CRKL plays a pivotal role in tumorigenesis of head and neck squamous cell carcinoma through the regulation of cell adhesion

Genomic landscape and preclinical models of angiosarcoma

Angiosarcoma is a cancer that develops in blood or lymphatic vessels that presents a significant clinical challenge due to its rarity and aggressive features. Clinical outcomes have not improved in decades, highlighting a need for innovative therapeutic strategies to treat the disease. Genetically, angiosarcomas exhibit high heterogeneity and complexity with many recurrent mutations. However, recent studies have identified some common features within anatomic and molecular subgroups. To identify potential therapeutic vulnerabilities, it is essential to understand and integrate the mutational landscape of angiosarcoma with the models that exist to study the disease. In this review, we will summarize the insights gained from reported genomic alterations in molecular and anatomic subtypes of angiosarcoma, discuss several potential actionable targets, and highlight the preclinical disease models available in the field.

USP53 Exerts Tumor-Promoting Effects in Triple-Negative Breast Cancer by Deubiquitinating CRKL

Breast cancer (BC) ranks in the top five malignant tumors in terms of morbidity and mortality rates. Among BC subtypes, TNBC has a high recurrence rate and metastasis rate and the worst prognosis. However, the exact mechanism by which TNBC develops is unclear. Here, we show that the deubiquitinase USP53 contributes to tumor growth and metastasis in TNBC. USP53 is overexpressed in TNBC, and this phenotype is linked to a poor prognosis. Functionally, USP53 promotes TNBC cell proliferation, migration, invasion, and epithelial-mesenchymal transition (EMT). More importantly, USP53 decreases the chemosensitivity of BC cells by enhancing v-crk sarcoma virus CT10 oncogene homologue (avian)-like (CRKL) expression. Mechanistically, USP53 directly binds CRKL to stabilize and deubiquitinate it, thereby preventing CRKL degradation. Overall, we discovered that USP53 deubiquitinates CRKL, encourages tumor development and metastasis, and reduces chemosensitivity in TNBC. These findings imply that USP53 might represent a new therapeutic target for the treatment of TNBC.

TAGLN2 promotes papillary thyroid carcinoma invasion via the Rap1/PI3K/AKT axis

TAGLN2, an actin-binding protein, functions as a binding protein to actin to facilitate the formation of intracellular cytoskeleton structures. TAGLN2 overexpression in papillary thyroid carcinoma (PTC) is reported in our previous study. This study aimed to examine the functions and molecular mechanisms of TAGLN2 in PTC. The clinical data analysis showed that TAGLN2 expression was associated with cervical lymph node metastasis in PTC. Gain- and loss-of-function approaches, as well as various cellular function, gene expression profiles, quantitative proteomics, and molecular biology experiments, were further exploited to explore the roles of TAGLN2 in PTC. The results showed that TAGLN2 overexpression significantly promoted the invasion of PTC cell lines (K1, TPC-1, and BCPAP). Besides, the results also indicated that TAGLN2 was associated with regulating proliferation, migration, angiogenesis, and adhesion of PTC cells. Gene expression profile, quantitative proteomics, and Western blotting were performed to identify the relevant pathways and key downstream molecules, and Rap1/PI3K/AKT signalling pathway, ITGB5, LAMC2, CRKL, vimentin, N-cadherin, and E-cadherin were finally focused on. Moreover, rescue experiments validated the involvement of the Rap1/PI3K/AKT signalling pathway in the TAGLN2-mediated invasion of PTC cells. Therefore, TAGLN2 may promote the invasion of PTC cells via the Rap1/PI3K/AKT signalling pathway and may be served as a potential therapeutic target for PTC. Developing antagonists targeting TAGLN2 may be a potentially effective therapeutic strategy for PTC.

Circ_0001206 regulates miR-665/CRKL axis to alleviate hypoxia/reoxygenation-induced cardiomyocyte injury in myocardial infarction

Aims

Myocardial infarction (MI) is a type of cardiovascular disease caused by myocardial necrosis. Growing evidences have suggested that circular RNAs (circRNAs) play crucial roles in cardiac hypoxia/reoxygenation (H/R)‐induced injury of MI.

