Abstract
61 Background: The SH2-containing protein tyrosine phosphatase 1 (SHP1) is an important negative regulator in cytokine-mediated signal transduction and cell cycling. Recent studies demonstrated that promoter methylation of SHP1 is frequently observed in gastric adenocarcinoma tissues. We tried in this in vitrostudy to reveal promoter hypermethylation and to investigate the effects of SHP1 in gastric carcinoma cell lines. Methods: We performed RT-PCR, Western blot, methylation specific PCR (MSP) and bisulfite pyrosequencing to demonstrate promoter hypermethylation of SHP1. To evaluate functional roles of SHP1, we transfected SHP1 plasmid and analyzed WST-1 assay, wound closure assay and Matrigel invasion assay. Results: We observed that both gene and protein expression of SHP1 were negative in 8 of 10 gastric cancer cell lines (SNU-1, SNU-5, SNU-16, SNU-638, SNU-719, MKN-28, MKN-45, AGS). MSP showed methylation-specific band only in all 10 gastric cancer lines. Bisulfite pyrosequencing revealed 96.5% and 97.3% of methylation frequency in AGS and SNU-719 cells. When treating SNU-719, MKN-28 and AGS cells with 5-Aza-2’-deoxycytidine (5-Aza-dc), SHP1 was re-expressed in all three cells. SHP1 expression is known to be correlated with Janus kinase (JAK) and signal transducers and activators of transcription (STAT) signaling pathway in epithelial cells. When introducing exogenous SHP1 in SNU-719 and MKN-28 cells by transient transfection, protein expression of constitutive phospho-JAK2 (Tyr 1007/1008) and phospho-STAT3 (Tyr 705) were substantially down-regulated both, which in turn decreased target gene expression of STAT3, including cyclin D1, MMP-9, VEGF and survivin. Induction of SHP1 significantly inhibited cell proliferation, migration and invasion in SNU-719 and MKN-28 cells. Conclusions: Epigenetic silencing of SHP1 is frequently caused by promoter hypermethylation in gastric carcinoma cell lines. Overexpression of SHP1 down-regulates JAK2/STAT3 pathway to modulate various target genes and inhibit cell proliferation, migration and invasion in gastric cancer cells.
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