Hypermethylation of Syk gene in promoter region associated with oncogenesis and metastasis of gastric carcinoma

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.

Identification of a Novel Protein-Based Prognostic Model in Gastric Cancers

Gastric cancer (GC) is the third leading cause of cancer-related deaths worldwide. However, there are still no reliable biomarkers for the prognosis of this disease. This study aims to construct a robust protein-based prognostic prediction model for GC patients. The protein expression data and clinical information of GC patients were downloaded from the TCPA and TCGA databases, and the expressions of 218 proteins in 352 GC patients were analyzed using bioinformatics methods. Additionally, Kaplan-Meier (KM) survival analysis and univariate and multivariate Cox regression analysis were applied to screen the prognosis-related proteins for establishing the prognostic prediction risk model. Finally, five proteins, including NDRG1_pT346, SYK, P90RSK, TIGAR, and XBP1, were related to the risk prognosis of gastric cancer and were selected for model construction. Furthermore, a significant trend toward worse survival was found in the high-risk group (p = 1.495 × 10-7). The time-dependent ROC analysis indicated that the model had better specificity and sensitivity compared to the clinical features at 1, 2, and 3 years (AUC = 0.685, 0.673, and 0.665, respectively). Notably, the independent prognostic analysis results revealed that the model was an independent prognostic factor for GC patients. In conclusion, the robust protein-based model based on five proteins was established, and its potential benefits in the prognostic prediction of GC patients were demonstrated.

Targeting the splicing isoforms of spleen tyrosine kinase affects the viability of colorectal cancer cells

Spleen tyrosine kinase (Syk) expression have been both positively and negatively associated with tumorigenesis. Our goal was to evaluate the contribution of Syk and its two splice variants, full length Syk (L) and short isoform Syk (S), in the tumor biology of colorectal cancer cells (CRC). The analysis of Syk expression in primary human colorectal tumors, as well as the analysis of TCGA database, revealed a high Syk mRNA expression score in colorectal cancer tumors, suggesting a tumor promotor role of Syk in CRC. Our analysis showed that Syk (L) isoform is highly expressed in the majority of the tumor tissues and that it remains expressed in tumors in which global Syk expression is downregulated, suggesting the dependence of tumors to Syk (L) isoform. We also identified a small cluster of tumor tissues, which express a high proportion of Syk (S) isoform. This specific cluster is associated with overexpressed genes related to translation and mitochondria, and down regulated genes implicated in the progression of mitosis. For our functional studies, we used short hairpin RNA tools to target the expression of Syk in CRC cells bearing the activating K-Ras (G13D) mutation. Our results showed that while global Syk knock down increases cell proliferation and cell motility, Syk (L) expression silencing affects the viability and induces the apoptosis of the cells, confirming the dependence of cells on Syk (L) isoform for their survival. Finally, we report the promising potential of compound C-13, an original non-enzymatic inhibitor of Syk isolated in our group. In vitro studies showed that C-13 exerts cytotoxic effects on Syk-positive CRC cells by inhibiting their proliferation and their motility, and by inducing their apoptosis, while Syk-negative cell lines viability was not affected. Moreover, the oral and intraperitoneal administration of C-13 reduced the tumor growth of CRC DLD-1 cells xenografts in Nude mice in vivo.

Analysis of SYK Gene as a Prognostic Biomarker and Suggested Potential Bioactive Phytochemicals as an Alternative Therapeutic Option for Colorectal Cancer: An In-Silico Pharmaco-Informatics Investigation

BACKGROUND

SYK gene regulates the expression of SYK kinase (Spleen tyrosine kinase), an important non-receptor protein-tyrosine kinase for immunological receptor-mediated signaling, which is also considered a tumor growth metastasis initiator. An onco-informatics analysis was adopted to evaluate the expression and prognostic value of the SYK gene in colorectal cancer (CRC), the third most fatal cancer type; of late, it may be a biomarker as another targeted site for CRC. In addition, identify the potential phytochemicals that may inhibit the overexpression of the SYK kinase protein and minimize the human CRC.

