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

Cytoskeleton remodeling induced by SMYD2 methyltransferase drives breast cancer metastasis

Malignant forms of breast cancer refractory to existing therapies remain a major unmet health issue, primarily due to metastatic spread. A better understanding of the mechanisms at play will provide better insights for alternative treatments to prevent breast cancer cell dispersion. Here, we identify the lysine methyltransferase SMYD2 as a clinically actionable master regulator of breast cancer metastasis. While SMYD2 is overexpressed in aggressive breast cancers, we notice that it is not required for primary tumor growth. However, mammary-epithelium specific SMYD2 ablation increases mouse overall survival by blocking the primary tumor cell ability to metastasize. Mechanistically, we identify BCAR3 as a genuine physiological substrate of SMYD2 in breast cancer cells. BCAR3 monomethylated at lysine K334 (K334me1) is recognized by a novel methyl-binding domain present in FMNLs proteins. These actin cytoskeleton regulators are recruited at the cell edges by the SMYD2 methylation signaling and modulate lamellipodia properties. Breast cancer cells with impaired BCAR3 methylation lose migration and invasiveness capacity in vitro and are ineffective in promoting metastases in vivo. Remarkably, SMYD2 pharmacologic inhibition efficiently impairs the metastatic spread of breast cancer cells, PDX and aggressive mammary tumors from genetically engineered mice. This study provides a rationale for innovative therapeutic prevention of malignant breast cancer metastatic progression by targeting the SMYD2-BCAR3-FMNL axis.

Cytoskeleton remodeling induced by SMYD2 methyltransferase drives breast cancer metastasis

Malignant forms of breast cancer refractory to existing therapies remain a major unmet health issue, primarily due to metastatic spread. A better understanding of the mechanisms at play will provide better insights for alternative treatments to prevent breast cancer cells dispersion. Here, we identify the lysine methyltransferase SMYD2 as a clinically actionable master regulator of breast cancer metastasis. While SMYD2 is overexpressed in aggressive breast cancers, we notice that it is not required for primary tumor growth. However, mammary-epithelium specific SMYD2 ablation increases mouse overall survival by blocking the primary tumor cells ability to metastasize. Mechanistically, we identify BCAR3 as a genuine physiological substrate of SMYD2 in breast cancer cells. BCAR3 monomethylated at lysine K334 (K334me1) is recognized by a novel methyl-binding domain present in FMNLs proteins. These actin cytoskeleton regulators are recruited at the cell edges by the SMYD2 methylation signaling and modulates lamellipodia properties. Breast cancer cells with impaired BCAR3 methylation loose migration and invasiveness capacity in vitro and are ineffective in promoting metastases in vivo . Remarkably, SMYD2 pharmacologic inhibition efficiently impairs the metastatic spread of breast cancer cells, PDX and aggressive mammary tumors from genetically engineered mice. This study provides a rationale for innovative therapeutic prevention of malignant breast cancer metastatic progression by targeting the SMYD2-BCAR3-FMNL axis.

L2pB1 Cells Contribute to Tumor Growth Inhibition

Natural IgM (nIgM) antibodies play critical roles in cancer immunosurveillance. However, the role of B-1 B cells, the lymphocytes that produce nIgM, remains to be elucidated. L2pB1 cells, a subpopulation of B-1 B cells, have a unique poly-self-reactive nIgM repertoire and are capable of phagocytosis, potent antigen presentation, and immunomodulation. Using an inducible knock-in and knockout mouse model, we investigated the effect of the loss of L2pB1 cells in a B16F10 melanoma model. Our results show active tumor infiltration of L2pB1 cells in wild type mice, and conversely, depletion of L2pB1 cells results in larger tumor mass and increased angiogenesis. In vitro analysis revealed that L2pB1 cells contribute to the growth inhibition of melanoma cells in both 2D cell culture and 3D tumor spheroids. Similar effects were observed in an MC38 murine colon cancer model. Moreover, our data suggest that one of the ways that L2pB1 cells can induce tumor cell death is via lipoptosis. Lastly, we tested whether L2pB1 cell-derived monoclonal nIgM antibodies can specifically recognize tumor spheroids. Nine of the 28 nIgM-secreting L2pB1 clones demonstrated specific binding to tumor spheroids but did not bind control murine embryonic fibroblasts. Our study provides evidence that L2pB1 cells contribute to cancer immunity through their unique nIgM repertoire, tumor recognition, and lipoptosis. Taken together, because of their ability to recognize common features of tumors that are independent of genetic mutations, L2pB1 cells and their nIgM could be potential candidates for cancer treatment that can overcome tumor heterogeneity-associated drug resistance.

