p130CAS forms a signaling complex with the adapter protein CRKL in hematopoietic cells transformed by the BCR/ABL oncogene

Interaction Network Provides Clues on the Role of BCAR1 in Cellular Response to Changes in Gravity

When culturing cells in space or under altered gravity conditions on Earth to investigate the impact of gravity, their adhesion and organoid formation capabilities change. In search of a target where the alteration of gravity force could have this impact, we investigated p130cas/BCAR1 and its interactions more thoroughly, particularly as its activity is sensitive to applied forces. This protein is well characterized regarding its role in growth stimulation and adhesion processes. To better understand BCAR1′s force-dependent scaffolding of other proteins, we studied its interactions with proteins we had detected by proteome analyses of MCF-7 breast cancer and FTC-133 thyroid cancer cells, which are both sensitive to exposure to microgravity and express BCAR1. Using linked open data resources and our experiments, we collected comprehensive information to establish a semantic knowledgebase and analyzed identified proteins belonging to signaling pathways and their networks. The results show that the force-dependent phosphorylation and scaffolding of BCAR1 influence the structure, function, and degradation of intracellular proteins as well as the growth, adhesion and apoptosis of cells similarly to exposure of whole cells to altered gravity. As BCAR1 evidently plays a significant role in cell responses to gravity changes, this study reveals a clear path to future research performing phosphorylation experiments on BCAR1.

Bifunctional Role of CrkL during Bone Remodeling

Coupled signaling between bone-forming osteoblasts and bone-resorbing osteoclasts is crucial to the maintenance of bone homeostasis. We previously reported that v-crk avian sarcoma virus CT10 oncogene homolog-like (CrkL), which belongs to the Crk family of adaptors, inhibits bone morphogenetic protein 2 (BMP2)-mediated osteoblast differentiation, while enhancing receptor activator of nuclear factor kappa-B ligand (RANKL)-induced osteoclast differentiation. In this study, we investigated whether CrkL can also regulate the coupling signals between osteoblasts and osteoclasts, facilitating bone homeostasis. Osteoblastic CrkL strongly decreased RANKL expression through its inhibition of runt-related transcription factor 2 (Runx2) transcription. Reduction in RANKL expression by CrkL in osteoblasts resulted in the inhibition of not only osteoblast-dependent osteoclast differentiation but also osteoclast-dependent osteoblast differentiation, suggesting that CrkL participates in the coupling signals between osteoblasts and osteoclasts via its regulation of RANKL expression. Therefore, CrkL bifunctionally regulates osteoclast differentiation through both a direct and indirect mechanism while it inhibits osteoblast differentiation through its blockade of both BMP2 and RANKL reverse signaling pathways. Collectively, these data suggest that CrkL is involved in bone homeostasis, where it helps to regulate the complex interactions of the osteoblasts, osteoclasts, and their coupling signals.

Elucidation of protein interactions necessary for the maintenance of the BCR-ABL signaling complex

Many patients with chronic myeloid leukemia in deep remission experience return of clinical disease after withdrawal of tyrosine kinase inhibitors (TKIs). This suggests signaling of inactive BCR-ABL, which allows the survival of cancer cells, and relapse. We show that TKI treatment inhibits catalytic activity of BCR-ABL, but does not dissolve BCR-ABL core signaling complex, consisting of CRKL, SHC1, GRB2, SOS1, cCBL, p85a-PI3K, STS1 and SHIP2. Peptide microarray and co-immunoprecipitation results demonstrate that CRKL binds to proline-rich regions located in C-terminal, intrinsically disordered region of BCR-ABL, that SHC1 requires pleckstrin homology, src homology and tyrosine kinase domains of BCR-ABL for binding, and that BCR-ABL sequence motif located in disordered region around phosphorylated tyrosine 177 mediates binding of three core complex members, i.e., GRB2, SOS1, and cCBL. Further, SHIP2 binds to the src homology and tyrosine kinase domains of BCR-ABL and its inositol phosphatase activity contributes to BCR-ABL-mediated phosphorylation of SHC1. Together, this study characterizes protein-protein interactions within the BCR-ABL core complex and determines the contribution of particular BCR-ABL domains to downstream signaling. Understanding the structure and dynamics of BCR-ABL interactome is critical for the development of drugs targeting integrity of the BCR-ABL core complex.

Overexpression of CrkL as a novel biomarker for poor prognosis in gastric cancer

BACKGROUND

The signaling adapter protein CrkL plays vital roles in multiple cancers. However, the expression pattern of CrkL protein and its clinical significance have not been well characterized in human gastric cancer (GC) so far.

OBJECTIVE

To investigate the association of tissue-based CrkL protein expression level with the clinicopathological characteristics and prognosis of GC patients.

METHODS

The expression level of CrkL protein in 380 GC patients was analyzed by immunohistochemistry. The associations of CrkL protein expression level with clinicopathologicalal characteristics and clinical outcome were evaluated.

RESULTS

Compared with the matched adjacent non-tumor tissues, CrkL protein expression level was significantly up-regulated in tumor tissues. In addition, there was a positive correlation between CrkL and Ki67 expression levels in GC patients. An elevated CrkL level statistically correlated with aggressive clinicopathologicalal characteristics, such as larger tumor size, deeper local invasion, more lymph node metastasis, advanced TNM stage, and poorer prognosis. Notably, multivariate analysis identified tissue-based CrkL level as an independent predictor for the unfavorable prognosis of GC.

CONCLUSIONS

These results indicate that CrkL protein may serve as a novel prognostic biomarker in GC.

CRKL regulates alternative splicing of cancer-related genes in cervical cancer samples and HeLa cell

BACKGROUND

Aberrant spliced isoforms are specifically associated with cancer progression and metastasis. The cytoplasmic adaptor CRKL (v-crk avian sarcoma virus CT10 oncogene homolog-like) is a CRK like proto-oncogene, which encodes a SH2 and SH3 (src homology) domain-containing adaptor protein. CRKL is tightly linked to leukemia via its binding partners BCR-ABL and TEL-ABL, upregulated in multiple types of human cancers, and induce cancer cell proliferation and invasion. However, it remains unclear whether signaling adaptors such as CRKL could regulate alternative splicing.

METHODS

We analyzed the expression level of CRKL in 305 cervical cancer tissue samples available in TCGA database, and then selected two groups of cancer samples with CRKL differentially expressed to analyzed potential CRKL-regulated alternative splicing events (ASEs). CRKL was knocked down by shRNA to further study CRKL-regulated alternative splicing and the activity of SR protein kinases in HeLa cells using RNA-Seq and Western blot techniques. We validated 43 CRKL-regulated ASEs detected by RNA-seq in HeLa cells, using RT-qPCR analysis of HeLa cell samples and using RNA-seq data of the two group of clinical cervical samples.

RESULTS

The expression of CRKL was mostly up-regulated in stage I cervical cancer samples. Knock-down of CRKL led to a reduced cell proliferation. CRKL-regulated alternative splicing of a large number of genes were enriched in cancer-related functional pathways, among which DNA repair and G2/M mitotic cell cycle, GnRH signaling were shared among the top 10 enriched GO terms and KEGG pathways by results from clinical samples and HeLa cell model. We showed that CRKL-regulated ASEs revealed by computational analysis using ABLas software in HeLa cell were highly validated by RT-qPCR, and also validated by cervical cancer clinical samples.

CONCLUSIONS

This is the first report of CRKL-regulation of the alternative splicing of a number of genes critical in tumorigenesis and cancer progression, which is consistent with CRKL reported role as a signaling adaptor and a kinase. Our results underline that the signaling adaptor CRKL might integrate the external and intrinsic cellular signals and coordinate the dynamic activation of cellular signaling pathways including alternative splicing regulation.