Methods and results

Hypoxia/reoxygenation model of H9C2 cells was established and circ_0001206 expression was detected via quantitative real‐time polymerase chain reaction. Ribonuclease R (RNase R) and Actinomycin D (Act D) assays verified the stability. Cell counting kit‐8 (CCK‐8), western blot, TUNEL, and flow cytometry assays evaluated cell viability and cell apoptosis. RNA pull‐down, RNA binding protein immunoprecipitation (RIP), and luciferase reporter assays explored the mechanisms underlying MI. All experimental data were presented with mean ± standard deviation (SD) and P < 0.05 indicated statistical significance. Circ_0001206 was low‐expressed in H9C2 cells under H/R treatment. Circ_0001206 was formed by cyclization of CRK like proto‐oncogene, adaptor protein (CRKL). Circ_0001206 overexpression promoted cell viability and inhibited cardiomyocyte apoptosis. It was confirmed that circ_0001206 regulated CRKL expression via acting as a competing endogenous RNA (ceRNA) of microRNA‐665 (miR‐665). CRKL played a protective role in MI.

Conclusions

Circ_0001206 regulates miR‐665/CRKL axis to alleviate H/R‐induced cardiomyocyte injury in MI. Our findings suggest that circ_0001206 might be a potential target for MI treatment.

Prognostic role of DFNA5 in head and neck squamous cell carcinoma revealed by systematic expression analysis

Background

The gasdermin E gene (GSDME, also known as DFNA5) is mutated in familial aging-related hearing loss. Recent studies have also revealed that the expression of DFNA5 is suppressed in many cancer types; however, little is known about the function of DFNA5 in head and neck squamous cell carcinoma (HNSCC). Accordingly, the aim of the present study was to evaluate the expression of DFNA5 and explore its prognostic value in HNSCC.

Result

We used a set of bioinformatics tools, including Oncomine, TIMER, TISIDB, cBioPortal, and GEPIA, to analyze the expression of DFNA5 in patients with HNSCC from public databases. Kaplan-Meier plotter was used to evaluate the potential prognostic significance of DFNA5. DFNA5 mRNA levels were significantly higher in HNSCC tissues than in normal tissues, and high DFNA5 expression was correlated with worse survival. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway analyses showed that DFNA5 expression has a strong positive correlation with cell adhesion and the integrin signaling pathway, whereas its expression was negatively correlated with the levels of infiltrating B cells (cor = − 0.223, P = 8.57e-07) and CD8 T cells (cor = − 0.223, P = 2.99e-07).

Conclusion

This study demonstrates that DFNA5 expression has prognostic value for HNSCC patients. Moreover, these results suggest that regulation of lymphocyte infiltration is the mechanism underlying the function of DFNA5 in HNSCC.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-021-08692-w.

Crk and CrkL as Therapeutic Targets for Cancer Treatment

Crk and CrkL are cellular counterparts of the viral oncoprotein v-Crk. Crk and CrkL are overexpressed in many types of human cancer, correlating with poor prognosis. Furthermore, gene knockdown and knockout of Crk and CrkL in tumor cell lines suppress tumor cell functions, including cell proliferation, transformation, migration, invasion, epithelial-mesenchymal transition, resistance to chemotherapy drugs, and in vivo tumor growth and metastasis. Conversely, overexpression of tumor cells with Crk or CrkL enhances tumor cell functions. Therefore, Crk and CrkL have been proposed as therapeutic targets for cancer treatment. However, it is unclear whether Crk and CrkL make distinct or overlapping contributions to tumor cell functions in various cancer types because Crk or CrkL have been examined independently in most studies. Two recent studies using colorectal cancer and glioblastoma cells clearly demonstrated that Crk and CrkL need to be ablated individually and combined to understand distinct and overlapping roles of the two proteins in cancer. A comprehensive understanding of individual and overlapping roles of Crk and CrkL in tumor cell functions is necessary to develop effective therapeutic strategies. This review systematically discusses crucial functions of Crk and CrkL in tumor cell functions and provides new perspectives on targeting Crk and CrkL in cancer therapy.