MATERIALS & METHODS

The differential expression of the SYK gene was analyzed using several transcriptomic databases, including Oncomine, UALCAN, GENT2, and GEPIA2. The server cBioPortal was used to analyze the mutations and copy number alterations, whereas GENT2, Gene Expression Profiling Interactive Analysis (GEPIA), Onco-Lnc, and PrognoScan were used to examine the survival rate. The protein-protein interaction network of SYK kinase and its co-expressed genes was conducted via Gene-MANIA. Considering the SYK kinase may be the targeted site, the selected phytochemicals were assessed by molecular docking using PyRx 0.8 packages. Molecular interactions were also observed by following the Ligplot+ version 2.2. YASARA molecular dynamics simulator was applied for the post-validation of the selected phytochemicals.

RESULTS

Our result reveals an increased level of mRNA expression of the SYK gene in colorectal adenocarcinoma (COAD) samples compared to those in normal tissues. A significant methylation level and various genetic alterations recurrence of the SYK gene were analyzed where the fluctuation of the SYK alteration frequency was detected across different CRC studies. As a result, a lower level of SYK expression was related to higher chances of survival. This was evidenced by multiple bioinformatics platforms and web resources, which demonstrated that the SYK gene can be a potential biomarker for CRC. In this study, aromatic phytochemicals, such as kaempferol and glabridin that target the macromolecule (SYK kinase), showed higher stability than the controls, and we have estimated that these bioactive potential phytochemicals might be a useful option for CRC patients after the clinical trial.

CONCLUSIONS

Our onco-informatics investigation suggests that the SYK gene can be a potential prognostic biomarker of CRC. On the contrary, SYK kinase would be a major target, and all selected compounds were validated against the protein using in-silico drug design approaches. Here, more in vitro and in vivo analysis is required for targeting SYK protein in CRC.

Spleen Tyrosine Kinase as a Target Therapy for Pseudomonas aeruginosa Infection

Spleen tyrosine kinase (SYK) is a nonreceptor tyrosine kinase which associates directly with extracellular receptors, and is critically involved in signal transduction pathways in a variety of cell types for the regulation of cellular responses. SYK is expressed ubiquitously in immune and nonimmune cells, and has a much wider biological role than previously recognized. Several studies have highlighted SYK as a key player in the pathogenesis of a multitude of diseases. Pseudomonas aeruginosa is an opportunistic gram-negative pathogen, which is responsible for systemic infections in immunocompromised individuals, accounting for a major cause of severe chronic lung infection in cystic fibrosis patients and subsequently resulting in a progressive deterioration of lung function. Inhibition of SYK activity has been explored as a therapeutic option in several allergic disorders, autoimmune diseases, and hematological malignancies. This review focuses on SYK as a therapeutic target, and describes the possibility of how current knowledge could be translated for therapeutic purposes to regulate the immune response to the opportunistic pathogen P. aeruginosa.

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.

Phosphorylation of spleen tyrosine kinase at tyrosine 348 (pSyk³⁴⁸) may be a marker of advanced phase of Chronic Myeloid Leukemia (CML)

We investigated Syk as a potential marker of CML progression. We observed a significant over-expression of Syk mRNA and constitutive phosphorylation of Syk Y348 in blast cells from six AP or BP-CML, but not in 15 CML in chronic phase. We could follow in vivo the recurrence of pSyk(348) throughout blast cell escape, despite observing storage of dasatinib in blast cells. A combination of dasatinib and R406 did not improve therapeutic efficacy in vitro. Our results strongly suggest that Syk activation could be a relevant biomarker of disease progression and dasatinib resistance but is probably not a molecular target.

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.

Hypermethylation and prognostic implication of Syk gene in human colorectal cancer

The study was aimed to investigate the relationship between hypermethylation of Syk gene and clinicopathological characteristics and long-term outcomes in colorectal cancer. The effect of Syk on cell proliferation and invasion ability was also assessed. Methylation and expression status of Syk were explored in CRC tissues and cell lines by MSP, qRT-PCR and western blot assay. The effects of Syk overexpression on tumorigenesis were studied by in vitro assay. The correlation between Syk methylation and clinical relevance in CRC patients was also analyzed. Syk methylation was found 48.6 % in CRC tissue samples and 57.1 % in cell lines, respectively. The loss of Syk expression could be restored by demethylation agent. Overexpression of Syk in CRC cell inhibited cell proliferation (p < 0.01) and invasion (p < 0.01). The methylation of Syk was significantly associated with histological grade (p = 0.002), lymph node status (p < 0.001) and TNM stage (p < 0.001). Five-year overall survival in methylated Syk group was significantly lower than that in unmethylated Syk group (59 vs. 80 %, p < 0.001). Multivariate analysis demonstrated that Syk methylation was an independent prognostic factor for overall survival. Syk is identified as a potential tumor suppressor in CRC progression. Syk methylation is correlated with poor overall survival, which acts as an independent prognostic indicator of CRC.