Prediction and prognostic significance of BCAR3 expression in patients with multiple myeloma

Background

Multiple myeloma (MM) is the plasma cell tumor, which is characterized by clonal proliferation of tumor cells, with high risk of progression to renal impairment, bone damage and amyloidosis. Although the survival rate of patients with MM has improved in the past decade, most people inevitably relapse. The treatment and prognosis of MM are still urgent problems. Breast Cancer Antiestrogen Resistance 3 (BCAR3) is a protein-coding gene that is associated with many tumors. However, there have been few studies on the relationship of BCAR3 and MM.

Methods

We analyzed 1878 MM patients (1930 samples) from 7 independent datasets. First, we compared the BCAR3 expression level of MM patients in different stages and MM patients with different amplification of 1q21. Second, we analyzed BCAR3 expression levels in MM patients with different molecular subtypes. Finally, we explored the event-free survival rate (EFS) and overall survival rate (OS) of MM patients with high or low BCAR3 expression, including patients before and after relapse, and their therapeutic responses to bortezomib and dexamethasone.

Results

The expression of BCAR3 showed a decreasing trend in stages I, II and III (P = 0.00068). With the increase of 1q21 amplification level, the expression of BCAR3 decreased (P = 0.022). Patients with high BCAR3 expression had higher EFS and OS (EFS: P < 0.0001, OS: P < 0.0001). The expression of BCAR3 gene before relapse was higher than that after relapse (P = 0.0045). BCAR3 is an independent factor affecting prognosis (EFS: P = 5.17E−03; OS: P = 3.33E−04).

Conclusion

We found that high expression level of BCAR3 predicted better prognosis of MM patients. Low expression of BCAR3 at diagnosis can predict early relapse. BCAR3 is an independent prognostic factor for MM. BCAR3 can be used as a potential biomarker.

Electronic supplementary material

The online version of this article (10.1186/s12967-018-1728-8) contains supplementary material, which is available to authorized users.

Up-regulation of NSP3 by Oligomeric Aβ Accelerates Neuronal Death Through Cas-independent Rap1A Activation

β-Amyloid (Aβ) plays an important role in the early pathogenesis of Alzheimer's disease (AD). In vitro studies have demonstrated that Aβ oligomers induce hippocampal and neocortical neuronal death. However the neurotoxic mechanisms by which soluble Aβ oligomers cause neuronal damage and death remain to be fully elucidated. To this end, we analyzed the gene expression profile of rat cerebral cortical neurons treated with Aβ oligomers in vitro. Aβ treatment induced the expression of novel SH2-containing protein 3 (NSP3), an adaptor molecule interacting with Cas family proteins. NSP3 expression was upregulated not only in oligomeric-Aβ-treated cultured neurons but also in the neocortex of aged Tg2576 mice. NSP3 overexpression in cultured cortical neurons accelerated neuronal death. The C-terminal region of NSP3 unbound to a Cas protein was necessary for the NSP3-induced acceleration of neuronal death, as was Cas-independent Rap1A activation downstream of NSP3. Moreover, NSP3 RNAi knockdown partially rescued Aβ-oligomer-treated neurons. These results indicate that NSP3 upregulation by soluble Aβ oligomers may accelerate neuronal death via Cas-independent Rap1A activation, implicating NSP3 in the pathogenesis of AD.

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.

Breast cancer antiestrogen resistance 3-p130Cas interactions promote adhesion disassembly and invasion in breast cancer cells

Adhesion turnover is critical for cell motility and invasion. We previously demonstrated that the adaptor molecule Breast Cancer Antiestrogen Resistance 3 (BCAR3) promotes adhesion disassembly and breast tumor cell invasion. One of two established binding partners of BCAR3 is the adaptor molecule, p130^Cas. In this study, we sought to determine whether signaling through the BCAR3/Cas complex was responsible for the cellular functions of BCAR3. We show that the entire pool of BCAR3 is in complex with Cas in invasive breast tumor cells and that these proteins co-localize in dynamic cellular adhesions. While accumulation of BCAR3 in adhesions did not require Cas binding, a direct interaction between BCAR3 and Cas was necessary for efficient dissociation of BCAR3 from adhesions. The dissociation rates of Cas and two other adhesion molecules, α-actinin and talin, were also significantly slower in the presence of a Cas-binding mutant of BCAR3, suggesting that turnover of the entire adhesion complex was delayed under these conditions. As was the case for adhesion turnover, BCAR3-Cas interactions were found to be important for BCAR3-mediated breast tumor cell chemotaxis toward serum and invasion in Matrigel. Previous work demonstrated that BCAR3 is a potent activator of Rac1, which in turn is an important regulator of adhesion dynamics and invasion. However, in contrast to wildtype BCAR3, ectopic expression of the Cas-binding mutant of BCAR3 failed to induce Rac1 activity in breast cancer cells. Together, these data show that the ability of BCAR3 to promote adhesion disassembly, tumor cell migration and invasion, and Rac1 activity is dependent on its ability to bind to Cas. The activity of BCAR3-Cas complexes as a functional unit in breast cancer is further supported by the co-expression of these molecules in multiple subtypes of human breast tumors.

