p130Cas regulates the activity of AND-34, a novel Ral, Rap1, and R-Ras guanine nucleotide exchange factor

BCAR3 and BCAR3-related competing endogenous RNA expression in hepatocellular carcinoma and their prognostic value

BACKGROUND

Hepatocellular carcinoma (HCC) is a malignant tumor that has a high incidence and mortality worldwide. Despite extensive studies, the detailed molecular mechanism of HCC development remains unclear. Studies have shown that the occurrence and development of HCC are closely related to abnormal gene expression. BCAR3 has been shown to be overexpressed in a variety of malignant tumors. However, the role of BCAR3 in HCC remains unclear.

AIM

To investigate the expression of BCAR3 and BCAR3-related competing endogenous RNAs (ceRNAs) in HCC and their clinical significance, in order to provide new ideas for the diagnosis and treatment of HCC.

METHODS

The data of HCC were obtained from the Cancer Genome Atlas database and The Genotype Tissue Expression, including transcriptome data and clinical information. Multiple common databases, including UALCAN, Timer 2.0, cBioPortal, LinkedOmics, starBase, Gene Ontology and Kyoto Encyclopedia of Genes and Genomes, were used to analyse the expression of BCAR3, prognostic value, genetic alteration, co-expressed genes, differentially expressed genes, BCAR3 gene-related ceRNAs and functional enrichment analysis in HCC patients. Kaplan-Meier analysis, univariate and multivariate Cox regression analysis were used to analyze survival prognosis and the Spearman test was used to measure correlations between BCAR3 and immune functions. And R language package was used to analyze the correlation between BCAR3 and immune invasion of HCC.

RESULTS

Our study indicated that BCAR3 was differentially expressed in various tumor tissues. The over-expression of BCAR3 gene was an unfavorable prognostic indicator for HCC patients, and associated with unfavorable cytogenetic risk and gene mutations. Moreover, most immune cells were positively correlated with BCAR3 (P < 0.05). According to the results of functional enrichment analysis, BCAR3 was involved in the positive regulation of epidermal growth factor receptor signaling pathway and ERBB signaling pathway, and was related to DNA replication and GTPase regulator activity. Finally, our study found that based on RAB30-DT and miR-19b-3p pathways, targeting BCAR3 might promote the occurrence and development of HCC.

CONCLUSION

Collectively, this study indicated that the BCAR3 gene was involved in the occurrence and development of HCC, and it might be a new biomarker and therapeutic target for HCC, but the specific mechanism remains to be further verified.

Mechanotransduction and the extracellular matrix: Key drivers of lung pathologies and drug responsiveness

The lung is a biomechanically active organ, with multiscale mechanical forces impacting the organ, tissue and cellular responses within this microenvironment. In chronic lung diseases, such as chronic obstructive pulmonary disease, pulmonary fibrosis and others, the structure of the lung is drastically altered impeding gas exchange. These changes are, in part, reflected in alterations in the composition, amount and organization of the extracellular matrix within the different lung compartments. The transmission of mechanical forces within lung tissue are broadcast by this complex mix of extracellular matrix components, in particular the collagens, elastin and proteoglycans and the crosslinking of these components. At both a macro and a micro level, the mechanical properties of the microenvironment have a key regulatory role in ascertaining cellular responses and the function of the lung. Cells adhere to, and receive signals from, the extracellular matrix through a number of different surface receptors and complexes which are important for mechanotransduction. This review summarizes the multiscale mechanics in the lung and how the mechanical environment changes in lung disease and aging. We then examine the role of mechanotransduction in driving cell signaling events in lung diseases and finish with a future perspective of the need to consider how such forces may impact pharmacological responsiveness in lung diseases.

Deciphering the Role of BCAR3 in Cancer Progression: Gene Regulation, Signal Transduction, and Therapeutic Implications

This review comprehensively explores the gene BCAR3, detailing its regulation at the gene, mRNA, and protein structure levels, and delineating its multifunctional roles in cellular signaling within cancer contexts. The discussion covers BCAR3's involvement in integrin signaling and its impact on cancer cell migration, its capability to induce anti-estrogen resistance, and its significant functions in cell cycle regulation. Further highlighted is BCAR3's modulation of immune responses within the tumor microenvironment, a novel area of interest that holds potential for innovative cancer therapies. Looking forward, this review outlines essential future research directions focusing on transcription factor binding studies, isoform-specific expression profiling, therapeutic targeting of BCAR3, and its role in immune cell function. Each segment builds towards a holistic understanding of BCAR3's operational mechanisms, presenting a critical evaluation of its therapeutic potential in oncology. This synthesis aims to not only extend current knowledge but also catalyze further research that could pivotally influence the development of targeted cancer treatments.

FAK and p130Cas modulate stiffness-mediated early transcription and cellular metabolism

Cellular metabolism is influenced by the stiffness of the extracellular matrix. Focal adhesion kinase (FAK) and its binding partner, p130Cas, transmit biomechanical signals about substrate stiffness to the cell to regulate a variety of cellular responses, but their roles in early transcriptional and metabolic responses remain largely unexplored. We cultured mouse embryonic fibroblasts with or without siRNA-mediated FAK or p130Cas knockdown and assessed the early transcriptional responses of these cells to placement on soft and stiff substrates by RNA sequencing and bioinformatics analyses. Exposure to the stiff ECM altered the expression of genes important for metabolic and biosynthetic processes, and these responses were influenced by knockdown of FAK and p130Cas. Our findings reveal that FAK-p130Cas signaling mechanotransduces ECM stiffness to early transcriptional changes that alter cellular metabolism and biosynthesis.

The Impact of ETV6-NTRK3 Oncogenic Gene Fusions on Molecular and Signaling Pathway Alterations

Chromosomal translocations creating fusion genes are common cancer drivers. The oncogenic ETV6-NTRK3 (EN) gene fusion joins the sterile alpha domain of the ETV6 transcription factor with the tyrosine kinase domain of the neurotrophin-3 receptor NTRK3. Four EN variants with alternating break points have since been detected in a wide range of human cancers. To provide molecular level insight into EN oncogenesis, we employed a proximity labeling mass spectrometry approach to define the molecular context of the fusions. We identify in total 237 high-confidence interactors, which link EN fusions to several key signaling pathways, including ERBB, insulin and JAK/STAT. We then assessed the effects of EN variants on these pathways, and showed that the pan NTRK inhibitor Selitrectinib (LOXO-195) inhibits the oncogenic activity of EN2, the most common variant. This systems-level analysis defines the molecular framework in which EN oncofusions operate to promote cancer and provides some mechanisms for therapeutics.

The RAL Enigma: Distinct Roles of RALA and RALB in Cancer

RALA and RALB are highly homologous small G proteins belonging to the RAS superfamily. Like other small GTPases, the RALs are molecular switches that can be toggled between inactive GDP-bound and active GTP-bound states to regulate diverse and critical cellular functions such as vesicle trafficking, filopodia formation, mitochondrial fission, and cytokinesis. The RAL paralogs are activated and inactivated by a shared set of guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs) and utilize similar sets of downstream effectors. In addition to their important roles in normal cell biology, the RALs are known to be critical mediators of cancer cell survival, invasion, migration, and metastasis. However, despite their substantial similarities, the RALs often display striking functional disparities in cancer. RALA and RALB can have redundant, unique, or even antagonistic functions depending on cancer type. The molecular basis for these discrepancies remains an important unanswered question in the field of cancer biology. In this review we examine the functions of the RAL paralogs in normal cellular physiology and cancer biology with special consideration provided to situations where the roles of RALA and RALB are non-redundant.

