Abstract 5840: IRE1a is required for ROS homeostasis and PERK protein stability in response to UVB irradiation

Abstract IRE1α is required for ROS homeostasis and PERK protein stability in response to UVB irradiation UV induced stress is one of the primary driving factors of human skin cancer. UV irradiation can activate Endoplasmic Reticulum (ER) stress and the Unfolded Protein Response (UPR). Inositol-requiring enzyme 1a (IRE1α) is one of the key players in the UPR. Previous studies have shown that UVB irradiation can activate IRE1α in human and mouse skin cells, but the function of IRE1α in the UV response has not yet been characterized. Here we show that IRE1α expression is transiently downregulated after UVB irradiation and that in the absence of IRE1α the stability and activation of PKR-like endoplasmic reticulum kinase (PERK) is compromised. Basal levels of PERK are reduced in the absecence of IRE1α. Following UV irradiation, loss of IRE1α not only causes rapid degradation of PERK protein but also suppresses phosphorylation of the PERK target, Nuclear factor erythroid-2-related factor 2 (NRF2), and NRF2 dependent antioxidant gene expression. Similarly, PERK protein is rapidly degraded following thapsigargin treatment in the absence of IRE1α, suggesting a general regulation of PERK stability by IRE1α. Additionally, keratinocytes with either knockout or knockdown of IRE1α have increased intracellular ROS and cytosolic calcium. Overexpression of both wildtype and RNase defective human IRE1α can rescue the increased ROS levels. Additionally, the increased ROS is also suppressed by treatment with an inhibitor of the ER localized Inositol triphosphate receptor (InsP3R) which regulates calcium efflux from the ER. Because PERK regulates cytosolic calcium through inhibiting InsP3R, our result suggests that IRE1α is critical for suppressing intracellular ROS through stabilization of PERK. We conclude that crosstalk between IRE1α and PERK is essential for the basal and UVB- induced oxidative stress response, and this may have important implications for UV related damage and skin cancer development. Citation Format: Jeongin Son, Stephen Worrel, Adam Glick. IRE1a is required for ROS homeostasis and PERK protein stability in response to UVB irradiation [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5840.