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.

iTRAQ analysis of hepatic proteins in free-living Mus spretus mice to assess the contamination status of areas surrounding Doñana National Park (SW Spain)

This work aims to develop and integrate new -omics tools that would be applicable to different ecosystem types for a technological updating of environmental evaluations. We used a 2nd-generation (iTRAQ-8plex) proteomic approach to identify/quantify proteins differentially expressed in the liver of free-living Mus spretus mice from Doñana National Park or its proximities. Mass spectrometry was performed in an LTQ Orbitrap system for iTRAQ reporter ion quantitation and protein identification using a Mus musculus database as reference. A prior IEF step improved the separation of the complex peptide mixture. Over 2000 identified proteins were altered, of which 118 changed by ≥2.5-fold in mice from at least two problem sites. Part of the results obtained with the iTRAQ analysis was confirmed by Western blot. Over 75% of the 118 proteins were upregulated in animals captured at polluted sites and only 16 proteins were downregulated. Upregulated proteins were involved in stress response; cell proliferation and apoptosis; signal transduction; metastasis or tumour suppression; xenobiotic export or vesicular trafficking; and metabolism. The downregulated proteins, all potentially harmful, were classified as oncoproteins and proteins favouring genome instability. The iTRAQ results presented here demonstrated that the survival of hepatic cells is compromised in animals living at polluted sites, which showed deep alterations in metabolism and the signalling pathways. The identified proteins may be useful as biomarkers of environmental pollution and provide insight about the metabolic pathways and/or physiological processes affected by pollutants in DNP and its surrounding areas.

CAS proteins in health and disease: an update

The CAS family of scaffolding proteins has increasingly attracted scrutiny as important for regulation of cancer-associated signaling. BCAR1 (also known as p130Cas), NEDD9 (HEF1, Cas-L), EFS (Sin), and CASS4 (HEPL) are regulated by and mediate cell attachment, growth factor, and chemokine signaling. Altered expression and activity of CAS proteins are now known to promote metastasis and drug resistance in cancer, influence normal development, and contribute to the pathogenesis of heart and pulmonary disease. In this article, we provide an update on recently published studies describing signals regulating and regulated by CAS proteins, and evidence for biological activity of CAS proteins in normal development, cancer, and other pathological conditions.

Investigation of binding phenomenon of NSP3 and p130Cas mutants and their effect on cell signalling

Members of the novel SH2-containing protein (NSP3) and Crk-associated substrate (p130Cas) protein families form a multi-domain signalling platforms that mediate cell signalling process. We analysed the damaging consequences of three mutations, each from NSP3 (NSP3(L469R), NSP3(L623E), NSP3(R627E)) and p130Cas (p130Cas(F794R), p130Cas(L787E), p130Cas(D797R)) protein with respect to their native biological partners. Mutations depicted notable loss in interaction affinity towards their corresponding biological partners. NSP3(L469R) and p130Cas(D797R) mutations were predicted as most prominent in docking analysis. Molecular dynamics (MD) studies were conducted to evaluate structural consequences of most prominent mutation in NSP3 and p130Cas obtained from the docking analysis. MD analysis confirmed that mutation in NSP3(L469R) and p130Cas(D797R) showed significant structural deviation, changes in conformations and increased flexibility, which in turn affected the binding affinity with their biological partners. Moreover, the root mean square fluctuation has indicated a rise in fluctuation of residues involved in moderate interaction acquired between the NSP3 and p130Cas. It has significantly affected the binding interaction in mutant complexes. The results obtained in this work present a detailed overview of molecular mechanisms involved in the loss of cell signalling associated with NSP3 and p130Cas protein.