Quantitative assessment of glioblastoma phenotypes in vitro establishes cell migration as a robust readout of Crk and CrkL activity

The expression levels of CT10 regulator of kinase (Crk) and Crk-like (CrkL) are elevated in many human cancers, including glioblastoma (GBM), and are believed to contribute to poor prognosis. Although Crk and CrkL have been proposed as therapeutic targets in these tumors, the lack of a reliable, quantitative assay to measure Crk and CrkL activity has hindered development of inhibitors. Here, we knocked down Crk, CrkL, or both using siRNAs in a human GBM cell line, U-118MG, to determine the respective, quantitative contributions of Crk and CrkL to cellular phenotypes. The combined use of specific and potent Crk and CrkL siRNAs induced effective knockdown of CrkII, CrkI, and CrkL. Whereas Crk knockdown did not affect cell morphology, proliferation, adhesion, or invasion, CrkL knockdown caused shrinkage of cells and inhibition of cell proliferation, adhesion, and invasion. Crk/CrkL double knockdown resulted in more pronounced morphological alterations and more robust inhibition of proliferation, adhesion, and invasion. Furthermore, Crk/CrkL double knockdown completely blocked cell migration, and this effect was rescued by transient overexpression of CrkL but not of Crk. Quantification of protein levels indicated that CrkL is expressed more abundantly than CrkII and CrkI in U-118MG cells. These results demonstrate both the predominant role of CrkL and the essential overlapping functions of Crk and CrkL in U-118MG cells. Furthermore, our study indicates that migration of U-118MG cells depends entirely on Crk and CrkL. Thus, impedance-based, real-time measurement of tumor cell migration represents a robust assay for monitoring Crk and CrkL activities.

Mechanisms of autoregulation of C3G, activator of the GTPase Rap1, and its catalytic deregulation in lymphomas

C3G is a guanine nucleotide exchange factor (GEF) that regulates cell adhesion and migration by activating the GTPase Rap1. The GEF activity of C3G is stimulated by the adaptor proteins Crk and CrkL and by tyrosine phosphorylation. Here, we uncovered mechanisms of C3G autoinhibition and activation. Specifically, we found that two intramolecular interactions regulate the activity of C3G. First, an autoinhibitory region (AIR) within the central domain of C3G binds to and blocks the catalytic Cdc25H domain. Second, the binding of the protein's N-terminal domain to its Ras exchanger motif (REM) is required for its GEF activity. CrkL activated C3G by displacing the AIR/Cdc25HD interaction. Two missense mutations in the AIR found in non-Hodgkin's lymphomas, Y554H and M555K, disrupted the autoinhibitory mechanism. Expression of C3G-Y554H or C3G-M555K in Ba/F3 pro-B cells caused constitutive activation of Rap1 and, consequently, the integrin LFA-1. Our findings suggest that sustained Rap1 activation by deregulated C3G might promote progression of lymphomas and that designing therapeutics to target C3G might treat these malignancies.

Copy number gains of the putative CRKL oncogene in laryngeal squamous cell carcinoma result in strong nuclear expression of the protein and influence cell proliferation and migration

Laryngeal squamous cell carcinoma is a major medical problem worldwide. Although our understanding of genetic changes and their consequences in laryngeal cancer has opened new therapeutic pathways over the years, the diagnostic as well as treatment options still need to be improved. In our previous study, we identified CRKL (22q11) as a novel putative oncogene overexpressed and amplified in a subset of LSCC tumors and cell lines. Here we analyze to what extent CRKL DNA copy number gains correlate with the higher expression of CRKL protein by performing IHC staining of the respective protein in LSCC cell lines (n = 3) and primary tumors (n = 40). Moreover, the importance of CRKL gene in regard to proliferation and motility of LSCC cells was analyzed with the application of RNA interference (siRNA). Beside the physiological cytoplasmic expression, the analysis of LSCC tumor samples revealed also nuclear expression of CRKL protein in 10/40 (25%) cases, of which three (7.5%), presented moderate or strong nuclear expression. Similarly, we observed a shift towards aberrantly strong nuclear abundance of the CRKL protein in LSCC cell lines with gene copy number amplifications. Moreover, siRNA mediated silencing of CRKL gene in the cell lines showing its overexpression, significantly reduced proliferation (p < 0.01) as well as cell migration (p < 0.05) rates. Altogether, these results show that the aberrantly strong nuclear localization of CRKL is a seldom but recurrent phenomenon in LSCC resulting from the increased DNA copy number and overexpression of the gene. Moreover, functional analyses suggest that proliferation and migration of the tumor cells depend on CRKL expression.