BCAR3 promotes head and neck cancer growth and is associated with poor prognosis

Breast cancer anti-estrogen resistance protein 3 (BCAR3) is involved in anti-estrogen resistance and other important aspects of breast cancer. However, the role of BCAR3 in other solid tumors remains unclear. The relationship between the clinicopathologic characteristics of head and neck squamous cell carcinoma (HNSCC) patients and BCAR3 was analyzed using the Wilcoxon’s signed-rank test and logistic regression. The association between BCAR3 expression and clinicopathologic features and survival was analyzed using Cox regression and the Kaplan–Meier method. In vivo and in vitro assays were performed to validate the effect of BCAR3 on HNSCC growth. BCAR3-related mRNAs were determined by calculating the Pearson’s correlation coefficient based on The Cancer Genome Atlas (TCGA). Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses, and gene set enrichment analysis (GSEA) were used to predict the potential functions of BCAR3. BCAR3 expression is overexpressed in HNSCC and was shown to be associated with perineural invasion (PNI) and poor survival. BCAR3 silencing significantly attenuated the proliferation of HNSCC cells, whereas BCAR3 depletion inhibited tumor growth in vitro. GO and KEGG functional enrichment analyses, and GSEA showed that BCAR3 expression in HNSCC was associated with biological processes, such as cell adhesion, actin binding, cadherin binding, and angiogenesis. BCAR3, which promotes HNSCC growth, is associated with perineural invasion and may be a potential molecular prognostic marker of poor survival in HNSCC.

Filopodome Mapping Identifies p130Cas as a Mechanosensitive Regulator of Filopodia Stability

Filopodia are adhesive cellular protrusions specialized in the detection of extracellular matrix (ECM)-derived cues. Although ECM engagement at focal adhesions is known to trigger the recruitment of hundreds of proteins ("adhesome") to fine-tune cellular behavior, the components of the filopodia adhesions remain undefined. Here, we performed a structured-illumination-microscopy-based screen to map the localization of 80 target proteins, linked to cell adhesion and migration, within myosin-X-induced filopodia. We demonstrate preferential enrichment of several adhesion proteins to either filopodia tips, filopodia shafts, or shaft subdomains, suggesting divergent, spatially restricted functions for these proteins. Moreover, proteins with phosphoinositide (PI) binding sites are particularly enriched in filopodia. This, together with the strong localization of PI(3,4)P2 in filopodia tips, predicts critical roles for PIs in regulating filopodia ultra-structure and function. Our mapping further reveals that filopodia adhesions consist of a unique set of proteins, the filopodome, that are distinct from classical nascent adhesions, focal adhesions, and fibrillar adhesions. Using live imaging, we observe that filopodia adhesions can give rise to nascent adhesions, which, in turn, form focal adhesions. We demonstrate that p130Cas (BCAR1) is recruited to filopodia tips via its C-terminal Cas family homology domain (CCHD) and acts as a mechanosensitive regulator of filopodia stability. Finally, we demonstrate that our map based on myosin-X-induced filopodia can be translated to endogenous filopodia and fascin- and IRSp53-mediated filopodia.

A novel spontaneous mutation of BCAR3 results in extrusion cataracts in CF#1 mouse strain

A substrain of mice originating from the CF#1 strain (an outbred colony) reared at Osaka Prefecture University (CF#1/lr mice) develops cataracts beginning at 4 weeks of age. Affected mice were fully viable and fertile and developed cataracts by 14 weeks of age. Histologically, CF#1/lr mice showed vacuolation of the lens cortex, swollen lens fibers, lens rupture and nuclear extrusion. To elucidate the mode of inheritance, we analyzed heterozygous mutant hybrids generated from CF#1/lr mice and wild-type BALB/c mice. None of the heterozygous mutants were affected, and the ratio of affected to unaffected mice was 1:3 among the offspring of the heterozygous mutants. For the initial genome-wide screening and further mapping, we used affected progeny of CF#1/lr × (CF#1/lr × BALB/c) mice. We concluded that the cataracts in CF#1/lr mice are inherited through an autosomal recessive mutation and that the mutant gene is located on mouse chromosome 3 between D3Mit79 and D3Mit216. In this region, we identified 8 genes associated with ocular disease. All 8 genes were sequenced and a novel point mutation (1 bp insertion of cytosine) in exon 7 of the Bcar3 gene was identified. This mutation produced a premature stop codon and a truncated protein. In conclusion, we have identified the first spontaneous mutation in the Bcar3 gene associated with lens extrusion cataracts. This novel cataract model may provide further knowledge of the molecular biology of cataractogenesis and the function of the BCAR3 protein.

Crocetin ester improves myocardial ischemia via Rho/ROCK/NF-κB pathway

Crocetin ester (CE) is the active ingredient of Crocus sativus L. stigmas and Gardenia jasminoides Ellis fruit. The main purpose of the present study was to investigate the protective effect of CE on isoproterenol (ISO)-induced acute myocardial ischemia (AMI) through Rho/ROCK/NF-κB pathway and explore its underlying mechanism. Administration of CE (25 and 50mg/kg) could significantly reduce the serum contents of pro-inflammatory cytokines including tumor necrosis factor-alpha (TNF-α), interleukin-1 beta (IL-1β) and interleukin-6 (IL-6). In addition, pretreatment with CE attenuated the contents of creatine kinase (CK), malondialdehyde (MDA) and the activities of lactate dehydrogenase (LDH), superoxide dismutase (SOD) in serum. Treatment with CE also improved the histopathological alteration and decreased the ST elevation. Furthermore, CE could ameliorate the cardiac expressions of Cu, Zn-superoxide dismutase (SOD1), MDA5, Rho, ROCK, p-IκB and p-NF-κBp65 in ISO-induced rats. It was assumed that CE might be a new therapeutic candidate for the treatment of AMI possibly through the inhibition of Rho/ROCK/NF-κB pathway.

Expression pattern of bcar3, a downstream target of Gata2, and its binding partner, bcar1, during Xenopus development

Primitive hematopoiesis generates red blood cells that deliver oxygen to the developing embryo. Mesodermal cells commit to a primitive blood cell fate during gastrulation and, in order to do so the mesoderm must receive non-cell autonomous signals transmitted from other germ layers. In Xenopus, the transcription factor Gata2 functions in ectodermal cells to generate or transmit the non-cell autonomous signals. Here we have identified Breast Cancer Antiestrogen Resistance 3 (bcar3) as a gene that is induced in ectodermal cells downstream of Gata2. Bcar3 and its binding partner Bcar1 function to transduce integrin signaling, leading to changes in cellular morphology, motility and adhesion. We show that gata2, bcar3 and bcar1 are co-expressed in ventral ectoderm from early gastrula to early tailbud stages. At later stages of development, bcar3 and bcar1 are co-expressed in the spinal cord, notochord, fin mesenchyme and pronephros but each shows additional unique sites of expression. These co-expression and unique expression patterns suggest that Bcar3 and Bcar1 may function together but also independently during Xenopus development.

Classic Ras Proteins Promote Proliferation and Survival via Distinct Phosphoproteome Alterations in Neurofibromin-Null Malignant Peripheral Nerve Sheath Tumor Cells

Neurofibromin, the tumor suppressor encoded by the neurofibromatosis type 1 (NF1) gene, potentially suppresses the activation of H-Ras, N-Ras, and K-Ras. However, it is not known whether these classic Ras proteins are hyperactivated in NF1-null nerve sheath tumors, how they contribute to tumorigenesis, and what signaling pathways mediate their effects. Here we show that H-Ras, N-Ras, and K-Ras are coexpressed with their activators (guanine nucleotide exchange factors) in neurofibromin-null malignant peripheral nerve sheath tumor (MPNST) cells, and that all 3 Ras proteins are activated. Dominant negative (DN) H-Ras, a pan-inhibitor of the classic Ras family, inhibited MPNST proliferation and survival, but not migration. However, NF1-null MPNST cells were variably dependent on individual Ras proteins. In some lines, ablation of H-Ras, N-Ras, and/or K-Ras inhibited mitogenesis. In others, ablation of a single Ras protein had no effect on proliferation; in these lines, ablation of a single Ras protein resulted in compensatory increases in the activation and/or expression of other Ras proteins. Using mass spectrometry-based phosphoproteomics, we identified 7 signaling networks affecting morphology, proliferation, and survival that are regulated by DN H-Ras. Thus, neurofibromin loss activates multiple classic Ras proteins that promote proliferation and survival by regulating several distinct signaling cascades.

