title: Ultraviolet B light induces G1 arrest in human melanocytes by prolonged inhibition of retinoblastoma protein phosphorylation associated with long-term expression of the p21Waf-1/SDI-1/Cip-1 protein.
abstract: UVB irradiation inhibits melanocyte proliferation by causing arrest in G1 (D. Barker, K. Dixon, E. E. Medrano, D. Smalara, S. Im, D. Mitchell, G. Babcock, and Z. A. Abdel-Malek. Cancer Res., 55: 4041-4046, 1995). To determine how, after UVB irradiation, signal transduction pathways, DNA damage, and cell cycle arrest interact in the human melanocyte, we analyzed here the possible activation of tyrosine kinases, the serine-threonine kinases Baf-1 and ERK2, the status of the transcription factor c-fos, and the activation of cell cycle checkpoints induced by expression of p53 protein. We found that in contrast to the UVC response, exposure to UVB irradiation did not stimulate the above kinases. UVB light induced a prolonged c-fos expression, suggesting a mechanism of induction different from the transient expression elicited by growth factors. The tumor suppressor p53 and the p53-inducible cyclin-dependent kinase inhibitor protein p21Waf-1/SDI-1/Cip-1 were expressed at high levels for at least 2 days after UV-irradiation. In parallel, phosphorylation of Rb, the retinoblastoma tumor suppressor gene product, was halted in UVB-irradiated cells and correlated with the expression of the protein p21Waf-1/SDI-1/Cip-1. Our data define for the first time how UVB irradiation affects the expression of crucial regulatory events needed for cell cycle progression in the human melanocyte.
authors.affiliation: Roy M. and Phyllis Gough Huffington Center on Aging, Baylor College of Medicine, Houston, Texas 77030, USA.
authors.forename: E E
authors.initials: EE
authors.lastname: Medrano
authors.forename: S
authors.initials: S
authors.lastname: Im
authors.forename: F
authors.initials: F
authors.lastname: Yang
authors.forename: Z A
authors.initials: ZA
authors.lastname: Abdel-Malek
mesh_terms: D002478:Cells, Cultured; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000096:biosynthesis*; D004249:DNA Damage; D016193:G1 Phase / Q000528:radiation effects*; D016762:Genes, fos; D006801:Humans; D008544:Melanocytes / Q000528:radiation effects*; D010766:Phosphorylation; D047428:Protein Kinase Inhibitors; D017346:Protein Serine-Threonine Kinases / Q000528:radiation effects; D011518:Proto-Oncogene Proteins / Q000528:radiation effects; D019908:Proto-Oncogene Proteins c-raf; D016160:Retinoblastoma Protein / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D016159:Tumor Suppressor Protein p53 / Q000096:biosynthesis; D014466:Ultraviolet Rays
chemical_list: C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D047428:Protein Kinase Inhibitors; D011518:Proto-Oncogene Proteins; D016160:Retinoblastoma Protein; D016159:Tumor Suppressor Protein p53; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D013755:Tetradecanoylphorbol Acetate