Involvement of p130(Cas) and p105(HEF1), a novel Cas-like docking protein, in a cytoskeleton-dependent signaling pathway initiated by ligation of integrin or antigen receptor on human B cells

The p130Cas-Crk/CrkL Axis: A Therapeutic Target for Invasive Cancers Unveiled by Collaboration Among p130Cas, Crk, and CrkL

Numerous studies have documented the involvement of p130Cas (Crk-associated substrate) in a wide range of cellular processes across different types of cells. These processes encompass cell transformation, the connection between the extracellular matrix and the actin cytoskeleton, cell migration and invasion, and cardiovascular development. Moreover, p130Cas has been associated with the regulation of various physiological processes, including mammary, bone, brain, muscle, and liver homeostasis. The diverse functions of p130Cas can be attributed to its possession of multiple protein-protein interaction domains, which sets it apart as a unique class of adaptor protein. It is well established that p130Cas interacts critically with the CT10 regulator of kinase (Crk) adaptor protein family members, including CrkII, CrkI, and Crk-like (CrkL), which is the basis for the naming of the Cas family. The Crk family proteins play a crucial role in integrating signals from various sources, such as growth factors, extracellular matrix molecules, bacterial pathogens, and apoptotic cells. An increasing body of evidence suggests that the dysregulation of Crk family proteins is linked to various human diseases, including cancer and increased susceptibility to pathogen infections. This review focuses primarily on the structural and functional aspects of the interaction between p130Cas and the Crk family proteins, providing insights into how these proteins regulate specific signaling events. Furthermore, we delve into the functions of p130Cas and the Crk family proteins in both normal and tumor cells to gain a comprehensive understanding of their collaborative roles in cellular physiology and pathology. This review demonstrates that tumor cell migration and invasion are the two cellular functions that have been studied the most for the p130Cas-Crk/CrkL axis. Understanding the tumor cell migration and invasion that require both p130Cas and Crk/CrkL is necessary to further evaluate the role of the p130Cas-Crk/CrkL axis in cancer. Establishing the contribution of the p130Cas-Crk/CrkL axis to cancer will facilitate the development of cancer drugs targeting the axis to inhibit cancer cell dissemination and improve patient outcomes.

Non-Muscle Myosin II A: Friend or Foe in Cancer?

Non-muscle myosin IIA (NM IIA) is a motor protein that belongs to the myosin II family. The myosin heavy chain 9 (MYH9) gene encodes the heavy chain of NM IIA. NM IIA is a hexamer and contains three pairs of peptides, which include the dimer of heavy chains, essential light chains, and regulatory light chains. NM IIA is a part of the actomyosin complex that generates mechanical force and tension to carry out essential cellular functions, including adhesion, cytokinesis, migration, and the maintenance of cell shape and polarity. These functions are regulated via light and heavy chain phosphorylation at different amino acid residues. Apart from physiological functions, NM IIA is also linked to the development of cancer and genetic and neurological disorders. MYH9 gene mutations result in the development of several autosomal dominant disorders, such as May-Hegglin anomaly (MHA) and Epstein syndrome (EPS). Multiple studies have reported NM IIA as a tumor suppressor in melanoma and head and neck squamous cell carcinoma; however, studies also indicate that NM IIA is a critical player in promoting tumorigenesis, chemoradiotherapy resistance, and stemness. The ROCK-NM IIA pathway regulates cellular movement and shape via the control of cytoskeletal dynamics. In addition, the ROCK-NM IIA pathway is dysregulated in various solid tumors and leukemia. Currently, there are very few compounds targeting NM IIA, and most of these compounds are still being studied in preclinical models. This review provides comprehensive evidence highlighting the dual role of NM IIA in multiple cancer types and summarizes the signaling networks involved in tumorigenesis. Furthermore, we also discuss the role of NM IIA as a potential therapeutic target with a focus on the ROCK-NM IIA pathway.

The scaffold protein NEDD9 is necessary for leukemia-cell migration and disease progression in a mouse model of chronic lymphocytic leukemia

The scaffold protein NEDD9 is frequently upregulated and hyperphosphorylated in cancers, and is associated with poor clinical outcome. NEDD9 promotes B-cell adhesion, migration and chemotaxis, pivotal processes for malignant development. We show that global or B-cell-specific deletion of Nedd9 in chronic lymphocytic leukemia (CLL) mouse models delayed CLL development, markedly reduced disease burden and resulted in significant survival benefit. NEDD9 was required for efficient CLL cell homing, chemotaxis, migration and adhesion. In CLL patients, peripheral NEDD9 expression was associated with adhesion and migration signatures as well as leukocyte count. Additionally, CLL lymph nodes frequently expressed high NEDD9 levels, with a subset of patients showing NEDD9 expression enriched in the CLL proliferation centers. Blocking activity of prominent NEDD9 effectors, including AURKA and HDAC6, effectively reduced CLL cell migration and chemotaxis. Collectively, our study provides evidence for a functional role of NEDD9 in CLL pathogenesis that involves intrinsic defects in adhesion, migration and homing.

The Non-receptor Tyrosine Kinase Pyk2 in Brain Function and Neurological and Psychiatric Diseases

Pyk2 is a non-receptor tyrosine kinase highly enriched in forebrain neurons. Pyk2 is closely related to focal adhesion kinase (FAK), which plays an important role in sensing cell contacts with extracellular matrix and other extracellular signals controlling adhesion and survival. Pyk2 shares some of FAK’s characteristics including recruitment of Src-family kinases after autophosphorylation, scaffolding by interacting with multiple partners, and activation of downstream signaling pathways. Pyk2, however, has the unique property to respond to increases in intracellular free Ca²⁺, which triggers its autophosphorylation following stimulation of various receptors including glutamate NMDA receptors. Pyk2 is dephosphorylated by the striatal-enriched phosphatase (STEP) that is highly expressed in the same neuronal populations. Pyk2 localization in neurons is dynamic, and altered following stimulation, with post-synaptic and nuclear enrichment. As a signaling protein Pyk2 is involved in multiple pathways resulting in sometimes opposing functions depending on experimental models. Thus Pyk2 has a dual role on neurites and dendritic spines. With Src family kinases Pyk2 participates in postsynaptic regulations including of NMDA receptors and is necessary for specific types of synaptic plasticity and spatial memory tasks. The diverse functions of Pyk2 are also illustrated by its role in pathology. Pyk2 is activated following epileptic seizures or ischemia-reperfusion and may contribute to the consequences of these insults whereas Pyk2 deficit may contribute to the hippocampal phenotype of Huntington’s disease. Pyk2 gene, PTK2B, is associated with the risk for late-onset Alzheimer’s disease. Studies of underlying mechanisms indicate a complex contribution with involvement in amyloid toxicity and tauopathy, combined with possible functional deficits in neurons and contribution in microglia. A role of Pyk2 has also been proposed in stress-induced depression and cocaine addiction. Pyk2 is also important for the mobility of astrocytes and glioblastoma cells. The implication of Pyk2 in various pathological conditions supports its potential interest for therapeutic interventions. This is possible through molecules inhibiting its activity or increasing it through inhibition of STEP or other means, depending on a precise evaluation of the balance between positive and negative consequences of Pyk2 actions.

