Progressive loss of Syk and abnormal proliferation in breast cancer cells

Spleen tyrosine kinase (SYK): an emerging target for the assemblage of small molecule antitumor agents

INTRODUCTION

Spleen tyrosine kinase (SYK), a nonreceptor tyrosine kinase, has emerged as a vital component in the complex symphony of cancer cell survival and division. SYK activation (constitutive) is documented in various B-cell malignancies, and its inhibition induces programmed cell death. In some instances, it also acts as a tumor suppressor.

AREAS COVERED

Involvement of the SYK in the cancer growth, specifically in the progression of chronic lymphocytic leukemia (CLL), diffuse large B cell lymphomas (DLBCLs), acute myeloid leukemia (AML), and multiple myeloma (MM) is discussed. Therapeutic strategies to target SYK in cancer, including investigational SYK inhibitors, combinations of SYK inhibitors with other drugs targeting therapeutically relevant targets, and recent advancements in constructing new structural assemblages as SYK inhibitors, are also covered.

EXPERT OPINION

The SYK inhibitor field is currently marred by the poor translation rate of SYK inhibitors from preclinical to clinical studies. Also, dose-limited toxicities associated with the applications of SYK inhibitors have been evidenced. Thus, the development of new SYK inhibitory structural templates is in the need of the hour. To accomplish the aforementioned, interdisciplinary teams should incessantly invest efforts to expand the size of the armory of SYK inhibitors.

Spleen tyrosine kinase facilitates the progression of papillary thyroid cancer regulated by the hsa_circ_0006417/miR-377-3p axis

Papillary thyroid cancer (PTC) is a prevalent malignancy worldwide. Spleen tyrosine kinase (SYK) is a crucial enzyme that participates in various biological processes, including cancer progression. This study aims to uncover the biological function of SYK in PTC. SYK expression patterns in PTC were evaluated using quantitative real time polymerase chain reaction (qRT-PCR), immunohistochemistry (IHC), and western blot. Cell function assays were performed to assess the effects of SYK on PTC. Bioinformatics analysis was conducted to identify intriguing microRNA (miRNA) and circular RNA (circRNA). Dual-Luciferase Reporter or RNA immunoprecipitation assays were used to investigate the correlation among SYK, miR-377-3p, and hsa_circ_0006417. SYK was upregulated in PTC. Overexpression of SYK exhibited a positive correlation with tumor size, lymph node metastasis, and unfavorable disease-free survival. Functional assays revealed that SYK exerted tumorigenic effect on PTC cells through mTOR/4E-BP1 pathway. Mechanistically, hsa_circ_0006417 and miR-377-3p regulated SYK expression, offering modulating its tumor-promoting effects. Collectively, SYK acts as an oncogene in PTC through mTOR/4E-BP1 pathway, which is regulated by the hsa_circ_0006417/miR-377-3p axis, thereby providing a potential alternative for PTC treatment.

Epigenetic upregulation of spleen tyrosine kinase in cancer cells through p53-dependent downregulation of DNA methyltransferase

Syk is a tumor suppressor gene in some solid tumors. Currently, it remains unknown how Syk gene hypermethylation is controlled by DNA methyltransferase (DNMT) and p53. In colorectal cancer HCT116 cells, we found that protein and mRNA levels of Syk were much higher in WT than in p53^-/- cells. Both p53 inhibitor PFT-α and p53 silencing can reduce the protein and mRNA expression of Syk in WT cells, while DNMT inhibitor 5-Aza-2'-dC can increase Syk expression in p53^-/- cells. Interestingly, the DNMT expression in p53^-/- HCT116 cells was higher than that in WT cells. PFT-α can not only enhance Syk gene methylation but also increase DNMT1 protein and mRNA levels in WT HCT116 cells. In metastatic lung cancer cell lines A549 and PC9, which express WT p53 and gain function of p53, respectively, PFT-α can also downregulate Syk mRNA and protein expression. However, the Syk methylation level was increased by PFT-α in A549 but not in PC9 cells. Likewise, 5-Aza-2'-dC transcriptionally increased Syk gene expression in A549 cells, but not in PC9 cells. In summary methylation of Syk promoter requires DNMT1, and p53 can upregulate Syk expression via downregulation of DNMT1 at the transcriptional level.

Study the Effect of Microinjection of Zn, Fe, and Cu Loaded in Montmorillonite on Development Activities in Fertilized Chicken Eggs

This study aims to reduce embryonic mortality, increase body weight, and improve immune system in chicken. A total of 240 eggs were assigned to three treatments (n = 60) and injected with cooper (Cu), zinc (Zn), and iron (Fe) loaded by montmorillonite (Mnt), and one untreated group (n = 60). Some hormones and enzymes related with growth were measured in terms of serum, and expression of some genes related to growth, immune, and programmed cell deaths that were determined in the liver and spleen of chicken by RT-qPCR. The embryonic death on the fifth and seventh days after injecting eggs with Fe-Mnt was less obvious than in other groups. The heaviest body weight was recorded for Fe-Mnt and Cu-Mnt treatment. Fe-Mnt treatment had higher serum GSH, SOD, GH, and Myostatin contents and lower MDA than those in the other treatments. Cu-Mnt treatment included the highest contents of CAT enzyme and IGF-1 hormone in serum. The highest expression of IGF-1, GH, BCL6, and SYK genes in liver tissue were recorded by Zn-Mnt, IGFBP2, FGF8, and IFNW1 genes by Cu-Mnt, and TC1RG1 and IFNW1 genes by Fe-Mnt in spleen tissue. In conclusion, Fe-Mnt was the best treatment for reducing embryonic mortality, and increasing body weight of chickens and expression of growth and immune genes, followed by Cu-Mnt treatment.

Gypenoside LI arrests the cell cycle of breast cancer in G0/G1 phase by down-regulating E2F1

ETHNOPHARMACOLOGICAL RELEVANCE

Gynostemma pentaphyllum (Thunb.) Makino, a traditional medicine in China, has been widely used for the treatment of various diseases. Gypenoside LI (Gyp LI) is a major constituent from steamed G. pentaphyllum. Previous studies have shown that gypnenoside LI possess inhibitory effect on the growth of many cancer cells. However, its pharmacological effect in breast cancer and the mechanism have not been reported yet.

AIM OF THE STUDY

To investigate the anti-breast cancer activity of gypenoside LI and underlying mechanisms of gypenoside LI in MDA-MB-231 and MCF-7 cells.

MATERIAL/METHODS

The cytotoxicity of gypenoside LI was determined by MTT, colony-formation and three-dimensional spheroid assay. The migration, cell apoptosis and the cell cycle were investigated through cell morphology observation, flow cytometry analysis and key proteins detection. The anticancer mechanisms of gypenoside LI were detected by RNA sequencing (RNA-seq) and Gene Set Enrichment Analysis (GSEA) transcriptome analysis.

RESULTS

Gypenoside LI inhibited cell proliferation, migration, induced cell apoptosis and cell cycle arrest. Gypenoside LI arrested cell cycle at G0/G1 phase by regulating E2F1. It also inhibited tumor proliferation by regulating the expression of ERCC6L. Interestingly, we found that E2F1 siRNA also down-regulated the expression of ERCC6L. Gypenoside LI showed potential anti-breast cancer cells activity, especially on triple-negative breast cancer cells.

CONCLUSIONS

These data indicate that gypenoside LI could inhibit human breast cancer cells through inhibiting proliferation and migration, inducing apoptosis, arresting cell cycle at G0/G1 phase by regulating E2F1. It could be used as potential multi-target chemopreventive agents for cancer.

