ER stress protein GRP78 as a therapeutic target combined with antiangiogenic therapy in renal cell carcinoma.

428 Background: Antiangiogenic therapy deprives oxygen and nutrition from the tumor. These stresses cause unfolded proteins in tumor cells. Glucose regulated protein 78 (GRP78) binds to unfolded proteins and its subsequent activation suppresses global mRNA translation to protect cells from excessive unfolded proteins. We investigated a potential role of GRP78 as a combined therapeutic target in renal cell carcinoma treated with antiangiogenic therapy. Methods: Renal cell carcinoma cells (Caki-1, Caki-2, UMRC-3, and UMRC-6) were used to investigate the effect of GRP78 knockdown, which was performed by small interfering RNA. Caki-1 xenografts were developed and treated with sunitinib 40mg/kg/day to evaluate in vivo expression of GRP78 during antiangiogenic therapy. Caki-1 cells stably overexpressing GRP78 were developed to investigate the role of GRP78 in cancer cell. Hypoxic stress was induced by 1% hypoxia chamber and hypoglycaemic stress was induced by glucose-free media. Downstream signalling pathways of GRP78 were evaluated by Western blots. Results: In vitro hypoxia and/or glucose deprivation induced GRP78 upregulation in Caki-1 cells. GRP78 was also induced in Caki-1 xenografts treated by sunitinib. Overexpression of GRP78 increased tumor proliferation in hypoxic and/or hypoglycemic stresses by activating PERK/eIF2α pathway and protected tumor cells from stress-induced apoptosis. Knockdown of GRP78 using small interference RNA inhibited cancer cell survival and induced apoptosis in renal cell carcinoma cells in vitro. GRP78 knockdown also sensitized renal cell carcinoma cells to ER stress-induced apoptosis and hypoxic and hypoplycemic stress-induces apoptosis. Conclusions: Antiangiogenic therapy induces ER stress by depriving oxygen and glucose from renal cell carcinoma. ER protein GRP78 has a critical role in protecting renal cell carcinoma cells from hypoxic and hypoglycemic stress induced by antiangiogenic therapy. Knockdown of GRP78 sensitizes RCC cells to apoptotic cell death from anti-angiogenic stresses. Our results suggest that GRP78 is a novel therapeutic target in renal cell carcinoma management.