Roles of paxillin phosphorylation in IL-3 withdrawal-induced Ba/F3 cell apoptosis

BACKGROUND

Ba/F3, a mouse pro-B cell line, is dependent on IL-3 for its survival and proliferation. IL-3 withdrawal causes cells to round, stop in G1 phase, then undergo apoptosis. Additionally, IL-3 is known to induce tyrosine phosphorylation of paxillin, a scaffold and signaling protein. We previously determined that overexpression of paxillin prohibited Ba/F3 cell apoptosis induced by IL-3 withdrawal.

OBJECTIVE

Address whether phosphorylation is essential for the anti-apoptotic effect of overexpressed paxillin.

METHODS

Mutations were introduced into paxillin cDNA at five phosphorylation sites-Y31F, Y40F, Y118F, Y181F, S273A, or S273D. After overexpression of paxillin mutants in Ba/F3 cells, the apoptotic proportions of cell populations were measured by an annexin V conjugation assay while cells were undergoing IL-3 withdrawal.

RESULTS

The anti-apoptotic effect of paxillin overexpression was abolished by site-directed mutagenesis replacing Y31, Y40, Y118, and Y181 with phenylalanine, and S273 with aspartic acid. In contrast, the mutation replacing S273 with alanine had no effect on the anti-apoptotic effect.

CONCLUSION

The above results suggest that paxillin-mediated phosphorylation at Y31, Y40, Y118, and Y181 is essential for the anti-apoptotic effect of paxillin overexpression in Ba/F3 cells and contributes to the cell survival signaling pathway triggered by IL-3. Conversely, phosphorylation at S273 is involved in the negative regulation of the anti-apoptotic action of overexpressed paxillin.

Caveolin-1 contributes to realgar nanoparticle therapy in human chronic myelogenous leukemia K562 cells

Chronic myelogenous leukemia (CML) is characterized by the t(9;22) (q34;q11)-associated Bcr-Abl fusion gene, which is an essential element of clinical diagnosis. As a traditional Chinese medicine, realgar has been widely used for the treatment of various diseases for >1,500 years. Inspired by nano-drug, realgar nanoparticles (NPs) have been prepared with an average particle size of <100 nm in a previous work. Compared with coarse realgar, the realgar NPs have higher bioavailability. As a principal constituent protein of caveolae, caveolin-1 (Cav-1) participates in regulating various cellular physiological and pathological processes including tumorigenesis and tumor development. In previous studies, it was found that realgar NPs can inhibit several types of tumor cell proliferation. However, the therapeutic effect of realgar NPs on CML has not been fully elucidated. In the present paper, it was demonstrated that realgar NPs can inhibit the proliferation of K562 cells and degrade Bcr-Abl fusion protein effectively. Both apoptosis and autophagy were activated in a dose-dependent manner in realgar NPs treated cells, and the induction of autophagy was associated with class I phosphoinositide 3-kinase/protein kinase B/mammalian target of rapamycin pathway. Morphological analysis indicated that realgar NPs induced differentiation effectively in CML cells. Furthermore, it was identified that Cav-1 might play a crucial role in realgar NP therapy. In order to study the effects of Cav-1 on K562 cells during realgar NP treatment, a Cav-1 overexpression cell model was established by using transient transfection. The results indicated that Cav-1 overexpression inhibited K562 cell proliferation, promoted endogenic autophagy, and increased the sensitivity of K562 cells to realgar NPs. Therefore, the results demonstrated that realgar NPs degraded Bcr-Abl oncoprotein, while the underlying mechanism might be related to apoptosis and autophagy, and Cav-1 might be considered as a potential target for clinical comprehensive therapy of CML.

Contribution of Crk adaptor proteins to host cell and bacteria interactions

The Crk adaptor family of proteins comprises the alternatively spliced CrkI and CrkII isoforms, as well as the paralog Crk-like (CrkL) protein, which is encoded by a different gene. Initially thought to be involved in signaling during apoptosis and cell adhesion, this ubiquitously expressed family of proteins is now known to play essential roles in integrating signals from a wide range of stimuli. In this review, we describe the structure and function of the different Crk proteins. We then focus on the emerging roles of Crk adaptors during Enterobacteriaceae pathogenesis, with special emphasis on the important human pathogens Salmonella, Shigella, Yersinia, and enteropathogenic Escherichia coli. Throughout, we remark on opportunities for future research into this intriguing family of proteins.

Inhibition of 32Dp210 cells harboring T315I mutation by a novel derivative of emodin correlates with down-regulation of BCR-ABL and its downstream signaling pathways

PURPOSE

The clinical outcome of chronic myeloid leukemia (CML) patients has been changed dramatically due to the development of imatinib (IM). However, the emergence of IM resistance, commonly associated with point mutations within the BCR-ABL kinase domain, remains a major clinical problem. Here, we investigated the effects of E35, a novel derivative of emodin, on the IM-resistant 32Dp210-T315I cells.

METHODS

Cell proliferation was measured by 3-(4,5-dimethylthiazol-2-yl)-2,5 diphenyltetrazolium bromide and colony formation assay. Induction of apoptosis was confirmed by DNA fragmentation assay and annexin V/PI staining assay. Real-time quantitative PCR was used to access the BCR-ABL gene expression. Changes of related signaling molecules were detected through Western blot.

RESULTS

E35 was found to potently inhibit proliferation of 32Dp210-T315I cells with an average IC50 of 2.4 µM at 48 h. Colony formation was almost fully suppressed in 1.0 μM E35 group. DNA fragmentation and annexin V/PI staining assay exhibited the typical DNA fragmentation and the increased proportion of early apoptotic cells, respectively. The induction of apoptosis was associated with increase of Bax to Bcl-2 expression ratio and activation of caspase cascades involving decrease of pro-caspase 9 and pro-caspase 3 and increase of PARP cleavage. The protein expression of P210(BCR-ABL) and p-P210(BCR-ABL) was down-regulated in the presence of E35, although the mRNA levels remained almost unchanged. Moreover, the activation of the P210(BCR-ABL) downstream signaling pathways including CrkL, Akt/mTOR and MEK/ERK was fully suppressed by E35.

CONCLUSION

Our study indicated that E35 might be a potential antileukemia agent against IM resistance in CML.

Real-time analysis of imatinib- and dasatinib-induced effects on chronic myelogenous leukemia cell interaction with fibronectin

Attachment of stem leukemic cells to the bone marrow extracellular matrix increases their resistance to chemotherapy and contributes to the disease persistence. In chronic myelogenous leukemia (CML), the activity of the fusion BCR-ABL kinase affects adhesion signaling. Using real-time monitoring of microimpedance, we studied in detail the kinetics of interaction of human CML cells (JURL-MK1, MOLM-7) and of control BCR-ABL-negative leukemia cells (HEL, JURKAT) with fibronectin-coated surface. The effect of two clinically used kinase inhibitors, imatinib (a relatively specific c-ABL inhibitor) and dasatinib (dual ABL/SRC family kinase inhibitor), on cell binding to fibronectin is described. Both imatinib and low-dose (several nM) dasatinib reinforced CML cell interaction with fibronectin while no significant change was induced in BCR-ABL-negative cells. On the other hand, clinically relevant doses of dasatinib (100 nM) had almost no effect in CML cells. The efficiency of the inhibitors in blocking the activity of BCR-ABL and SRC-family kinases was assessed from the extent of phosphorylation at autophosphorylation sites. In both CML cell lines, SRC kinases were found to be transactivated by BCR-ABL. In the intracellular context, EC50 for BCR-ABL inhibition was in subnanomolar range for dasatinib and in submicromolar one for imatinib. EC50 for direct inhibition of LYN kinase was found to be about 20 nM for dasatinib and more than 10 µM for imatinib. Cells pretreated with 100 nM dasatinib were still able to bind to fibronectin and SRC kinases are thus not necessary for the formation of cell-matrix contacts. However, a minimal activity of SRC kinases might be required to mediate the increase in cell adhesivity induced by BCR-ABL inhibition. Indeed, active (autophosphorylated) LYN was found to localize in cell adhesive structures which were visualized using interference reflection microscopy.