Systematic Analysis of Spleen Tyrosine Kinase Expression and its Clinical Outcomes in Various Cancers

Background:

Spleen tyrosine kinase (SYK) is an important enzyme in the proliferation and differentiation of all hematopoietic tissues. Its role as a cancer driver is well documented in liquid tumors; however, cumulative evidence has suggested an opposite role in other tumor types.

Objectives:

To systematically assess the expression of SYK, its prognostic value and epigenetic status in different cancers using bioinformatics tools.

Methods:

In this bioinformatics study, Oncomine database and cBioPortal were used to study the SYK gene expression, Kaplan–Meier plotter to study its prognostic value and MethHC to assess the SYK gene methylation in various cancers.

Results:

From 542 unique analyses of the SYK gene, it was found to be overexpressed in bladder, breast and colon cancers but downregulated in leukemia, lymphoma and myeloma. Compared with normal tissues, breast and brain tumors showed an overexpression of the SYK gene, whereas lymphoma and leukemia had lower expression. The Kaplan–Meier survival analysis revealed that SYK expression in pancreatic, gastric, liver and lung patients were correlated with better overall survival. Using cBioPortal, prostate cancer was found to have the highest SYK gene mutation frequency, and the mean expression was highest in diffuse large B-cell lymphoma, acute myeloid leukemia and thymoma. Using the MethHC database, SYK promoter hypermethylation was found to be significantly higher in breast, renal, liver, lung, pancreatic, prostatic, skin and stomach cancers compared with the normal tissue (P < 0.005).

Conclusion:

The results of this study indicate the potential use of SYK as a diagnostic and therapeutic target for different type of cancers. However, further experimental data are required to validate these results before use of SYK in clinical settings.

The Syk Kinase Promotes Mammary Epithelial Integrity and Inhibits Breast Cancer Invasion by Stabilizing the E-Cadherin/Catenin Complex

While first discovered in immunoreceptor signaling, the Syk protein kinase behaves as a tumor and metastasis suppressor in epithelial cells. Its reduced expression in breast and other carcinomas is correlated with decreased survival and increased metastasis risk, but its action mechanism remains largely unknown. Using phosphoproteomics we found that Syk phosphorylated E-cadherin and α-, β-, and p120-catenins on multiple tyrosine residues that concentrate at intercellular junctions. Increased Syk expression and activation enhanced E-cadherin/catenin phosphorylation, promoting their association and complex stability. In human breast cancer cells, Syk stimulated intercellular aggregation, E-cadherin recruitment and retention at adherens junctions, and promoted epithelial integrity, whereas it inhibited cell migration and invasion. Opposite effects were obtained with Syk knockdown or non-phosphorylatable mutant E-cadherin expression. Mechanistically, Syk stimulated the interaction of the E-cadherin/catenin complex with zonula occludens proteins and the actin cytoskeleton. Conditional Syk knockout in the lactating mouse mammary gland perturbed alveologenesis and disrupted E-cadherin localization at adherens junctions, corroborating the observations in cells. Hence, Syk is involved in the maintenance of the epithelial integrity of the mammary gland via the phosphorylation and stabilization of the E-cadherin/catenin adherens junction complex, thereby inhibiting cell migration and malignant tumor invasion.

Expression of Syk and MAP4 proteins in ovarian cancer

Purpose

We have previously reported on the prognostic importance of the calpain family of proteins in ovarian cancer, especially calpain-2. Spleen tyrosine kinase (Syk) phosphorylates a variety of cytoskeletal proteins with studies suggesting potential interactions between Syk and conventional calpains. Microtubule-associated protein 4 (MAP4) has been reported to be regulated by Syk.

Methods

The current study assessed Syk and MAP4 protein expression, by immunohistochemistry on a tissue microarray comprised of cores from primary ovarian carcinomas (n = 575), to evaluate associations with patient clinical outcomes and other clinicopathological factors and sought to determine whether there were any correlations between the expression of Syk, MAP4 and the calpain system.

Results

MAP4 expression was significantly associated with ovarian cancer histological subtype (P < 0.001), stage (P = 0.001), grade (P < 0.001) and residual tumour (P = 0.005). Despite this finding, we found no significant association existing between MAP4 expression and overall survival. Syk expression was also found significantly associated with histological subtype (P < 0.001). Syk seems to play a contradictory role with respect to tumour progression: low cytoplasmic Syk expression was significantly associated with low stage (P = 0.013), and low nuclear Syk expression with chemo-resistance in patients treated with taxane-containing therapy (P = 0.006). Interestingly, despite the lack of association in the whole cohort, high nuclear Syk expression was significantly associated with better overall survival in certain subgroups (P = 0.001).

Conclusions

The current study indicates a lack of correlation between calpain-2 expression and Syk and MAP4. Syk, MAP4 and calpain-1 appeared to significantly correlate with each other in the whole cohort, with calpain-1 being more highly associated with MAP4 and Syk in mucinous carcinomas. Overall, the current results suggest that Syk, MAP4, and calpain-1 expression are correlated with each other and these proteins may be involved in early stages of tumour spread.

Electronic supplementary material

The online version of this article (10.1007/s00432-019-02856-9) contains supplementary material, which is available to authorized users.

Endocrine Resistance in Hormone Receptor Positive Breast Cancer-From Mechanism to Therapy

The importance and role of the estrogen receptor (ER) pathway has been well-documented in both breast cancer (BC) development and progression. The treatment of choice in women with metastatic breast cancer (MBC) is classically divided into a variety of endocrine therapies, 3 of the most common being: selective estrogen receptor modulators (SERM), aromatase inhibitors (AI) and selective estrogen receptor down-regulators (SERD). In a proportion of patients, resistance develops to endocrine therapy due to a sophisticated and at times redundant interference, at the molecular level between the ER and growth factor. The progression to endocrine resistance is considered to be a gradual, step-wise process. Several mechanisms have been proposed but thus far none of them can be defined as the complete explanation behind the phenomenon of endocrine resistance. Although multiple cellular, molecular and immune mechanisms have been and are being extensively studied, their individual roles are often poorly understood. In this review, we summarize current progress in our understanding of ER biology and the molecular mechanisms that predispose and determine endocrine resistance in breast cancer patients.

Prognostic value of spleen tyrosine kinase in human solid tumors

Background

Spleen tyrosine kinase (SYK) was reported to be dysregulated in solid tumors and played an important role in cancer progression. However, the clinical and prognostic values of SYK in solid tumors remain unclear. This meta-analysis investigated the association between SYK expression and clinical outcomes in the patients with solid tumors.

Methods

A comprehensive literature search was conducted by screening the online electronic databases of PubMed, Embase, and the China National Knowledge Infrastructure. The hazard ratio (HR) with its corresponding 95% CI was used to explore the prognostic value of SYK.

Results

We analyzed a total of 1,075 patients from 10 studies, which met the criteria for this meta-analysis. Our pooled results demonstrated that a low expression of SYK did not correlate significantly with shorter overall survival (OS; HR=0.64, 95% CI: 0.34-1.21, P=0.169) or poorer disease-free survival (HR=0.51, 95% CI: 0.13-2.02, P=0.338). However, in a subgroup analysis based on tumor type and test method, under-expression of SYK was positively associated with worse OS in the groups of breast cancer (BC; HR=0.51, 95% CI: 0.32-0.80, P=0.003), hepatocellular carcinoma (HCC; HR=0.44, 95% CI: 0.29-0.69, P<0.001), methylation (HR=0.39, 95% CI: 0.30-0.51, P<0.001), and quantitative reverse transcription polymerase chain reaction (HR=0.24, 95% CI: 0.09-0.65, P=0.005).

Conclusion

This meta-analysis demonstrated that under-expression of SYK may serve as a predictive biomarker for poor prognosis in BC and HCC patients. In other solid tumors, the clinical usefulness should be confirmed by large-scale studies.

