Role of ITPR1/HIF-2α axis in protecting renal cancer cells against natural killer cells.

Abstract

417 Background: Clear cell renal cell carcinomas frequently display inactivation of VHL gene leading to increased level of hypoxia inducible factors (HIFs). The specific role of VHL mutations and selective activation of HIF-2 alpha in modulating RCC susceptibility to cytotoxic immune response remains largely unknown. Methods: In this study, we used 786-0 RCC VHL-mutated cell line selectively induces HIF-2 alpha stabilization.Chromium release cytotoxicity assay was regularly used to evaluate tumor target cells sensitivity to NK-mediated lysis. Confocal microscopy was aso used to analyse immunologic synapse formation and for autophagy studies. Immunochemistry staining using RCC tissue microarrays was performed to evaluate HIF-2 alpha and ITPR1 expression in RCC patients. Results: We demonstrated that the RCC cell line 786-0 with mutated VHL was resistant to NK-mediated lysis as compared to the VHL-corrected cell line (WT7). This resistance was found to require HIF-2α stabilization. Based on global gene expression profiling and ChIP assay, we found ITPR1 (inositol 1,4,5-trisphosphate receptor, type 1) as a direct novel target of HIF-2α and targeting ITPR1 significantly increased susceptibility of 786-0 cells to NK-mediated lysis. Interestingly, using a large group (235) of RCC patients,we demonstrated the existence of a significant correlation between HIF-2α and ITPR1 expression Mechanistically, HIF-2α in 786-0 cells lead to overexpression of ITPR1, which subsequently regulated the NK mediated killing through the activation of autophagy in target cells by NK derived signal. Both ITPR1 and Beclin-1 silencing in 786-0 cells inhibited NK-induced autophagy and subsequently increased Granzyme B activity in target cells. Finally, in vivo ITPR1 targeting significantly enhanced the NK-mediated tumor regression. Conclusions: Our data provide insights into the link between HIF-2α, the ITPR1-related pathway and natural immunity and strongly suggest a role for the HIF-2α /ITPR1 axis in regulating RCC cell survival. Futur NK cell-based immunotherapy should integrate HIF-2/ITPR1 axis as intrinsic feature of resistance tumor cells to improve NK cell response in RCC patients.