title: Ultraviolet-B-induced G1 arrest is mediated by downregulation of cyclin-dependent kinase 4 in transformed keratinocytes lacking functional p53.
abstract: In order to identify potential novel targets for ultraviolet-B-induced skin tumorigenesis, we assessed the effect of ultraviolet-B exposure on cell cycle progression of transformed keratinocytes with mutant p53. We show that ultraviolet-B exposure of human epidermoid carcinoma A431 cells results in G1 cell cycle arrest in both asynchronously growing and synchronized cells. A significant increase in G1 cell population was observed following exposure to doses of ultraviolet-B as low as 10 mJ per cm2. When irradiated with ultraviolet-B, cells synchronized in G1 with mimosine did not exit G1. G1 cell cycle arrest was associated with a decrease in the hyperphosphorylated forms of retinoblastoma protein that was detectable within 4 h and gradually disappeared by 12 h. We also observed a decrease in cyclins D1, D2, and D3, and cyclin-dependent kinase 4 proteins, and a concomitant decrease in cyclin-dependent kinase 4/cyclin D1 associated kinase activity, whereas ultraviolet-B exposure had no effect on cyclin-dependent kinase 2 and cyclin-dependent kinase 6 levels during this time period. Incubation of cells with proteasome inhibitors MG-115 and MG-132 prevented the decrease in cyclin D1, D2, and D3, and cyclin-dependent kinase 4 protein. Taken together, our results suggest that ultraviolet-B-induced cell cycle arrest in A431 cells is mediated by cyclin-dependent kinase 4 downregulation. This identifies a novel pathway for G1 cell cycle arrest in transformed keratinocytes following ultraviolet-B irradiation.
authors: Department of Dermatology, College of Physicians and Surgeons, Columbia University, New York, New York, USA.
authors: Arianna L
authors: AL
authors: Kim
authors: Mohammad
authors: M
authors: Athar
authors: David R
authors: DR
authors: Bickers
authors: Jean
authors: J
authors: Gautier
mesh_terms: D002294:Carcinoma, Squamous Cell; D002461:Cell Line, Transformed; D019938:Cyclin D1 / Q000235:genetics / Q000378:metabolism; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases / Q000235:genetics / Q000378:metabolism*; D003546:Cysteine Endopeptidases; D015536:Down-Regulation / Q000528:radiation effects; D016193:G1 Phase / Q000528:radiation effects*; D015971:Gene Expression Regulation, Enzymologic / Q000528:radiation effects; D006801:Humans; D015603:Keratinocytes / Q000166:cytology / Q000201:enzymology* / Q000528:radiation effects; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors; D010766:Phosphorylation; D046988:Proteasome Endopeptidase Complex; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger / Q000032:analysis; D016160:Retinoblastoma Protein / Q000378:metabolism; D012878:Skin Neoplasms; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000235:genetics*; D014466:Ultraviolet Rays
chemical_list: D009097:Multienzyme Complexes; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D016160:Retinoblastoma Protein; D016159:Tumor Suppressor Protein p53; D019938:Cyclin D1; C495900:CDK4 protein, human; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex