Galectin-4 contributes to the maintenance of expression and activation of multiple receptor-type kinases involved in peritoneal metastasis.

Owing to the lack of effective therapeutic strategies, peritoneal metastasis of metastatic and recurrent gastric cancers is associated with poor prognosis. Our previous study showed that galectin-4 suppression attenuated the peritoneal metastasis of malignant gastric cancer cells in a mouse model; however, the underlying mechanisms are unclear. Therefore, we aimed to elucidate the role of galectin-4 in signal transduction by identifying interacting molecules and the relationship to glycans. Antibody array analysis and proximity ligation assays revealed a close association between galectin-4 and multiple receptor tyrosine kinases (RTKs), including c-MET and EGFR. In galectin-4 knockout (KO) cells, tyrosine phosphorylation of RTKs proximal to galectin-4 was markedly reduced. Enhanced tyrosine phosphorylation promoted cell surface exposure and colocalization of galectin-4 and tyrosine-phosphorylated (PY) proteins. Surface plasmon resonance and inhibition assays further revealed that galectin-4 binds to tyrosine-phosphorylated molecules via its carbohydrate recognition domain. Consistently, overexpression of B3GALT5, a β1-3-galactosyltransferase, altered the localization of PY proteins and galectin-4, suggesting competitive regulation of galectin-4 binding by glycosylation and tyrosine phosphorylation. Notably, galectin-4 KO cells exhibited reduced c-MET surface expression. Collectively, these findings suggest that galectin-4 plays a critical role in maintaining the expression and activation of multiple signaling molecules involved in peritoneal metastasis.