Serum spleen tyrosine kinase and vascular endothelial growth factor-C levels predict lymph node metastasis of oesophageal squamous cell carcinoma

OBJECTIVES

Lymph node involvement is a key feature and an independent prognostic factor of oesophageal squamous cell carcinoma. However, an accurate and robust assay to predict the lymphatic spread of oesophageal squamous cell carcinoma is unavailable. The purpose of this study was to determine whether serum vascular endothelial growth factor-C (VEGF-C) and spleen tyrosine kinase levels are potential markers of lymph node metastasis in patients with oesophageal squamous cell carcinoma.

METHODS

In the study, 108 patients with oesophageal squamous cell carcinoma and 24 healthy subjects participated. Serum spleen tyrosine kinase and VEGF-C concentrations were examined by enzyme-linked immunosorbent assays.

RESULTS

Patients with oesophageal squamous cell carcinoma had significantly elevated VEGF-C and decreased spleen tyrosine kinase in serum when compared with normal controls (P < 0.05). Pearson's correlation analysis revealed that serum spleen tyrosine kinase was negatively correlated with the serum VEGF-C level in oesophageal squamous cell carcinoma patients (r = -0.453, P = 0.000). In addition, surgical resections of the oesophageal tumour profoundly brought both serum spleen tyrosine kinase and VEGF-C closer to the normal range at 2 weeks after operation (P < 0.05). Statistical analysis showed that enhanced serum VEGF-C and reduced spleen tyrosine kinase significantly correlated with the stage of regional lymph node metastasis, tumour size and the status of primary tumour extension, but not with other clinicopathological features of the patients (P < 0.05).

CONCLUSIONS

Our data suggest that both serum spleen tyrosine kinase and VEGF-C levels are valuable in the preoperative evaluation of lymph node metastasis in patients with oesophageal squamous cell carcinoma.

Involvement of the Syk-mTOR pathway in follicular lymphoma cell invasion and angiogenesis

Follicular lymphoma (FL) is the second-most common non-Hodgkin's lymphoma. The disease affects the lymph nodes, and 50% of patients present with bone marrow infiltration; however, the mechanisms involved in dissemination of the disease are not yet known. We previously reported that FL cells display an overexpression of Syk, a tyrosine kinase involved in many cellular processes including cell migration. Therefore, we sought to explore its role in the invasive process. Here, we show that FL patients display higher matrix metalloproteinase (MMP)-9 and vascular endothelial growth factor (VEGF) levels than healthy donors. Moreover, using Syk small interfering RNA and the Syk inhibitor R406, we demonstrate that, in FL cells, Syk is involved in the regulation of MMP-9 and VEGF expression, and that invasion and angiogenesis is mediated through a phosphatidylinositol-3 kinase (PI3K)-mammalian target of rapamycin module. Finally, using a FL xenograft mouse model we observe that fostamatinib (R788), inhibits MMP-9 expression and angiogenesis in vivo. Altogether, this study provides strong evidence that Syk represents an encouraging therapeutic target in FL and suggests the potential use of fostamatinib as an anti-invasive and anti-angiogenic drug.

The role of Syk kinase in ultraviolet-mediated skin damage

BACKGROUND

Ultraviolet (UV) irradiation is the main cause of skin photodamage; the resulting modulation of matrix metalloproteinases (MMPs) leads to collagen degradation. There is no easily accessible molecular indicator of early skin UV damage.

OBJECTIVES

In this study, we investigated the effects of Syk kinase on MMP expression and evaluated the sensitivity and usefulness of Syk as an early indicator of skin UV damage.

METHODS

Human dermal fibroblasts (HDFs) were transfected with Syk cDNA to overexpress Syk. MMP-1 expression and Syk activity were determined by Western blot after UV exposure. The effect of Syk on MMP-1 expression in HDFs was further explored by either Syk siRNA or a selective Syk inhibitor. Possible downstream molecules of Syk were also evaluated in HDFs upon UV exposure. The relationship between Syk and collagenase was further explored in vivo (MMP-13, hairless mice).

