The role of leptin in gastric cancer: clinicopathologic features and molecular mechanisms.

Obesity is associated with certain types of cancer, including gastric cancer. However, it is still unclear whether obesity-related cytokine, leptin, is implicated in gastric cancer. Therefore, we aimed to investigate the role of leptin in gastric cancer. The expression of leptin and its receptor, Ob-R, was assessed by immunohistochemical staining and was compared in patients with gastric adenoma (n=38), early gastric cancer (EGC) (n=38), and advanced gastric cancer (AGC) (n=38), as a function of their clinicopathological characteristics. Gastric cancer cell lines were studied to investigate the effects of leptin on the signal transducer and activator of transcription-3 (STAT3) and extracellular receptor kinase 1/2 (ERK1/2) signaling pathways using MTT assays, immunoblotting, and inhibition studies. Leptin was expressed in gastric adenomas (42.1%), EGCs (47.4%), and AGCs (43.4%). Ob-R expression tended to increase from gastric adenoma (2%), through EGC (8%), to AGC (18%). Leptin induced the proliferation of gastric cancer cells by activating STAT3 and ERK1/2 and up-regulating the expression of vascular endothelial growth factor (VEGF). Blocking Ob-R with pharmacological inhibitors and by RNAi decreased both the leptin-induced activation of STAT3 and ERK1/2 and the leptin-induced expression of VEGF. Leptin plays a role in gastric cancer by stimulating the proliferation of gastric cancer cells via activating the STAT3 and ERK1/2 pathways.