Chronic Cigarette Smoke Mediated Global Changes in Lung Mucoepidermoid Cells: A Phosphoproteomic Analysis

Proteomics analysis of chronic cigarette smoke exposure is a rapidly emerging postgenomics research field. While smoking is a major cause of lung cancer, functional studies using proteomics approaches could enrich our mechanistic understanding of the elusive lung cancer global molecular signaling and cigarette smoke relationship. We report in this study on a stable isotope labeling by amino acids in cell culture-based quantitative phosphoproteomic analysis of a human lung mucoepidermoid carcinoma cell line, H292 cells, chronically exposed to cigarette smoke. Using high resolution Orbitrap Velos mass spectrometer, we identified the hyperphosphorylation of 493 sites, which corresponds to 341 proteins and 195 hypophosphorylated sites, mapping to 142 proteins upon smoke exposure (2.0-fold change). We report differential phosphorylation of multiple kinases, including PAK6, EPHA4, LYN, mitogen-activated protein kinase, and phosphatases, including TMEM55B, PTPN14, TIGAR, among others, in response to chronic cigarette smoke exposure. Bioinformatics analysis revealed that the molecules differentially phosphorylated upon chronic exposure of cigarette smoke are associated with PI3K/AKT/mTOR and CDC42-PAK signaling pathways. These signaling networks are involved in multiple cellular processes, including cell polarity, cytoskeletal remodeling, cellular migration, protein synthesis, autophagy, and apoptosis. The present study contributes to emerging proteomics insights on cigarette smoke mediated global signaling in lung cells, which in turn may aid in development of precision medicine therapeutics and postgenomics biomarkers.

Preclinical and clinical studies of the NEDD9 scaffold protein in cancer and other diseases

Cancer progression requires a significant reprogramming of cellular signaling to support the essential tumor-specific processes that include hyperproliferation, invasion (for solid tumors) and survival of metastatic colonies. NEDD9 (also known as CasL and HEF1) encodes a multi-domain scaffolding protein that assembles signaling complexes regulating multiple cellular processes relevant to cancer. These include responsiveness to signals emanating from the T and B cell receptors, integrins, chemokine receptors, and receptor tyrosine kinases, as well as cytoplasmic oncogenes such as BCR-ABL and FAK- and SRC-family kinases. Downstream, NEDD9 regulation of partners including CRKL, WAVE, PI3K/AKT, ERK, E-cadherin, Aurora-A (AURKA), HDAC6, and others allow NEDD9 to influence functions as pleiotropic as migration, invasion, survival, ciliary resorption, and mitosis. In this review, we summarize a growing body of preclinical and clinical data that indicate that while NEDD9 is itself non-oncogenic, changes in expression of NEDD9 (most commonly elevation of expression) are common features of tumors, and directly impact tumor aggressiveness, metastasis, and response to at least some targeted agents inhibiting NEDD9-interacting proteins. These data strongly support the relevance of further development of NEDD9 as a biomarker for therapeutic resistance. Finally, we briefly discuss emerging evidence supporting involvement of NEDD9 in additional pathological conditions, including stroke and polycystic kidney disease.

Bioinformatic approaches to augment study of epithelial-to-mesenchymal transition in lung cancer

Bioinformatic approaches are intended to provide systems level insight into the complex biological processes that underlie serious diseases such as cancer. In this review we describe current bioinformatic resources, and illustrate how they have been used to study a clinically important example: epithelial-to-mesenchymal transition (EMT) in lung cancer. Lung cancer is the leading cause of cancer-related deaths and is often diagnosed at advanced stages, leading to limited therapeutic success. While EMT is essential during development and wound healing, pathological reactivation of this program by cancer cells contributes to metastasis and drug resistance, both major causes of death from lung cancer. Challenges of studying EMT include its transient nature, its molecular and phenotypic heterogeneity, and the complicated networks of rewired signaling cascades. Given the biology of lung cancer and the role of EMT, it is critical to better align the two in order to advance the impact of precision oncology. This task relies heavily on the application of bioinformatic resources. Besides summarizing recent work in this area, we use four EMT-associated genes, TGF-β (TGFB1), NEDD9/HEF1, β-catenin (CTNNB1) and E-cadherin (CDH1), as exemplars to demonstrate the current capacities and limitations of probing bioinformatic resources to inform hypothesis-driven studies with therapeutic goals.

Adaptors for disorders of the brain? The cancer signaling proteins NEDD9, CASS4, and PTK2B in Alzheimer's disease

No treatment strategies effectively limit the progression of Alzheimer's disease (AD), a common and debilitating neurodegenerative disorder. The absence of viable treatment options reflects the fact that the pathophysiology and genotypic causes of the disease are not well understood. The advent of genome-wide association studies (GWAS) has made it possible to broadly investigate genotypic alterations driving phenotypic occurrences. Recent studies have associated single nucleotide polymorphisms (SNPs) in two paralogous scaffolding proteins, NEDD9 and CASS4, and the kinase PTK2B, with susceptibility to late-onset AD (LOAD). Intriguingly, NEDD9, CASS4, and PTK2B have been much studied as interacting partners regulating oncogenesis and metastasis, and all three are known to be active in the brain during development and in cancer. However, to date, the majority of studies of these proteins have emphasized their roles in the directly cancer relevant processes of migration and survival signaling. We here discuss evidence for roles of NEDD9, CASS4 and PTK2B in additional processes, including hypoxia, vascular changes, inflammation, microtubule stabilization and calcium signaling, as potentially relevant to the pathogenesis of LOAD. Reciprocally, these functions can better inform our understanding of the action of NEDD9, CASS4 and PTK2B in cancer.

Focal adhesion protein expression in human diffuse large B-cell lymphoma

AIMS

Focal adhesions have been associated with poor prognosis in multiple cancer types, but their prognostic value in diffuse large B-cell lymphoma (DLBCL) has not been evaluated. The aim of this study was to investigate the expression patterns and the prognostic value of the focal adhesion proteins FAK, Pyk2, p130Cas and HEF1 in DLBCL.

METHODS AND RESULTS

Focal adhesion protein expression was examined using immunohistochemistry in normal lymphoid tissues and in 60 DLBCL patient samples. Kaplan-Meier survival and Cox regression analysis were performed to evaluate the correlation of focal adhesion protein expression with patient prognosis. FAK, Pyk2, p130Cas and HEF1 expression was mostly found in the germinal centres of normal human lymphoid tissues. When assessed in DLBCL samples, FAK, Pyk2, p130Cas and HEF1 were highly expressed in 45%, 34%, 42% and 45% of the samples, respectively. Multivariate Cox analysis revealed that decreased FAK expression was a significant independent predictor of poorer disease outcome.

CONCLUSIONS

FAK expression is an independent prognostic factor in DLBCL. Our results suggest that the addition of FAK immunostaining to the current immunohistochemical algorithms may facilitate risk stratification of DLBCL patients.

