstrate that chemical inhibition of RhoA is sufficient to reverse HEF1-dependent cellular arrest at cytokinesis. Finally, we demonstrate that HEF1 associates with the RhoA-GTP exchange factor ECT2, an orthologue of the Drosophila cytokinetic regulator Pebble, providing a direct means for HEF1 control of RhoA. We conclude that HEF1 is a novel component of the cell division control machinery and that HEF1 activity impacts division as well as cell attachment signaling events.

The focal adhesion scaffolding protein HEF1 regulates activation of the Aurora-A and Nek2 kinases at the centrosome

Although HEF1 has a well-defined role in integrin-dependent attachment signalling at focal adhesions, it relocalizes to the spindle asters at mitosis. We report here that overexpression of HEF1 causes an increase in centrosome numbers and multipolar spindles, resembling defects induced by manipulation of the mitotic regulatory kinase Aurora-A (AurA). We show that HEF1 associates with and controls activation of AurA. We also show that HEF1 depletion causes centrosomal splitting, mono-astral spindles and hyperactivation of Nek2, implying additional action earlier in the cell cycle. These results provide new insight into the role of an adhesion protein in coordination of cell attachment and division.

Detection of peptides, proteins, and drugs that selectively interact with protein targets

Genome sequencing has been completed for multiple organisms, and pilot proteomic analyses reported for yeast and higher eukaryotes. This work has emphasized the facts that proteins are frequently engaged in multiple interactions, and that governance of protein interaction specificity is a primary means of regulating biological systems. In particular, the ability to deconvolute complex protein interaction networks to identify which interactions govern specific signaling pathways requires the generation of biological tools that allow the distinction of critical from noncritical interactions. We report the application of an enhanced Dual Bait two-hybrid system to allow detection and manipulation of highly specific protein-protein interactions. We summarize the use of this system to detect proteins and peptides that target well-defined specific motifs in larger protein structures, to facilitate rapid identification of specific interactors from a pool of putative interacting proteins obtained in a library screen, and to score specific drug-mediated disruption of protein-protein interaction.

Novel gain of function activity of p53 mutants: activation of the dUTPase gene expression leading to resistance to 5-fluorouracil

Mutated forms of p53 are often expressed in a variety of human tumors. In addition to loss of function of the p53 tumor suppressor, mutant p53s contribute to malignant process by acquisition of novel functions that enhance transformed properties of cells and resistance to anticancer therapy in vitro, and increase tumorigenecity, invasiveness and metastatic ability in vivo. Searching for genes that change expression in response to p53 gain of function mutants may give a clue to the mechanisms underlying their oncogenic effects. Recently by subtraction hybridization cloning we found that the dUTPase gene is transcriptionally upregulated in p53-null mouse fibroblasts expressing the exogenous human tumor-derived His175 p53 mutant. Here we show that conditional expression of His175 and Trp248 hot-spot p53 mutants in p53-negative mouse 10(1) fibroblasts and human SK-OV3 and H1299 tumor cells results in increase in dUTPase gene transcription, an important marker predicting the efficacy of cancer therapy with fluoropyrimidine drugs. Using tetracycline-regulated retroviral vectors for conditional expression of p53 mutants, we found that transcription of the dUTPase gene is increased within 24 h after tetracycline withdrawal, and the cells acquire higher resistance to 5-FU. Additional inactivation of the N-terminal transcription activation domain of mutant p53 (substitutions in amino-acid residues 22 and 23) results in abrogation of both induction of dUTPase transcripts and 5-FU resistance.

Signal transduction driving technology driving signal transduction: factors in the design of targeted therapies

A significant number of human diseases can be attributed to defects in cellular signal transduction pathways. Large-scale proteomics projects now in progress seek to better define critical components of signal transduction networks, to enable more intelligent design of therapeutic agents that can specifically correct disease-specific signaling alterations by targeting individual proteins. A complicating factor in this endeavor is the fact that intracellular signaling involves many diverse mechanisms that in sum finely modulate the activity of individual proteins in response to different biological inputs. Ability to develop reagents that selectively correct disease-associated signaling activities, while leaving intact benign or essential activities, encompassed within a single protein requires an intimate knowledge of pathway-specific control mechanisms. To illustrate these points, we provide examples of some of the complex control mechanisms regulating the Cas proteins, which contribute to integrin-dependent biological response. We then discuss issues involved in systematically incorporating information related to complex control mechanisms in proteomic databases. Finally, we describe some recent instances in which protein interaction technologies have been specifically adapted to identify small molecule agents that regulate protein response in physiologically desirable ways, and discuss issues relevant to future drug discovery efforts.