Phosphorylated immunoreceptor tyrosine-based activation motifs and integrin cytoplasmic domains activate spleen tyrosine kinase via distinct mechanisms

Spleen tyrosine kinase (Syk) is involved in cellular adhesion and also in the activation and development of hematopoietic cells. Syk activation induced by genomic rearrangement has been linked to certain T-cell lymphomas, and Syk inhibitors have been shown to prolong survival of patients with B-cell lineage malignancies. Syk is activated either by its interaction with a double-phosphorylated immunoreceptor tyrosine-based activation motif (pITAM), which induces rearrangements in the Syk structure, or by the phosphorylation of specific tyrosine residues. In addition to its immunoreceptor function, Syk is activated downstream of integrin pathways, and integrins bind to the same region in Syk as does pITAM. However, it is unknown whether integrins and pITAM use the same mechanism to activate Syk. Here, using purified Syk protein and fluorescence-based enzyme assay we investigated whether interaction of the integrin β₃ cytoplasmic domain with the Syk regulatory domain causes changes in Syk activity similar to those induced by pITAM peptides. We observed no direct Syk activation by soluble integrin peptide, and integrin did not compete with pITAM-induced activation even though at high concentrations, the integrin cytoplasmic domain peptide competed with Syk's substrate. However, clustered integrin peptides induced Syk activation, presumably via a transphosphorylation mechanism. Moreover, the clustered integrins also activated a Syk variant in which tyrosines were replaced with phenylalanine (Y348F/Y352F), indicating that clustered integrin-induced Syk activation involved other phosphorylation sites. In conclusion, integrin cytoplasmic domains do not directly induce Syk conformational changes and do not activate Syk via the same mechanism as pITAM.

Unperturbed Immune Function despite Mutation of C-Terminal Tyrosines in Syk Previously Implicated in Signaling and Activity Regulation

The nonreceptor tyrosine kinase Syk, a central regulator of immune cell differentiation and activation, is a promising drug target for treatment of leukemia and allergic and inflammatory diseases. The clinical failure of Syk inhibitors underscores the importance of understanding the regulation of Syk function and activity. A series of previous studies emphasized the importance of three C-terminal tyrosines in Syk for kinase activity regulation, as docking sites for downstream effector molecules, and for Ca²⁺ mobilization. Here, we investigated the roles of these C-terminal tyrosines in the mouse. Surprisingly, expression of a triple tyrosine-to-phenylalanine human Syk mutant, SYK(Y3F), was not associated with discernible signaling defects either in reconstituted DT40 cells or in B or mast cells from mice expressing SYK(Y3F) instead of wild-type Syk. Remarkably, lymphocyte differentiation, calcium mobilization, and 2,4,6-trinitrophenyl (TNP)-specific immune responses were unperturbed in SYK(Y3F) mice. These results emphasize the capacity of immune cells to compensate for specific molecular defects, likely using redundant intermolecular interactions, and highlight the importance of in vivo analyses for understanding cellular signaling mechanisms.

Bioinformatics analysis of gene expression data for the identification of critical genes in breast invasive carcinoma

Gene expression data were analyzed in order to identify critical genes in breast invasive carcinoma (BRCA). Data from 1,073 BRCA samples and 99 normal samples were analyzed, which were obtained from The Cancer Genome Atlas. Differentially expressed genes (DEGs) were identified using the significance analysis of microarrays method and a functional enrichment analysis was performed using the Database for Annotation, Visualization and Integrated Discovery. Relevant microRNAs (miRNAs), transcription factors (TFs) and associated small molecule drugs were revealed by Fisher's exact test. Furthermore, protein-protein interaction (PPI) information was downloaded from the Human Protein Reference Database. Interactions with a Pearson's correlation coefficient >0.5 were identified and PPI networks were subsequently constructed. A survival analysis was also conducted according to the Kaplan-Meier method. Initially, the 1,073 BRCA samples were clustered into seven groups, and 5,394 DEGs that were identified in ≥4 groups were selected. These DEGs were involved in the cell cycle, ubiquitin-mediated proteolysis, oxidative phosphorylation and human immunodeficiency virus infection. In addition, TFs, including Sp1 transcription factor, DAN domain BMP antagonist family member 5, MYCN proto-oncogene, bHLH transcription factor and cAMP responsive element binding protein (CREB)1, were identified in the BRCA groups. Seven PPI networks were subsequently constructed and the top 10 hub genes were acquired, including RB transcriptional corepressor 1, inhibitor of nuclear factor (NF)-κB kinase subunit γ, NF-κB subunit 2, transporter 1, ATP binding cassette subfamily B member, CREB binding protein and proteasome subunit α3. A significant difference in survival was observed between the two combined groups (groups-2, −4 and −5 vs. groups-1, −3, −6 and −7). In conclusion, numerous critical genes were detected in BRCA, and relevant miRNAs, TFs and small molecule drugs were identified. These findings may advance understanding regarding the pathogenesis of BRCA.

Activated spleen tyrosine kinase promotes malignant progression of oral squamous cell carcinoma via mTOR/S6 signaling pathway in an ERK1/2-independent manner

Spleen tyrosine kinase (SYK), a non-receptor cytoplasmic tyrosine enzyme, is well known for its ability in certain pathways through immune receptors. Recently, SYK role in cancer has been widely studied. SYK plays a dual role as a tumor suppressor and tumor promoter. Nevertheless, its role in oral squamous cell carcinoma (OSCC) has not been fully investigated. In the current study, samples from OSCC tumors and adjacent normal counterparts were collected and SYK expression was evaluated by real-time qPCR. SYK mRNA expression in tumors was higher than the normal tissues. And high SYK expression was confirmed by immunohistochemistry analysis and closely related to worse overall survival. The expression of SYK mRNA and protein was detected in 2 of 4 OSCC cell lines. SYK pharmacological suppression and RNAi-mediated knockdown inhibited proliferation, migration, and invasion of SYK-positive cells by reducing phosphorylated ERK1/2 and mTOR levels. One inhibitor of MEK, PD98059, also suppressed the same cancer-associated phenotypes of SYK-positive cells by decreasing phosphorylated ERK1/2 but increasing phosphorylated mTOR. Piceatannol, one pharmacological inhibitor of SYK, attenuated tumor growth in vivo. Overall, our results revealed a novel mechanism triggered by SYK to increase OSCC tumoriogenesis and tumor progression.

Reconstruction and signal propagation analysis of the Syk signaling network in breast cancer cells

The ability to build in-depth cell signaling networks from vast experimental data is a key objective of computational biology. The spleen tyrosine kinase (Syk) protein, a well-characterized key player in immune cell signaling, was surprisingly first shown by our group to exhibit an onco-suppressive function in mammary epithelial cells and corroborated by many other studies, but the molecular mechanisms of this function remain largely unsolved. Based on existing proteomic data, we report here the generation of an interaction-based network of signaling pathways controlled by Syk in breast cancer cells. Pathway enrichment of the Syk targets previously identified by quantitative phospho-proteomics indicated that Syk is engaged in cell adhesion, motility, growth and death. Using the components and interactions of these pathways, we bootstrapped the reconstruction of a comprehensive network covering Syk signaling in breast cancer cells. To generate in silico hypotheses on Syk signaling propagation, we developed a method allowing to rank paths between Syk and its targets. We first annotated the network according to experimental datasets. We then combined shortest path computation with random walk processes to estimate the importance of individual interactions and selected biologically relevant pathways in the network. Molecular and cell biology experiments allowed to distinguish candidate mechanisms that underlie the impact of Syk on the regulation of cortactin and ezrin, both involved in actin-mediated cell adhesion and motility. The Syk network was further completed with the results of our biological validation experiments. The resulting Syk signaling sub-networks can be explored via an online visualization platform.