Role of the β1 integrin molecule in T-cell activation and migration

Abstract β1 integrins play crucial roles in a variety of cell processes such as adhesion, migration, proliferation, and differentiation of lymphocytes. To understand the molecular mechanisms of these various biological effects, it is particularly important to analyze cell signaling through the β1 integrins. Our previous study showed that PLC-γ, pp125FAK (focal adhesion kinase), pp105, paxillin, p59fyn, p56lck, and ERK1/2 are phosphorylated in their tyrosine residues upon engagement of β1 integrins. We identified pp105 as Cas (Crk-associated substrate)-related protein and successfully cloned its cDNA. pp105 is a Cas homologue predominantly expressed in the cells of lymphoid lineage, which led us to designate it Cas-L. Like p130Cas, Cas-L contains a single SH3 domain and multiple SH2-binding sites (YXXP motif), which are suggested to bind SH2 domains of Crk, Nck, and SHPTP2. Subsequent studies revealed that pp125FAK binds Cas-L on its SH3 domain and phosphorylates its tyrosine residues upon β1 integrin stimulation. Since Cas-L is preferentially expressed in lymphocytes, it is conceivable that Cas-L plays an important role in lymphocyte-specific signals. We have shown that Cas-L is involved in the T-cell receptor (TCR)/CD3 signaling pathway as well as the β1 integrin signaling pathway. Cas-L is transiently phosphorylated following CD3 crosslinking and tyrosine-phosphorylated Cas-L binds to Crk and C3G. Furthermore, a Cas-L mutant (Cas-LΔSH3), which lacks the binding site for FAK, is still tyrosine-phosphorylated upon CD3 crosslinking but not upon β1 integrin crosslinking, suggesting that FAK is not involved in CD3-dependent Cas-L phosphorylation. Finally, we have identified a crucial role of Cas-L in β1 integrin-mediated T-cell co-stimulation. We have found that this co-stimulatory pathway is impaired in the Jurkat T-cell line, and that the expression level of Cas-L is reduced in the Jurkat cells compared to peripheral T-cells. The transfection of Cas-L cDNA into Jurkat cells restored the β1 integrin-mediated co-stimulation, while the transfection of Cas-LΔSH3 mutant failed to do so, which contrasts with the case of CD3-mediated signaling. These results indicate that Cas-L plays a key role, through the association and phosphorylation by FAK, in β1 integrin-mediated T-cell co-stimulation. Moreover, tyrosine phosphorylation of Cas-L is critical for T-cell receptor and β1 integrin-induced T-lymphocyte migration. Taken together, Cas-L might be the bi-modal docking protein which assembles the signals through β1 integrins and TCR/CD3, and which participates in a variety of T-cell functions.

The adaptor protein Crk in immune response

The adaptor proteins Crk (CT10 (chicken tumor virus number 10) regulator of kinase), including CrkI, CrkII and Crk-like, are important signal molecules that regulate a variety of cellular processes. Considerable progress has been made in understanding the roles of the Crk family proteins in signal transduction, with a focus on cellular transformation and differentiation. However, since Crk was identified in 1988, very few studies have addressed how Crk regulates the immune response. Recent work demonstrates that Crk proteins function as critical signal molecules in regulating immune cell functions. Emerging data on the roles of Crk in activation and inhibitory immunoreceptor signaling suggest that Crk proteins are potential immunotherapeutic targets in cancer and infectious diseases. The aim of this review is to summarize recent key findings regarding the role of Crk in immune responses mediated by T, B and natural killer (NK) cells. In particular, the roles of Crk in NK cell functions are discussed.

Escherichia coli virulence protein NleH1 interaction with the v-Crk sarcoma virus CT10 oncogene-like protein (CRKL) governs NleH1 inhibition of the ribosomal protein S3 (RPS3)/nuclear factor κB (NF-κB) pathway

Enterohemorrhagic Escherichia coli and other attaching/effacing bacterial pathogens cause diarrhea in humans. These pathogens use a type III secretion system to inject virulence proteins (effectors) into host cells, some of which inhibit the innate immune system. The enterohemorrhagic E. coli NleH1 effector prevents the nuclear translocation of RPS3 (ribosomal protein S3) to inhibit its participation as a nuclear "specifier" of NF-κB binding to target gene promoters. NleH1 binds to RPS3 and inhibits its phosphorylation on Ser-209 by IκB kinase-β (IKKβ). However, the precise mechanism of this inhibition is unclear. NleH1 possesses a Ser/Thr protein kinase activity that is essential both for its ability to inhibit the RPS3/NF-κB pathway and for full virulence of the attaching/effacing mouse pathogen Citrobacter rodentium. However, neither RPS3 nor IKKβ is a substrate of NleH1 kinase activity. We therefore screened ∼9,000 human proteins to identify NleH1 kinase substrates and identified CRKL (v-Crk sarcoma virus CT10 oncogene-like protein), a substrate of the BCR/ABL kinase. Knockdown of CRKL abundance prevented NleH1 from inhibiting RPS3 nuclear translocation and NF-κB activity. CRKL residues Tyr-198 and Tyr-207 were required for interaction with NleH1. Lys-159, the kinase-active site of NleH1, was necessary for its interaction with CRKL. We also identified CRKL as an IKKβ interaction partner, mediated by CRKL Tyr-198. We propose that the CRKL interaction with IKKβ recruits NleH1 to the IKKβ complex, where NleH1 then inhibits the RPS3/NF-κB pathway.

A system for reconstructing B cell antigen receptor signaling in the mouse myeloma J558L cell line

B cell antigen receptor (BCR) signaling is positively and negatively regulated by various cell surface receptors such as CD19 and CD45. Functional analysis of these receptors has been performed using gene targeting technology, which is a valid approach to elucidate their functions. However, this type of analysis is restricted when multiple molecules are evaluated simultaneously. From a different perspective, synthetic biology provides a high degree of freedom for analyzing various molecules. Here we developed a system to reconstruct BCR signaling using the J558L myeloma cell line in combination with the protein-based Ca(2+) indicator YC3.60. BCR-reconstituted J558L cells harboring YC3.60 (J558Lμv11 cells) permitted monitoring of Ca(2+) mobilization. Reconstituting CD19 in J558Lμv11 cells resulted in detectable BCR-induced Ca(2+) mobilization but with kinetics different from that of CD45-expressing cells. Furthermore, we evaluated the validity of the J558L system by proteomic analysis of tyrosine-phosphorylated proteins after antigen stimulation. Identification of more than 100 BCR-induced tyrosine-phosphorylated proteins in J558Lμv11 cells revealed a similarity to that observed in B cells, and a novel member, non-receptor protein tyrosine kinase Fer, was found. Thus, this reconstruction system using J558L cells appeared to be valid for comprehensively investigating BCR signaling.

A requirement for Nedd9 in luminal progenitor cells prior to mammary tumorigenesis in MMTV-HER2/ErbB2 mice

Overexpression of the NEDD9/HEF1/Cas-L scaffolding protein is frequent, and drives invasion and metastasis in breast, head and neck, colorectal, melanoma, lung and other types of cancer. We have examined the consequences of genetic ablation of Nedd9 in the MMTV-HER2/ERBB2/neu mouse mammary tumor model. Unexpectedly, we found that only a limited effect on metastasis in MMTV-neu;Nedd9(-/-) mice compared with MMTV-neu;Nedd9(+/+) mice, but instead a dramatic reduction in tumor incidence (18 versus 80%), and a significantly increased latency until tumor appearance. Orthotopic reinjection and tail-vein injection of cells arising from tumors, coupled with in vivo analysis, indicated tumors arising in MMTV-neu;Nedd9(-/-) mice had undergone mutational selection that overcame the initial requirement for Nedd9. To better understand the defects in early tumor growth, we compared mammary progenitor cell pools from MMTV-neu;Nedd9(-/-) versus MMTV-neu;Nedd9(+/+) mice. The MMTV-neu;Nedd9(-/-) genotype selectively reduced both the number and colony-forming potential of mammary luminal epithelial progenitor cells, while not affecting basal epithelial progenitors. MMTV-neu;Nedd9(-/-) mammospheres had striking defects in morphology and cell polarity. All of these defects were seen predominantly in the context of the HER2/neu oncogene, and were not associated with randomization of the plane of mitotic division, but rather with depressed expression the cell attachment protein FAK, accompanied by increased sensitivity to small molecule inhibitors of FAK and SRC. Surprisingly, in spite of these significant differences, only minimal changes were observed in the gene expression profile of Nedd9(-/-) mice, indicating critical Nedd9-dependent differences in cell growth properties were mediated via post-transcriptional regulation of cell signaling. Coupled with emerging data indicating a role for NEDD9 in progenitor cell populations during the morphogenesis of other tissues, these results indicate a functional requirement for NEDD9 in the growth of mammary cancer progenitor cells.