Receptor tyrosine kinases modulate distinct transcriptional programs by differential usage of intracellular pathways

Receptor tyrosine kinases (RTKs) signal through shared intracellular pathways yet mediate distinct outcomes across many cell types. To investigate the mechanisms underlying RTK specificity in craniofacial development, we performed RNA-seq to delineate the transcriptional response to platelet-derived growth factor (PDGF) and fibroblast growth factor (FGF) signaling in mouse embryonic palatal mesenchyme cells. While the early gene expression profile induced by both growth factors is qualitatively similar, the late response is divergent. Comparing the effect of MEK (Mitogen/Extracellular signal-regulated kinase) and PI3K (phosphoinositide-3-kinase) inhibition, we find the FGF response is MEK dependent, while the PDGF response is PI3K dependent. Furthermore, FGF promotes proliferation but PDGF favors differentiation. Finally, we demonstrate overlapping domains of PDGF-PI3K signaling and osteoblast differentiation in the palate and increased osteogenesis in FGF mutants, indicating this differentiation circuit is conserved in vivo. Our results identify distinct responses to PDGF and FGF and provide insight into the mechanisms encoding RTK specificity.

DOI:http://dx.doi.org/10.7554/eLife.07186.001

Cells produce many different proteins that play a variety of important roles. For example, proteins called receptor tyrosine kinases can detect particular molecules and send signals to other parts of the cell to regulate the activity (or “expression”) of genes involved in cell division, movement, and other processes.

Humans have 58 receptor tyrosine kinases, and defects in these proteins have been linked to diseases such as cancer and diabetes. However, many different receptors regulate the activities of shared sets of genes, so it is not clear how an individual receptor can specifically control the genes involved in a particular process.

Two receptor tyrosine kinases called PDGFR and FGFR are crucial for the development of the face, palate, and head in humans and other animals. Vasudevan et al. used a technique called RNA-sequencing to find out which genes are regulated by these receptors in mouse palate cells. The experiments show that there is a common set of genes whose activities change quickly—within 1 hour—in response to the activation of either PDGFR or FGFR. However, several hours later, cells in which PDGFR is activated have different patterns of gene expression compared to those with active FGFR.

Vasudevan et al. also found that FGFR promotes cell division, while PDGFR promotes the changing of palate cells into different types with more specialized roles. These different outcomes arise because PDGFR and FGFR use different signaling pathways that involve distinct proteins. For example, a protein called PI3K is critical for changes in gene expression in response to PDGFR but not FGFR.

These results suggest that PGDRF and FGFR control different cellular processes in the palate by sending distinct signals into the cell. Understanding the receptor tyrosine kinases and the networks of genes they activate will help us to identify the signals that are important for other processes, such as the development of the face.

DOI:http://dx.doi.org/10.7554/eLife.07186.002

Breast cancer anti-estrogen resistance 3 inhibits transforming growth factor β/Smad signaling and associates with favorable breast cancer disease outcomes

INTRODUCTION

This study helps to define the implications of breast cancer anti-estrogen resistance 3 (BCAR3) in breast cancer and extends the current understanding of its molecular mechanism of action. BCAR3 has been shown to promote cell proliferation, migration and attachment to extracellular matrix components. However, in a cohort of metastatic breast cancer patients who received tamoxifen treatment, high BCAR3 mRNA levels were associated with favorable progression-free survival outcome. These results suggest that, besides its established roles, BCAR3 may have additional mechanisms of action that regulate breast cancer aggressive phenotype. In this study, we investigated whether BCAR3 is a novel antagonist of the canonical transforming growth factor β (TGFβ) pathway, which induces potent migration and invasion responses in breast cancer cells.

METHODS

We surveyed functional genomics databases for correlations between BCAR3 expression and disease outcomes of breast cancer patients. We also studied how BCAR3 could regulate the TGFβ/Smad signaling axis using Western blot analysis, coimmunoprecipitation and luciferase assays. In addition, we examined whether BCAR3 could modulate TGFβ-induced cell migration and invasion by using an automated imaging system and a confocal microscopy imaging-based matrix degradation assay, respectively.

RESULTS

Relatively low levels of BCAR3 expression in primary breast tumors correlate with poor distant metastasis-free survival and relapse-free survival outcomes. We also found a strong correlation between the loss of heterozygosity at BCAR3 gene alleles and lymph node invasion in human breast cancer, further suggesting a role for BCAR3 in preventing disease progression. In addition, we found BCAR3 to inhibit Smad activation, Smad-mediated gene transcription, Smad-dependent cell migration and matrix digestion in breast cancer cells. Furthermore, we found BCAR3 to be downregulated by TGFβ through proteasome degradation, thus defining a novel positive feedback loop mechanism downstream of the TGFβ/Smad signaling pathway.

CONCLUSION

BCAR3 is considered to be associated with aggressive breast cancer phenotypes. However, our results indicate that BCAR3 acts as a putative suppressor of breast cancer progression by inhibiting the prometastatic TGFβ/Smad signaling pathway in invasive breast tumors. These data provide new insights into BCAR3's molecular mechanism of action and highlight BCAR3 as a novel TGFβ/Smad antagonist in breast cancer.

OSBP-related protein 3 (ORP3) coupling with VAMP-associated protein A regulates R-Ras activity

ORP3 is an R-Ras interacting oxysterol-binding protein homolog that regulates cell adhesion and is overexpressed in several cancers. We investigated here a novel function of ORP3 dependent on its targeting to both the endoplasmic reticulum (ER) and the plasma membrane (PM). Using biochemical and cell imaging techniques we demonstrate the mechanistic requirements for the subcellular targeting and function of ORP3 in control of R-Ras activity. We show that hyperphosphorylated ORP3 (ORP3-P) selectively interacts with the ER membrane protein VAPA, and ORP3-VAPA complexes are targeted to PM sites via the ORP3 pleckstrin homology (PH) domain. A novel FFAT (two phenylalanines in an acidic tract)-like motif was identified in ORP3; only disruption of both the FFAT-like and canonical FFAT motif abolished the phorbol-12-myristate-13-acetate (PMA) stimulated interaction of ORP3-P with VAPA. Co-expression of ORP3 and VAPA induced R-Ras activation, dependent on the interactions of ORP3 with VAPA and the PM. Consistently, downstream AktS473 phosphorylation and β1-integrin activity were enhanced by ORP3-VAPA. To conclude, phosphorylation of ORP3 controls its association with VAPA. Furthermore, we present evidence that ORP3-VAPA complexes stimulate R-Ras signaling.

Mechanisms associated with resistance to tamoxifen in estrogen receptor-positive breast cancer (review)

Anti-estrogens such as tamoxifen are widely used in the clinic to treat estrogen receptor-positive breast tumors. Patients with estrogen receptor-positive breast cancer initially respond to treatment with anti-hormonal agents such as tamoxifen, but remissions are often followed by the acquisition of resistance and, ultimately, disease relapse. The development of a rationale for the effective treatment of tamoxifen-resistant breast cancer requires an understanding of the complex signal transduction mechanisms. In the present study, we explored some mechanisms associated with resistance to tamoxifen, such as pharmacologic mechanisms, loss or modification in estrogen receptor expression, alterations in co-regulatory proteins and the regulation of the different signaling pathways that participate in different cellular processes such as survival, proliferation, stress, cell cycle, inhibition of apoptosis regulated by the Bcl-2 family, autophagy, altered expression of microRNA, and signaling pathways that regulate the epithelial-mesenchymal transition in the tumor microenvironment. Delineation of the molecular mechanisms underlying the development of resistance may aid in the development of treatment strategies to enhance response and compromise resistance.

