Translational control of a human mRNA splice variant regulates the fate of UVB-irradiated human keratinocytes.

In response to sublethal ultraviolet B (UVB) irradiation, human keratinocytes transiently block progression of the cell cycle to allow ample time for DNA repair and cell fate determination. These cellular activities are important for avoiding the initiation of carcinogenesis in skin. Central to these processes is the repression of initiation of mRNA translation through GCN2 phosphorylation of eIF2 alpha (eIF2 alpha-P). Concurrent with reduced global protein synthesis, eIF2 alpha-P and the accompanying integrated stress response (ISR) selectively enhance translation of mRNAs involved in stress adaptation. In this study, we elucidated a mechanism for eIF2 alpha-P cytoprotection in response to UVB in human keratinocytes. Loss of eIF2 alpha-P induced by UVB diminished G1 arrest, DNA repair, and cellular senescence coincident with enhanced cell death in human keratinocytes. Genome-wide analysis of translation revealed that the mechanism for these critical adaptive responses by eIF2 alpha-P involved induced expression of CDKN1A encoding the p21 (CIP1/WAF1) protein. We further show that human CDKN1A mRNA splice variant 4 is preferentially translated following stress-induced eIF2 alpha-P by a mechanism mediated in part by upstream ORFs situated in the 5'-leader of CDKN1A mRNA. We conclude that eIF2 alpha-P is cytoprotective in response to UVB by a mechanism featuring translation of a specific splice variant of CDKN1A that facilitates G1 arrest and subsequent DNA repair.