Increased Soluble CrkL in Serum of Breast Cancer Patients Is Associated with Advanced Disease

Over-expression of Crk-like protein (CrkL), an intracellular adaptor protein, in breast cancer biopsies has been linked to poor prognosis. CrkL can be secreted from cancer cells binding to β1 integrin on the cell membrane. In this study, we evaluated, for the first time, the levels of soluble CrkL in serum of breast cancer patients. Expression of CrkL and secreted fractions from human breast cancer cell lines and clinical patient samples were assessed by immunohistochemistry and Enzyme Linked Immuno-Sorbent Assay (ELISA). CrkL levels in tissues and sera of patients with different disease stages were compared and statistically analyzed by Chi-square test and Student’s t-test. Culture media from human breast cancer cell lines SUM159, MDA-MB231, and MCF7 showed over a 21-, 15-, and 11-fold higher concentration of soluble CrkL as compared to normal breast epithelium cell line MCF10A. Expression of CrkL was elevated in 85% of breast tumor tissue sections. Serum levels of CrkL were significantly higher in breast cancer patients than in healthy donors. All patients with metastatic disease had significantly elevated concentration of soluble CrkL in the serum with on average three-fold increase from the baseline. The data suggest that soluble fraction of CrkL can be further evaluated as a serum biomarker for advanced disease in breast cancer patients.

Loss of TRIM29 Alters Keratin Distribution to Promote Cell Invasion in Squamous Cell Carcinoma

: TRIM29 (tripartite motif-containing protein 29) is a TRIM family protein that has been implicated in breast, colorectal, and pancreatic cancers. However, its role in stratified squamous epithelial cells and tumors has not been elucidated. Here, we investigate the expression of TRIM29 in cutaneous head and neck squamous cell carcinomas (SCC) and its functions in the tumorigenesis of such cancers. TRIM29 expression was lower in malignant SCC lesions than in adjacent normal epithelial tissue or benign tumors. Lower expression of TRIM29 was associated with higher SCC invasiveness. Primary tumors of cutaneous SCC showed aberrant hypermethylation of TRIM29. Depletion of TRIM29 increased cancer cell migration and invasion; conversely, overexpression of TRIM29 suppressed these. Comprehensive proteomics and immunoprecipitation analyses identified keratins and keratin-interacting protein FAM83H as TRIM29 interactors. Knockdown of TRIM29 led to ectopic keratin localization of keratinocytes. In primary tumors, lower TRIM29 expression correlated with the altered expression of keratins. Our findings reveal an unexpected role for TRIM29 in regulating the distribution of keratins, as well as in the migration and invasion of SCC. They also suggest that the TRIM29-keratin axis could serve as a diagnostic and prognostic marker in stratified epithelial tumors and may provide a target for SCC therapeutics. SIGNIFICANCE: These findings identify TRIM29 as a novel diagnostic and prognostic marker in stratified epithelial tissues.

Genomic analysis of head and neck cancer cases from two high incidence regions

We investigated how somatic changes in HNSCC interact with environmental and host risk factors and whether they influence the risk of HNSCC occurrence and outcome. 180-paired samples diagnosed as HNSCC in two high incidence regions of Europe and South America underwent targeted sequencing (14 genes) and evaluation of copy number alterations (SCNAs). TP53, PIK3CA, NOTCH1, TP63 and CDKN2A were the most frequently mutated genes. Cases were characterized by a low copy number burden with recurrent focal amplification in 11q13.3 and deletion in 15q22. Cases with low SCNAs showed an improved overall survival. We found significant correlations with decreased overall survival between focal amplified regions 4p16, 10q22 and 22q11, and losses in 12p12, 15q14 and 15q22. The mutational landscape in our cases showed an association to both environmental exposures and clinical characteristics. We confirmed that somatic copy number alterations are an important predictor of HNSCC overall survival.