Negative regulation of the RalGAP complex by 14-3-3

RGC1 and RGC2 comprise a functional RalGAP complex (RGC) that suppresses RalA activity. The PI3-kinase/Akt signaling pathway activates RalA through phosphorylation-mediated inhibition of the RGC. Here we identify a novel phosphorylation-dependent interaction between 14-3-3 and the RGC. 14-3-3 binds to the complex through an Akt-phosphorylated residue, threonine 715, on RGC2. Interaction with 14-3-3 does not alter in vitro activity of the GTPase-activating protein complex. However, blocking the interaction between 14-3-3 and RGC2 in cells increases suppression of RalA activity by the RGC, suggesting that 14-3-3 inhibits the complex through a non-catalytic mechanism. Together, these data show that 14-3-3 negatively regulates the RGC downstream of the PI3-kinase/Akt signaling pathway.

p130Cas: a key signalling node in health and disease

p130Cas/breast cancer anti-oestrogen resistance 1 (BCAR1) is a member of the Cas (Crk-associated substrate) family of adaptor proteins, which have emerged as key signalling nodes capable of interactions with multiple proteins, with important regulatory roles in normal and pathological cell function. The Cas family of proteins is characterised by the presence of multiple conserved motifs for protein-protein interactions, and by extensive tyrosine and serine phosphorylations. Recent studies show that p130Cas contributes to migration, cell cycle control and apoptosis. p130Cas is essential during early embryogenesis, with a critical role in cardiovascular development. Furthermore, p130Cas has been reported to be involved in the development and progression of several human cancers. p130Cas is able to perform roles in multiple processes due to its capacity to regulate a diverse array of signalling pathways, transducing signals from growth factor receptor tyrosine kinases, non-receptor tyrosine kinases, and integrins. In this review we summarise the current understanding of the structure, function, and regulation of p130Cas, and discuss the importance of p130Cas in both physiological and pathophysiological settings, with a focus on the cardiovascular system and cancer.

NSP-CAS Protein Complexes: Emerging Signaling Modules in Cancer

The CAS (CRK-associated substrate) family of adaptor proteins comprises 4 members, which share a conserved modular domain structure that enables multiple protein-protein interactions, leading to the assembly of intracellular signaling platforms. Besides their physiological role in signal transduction downstream of a variety of cell surface receptors, CAS proteins are also critical for oncogenic transformation and cancer cell malignancy through associations with a variety of regulatory proteins and downstream effectors. Among the regulatory partners, the 3 recently identified adaptor proteins constituting the NSP (novel SH2-containing protein) family avidly bind to the conserved carboxy-terminal focal adhesion-targeting (FAT) domain of CAS proteins. NSP proteins use an anomalous nucleotide exchange factor domain that lacks catalytic activity to form NSP-CAS signaling modules. Additionally, the NSP SH2 domain can link NSP-CAS signaling assemblies to tyrosine-phosphorylated cell surface receptors. NSP proteins can potentiate CAS function by affecting key CAS attributes such as expression levels, phosphorylation state, and subcellular localization, leading to effects on cell adhesion, migration, and invasion as well as cell growth. The consequences of these activities are well exemplified by the role that members of both families play in promoting breast cancer cell invasiveness and resistance to antiestrogens. In this review, we discuss the intriguing interplay between the NSP and CAS families, with a particular focus on cancer signaling networks.

Protein tyrosine phosphatase α phosphotyrosyl-789 binds BCAR3 to position Cas for activation at integrin-mediated focal adhesions

Integrin-mediated focal adhesions connect the extracellular matrix and cytoskeleton to regulate cell responses, such as migration. Protein tyrosine phosphatase α (PTPα) regulates integrin signaling, focal adhesion formation, and migration, but its roles in these events are incompletely understood. The integrin-proximal action of PTPα activates Src family kinases, and subsequent phosphorylation of PTPα at Tyr789 acts in an unknown manner to promote migration. PTPα-null cells were used in reconstitution assays to distinguish PTPα-Tyr789-dependent signaling events. This showed that PTPα-Tyr789 regulates the localization of PTPα and the scaffolding protein Cas to adhesion sites where Cas interacts with and is phosphorylated by Src to initiate Cas signaling. Linking these events, we identify BCAR3 as a molecular connector of PTPα and Cas, with phospho-Tyr789 PTPα serving as the first defined cellular ligand for the BCAR3 SH2 domain that recruits BCAR3-Cas to adhesions. Our findings reveal a novel role of PTPα in integrin-induced adhesion assembly that enables Src-mediated activation of the pivotal function of Cas in migration.

Finding the weakest link: exploring integrin-mediated mechanical molecular pathways

From the extracellular matrix to the cytoskeleton, a network of molecular links connects cells to their environment. Molecules in this network transmit and detect mechanical forces, which subsequently determine cell behavior and fate. Here, we reconstruct the mechanical pathway followed by these forces. From matrix proteins to actin through integrins and adaptor proteins, we review how forces affect the lifetime of bonds and stretch or alter the conformation of proteins, and how these mechanical changes are converted into biochemical signals in mechanotransduction events. We evaluate which of the proteins in the network can participate in mechanotransduction and which are simply responsible for transmitting forces in a dynamic network. Besides their individual properties, we also analyze how the mechanical responses of a protein are determined by their serial connections from the matrix to actin, their parallel connections in integrin clusters and by the rate at which force is applied to them. All these define mechanical molecular pathways in cells, which are emerging as key regulators of cell function alongside better studied biochemical pathways.

Breast cancer anti-estrogen resistance 3 (BCAR3) protein augments binding of the c-Src SH3 domain to Crk-associated substrate (p130cas)

The focal adhesion adapter protein p130(cas) regulates adhesion and growth factor-related signaling, in part through Src-mediated tyrosine phosphorylation of p130(cas). AND-34/BCAR3, one of three NSP family members, binds the p130(cas) carboxyl terminus, adjacent to a bipartite p130(cas) Src-binding domain (SBD) and induces anti-estrogen resistance in breast cancer cell lines as well as phosphorylation of p130(cas). Only a subset of the signaling properties of BCAR3, specifically augmented motility, are dependent upon formation of the BCAR3-p130(cas) complex. Using GST pull-down and immunoprecipitation studies, we show that among NSP family members, only BCAR3 augments the ability of p130(cas) to bind the Src SH3 domain through an RPLPSPP motif in the p130(cas) SBD. Although our prior work identified phosphorylation of the serine within the p130(cas) RPLPSPP motif, mutation of this residue to alanine or glutamic acid did not alter BCAR3-induced Src SH3 domain binding to p130(cas). The ability of BCAR3 to augment Src SH3 binding requires formation of a BCAR3-p130(cas) complex because mutations that reduce association between these two proteins block augmentation of Src SH3 domain binding. Similarly, in MCF-7 cells, BCAR3-induced tyrosine phosphorylation of the p130(cas) substrate domain, previously shown to be Src-dependent, was reduced by an R743A mutation that blocks BCAR3 association with p130(cas). Immunofluorescence studies demonstrate that BCAR3 expression alters the intracellular location of both p130(cas) and Src and that all three proteins co-localize. Our work suggests that BCAR3 expression may regulate Src signaling in a BCAR3-p130(cas) complex-dependent fashion by altering the ability of the Src SH3 domain to bind the p130(cas) SBD.

NSP-Cas protein structures reveal a promiscuous interaction module in cell signaling

NSP and Cas family proteins form multidomain signaling platforms that mediate cell migration and invasion through a collection of distinct signaling motifs. Members of each family interact via their respective C-terminal domains, but the mechanism of this association has remained enigmatic. Here we present the crystal structures of the C-terminal domain from the human NSP protein BCAR3 and the complex of NSP3 with p130Cas. BCAR3 adopts the Cdc25-homology fold of Ras GTPase exchange factors, but exhibits a “closed” conformation incapable of enzymatic activity. The NSP3–p130Cas complex structure reveals that this closed conformation is instrumental for interaction of NSP proteins with a focal adhesion-targeting domain present in Cas proteins. This enzyme to adaptor conversion enables high affinity, yet promiscuous, interactions between NSP and Cas proteins and represents an unprecedented mechanistic paradigm linking cellular signaling networks.