The Hepatocyte Growth Factor (HGF)/Met Axis: A Neglected Target in the Treatment of Chronic Myeloproliferative Neoplasms?

Met is the receptor of hepatocyte growth factor (HGF), a cytoprotective cytokine. Disturbing the equilibrium between Met and its ligand may lead to inappropriate cell survival, accumulation of genetic abnormalities and eventually, malignancy. Abnormal activation of the HGF/Met axis is established in solid tumours and in chronic haematological malignancies, including myeloma, acute myeloid leukaemia, chronic myelogenous leukaemia (CML), and myeloproliferative neoplasms (MPNs). The molecular mechanisms potentially responsible for the abnormal activation of HGF/Met pathways are described and discussed. Importantly, inCML and in MPNs, the production of HGF is independent of Bcr-Abl and JAK2V617F, the main molecular markers of these diseases. In vitro studies showed that blocking HGF/Met function with neutralizing antibodies or Met inhibitors significantly impairs the growth of JAK2V617F-mutated cells. With personalised medicine and curative treatment in view, blocking activation of HGF/Met could be a useful addition in the treatment of CML and MPNs for those patients with high HGF/MET expression not controlled by current treatments (Bcr-Abl inhibitors in CML; phlebotomy, hydroxurea, JAK inhibitors in MPNs).

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.

The role of focal adhesion kinase in the regulation of cellular mechanical properties

The regulation of mechanical properties is necessary for cell invasion into connective tissue or intra- and extravasation through the endothelium of blood or lymph vessels. Cell invasion is important for the regulation of many healthy processes such as immune response reactions and wound healing. In addition, cell invasion plays a role in disease-related processes such as tumor metastasis and autoimmune responses. Until now the role of focal adhesion kinase (FAK) in regulating mechanical properties of cells and its impact on cell invasion efficiency is still not well known. Thus, this review focuses on mechanical properties regulated by FAK in comparison to the mechano-regulating protein vinculin. Moreover, it points out the connection between cancer cell invasion and metastasis and FAK by showing that FAK regulates cellular mechanical properties required for cellular motility. Furthermore, it sheds light on the indirect interaction of FAK with vinculin by binding to paxillin, which then impairs the binding of paxillin to vinculin. In addition, this review emphasizes whether FAK fulfills regulatory functions similar to vinculin. In particular, it discusses the differences and the similarities between FAK and vinculin in regulating the biomechanical properties of cells. Finally, this paper highlights that both focal adhesion proteins, vinculin and FAK, synergize their functions to regulate the mechanical properties of cells such as stiffness and contractile forces. Subsequently, these mechanical properties determine cellular invasiveness into tissues and provide a source sink for future drug developments to inhibit excessive cell invasion and hence, metastases formation.

Acquisition of the metastatic phenotype is accompanied by H2O2-dependent activation of the p130Cas signaling complex

Reactive oxygen species (ROS) have emerged as cellular signaling molecules and are implicated in metastatic disease by their ability to drive invasion and migration. Here, we define the signaling adaptor protein p130Cas (Crk-associated substrate) as a key redox-responsive molecular trigger that is engaged in highly invasive metastatic bladder tumor cell lines. Endogenous shifts in steady-state hydrogen peroxide (H2O2) that accompany the metastatic phenotype increase p130Cas phosphorylation, membrane recruitment and association with the scaffolding protein Crk, and subsequent Rac1 activation and actin reorganization. Both enzymatic and nonenzymatic scavenging of H2O2 abrogates p130Cas-dependent signaling and the migratory and invasive activity of the metastatic bladder tumor cells. Disruption of p130Cas attenuates both invasion and migration of the metastatic variant (253J-BV). 253J-BV cells displayed an increase in global thiol oxidation and a concomitant decrease in total phosphatase activity, common target proteins of active-site cysteine oxidation. The dependence of phosphatases on regulation of p130Cas was highlighted when depletion of PTPN12 enhanced p130cas phosphorylation and the migratory behavior of a noninvasive parental bladder tumor control (253J). These data show that the metastatic phenotype is accompanied by increases in steady-state H2O2 production that drive promigratory signaling and suggest that antioxidant-based therapeutics may prove useful in limiting bladder tumor invasiveness.

C3G forms complexes with Bcr-Abl and p38α MAPK at the focal adhesions in chronic myeloid leukemia cells: implication in the regulation of leukemic cell adhesion

Background

Previous studies by our group and others have shown that C3G interacts with Bcr-Abl through its SH3-b domain.

Results

In this work we show that C3G and Bcr-Abl form complexes with the focal adhesion (FA) proteins CrkL, p130Cas, Cbl and Abi1 through SH3/SH3-b interactions. The association between C3G and Bcr-Abl decreased upon Abi1 or p130Cas knock-down in K562 cells, which suggests that Abi1 and p130Cas are essential partners in this interaction. On the other hand, C3G, Abi1 or Cbl knock-down impaired adhesion to fibronectin, while p130Cas silencing enhanced it. C3G, Cbl and p130Cas-SH3-b domains interact directly with common proteins involved in the regulation of cell adhesion and migration. Immunoprecipitation and immunofluorescence studies revealed that C3G form complexes with the FA proteins paxillin and FAK and their phosphorylated forms. Additionally, C3G, Abi1, Cbl and p130Cas regulate the expression and phosphorylation of paxillin and FAK. p38α MAPK also participates in the regulation of adhesion in chronic myeloid leukemia cells. It interacts with C3G, CrkL, FAK and paxillin and regulates the expression of paxillin, CrkL and α5 integrin, as well as paxillin phosphorylation. Moreover, double knock-down of C3G/p38α decreased adhesion to fibronectin, similarly to the single silencing of one of these genes, either C3G or p38α. These suggest that C3G and p38α MAPK are acting through a common pathway to regulate cell adhesion in K562 cells, as previously described for the regulation of apoptosis.

Conclusions

Our results indicate that C3G-p38αMAPK pathway regulates K562 cell adhesion through the interaction with FA proteins and Bcr-Abl, modulating the formation of different protein complexes at FA.

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.

Src, p130Cas, and Mechanotransduction in Cancer Cells

Anchorage-independent growth is the most significant hallmark of cell transformation, which has an intimate relevance to cancer. Anchorage or adhesion physically links cells to the extracellular matrix and allows the transmission of external mechanical cues to intracellular signaling machineries. Transformation involves acquiring the ability to proliferate without requiring mechanically initiated signal transduction, known as mechanotransduction. A number of signaling and cytoskeletal molecules are located at focal adhesions. Src and its related proteins, including p130Cas, localize to adhesion sites, where their functions can be mechanically regulated. In addition, the aberrant activation and expression of Src and p130Cas are linked to transformation and malignancy both in vitro and in vivo. These findings shed light on the importance of mechanotransduction in tumorigenesis and the regulation of cancer progression and also provide insights into the mechanical aspects of cancer signaling.

