title: Role of INK4a/Arf locus-encoded senescent checkpoints activated in normal and psoriatic keratinocytes.
abstract: During malignant transformation in skin, epidermal keratinocytes (KCs) frequently acquire the capacity to by-pass cellular senescence, a response that normally limits their unrestricted proliferation. Despite growing interest in the role for senescence during aging of skin and cutaneous carcinogenesis, little is known regarding regulation of three proteins encoded by the INK4a/ARF locus (p12, p14(ARF), p16) in KCs. In this study, several molecular pathways are explored using cultured KCs and KCs freshly isolated from psoriatic plaques. p16 and p14(ARF) are predominantly expressed spontaneously when foreskin-derived early-passage KCs undergo confluency-induced premature senescence. Induction of p14(ARF) on confluency occurred with low E2F-1 levels. Suspension of KCs in methylcellulose induced p12 expression. Addition of various cytokines (interferon-gamma, tumor necrosis factor-alpha) or a phorbol ester [12-O-tetradecanoylphorbol-13-acetate (TPA)] only induced p16, but not p14(ARF). Confluent KCs up-regulated Ras activity and the downstream signaling involving ERK. Addition of MAPK inhibitor blocked cytokine and TPA-induced p16 expression. Confluency and interferon-gamma induced premature senescence and p16 expression was linked to induction of the transcription factor Egr-1. KCs derived from chronic psoriatic plaques were characterized by enhanced p16, p14(ARF), and p12 expression accompanied by elevated Egr-1 levels. These results demonstrate that multiple and highly divergent stimuli can trigger the senescent checkpoint in human KCs with differential regulation of p16, p14(ARF), and p12. Although abnormal mitogenic signaling by oncogenic Ras is generally cited as being responsible for induction of premature senescence, our findings indicate that a broader perspective is warranted, to include confluency and cytokine-/TPA-induced pathways for KCs.
authors.affiliation: Department of Pathology, Loyola University Medical Center, Maywood, Illinois 60153, USA.
authors.forename: Vijaya
authors.initials: V
authors.lastname: Chaturvedi
authors.forename: Mirjana
authors.initials: M
authors.lastname: Cesnjaj
authors.forename: Patricia
authors.initials: P
authors.lastname: Bacon
authors.forename: Jeffery
authors.initials: J
authors.lastname: Panella
authors.forename: Divaker
authors.initials: D
authors.lastname: Choubey
authors.forename: Manuel O
authors.initials: MO
authors.lastname: Diaz
authors.forename: Brian J
authors.initials: BJ
authors.lastname: Nickoloff
mesh_terms: D002455:Cell Division / Q000187:drug effects / Q000235:genetics; D002478:Cells, Cultured; D016922:Cellular Senescence / Q000502:physiology; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000096:biosynthesis* / Q000235:genetics; D016207:Cytokines / Q000494:pharmacology; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000235:genetics; D051766:Early Growth Response Protein 1; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects; D017930:Genes, Reporter; D018816:Genes, cdc / Q000502:physiology; D006801:Humans; D017874:Immediate-Early Proteins; D015603:Keratinocytes / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D008747:Methylcellulose / Q000494:pharmacology; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D011565:Psoriasis / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D012016:Reference Values; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014157:Transcription Factors / Q000096:biosynthesis / Q000235:genetics; D014162:Transfection; D025803:Tumor Suppressor Protein p14ARF / Q000096:biosynthesis* / Q000235:genetics; D018631:ras Proteins / Q000378:metabolism
chemical_list: D019941:Cyclin-Dependent Kinase Inhibitor p16; D016207:Cytokines; D004268:DNA-Binding Proteins; C497325:EGR1 protein, human; D051766:Early Growth Response Protein 1; D004791:Enzyme Inhibitors; D017874:Immediate-Early Proteins; D014157:Transcription Factors; D025803:Tumor Suppressor Protein p14ARF; D008747:Methylcellulose; D020928:Mitogen-Activated Protein Kinases; D018631:ras Proteins; D013755:Tetradecanoylphorbol Acetate