Activation of Ras/Erk pathway by a novel MET-interacting protein RanBPM.

MET is a receptor protein-tyrosine kinase (RPTK) for hepatocyte growth factor (HGF), which is a multifunctional cytokine controlling cell growth, morphogenesis, and motility. MET overexpression has been identified in a variety of human cancers. Oncogenic missense mutations of the tyrosine kinase domain of the MET gene have been identified in human papillary renal cell carcinomas. In this study, RanBPM, also known as RanBP9, is identified as a novel interacting protein of MET through yeast two-hybrid screen. RanBPM contains a conserved SPRY (repeats in splA and RyR) domain. We demonstrate that RanBPM can interact with MET in vitro and in vivo, and the interaction can be strengthened by HGF stimulation. RanBPM interacts with the tyrosine kinase domain of MET through its SPRY domain. We show that RanBPM can induce GTP-Ras association and Erk phosphorylation and elevate serum response element-luciferase (SRE-LUC) expression, indicating that RanBPM can activate the Ras-Erk-SRE pathway. We demonstrate that RanBPM, which itself is not a guanine exchange protein, stimulates Ras activation by recruiting Sos. On the cellular level, A704 cells, a human renal carcinoma cell line, transfected with RanBPM exhibit increased migration ability. Our data suggest that RanBPM, functioning as an adaptor protein for the MET tyrosine kinase domain, can augment the HGF-MET signaling pathway and that RanBPM overexpression may cause constitutive activation of the Ras signaling pathway.