UVB radiation-activated genes induced by transcriptional and posttranscriptional mechanisms in rat keratinocytes

Abstract

The mechanisms utilized by ultraviolet B (UVB) radiation in the regulation of gene expression, as well as the genetic targets for transmission of the UVB signal, remain incompletely understood. To elucidate the mechanisms and targets for UVB activation in mammalian cells, we screened a keratinocyte cDNA library with differentially subtracted UVB-enriched 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) binding protein, and the surfeit locus. The temporal kinetics of maximal RNA induction following UVB exposure were heterogeneous, varying from 1 to 24 h post-UVB radiation. Analysis of the regulation of gene expression 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 early genes, treatment of keratinocytes with both serum and cycloheximide 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 transcriptional and posttranscriptional mechanisms for the modulation of keratinocyte gene expression. The identification of a group of UVB-inducible keratinocyte genes should prove useful for the characterization of the genomic response to UVB radiation and the analysis of the molecular mechanisms underlying the UVB regulation of gene expression.