The metastasis gene NEDD9 product acts through integrin β3 and Src to promote mesenchymal motility and inhibit amoeboid motility

Neural precursor expressed, developmentally down-regulated 9 (NEDD9), a member of the Cas family of signal transduction molecules, is amplified at the genetic level in melanoma, and elevated expression levels have been shown to correlate with melanoma progression and metastasis. NEDD9 interacts with the guanine nucleotide exchange factor DOCK3 to promote Rac activation and the elongated, mesenchymal-type of tumour cell invasion, but the molecular mechanisms through which NEDD9 promotes melanoma metastasis are not fully understood. We show that signalling through increased NEDD9 levels requires integrin β3 signalling, which leads to elevated phosphorylation of integrin β3. This results in increased Src and FAK but decreased ROCK signalling to drive elongated, mesenchymal-type invasion in environments that contain vitronectin. NEDD9 overexpression does not affect ROCK signalling through activation of RhoA but decreases ROCKII signalling through Src-dependent phosphorylation of a negative regulatory site Tyr722. In NEDD9-overexpressing melanoma cells, inhibition of Src with dasatinib results in a switch from Rac-driven elongated, mesenchymal-type invasion to ROCK-dependent rounded, amoeboid invasion. These findings brings into question whether dasatinib would work as a therapeutic agent to block melanoma invasion and metastasis. On the basis of the in vitro data presented here, a combination treatment of dasatinib and a ROCK inhibitor might be a better alternative in order to inhibit both elongated, mesenchymal-type and rounded, amoeboid motility.

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).

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.

The WAVE2 complex regulates T cell receptor signaling to integrins via Abl- and CrkL-C3G-mediated activation of Rap1

WAVE2 regulates T cell receptor (TCR)–stimulated actin cytoskeletal dynamics leading to both integrin clustering and affinity maturation. Although WAVE2 mediates integrin affinity maturation by recruiting vinculin and talin to the immunological synapse in an Arp2/3-dependent manner, the mechanism by which it regulates integrin clustering is unclear. We show that the Abl tyrosine kinase associates with the WAVE2 complex and TCR ligation induces WAVE2-dependent membrane recruitment of Abl. Furthermore, we show that WAVE2 regulates TCR-mediated activation of the integrin regulatory guanosine triphosphatase Rap1 via the recruitment and activation of the CrkL–C3G exchange complex. Moreover, we demonstrate that although Abl does not regulate the recruitment of CrkL–C3G into the membrane, it does affect the tyrosine phosphorylation of C3G, which is required for its guanine nucleotide exchange factor activity toward Rap1. This signaling node regulates not only TCR-stimulated integrin clustering but also affinity maturation. These findings identify a previously unknown mechanism by which the WAVE2 complex regulates TCR signaling to Rap1 and integrin activation.

Tyrosine phosphorylation of the nuclear receptor coactivator AIB1/SRC-3 is enhanced by Abl kinase and is required for its activity in cancer cells

Overexpression and activation of the steroid receptor coactivator amplified in breast cancer 1 (AIB1)/steroid receptor coactivator-3 (SRC-3) have been shown to have a critical role in oncogenesis and are required for both steroid and growth factor signaling in epithelial tumors. Here, we report a new mechanism for activation of SRC coactivators. We demonstrate regulated tyrosine phosphorylation of AIB1/SRC-3 at a C-terminal tyrosine residue (Y1357) that is phosphorylated after insulin-like growth factor 1, epidermal growth factor, or estrogen treatment of breast cancer cells. Phosphorylated Y1357 is increased in HER2/neu (v-erb-b2 erythroblastic leukemia viral oncogene homolog 2) mammary tumor epithelia and is required to modulate AIB1/SRC-3 coactivation of estrogen receptor alpha (ERalpha), progesterone receptor B, NF-kappaB, and AP-1-dependent promoters. c-Abl (v-Abl Abelson murine leukemia viral oncogene homolog 1) tyrosine kinase directly phosphorylates AIB1/SRC-3 at Y1357 and modulates the association of AIB1 with c-Abl, ERalpha, the transcriptional cofactor p300, and the methyltransferase coactivator-associated arginine methyltransferase 1, CARM1. AIB1/SRC-3-dependent transcription and phenotypic changes, such as cell growth and focus formation, can be reversed by an Abl kinase inhibitor, imatinib. Thus, the phosphorylation state of Y1357 can function as a molecular on/off switch and facilitates the cross talk between hormone, growth factor, and intracellular kinase signaling pathways in cancer.

MUC1 initiates Src-CrkL-Rac1/Cdc42-mediated actin cytoskeletal protrusive motility after ligating intercellular adhesion molecule-1

MUC1, a transmembrane glycoprotein of the mucin family, when aberrantly expressed on breast cancer cells is correlated with increased lymph node metastases. We have previously shown that MUC1 binds intercellular adhesion molecule-1 (ICAM-1) on surrounding accessory cells and facilitates transendothelial migration of MUC1-bearing cells. Nevertheless, the underlying molecular mechanism is still obscure. In the present study, we used a novel assay of actin cytoskeletal reorganization to show that by ligating ICAM-1, MUC1 triggers Rac1- and Cdc42-dependent actin cytoskeletal protrusive activity preferentially at the heterotypic cell-cell contact sites. Further, we show that these MUC1/ICAM-1 interaction-initiated lamellipodial and filopodial protrusions require Src family kinase and CT10 regulator of kinase like (CrkL) accompanied by the rapid formation of a Src-CrkL signaling complex at the MUC1 cytoplasmic domain. Through inhibition of Src kinase activity, we further revealed that Src is required for recruiting CrkL to the MUC1 cytoplasmic domain as well as mediating the observed actin cytoskeleton dynamics. These findings suggest a novel MUC1-Src-CrkL-Rac1/Cdc42 signaling cascade following ICAM-1 ligation, through which MUC1 regulates cytoskeletal reorganization and directed cell motility during cell migration.

Focal adhesion targeting of v-Crk is essential for FAK phosphorylation and cell migration in mouse embryo fibroblasts deficient src family kinases or p130CAS

We examined the consequences of v-Crk expression in mouse embryo fibroblasts deficient Src family kinases or p130CAS. We found that Src kinases are essential for p130CAS/v-Crk signaling leading to FAK phosphorylation and cell migration in which Src is likely to mediate the focal adhesion targeting of v-Crk. SYF cells showed only low levels of FAK phosphorylation and cell migration, even in the presence of v-Crk. Expression of v-Crk restored migration of p130CAS-deficient cells to the level of wild-type cells, most likely through the targeting of v-Crk to focal adhesions by cSrc. In addition, we identified a new v-Crk-interacting protein that mediates v-Crk signaling in p130CAS-deficient cells. Using RT-PCR and caspase cleavage assays, we confirmed that this protein is not p130CAS and is responsible for maintaining v-Crk/Src signaling and migration in these. These findings suggest that focal adhesion targeting of v-Crk is essential in v-Crk-mediated cellular signaling and that v-Crk must form a complex with p130CAS or a p130CAS substitute to transduce signaling from the extracellular matrix.

