Roles of XB130, a novel adaptor protein, in cell cycle progression of gastric cancer cells via regulation of c-Myc

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Adaptor proteins can participate in the regulation of various cellular functions, depending on the functional role of their interacting partners. We have cloned a novel adaptor protein, XB130, which has been implicated as a substrate and regulator of tyrosine kinase-mediated signaling and in controlling cell proliferation and apoptosis in thyroid and lung cancer cells. However, its expression and role in gastrointestinal cancer have not been investigated. In the present study, we sought to determine the role of XB130 in gastric and esophageal cancer cells and examine its expression and effects on the prognosis of patients with upper gastrointestinal cancer. Using knockdown experiments with XB130 siRNA, we found that XB130 regulate cell cycle progression via c-Myc and p21 in gastric and esophageal cancer cells. Immunohistochemical analysis revealed that expression of XB130 in cancer tissue was observed in 71.2% of patients with esophageal cancer, and that XB130 expression in the nucleus was an independent prognostic factor. The present study leads to the discovery of XB130 as an important prognostic factor in upper gastrointestinal cancer, and has the potential to present as a novel mediator and/or biomarker.