Disturbance of Ca2+ homeostasis converts pro-Met into non-canonical tyrosine kinase p190MetNCin response to endoplasmic reticulum stress in MHCC97 cells

Abstract

c-Met, the tyrosine-kinase receptor for hepatocyte growth factor, plays a critical role in the tumorigenesis of hepatocellular carcinoma (HCC). However, the underlying mechanism remains incompletely understood. The mature c-Met protein p190Metαβ(consistsofa α subunit and a β subunit) is processed from pro-Met. Here we show that pro-Met is processed into p190MetNC by sarco/ endoplasmic reticulum calcium-ATPase (SERCA) inhibitor thapsigargin. p190MetNC compensates for the degradation of p190Metαβ and protects human HCC cells from apoptosis mediated by endoplasmic reticulum (ER) stress. In comparison with p190Met αβ, p190MetNC is not cleaved and is expressed as a single-chain polypeptide. Thapsigargin-initiated p190MetNC expression depends on the disturbance of ER calcium homeostasis. Once induced, p190MetNC is activated independent of hepatocyte growth factor engagement. p190MetNC contributes to sustained high basal activation of c-Met downstream pathways during ER calcium disturbance-mediated ER stress. Both p38 MAPK-promoted glucose-regulated protein 78 (GRP78) expression and sustained high basal activation of PI3K/Akt and MEK/ERK are involved in the cytoprotective function of p190MetNC. Importantly, the expression of p190MetNC is detected in some HCC cases. Taken together, these data provide a potential mechanism to explain how c-Met promotes HCC cells survival in response to ER stress. We propose that context-specific processing of c-Met protein is implicated in HCC progression in stressful microenvironments. © 2012 by The American Society for Biochemistry and Molecular Biology, Inc.