Objective: Glucose-regulated protein 78 (Grp78) is an endoplasmic reticulum chaperone; it maintains endoplasmic reticulum homeostasis and modulates unfolded protein response. The protein is overexpressed in various cancer types, including renal cell carcinoma (RCC). Increased Grp78 expression in patients with RCC is correlated with more aggressive tumors and poorer prognoses. This study investigated the role of Grp78 in regulating tumorigenesis and evaluated the potential of Grp78-targeted therapy for RCC.
Methods: The expression level of Grp78 was examined in von Hippel-Lindau (VHL)-intact or VHL-null RCC cell lines by reverse transcription polymerase chain reaction and Western blot. Specific Grp78 ribonucleic acid interference was applied as a molecularly Grp78-targeted therapeutic approach. This method enabled us to assess the effects of manipulating Grp78 expression to regulate RCC cell growth.
Results: The Grp78 messenger ribonucleic acid and protein were expressed in both VHL-intact and VHL-null RCC cell lines. The specific inhibition of Grp78 expression suppressed RCC cell growth and colony formation significantly, and induced G1 cell-cycle arrest. We also showed that inhibiting Grp78 expression increased the cells' resistance to the cytotoxicity of the S-phase-specific anticancer drug 5-fluorouracil. This effect was regulated by the unfolded protein response-induced suppression of G1/S transition-related cyclins (D1, E1, and E2) and cyclin-dependent kinase (CDK4 and CDK6) protein expression.
Conclusion: Overall, our findings indicate the regulatory function of Grp78 in RCC cell proliferation, and provide a molecular-based mechanism of Grp78 positivity in the progression of RCC.
Keywords: Cell cycle; Chemotherapy; Grp78; Herp; UPR; VHL.
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