title: Knockdown of p53 levels in human keratinocytes accelerates Mcl-1 and Bcl-x(L) reduction thereby enhancing UV-light induced apoptosis.
abstract: Ultraviolet (UV) light exposure is a common cause of epithelial-derived skin cancers, and the epidermal response to UV-light has been extensively studied using both mouse models and cultured human keratinocytes (KCs). Elimination of cells with UV-induced DNA damage via apoptosis provides a powerful mechanism to minimize retention or expansion of genetically abnormal cells. This cell editing function has largely been ascribed to the biological role of the p53 tumor suppressor gene, as mutations or deletions involving p53 have been linked to skin cancer development. Rather than introducing mutations, or using cells with complete loss of wild-type p53, we used an siRNA-based approach to knockdown, but not eliminate, p53 levels in primary cultures of human KCs followed by UV-irradiation. Surprisingly, when p53 levels were reduced by 50-80% the apoptosis induced by exposure to UV-light was accelerated and markedly enhanced (two- to three- fold) compared to control siRNA treated KCs. The p53 siRNA treated KCs were characterized by elevated E2F-1 levels accompanied by accelerated elimination of the Mcl-1 and Bcl-x(L) antiapoptotic proteins, as well as enhanced Bax oligomerization. Forced overexpression of either Mcl-1 or Bcl-x(L) reduced the UV-light enhanced apoptotic response in p53 siRNA treated KCs. We conclude that p53 not only can provide proapoptotic signals but also regulates a survival pathway influencing Mcl-1 and Bcl-x(L) levels. This overlooked survival function of p53 may explain previous paradoxical responses noted by investigators using p53 heterozygous and knockout mouse models, and opens up the possibility that not all liaisons within the cell involving p53 necessarily represent fatal attractions.
authors.affiliation: Department of Pathology, Oncology Institute, Loyola University Medical Center, Maywood, IL 60153, USA.
authors.forename: Vijaya
authors.initials: V
authors.lastname: Chaturvedi
authors.forename: Leonid A
authors.initials: LA
authors.lastname: Sitailo
authors.forename: Jian-Zhong
authors.initials: JZ
authors.lastname: Qin
authors.forename: Barbara
authors.initials: B
authors.lastname: Bodner
authors.forename: Mitchell F
authors.initials: MF
authors.lastname: Denning
authors.forename: Jonathan
authors.initials: J
authors.lastname: Curry
authors.forename: Wengeng
authors.initials: W
authors.lastname: Zhang
authors.forename: Douglas
authors.initials: D
authors.lastname: Brash
authors.forename: Brian J
authors.initials: BJ
authors.lastname: Nickoloff
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000528:radiation effects; D002470:Cell Survival; D004249:DNA Damage; D015536:Down-Regulation; D006801:Humans; D015603:Keratinocytes / Q000378:metabolism / Q000502:physiology* / Q000528:radiation effects; D051379:Mice; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009363:Neoplasm Proteins / Q000096:biosynthesis / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000096:biosynthesis / Q000378:metabolism*; D034622:RNA Interference; D016159:Tumor Suppressor Protein p53 / Q000502:physiology*; D014466:Ultraviolet Rays / Q000009:adverse effects*; D015854:Up-Regulation; D051020:bcl-X Protein
chemical_list: C494811:BCL2L1 protein, human; C494812:Bcl2l1 protein, mouse; C579094:Mcl1 protein, mouse; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009363:Neoplasm Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D016159:Tumor Suppressor Protein p53; D051020:bcl-X Protein