Endoplasmic reticulum heat shock protein gp96 maintains liver homeostasis and promotes hepatocellular carcinogenesis

Abstract

gp96, or grp94, is an endoplasmic reticulum (ER)-localized heat shock protein 90 paralog that acts as a protein chaperone and plays an important role for example in ER homeostasis, ER stress, Wnt and integrin signaling, and calcium homeostasis, which are vital processes in oncogenesis. However, the cancer-intrinsic function of gp96 remains controversial. We studied the roles of gp96 in liver biology in mice via an Albumin promoter-driven Cre recombinase-mediated disruption of gp96 gene, hsp90b1. The impact of gp96 status on hepatic carcinogenesis in response to diethyl-nitrosoamine (DENA) was probed. The roles of gp96 on human hepatocellular carcinoma cells (HCC) were also examined pharmacologically with a targeted gp96 inhibitor. We demonstrated that gp96 maintains liver development and hepatocyte function in vivo, and its loss genetically promotes adaptive accumulation of long chain ceramides, accompanied by steatotic regeneration of residual gp96+ hepatocytes. The need for compensatory expansion of gp96+ cells in the gp96- background predisposes mice to develop carcinogen-induced hepatic hyperplasia and cancer from gp96+ but not gp96- hepatocytes. We also found that genetic and pharmacological inhibition of gp96 in human HCCs perturbed multiple growth signals, and attenuated proliferation and expansion. gp96 is a pro-oncogenic chaperone and an attractive therapeutic target for HCC.