Role of p21(WAF1/CIP1) as an attenuator of both proliferative and drug-induced apoptotic signals in BCR-ABL-transformed hematopoietic cells

The constitutive tyrosine kinase activity of the BCR-ABL fusion protein plays a crucial role in the pathogenesis of chronic myeloid leukemia and promotes growth factor-independent survival of hematopoietic cells. In 32D cells, expression levels of retrovirally transduced BCR-ABL were positively correlated with the levels of the cell cycle regulator protein p21, and this upregulation of p21 expression depended on the kinase activity of BCR-ABL. To assess the role of p21 on BCR-ABL-positive hematopoietic cells, we compared proliferation and drug-induced apoptosis in bone marrow (BM) cells from wild-type and p21 knockout mice after retroviral transfer of the BCR-ABL fusion gene. As compared with wild-type cells, p21 knockout cells showed increased proliferation, suggesting that p21 acted as an attenuator of BCR-ABL-mediated cell proliferation. In marked contrast, deletion of p21 promoted apoptosis induction by imatinib and taxol in BCR-ABL-transformed BM cells. These findings demonstrate that p21 has a dual function in BCR-ABL-transformed murine BM cells: It attenuates the effects of two apparently opposed phenomena such as BCR-ABL-mediated cell proliferation and drug-induced apoptosis. This dual function of p21 calls for a cautious evaluation of the suitability of p21 as a secondary target in anticancer therapy.

Proline-rich tyrosine kinase2 is involved in F-actin organization during in vitro maturation of rat oocyte

Microfilaments (actin filaments) regulate various dynamic events during meiotic maturation. Relatively, little is known about the regulation of microfilament organization in mammalian oocytes. Proline-rich tyrosine kinase2 (Pyk2), a protein tyrosine kinase related to focal adhesion kinase (FAK) is essential in actin filaments organization. The present study was to examine the expression and localization of Pyk2, and in particular, its function during rat oocyte maturation. For the first time, by using Western blot and confocal laser scanning microscopy, we detected the expression of Pyk2 in rat oocytes and found that Pyk2 and Try402 phospho-Pyk2 were localized uniformly at the cell cortex and surrounded the germinal vesicle (GV) or the condensed chromosomes at the GV stage or after GV breakdown. At the metaphase and the beginning of anaphase, Pyk2 distributed asymmetrically both in the ooplasm and the cortex with a marked staining associated with the chromosomes and the region overlying the meiotic spindle. At telophase, Pyk2 was observed in the cleavage furrows in addition to its cortex and cytoplasm localization. The dynamics of Pyk2 were similar to that of F-actin, and this kinase was found to co-localize with microfilaments in several developmental stages during rat oocyte maturation. Microinjection of Pyk2 antibody demolished the microfilaments assembly and also inhibited the first polar body (PB1) emission. These findings suggest an important role of Pyk2 for rat oocyte maturation by regulating the organization of actin filaments.

PRL-1 Tyrosine Phosphatase Regulates c-Src Levels, Adherence, and Invasion in Human Lung Cancer Cells

Phosphatases of regenerating liver (PRL) constitute a subfamily of the protein tyrosine phosphatases that are implicated in oncogenic and metastatic phenotypes. In this study, we evaluated the role of PRL-1 in cell proliferation and metastatic processes in human lung cancer cells. We stably transfected human A549 lung cancer cells with several short hairpin RNAs for PRL-1 and found decreased invasive activity in the resulting clones compared with control cells. In addition, cells with suppressed PRL-1 exhibited greater adherence and cell spreading on fibronectin and a decreased proliferation rate compared with control cells. To address possible mechanisms for the altered phenotypes, we examined known biochemical regulators of adhesion and invasion. Inhibition of PRL-1 decreased c-Src and p130Cas expression and Rac1 and Cdc42 activation without any apparent modification of focal adhesion kinase (FAK) expression. Total tyrosine FAK phosphorylation and Tyr397 phosphorylation levels were continuously elevated in PRL-1 knockdown cells plated on fibronectin. In immunofluorescence studies, reduction in PRL-1 seemed to decrease cell membrane protrusions with a reduction in actin fiber extensions in spite of continuous phosphorylation of Tyr397 FAK, which could reflect reduced adhesion turnover. Our data implicate PRL-1 in the fundamental process of cell adhesion and migration in human lung cancer cells by affecting Rac1, Cdc42, and c-Src activation. These results support the hypothesis that PRL-1 plays an important role in maintaining the malignant phenotype by exploiting Src activation processes, and that PRL-1 could be a promising therapeutic target for cancer metastasis and cell growth.

Assaying Bcr-Abl kinase activity and inhibition in whole cell extracts by phosphorylation of substrates immobilized on agarose beads

There is a current and increasing demand for simple, robust, nonradioactive assays of protein tyrosine kinase activity with applications for clinical diagnosis and high-throughput screening of potential molecularly targeted therapeutic agents. One significant challenge is to detect and measure the activity of specific kinases with key roles in cell signaling as an approach to distinguish normal cells from cancer cells and as a means of evaluating targeted drug efficacy and resistance in cancer cells. Here, we describe a method in which kinase substrates fused to glutathione-S-transferase and immobilized on glutathione agarose beads are phosphorylated, eluted, and then assayed to detect kinase activity. The activity of recombinant, purified c-Abl kinase or Bcr-Abl kinase in whole cell extracts can be detected with equivalent specificity, sensitivity, and reproducibility. Similarly, inhibition of recombinant c-Abl or Bcr-Abl in cells or cell extracts by imatinib mesylate and other Bcr-Abl targeted kinase inhibitors is readily assayed. This simple kinase assay is sufficiently straightforward and robust for use in clinical laboratories and is potentially adaptable to high-throughput assay formats.

Interaction of Bcr/Abl with C3G, an exchange factor for the small GTPase Rap1, through the adapter protein Crkl

The Bcr/Abl oncoprotein is directly responsible for the development of chronic myelogenous leukemia and Philadelphia chromosome-positive acute lymphoblastic leukemia in humans. The adapter protein Crkl is one of the most prominently tyrosine-phosphorylated substrates of Bcr/Abl in cells and tissues isolated from such patients. The guanine nucleotide exchange factor for the small GTPase Rap1, C3G, binds constitutively to Crkl. Here, we report that Crkl mediates the formation of protein complexes that include C3G and Bcr/Abl. These complexes contain highly elevated levels of tyrosine-phosphorylated C3G and P130Cas, a scaffolding protein. Moreover, the presence of Rap1 further promoted tyrosine phosphorylation of C3G and Cas. Co-expression of Crkl and C3G with Bcr/Abl generated increased levels of activated Rap1. In addition, lysates from leukemic cells of P190 BCR/ABL transgenic mice and of the myelogenous leukemia cell line K562 contained tyrosine-phosphorylated C3G and activated Rap1. These data suggest a role for C3G-mediated Rap1 activation in Bcr/Abl-induced leukemia development.

Gene selection from microarray data for cancer classification--a machine learning approach

A DNA microarray can track the expression levels of thousands of genes simultaneously. Previous research has demonstrated that this technology can be useful in the classification of cancers. Cancer microarray data normally contains a small number of samples which have a large number of gene expression levels as features. To select relevant genes involved in different types of cancer remains a challenge. In order to extract useful gene information from cancer microarray data and reduce dimensionality, feature selection algorithms were systematically investigated in this study. Using a correlation-based feature selector combined with machine learning algorithms such as decision trees, naïve Bayes and support vector machines, we show that classification performance at least as good as published results can be obtained on acute leukemia and diffuse large B-cell lymphoma microarray data sets. We also demonstrate that a combined use of different classification and feature selection approaches makes it possible to select relevant genes with high confidence. This is also the first paper which discusses both computational and biological evidence for the involvement of zyxin in leukaemogenesis.