RESULTS

Our studies in HDFs demonstrated that both a Syk inhibitor and Syk siRNA were able to inhibit MMP-1 expression in HDFs exposed to UV and that overexpression of Syk increased MMP-1 expression and the activity of JNK kinase, but not p38 or Erk1/2 MAP kinase. UV exposure enhanced both expression and activity of Syk in HDFs. Experiments with hairless mice suggested that Syk expression is an earlier indicator of UV exposure than MMP-13 expression.

CONCLUSIONS

Our results demonstrate that Syk expression correlates well with increase of MMPs (MMP-1 in humans and MMP-13 in mice) in response to UV exposure. The findings suggest that Syk may be a novel target for the prevention and treatment of skin photodamage by modulating MMPs.

Advances in melanoma senescence and potential clinical application

Normal cells possess a limited proliferative life span, after which they enter a state of irreversible growth arrest, called replicative senescence, which acts as a potent barrier against transformation. Transformed cells have escaped the process of replicative senescence and theoretically can not re-enter senescence. However, recent observations showed that transformed cells, and particularly the melanoma cells, can still undergo oncogene or stress-induced senescence. This senescence state is accompanied by many of the markers associated with replicative senescence, such as flattened shape, increased acidic β-galactosidase activity, characteristic changes in gene expression and growth arrest. Interestingly, in some cancers, senescence induction following chemotherapy has been correlated with a favorable patient outcome. In this review, we gathered recent results describing senescence-like phenotype induction in melanoma cells and discuss why senescence may also be exploited as a therapeutic strategy in melanoma.

Analysis of Syk expression in bovine lymphoma and persistent lymphocytosis induced by bovine leukemia virus

Spleen tyrosine kinase (Syk) is closely related to various cell reactions. In B-cells, Syk is involved in early B-cell receptor signaling, which affects cellular survival, proliferation and differentiation. Although the kinetics of Syk mRNA and its activity are variable in different types of tumor cells, Syk may have a relation to tumor progression in many human tumors, including B-cell lymphoma/leukemia. In this study we examined whether Syk mRNA expression was changed in bovine leukemia virus (BLV)-induced persistent lymphocytosis (PL) and lymphoma. As a result, we demonstrated that the Syk mRNA expression was significantly increased in PL samples, whereas it was decreased in tumor samples. Moreover one cow, which Syk mRNA expression has been lowest among PL cattle, developed lymphoma three months later and the expression significantly decreased. These data suggest that Syk mRNA expression dynamics is closely related to BLV-induced disease.

Spleen tyrosine kinases: biology, therapeutic targets and drugs

Spleen tyrosine kinase (Syk) is an intriguing protein tyrosine kinase involved in signal transduction in a variety of cell types, and its aberrant regulation is associated with different allergic disorders and antibody-mediated autoimmune diseases such as rheumatoid arthritis, asthma and allergic rhinitis. Syk also plays an important part in the uncontrolled growth of tumor cells, particularly B cells. For these reasons, Syk is considered one of the most interesting biological targets of the last decade, as proved by the great number of papers and patents published, and the possibility of treating these pathologies by means of Syk kinase inhibitors has led to a great interest from the pharmaceutical and biotech industry.

Syk tyrosine kinase acts as a pancreatic adenocarcinoma tumor suppressor by regulating cellular growth and invasion

We have identified the nonreceptor tyrosine kinase syk as a marker of differentiation/tumor suppressor in pancreatic ductal adenocarcinoma (PDAC). Syk expression is lost in poorly differentiated PDAC cells in vitro and in situ, and stable reexpression of syk in endogenously syk-negative Panc1 (Panc1/syk) cells retarded their growth in vitro and in vivo and reduced anchorage-independent growth in vitro. Panc1/syk cells exhibited a more differentiated morphology and down-regulated cyclin D1, akt, and CD171, which are overexpressed by Panc1 cells. Loss of PDAC syk expression in culture is due to promoter methylation, and reversal of promoter methylation caused reexpression of syk and concomitant down-regulation of CD171. Moreover, suppression of syk expression in BxPC3 cells caused de novo CD171 expression, consistent with the reciprocal expression of syk and CD171 we observe in situ. Importantly, Panc1/syk cells demonstrated dramatically reduced invasion in vitro. Affymetrix analysis identified statistically significant regulation of >2000 gene products by syk in Panc1 cells. Of these, matrix metalloproteinase-2 (MMP2) and tissue inhibitor of metalloproteinase-2 were down-regulated, suggesting that the MMP2 axis might mediate Panc1/mock invasion. Accordingly, MMP2 inhibition suppressed the in vitro invasion of Panc1/mock cells without effect on Panc1/syk cells. This study demonstrates a prominent role for syk in regulating the differentiation state and invasive phenotype of PDAC cells.

