title: The roles of translation initiation regulation in ultraviolet light-induced apoptosis.
abstract: Ultraviolet light (UV) inhibits translation initiation through activation of kinases that phosphorylate the alpha-subunit of eukaryotic initiation factor 2 (eIF2alpha). Two eIF2alpha kinases, PERK and GCN2, are known to phosphorylate the Serine-51 of eIF2alpha in response to UV-irradiation. In this report, we present evidence that phosphorylation of eIF2alpha plays a role in UV-induced apoptosis. Our data show that wild-type mouse embryo fibroblasts (MEF(s/s)) are less sensitive to UV-induced apoptosis than MEF(A/A) cells in which the phosphorylation site, Ser51, of eIF2alpha is replaced with a non-phosphorylatable Ala (Ser51Ala). PARP expression in MEF(A/A) cells is reduced without being cleaved after UV-irradiation. In contrast, PARP is cleaved without a significant decrease in parental PARP in MEF(S/S) cells after UV-irradiation. Our data also show that MEF(GCN2-/-) cells, in which GCN2 is knocked out, are more sensitive to UV-irradiation, agreeing with the observation from MEF(A/A) cells. However, MEF(PERK-/-) cells, in which PERK is knocked out, are less sensitive to UV-irradiation. In addition, MCF-7-PERKDeltaC cells, which are stably transfected with a kinase domain deleted mutant of PERK (PERKDeltaC), are more resistant to UV-induced apoptosis than parental MCF-7 cells. Overexpression of wild-type PERK sensitizes MCF-7 cells to UV-induced apoptosis without directly inducing cell death. These results suggest that the level of eIF2alpha phosphorylation impacts PARP expression upon UV-irradiation. The eIF2alpha kinases may mediate UV-induced apoptosis via an eIF2alpha dependent or independent signaling pathway.
authors.affiliation: Department of Chemistry and Biochemistry and Edison Biotechnology Institute, Ohio University, Athens, OH 45701, USA.
authors.forename: Suzanne H
authors.initials: SH
authors.lastname: Parker
authors.forename: Todd A
authors.initials: TA
authors.lastname: Parker
authors.forename: Kimberly S
authors.initials: KS
authors.lastname: George
authors.forename: Shiyong
authors.initials: S
authors.lastname: Wu
mesh_terms: D000818:Animals; D017209:Apoptosis; D004307:Dose-Response Relationship, Radiation; D015536:Down-Regulation; D004847:Epithelial Cells / Q000378:metabolism; D005260:Female; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D051379:Mice; D010442:Peptide Chain Initiation, Translational / Q000502:physiology* / Q000528:radiation effects; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D014466:Ultraviolet Rays; D019892:eIF-2 Kinase / Q000235:genetics / Q000378:metabolism; D000097782:NF-kappaB-Inducing Kinase
chemical_list: D017346:Protein Serine-Threonine Kinases; D019892:eIF-2 Kinase; D000097782:NF-kappaB-Inducing Kinase; C070634:Eif2ak4 protein, mouse