Fibroblast Growth Requires CT10 Regulator of Kinase (Crk) and Crk-like (CrkL)

CT10 regulator of kinase (Crk) and Crk-like (CrkL) are the cellular counterparts of the viral oncogene v-Crk Elevated levels of Crk and CrkL have been observed in many human cancers; inhibition of Crk and CrkL expression reduced the tumor-forming potential of cancer cell lines. Despite a close relationship between the Crk family proteins and tumorigenesis, how Crk and CrkL contribute to cell growth is unclear. We ablated endogenous Crk and CrkL from cultured fibroblasts carrying floxed alleles of Crk and CrkL by transfection with synthetic Cre mRNA (synCre). Loss of Crk and CrkL induced by synCre transfection blocked cell proliferation and caused shrinkage of the cytoplasm and the nucleus, formation of adherens junctions, and reduced cell motility. Ablation of Crk or CrkL alone conferred a much more modest reduction in cell proliferation. Reintroduction of CrkI, CrkII, or CrkL individually rescued cell proliferation in the absence of the endogenous Crk and CrkL, suggesting that Crk and CrkL play overlapping functions in regulating fibroblast growth. Serum and basic FGF induced phosphorylation of Akt, MAP kinases, and S6 kinase and Fos expression in the absence of Crk and CrkL, suggesting that cells lacking Crk and CrkL are capable of initiating major signal transduction pathways in response to extracellular stimuli. Furthermore, cell cycle and cell death analyses demonstrated that fibroblasts lacking Crk and CrkL become arrested at the G₁-S transition and undergo a modest apoptosis. Taken together, our results suggest that Crk and CrkL play essential overlapping roles in fibroblast growth.

CRKL knockdown promotes in vitro proliferation, migration and invasion, in vivo tumor malignancy and lymph node metastasis of murine hepatocarcinoma Hca-P cells

Our previous study (Biomed Pharmacother 2015;69:11) demonstrated that the over-expression of CRKL, a chicken tumor virus number 10 regulator of kinase-like protein, suppresses in vitro proliferation, invasion and migration of murine hepatocarcinoma Hca-P cell, a murine HCC cell with lymph node metastatic (LNM) rate of ∼25%. In current work, we investigated the effects of CRKL knockdown on the in vitro cell proliferation, migration and invasion, and on the in vivo tumor malignancy and LNM rate and level for Hca-P cells. Western blotting assay indicated that CRKL was down-regulated by ∼90% in a monoclonal CrkL-shRNA-transfected Hca-P cells. Compared with Hca-P and unrelated-shRNA-transfected Hca-P cell, the in vitro proliferation, migration and invasion potentials were significantly enhanced following CRKL stable deregulation. CRKL knock-down significantly promoted the tumorigenicity malignancy, LNM rates and level of Hca-P-transplanted mice. Consistent with our previous work, it can be concluded CRKL plays an important role in hepatocarcinoma cell proliferation, invasion and migration as well hepatocarcinoma malignancy and metastasis. It functions as a potential tumor suppressor in hepatocarcinoma.