The TRAF-interacting protein (TRAIP) is a novel E2F target with peak expression in mitosis

The TRAF-interacting protein (TRAIP) is an E3 ubiquitin ligase required for cell proliferation. TRAIP mRNA is downregulated in human keratinocytes after inhibition of the PI3K/AKT/mTOR signaling. Since E2F transcription factors are downstream of PI3K/AKT/mTOR we investigated whether they regulate TRAIP expression. E2F1 expression significantly increased the TRAIP mRNA level in HeLa cells. Reporter assays with the 1400bp 5′-upstream promoter in HeLa cells and human keratinocytes showed that E2F1-, E2F2- and E2F4-induced upregulation of TRAIP expression is mediated by 168bp upstream of the translation start site. Mutating the E2F binding site within this fragment reduced the E2F1- and E2F2-dependent promoter activities and protein-DNA complex formation in gel shift assays. Abundance of TRAIP mRNA and protein was regulated by the cell cycle with a peak in G2/M. Expression of GFP and TRAIP-GFP demonstrated that TRAIP-GFP protein has a lower steady-state concentration than GFP despite similar mRNA levels. Cycloheximide inhibition experiments indicated that the TRAIP protein has a half-life of around four hours. Therefore, the combination of cell cycle-dependent transcription of the TRAIP gene by E2F and rapid protein degradation leads to cell cycle-dependent expression with a maximum in G2/M. These findings suggest that TRAIP has important functions in mitosis and tumorigenesis.

Systematic Mapping of Kinase Addiction Combinations in Breast Cancer Cells by Integrating Drug Sensitivity and Selectivity Profiles

Chemical perturbation screens offer the possibility to identify actionable sets of cancer-specific vulnerabilities. However, most inhibitors of kinases or other cancer targets result in polypharmacological effects, which complicate the identification of target dependencies directly from the drug-response phenotypes. In this study, we developed a chemical systems biology approach that integrates comprehensive drug sensitivity and selectivity profiling to provide functional insights into both single and multi-target oncogenic signal addictions. When applied to 21 breast cancer cell lines, perturbed with 40 kinase inhibitors, the subtype-specific addiction patterns clustered in agreement with patient-derived subtypes, while showing considerable variability between the heterogeneous breast cancers. Experimental validation of the top predictions revealed a number of co-dependencies between kinase targets that led to unexpected synergistic combinations between their inhibitors, such as dasatinib and axitinib in the triple-negative basal-like HCC1937 cell line.

SYK interaction with ITGβ4 suppressed by Epstein-Barr virus LMP2A modulates migration and invasion of nasopharyngeal carcinoma cells

Epstein-Barr virus (EBV)-encoded Latent Membrane Protein 2A (LMP2A) is an EBV latency-associated protein regularly expressed in nasopharyngeal carcinoma (NPC). In B cells, LMP2A activity resembles that of a constitutively activated antigen receptor, which recruits the Syk tyrosine kinase to activate a set of downstream signaling pathways. LMP2A also downregulates cellular Syk levels. In the present study, we demonstrate that Syk interacts with the integrin β4 subunit (ITGβ4) of integrin α6β4 in epithelial cells and that concurrent LMP2A expression interferes with this interaction by competitive binding to Syk. We find that both Syk and LMP2A have an effect on ITGβ4 cell surface expression. However, in LMP2A expressing cells, ITGβ4 remains concentrated at the cellular protrusions, an expression pattern characteristic of motile cells, including NPC-derived epithelial cells. This effect of LMP2A on ITGβ4 localization is associated with a greater propensity for migration and invasion in-vitro, and may contribute to the invasive property of LMP2A-expressing NPC.

Downregulation of spleen tyrosine kinase in hepatocellular carcinoma by promoter CpG island hypermethylation and its potential role in carcinogenesis

Spleen tyrosine kinase (SYK) has predominantly been studied in hematopoietic cells, where it is involved in immunoreceptor-mediated signaling. However, SYK expression has been shown in numerous non-hematopoietic cells, and its downregulation has been shown to be involved in tumor formation and progression. SYK methylation has been demonstrated to identify a subset of hepatocellular carcinoma (HCC) cases with poor prognosis, but little is known regarding the biological role of SYK in HCC. We found that SYK methylation is a common event in HCC, and is inversely associated with its expression. We established stable HCC cell lines with inducible SYK expression vectors, and compared the differential RNA expression profiles of HCC cell lines with or without the induction of SYK. Gene ontology analysis revealed that the SYK-regulated genes were enriched for genes involved in cell adhesion. Accordingly, we found that the induction of SYK expression increased the adhesion of cells to fibronectin and decreased cell migration and invasion, and that cessation of SYK overexpression increased cell migration and invasion. Our findings suggest that SYK is involved in regulating cell to matrix adhesions, and that SYK loss affects the migration, and invasion of HCC cells.

Calling in SYK: SYK's dual role as a tumor promoter and tumor suppressor in cancer

SYK (spleen tyrosine kinase) is well-characterized in the immune system as an essential enzyme required for signaling through multiple classes of immune recognition receptors. As a modulator of tumorigenesis, SYK has a bit of a schizophrenic reputation, acting in some cells as a tumor promoter and in others as a tumor suppressor. In many hematopoietic malignancies, SYK provides an important survival function and its inhibition or silencing frequently leads to apoptosis. In cancers of non-immune cells, SYK provides a pro-survival signal, but can also suppress tumorigenesis by restricting epithelial-mesenchymal transition, enhancing cell-cell interactions and inhibiting migration.

TRAIP is a regulator of the spindle assembly checkpoint

Accurate chromosome segregation during mitosis is temporally and spatially coordinated by fidelity-monitoring checkpoint systems. Deficiencies in these checkpoint systems can lead to chromosome segregation errors and aneuploidy, and promote tumorigenesis. Here, we report that the TRAF-interacting protein (TRAIP), a ubiquitously expressed nucleolar E3 ubiquitin ligase important for cellular proliferation, is localized close to mitotic chromosomes. Its knockdown in HeLa cells by RNA interference (RNAi) decreased the time of early mitosis progression from nuclear envelope breakdown (NEB) to anaphase onset and increased the percentages of chromosome alignment defects in metaphase and lagging chromosomes in anaphase compared with those of control cells. The decrease in progression time was corrected by the expression of wild-type but not a ubiquitin-ligase-deficient form of TRAIP. TRAIP-depleted cells bypassed taxol-induced mitotic arrest and displayed significantly reduced kinetochore levels of MAD2 (also known as MAD2L1) but not of other spindle checkpoint proteins in the presence of nocodazole. These results imply that TRAIP regulates the spindle assembly checkpoint, MAD2 abundance at kinetochores and the accurate cellular distribution of chromosomes. The TRAIP ubiquitin ligase activity is functionally required for the spindle assembly checkpoint control.

Syk interacts with and phosphorylates nucleolin to stabilize Bcl-x(L) mRNA and promote cell survival

The Syk protein tyrosine kinase, a well-characterized regulator of immune cell function, plays an increasingly recognized role in tumorigenesis as a promoter of cell survival in both hematological and nonhematological malignancies. We show here that the expression of Syk in MCF7 or MDA-MB-231 breast cancer cells or in DG75 B-lymphoma cells protects cells from apoptosis induced by oxidative or genotoxic stress by stabilizing the mRNA for Bcl-x(L), an antiapoptotic protein. Syk binds robustly to nucleolin and phosphorylates it on tyrosine, enhancing its ability to bind the Bcl-x(L) mRNA. Consequently, reducing the level of nucleolin by RNA interference attenuates the ability of Syk to protect cells from stress-induced cell death.