Impact of the integrin signaling adaptor protein NEDD9 on prognosis and metastatic behavior of human lung cancer

PURPOSE

In a substantial population of non-small cell lung cancer (NSCLC), expression and activation of EGF receptor (EGFR) have been reported and is regarded as a novel molecular target. A growing body of evidence has shown the signaling crosstalk between EGFR and integrins in cellular migration and invasion. NEDD9 is an integrin signaling adaptor protein composed of multiple domains serving as substrate for a variety of tyrosine kinases. In the present study, we aimed at elucidating a role of NEDD9 in the signaling crosstalk between EGFR and integrins.

EXPERIMENTAL DESIGN

Using NSCLC cell lines, we conducted immunoblotting and cellular migration/invasion assay in vitro. Next, we analyzed metastasis assays in vivo by the use of xenograft transplantation model. Finally, we retrospectively evaluated clinical samples and records of patients with NSCLCs.

RESULTS

We showed that tyrosine phosphorylation of NEDD9 was reduced by the inhibition of EGFR in NSCLC cell lines. Overexpression of constitutively active EGFR caused tyrosine phosphorylation of NEDD9 in the absence of integrin stimulation. By gene transfer and gene knockdown, we showed that NEDD9 plays a pivotal role in cell migration and invasion of those cells in vitro. Furthermore, overexpression of NEDD9 promoted lung metastasis of an NSCLC cell line in NOD/Shi-scid, IL-2Rγ(null) mice (NOG) mice. Finally, univariate and multivariate Cox model analysis of NSCLC clinical specimens revealed a strong correlation between NEDD9 expression and recurrence-free survival as well as overall survival.

CONCLUSION

Our data thus suggest that NEDD9 is a promising biomarker for the prognosis of NSCLCs and its expression can promote NSCLC metastasis.

Analysis of SRC oncogenic signaling in colorectal cancer by stable isotope labeling with heavy amino acids in mouse xenografts

The non-receptor tyrosine kinase SRC is frequently deregulated in human colorectal cancer (CRC), and SRC increased activity has been associated with poor clinical outcomes. In nude mice engrafted with human CRC cells, SRC over-expression favors tumor growth and is accompanied by a robust increase in tyrosine phosphorylation in tumor cells. How SRC contributes to this tumorigenic process is largely unknown. We analyzed SRC oncogenic signaling in these tumors by means of a novel quantitative proteomic analysis. This method is based on stable isotope labeling with amino acids of xenograft tumors by the addition of [(13)C(6)]-lysine into mouse food. An incorporation level greater than 88% was obtained in xenograft tumors after 30 days of the heavy lysine diet. Quantitative phosphoproteomic analysis of these tumors allowed the identification of 61 proteins that exhibited a significant increase in tyrosine phosphorylation and/or association with tyrosine phosphorylated proteins upon SRC expression. These mainly included molecules implicated in vesicular trafficking and signaling and RNA binding proteins. Most of these proteins were specific targets of SRC signaling in vivo, as they were not identified by analysis via stable isotope labeling by amino acids in cell culture (SILAC) of the same CRC cells in culture. This suggests that oncogenic signaling induced by SRC in tumors significantly differs from that induced by SRC in cell culture. We next confirmed this notion experimentally with the example of the vesicular trafficking protein and SRC substrate TOM1L1. We found that whereas TOM1L1 depletion only slightly affected SRC-induced proliferation of CRC cells in vitro, it drastically decreased tumor growth in xenografted nude mice. We thus concluded that this vesicular trafficking protein plays an important role in SRC-induced tumor growth. Overall, these data show that SILAC analysis in mouse xenografts is a valuable approach for deciphering tyrosine kinase oncogenic signaling in vivo.

The centrosomal kinase Plk1 localizes to the transition zone of primary cilia and induces phosphorylation of nephrocystin-1

Polo-like kinase (Plk1) plays a central role in regulating the cell cycle. Plk1-mediated phosphorylation is essential for centrosome maturation, and for numerous mitotic events. Although Plk1 localizes to multiple subcellular sites, a major site of action is the centrosomes, which supports mitotic functions in control of bipolar spindle formation. In G0 or G1 untransformed cells, the centriolar core of the centrosome differentiates into the basal body of the primary cilium. Primary cilia are antenna-like sensory organelles dynamically regulated during the cell cycle. Whether Plk1 has a role in ciliary biology has never been studied. Nephrocystin-1 (NPHP1) is a ciliary protein; loss of NPHP1 in humans causes nephronophthisis (NPH), an autosomal-recessive cystic kidney disease. We here demonstrate that Plk1 colocalizes with nephrocystin-1 to the transition zone of primary cilia in epithelial cells. Plk1 co-immunoprecipitates with NPHP1, suggesting it is part of the nephrocystin protein complex. We identified a candidate Plk1 phosphorylation motif (D/E-X-S/T-φ-X-D/E) in nephrocystin-1, and demonstrated in vitro that Plk1 phosphorylates the nephrocystin N-terminus, which includes the specific PLK1 phosphorylation motif. Further, induced disassembly of primary cilia rapidly evoked Plk1 kinase activity, while small molecule inhibition of Plk1 activity or RNAi-mediated downregulation of Plk1 limited the first and second phase of ciliary disassembly. These data identify Plk1 as a novel transition zone signaling protein, suggest a function of Plk1 in cilia dynamics, and link Plk1 to the pathogenesis of NPH and potentially other cystic kidney diseases.

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.

Breast cancer anti-estrogen resistance protein 1 (BCAR1/p130cas) in pulmonary disease tissue and serum

OBJECTIVE

The purpose of the study was to evaluate clinical presentation of breast cancer anti-estrogen resistance protein 1 (BCAR1, also known as p130cas) expression in pulmonary diseases, and to assess its potential as a molecular marker for diagnosis and prognosis.

METHODS

Between March 2008 and August 2010, we enrolled a total of 80 patients (group A) with non-small-cell lung cancer (NSCLC), 48 patients (group B) with pulmonary tuberculosis (including 27 cases of tuberculoma and 21 cases of cavitary pulmonary tuberculosis), and 32 patients (group C) with other benign pulmonary mass (hamartoma in 15 cases, inflammatory pseudotumor in 10 cases, fibroid tumor in 7 cases). Additionally, 160 healthy age- and sex-matched volunteers were recruited as healthy controls. Tissue BCAR1 expression was investigated by using tissue microarray and immunohistochemistry. BCAR1 and tumor markers (carcinoma embryonic antigen [CEA] and the cancer antigens CA19-9 and CA125) in serum were assayed by using ELISA and immunoradiometrics, respectively.

