UVB RADIATION-ACTIVATED GENES INDUCED BY TRANSCRIPTIONAL AND POSTTRANSCRIPTIONAL MECHANISMS IN RAT KERATINOCYTES

The mechanisms utilized by ultraviolet B (UVB) radiation in the regula tion of gene expression, as well as the genetic targets for transmissi on of the WE signal, remain incompletely understood. To elucidate the mechanisms and targets for WE activation in mammalian cells, we screen ed a keratinocyte cDNA library with differentially subtracted UVB-enri ched cDNA probes. Twenty-three UVB-induced cDNA clones were isolated, including cDNAs for keratin, elongation factor-1 alpha, ferritin heavy chain, thioltransferase, cyclin G, cornifin, cellubrevin, poly(A) bin ding protein, and the surfeit locus. The temporal kinetics of maximal RNA induction following UVB exposure were heterogeneous, varying from 1 to 24 h post-WB radiation. Analysis of the regulation of gene expres sion demonstrated that the levels of most UVB-induced mRNAs were also independently induced by serum and cycloheximide, features previously described for genes induced by DNA damage and members of the immediate early gene family. In contrast to results from studies of immediate e arly genes, treatment of keratinocytes with both serum and cycloheximi de resulted in superinduction of only one mRNA transcript. Nuclear run -on assays demonstrated that UVB radiation increased the transcription rate in 8 of 23 genes, suggesting that UVB radiation utilizes both tr anscriptional and posttranscriptional mechanisms for the modulation of keratinocyte gene expression. The identification of a group of UVB-in ducible keratinocyte genes should prove useful for the characterizatio n of the genomic response to WE radiation and the analysis of the mole cular mechanisms underlying the UVB regulation of gene expression.