title: Translational Repression Protects Human Keratinocytes from UVB-Induced Apoptosis through a Discordant eIF2 Kinase Stress Response.
abstract: This study delineates the mechanisms by which UVB regulates protein synthesis in human keratinocytes and the importance of translational control in cell survival. Translation initiation is regulated by phosphorylation of eukaryotic initiation factor 2 (eIF2-P) that causes decreased global protein synthesis coincident with enhanced translation of selected stress-related transcripts, such as activating transcription factor 4 (ATF4). ATF4 is a transcriptional activator of the integrated stress response (ISR) that has cytoprotective functions as well as apoptotic signals through the downstream transcriptional regulator C/EBP homologous protein (CHOP; GADD153/DDIT3). We determined that UVB irradiation is a potent inducer of eIF2-P in keratinocytes, leading to decreased levels of translation initiation. However, expression of ATF4 or CHOP was not induced by UVB as compared with traditional ISR activators. The rationale for this discordant response is that ATF4 mRNA is reduced by UVB, and despite its ability to be preferentially translated, there are diminished levels of available transcript. Forced expression of ATF4 and CHOP protein before UVB irradiation significantly enhanced apoptosis, suggesting that this portion of the ISR is deleterious in keratinocytes following UVB. Inhibition of eIF2-P and translational control reduced viability following UVB that was alleviated by cycloheximide (CHX), indicating that translation repression through eIF2-P is central to keratinocyte survival.
authors.affiliation: Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, Indiana, USA.
authors.forename: Ann E
authors.initials: AE
authors.lastname: Collier
authors.affiliation: Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, Indiana, USA. Electronic address: rwek@iu.edu.
authors.forename: Ronald C
authors.initials: RC
authors.lastname: Wek
authors.affiliation: Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, Indiana, USA; Department of Dermatology, Indiana University School of Medicine, Indianapolis, Indiana USA. Electronic address: dspanda@iupui.edu.
authors.forename: Dan F
authors.initials: DF
authors.lastname: Spandau
mesh_terms: D051701:Activating Transcription Factor 4 / Q000378:metabolism* / Q000528:radiation effects; D017209:Apoptosis / Q000502:physiology / Q000528:radiation effects*; D002478:Cells, Cultured; D006801:Humans; D015151:Immunoblotting; D015603:Keratinocytes / Q000166:cytology / Q000378:metabolism* / Q000528:radiation effects*; D012333:RNA, Messenger / Q000378:metabolism; D060888:Real-Time Polymerase Chain Reaction; D013312:Stress, Physiological / Q000502:physiology*; D051742:Transcription Factor CHOP / Q000378:metabolism* / Q000528:radiation effects; D014466:Ultraviolet Rays / Q000009:adverse effects; D056811:Unfolded Protein Response / Q000502:physiology / Q000528:radiation effects; D019892:eIF-2 Kinase / Q000378:metabolism* / Q000528:radiation effects
chemical_list: D012333:RNA, Messenger; D051701:Activating Transcription Factor 4; D051742:Transcription Factor CHOP; D019892:eIF-2 Kinase