Global phosphoproteomics of activated B cells using complementary metal ion functionalized soluble nanopolymers

Engagement of the B cell receptor for antigen (BCR) leads to immune responses through a cascade of intracellular signaling events. Most studies to date have focused on the BCR and protein tyrosine phosphorylation. Because spleen tyrosine kinase, Syk, is an upstream kinase in multiple BCR-regulated signaling pathways, it also affects many downstream events that are modulated through the phosphorylation of proteins on serine and threonine residues. Here, we report a novel phosphopeptide enrichment strategy and its application to a comprehensive quantitative phosphoproteomics analysis of Syk-dependent downstream signaling events in B cells, focusing on serine and threonine phosphorylation. Using a combination of the Syk inhibitor piceatannol, SILAC quantification, peptide fractionation, and complementary PolyMAC-Ti and PolyMAC-Zr enrichment techniques, we analyzed changes in BCR-stimulated protein phosphorylation that were dependent on the activity of Syk. We identified and quantified over 13,000 unique phosphopeptides, with a large percentage dependent on Syk activity in BCR-stimulated B cells. Our results not only confirmed many known functions of Syk, but more importantly, suggested many novel roles, including in the ubiquitin proteasome pathway, that warrant further exploration.

Getting Syk: spleen tyrosine kinase as a therapeutic target

Spleen tyrosine kinase (Syk) is a cytoplasmic protein tyrosine kinase well known for its ability to couple immune cell receptors to intracellular signaling pathways that regulate cellular responses to extracellular antigens and antigen-immunoglobulin (Ig) complexes of particular importance to the initiation of inflammatory responses. Thus, Syk is an attractive target for therapeutic kinase inhibitors designed to ameliorate the symptoms and consequences of acute and chronic inflammation. Its more recently recognized role as a promoter of cell survival in numerous cancer cell types ranging from leukemia to retinoblastoma has attracted considerable interest as a target for a new generation of anticancer drugs. This review discusses the biological processes in which Syk participates that have made this kinase such a compelling drug target.

Nanomechanical property maps of breast cancer cells as determined by multiharmonic atomic force microscopy reveal Syk-dependent changes in microtubule stability mediated by MAP1B

The Syk protein-tyrosine kinase, a well-characterized modulator of immune recognition receptor signaling, also plays important, but poorly characterized, roles in tumor progression, acting as an inhibitor of cellular motility and metastasis in highly invasive cancer cells. Multiharmonic atomic force microscopy (AFM) was used to map nanomechanical properties of live MDA-MB-231 breast cancer cells either lacking or expressing Syk. The expression of Syk dramatically altered the cellular topography, reduced cell height, increased elasticity, increased viscosity, and allowed visualization of a more substantial microtubule network. The microtubules of Syk-expressing cells were more stable to nocodazole-induced depolymerization and were more highly acetylated than those of Syk-deficient cells. Silencing of MAP1B, a major substrate for Syk in MDA-MB-231 cells, attenuated Syk-dependent microtubule stability and reversed much of the effect of Syk on cellular topography, stiffness, and viscosity. This study illustrates the use of multiharmonic AFM both to quantitatively map the local nanomechanical properties of living cells and to identify the underlying mechanisms by which these properties are modulated by signal transduction machinery.

SYK Allelic Loss and the Role of Syk-Regulated Genes in Breast Cancer Survival

Heterozygotic loss of SYK, a non-receptor tyrosine kinase, gives rise to mouse mammary tumor formation where Syk protein levels are reduced by about half; loss of SYK mRNA is correlated with invasive cell behavior in in vitro models; and SYK loss has been correlated with distant metastases in patients. Here, allelic loss of the SYK gene was explored in breast ductal carcinoma in situ (DCIS) using fluorescence in situ hybridization and pyrosequencing, respectively, and in infiltrating ductal carcinoma (IDC) using genomic data from The Cancer Genome Atlas (TCGA). Allelic loss was present in a subset of DCIS cases where adjacent IDC was present. SYK copy number loss was found in about 26% of 1002 total breast cancer cases and 30% of IDC cases. Quantitative immunofluorescence revealed Syk protein to be six-fold higher in infiltrating immune cells compared with epithelial cells. This difference distorted tumor cell mRNA and protein levels in extracts. 20% of 1002 IDC cases contained elevated immune cell infiltration as estimated by elevated immune-specific mRNAs. In cases without immune cell infiltration, loss of SYK copy number was associated with a significant reduction of SYK mRNA. Here we define a 55 Gene Set consisting of Syk interacting, motility- and invasion-related genes. We found that overall survival was significantly reduced in IDC and Luminal A+B cases where copy number and mutations of these 55 genes were affected (Kaplan-Meier, Logrank test p-value 0.007141 and Logrank test p-value 0.001198, respectively). We conclude that reduction in Syk expression and contributions of genomic instability to copy number and mutations in the 55 Syk interacting genes significantly contribute to poorer overall patient survival. A closer examination of the role of Syk interacting motility and invasion genes and their prognostic and/or causative association with metastatic disease and patient outcome is warranted.

Expression of variant isoforms of the tyrosine kinase SYK determines the prognosis of hepatocellular carcinoma

The spleen tyrosine kinase (SYK) has been reported as a novel biomarker for human hepatocellular carcinoma, but the functional contributions of its two isoforms SYK(L) and SYK(S) are undefined. In this study, we investigated their biologic functions and possible prognostic values in hepatocellular carcinoma. SYK(L) was downregulated in 38% of human specimens of hepatocellular carcinoma examined, whereas SYK(S) was detectable in 40% of these specimens but not in normal liver tissue samples without cirrhosis. SYK(S) expression correlated with pathologic parameters characteristic of tumor metastasis, including multiple tumors (P = 0.003) and vascular invasion (P = 0.001). Further, SYK(S) was specifically associated with epithelial-mesenchymal transition (EMT) in hepatocellular carcinoma specimens. Functional studies showed that SYK(S) promoted tumor growth, suppressed apoptosis, and induced EMT through the extracellular signal-regulated kinase pathway, countering the opposite effects of SYK(L). Patients with SYK(L(+)/S(-)) tumors exhibited longer overall survival and time to recurrence than those with SYK(L(-)/S(-)) or SYK(L(+)/S(+)) tumors (P < 0.001). Taken together, our findings showed that SYK(S) enhances invasion, whereas SYK(L) inhibits metastasis in hepatocellular carcinoma. We suggest that SYK(L) downregulation or SYK(S) elevation are strong predictors of poor survival in patients with hepatocellular carcinoma, indicative of a need for aggressive therapeutic intervention.

IgE induces proliferation in human airway smooth muscle cells: role of MAPK and STAT3 pathways

Airway remodeling is not specifically targeted by current asthma medications, partly owing to the lack of understanding of remodeling mechanisms, altogether posing great challenges in asthma treatment. Increased airway smooth muscle (ASM) mass due to hyperplasia/hypertrophy contributes significantly to overall airway remodeling and correlates with decline in lung function. Recent evidence suggests that IgE sensitization can enhance the survival and mediator release in inflammatory cells. Human ASM (HASM) cells express both low affinity (FcεRII/CD23) and high affinity IgE Fc receptors (FcεRI), and IgE can modulate the contractile and synthetic function of HASM cells. IgE was recently shown to induce HASM cell proliferation but the detailed mechanisms remain unknown. We report here that IgE sensitization induces HASM cell proliferation, as measured by ³H-thymidine, EdU incorporation, and manual cell counting. As an upstream signature component of FcεRI signaling, inhibition of spleen tyrosine kinase (Syk) abrogated the IgE-induced HASM proliferation. Further analysis of IgE-induced signaling depicted an IgE-mediated activation of Erk 1/2, p38, JNK MAPK, and Akt kinases. Lastly, lentiviral-shRNA-mediated STAT3 silencing completely abolished the IgE-mediated HASM cell proliferation. Collectively, our data provide mechanisms of a novel function of IgE which may contribute, at least in part, to airway remodeling observed in allergic asthma by directly inducing HASM cell proliferation.