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.

Hepatitis C virus NS5A protein interacts with and negatively regulates the non-receptor protein tyrosine kinase Syk

Hepatitis C virus (HCV) is the major causative agent of hepatocellular carcinoma. However, the precise mechanism underlying the carcinogenesis is yet to be elucidated. It has recently been reported that Syk, a non-receptor protein tyrosine kinase, functions as a potent tumour suppressor in human breast carcinoma. This study first examined the possible effect of HCV infection on expression of Syk in vivo. Immunohistochemical analysis revealed that endogenous Syk, which otherwise was expressed diffusely in the cytoplasm of normal hepatocytes, was localized near the cell membrane with a patchy pattern in HCV-infected hepatocytes. The possible interaction between HCV proteins and Syk in human hepatoma-derived Huh-7 cells was then examined. Immunoprecipitation analysis revealed that NS5A interacted strongly with Syk. Deletion-mutation analysis revealed that an N-terminal portion of NS5A (aa 1-175) was involved in the physical interaction with Syk. An in vitro kinase assay demonstrated that NS5A inhibited the enzymic activity of Syk and that, in addition to the N-terminal 175 residues, a central portion of NS5A (aa 237-302) was required for inhibition of Syk. Moreover, Syk-mediated phosphorylation of phospholipase C-gamma1 was downregulated by NS5A. An interaction of NS5A with Syk was also detected in Huh-7.5 cells harbouring an HCV RNA replicon or infected with HCV. In conclusion, these results demonstrated that NS5A interacts with Syk resulting in negative regulation of its kinase activity. The results indicate that NS5A may be involved in the carcinogenesis of hepatocytes through the suppression of Syk kinase activities.

Epigenetic contributions to cancer metastasis

The molecular basis of cancer encompasses both genetic and epigenetic alterations. These epigenetic changes primarily involve global DNA methylation changes in the form of widespread loss of methylation along with concurrent hypermethylation events in gene regulatory regions that can repress tissue-specific gene expression. Increasingly, the importance of these epigenetic changes to the metastatic process is being realized. Cells may acquire an epi-genotype that permits their dissemination from the primary tumour mass or the ability to survive and proliferate at a secondary tissue site. These epigenetic changes may be cancer-type specific, or in some cases may involve a common target gene providing a selective advantage to multiple metastatic cell types. In this review, I examine the growing volume of literature related to the epigenetic contributions to cancer metastasis. I discuss the functional importance of these epigenetic phenomena and how new epigenetic biomarkers may permit the identification of diagnostic signatures of metastasis and the development of new cancer therapies.

Spleen tyrosine kinase (Syk) as a novel target for allergic asthma and rhinitis

Allergic asthma and rhinitis are prevalent diseases in the modern world, both marked by inflammation of the airways. The spleen tyrosine kinase (Syk) plays a critical role in the regulation of such immune and inflammatory responses. Although Syk is best known as a key component of immunoreceptor signalling complexes in leukocytes, recent studies demonstrated Syk expression in cells outside the haematopoietic lineage. Moreover, in recent years, it has been established that Syk is involved in various signalling cascades including those originating from integrin and cytokine receptors. Thus, Syk likely has a much wider biological role than previously recognised. Specific inhibition of Syk using aerosolised antisense oligonucleotides in liposome complexes significantly decreased lung inflammatory responses in experimental asthma and acute lung injury models. In addition, pharmacological inhibitors of Syk have been recently developed with potential for use as therapeutics. However, in the development and the rational delivery of drugs targeting Syk, it is important to consider the multiple cell types that express this kinase and the potential effects of its inhibition on various physiological functions. This review focuses on the recent data and the emerging ideas about Syk as a therapeutic target.