Crk and CrkL are required for cell transformation by v-fos and v-ras

Crk and CrkL are SH2- and SH3-containing cytosolic adaptor proteins that can induce anchorage-independent growth of fibroblasts. Crk and CrkL play key roles in maintaining cytoskeletal integrity, cell motility and migration. We investigated the role of these two proteins in oncogenic transformation induced by v-fos and v-ras oncogenes using cell lines and fibroblasts carrying conditional alleles of Crk or CrkL. Transformation was assessed by cell morphology, saturation density and anchorage-independent growth in soft agar. We found that cell lines expressing v-fos or v-ras in the absence of Crk or CrkL displayed no evident morphological alterations and reduced anchorage-independent growth compared to those retaining Crk and CrkL. Similarly, overexpression of v-fos in mouse embryonic fibroblasts conferred a growth advantage and induced morphological changes, both of which were abrogated in the absence of either Crk or CrkL. In contrast, Crk, but not CrkL, contributed to v-ras-induced transformation of embryonic fibroblasts. These results suggest that both Crk and CrkL are required for the acquisition of cellular transformation by v-fos, whereas Crk plays a more prominent role than CrkL in v-ras-induced transformation.

The role of CT10 regulation of kinase-like in cancer

ABSTRACT 

V-crk avian sarcoma virus CT10 oncogene homolog-like (CRKL) is a member of CRK family. It acts as an adaptor protein in intracellular signal transduction. CRKL has been reported overexpressed in a variety of cancers affecting the aggressive and malignant behaviors of cancer cells. CRKL seems to show a tumor-promotion role in gastric cancer, glioblastoma multiforme, hepatocellular carcinoma, bladder cancer, lung cancer, colon cancer, ovarian cancer, leukemia, breast cancer, head and neck cancer, rhabdomyosarcoma and neuroblastoma. The association of CRKL with malignant tumors and its potential action mechanisms were summarized. CRKL has the potential to be used as a biomarker for the diagnosis, treatment and prognosis of certain tumors.

The clinical implications of Crk-like adaptor protein expression in papillary thyroid microcarcinoma

Papillary thyroid microcarcinoma (PMC) is the most common subtype of thyroid carcinomas with satisfactory prognosis. Crk-like (CrkL) adaptor protein was identified in the development of many carcinomas. However, the clinical implications of CrkL protein in PMC were still unknown. Here, we conducted immunohistochemistry to test and analyze CrkL expression in papillary thyroid carcinoma (PTC) (50 cases), PMC (50 cases), and nodular goiter (50 cases), and then western blot further identified the expression of CrkL proteins. In our present study, the positive rate and the mean optical density (MOD) value of CrkL expression in PTC and PMC tissues were statistically significantly different, compared with nodular goiter (p = 0.021, 0.037) and normal thyroid tissues (p = 0.003, 0.009), respectively. In addition, CrkL expression was not associated with age, gender, and tumor number. Conversely, significant differences between CrkL expression and metastasis (p < 0.01) and violation of capsule (p < 0.01) were observed. Notably, western blot indeed identified that the metastasis group of either PTC or PMC tissues had about twofold increased expression of CrkL compared with their non-metastasis groups (p < 0.05). In conclusion, CrkL is highly expressed in papillary thyroid carcinoma and papillary thyroid microcarcinoma and closely correlated to metastasis. Therefore, it is essential to carry out neck lymph node clearance in patients with papillary thyroid microcarcinoma.

Molecular dynamics of the proline switch and its role in Crk signaling

The Crk adaptor proteins play a central role as a molecular timer for the formation of protein complexes including various growth and differentiation factors. The loss of regulation of Crk results in many kinds of cancers. A self-regulatory mechanism for Crk was recently proposed, which involves domain–domain rearrangement. It is initiated by a cis–trans isomerization of a specific proline residue (Pro238 in chicken Crk II) and can be accelerated by Cyclophilin A. To understand how the proline switch controls the autoinhibition at the molecular level, we performed large-scale molecular dynamics and metadynamics simulations in the context of short peptides and multidomain constructs of chicken Crk II. We found that the equilibrium and kinetic properties of the macrostates are regulated not only by the local environments of specified prolines but also by the global organization of multiple domains. We observe the two macrostates (cis closed/autoinhibited and trans open/uninhibited) consistent with NMR experiments and predict barriers. We also propose an intermediate state, the trans closed state, which interestingly was reported to be a prevalent state in human Crk II. The existence of this macrostate suggests that the rate of switching off the autoinhibition by Cyp A may be limited by the relaxation rate of this intermediate state.