RESULTS

BCAR1 expression was detected (either in the nucleus, the cytoplasm, or both) in tumor cells in 79 of the 80 NSCLC cases in group A, and in fibroblasts in 41 of the 48 pulmonary tuberculosis cases in group B. However, it was not detected in the normal adjacent tissue in 70 of the 80 cases in group A and in 47 of the 48 cases in group B. In group C, BCAR1 expression was negative in all 32 cases. Additionally, we investigated adjacent tissue with acute or chronic inflammation in 20 cases from group C, and found no expression of BCAR1. Serum BCAR1 levels were significantly higher in patients with NSCLC than in the control group, increased gradually with the progression of tumor staging, and decreased after removal of the tumors. The levels were significantly lower in bronchioloalveolar carcinoma than in other subtypes of carcinoma (Mann-Whitney U test, Z = -5.089; p < 0.001). Serum BCAR1 levels were significantly higher in patients with pulmonary tuberculosis than in the control group, were positively and significantly correlated with the diameter of the tuberculosis lesion (Spearman's rho, correlation coefficient 0.753; p < 0.001), and decreased after removal of the tuberculosis lesions. The levels were significantly higher in patients with cavitary pulmonary tuberculosis than in those with tuberculoma (517.6 ± 326.5 vs 282.2 ± 137.6; Student's t-test, t = -3.387; p = 0.001). In group C, there was no appreciable difference in serum BCAR1 levels compared with the matched controls (222.8 ± 111.0 vs 201.6 ± 35.7; Dunnett's T3 test, p = 0.993). The discrimination power of combining BCAR1 and tumor markers in NSCLC versus benign lung diseases was higher than that of sole use of BCAR1 as a marker (maximal sum of sensitivity and specificity: 1.538 vs 1.237).

CONCLUSION

We conclude that a combined assay of serum BCAR1 and traditional tumor markers is potentially applicable for distinguishing NSCLC from benign lung diseases. However, the clinical utility of serum BCAR1 as a molecular marker for prognosis in NSCLC or pulmonary tuberculosis requires further clarification and verification.

A novel inhibitor of focal adhesion signaling induces caspase-independent cell death in diffuse large B-cell lymphoma

Focal adhesion (FA) proteins have been associated with transformation, migration, metastasis, and poor outcome in many neoplasias. We previously showed that these proteins were inhibited by E7123, a new celecoxib derivative with antitumor activity, in acute myeloid leukemia. However, little is known about FAs in diffuse large B cell lymphoma (DLBCL). This paper aimed to determine whether E7123 was effective against DLBCL and whether FAs were involved in its action. We evaluated the cytotoxicity and mechanism of action of E7123 and celecoxib in DLBCL cell lines. We also assessed the E7123 in vivo activity in a DLBCL xenograft model and studied FA signaling in primary DLBCL patient samples. We found that E7123 showed higher antitumor effect than celecoxib against DLBCL cells. Its mechanism of action involved deregulation of FA, AKT, and Mcl-1 proteins, a pathway that is activated in some patient samples, apoptosis-inducing factor release and induction of caspase-independent cell death. Moreover, E7123 showed suppression of in vivo tumor growth. These findings indicate that E7123 is effective against DLBCL in vitro and in vivo, with a mechanism of action that differs from that of most current therapies for this malignancy. Our results support further preclinical evaluation of E7123.

NEDD9 and BCAR1 negatively regulate E-cadherin membrane localization, and promote E-cadherin degradation

The Cas scaffolding proteins (NEDD9/HEF1/CAS-L, BCAR1/p130Cas, EFSSIN, and HEPL/CASS4) regulate cell migration, division and survival, and are often deregulated in cancer. High BCAR1 expression is linked to poor prognosis in breast cancer patients, while upregulation of NEDD9 contributes to the metastatic behavior of melanoma and glioblastoma cells. Our recent work knocking out the single Drosophila Cas protein, Dcas, identified a genetic interaction with E-cadherin. As E-cadherin is often downregulated during epithelial-mesenchymal transition (EMT) prior to metastasis, if such an activity was conserved in mammals it might partially explain how Cas proteins promote aggressive tumor behavior. We here establish that Cas proteins negatively regulate E-cadherin expression in human mammary cells. Cas proteins do not affect E-cadherin transcription, but rather, BCAR1 and NEDD9 signal through SRC to promote E-cadherin removal from the cell membrane and lysosomal degradation. We also find mammary tumors arising in MMTV-polyoma virus T-antigen mice have enhanced junctional E-cadherin in a Nedd9^−/− background. Cumulatively, these results suggest a new role for Cas proteins in cell-cell adhesion signaling in cancer.

Dcas supports cell polarization and cell-cell adhesion complexes in development

Mammalian Cas proteins regulate cell migration, division and survival, and are often deregulated in cancer. However, the presence of four paralogous Cas family members in mammals (BCAR1/p130Cas, EFS/Sin1, NEDD9/HEF1/Cas-L, and CASS4/HEPL) has limited their analysis in development. We deleted the single Drosophila Cas gene, Dcas, to probe the developmental function of Dcas. Loss of Dcas had limited effect on embryonal development. However, we found that Dcas is an important modulator of the severity of the developmental phenotypes of mutations affecting integrins (If and mew) and their downstream effectors Fak56D or Src42A. Strikingly, embryonic lethal Fak56D-Dcas double mutant embryos had extensive cell polarity defects, including mislocalization and reduced expression of E-cadherin. Further genetic analysis established that loss of Dcas modified the embryonal lethal phenotypes of embryos with mutations in E-cadherin (Shg) or its signaling partners p120- and beta-catenin (Arm). These results support an important role for Cas proteins in cell-cell adhesion signaling in development.

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.

Interferon-inducible factor 16 is a novel modulator of glucocorticoid action

Previously, we used cDNA expression profiling to identify genes associated with glucocorticoid (Gc) sensitivity. We now identify which of these directly influence Gc action. Interferon-inducible protein 16 (IFI16), bone morphogenetic protein receptor type II (BMPRII), and regulator of G-protein signaling 14 (RGS14) increased Gc transactivation, whereas sialyltransferase 4B (SIAT4B) had a negative effect. Amyloid β (A4) precursor-protein binding, family B, member 1 (APBB1/Fe65) and neural cell expressed developmentally down-regulated 9 (NEDD9) were without effect. Only IFI16 potentiated Gc repression of NF-κB. In addition, IFI16 affected basal expression, and Gc induction of endogenous target genes. IFI16 did not affect glucocorticoid receptor (GR) expression, ligand-dependent repression of GR expression, or the ligand-dependent induction of GR phosphorylation on Ser-211 or Ser-203. Coimmunoprecipitation revealed an interaction, suggesting that IFI16 modulation of GR function is mediated by protein crosstalk. Transfection analysis with GR mutants showed that the ligand-binding domain of GR binds IFI16 and is the target domain for IFI16 regulation. Analysis of human lung sections identified colocalization of GR and IFI16, suggesting a physiologically relevant interaction. We demonstrate that IFI16 is a novel modulator of GR function and show the importance of analyzing variation in Gc sensitivity in humans, using appropriate technology, to drive discovery.—Berry, A., Matthews, L. Jangani, M., Plumb, J., Farrow, S., Buchan, N., Wilson, P. A., Singh, D., Ray, D., W., Donn, R. P. Interferon-inducible factor 16 is a novel modulator of glucocorticoid action.