Deregulated Syk inhibits differentiation and induces growth factor-independent proliferation of pre-B cells

The nonreceptor protein spleen tyrosine kinase (Syk) is a key mediator of signal transduction in a variety of cell types, including B lymphocytes. We show that deregulated Syk activity allows growth factor–independent proliferation and transforms bone marrow–derived pre–B cells that are then able to induce leukemia in mice. Syk-transformed pre–B cells show a characteristic pattern of tyrosine phosphorylation, increased c-Myc expression, and defective differentiation. Treatment of Syk-transformed pre–B cells with a novel Syk-specific inhibitor (R406) reduces tyrosine phosphorylation and c-Myc expression. In addition, R406 treatment removes the developmental block and allows the differentiation of the Syk-transformed pre–B cells into immature B cells. Because R406 treatment also prevents the proliferation of c-Myc–transformed pre–B cells, our data indicate that endogenous Syk kinase activity may be required for the survival of pre–B cells transformed by other oncogenes. Collectively, our data suggest that Syk is a protooncogene involved in the transformation of lymphocytes, thus making Syk a potential target for the treatment of leukemia.

The future of antisense oligonucleotides in the treatment of respiratory diseases

Antisense oligonucleotides (ASO) are short synthetic DNA molecules designed to inhibit translation of a targeted gene to protein via interaction with messenger RNA. More recently, small interfering (si)RNA have been developed as potent tools to specifically inhibit gene expression. ASO directed against signaling molecules, cytokine receptors, and transcription factors involved in allergic immune and inflammatory responses, have been applied in experimental models of asthma and demonstrate potential as therapeutics. Several ASO-based drugs directed against oncogenes have been developed for therapy of lung cancer, and some have recently reached clinical trials. ASO and siRNA to respiratory syncytial virus infection have demonstrated good potential to treat this condition, particularly in combination with an antiviral drug. Although ASO-based therapeutics are promising for lung diseases, issues of specificity, identification of correct molecular targets, delivery and carrier systems, as well as potential adverse effects must be carefully evaluated before clinical application.

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Nucleocytoplasmic trafficking of the Syk protein tyrosine kinase

The protein tyrosine kinase Syk couples the B-cell receptor (BCR) for antigen to multiple intracellular signaling pathways and also modulates cellular responses to inducers of oxidative stress in a receptor-independent fashion. In B cells, Syk is found in both the nuclear and cytoplasmic compartments but contains no recognizable nuclear localization or export signals. Through the analysis of a series of deletion mutants, we identified the presence of an unconventional shuttling sequence near the junction of the catalytic domain and the linker B region that accounts for Syk's subcellular localization. This localization is altered following prolonged engagement of the BCR, which causes Syk to be excluded from the nucleus. Nuclear exclusion requires the receptor-mediated activation of protein kinase C and new protein synthesis. Both of these processes also potentiate the activation of caspase 3 in cells in response to oxidative stress in a manner that is dependent on the localization of Syk outside of the nucleus. In contrast, restriction of Syk to the nucleus greatly diminishes the stress-induced activation of caspase 3.

Differential expression of spleen tyrosine kinase Syk isoforms in tissues: effects of the microbial flora

Spleen tyrosine kinase (Syk) is expressed widely in hematopoietic and non-hematopoietic cells. The widespread distribution of Syk and its involvement in host defense and allergic reactions, prompted us analyze the influence of microbial exposure on Syk expression. We compared the distribution of Syk in various tissues of germ-free and conventional mice using immunohistochemistry, Western blot analysis and real time RT-PCR. Total Syk expression was similar between germ-free and conventional mice. Since it has been claimed that Syk isoforms are differentially expressed, we studied the distribution and abundance of Syk (L) and Syk (S) isoforms in tissues from these mice. In contrast to previous reports, we found broad tissue expression of Syk (S). Interestingly, in germ-free mice the amount of Syk (S) but not Syk L protein was selectively increased in lung and spleen. In summary, our study reveals new and broad tissue expression of both Syk isoforms and demonstrates that lack of microbial flora results in selectively increased expression of Syk (S) isoform in lung and spleen.

The Syk tyrosine kinase: a new negative regulator in tumor growth and progression

The spleen tyrosine kinase Syk was long thought to be a hematopoietic cell-specific signaling molecule. Recent evidence demonstrated that it is also expressed by many non-hematopoietic cell types and that it plays a negative role in cancer. A significant drop in its expression was first observed during breast cancer progression, but an anomalous Syk expression has now also been evidenced in many other tumor types. Mechanistic studies using Syk re-expression demonstrated its suppressive function in tumorigenesis and metastasis formation, which is surprising for a tyrosine kinase. Loss of Syk expression is regulated, albeit not exclusively, by its promoter hypermethylation. The molecular mechanism of its tumor-suppressive function remains largely unknown; the identification of its activators and effectors in non-hematopoietic cells will be a challenge for the years to come. An increasing number of clinical studies reveal a correlation between reduced Syk expression and an increased risk for metastasis formation, and assign Syk as a potential new prognostic marker in different tumor types.