Syk inhibits the activity of protein kinase A by phosphorylating tyrosine 330 of the catalytic subunit

The Syk protein-tyrosine kinase can have multiple effects on cancer cells, acting in some as a tumor suppressor by inhibiting motility and in others as a tumor promoter by enhancing survival. Phosphoproteomic analyses identified PKA as a Syk-specific substrate. Syk catalyzes the phosphorylation of the catalytic subunit of PKA (PKAc) both in vitro and in cells on Tyr-330. Tyr-330 lies within the adenosine-binding motif in the C-terminal tail of PKAc within a cluster of acidic amino acids (DDYEEEE), which is a characteristic of Syk substrates. The phosphorylation of PKAc on Tyr-330 by Syk strongly inhibits its catalytic activity. Molecular dynamics simulations suggest that this additional negative charge prevents the C-terminal tail from interacting with the substrate and the nucleotide-binding site to stabilize the closed conformation of PKAc, thus preventing catalysis from occurring. Phosphoproteomic analyses and Western blotting studies indicate that Tyr-330 can be phosphorylated in a Syk-dependent manner in MCF7 breast cancer cells and DT40 B cells. The phosphorylation of a downstream substrate of PKAc, cAMP-responsive element-binding protein (CREB), is inhibited in cells expressing Syk but can be rescued by a selective inhibitor of Syk. Modulation of CREB activity alters the expression of the CREB-regulated gene BCL2 and modulates cellular responses to genotoxic agents. Thus, PKA is a novel substrate of Syk, and its phosphorylation on Tyr-330 inhibits its participation in downstream signaling pathways.

The role of the TRAF-interacting protein in proliferation and differentiation

Ubiquitination of proteins is a post-translational modification, which decides on the cellular fate of the protein. Addition of ubiquitin moieties to proteins is carried out by the sequential action of three enzymes: E1, ubiquitin-activating enzyme; E2, ubiquitin-conjugating enzyme; and E3, ubiquitin ligase. The TRAF-interacting protein (TRAIP, TRIP, RNF206) functions as Really Interesting New Gene (RING)-type E3 ubiquitin ligase, but its physiological substrates are not yet known. TRAIP was reported to interact with TRAF [tumor necrosis factor (TNF) receptor-associated factors] and the two tumor suppressors CYLD and Syk (spleen tyrosine kinase). Ectopically expressed TRAIP was shown to inhibit nuclear factor-kappa B (NF-κB) signalling. However, recent results suggested a role for TRAIP in biological processes other than NF-κB regulation. Knock-down of TRAIP in human epidermal keratinocytes repressed cellular proliferation and induced a block in the G1/S phase of the cell cycle without affecting NF-κB signalling. TRAIP is necessary for embryonal development as mutations affecting the Drosophila homologue of TRAIP are maternal effect-lethal mutants, and TRAIP knock-out mice die in utero because of aberrant regulation of cell proliferation and apoptosis. These findings underline the tight link between TRAIP and cell proliferation. In this review, we summarize the data on TRAIP and put them into a larger perspective regarding the role of TRAIP in the control of tissue homeostasis.

Migration inhibition of mammary epithelial cells by Syk is blocked in the presence of DDR1 receptors

The non-receptor tyrosine kinase Syk is a well-characterized hematopoietic signal transducer, which is also expressed in non-hematopoietic cells. In epithelial cells, the function of Syk is not wholly known. It interacts with the receptor tyrosine kinase DDR1 and is frequently lost from metastatic mammary tumors. Here, using genetic tracing, we demonstrate Syk expression in murine mammary epithelium, myoepithelium and skin epithelium, but not in intestinal or lung epithelia. Investigating possible functions of Syk, we found a substantial suppression of cell mobility that depended on Syk kinase activity in trans-well migration and wounding assays. Co-expression of DDR1 resulted in constitutive interaction and strong activation of Syk kinase. Most importantly, Syk-mediated migration inhibition was blocked in the presence of DDR1, while conversely DDR1 knockdown restored migration inhibition. Our study identifies Syk as a potent inhibitor of epithelial migration and describes a first functional consequence of the interaction with the collagen receptor DDR1.

Spleen tyrosine kinase mediates BEAS-2B cell migration and proliferation and human rhinovirus-induced expression of vascular endothelial growth factor and interleukin-8

Spleen tyrosine kinase (Syk) is an immunoregulatory tyrosine kinase that was identified originally in leukocytes. It is a key regulator of innate immunity as well as hematopoietic cell differentiation and proliferation. A role for Syk in regulating normal cellular functions in nonhematopoietic cells is increasingly recognized. We have shown previously robust Syk expression in airway epithelium, where it regulates the early inflammatory response to human rhinovirus (HRV) infections, and HRV cell entry by clathrin-mediated endocytosis. To test the hypothesis that Syk plays a role in modulating airway epithelial cell proliferation, migration, and production of vascular endothelial growth factor and interleukin-8, we studied the BEAS-2B human bronchial epithelial cell line and primary human airway epithelia from normal and asthmatic donors using Syk-specific pharmacologic inhibitors and small interfering RNA. Using an in vitro "wounding" model, we demonstrated significant impairment of "wound" closure after treatment with the Syk inhibitors N4-(2,2-dimethyl-3-oxo-4H-pyrid[1,4]oxazin-6-yl)-5-fluoro-N2-(3,4,5-trimethoxyphenyl)-2,4-pyrimidinediamine (R406) and 2-[7-(3,4-dimethoxyphenyl)-imidazo[1,2-c]pyrimidin-5-ylamino]-nicotinamide dihydrochloride (BAY61-3606), overexpression of the kinase-inactive Syk(K396R) mutant, and Syk knockdown by small interfering RNA. HRV infection also impaired wound healing, an effect that was partly Syk-dependent because wound healing was impaired further when HRV infection occurred in the presence of Syk inhibition. Further investigation of potential regulatory mechanisms revealed that inhibition of Syk suppressed HRV-induced vascular endothelial growth factor expression while promoting the activation of caspase-3, a mediator of epithelial cell apoptosis. Together, these results indicate that Syk plays a role in promoting epithelial cell proliferation and migration, while mitigating the effects of apoptosis.

Quantitative phosphoproteomics revealed interplay between Syk and Lyn in the resistance to nilotinib in chronic myeloid leukemia cells

In this study, we have addressed how Lyn kinase signaling mediates nilotinib-resistance by quantitative phospho-proteomics using Stable Isotope Labeling with Amino acid in Cell culture. We have found an increased tyrosine phosphorylation of 2 additional tyrosine kinases in nilotinib-resistant cells: the spleen tyrosine kinase Syk and the UFO family receptor tyrosine kinase Axl. This increased tyrosine phosphorylation involved an interaction of these tyrosine kinases with Lyn. Inhibition of Syk by the inhibitors R406 or BAY 61-3606 or by RNA interference restored the capacity of nilotinib to inhibit cell proliferation. Conversely, coexpression of Lyn and Syk were required to fully induce resistance to nilotinib in drug-sensitive cells. Surprisingly, the knockdown of Syk also strongly decreased tyrosine phosphorylation of Lyn and Axl, thus uncovering interplay between Syk and Lyn. We have shown the involvement of the adaptor protein CDCP-1 in resistance to nilotinib. Interestingly, the expression of Axl and CDCP1 were found increased both in a nilotinib-resistant cell line and in nilotinib-resistant CML patients. We conclude that an oncogenic signaling mediated by Lyn and Syk can bypass the need of Bcr-Abl in CML cells. Thus, targeting these kinases may be of therapeutic value to override imatinib or nilotinib resistance in CML.