p130Cas mediates the transforming properties of the anaplastic lymphoma kinase

Translocations of the anaplastic lymphoma kinase (ALK) gene have been described in anaplastic large-cell lymphomas (ALCLs) and in stromal tumors. The most frequent translocation, t(2;5), generates the fusion protein nucleophosmin (NPM)-ALK with intrinsic tyrosine kinase activity. Along with transformation, NPM-ALK induces morphologic changes in fibroblasts and lymphoid cells, suggesting a direct role of ALK in cell shaping. In this study, we used a mass-spectrometry-based proteomic approach to search for proteins involved in cytoskeleton remodeling and identified p130Cas (p130 Crk-associated substrate) as a novel interactor of NPM-ALK. In 293 cells and in fibroblasts as well as in human ALK-positive lymphoma cell lines, NPM-ALK was able to bind p130Cas and to induce its phosphorylation. Both of the effects were dependent on ALK kinase activity and on the adaptor protein growth factor receptor-bound protein 2 (Grb2), since no binding or phosphorylation was found with the kinase-dead mutant NPM-ALK(K210R) or in the presence of a Grb2 dominant-negative protein. Phosphorylation of p130Cas by NPM-ALK was partially independent from Src (tyrosine kinase pp60c-src) kinase activity, as it was still detectable in Syf-/- cells. Finally, p130Cas-/- (also known as Bcar1-/-) fibroblasts expressing NPM-ALK showed impaired actin filament depolymerization and were no longer transformed compared with wild-type cells, indicating an essential role of p130Cas activation in ALK-mediated transformation.

The 1.1 A resolution crystal structure of the p130cas SH3 domain and ramifications for ligand selectivity

The Crk-associated tyrosine kinase substrate p130cas (CAS) is a docking protein containing an SH3 domain near its N terminus, followed by a short proline-rich segment, a large central substrate domain composed of 15 repeats of the four amino acid sequence YxxP, a serine-rich region and a carboxy-terminal domain, which possesses consensus binding sites for the SH2 and SH3 domains of Src (YDYV and RPLPSPP, respectively). The SH3 domain of CAS mediates its interaction with several proteins involved in signaling pathways such as focal adhesion kinase (FAK), tyrosine phosphatases PTP1B and PTP-PEST, and the guanine nucleotide exchange factor C3G. As a homolog of the corresponding Src docking domain, the CAS SH3 domain binds to proline-rich sequences (PxxP) of its interacting partners that can adopt a polyproline type II helix. We have determined a high-resolution X-ray structure of the recombinant human CAS SH3 domain. The domain, residues 1-69, crystallized in two related space groups, P2(1) and C222(1), that provided diffraction data to 1.1 A and 2.1 A, respectively. The crystal structure shows, in addition to the conserved SH3 domain architecture, the way in which the CAS characteristic amino acids form an atypically charged ligand-binding surface. This arrangement provides a rationale for the unusual ligand recognition motif exhibited by the CAS SH3 domain. The structure enables modelling of the docking interactions to its ligands, for example from focal adhesion kinase, and supports structure-based drug design of inhibitors of the CAS-FAK interaction.

p130cas but not paxillin is essential for Caco-2 intestinal epithelial cell spreading and migration on collagen IV

We have previously observed that collagen IV regulates Caco-2 intestinal epithelial cell spreading and migration via Src kinase and stimulates Src-dependent tyrosine phosphorylation of p130cas. We observed that collagen IV also stimulated Src-dependent phosphorylation of both paxillin Tyr31 and paxillin Tyr118. Caco-2 transfection with paxillin or p130cas siRNAs inhibited expression of these proteins by more than 90% for at least 5 days after transfection. Although p130cas siRNA inhibited cell spreading on collagen IV by 33%, three different paxillin siRNAs did not inhibit cell spreading. p130cas siRNA did not affect Src Tyr416 or Src Tyr527 phosphorylation, FAK Tyr397 phosphorylation, or Src-dependent phosphorylation of FAK Tyr925, suggesting that p130cas did not inhibit cell spreading by altering FAK or Src activity. Rat p130cas expression after siRNA knock-out of endogenous human p130cas in Caco-2 cells reduced cell spreading inhibition by 71%. In contrast, expression of rat p130cas from which the Src-phosphorylated substrate domain was deleted did not rescue siRNA inhibition of cell spreading. Combined treatment with siRNAs to Crk and CrkL, which bind to the p130cas substrate domain, inhibited cell spreading by 54%. Both p130cas siRNA and the combined Crk/CrkL siRNAs strongly inhibited (52 and 46% inhibition, respectively) Caco-2 sheet migration on collagen IV and noticeably inhibited lamellipodial extension, whereas paxillin siRNA only inhibited migration by 18% and did not noticeably affect lamellipodial extension. These results suggest that Src may regulate Caco-2 migration on collagen IV via both p130cas and paxillin but that Src phosphorylation of p130cas is more important for this process.

The cancer chemopreventive agent resveratrol induces tensin, a cell–matrix adhesion protein with signaling and antitumor activities

During a search to identify resveratrol (3,5,4'-trihydroxy-trans-stilbene, RV) target genes in the human erythroleukemic K562 cell line, we show here that the tensin gene and protein levels are remarkably induced by this dietary polyphenol. Tensin, a cell-matrix adhesion protein binding the integrins and cytoskeletal actin filaments also interacts with PI3-kinase and JNK signaling pathways. Tensin induction by RV is associated with increased K562 cell adhesion to fibronectin, cell spreading and actin polymerization. The same responses were observed in the tensin-deficient MCF7 human breast cancer cell line. In K562 and MCF7 cells treated by RV, tensin was found in punctate and intracytoplasmic areas. In MCF7 epithelial cells, induction of tensin is not exclusively associated with plasma membrane-bound vinculin, suggesting a dual localization of tensin in both focal and fibrillar adhesions. Pharmacological blockade of PI3-kinase and Rho GTPases/Rho-kinase resulted in selective depletion of focal adhesions, disorganization of tensin localization and disruption of stress fibers. RV increased cell motility and attachment to fibronectin in MCF7 cells submitted to mechanical laminar flow stress, and abrogated estrogen-induced MCF7 cancer cell invasion. Our data support the conclusion that induction of tensin by RV contributes to the chemopreventive and anti-invasive activity of this natural dietary compound in tensin-negative and -deficient leukemic cells or epithelioid cancers.

The prognostic value of BCAR1 in patients with primary breast cancer

PURPOSE

BCAR1, the human homologue of the rat p130Cas protein, was identified in a functional screen for human breast cancer cell proliferation resistant to antiestrogen drugs. Here, we study the prognostic value of quantitative BCAR1 levels in a large series of breast cancer specimens.

EXPERIMENTAL DESIGN

A specific ELISA was developed to measure BCAR1 protein levels in 2593 primary breast tumor cytosols. Tumor levels of BCAR1 were correlated with relapse-free survival (RFS) and overall survival (OS) and compared with collected data on urokinase-type plasminogen activator (uPA) and plasminogen activator inhibitor 1 (PAI-1).

RESULTS

In tumor cytosols, BCAR1 protein levels varied between 0.02 and 23 ng/mg protein. BCAR1 levels exhibited a positive correlation with steroid hormone receptor levels, age and menopausal status, and uPA and PAI-1 levels. The level of BCAR1 (continuous or categorized as low, intermediate, or high) was inversely related with RFS and OS time. Multivariate analysis showed that BCAR1 levels contributed independently to a base model containing the traditional prognostic factors for both RFS and OS (both P < 0.0001). When added together with uPA and PAI-1 in the multivariate model, BCAR1 contributed independently of PAI-1 and was favored over uPA. Interaction tests allowed for additional analyses of BCAR1 protein levels in clinically relevant subgroups stratified by nodal and menopausal status.

CONCLUSIONS

The quantitative BCAR1 protein level represents a prognostic factor for RFS and OS in primary breast cancer, independent of the traditional prognostic factors and the other novel marker PAI-1.