The Syk tyrosine kinase localizes to the centrosomes and negatively affects mitotic progression

We showed previously that the spleen tyrosine kinase Syk is expressed by mammary epithelial cells and that it suppresses malignant growth of breast cancer cells. The exact molecular mechanism of its tumor-suppressive activity remains, however, to be identified. Here, we show that Syk colocalizes and copurifies with the centrosomal component gamma-tubulin and exhibits a catalytic activity within the centrosomes. Moreover, its centrosomal localization depends on its intact kinase activity. Centrosomal Syk expression is persistent in interphase but promptly drops during mitosis, obviously resulting from its ubiquitinylation and proteasomal degradation. Conversely, unrestrained exogenous expression of a fluorescently tagged Discosoma sp. red fluorescent protein (DsRed)-Syk chimera engenders abnormal cell division and cell death. Transient DsRed-Syk overexpression triggers an abrupt cell death lacking hallmarks of classic apoptosis but reminiscent of mitotic catastrophe. Surviving stable DsRed-Syk-transfected cells exhibit multipolar mitotic spindles and contain multiple abnormally sized nuclei and supernumerary centrosomes, revealing anomalous cell division. Taken together, these results show that Syk is a novel centrosomal kinase that negatively affects cell division. Its expression is strictly controlled in a spatiotemporal manner, and centrosomal Syk levels need to decline to allow customary progression of mitosis.

The non-receptor-associated tyrosine kinase Syk is a regulator of metastatic behavior in human melanoma cells

Melanoma is one of the most aggressive neoplastic transformations and characterized by a high metastatic potential. The current study was performed to assess the impact of "spleen tyrosine kinase" (Syk), a non-receptor-associated tyrosine kinase, on growth and metastatic behavior of melanoma cells in vitro and in a severe combined immunodeficient (SCID)-mouse/human-melanoma xenotransplantation model in vivo. Syk was expressed in melanocytes but was found to be downregulated in melanoma cells. Vector-driven expression of Syk in two different melanoma cell lines did not influence growth speed, but significantly reduced the invasive growth potential of both cell lines in a Matrigel assay in vitro. In a SCID-mouse/human melanoma xenotransplantation model, Syk expressing Mel-Juso cells exhibited delayed and reduced tumor growth. After intravenous as well as subcutaneous injection of tumor cells, Syk-transfected cells formed significantly fewer metastatic tumor lesions than control cells. The presented data define Syk as a novel regulator of metastatic behavior of melanoma cells.

Survey of differentially methylated promoters in prostate cancer cell lines

DNA methylation and copy number in the genomes of three immortalized prostate epithelial and five cancer cell lines (LNCaP, PC3, PC3M, PC3M-Pro4, and PC3M-LN4) were compared using a microarray-based technique. Genomic DNA is cut with a methylation-sensitive enzyme HpaII, followed by linker ligation, polymerase chain reaction (PCR) amplification, labeling, and hybridization to an array of promoter sequences. Only those parts of the genomic DNA that have unmethylated restriction sites within a few hundred base pairs generate PCR products detectable on an array. Of 2732 promoter sequences on a test array, 504 (18.5%) showed differential hybridization between immortalized prostate epithelial and cancer cell lines. Among candidate hypermethylated genes in cancer-derived lines, there were eight (CD44, CDKN1A, ESR1, PLAU, RARB, SFN, TNFRSF6, and TSPY) previously observed in prostate cancer and 13 previously known methylation targets in other cancers (ARHI, bcl-2, BRCA1, CDKN2C, GADD45A, MTAP, PGR, SLC26A4, SPARC, SYK, TJP2, UCHL1, and WIT-1). The majority of genes that appear to be both differentially methylated and differentially regulated between prostate epithelial and cancer cell lines are novel methylation targets, including PAK6, RAD50, TLX3, PIR51, MAP2K5, INSR, FBN1, and GG2-1, representing a rich new source of candidate genes used to study the role of DNA methylation in prostate tumors.