The retinoic acid inducible Cas-family signaling protein Nedd9 regulates neural crest cell migration by modulating adhesion and actin dynamics

Cell migration is essential for the development of numerous structures derived from embryonic neural crest cells (NCCs), however the underlying molecular mechanisms are incompletely understood. NCCs migrate long distances in the embryo and contribute to many different cell types, including peripheral neurons, glia and pigment cells. In the present work we report expression of Nedd9, a scaffolding protein within the integrin signaling pathway, in non-lineage-restricted neural crest progenitor cells. In particular, Nedd9 was found to be expressed in the dorsal neural tube at the time of neural crest delamination and in early migrating NCCs. To analyze the role of Nedd9 in neural crest development we performed loss- and gain-of-function experiments and examined the subsequent effects on delamination and migration in vitro and in vivo. Our results demonstrate that loss of Nedd9 activity in chick NCCs perturbs cell spreading and the density of focal complexes and actin filaments, properties known to depend on integrins. Moreover, a siRNA dose-dependent decrease in Nedd9 activity results in a graded reduction of NCC's migratory distance while forced overexpression increases it. Retinoic acid (RA) was found to regulate Nedd9 expression in NCCs. Our results demonstrate in vivo that Nedd9 promotes the migration of NCCs in a graded manner and suggest a role for RA in the control of Nedd9 expression levels.

An extensive survey of tyrosine phosphorylation revealing new sites in human mammary epithelial cells

Protein tyrosine phosphorylation represents a central regulatory mechanism in cell signaling. Here, we present an extensive survey of tyrosine phosphorylation sites in a normal-derived human mammary epithelial cell (HMEC) line by applying antiphosphotyrosine peptide immunoaffinity purification coupled with high sensitivity capillary liquid chromatography tandem mass spectrometry. A total of 481 tyrosine phosphorylation sites (covered by 716 unique peptides) from 285 proteins were confidently identified in HMEC following the analysis of both the basal condition and acute stimulation with epidermal growth factor (EGF). The estimated false discovery rate was 1.0% as determined by searching against a scrambled database. Comparison of these data with existing literature showed significant agreement for previously reported sites. However, we observed 281 sites that were not previously reported for HMEC cultures and 29 of which have not been reported for any human cell or tissue system. The analysis showed that a majority of highly phosphorylated proteins were relatively low-abundance. Large differences in phosphorylation stoichiometry for sites within the same protein were also observed, raising the possibility of more important functional roles for such highly phosphorylated pTyr sites. By mapping to major signaling networks, such as the EGF receptor and insulin growth factor-1 receptor signaling pathways, many known proteins involved in these pathways were revealed to be tyrosine phosphorylated, which provides interesting targets for future hypothesis-driven and targeted quantitative studies involving tyrosine phosphorylation in HMEC or other human systems.

Phosphorylation of human enhancer of filamentation (HEF1) on serine 369 induces its proteasomal degradation

Human enhancer of filamentation 1 (HEF1) is a multi-domain docking protein of the p130 Cas family. HEF1 is present at focal adhesions and is involved in integrin signalling mediating cytoskeleton reorganization associated with cell migration, adhesion or apoptosis. HEF1 functions are regulated in part by phosphorylation on tyrosine residues. HEF1 is also phosphorylated on serines/threonines leading to two isoforms refered to as p105 and p115. In most cases, the serine/threonine kinase(s) responsible for HEF1 phosphorylation have not been identified. In the present study, we have investigated HEF1 ser/thr phosphorylation. In the HCT-116 cell line transiently overexpressing Flag-HEF1 we showed that Hesperadin, a synthetic indolinone displaying antiproliferative effect and described as an inhibitor of various kinases including Aurora-B, prevented HEF1 phosphorylation induced by the ser/thr phosphatase PP2A inhibitor: okadaic acid (OA). In addition we showed that conversion of endogenous HEF1 p105 to p115 in HaCaT cells was prevented upon treatment with Hesperadin, resulting in accumulation of p105HEF1. We also identified serine 369 as the target site of phosphorylation by this Hesperadin-inhibited kinase in HCT-116. Finally, we provide evidence that phosphorylation on serine 369 but not phosphorylation on serine 296, triggers HEF1 degradation by the proteasomal machinery. These data suggest that conversion of p105 to p115 results from a ser-369-dependent phosphorylation mediated by an Hesperadin-sensitive kinase and regulates the half-life of HEF1.

Original triazine inductor of new specific molecular targets, with antitumor activity against nonsmall cell lung cancer

Despite our growing insight into carcinogenesis, treatment of tumors, especially nonsmall cell lung cancer (NSCLC), remains limited and it is urgent to develop strategies that target tumor cells and their genetic features. Drug discovery efforts have historically focused on the search for compounds that modulate the protein products of genes. Current drug therapy targets only a few hundred endogenous targets, mainly proteins, such as receptors and enzymes. But now, the interest in specifically targeting RNA is increasing, both for target validation and/or therapeutic purposes. In this regard, our work was concerned with the induction of new molecular targets correlated to a cytostatic effect on NSCLC cell line, after treatment with a new triazin named A190. The in vitro study of cell cycle and apoptosis induction demonstrated the antiproliferative potential of this new compounds, and the use of quantitative RT-PCR analysis permit to display an original mechanism of action involving 2 genes: HEF1 and B2. The antitumor effect was also confirmed by the good results in vivo on nude mice xenografts.

TCR-induced downregulation of protein tyrosine phosphatase PEST augments secondary T cell responses

We report that the protein tyrosine phosphatase PTP-PEST is expressed in resting human and mouse CD4(+) and CD8(+) T cells, but not in Jurkat T leukemia cells, and that PTP-PEST protein, but not mRNA, was dramatically downregulated in CD4(+) and CD8(+) primary human T cells upon T cell activation. This was also true in mouse CD4(+) T cells, but less striking in mouse CD8(+) T cells. PTP-PEST reintroduced into Jurkat at levels similar to those in primary human T cells, was a potent inhibitor of TCR-induced transactivation of reporter genes driven by NFAT/AP-1 and NF-kappaB elements and by the entire IL-2 gene promoter. Introduction of PTP-PEST into previously activated primary human T cells also reduced subsequent IL-2 production by these cells in response to TCR and CD28 stimulation. The inhibitory effect of PTP-PEST was associated with dephosphorylation the Lck kinase at its activation loop site (Y394), reduced early TCR-induced tyrosine phosphorylation, reduced ZAP-70 phosphorylation and inhibition of MAP kinase activation. We propose that PTP-PEST tempers T cell activation by dephosphorylating TCR-proximal signaling molecules, such as Lck, and that down-regulation of PTP-PEST may be a reason for the increased response to TCR triggering of previously activated T cells.