Phosphorylation of paxillin tyrosines 31 and 118 controls polarization and motility of lymphoid cells and is PMA-sensitive

Tyrosine phosphorylation of paxillin regulates actin cytoskeleton-dependent changes in cell morphology and motility in adherent cells. In this report we investigated the involvement of paxillin tyrosine phosphorylation in the regulation of actin cytoskeleton-dependent polarization and motility of a non-adherent IL-3-dependent murine pre-B lymphocytic cell line Baf3. We also assessed the effect of phorbol myristate acetate (PMA), a phorbol ester analogous to those currently in clinical trials for the treatment of leukemia, on paxillin phosphorylation. Using tyrosine-to-phenylalanine phosphorylation mutants of paxillin and phosphospecific antibody we demonstrated that IL-3 stimulated phosphorylation of paxillin tyrosine residues 31 and 118, whereas the tyrosines 40 and 181 were constitutively phosphorylated. Phosphorylation of paxillin residues 31 and 118 was required for cell polarization and motility. In the presence of IL-3, PMA dramatically reduced the phosphorylation of residues 31 and 118, which was accompanied by inhibition of cell polarization and motility. This PMA effect was partially recapitulated by expression of exogenous tyrosine 31 and 118 mutants of paxillin. We also demonstrated that PMA inhibited the IL-3-induced and activation-dependent tyrosine phosphorylation of focal adhesion kinase. Thus, our results indicate that phosphorylation of paxillin tyrosine residues 31 and 118 regulates actin-dependent polarization and motility of pre-B Baf3 cells, both of which could be inhibited by PMA. They also suggest that inhibition of upstream signaling by PMA contributes to the decrease of paxillin phosphorylation and subsequent changes in cell morphology.

Src and Cas Are Essentially but Differentially Involved in Angiotensin II-Stimulated Migration of Vascular Smooth Muscle Cells via Extracellular Signal-Regulated Kinase 1/2 and c-Jun NH2-Terminal Kinase Activation

Angiotensin II (Ang II) plays an important role in several cardiovascular diseases associated with vascular smooth muscle cell (VSMC) growth and migration. Src activity is known to be required for the migration of a number of cell types. p130Cas was reported to be essential for cell migration and actin filament reorganization. Mitogen-activated protein (MAP) kinases were also reported to be critical regulatory factors for growth and migration of VSMC. However, precise intracellular mechanisms involving c-Src, p130Cas, and MAP kinases in Ang II-stimulated migration of VSMC have not been well elucidated. Here we demonstrated that Ang II rapidly and significantly stimulated tyrosine phosphorylation of Src and Cas and their association in rat aortic smooth muscle cells (RASMC). Ang II-stimulated tyrosine phosphorylation of Src and Cas and activation of ERK1/2 and JNK, but not p38, were potently inhibited by Src family tyrosine kinase inhibitors, herbimycin A (HA) and PP2. Ang II-stimulated Src and Cas association, tyrosine phosphorylation of Cas, and activation of ERK1/2 and JNK were suppressed in kinase-inactive Src (KI Src)-overexpressed RASMC. Ang II-stimulated JNK activation but not ERK1/2 activation was blocked in substrate domain-deleted Cas (DeltaSD Cas)-overexpressed RASMC. In addition, HA, PP2, ERK1/2 inhibitor, 2'-amino-3'-methoxyflavone (PD98059) and JNK inhibitor, and anthra[1,9-cd]pyrazol-6(2H)-one (SP600125) significantly inhibited Ang II-stimulated migration of RASMC. Ang II-induced colocalization of Src and Cas and migration were inhibited in both KI Src- and DeltaSD Cas-overexpressed RASMC. These findings suggest that Src and Cas are essentially but differentially involved in Ang II-stimulated migration of VSMC through the activation of ERK1/2 and JNK.

Cleavage of p130Cas in anoikis

p130Cas is a multifunctional signaling adaptor protein. It integrates and relays signals generated from a variety of extracellular stimuli and regulates a number of cellular activities including cell death. In this study, we analyzed the regulation and function of p130Cas in anoikis, a type of apoptosis caused by disruption of cell-matrix interactions. We found that p130Cas was specifically cleaved during anoikis in anoikis-sensitive epithelial cells, but not in anoikis-resistant tumor cells. There is a close correlation between p130Cas cleavage and anoikis. Furthermore, we found that the cleavage of p130Cas, as well as another focal adhesion component FAK, is different from that of caspase substrate PARP and spectrin. Although caspases and calpain were found to be involved in the cleavage of p130Cas, there appear to be other unidentified proteases that are mainly responsible for the cleavage of p130Cas, particularly at the early stage of anoikis. Overexpression of the p130Cas cleavage product induced apoptosis. Taken together, these data suggest that there are novel proteases involved in the cleavage of p130Cas during anoikis, which may be functionally involved in the onset of anoikis. p130Cas may have a dual role in the regulation of anoikis. On one hand, it mediates a survival signal from cell-matrix interactions when cells are attached to the extracellular matrix. On the other hand, it participates in executing cell death when cell-matrix interactions are disrupted. These observations provide new insights into the understanding of the function of p130Cas and the molecular mechanism of anoikis.

The cholecystokinin system in the rat retina: receptor expression and in vivo activation of tyrosine phosphorylation pathways

High levels of endogenous cholecystokinin (CCK) are present in the rat retina and restricted to amacrine cells. Two types of CCK receptors exist but their expression and intracellular transduction pathways coupled in the rat retina are unknown. The aims of this study were to investigate CCK receptors expression in rat retina and to study downstream tyrosine phosphorylation pathways. For this purpose, total mRNA isolated from rat retina was subjected to RT-PCR analysis. Isolated rat retinas were incubated in presence of CCK. Soluble proteins in retinal homogenates were immunoprecipitated with anti-phoshpotyrosine or anti-p130(Cas) specific monoclonal antibodies and subjected to SDS-PAGE, followed by Western blotting analysis. Both types of CCK receptor mRNAs, A and B, are present in the rat retina. Incubation of retina with CCK induced a rapid increase in several phosphotyrosine-containing bands with molecular masses greater than 30 kDa. Western Blotting and immunoprecipitation with a specific monoclonal antibody identified one of the phosphotyrosine bands as the adapter protein p130(Cas). Tyrosine phosphorylation of p130(Cas) induced by CCK in rat retina was time and concentration dependent: CCK induced tyrosine phosphorylation of p130(Cas) occurred rapidly with the maximum effect observed at 2.5 min incubation with 1 microM CCK. Our data clearly identified CCK-A and CCK-B receptor mRNAs in the rat retina and demonstrated that they are functional, stimulating tyrosine phosphorylation pathways. Our results provide novel biochemical information to further understand the physiological role of CCK A and B receptors in rat retina.