Alternative splicing of SYK regulates mitosis and cell survival

Most human genes produce multiple mRNA isoforms through alternative splicing. However, the biological relevance of most splice variants remains unclear. In this study, we evaluated the functional impact of alternative splicing in cancer cells. We modulated the splicing pattern of 41 cancer-associated splicing events and scored the effects on cell growth, viability and apoptosis, identifying three isoforms essential for cell survival. Specifically, changing the splicing pattern of the spleen tyrosine kinase gene (SYK) impaired cell-cycle progression and anchorage-independent growth. Notably, exposure of cancer cells to epithelial growth factor modulated the SYK splicing pattern to promote the pro-survival isoform that is associated with cancer tissues in vivo. The data suggest that splicing of selected genes is specifically modified during tumor development to allow the expression of isoforms that promote cancer cell survival.

Reactivation of Syk gene by AZA suppresses metastasis but not proliferation of breast cancer cells

Spleen tyrosine kinase (Syk) is reported to be involved in the suppression of proliferation and invasion of breast cancer. Methylation-mediated Syk gene silencing is found in a subset of breast cancer. In this study, we used a DNA methyltransferase inhibitor, 5-aza-2-deoxycytidine (AZA), to restore Syk expression of breast cancer cells. Surprisingly, we found that AZA treatment could reestablish the expression of Syk, but not affect the proliferation of breast cancer cells. Moreover, tumor formation in situ by MDA-MB-435s treated with (+) or without (-) AZA in a nude mice MFP (Mammary fat pad) model did not show significant difference, too. Interestingly, pulmonary metastasis was still significantly suppressed in MDA-MB-435s(+) group (1/9 vs. 7/9). Our findings suggested Syk may be more correlated to metastasis rather than proliferation. This study implied a potential use of Syk methylation as a valuable biomarker to detect high metastatic potential cancerous lesions and the prospect of AZA to join the arsenal of drug candidates to be developed as a new reagent for management of advanced breast cancer.

The TRAF-interacting protein (TRIP) is a regulator of keratinocyte proliferation

The TRAF-interacting protein (TRIP/TRAIP) is a RING-type E3 ubiquitin ligase inhibiting tumor necrosis factor-α (TNF-α)-mediated NF-κB activation. TRIP ablation results in early embryonic lethality in mice. To investigate TRIP function in epidermis, we examined its expression and the effect of TRIP knockdown (KD) in keratinocytes. TRIP mRNA expression was strongly downregulated in primary human keratinocytes undergoing differentiation triggered by high cell density or high calcium. Short-term phorbol-12-myristate-13-acetate (TPA) treatment or inhibition of phosphatidylinositol-3 kinase signaling in proliferative keratinocytes suppressed TRIP transcription. Inhibition by TPA was protein kinase C dependent. Keratinocytes undergoing KD of TRIP expression by lentiviral short-hairpin RNA (shRNA; T4 and T5) had strongly reduced proliferation rates compared with control shRNA. Cell cycle analysis demonstrated that TRIP-KD caused growth arrest in the G1/S phase. Keratinocytes with TRIP-KD resembled differentiated cells consistent with the augmented expression of differentiation markers keratin 1 and filaggrin. Luciferase-based reporter assays showed no increase in NF-κB activity in TRIP-KD keratinocytes, indicating that NF-κB activity in keratinocytes is not regulated by TRIP. TRIP expression was increased by ∼2-fold in basal cell carcinomas compared with normal skin. These results underline the important role of TRIP in the regulation of cell cycle progression and the tight linkage of its expression to keratinocyte proliferation.

Integration of genetic signature and TNM staging system for predicting the relapse of locally advanced colorectal cancer

PURPOSE

To identify potential genetic markers in treated stage II-III colorectal cancer patients and predict 3-year tumor relapse using statistical models based on important clinical factors and significant genetic markers.

METHODS

Gene expression profiling by cDNA-mediated Annealing, Selection, extension and Ligation assay was performed in a prospectively collected 95 stage II-III colorectal cancer patients with Fluorouracil-based adjuvant chemotherapy. We studied the gene expression level of 502 genes for patients with different outcomes. The prognostic effect of genetic signature was evaluated in multivariate analysis. We further integrated the genetic signature to clinical Classification of Malignant Tumors (TNM) staging system for predicting of 3-year tumor relapse.

RESULTS

An 8-gene signature was identified to well discriminate patients with different treatment outcomes. An integrated risk factor, which including 8-gene signature and TNM staging has been developed. ROC curve revealed that our integrated risk factor was better than genetic signature or current sixth edition TNM staging system alone.

CONCLUSIONS

Our 8-gene signature was promising in predicting 3-year disease-free survival rate for locally advanced colorectal cancer. The integrated risk factor, which combining genetic signature with clinical TNM staging system may further improve the outcome prediction.

In-depth analyses of kinase-dependent tyrosine phosphoproteomes based on metal ion-functionalized soluble nanopolymers

The ability to obtain in-depth understanding of signaling networks in cells is a key objective of systems biology research. Such ability depends largely on unbiased and reproducible analysis of phosphoproteomes. We present here a novel proteomics tool, polymer-based metal ion affinity capture (PolyMAC), for the highly efficient isolation of phosphopeptides to facilitate comprehensive phosphoproteome analyses. This approach uses polyamidoamine dendrimers multifunctionalized with titanium ions and aldehyde groups to allow the chelation and subsequent isolation of phosphopeptides in a homogeneous environment. Compared with current strategies based on solid phase micro- and nanoparticles, PolyMAC demonstrated outstanding reproducibility, exceptional selectivity, fast chelation times, and high phosphopeptide recovery from complex mixtures. Using the PolyMAC method combined with antibody enrichment, we identified 794 unique sites of tyrosine phosphorylation in malignant breast cancer cells, 514 of which are dependent on the expression of Syk, a protein-tyrosine kinase with unusual properties of a tumor suppressor. The superior sensitivity of PolyMAC allowed us to identify novel components in a variety of major signaling networks, including cell migration and apoptosis. PolyMAC offers a powerful and widely applicable tool for phosphoproteomics and molecular signaling.

Tumor suppressor function of Syk in human MCF10A in vitro and normal mouse mammary epithelium in vivo

The normal function of Syk in epithelium of the developing or adult breast is not known, however, Syk suppresses tumor growth, invasion, and metastasis in breast cancer cells. Here, we demonstrate that in the mouse mammary gland, loss of one Syk allele profoundly increases proliferation and ductal branching and invasion of epithelial cells through the mammary fat pad during puberty. Mammary carcinomas develop by one year. Syk also suppresses proliferation and invasion in vitro. siRNA or shRNA knockdown of Syk in MCF10A breast epithelial cells dramatically increased proliferation, anchorage independent growth, cellular motility, and invasion, with formation of functional, extracellular matrix-degrading invadopodia. Morphological and gene microarray analysis following Syk knockdown revealed a loss of luminal and differentiated epithelial features with epithelial to mesenchymal transition and a gain in invadopodial cell surface markers CD44, CD49F, and MMP14. These results support the role of Syk in limiting proliferation and invasion of epithelial cells during normal morphogenesis, and emphasize the critical role of Syk as a tumor suppressor for breast cancer. The question of breast cancer risk following systemic anti-Syk therapy is raised since only partial loss of Syk was sufficient to induce mammary carcinomas.

