title: C/EBPbeta represses p53 to promote cell survival downstream of DNA damage independent of oncogenic Ras and p19(Arf).
abstract: CCAAT/enhancer-binding protein-beta (C/EBPbeta) is a mediator of cell survival and tumorigenesis. When C/EBPbeta(-/-) mice are treated with carcinogens that produce oncogenic Ras mutations in keratinocytes, they respond with abnormally elevated keratinocyte apoptosis and a block in skin tumorigenesis. Although this aberrant carcinogen-induced apoptosis results from abnormal upregulation of p53, it is not known whether upregulated p53 results from oncogenic Ras and its ability to induce p19(Arf) and/or activate DNA-damage response pathways or from direct carcinogen-induced DNA damage. We report that p19(Arf) is dramatically elevated in C/EBPbeta(-/-) epidermis and that C/EBPbeta represses a p19(Arf) promoter reporter. To determine whether p19(Arf) is responsible for the proapoptotic phenotype in C/EBPbeta(-/-) mice, C/EBPbeta(-/-);p19(Arf-/-) mice were generated. C/EBPbeta(-/-);p19(Arf-/-) mice responded to carcinogen treatment with increased p53 and apoptosis, indicating p19(Arf) is not essential. To ascertain whether oncogenic Ras activation induces aberrant p53 and apoptosis in C/EBPbeta(-/-) epidermis, we generated K14-ER:Ras;C/EBPbeta(-/-) mice. Oncogenic Ras activation induced by 4-hydroxytamoxifen did not produce increased p53 or apoptosis. Finally, when C/EBPbeta(-/-) mice were treated with differing types of DNA-damaging agents, including alkylating chemotherapeutic agents, they displayed aberrant levels of p53 and apoptosis. These results indicate that C/EBPbeta represses p53 to promote cell survival downstream of DNA damage and suggest that inhibition of C/EBPbeta may be a target for cancer cotherapy to increase the efficacy of alkylating chemotherapeutic agents.
authors.affiliation: Cell Signaling and Cancer Group, Department of Environmental and Molecular Toxicology, North Carolina State University, Raleigh, NC 27695-7633, USA.
authors.forename: S J
authors.initials: SJ
authors.lastname: Ewing
authors.forename: S
authors.initials: S
authors.lastname: Zhu
authors.forename: F
authors.initials: F
authors.lastname: Zhu
authors.forename: J S
authors.initials: JS
authors.lastname: House
authors.forename: R C
authors.initials: RC
authors.lastname: Smart
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D022782:CCAAT-Enhancer-Binding Protein-beta / Q000172:deficiency / Q000378:metabolism*; D002273:Carcinogens / Q000633:toxicity; D002470:Cell Survival / Q000187:drug effects; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000378:metabolism; D003520:Cyclophosphamide / Q000008:administration & dosage / Q000494:pharmacology; D004249:DNA Damage; D000078404:Epidermal Cells; D004817:Epidermis / Q000187:drug effects / Q000378:metabolism; D007274:Injections, Intraperitoneal; D015603:Keratinocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D051379:Mice; D015689:Oncogene Protein p21(ras) / Q000378:metabolism; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D012097:Repressor Proteins / Q000378:metabolism*; D015533:Transcriptional Activation / Q000187:drug effects; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism*
chemical_list: D022782:CCAAT-Enhancer-Binding Protein-beta; D002273:Carcinogens; C417743:Cdkn2a protein, mouse; D019941:Cyclin-Dependent Kinase Inhibitor p16; D012097:Repressor Proteins; D016159:Tumor Suppressor Protein p53; D003520:Cyclophosphamide; D015689:Oncogene Protein p21(ras)