Effects of the Tyrosine Kinase Inhibitor Imatinib Mesylate on a Bcr-Abl-Positive Cell Line: Suppression of Autonomous Cell Growth but No Effect on Decreased Adhesive Property and Morphological Changes

Expression of the Bcr-Abl oncoprotein alters various aspects of hematopoietic cells. We investigated the effects of a Bcr-Abl tyrosine kinase inhibitor, imatinib mesylate, on the proliferation, adhesive properties, and morphology of a Bcr-Abl-transferred cell line, TF-1 Bcr-Abl, in comparison with parental TF-1. First, the factor-independent growth of TF-1 Bcr-Abl was inhibited in the presence of imatinib mesylate, but this inhibition was overcome by addition of exogenous granulocyte-macrophage colony-stimulating factor. Imatinib mesylate remarkably reduced tyrosine phosphorylation of Bcr-Abl, Cbl, and Crkl in a time-dependent manner, and their complex formation also was affected. Imatinib mesylate inhibited activation of Stat5 rather than the MEK-ERK1/2 pathway. TF-1 Bcr-Abl cells exhibited a round shape, unlike TF-1, and the adhesive property to fibronectin was much lower than that of TF-1. Although the Bcr-Abl oncoprotein may be involved negatively in cell adhesion, the decreased adhesion and altered morphology of TF-1 Bcr-Abl cells were minimally affected by imatinib mesylate and seemed independent of Bcr-Abl kinase activity. The present data indicated that the Bcr-Abl-specific kinase inhibitor cannot control Bcr-Abl-induced cell alterations other than autonomous growth.

blistery encodes Drosophila tensin protein and interacts with integrin and the JNK signaling pathway during wing development

Tensin is an actin-binding protein that is localized in focal adhesions. At focal adhesion sites, tensin participates in the protein complex that establishes transmembrane linkage between the extracellular matrix and cytoskeletal actin filaments. Even though there have been many studies on tensin as an adaptor protein, the role of tensin during development has not yet been clearly elucidated. Thus, this study was designed to dissect the developmental role of tensin by isolating Drosophila tensin mutants and characterizing its role in wing development. The Drosophila tensin loss-of-function mutations resulted in the formation of blisters in the wings, which was due to a defective wing unfolding process. Interestingly, by(1)-the mutant allele of the gene blistery (by)-also showed a blistered wing phenotype, but failed to complement the wing blister phenotype of the Drosophila tensin mutants, and contains Y62N/T163R point mutations in Drosophila tensin coding sequences. These results demonstrate that by encodes Drosophila tensin protein and that the Drosophila tensin mutants are alleles of by. Using a genetic approach, we have demonstrated that tensin interacts with integrin and also with the components of the JNK signaling pathway during wing development; overexpression of by in wing imaginal discs significantly increased JNK activity and induced apoptotic cell death. Collectively, our data suggest that tensin relays signals from the extracellular matrix to the cytoskeleton through interaction with integrin, and through the modulation of the JNK signal transduction pathway during Drosophila wing development.

Anchorage-independent phosphorylation of p130(Cas) protects lung adenocarcinoma cells from anoikis

The regulation and function of the signaling adaptor protein p130(Cas) in tumor cell anchorage-independent survival, or anoikis resistance, were investigated in human lung adenocarcinoma cells. The tyrosine phosphorylation and function of p130(Cas) during cell detachment were analyzed in tumor cells and compared with that of normal epithelial cells. Cell detachment trigged rapid dephosphorylation of p130(Cas) in the nontumorigenic and anoikis-sensitive normal epithelial cells, but had no effect on the tyrosine phosphorylation of p130(Cas) in the anoikis-resistant lung adenocarcinoma cells. Further analysis revealed that the total tyrosine kinase activities associated with p130(Cas) in the lung tumor cells are anchorage-independent and are significantly higher than that in the normal cells, in which the p130(Cas)-associated tyrosine kinase activities are anchorage-dependent. Analysis of two known p130(Cas)-associated tyrosine kinases FAK and Src indicated that the regulation of tyrosine phosphorylation of FAK and Src are altered in the tumor cells. Inhibition of Src specifically abolished phosphorylation of p130(Cas) and induced anoikis. Furthermore, overexpression of dominant-negative forms of p130(Cas) also induced apoptosis. Taken together, these data suggest that p130(Cas) mediates a cell survival signal from cell-matrix interaction. Alterations in tumor cells that lead to constitutive phosphorylation of p130(Cas) can prevent cells from anoikis, hence contribute to tumor cell anchorage independence and metastasis.

Translocation of CrkL to focal adhesions mediates integrin-induced migration downstream of Src family kinases

The adapter protein Crk-Like (CrkL) can associate with the Src substrate p130(Cas) (Cas). The biological role of CrkL downstream of Cas, however, has been largely obscure. Consistent with the ability of CrkL to biochemically associate with Cas, we found that Src triggers translocation of CrkL to focal adhesions (FAs) in a manner dependent on Cas. Forced localization of CRKL to FAs (FA-CRKL) by itself was sufficient to induce activation of Rac1 and Cdc42 and rescued haptotaxis defects of mouse embryonic fibroblasts (MEFs) lacking Src, Yes, and Fyn, three broadly expressed Src family members required for integrin-induced migration. Consistent with Rac1 activation, FA-CRKL induced cotranslocation of a Rac1 activator, Dock1, to focal adhesions. These results therefore indicate a role for CrkL in mediating Src signaling by activating small G proteins at focal adhesions. Furthermore, MEFs lacking CrkL show impaired integrin-induced migration despite expression of a closely related protein, Crk-II, in these cells. These results therefore provide formal evidence that CrkL plays a specific role in integrin-induced migration as a downstream mediator of Src.

Molecular and cellular biology of small cell lung cancer

For any tumor to become cancerous, various genetic mutations and biologic alterations must occur in the cell that in combination render it a malignant neoplasm. Small cell lung cancer (SCLC) is a neoplasm associated with several molecular and cellular abnormalities. SCLC is associated with early and frequent metastasis as well as a poor ultimate response to chemotherapy. New and novel therapies based on understanding the mechanisms of transformation are needed. SCLC is associated with multiple chromosomal abnormalities, the most common of which is chromosome 3p deletion, as well as with abnormal oncogenes and tumor-suppressor genes. Along with the genetic alterations, SCLC has been shown to overexpress various cell surface receptors, including receptor tyrosine kinases (RTKs), G-protein-coupled receptors, integrins, and others. Some downstream molecules are also activated, such as phosphatidylinositol 3'-kinase, and would serve as good candidates for therapeutic strategies.

Cytogenetic and molecular genetic aspects of chronic myeloid leukaemia

Chronic myeloid leukaemia (CML) is caused by the product of the BCR-ABL oncogene, located on the Philadelphia (Ph) chromosome. BCR-ABL is generated as a result of a reciprocal t(9;22) chromosomal translocation. The mechanisms responsible for this illegitimate recombination event remain elusive but are presumed to require a close spatial association of the translocation partners (chromosomes 9 and 22). BCR-ABL fusion transcripts can be detected by a sensitive reverse transcription-polymerase chain reaction (RT-PCR) in the leucocytes of some healthy individuals suggesting that chromosomal translocations may occur frequently in the general population. The presence of BCR-ABL fusion transcripts does not imply that the individual will inevitably develop CML since other conditions must be favourable for expansion of the abnormal clone. Breakpoints in the ABL gene occur within a 5' segment. BCR-ABL fusion transcripts lack ABL exon a1 and consist of BCR exons fused directly to ABL exon a2. The breakpoints in the BCR gene on chromosome 22 are found within three defined regions. Depending on the position of the BCR breakpoint, fusion genes are generated that encode 190-, 210- or 230-kD forms of the Bcr-Abl tyrosine kinase. Since the ABL component of the fusion gene is largely invariant, it follows that variability in disease phenotype may be due to protein sequences encoded by the translocation partner, BCR. Different disease phenotypes are associated with each of the three Bcr-Abl oncoproteins, p190(Bcr-Abl), p210(Bcr-Abl )and p230(Bcr-Abl). Mechanisms associated with malignant transformation include altered cellular adhesion, activation of mitogenic signalling pathways, inhibition of apoptosis and proteasomal degradation of physiologically important cellular proteins. CML is subject to an inexorable progression from an 'indolent' chronic phase to a terminal blast crisis. Disease progression is presumed to be associated with the phenomenon of genomic instability.