The human Rgr oncogene is overexpressed in T-cell malignancies and induces transformation by acting as a GEF for Ras and Ral

The Ras superfamily of GTPases is involved in the modification of many cellular processes including cellular motility, proliferation and differentiation. Our laboratory has previously identified the RalGDS-related (Rgr) oncogene in a DMBA (7,12-dimethylbenz[α]anthracene)-induced rabbit squamous cell carcinoma and its human orthologue, hRgr. In this study, we analyzed the expression levels of the human hRgr transcript in a panel of human hematopoietic malignancies and found that a truncated form (diseased-truncated (Dtr-hrgr)) was significantly overexpressed in many T-cell-derived neoplasms. Although the Rgr proto-oncogene belongs to the RalGDS family of guanine nucleotide exchange factors (GEFs), we show that upon the introduction of hRgr into fibroblast cell lines, it is able to elicit the activation of both Ral and Ras GTPases. Moreover, in vitro guanine nucleotide exchange assays confirm that hRgr promotes Ral and Ras activation through GDP dissociation, which is a critical characteristic of GEF proteins. hRgr has guanine nucleotide exchange activity for both small GTPases and this activity was reduced when a point mutation within the catalytic domain (CDC25) of the protein, (cd) Dtr-hRgr, was utilized. These observations prompted the analysis of the biological effects of hRgr and (cd) hRgr expression in cultured cells. Here, we show that hRgr increases proliferation in low serum, increases invasion, reduces anchorage dependence and promotes the progression into the S phase of the cell cycle; properties that are abolished or severely reduced in the presence of the catalytic dead mutant. We conclude that the ability of hRgr to activate both Ral and Ras is responsible for its transformation-inducing phenotype and it could be an important contributor in the development of some T-cell malignancies.

BCAR3/AND-34 can signal independent of complex formation with CAS family members or the presence of p130Cas

BCAR3 binds to the carboxy-terminus of p130Cas, a focal adhesion adapter protein. Both BCAR3 and p130Cas have been linked to resistance to anti-estrogens in breast cancer, Rac activation and cell motility. Using R743A BCAR3, a point mutant that has lost the ability to bind p130Cas, we find that BCAR3-p130Cas complex formation is not required for BCAR3-mediated anti-estrogen resistance, Rac activation or discohesion of epithelial breast cancer cells. Complex formation was also not required for BCAR3-induced lamellipodia formation in BALB/c-3T3 fibroblasts but was required for optimal BCAR3-induced motility. Although both wildtype and R743A BCAR3 induced phosphorylation of p130Cas and the related adapter protein HEF1/NEDD9, chimeric NSP3:BCAR3 experiments demonstrate that such phosphorylation does not correlate with BCAR3-induced anti-estrogen resistance or lamellipodia formation. Wildtype but not R743A BCAR3 induced lamellipodia formation and augmented cell motility in p130Cas(-/-) murine embryonic fibroblasts (MEFs), suggesting that while p130Cas itself is not strictly required for these endpoints, complex formation with other CAS family members is, at least in cells lacking p130Cas. Overall, our work suggests that many, but not all, BCAR3-mediated signaling events in epithelial and mesenchymal cells are independent of p130Cas association. These studies also indicate that disruption of the BCAR3-p130Cas complex is unlikely to reverse BCAR3-mediated anti-estrogen resistance.

Integrin signalling adaptors: not only figurants in the cancer story

Current evidence highlights the ability of adaptor (or scaffold) proteins to create signalling platforms that drive cellular transformation upon integrin-dependent adhesion and growth factor receptor activation. The understanding of the biological effects that are regulated by these adaptors in tumours might be crucial for the identification of new targets and the development of innovative therapeutic strategies for human cancer. In this Review we discuss the relevance of adaptor proteins in signalling that originates from integrin-mediated cell-extracellular matrix (ECM) adhesion and growth factor stimulation in the context of cell transformation and tumour progression. We specifically underline the contribution of p130 Crk-associated substrate (p130CAS; also known as BCAR1), neural precursor cell expressed, developmentally down-regulated 9 (NEDD9; also known as HEF1), CRK and the integrin-linked kinase (ILK)-pinch-parvin (IPP) complex to cancer, along with the more recently identified p140 Cas-associated protein (p140CAP; also known as SRCIN1).

Integrin signaling switches the cytoskeletal and exocytic machinery that drives neuritogenesis

Neurons establish their unique morphology by elaborating multiple neurites that subsequently form axons and dendrites. Neurite initiation entails significant surface area expansion, necessitating addition to the plasma membrane. We report that regulated membrane delivery coordinated with the actin cytoskeleton is crucial for neuritogenesis and identify two independent pathways that use distinct exocytic and cytoskeletal machinery to drive neuritogenesis. One pathway uses Ena/VASP-regulated actin dynamics coordinated with VAMP2-mediated exocytosis and involves a novel role for Ena/VASP in exocytosis. A second mechanism occurs in the presence of laminin through integrin-dependent activation of FAK and src and uses coordinated activity of the Arp2/3 complex and VAMP7-mediated exocytosis. We conclude that neuritogenesis can be driven by two distinct pathways that differentially coordinate cytoskeletal dynamics and exocytosis. These regulated changes and coordination of cytoskeletal and exocytic machinery may be used in other physiological contexts involving cell motility and morphogenesis.

Regulation of T-lymphocyte physiology by the Chat-H/CasL adapter complex

The Cas family of proteins consists of at least four members implicated in the regulation of diverse cellular processes such as cell proliferation, adhesion, motility, and cancer cell metastasis. Cas family members have conserved C-termini that mediate constitutive heterotypic interactions with members of a different group of proteins, the NSP family. Both the Cas and NSP proteins have conserved domains that mediate protein-protein interactions with other cytoplasmic intermediates. Signaling modules assembled by these proteins in turn regulate signal transduction downstream of a variety of receptors including integrin, chemokine, and antigen receptors. T lymphocytes express the NSP protein NSP3/Chat-H and the Cas protein Hef1/CasL, which are found in a constitutive complex in naive T cells. We recently showed that Chat-H and Hef1/CasL regulate integrin-mediated adhesion and promote T-cell migration and trafficking downstream of activated chemokine receptors. It is currently unclear if the Chat-H/CasL module also plays a role in antigen receptor signaling. Here we review our current knowledge of how Chat-H and Hef1/CasL regulate T-cell physiology and whether this protein complex plays a functional role downstream of T-cell receptor activation.

CAS proteins in normal and pathological cell growth control

Proteins of the CAS (Crk-associated substrate) family (BCAR1/p130Cas, NEDD9/HEF1/Cas-L, EFS/SIN and CASS4/HEPL) are integral players in normal and pathological cell biology. CAS proteins act as scaffolds to regulate protein complexes controlling migration and chemotaxis, apoptosis, cell cycle, and differentiation, and have more recently been linked to a role in progenitor cell function. Reflecting these complex functions, over-expression of CAS proteins has now been strongly linked to poor prognosis and increased metastasis in cancer, as well as resistance to first-line chemotherapeutics in multiple tumor types including breast and lung cancers, glioblastoma, and melanoma. Further, CAS proteins have also been linked to additional pathological conditions including inflammatory disorders, Alzheimer's and Parkinson's disease, as well as developmental defects. This review will explore the roles of the CAS proteins in normal and pathological states in the context of the many mechanistic insights into CAS protein function that have emerged in the past decade.

p130Cas substrate domain signaling promotes migration, invasion, and survival of estrogen receptor-negative breast cancer cells

Elevated Src tyrosine kinase activity is commonly observed in breast cancer and likely contributes to neoplasia and malignancy. p130Cas ("Crk-associated substrate") is a major Src substrate found at the sites where integrins mediate cell adhesion to the extracellular matrix. Src phosphorylates multiple tyrosines in the p130Cas "substrate domain" (SD) and this signaling event has been implicated in the promotion of cell motility, primarily from studies on fibroblasts. In breast cancer, studies on p130Cas have focused on its role in conferring antiestrogen resistance to cells that express the estrogen receptor (ER+). However, little is known regarding the role of p130Cas in the more aggressive estrogen receptor negative (ER-) breast cancers for which there is a need for development of effective targeted therapies. We found high levels of p130Cas SD tyrosine phosphorylation to be a common characteristic of ER- breast cancer cell lines, with particularly high levels observed for the BT-549 cell line. Using RNA interference to knock down p130Cas expression in BT-549 cells, combined with rescue by WT p130Cas versus a signaling-deficient control, we provide evidence that p130Cas SD tyrosine phosphorylation is an important signaling event in the migration, invasion, proliferation, and survival of this ER-breast cancer cell line.

