Abstract
Diffuse-type gastric cancer (DGC) is a highly invasive subtype of gastric adenocarcinoma that frequently exhibits scattered peritoneal metastasis. Previous studies have shown that the genes of receptor tyrosine kinases (RTKs), such as fibroblast growth factor receptor 2 (FGFR2) or Met, are amplified in some DGC cell lines, leading to the constitutive activation of corresponding RTKs. In these cell lines, the survival of cancer cells appears to be dependent on the activation of RTKs. To gain novel insights into the downstream signaling pathways of RTKs specific to DGC, phosphotyrosine-containing proteins associated with activated FGFR2 were purified through two sequential rounds of immunoprecipitation from the lysates of two DGC cell lines. As a result, transferrin receptor 1 (TfR1) was identified as the binding partner of FGFR2. Biochemical analysis confirmed that TfR1 protein binds to FGFR2 and is phosphorylated at tyrosine 20 (Tyr20) in an FGFR2 kinase activity-dependent manner. The knockdown of TfR1 and treatment with an inhibitor of FGFR2 caused significant impairment in iron uptake and suppression of cellular proliferation in vitro. Moreover, the suppression of expression levels of TfR1 in the DGC cells significantly reduced their tumorigenicity and potency of peritoneal dissemination. It was indicated that TfR1, when phosphorylated by the binding partner FGFR2 in DGC cells, promotes proliferation and tumorigenicity of these cancer cells. These results suggest that the control of TfR1 function may serve as a therapeutic target in DGC with activated FGFR2.