title: C/EBPalpha is a DNA damage-inducible p53-regulated mediator of the G1 checkpoint in keratinocytes.
abstract: The basic leucine zipper transcription factor, CCAAT/enhancer binding protein alpha (C/EBPalpha), is abundantly expressed in keratinocytes of the skin; however, its function in skin is poorly characterized. UVB radiation is responsible for the majority of human skin cancers. In response to UVB-induced DNA damage, keratinocytes activate cell cycle checkpoints that arrest cell cycle progression and prevent replication of damaged DNA, allowing time for DNA repair. We report here that UVB radiation is a potent inducer of C/EBPalpha in human and mouse keratinocytes, as well as in mouse skin in vivo. UVB irradiation of keratinocytes resulted in the transcriptional up-regulation of C/EBPalpha mRNA, producing a >70-fold increase in C/EBPalpha protein levels. N-Methyl-N'-nitro-N-nitrosoguanidine, etoposide, and bleomycin also induced C/EBPalpha. UVB-induced C/EBPalpha was accompanied by an increase in p53 protein and caffeine, an inhibitor of ataxia-telangiectasia-mutated kinase, and ataxia-telangiectasia-mutated and Rad3-related kinase inhibited UVB-induced increases in both C/EBPalpha and p53. UVB irradiation of p53-null or mutant p53-containing keratinocytes failed to induce C/EBPalpha. UVB irradiation of C/EBPalpha knockdown keratinocytes displayed a greatly diminished DNA damage G(1) checkpoint, and this was associated with increased sensitivity to UVB-induced apoptosis. Our results uncover a novel role for C/EBPalpha as a p53-regulated DNA damage-inducible gene that has a critical function in the DNA damage G(1) checkpoint response in keratinocytes.
authors.affiliation: Department of Environmental and Molecular Toxicology, North Carolina State University, Raleigh, NC 27695-7633, USA.
authors.forename: Kyungsil
authors.initials: K
authors.lastname: Yoon
authors.forename: Robert C
authors.initials: RC
authors.lastname: Smart
mesh_terms: D000818:Animals; D015153:Blotting, Western; D022763:CCAAT-Enhancer-Binding Protein-alpha / Q000378:metabolism*; D020169:Caspases / Q000032:analysis; D002460:Cell Line; D002478:Cells, Cultured; D004249:DNA Damage; D004307:Dose-Response Relationship, Radiation; D024202:Electrophoretic Mobility Shift Assay; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D016193:G1 Phase; D006801:Humans; D007150:Immunohistochemistry; D015603:Keratinocytes / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology / Q000528:radiation effects*; D007700:Kinetics; D008769:Methylnitronitrosoguanidine / Q000494:pharmacology; D051379:Mice; D008810:Mice, Inbred C57BL; D008815:Mice, Inbred Strains; D009153:Mutagens / Q000494:pharmacology; D041681:NIH 3T3 Cells; D011233:Precipitin Tests; D051381:Rats; D012190:Retroviridae / Q000235:genetics; D012867:Skin / Q000378:metabolism; D013997:Time Factors; D016159:Tumor Suppressor Protein p53 / Q000172:deficiency / Q000378:metabolism*; D014466:Ultraviolet Rays
chemical_list: D022763:CCAAT-Enhancer-Binding Protein-alpha; D009153:Mutagens; D016159:Tumor Suppressor Protein p53; D008769:Methylnitronitrosoguanidine; D020169:Caspases