BCAR3 regulates Src/p130 Cas association, Src kinase activity, and breast cancer adhesion signaling

The nonreceptor protein-tyrosine kinase c-Src is frequently overexpressed and/or activated in a variety of cancers, including those of the breast. Several heterologous binding partners of c-Src have been shown to regulate its catalytic activity by relieving intramolecular autoinhibitory interactions. One such protein, p130(Cas) (Cas), is expressed at high levels in both breast cancer cell lines and breast tumors, providing a potential mechanism for c-Src activation in breast cancers. The Cas-binding protein BCAR3 (breast cancer antiestrogen resistance-3) is expressed at high levels in invasive breast cancer cell lines, and this molecule has previously been shown to coordinate with Cas to increase c-Src activity in COS-1 cells. In this study, we show for the first time using gain- and loss-of-function approaches that BCAR3 regulates c-Src activity in the endogenous setting of breast cancer cells. We further show that BCAR3 regulates the interaction between Cas and c-Src, both qualitatively as well as quantitatively. Finally, we present evidence that the coordinated activity of these proteins contributes to breast cancer cell adhesion signaling and spreading. Based on these data, we propose that the c-Src/Cas/BCAR3 signaling axis is a prominent regulator of c-Src activity, which in turn controls cell behaviors that lead to aggressive and invasive breast tumor phenotypes.

AND-34/BCAR3 regulates adhesion-dependent p130Cas serine phosphorylation and breast cancer cell growth pattern

NSP protein family members associate with p130Cas, a focal adhesion adapter protein best known as a Src substrate that integrates adhesion-related signaling. Over-expression of AND-34/BCAR3/NSP2 (BCAR3), but not NSP1 or NSP3, induces anti-estrogen resistance in human breast cancer cell lines. BCAR3 over-expression in epithelial MCF-7 cells augments levels of a phosphorylated p130Cas species that migrates more slowly on SDS-PAGE while NSP1 and NSP3 induce modest or no phosphorylation, respectively. Conversely, reduction in BCAR3 expression in mesenchymal MDA-231 cells by inducible shRNA results in loss of such p130Cas phosphorylation. Replacement of NSP3's serine/proline-rich domain with that of AND-34/BCAR3 instills the ability to induce p130Cas phosphorylation. Phospho-amino acid analysis demonstrates that BCAR3 induces p130Cas serine phosphorylation. Mass spectrometry identified phosphorylation at p130Cas serines 139, 437 and 639. p130Cas serine phosphorylation accumulates for several hours after adhesion of MDA-231 cells to fibronectin and is dependent upon BCAR3 expression. BCAR3 knockdown alters p130Cas localization and converts MDA-231 growth to an epithelioid pattern characterized by striking cohesiveness and lack of cellular projections at colony borders. These studies demonstrate that BCAR3 regulates p130Cas serine phosphorylation that is adhesion-dependent, temporally distinct from previously well-characterized rapid Fak and Src kinase-mediated p130Cas tyrosine phosphorylation and that correlates with invasive phenotype.

The substrate domain of BCAR1 is essential for anti-estrogen-resistant proliferation of human breast cancer cells

To unravel the mechanisms underlying failure of endocrine therapy of breast cancer, we have previously executed a functional genetic screen and identified the adaptor protein BCAR1 to be causative for tamoxifen resistance. As a consequence of the manifold of interactions with other proteins, we characterized the contribution of individual protein domains of BCAR1 to anti-estrogen-resistant proliferation of human breast cancer cells. We took advantage of the observation that the closely related family member HEF1 was unable to support long-term anti-estrogen-resistant cell proliferation. Chimerical proteins containing defined domains of BCAR1 and HEF1 were evaluated for anti-estrogen-resistant growth. Exchange of the SH3 and C-terminal domains did not modify the capacity to support cell proliferation. Full support of anti-estrogen resistant proliferation was observed for chimerical molecules containing the central part of BCAR1. The bi-partite SRC-binding site or the Serine-rich domain did not explain the differential capacity of BCAR1. These findings indicate that the differences between BCAR1 and HEF1 with respect to support of anti-estrogen resistance reside in the substrate domain which contains multiple sites for tyrosine phosphorylation. The crucial interactions required for anti-estrogen resistance occur within the substrate domain of BCAR1. Further deciphering of these interactions may resolve the growth regulatory mechanism and provide an explanation for the observation that primary tumors with high levels of BCAR1 are likely to fail on tamoxifen therapy. This information may also help to devise alternative personalized treatment strategies with improved outcome for breast cancer patients.

Pyk2 mediates endothelin-1 signaling via p130Cas/BCAR3 cascade and regulates human glomerular mesangial cell adhesion and spreading

Calcium-regulated non-receptor proline-rich tyrosine kinase 2 (Pyk2) is a critical mediator of endothelin-1 (ET-1) signaling in human glomerular mesangial cells (GMC). We aimed to identify which small G-protein is acting downstream of Pyk2. Dominant interfering Pyk2 construct, termed calcium regulated non kinase (CRNK) or green fluorescent protein (control) were expressed in GMC using adenovirus-mediated gene transfer. ET-1 stimulation resulted in a significant increase of Pyk2 phosphorylation accompanied by GTP-loading of Rap1 and RhoA. CRNK expression inhibited ET-1-induced autophosphorylation of endogenous Pyk2 and diminished Rap1, but not RhoA, activation. The mechanism linking Pyk2 and Rap1 included (1) increased autophosphorylation of Pyk2 associated with p130Cas, (2) augmented p130Cas Y165 and Y249 phosphorylation, and (3) enhanced p130Cas-BCAR3 complex formation. CRNK expression prevented p130Cas phosphorylation and attenuated p130Cas association with BCAR3. Downregulation of endogenous BCAR3 protein expression using an siRNA technique led to a significant decrease in Rap1 activation in response to ET-1. We observed that endogenous Pyk2 was important for GMC adhesion and spreading. Our data suggest that ET-1 stimulated the GTPase Rap1 (but neither RhoA nor Ras) by a mechanism involving Pyk2 activation and recruitment of the p130Cas/BCAR3 complex in GMC.

Src-dependent repression of ARF6 is required to maintain podosome-rich sealing zones in bone-digesting osteoclasts

Bone digestion occurs when osteoclasts adhere onto bone surfaces and polarize to form acidic, hydrolase-rich resorption lacunae. For this process, they condense their actin-rich podosomes in tight belts to establish sealing zones, which segregate their basal membranes from those facing resorption lacunae. This polarization process remains poorly understood. Here, we combined quantitative proteomics and gene silencing to identify new substrates of the Src tyrosine kinase, a key regulator of osteoclast function. We now report that a depletion of the ARF GTPase-activating protein GIT2, which localizes to sealing zones upon Src phosphorylation, or a lack of GTP hydrolysis on ARF6 impairs sealing zone formation and polarized membrane traffic. Surprisingly, the Rho guanine nucleotide exchange factors alpha and beta PIX, which usually coordinate ARF and Rho signaling, were found to be dispensable. We conclude that the Src-dependent localization of GIT2 is essential for down-regulating ARF6 activity at sealing zones, and thus for maintaining osteoclast polarity.

