title: Radiation response and cell cycle regulation of p53 rescued malignant keratinocytes.
abstract: Mutations in the tumor suppressor gene p53 were found in more than 90% of all human squamous cell carcinomas (SCC). To study the function of p53 in a keratinocyte background, a tetracycline-controlled p53 transgene was introduced into a human SCC cell line (SCC15), lacking endogenous p53. Conditional expression of wild-type p53 protein upon withdrawal of tetracycline was accompanied with increased expression of p21(WAF1/Cip1) resulting in reduced cell proliferation. Flow-cytometric analysis revealed that these cells were transiently arrested in the G1/S phase of the cell cycle. However, when SCC15 cells expressing p53 were exposed to ionizing radiation (IR), a clear shift from a G1/S to a G2/M cell cycle arrest was observed. This effect was greatly depending on the presence of wild-type p53, as it was not observed to the same extent in SCC15 cells lacking p53. Unexpectedly, the p53- and IR-dependent G2/M cell cycle arrest in the keratinocyte background was not depending on increased expression or stabilization of 14-3-3sigma, a p53-regulated effector of G2/M progression in colorectal cancer cells. In keratinocytes, 14-3-3sigma (stratifin) is involved in terminal differentiation and its cell cycle function in this cell type might diverge from the one it fulfills in other cellular backgrounds.
authors.affiliation: Department of Molecular Genetics, Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden University, Einsteinweg 55, 2333 CC Leiden, The Netherlands.
authors.forename: Maarten
authors.initials: M
authors.lastname: Niemantsverdriet
authors.forename: Wim
authors.initials: W
authors.lastname: Jongmans
authors.forename: Claude
authors.initials: C
authors.lastname: Backendorf
mesh_terms: D048948:14-3-3 Proteins; D014408:Biomarkers, Tumor / Q000235:genetics / Q000378:metabolism; D002294:Carcinoma, Squamous Cell / Q000378:metabolism* / Q000473:pathology; D002453:Cell Cycle / Q000528:radiation effects*; D018797:Cell Cycle Proteins / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D050759:Cyclin-Dependent Kinase Inhibitor p21; D005092:Exonucleases / Q000235:genetics / Q000378:metabolism; D005095:Exoribonucleases; D015972:Gene Expression Regulation, Neoplastic / Q000528:radiation effects*; D006801:Humans; D015603:Keratinocytes / Q000378:metabolism* / Q000473:pathology / Q000528:radiation effects*; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013752:Tetracycline / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism*
chemical_list: D048948:14-3-3 Proteins; D014408:Biomarkers, Tumor; C493956:CDKN1A protein, human; D018797:Cell Cycle Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; D009363:Neoplasm Proteins; D016159:Tumor Suppressor Protein p53; D005092:Exonucleases; D005095:Exoribonucleases; C413442:SFN protein, human; D013752:Tetracycline