Association of the breast cancer antiestrogen resistance protein 1 (BCAR1) and BCAR3 scaffolding proteins in cell signaling and antiestrogen resistance

Most breast cancers are estrogen receptor-positive and treated with antiestrogens, but aberrant signaling networks can induce drug resistance. One of these networks involves the scaffolding protein BCAR1/p130CAS, which regulates cell growth and migration/invasion. A less investigated scaffolding protein that also confers antiestrogen resistance is the SH2 domain-containing protein BCAR3. BCAR1 and BCAR3 bind tightly to each other through their C-terminal domains, thus potentially connecting their associated signaling networks. However, recent studies using BCAR1 and BCAR3 interaction mutants concluded that association between the two proteins is not critical for many of their interrelated activities regulating breast cancer malignancy. We report that these previously used BCAR mutations fail to cause adequate loss-of-function of the complex. By using structure-based BCAR1 and BCAR3 mutants that lack the ability to interact, we show that BCAR3-induced antiestrogen resistance in MCF7 breast cancer cells critically depends on its ability to bind BCAR1. Interaction with BCAR3 increases the levels of phosphorylated BCAR1, ultimately potentiating BCAR1-dependent antiestrogen resistance. Furthermore, antiestrogen resistance in cells overexpressing BCAR1/BCAR3 correlates with increased ERK1/2 activity. Inhibiting ERK1/2 through overexpression of the regulatory protein PEA15 negates the resistance, revealing a key role for ERK1/2 in BCAR1/BCAR3-induced antiestrogen resistance. Reverse-phase protein array data show that PEA15 levels in invasive breast cancers correlate with patient survival, suggesting that PEA15 can override ERK1/2 activation by BCAR1/BCAR3 and other upstream regulators. We further uncovered that the BCAR3-related NSP3 can also promote antiestrogen resistance. Thus, strategies to disrupt BCAR1-BCAR3/NSP3 complexes and associated signaling networks could ultimately lead to new breast cancer therapies.

Breast cancer antiestrogen resistance 3 (BCAR3) promotes cell motility by regulating actin cytoskeletal and adhesion remodeling in invasive breast cancer cells

Metastatic breast cancer is incurable. In order to improve patient survival, it is critical to develop a better understanding of the molecular mechanisms that regulate metastasis and the underlying process of cell motility. Here, we focus on the role of the adaptor molecule Breast Cancer Antiestrogen Resistance 3 (BCAR3) in cellular processes that contribute to cell motility, including protrusion, adhesion remodeling, and contractility. Previous work from our group showed that elevated BCAR3 protein levels enhance cell migration, while depletion of BCAR3 reduces the migratory and invasive capacities of breast cancer cells. In the current study, we show that BCAR3 is necessary for membrane protrusiveness, Rac1 activity, and adhesion disassembly in invasive breast cancer cells. We further demonstrate that, in the absence of BCAR3, RhoA-dependent signaling pathways appear to predominate, as evidenced by an increase in RhoA activity, ROCK-mediated phosphorylation of myosin light chain II, and large ROCK/mDia1-dependent focal adhesions. Taken together, these data establish that BCAR3 functions as a positive regulator of cytoskeletal remodeling and adhesion turnover in invasive breast cancer cells through its ability to influence the balance between Rac1 and RhoA signaling. Considering that BCAR3 protein levels are elevated in advanced breast cancer cell lines and enhance breast cancer cell motility, we propose that BCAR3 functions in the transition to advanced disease by triggering intracellular signaling events that are essential to the metastatic process.

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.

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.

Protein pathway activation mapping reveals molecular networks associated with antiestrogen resistance in breast cancer cell lines

Previously, we have identified a panel of breast cancer antiestrogen resistance (BCAR) genes. Several of these genes have clinical relevance because mRNA or protein levels associate with tamoxifen resistance or tumor aggressiveness. We postulated that changes in activation status of protein signaling networks induced by BCAR genes may provide better insight into the mechanisms underlying antiestrogen resistance. Key signal transduction pathways were analyzed for changes in activation or expression using reverse-phase protein microarrays probed with 78 antibodies against signaling proteins with known roles in tumorigenesis. We used ZR-75-1-derived cell lines transduced with AKT1, AKT2, BCAR1, BCAR3, BCAR4, EGFR, GRB7, HRAS, HRAS(v12) or HEF1 and MCF7-derived cell lines transduced with BCAR3, BCAR4 or EGFR. In the antiestrogen-resistant cell lines, we observed increased phosphorylation of several pathways involved in cell proliferation and survival. All tamoxifen-resistant cell lines contained high levels of phosphorylated AKT and its biochemically linked substrates Forkhead box O1/3. The activation of ERBB2, ERBB3 and the downstream modulators focal adhesion kinase and SHC were activated in cells with overexpression of BCAR4. Remarkable differences were observed for the levels of activated AMPK alpha1, cyclins, STAT5, STAT6, ERK1/2 and BCL2. The comparison of the cell signaling networks in estrogen-dependent and -independent cell lines revealed biochemically linked kinase-substrate markers that comprised systemically activated signaling pathways involved in tamoxifen resistance. Our results show that this model provides insights into the molecular and cellular mechanisms of breast cancer progression and antiestrogen resistance. This knowledge may help the development of novel targeted treatments.

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.