Structural insights into the association between BCAR3 and Cas family members, an atypical complex implicated in anti-oestrogen resistance

The association between novel Src homology 2-containing protein (NSP) and Crk-associated substrate (Cas) family members contributes to integrin and receptor tyrosine kinase signalling and is involved in conferring anti-oestrogen resistance to human breast carcinomas. The precise role of this association in tumorigenesis remains controversial, and the molecular basis for the complex NSP and Cas protein form is unknown. Here we present a pluridisciplinary approach, including small-angle X-ray scattering, that provides first insights into the structure of the complex formed between breast cancer anti-oestrogen resistance 3 (BCAR3, an NSP family member) and human enhancer of filamentation 1 (HEF1, also named NEDD9 or Cas-L, a Cas family protein). Our analysis corroborates a four-helix bundle structure for the NSP-binding domain of HEF1 and a Cdc25-like guanine nucleotide exchange factor (GEF) fold for the Cas-binding domain of BCAR3. Using residues located on helix 2 of the four-helix bundle, HEF1 binds very tightly to a site on BCAR3 that is remote from the putative guanosine triphosphatase binding site of the GEF domain, but similar to a site implicated in allosteric regulation of the homologous SOS (Son of Sevenless) GEF domain. Thus, the association between NSP and Cas proteins might not only create a very stable link between these molecules, co-localising their cellular functions, but also modulate the function of the NSP GEF domains. Such modulation may explain, at least in part, the controversial results published for NSP GEF function.

Induction of cell retraction by the combined actions of Abl-CrkII and Rho-ROCK1 signaling

Dynamic modulation of cell adhesion is integral to a wide range of biological processes. The small guanosine triphosphatase (GTPase) Rap1 is an important regulator of cell–cell and cell–matrix adhesions. We show here that induced expression of activated Abl tyrosine kinase reduces Rap1-GTP levels through phosphorylation of Tyr221 of CrkII, which disrupts interaction of CrkII with C3G, a guanine nucleotide exchange factor for Rap1. Abl-dependent down-regulation of Rap1-GTP causes cell rounding and detachment only when the Rho–ROCK1 pathway is also activated, for example, by lysophosphatidic acid (LPA). During ephrin-A1–induced retraction of PC3 prostate cancer cells, we show that endogenous Abl is activated and disrupts the CrkII–C3G complex to reduce Rap1-GTP. Interestingly, ephrin-A1–induced PC3 cell retraction also requires LPA, which stimulates Rho to a much higher level than that is activated by ephrin-A1. Our results establish Rap1 as another downstream target of the Abl–CrkII signaling module and show that Abl–CrkII collaborates with Rho–ROCK1 to stimulate cell retraction.

BCAR3 regulates EGF-induced DNA synthesis in normal human breast MCF-12A cells

BCAR3 (breast cancer anti-estrogen resistance 3) is a signal transducer containing an SH2 domain, a proline/serine-rich domain and a GDP-exchange factor homologous domain, whose role in signaling pathways is currently unclear. Furthermore, BCAR3 is implicated in anti-estrogen resistance of breast cancer cells. In the present study, we investigated the functional role of BCAR3 in a mitogenic signaling pathway of EGF in non-tumorigenic human breast epithelial MCF-12A cells. Microinjection of an anti-BCAR3 antibody, siRNAs targeting BCAR3 and an SH2 domain of BCAR3 inhibited EGF-induced DNA synthesis. Direct association of BCAR3 with activated EGF receptor and Cas was observed. Lastly, microinjection of a BCAR3 expression plasmid induced DNA synthesis. These findings suggest that the BCAR3 protein, through its SH2 domain, is involved in the signaling pathways of EGF leading to cell cycle progression, and that BCAR3 itself is part of a mitogenic signaling pathway.

Characterization of AND-34 function and signaling

AND-34 is a member of a novel family of proteins (NSP1, NSP2, and NSP3) that have an amino-terminal SH2 domain but bind by a carboxy-terminal GEF (Cdc25)-like domain to the carboxy-terminus of the focal adhesion adapter protein p130Cas. Direct GEF activity of AND-34 toward Ras subfamily members has not been demonstrated with purified protein. Overexpression of AND-34 in epithelial breast cancer cells leads to activation of Rac and Cdc42 by a PI3K-dependent mechanism. This chapter will describe the techniques we used to examine AND-34-induced Rac, Cdc42, Akt, and PAK1 activation in human breast cancer cell lines and in murine lymphoid cell lines. In addition, we summarize techniques used to determine that AND-34 overexpression does not activate R-Ras in MCF-7 cells.

AND-34/BCAR3 differs from other NSP homologs in induction of anti-estrogen resistance, cyclin D1 promoter activation and altered breast cancer cell morphology

Over-expression of AND-34/BCAR3/NSP2 (BCAR3) or its binding-partner p130Cas/BCAR1 generates anti-estrogen resistance in human breast cancer lines. Here, we have compared BCAR3 to two related homologs, NSP1 and NSP3/CHAT/SHEP, with regards to expression, anti-estrogen resistance, and signaling. BCAR3 is expressed at higher levels in ERalpha-negative, mesenchymal, than in ERalpha-positive, epithelial, breast cancer cell lines. Characterization of "intermediate" epithelial-like cell lines with variable ER-alpha expression reveals that BCAR3 expression correlates with both mesenchymal and ERalpha-negative phenotypes. Levels of the BCAR3/p130Cas complex correlate more strongly with the ERalpha-negative, mesenchymal phenotype than levels of either protein alone. NSP1 and NSP3 are expressed at lower levels than BCAR3 and without correlation to ERalpha/mesenchymal status. Among NSP-transfectants, only BCAR3 transfectants induce anti-estrogen resistance and augment transcription of cyclin D1 promoter constructs. Over-expression of all homologs results in activation of Rac, Cdc42 and Akt, suggesting that these signals are insufficient to induce anti-estrogen resistance. BCAR3 but not NSP1 nor NSP3 transfectants show altered morphology, transitioning from polygonal cell groups to rounded, single cells with numerous blebs. Whereas stable over-expression of BCAR3 in MCF-7 cells does not lead to classic epithelial-to-mesenchymal transition, it does result in down-regulation of cadherin-mediated adhesion and augmentation of fibronectin expression. These studies suggest that BCAR's ability to induce anti-estrogen resistance is greater than that of other NSP homologs and may result from altered interaction of breast cancer cells with each other and the extracellular matrix.

Breast cancer antiestrogen resistance-3 expression regulates breast cancer cell migration through promotion of p130Cas membrane localization and membrane ruffling

Antiestrogens such as tamoxifen are widely used in the clinic to treat estrogen receptor-positive breast tumors. Resistance to tamoxifen can occur either de novo or develop over time in a large proportion of these tumors. Additionally, resistance is associated with enhanced motility and invasiveness in vitro. One molecule that has been implicated in tamoxifen resistance, breast cancer antiestrogen resistance-3 (BCAR3), has also been shown to regulate migration of fibroblasts. In this study, we investigated the role of BCAR3 in breast cancer cell migration and invasion. We found that BCAR3 was highly expressed in multiple breast cancer cell lines, where it associated with another protein, p130(Cas) (also known as breast cancer antiestrogen resistance-1; BCAR1), that plays a role in both tamoxifen resistance and cell motility. In cells with relatively low migratory potential, BCAR3 overexpression resulted in enhanced migration and colocalization with p130(Cas) at the cell membrane. Conversely, BCAR3 depletion from more aggressive breast cancer cell lines inhibited migration and invasion. This coincided with a relocalization of p130(Cas) away from the cell membrane and an attenuated response to epidermal growth factor stimulation that was characterized by a loss of membrane ruffles, decreased migration toward EGF, and disruption of p130(Cas)/Crk complexes. Based on these data, we propose that the spatial and temporal regulation of BCAR3/p130(Cas) interactions within the cell is important for controlling breast cancer cell motility.

