ULTRAVIOLET-A IRRADIATION UP-REGULATES TYPE-VII COLLAGEN EXPRESSION IN HUMAN DERMAL FIBROBLASTS

Type VII collagen, a major component of skin-anchoring fibrils, is syn thesized by both fibroblasts and keratinocytes, the two principal cell types in the skin, In this study, we examined the effects of ultravio let A (UVA) irradiation on the expression of type VII collagen in huma n fibroblasts. UVA irradiation (0-15 J/cm(2)) caused a dose-dependent increase (5- to 10-fold) in type VII collagen mRNA levels as detected by northern blot analysis, The UVA-induced enhancement of type VII col lagen gene expression correlated with an increase in its protein level by immunoblot analysis of proteins secreted into the conditioned medi um. The effect of UVA was observed at 12 h and reached its maximum by 18 h Under these conditions, however, the expression of fibronectin, a major dermal matrix protein, remained unchanged, suggesting that the induction of type VII collagen expression was selective, Actinomycin D , a transcription inhibitor, blocked the UVA-mediated induction of typ e VII collagen gene expression, whereas cycloheximide, a protein synth esis inhibitor, superinduced the expression of type VII collagen, sugg esting that ne novo protein synthesis was not required for the action of UVA, Interestingly, in contrast to the increased type VII collagen expression in fibroblasts in response to UVA, a slight decrease in typ e VII collagen mRNA level was observed in the UVA-irradiated keratinoc ytes, suggesting that the effect of UVA on the type VII collagen expre ssion is cell type specific.