Identification of Pax5 target genes in early B cell differentiation

The transcription factor Pax5 is essential for B cell commitment in the mouse, where it represses lineage-inappropriate gene expression while simultaneously activating the B cell gene expression program. In this study we have performed a global gene expression screen of wild-type and Pax5-deficient pro-B cells in an attempt to identify the crucial Pax5 targets in early B lymphopoiesis. These studies have identified 109 Pax5 targets comprising 61% activated and 39% repressed genes. Interestingly, Pax5 directly regulates the genes encoding a number of transcription factors that are required at the pre-B cell stage of differentiation, including Irf8, Spib, and Ikzf3 (Aiolos), suggesting that a key function of Pax5 is to activate secondary transcription factors that further reinforce the B cell program. Pax5 is also required for the expression of many genes known to be involved in adhesion and signaling, indicating that Pax5 modulates the homing and or migration properties of B cell progenitors. Finally, Pax5 also represses a cohort of genes that are involved in multiple biological processes, many of which are not typically associated with B cells. These include the repression of the adhesion molecule Embigin, which is expressed in bone marrow progenitors, T cells, and myeloid cells but is specifically repressed by Pax5 in B cells.

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

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

Use of gene expression profiling to identify a novel glucocorticoid sensitivity determining gene, BMPRII

Wide variation in glucocorticoid (Gc) sensitivity exists between individuals which may influence susceptibility to, and treatment response of, inflammatory diseases. To determine a genetic fingerprint of Gc sensitivity 100 healthy human volunteers were polarized into the 10% most Gc-sensitive and 10% most Gc-resistant following a low dose dexamethasone (0.25 mg) suppression test. Gene expression profiling of primary lymphocytes identified the 98 most significantly Gc regulated genes. These genes were used to build a subnetwork of Gc signaling, with 54 genes mapping as nodes, and 6 non-Gc regulated genes inferred as signaling nodes. Twenty four of the 98 genes showed a difference in Gc response in vitro dependent on the Gc sensitivity of their donor individuals in vivo. A predictive model was built using both partial least squares discriminate analysis and support vector machines that predicted donor glucocorticoid sensitivity with 87% accuracy. Discriminating genes included bone morphogenetic protein receptor, type II (BMPRII). Transfection studies showed that BMPRII modulated Gc action. These studies reveal a broad base of gene expression that predicts Gc sensitivity and determine a Gc signaling network in human primary T lymphocytes. Furthermore, this combined gene profiling, and functional analysis approach has identified BMPRII as a modulator of Gc signaling.

New concepts regarding focal adhesion kinase promotion of cell migration and proliferation

Focal adhesion kinase (FAK) is a non-receptor cytoplasmic tyrosine kinase that plays a key role in the regulation of proliferation and migration of normal and tumor cells. FAK associates with integrin receptors and recruits other molecules to the site of this interaction thus forming a signaling complex that transmits signals from the extracellular matrix to the cell cytoskeleton. Crk-associated substrate (CAS) family members appear to play a pivotal role in FAK regulation of cell migration. Cellular Src bound to FAK phosphorylates CAS proteins leading to the recruitment of a Crk family adaptor molecule and activation of a small GTPase and c-Jun N-terminal kinase (JNK) promoting membrane protrusion and cell migration. The relocalization of CAS and signaling through specific CAS family members appears to determine the outcome of this pathway. FAK also plays an important role in regulating cell cycle progression through transcriptional control of the cyclin D1 promoter by the Ets B and Kruppel-like factor 8 (KLF8) transcription factors. FAK regulation of cell cycle progression in tumor cells requires Erk activity, cyclin D1 transcription, and the cyclin-dependent kinase (cdk) inhibitor p27Kip1. The ability of FAK to integrate integrin and growth factor signals resulting in synergistic promotion of cell migration and proliferation, and its potential regulation by nuclear factor kappa B (NFkappaB) and p53 and a ubiquitously expressed inhibitory protein, suggest that it is remarkable in its capacity to integrate multiple extracellular and intracellular stimuli.

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

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

Interaction partners for human ZNF384/CIZ/NMP4--zyxin as a mediator for p130CAS signaling?

Transcription factor ZNF384/CIZ/NMP4 was first cloned in rat as a p130Cas-binding protein and has a role in bone metabolism and spermatogenesis. It is recurrently involved in translocations in acute lymphoblastic leukemia. Translocations t(12;17) and t(12;22) fuse ZNF384 to RNA-binding proteins TAF15 and EWSR1, while a translocation t(12;19) generates an E2A/ZNF384 fusion. We screened for ZNF384 interacting proteins using yeast two-hybrid technology. In contrast to its rat homolog, human ZNF384 does not interact with p130CAS. Zyxin, PCBP1, and vimentin, however, were identified as ZNF384-binding partners. Given the interaction between human zyxin and p130CAS, these results suggest that zyxin indirectly enables the interaction of ZNF384 with p130CAS which is described in rat.

Cell adhesion regulates Ser/Thr phosphorylation and proteasomal degradation of HEF1

Human enhancer of filamentation 1 (HEF1), a multifunctional docking protein of the Cas family, participates in integrin and growth factor signaling pathways that regulate global cellular processes including growth, motility and apoptosis. HEF1 consists of two isoforms, p105 and p115, the larger molecular weight form resulting from Ser/Thr phosphorylation of p105HEF1. The molecular mechanisms that regulate the interconversion of the two HEF1 species as well as the function of HEF1 Ser/Thr phosphorylation are unknown. Our study reveals that cell adhesion and detachment regulate the interconversion of the two HEF1 isoforms. Experiments using various inhibitors of cytoskeletal organization indicated that disruption of actin microfilaments but not intermediate filaments or microtubules resulted in a complete conversion of p115HEF1 to p105HEF1. The conversion of p115HEF1 to p105HEF1 was prevented by inhibition of protein phosphatase 2A (PP2A), suggesting that cytoskeletal regulation of PP2A activity controlled the dephosphorylation of p115HEF1. Degradation of endogenous HEF1 was dependent on proteasomes with the p115 species of HEF1 being preferentially targeted for turnover. Dephosphorylation of HEF1 by suspending cells or disrupting actin filaments protected HEF1 from degradation. These results suggest that the adhesion-dependent actin organization regulates proteasomal turnover of HEF1 through the activity of PP2A.

The Cas family docking protein, HEF1, promotes the formation of neurite-like membrane extensions

The Cas family proteins are a family of adhesion docking molecules that mediate protein-protein interactions and contribute to a number of signal transduction pathways. Recent studies of two family members, p130Cas and Sin, have suggested that they may play a role in neurite formation. The current study demonstrates that the third family member, HEF1, can also stimulate the formation of neurite-like processes, in the presence of Rho kinase inhibitors. The HEF1-promoted processes actively extend from the cell body and resemble neurites both in the manner of process extension and in the distribution of adhesion-associated molecules. The HEF1-promoted processes are dependent on the presence of an intact microtubule system and can be inhibited by co-expression of either constitutively active Rac or Cdc42 GTPase. Together, our data support a role for the Cas proteins in regulating cellular morphologies that contribute to tissue specialization.