Transcription factor Pax5 activates the chromatin of key genes involved in B cell signaling, adhesion, migration, and immune function

The transcription factor Pax5 represses B lineage-inappropriate genes and activates B cell-specific genes in B lymphocytes. Here we have identified 170 Pax5-activated genes. Conditional mutagenesis demonstrated that the Pax5-regulated genes require continuous Pax5 activity for normal expression in pro-B and mature B cells. Expression of half of the Pax5-activated genes is either absent or substantially reduced upon Pax5 loss in plasma cells. Direct Pax5 target genes were identified based on their protein synthesis-independent activation by a Pax5-estrogen receptor fusion protein. Chromatin immunoprecipitation (ChIP) of Pax5 together with chromatin profiling by ChIP-on-chip analysis demonstrated that Pax5 directly activates the chromatin at promoters or putative enhancers of Pax5 target genes. The Pax5-activated genes code for key regulatory and structural proteins involved in B cell signaling, adhesion, migration, antigen presentation, and germinal-center B cell formation, thus revealing a complex regulatory network that is activated by Pax5 to control B cell development and function.

Molecular basis for HEF1/NEDD9/Cas-L action as a multifunctional co-ordinator of invasion, apoptosis and cell cycle

Upregulation of the scaffolding protein HEF1, also known as NEDD9 and Cas-L, has recently been identified as a pro-metastatic stimulus in a number of different solid tumors, and has also been strongly associated with pathogenesis of BCR-Abl-dependent tumors. As the evidence mounts for HEF1/NEDD9/Cas-L as a key player in metastatic cancer, it is timely to review the molecular regulation of HEF1/NEDD9/Cas-L. Most of the mortality associated with cancer arises from uncontrolled metastases, thus a better understanding of the properties of proteins specifically associated with promotion of this process may yield insights that improve cancer diagnosis and treatment. In this review, we summarize the extensive literature regarding HEF1/NEDD9/Cas-L expression and function in signaling relevant to cell attachment, migration, invasion, cell cycle, apoptosis, and oncogenic signal transduction. The complex function of HEF1/NEDD9/Cas-L revealed by this analysis leads us to propose a model in which alleviation of cell cycle checkpoints and acquired resistance to apoptosis is permissive for a HEF1/NEDD9/Cas-L-promoted pro-metastatic phenotype.

Focal adhesion kinase is required for CXCL12-induced chemotactic and pro-adhesive responses in hematopoietic precursor cells

Hematopoietic stem/progenitor cells (HSC/P) reside in the bone marrow in distinct anatomic locations (niches) to receive growth, survival and differentiation signals. HSC/P localization and migration between niches depend on cell-cell and cell-matrix interactions, which result from the cooperation of cytokines, chemokines and adhesion molecules. The CXCL12-CXCR4 pathway, in particular, is essential for myelopoiesis and B lymphopoiesis but the molecular mechanisms of CXCL12 action remain unclear. We previously noted a strong correlation between prolonged CXCL12-mediated focal adhesion kinase (FAK) phosphorylation and sustained pro-adhesive responses in progenitor B cells, but not in mature B cells. Although FAK has been well studied in adherent fibroblasts, its function in hematopoietic cells is not defined. We used two independent approaches to reduce FAK expression in (human and mouse) progenitor cells. RNA interference (RNAi)-mediated FAK silencing abolished CXCL12-induced responses in human pro-B leukemia, REH cells. FAK-deficient REH cells also demonstrated reduced CXCL12-induced activation of the GTPase Rap1, suggesting the importance of FAK in CXCL12-mediated integrin activation. Moreover, in FAK(flox/flox) hematopoietic precursor cells, Cre-mediated FAK deletion resulted in impaired CXCL12-induced chemotaxis. These studies suggest that FAK may function as a key intermediary in signaling pathways controlling hematopoietic cell lodgment and lineage development.

Pathways to tamoxifen resistance

Therapies that target the synthesis of estrogen or the function of estrogen receptor(s) have been developed to treat breast cancer. While these approaches have proven to be beneficial to a large number of patients, both de novo and acquired resistance to these drugs is a significant problem. Recent advances in our understanding of the molecular mechanisms that contribute to resistance have provided a means to begin to predict patient responses to these drugs and develop rational approaches for combining therapeutic agents to circumvent or desensitize the resistant phenotype. Here, we review common mechanisms of antiestrogen resistance and discuss the implications for prediction of response and design of effective combinatorial treatments.

R-Ras promotes metastasis of cervical cancer epithelial cells

Mutations in the small GTPase R-Ras that promote constitutive activation of this signaling molecule have been observed in a variety of invasive cancer cell types. We previously reported that expression of an oncogenic form of R-Ras (R-Ras87L) in a cell line of cervical cancer (C33A cells) augments cell growth in vitro and tumorigenicity in vivo. Because increased tumorigenicity in vivo often precedes metastasis, we now examined whether the expression of R-Ras87L also increased the metastatic potential of C33A cells. Accelerated tumor growth was observed in athymic mice after subcutaneous injection of R-Ras87L-expressing C33A cells. In addition, increased metastasis to the liver, in immunodeficient SCID mice, was observed after intravenous injection of R-Ras87L-expressing C33A cells. Also, R-Ras87L-expressing cells presented decreased membrane expression of MHC class I molecules, and beta1 integrins, but increased levels of PI 3-K and Akt activities. C33A cells expressing R-Ras87L also migrated more over collagen I in wound assays. Inhibition of the PI 3-K/Akt/mTOR pathway by pharmacological means blocked R-Ras87L-induced accelerated growth and migration over collagen I. These results suggest oncogenic R-Ras has a central role in cancer progression towards a metastatic phenotype, through the activation of the PI 3-K/Akt/mTOR signaling pathway.

The hematopoietic isoform of Cas-Hef1-associated signal transducer regulates chemokine-induced inside-out signaling and T cell trafficking

Leukocyte migration and trafficking is dynamically regulated by various chemokine and adhesion molecules and is vital to the proper function of the immune system. We describe a role for the Cas and Hef-1-associated signal transducer in hematopoietic cells (Chat-H) as a critical regulator of T lymphocyte migration, by using lentivirus-mediated RNA interference (RNAi). Impaired migration of Chat-H-depleted cells coincided with defective inside-out signaling shown by diminished chemokine-induced activation of the Rap-1 GTPase and integrin-mediated adhesion. Localization of Chat-H to the plasma membrane, association with its binding partner Crk-associated substrate in lymphocytes (CasL), and Chat-H-mediated CasL serine-threonine phosphorylation were required for T cell migration. These results identify Chat-H as a critical signaling intermediate acting upstream of Rap1 to regulate chemokine-induced adhesion and migration.

The R-Ras GTPase mediates cross talk between estrogen and insulin signaling in breast cancer cells

The signaling cascades activated by insulin and IGF-1 contribute to the control of multiple cellular functions, including glucose metabolism and cell proliferation. In most cases these effects are mediated, at least in part, by insulin receptor substrates (IRS), one of which is insulin receptor substrate 1 (IRS-1). R-Ras is a member of the Ras family of GTPases and is involved in a variety of biological processes, including integrin activation, cell migration, and control of cell proliferation. Here we demonstrate that both R-Ras and BCAR3, a regulator of R-Ras activity that has been implicated in breast cancer, regulate the level of IRS-1 protein in estrogen-dependent MCF-7 and ZR75 breast cancer cells. In particular, expression of a constitutively activated R-Ras mutant, R-Ras38V, or of BCAR3 accelerates the degradation of IRS-1, leading to the impairment of signaling through insulin but not epidermal growth factor receptors. Moreover, knockdown of endogenous R-Ras levels in MCF-7 cells inhibits IRS-1 degradation induced by estrogen signaling blockade but not by long-term insulin treatment. Consistent with these results, both R-Ras38V expression and estrogen signaling blockade lead to the degradation of IRS-1, at least in part, through calpain activity. These findings show that R-Ras activity mediates inhibition of insulin signaling associated with suppression of estrogen action, implicating this GTPase in a growth-inhibitory mechanism associated with antiestrogen treatment of breast cancer.