Role of the protein tyrosine kinase Syk in regulating cell-cell adhesion and motility in breast cancer cells

The expression of the Syk protein tyrosine kinase in breast cancer cells is inversely correlated with invasive growth and metastasis. The expression of Syk inhibits cell motility while supporting the formation of cell clusters by enhancing cell-cell contacts and promoting the redistribution of the adhesion proteins cortactin and vinculin to these contacts. Syk associates physically with cortactin and catalyzes its phosphorylation on tyrosine. The clustering of integrins leads to the phosphorylation of Syk and of numerous cellular proteins in a manner dependent on the activity of the kinase and on the presence of tyrosine 342 located in the linker B region. The ability of Syk to participate in integrin-mediated protein tyrosine phosphorylation correlates well with its ability to inhibit cell motility.

Phosphoproteomic analysis of Syk kinase signaling in human cancer cells reveals its role in cell-cell adhesion

The spleen tyrosine kinase Syk has predominantly been studied in hematopoietic cells in which it is involved in immunoreceptor-mediated signaling. Recently, Syk expression was evidenced in numerous nonhematopoietic cells and shown to be involved in tumor formation and progression. The Syk downstream signaling effectors in nonhematopoietic cells remain, however, to be uncovered, and were investigated using MS-based quantitative phosphoproteomics. Two strategies, based on the inhibition of the Syk catalytic activity and on the loss of Syk expression were employed to identify phosphotyrosine-dependent complexes. Quantitative measurements were obtained on 350 proteins purified with phosphotyrosine affinity columns using the SILAC method. Forty-one proteins are dependent on both Syk expression and catalytic activity and were selected as signaling effectors. They are involved in a variety of biological processes such as signal transduction, cell-cell adhesion and cell polarization. We investigated the functional involvement of Syk in cell-cell adhesion and demonstrated the phosphorylation of E-cadherin and alpha-catenin. In addition, Syk is localized at cell-cell contacts, and Syk-mediated phosphorylation of E-cadherin seems to be important for the proper localization of p120-catenin at adherens junctions. Identification of the biochemical pathways regulated by Syk in human cancer cells will help to uncover its role in tumor formation and progression.

Spleen tyrosine kinase as a novel candidate tumor suppressor gene for human oral squamous cell carcinoma

We analyzed the mutational and methylation status of the spleen tyrosine kinase (Syk) gene and both mRNA and protein levels in primary oral squamous cell carcinoma (OSCC) and OSCC-derived cell lines and examined the function of the Syk gene in OSCC-derived cell lines in vitro. Using quantitative real-time reverse transcription polymerase chain reaction, Western blotting and immunofluorescence on 7 OSCC-derived cell lines and normal oral keratinocytes (NOKs), Syk mRNA and protein expression were commonly downregulated in all cell lines compared to the NOKs. Although no sequence variation in the coding region of the Syk gene was identified in these cell lines, we found frequent hypermethylation in the CpG island region. Syk expression was restored by experimental demethylation. In addition, using a wound healing assay and in vitro invasion assay, we performed functional analysis using Syk transfected into the OSCC-derived cell lines, and they showed significant inhibition of motility and invasiveness. In clinical samples, high frequencies of Syk downregulation were detected by immunohistochemistry (33 of 53 [62%]). Furthermore, the Syk expression status was correlated significantly (p = 0.047) with tumor metastasis to cervical lymph nodes. These results suggest that the Syk gene is frequently inactivated during oral carcinogenesis and that an epigenetic mechanism may regulate loss of expression possibly leading to metastasis.

Spleen tyrosine kinase functions as a tumor suppressor in melanoma cells by inducing senescence-like growth arrest

Loss of tumor-suppressive pathways that control cellular senescence is a crucial step in malignant transformation. Spleen tyrosine kinase (Syk) is a cytoplasmic tyrosine kinase that has been recently implicated in tumor suppression of melanoma, a deadly skin cancer derived from pigment-producing melanocytes. However, the mechanism by which Syk suppresses melanoma growth remains unclear. Here, we report that reexpression of Syk in melanoma cells induces a p53-dependent expression of the cyclin-dependent kinase (cdk) inhibitor p21 and a senescence program. We first observed that Syk expression is lost in a subset of melanoma cell lines, primarily by DNA methylation-mediated gene silencing and restored after treatment with the demethylating agent 5-aza-2-deoxycytidine. We analyzed the significance of epigenetic inactivation of Syk and found that reintroduction of Syk in melanoma cells dramatically reduces clonogenic survival and three-dimensional tumor spheroid growth and invasion. Remarkably, melanoma cells reexpressing Syk display hallmarks of senescent cells, including reduction of proliferative activity and DNA synthesis, large and flattened morphology, senescence-associated beta-galactosidase activity, and heterochromatic foci. This phenotype is accompanied by hypophosphorylated retinoblastoma protein (Rb) and accumulation of p21, which depends on functional p53. Our results highlight a new role for Syk tyrosine kinase in regulating cellular senescence and identify Syk-mediated senescence as a novel tumor suppressor pathway the inactivation of which may contribute to melanoma tumorigenicity.

The protein-tyrosine kinase Syk interacts with TRAF-interacting protein TRIP in breast epithelial cells

The nonreceptor, protein-tyrosine kinase Syk is a suppressor of breast cancer progression whose expression is inversely correlated with the invasive behavior of cancer cells. In contrast, Syk has a positive function in murine mammary tumor virus-mediated tumorigenesis. A yeast two-hybrid screen using a library from human mammary gland identified tumor necrosis factor (TNF) receptor-associated factor-interacting protein (TRIP) as an Syk-binding partner. This interaction is mediated by the C-terminal region of TRIP and is enhanced by the treatment of cells with TNF and the tyrosine phosphorylation of Syk. Syk and TRIP have opposing functions in TNF-signaling pathways. Syk enhances the activation of nuclear factor-kappaB by TNF and this is antagonized by TRIP. The overexpression of TRIP sensitizes cells to TNF-induced apoptosis, an effect that can be reversed by the coexpression of Syk.

Syk tyrosine kinase is linked to cell motility and progression in squamous cell carcinomas of the head and neck

Syk, a non-receptor tyrosine kinase, is an important component of immunoreceptor signaling in hematopoietic cells. It has been implicated in key regulatory pathways including phosphoinositide 3-kinase and phospholipase Cgamma (PLCgamma) activation in B cells and integrin signaling in platelets and bronchial epithelial cells. Recently, potential roles in cancer have been reported. In breast cancers, reduced Syk expression was associated with invasion, and its overexpression in cell lines was shown to inhibit cell motility. In contrast, Syk has been shown to mediate chemomigration in nasopharyngeal carcinoma cells. Its role in squamous cell carcinomas of the head and neck (SCCHN) has not yet been investigated. Syk mRNA and protein expression was detected in 6 of 10 SCCHN cell lines. When Syk was transfected into Syk-negative cells (SIHN-011A), chemomigration was enhanced in vitro and this was associated with activation of PLCgamma1. Conversely, abrogation of Syk activity by pharmacologic inhibition or small interfering RNA in HN6 cells with high levels of endogenous expression inhibited migration, haptotaxis, and engagement with matrix proteins; this was accompanied by decreased levels of phosphorylated AKT. Similar effects were seen in Syk-positive CAL 27 cells but not in Syk-negative SIHN-011A cells. Immunoprecipitation suggested co-association of Syk with epidermal growth factor receptor and GRB-2. Syk expression in SCCHN patient tissues was examined by semiquantitative real-time PCR (n = 45) and immunohistochemistry (n = 38) in two independent cohorts. Higher levels of Syk expression were observed in tumors and lymph node metastases relative to normal tissues. High Syk expression significantly correlated with worse survival and may be of prognostic value in SCCHN due to its potential role in cell migration and invasion.