title: TNF-alpha impairs the S-G2/M cell cycle checkpoint and cyclobutane pyrimidine dimer repair in premalignant skin cells: role of the PI3K-Akt pathway.
abstract: Tumor necrosis factor-alpha (TNF-alpha) is induced by UVB radiation and has been implicated in the early stages of skin carcinogenesis. Here, we show that in normal keratinocytes and the transformed keratinocyte cell lines, HaCaT and A431, TNF-alpha stimulates protein kinase B/Akt, which results in activation of the survival complex mTORC1 (mammalian target of rapamycin complex 1) and inhibition of the proapoptotic proteins Bad and FoxO3a. In UVB-irradiated HaCaT cells (10-20 mJ cm(-2)), TNF-alpha increased the proportion of cycling cells and enhanced the rate of apoptosis. A significantly higher proportion of UVB-treated HaCaT cells containing unrepaired cyclobutane pyrimidine dimers (CPDs) escaped the G2/M cell cycle checkpoint in the presence of TNF-alpha (9.5+/-3.3 vs 4.8+/-2.2%). After treatment with the PI3K inhibitor LY294002, only 1.2+/-0.7% of CPD-containing HaCaT cells were actively cycling. TNF-alpha enhanced apoptosis less potently and did not increase the level of CPD or stimulate cell cycle progression in normal keratinocytes. Our data suggest that TNF-alpha overrides the G2/M checkpoint in premalignant skin cells and allows for some cells containing unrepaired CPD to enter the cell cycle. The effect of TNF-alpha seems to be dependent on Akt activation and may constitute a relevant mechanism enhancing mutagenesis and tumor development.
authors.affiliation: Department of Dermatology, University of Copenhagen, Bispebjerg Hospital, Copenhagen, Denmark. Af16@bbh.regionh.dk
authors.forename: Annesofie
authors.initials: A
authors.lastname: Faurschou
authors.forename: Robert
authors.initials: R
authors.lastname: Gniadecki
authors.forename: Damien
authors.initials: D
authors.lastname: Calay
authors.forename: Hans Christian
authors.initials: HC
authors.lastname: Wulf
mesh_terms: D002453:Cell Cycle / Q000187:drug effects; D002460:Cell Line; D049109:Cell Proliferation; D002470:Cell Survival; D002867:Chromones / Q000494:pharmacology; D004247:DNA / Q000235:genetics; D004260:DNA Repair / Q000235:genetics*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors / Q000378:metabolism; D018816:Genes, cdc; D006801:Humans; D015603:Keratinocytes / Q000378:metabolism / Q000473:pathology* / Q000528:radiation effects; D000076222:Mechanistic Target of Rapamycin Complex 1; D009025:Morpholines / Q000494:pharmacology; D046912:Multiprotein Complexes; D051058:Oncogene Protein v-akt / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D011230:Precancerous Conditions / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D011506:Proteins; D011740:Pyrimidine Dimers / Q000235:genetics*; D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases; D014157:Transcription Factors / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism*; D051025:bcl-Associated Death Protein / Q000378:metabolism
chemical_list: D002867:Chromones; D004247:DNA; D004791:Enzyme Inhibitors; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors; D000076222:Mechanistic Target of Rapamycin Complex 1; D009025:Morpholines; D046912:Multiprotein Complexes; D051058:Oncogene Protein v-akt; D019869:Phosphatidylinositol 3-Kinases; D011506:Proteins; D011740:Pyrimidine Dimers; D058570:TOR Serine-Threonine Kinases; D014157:Transcription Factors; D014409:Tumor Necrosis Factor-alpha; D051025:bcl-Associated Death Protein; C494819:BAD protein, human; C499517:FOXO3 protein, human; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one