<p>The protein tyrosine phosphatase 1B (<i>PTP1B</i>), a non-transmembrane protein tyrosine phosphatase, has been implicated in gastric pathogenesis. Several lines of recent evidences have shown that <i>PTP1B</i> is highly amplified in breast and prostate cancers. The aim of this study was to investigate <i>PTP1B</i> amplification in gastric cancer and its association with poor prognosis of gastric cancer patients, and further determine the role of <i>PTP1B</i> in gastric tumorigenesis. Our data demonstrated that <i>PTP1B</i> was significantly up-regulated in gastric cancer tissues as compared with matched normal gastric tissues by using quantitative RT-PCR (qRT-PCR) assay. In addition, copy number analysis showed that <i>PTP1B</i> was amplified in 68/131 (51.9%) gastric cancer cases, whereas no amplification was found in the control subjects. Notably, <i>PTP1B</i> amplification was positively associated with its protein expression, and was significantly related to poor survival of gastric cancer patients. Knocking down <i>PTP1B</i> expression in gastric cancer cells significantly inhibited cell proliferation, colony formation, migration and invasion, and induced cell cycle arrested and apoptosis. Mechanically, <i>PTP1B</i> promotes gastric cancer cell proliferation, survival and invasiveness through modulating Src-related signaling pathways, such as Src/Ras/MAPK and Src/phosphatidylinositol-3-kinase (PI3K)/Akt pathways. Collectively, our data demonstrated frequent overexpression and amplification <i>PTP1B</i> in gastric cancer, and further determined the oncogenic role of <i>PTP1B</i> in gastric carcinogenesis. Importantly, <i>PTP1B</i> amplification predicts poor survival of gastric cancer patients.</p
