Oxidative stress mediated Ca2+ release manifests endoplasmic reticulum stress leading to unfolded protein response in UV-B irradiated human skin cells

Background: Exposure of skin to ultraviolet (UV) radiation, an environmental stressor induces number of adverse biological effects (photodamage), including cancer. The damage induced by UV-irradiation in skin cells is initiated by the photochemical generation of reactive oxygen species (ROS) and induction of endoplasmic reticulum (ER) stress and consequent activation of unfolded protein response (UPR). Objective: To decipher cellular and molecular events responsible for UV-B mediated ER stress and UPR activation in skin cells. Methods: The study was performed on human skin fibroblast (Hs68) and keratinocyte (HaCaT) cells exposed to UV-B radiations in lab conditions. Different parameters of UVB induced cellular and molecular changes were analyzed using Western-blotting, microscopic studies and flow cytometry. Results: Our results depicted that UV-B induces an immediate ROS generation that resulted in emptying of ER Ca2+ stores inducing ER stress and activation of PERK-peIF2 alpha-CHOP pathway. Quenching ROS generation by anti-oxidants prevented Ca2+ release and subsequent induction of ER stress and UPR activation. UV-B irradiation induced PERK dependent G2/M phase cell cycle arrest in Hs68 and G1/S phase cell cycle arrest in HaCaT. Also our study reflects that UV-B exposure leads to loss of mitochondrial membrane potential, activation of apoptotic cascade as evident by AnnexinV/PI staining, decreased expression of Bcl-2 and increased cleavage of PARP-1 protein. Conclusion: UV-B induced Ca2+ deficit within ER lumen was mediated by immediate ROS generation. Insufficient Ca2+ concentration within ER lumen developed ER stress leading to UPR activation. These changes were reversed by use of anti-oxidants which quench ROS. (C) 2014 Japanese Society for Investigative Dermatology. Published by Elsevier Ireland Ltd. All rights reserved.