The association of Crk-like adapter protein with poor prognosis in glioma patients

Glioma is the most common of brain tumors that greatly affects patient survival. In our precious study, Crk-like adapter protein (CrkL) was identified as a key regulator in glioblastoma development [1]. Here, we aimed to investigate the correlation of CrkL with patient prognosis as well as pathological indicators. Immunohistochemistry was available to evaluate CrkL expression in 49 gliomas of distinct malignancy grade, and positive stained sites were analyzed. CrkL protein was detected in cell lines by Western blot as well. We observed CrkL protein stained in 59.2 % (29 out of 49) of all glioma tissues, including 41.4 % of low-grade (I + II) gliomas, and 85.0 % of high-grade (III + IV) gliomas. Of four grades, grade IV exhibited the highest CrkL level. CrkL protein was also identified in cell lines NHA, U87, U251, T98G, and A172 by Western blot. On the other hand, CrkL expression was significantly associated with the patient's age and WHO grade, and patients with high CrkL expression had a significantly shorter median survival time (17 months) than those (median survival time 52 months) with low CrkL expression (p<0.001). According to Cox regression, CrkL can be suggested as an independent prognostic factor. In conclusion, CrkL is differently expressed in different grades of gliomas, and correlated to WHO grade. CrkL also independently indicates poor prognosis in old glioma patients, which can further be recommended as an effective prognostic biomarker or therapeutic target.

NS1-binding protein abrogates the elevation of cell viability by the influenza A virus NS1 protein in association with CRKL

The influenza A virus non-structural protein 1 (NS1) is a multifunctional virulence factor consisting of an RNA binding domain and several Src-homology (SH) 2 and SH3 binding motifs, which promotes virus replication in the host cell and helps to evade antiviral immunity. NS1 modulates general host cell physiology in association with various cellular molecules including NS1-binding protein (NS1-BP) and signaling adapter protein CRK-like (CRKL), while the physiological role of NS1-BP during influenza A virus infection especially in association with NS1 remains unclear. In this study, we analyzed the intracellular association of NS1-BP, NS1 and CRKL to elucidate the physiological roles of these molecules in the host cell. In HEK293T cells, enforced expression of NS1 of A/Beijing (H1N1) and A/Indonesia (H5N1) significantly induced excessive phosphorylation of ERK and elevated cell viability, while the over-expression of NS1-BP and the abrogation of CRKL using siRNA abolished such survival effect of NS1. The pull-down assay using GST-fusion CRKL revealed the formation of intracellular complexes of NS1-BP, NS1 and CRKL. In addition, we identified that the N-terminus SH3 domain of CRKL was essential for binding to NS1-BP using GST-fusion CRKL-truncate mutants. This is the first report to elucidate the novel function of NS1-BP collaborating with viral protein NS1 in modulation of host cell physiology. In addition, an alternative role of adaptor protein CRKL in association with NS1 and NS1-BP during influenza A virus infection is demonstrated.

Models of crk adaptor proteins in cancer

The Crk family of adaptor proteins (CrkI, CrkII, and CrkL), originally discovered as the oncogene fusion product, v-Crk, of the CT10 chicken retrovirus, lacks catalytic activity but engages with multiple signaling pathways through their SH2 and SH3 domains. Crk proteins link upstream tyrosine kinase and integrin-dependent signals to downstream effectors, acting as adaptors in diverse signaling pathways and cellular processes. Crk proteins are now recognized to play a role in the malignancy of many human cancers, stimulating renewed interest in their mechanism of action in cancer progression. The contribution of Crk signaling to malignancy has been predominantly studied in fibroblasts and in hematopoietic models and more recently in epithelial models. A mechanistic understanding of Crk proteins in cancer progression in vivo is still poorly understood in part due to the highly pleiotropic nature of Crk signaling. Recent advances in the structural organization of Crk domains, new roles in kinase regulation, and increased knowledge of the mechanisms and frequency of Crk overexpression in human cancers have provided an incentive for further study in in vivo models. An understanding of the mechanisms through which Crk proteins act as oncogenic drivers could have important implications in therapeutic targeting.