Biological validation of differentially expressed genes in chronic lymphocytic leukemia identified by applying multiple statistical methods to oligonucleotide microarrays

Oligonucleotide microarrays are a powerful tool for profiling the expression levels of thousands of genes. Different statistical methods for identifying differentially expressed genes can yield different results. To our knowledge, no experimental test has been performed to decide which method best identifies genes that are truly differentially expressed. We applied three statistical methods (dChip, t-test on log-transformed data, and Wilcoxon test) to identify differentially expressed genes in previously untreated patients with chronic lymphocytic leukemia (CLL). We used a training set of Affymetrix Hu133A microarray data from 11 patients with unmutated immunoglobulin (Ig) heavy chain variable region (VH) genes and 8 patients with mutated Ig VH genes. Differential expression was validated using semiquantitative real-time polymerase chain reaction assays and by validating models to predict the somatic mutation status of an independent test set of nine CLL samples. The methods identified 144 genes that were differentially expressed between cases of CLL with unmutated compared with mutated Ig VH genes. Eighty genes were identified by Wilcoxon test, 60 by t-test, and 65 by dChip, but only 11 were identified by all three methods. Greater agreement was found between the t-test and the Wilcoxon test. Differential expression was validated by semiquantitative real-time polymerase chain reaction assays for 83% of individual genes, regardless of the statistical method. However, the Wilcoxon test gave the most accurate predictions on new samples, and dChip, the least accurate. We found that all three methods were equally good for finding differentially expressed genes, but they found different genes. The genes selected by the nonparametric Wilcoxon test are the most robust for predicting the status of new cases. A comprehensive list of all differentially expressed genes can only be obtained by combining the results of multiple statistical tests.

Crk-Associated Substrate Lymphocyte Type Is Required for Lymphocyte Trafficking and Marginal Zone B Cell Maintenance

The lymphocyte-specific Cas family protein Cas-L (Crk-associated substrate lymphocyte type) has been implicated to function in lymphocyte movement, mediated mainly by integrin signaling. However, its physiological role is poorly understood. In this study we analyzed the function of Cas-L in lymphocytes using gene-targeted mice. The mutant mice showed a deficit of marginal zone B (MZB) cells and a decrease of cell number in secondary lymphoid organs. An insufficient chemotactic response and perturbed cell adhesion were observed in Cas-L-deficient lymphocytes, suggesting that the aberrant localization was responsible for the deficit of MZB cells. Moreover, we found that lymphocyte trafficking was altered in Cas-L-deficient mice, which gave a potential reason for contraction of secondary lymphoid tissues. Thus, Cas-L affects homeostasis of MZB cells and peripheral lymphoid organs, which is considered to be relevant to impaired lymphocyte migration and adhesion.

Regulation of integrin-mediated cellular responses through assembly of a CAS/Crk scaffold

The molecular coupling of CAS and Crk in response to integrin activation is an evolutionary conserved signaling module that controls cell proliferation, survival and migration. However, when deregulated, CAS/Crk signaling also contributes to cancer progression and developmental defects in humans. Here we highlight recent advances in our understanding of how CAS/Crk complexes assemble in cells to modulate the actin cytoskeleton, and the molecular mechanisms that regulate this process. We discuss in detail the spatiotemporal dynamics of CAS/Crk assembly and how this scaffold recruits specific effector proteins that couple integrin signaling networks to the migration machinery of cells. We also highlight the importance of CAS/Crk signaling in the dual regulation of cell migration and survival mechanisms that operate in invasive cells during development and pathological conditions associated with cancer metastasis.

Cloning and expression of an SH3 domain-containing protein (Xchef-1), a novel downstream target of activin/nodal signaling

The activity of the activin/nodal signaling cascade is essential for the proper specification of germ layers during gastrulation. Many of the components of this signaling pathway have been identified, but relatively few downstream targets have been discovered. Using cDNA microarrays, we have identified a novel SH3-domain-containing gene we have named Xchef-1 that is upregulated in response to activin/nodal signaling. Xchef-1 is a direct downstream target of activin and is expressed in the marginal zones of gastrulating Xenopus embryos in a dynamic pattern reminiscent of nodal expression. At neurula stages, Xchef-1 is expressed in neural crest of the head and trunk as well as in the anterior neural plate. These domains of expression are then restricted at tailbud stages to the branchial arches, and the region of the future gall bladder.

Involvement of crk adapter proteins in regulation of lymphoid cell functions

The Crk adapter proteins consist of Src homology 2 (SH2) SH2 and SH3 domains, which bind tyrosine-phosphorylated peptides and polyproline-rich motives, respectively. They are linked to multiple signaling pathways in different cell types, including lymphocytes, and because of their lack of catalytic activity, many studies on Crk were aimed at the identification of their binding partners and determination of the physiologic meaning of these interactions. Crk proteins were found to be involved in the early steps of lymphocyte activation through their SH2-mediated transient interaction with signal-transducing molecules, such as Cbl, ZAP-70, CasL, and STAT5. In addition, Crk proteins are constitutively associated with effector molecules that mediate cell adhesion and thereby regulate lymphocyte extravasation and recruitment to sites of inflammation. This article describes selected studies of Crk, performed predominantly in lymphocytes, and discusses their potential relevance to the role of Crk in the regulation of lymphocyte functions.

Atrophin-1-interacting Protein 4/Human Itch Is a Ubiquitin E3 Ligase for Human Enhancer of Filamentation 1 in Transforming Growth Factor-β Signaling Pathways

Atrophin-1-interacting protein 4 (AIP4) is the human homolog of the mouse Itch protein (hItch), an E3 ligase for Notch and JunB. Human enhancer of filamentation 1 (HEF1) has been implicated in signaling pathways such as those mediated by integrin, T cell receptor, and B cell receptor and functions as a multidomain docking protein. Recent studies suggest that HEF1 is also involved in the transforming growth factor-beta (TGF-beta) signaling pathways, by interacting with Smad3, a key signal transducer downstream of the TGF-beta type I receptor. The interaction of Smad3 with HEF1 induces HEF1 proteasomal degradation, which was further enhanced by TGF-beta stimulation. The detailed molecular mechanisms of HEF1 degradation regulated by Smad3 were poorly understood. Here we report our studies that demonstrate the function of AIP4 as an ubiquitin E3 ligase for HEF1. AIP4 forms a complex with both Smad3 and HEF1 through its WW domains in a TGF-beta-independent manner and regulates HEF1 ubiquitination and degradation, which can be enhanced by TGF-beta stimulation. These findings reveal a new mechanism for Smad3-regulated proteasomal degradation events and also broaden the network of cross-talk between the TGF-beta signaling pathway and those involving HEF1 and AIP4.

Direct interaction between Smad3, APC10, CDH1 and HEF1 in proteasomal degradation of HEF1

Background

The Transforming Growth Factor-β (TGF-β) regulates myriad cellular events by signaling through members of the Smad family signal transducers. As a key signal transducer of TGF-β, Smad3 exhibits the property of receptor-activated transcriptional modulator and also the novel ability of regulating the proteasomal degradation of two Smad3 interacting proteins, SnoN and HEF1. It has been shown that Smad3 recruits two types of Ub E3 ligases, Smurf2 and the Anaphase Promoting Complex (APC), to mediate SnoN ubiquitination, thereby enhancing SnoN degradation. The molecular mechanisms underlying Smad3-regulated HEF1 degradation are not well understood. Furthermore, it is not clear how Smad3 recruits the APC complex.

Results

We detected physical interaction between Smad3 and an APC component APC10, as well as the interaction between HEF1 and CDH1, which is the substrate-interacting component within APC. Detailed domain mapping studies revealed distinct subdomains within the MH2 domain of Smad3 for binding to APC10 and HEF1 and suggests the formation of a complex of these four proteins (Smad3, HEF1, APC10 and CDH1). In addition, the protein levels of HEF1 are subjected to the regulation of overexpressed APC10 and CDH1.

Conclusions

Our data suggests that Smad3 may recruit the APC complex via a direct interaction with the APC subunit APC10 to regulate the ubiquitination and degradation of its interactor HEF1, which is recognized as an ubiquitination substrate by the CDH1 subunit of the APC complex.