Aims: The role of ultraviolet C light (UVC)-induced phosphorylation of the eukaryotic initiation factor 2 (eIF2) in the regulation of cyclooxygenase-2 (COX-2) expression at both transcriptional and translational levels is investigated.
Main methods: Western analysis was used to determine COX expressions. Immunoprecipitation after [(35)S]-Met/Cys metabolic labeling was used to determine the rate for COX-2 synthesis and turnover. Quantitative real-time PCR was used to determine COX-2 mRNA levels. Ingenuity Pathways Analysis 6 was used for mapping COX-2 activation network.
Key findings: UVC induces COX-2 expression in wild-type mouse embryo fibroblasts (MEF(S/S)) and that the inducibility is reduced in MEF(A/A) cells in which the phosphorylation site, Ser-51 in the eIF2alpha, is replaced with a nonphosphorylatable Ala (S51A). UVC-induced transcription of COX-2 is delayed in MEF(A/A) cells, which correlates with NF-kappaB activation as previously reported (Wu, S, Tan, M, Hu, Y, Wang, JL, Scheuner, D, Kaufman, RJ, Ultraviolet light activates NFkappaB through translational inhibition of IkappaBalpha synthesis. The Journal of Biological Chemistry, 279, 34898-34902, 2004). The translational efficiency of COX-2 is higher in MEF(A/A) cells than in MEF(S/S) cells at 4 h, but not at 24 h post-UVC. The translation efficiency is correlated to the ratio of activated COX-2 binding protein HuR/TIAR. In addition, the newly synthesized COX-2 protein is more stable in MEF(A/A) cells than in MEF(S/S) cells. The results demonstrated a complex and dynamic regulation of COX-2 expression.
Significance: UVC induces a prolonged expression of COX-2. While transcriptional regulation of COX-2 expression is intensively studied, the role of translational regulation of COX-2 synthesis upon UVC-irradiation is not yet clear. This study elucidated a novel eIF2alpha phosphorylation-centered network for the regulation of COX-2 expression after UVC-irradiation.