UVB-specific regulation of gene expression in human melanocytic cells: cell cycle effects and implication in the generation of melanoma

Analysis of the expression of a number of known genes in cultured human cel ls has revealed UVB-induced changes that may be specific for melanocytic ce lls. The response of c-fos, p53 and HIV-LTR reporter constructs to UVB and UVC was reduced in MM96L melanoma cells compared to HeLa. Cell cycle arrest produced by UVA, gamma radiation, cisplatin or the antimetabolite deoxyino sine differed from that of UVB. Cell cycle analysis after multiple doses of UVB raised the possibility that UVB-induced pRb depletion could result in increased mutation and thus enhanced tumourigenesis of irradiated melanocyt es in skin subjected to a defined pattern of UVB exposure. To extend the an alysis of gene expression in cultured melanocytic cells to uncharacterised genes, promoter trap cell clones containing unknown genes 'tagged' by a bet a-galactosidase reporter construct were generated from MM96L cells. Altered gene expression in clones treated with a panel of DNA-damaging agents was quantitated by measurement of beta-galactosidase activity. Of the clones co ntaining 'tagged' endogenous promoters induced by UVB, 52% were induced onl y by WE and not by other DNA-damaging agents (cisplatin, N-methyl-N-nitro-n itrsoguanidine, fotemustine). One third of the clones were also activated b y TPA suggesting that general DNA damage responses involving PKC are activa ted less frequently than unique pathways of gene activation. Overall, 60% o f the 50 clones that responded to the panel of agents were induced by only one of the agents, indicating that a high proportion of genes are induced b y agent-specific mechanisms. In the long term, promoter trapping may allow the full repertoire of UVB-inducible genes to be characterised. (C) 1998 El sevier Science B.V. All rights reserved.