Wavelength-specific induction of immediate early genes by ultraviolet radiation

Exposure of skin in vivo to ultraviolet B (UVB) or ultraviolet A (UVA) radiation produces a variety of distinct clinical manifestations. In the present study, we characterized the immediate early genes that are activated in an epidermoid carcinoma cell line (A431) when exposed to UVB (FS20 sunlamp) or UVA radiation (window glass-filtered black light). We observed that: (a) c-jun mRNA expression is upregulated predominantly by UVB; (b) fra- 1 and c-myc are downregulated by UVB, whereas both are upregulated by UVA; (c) fra-2 and AP-2 are downregulated modestly by UVB, (d) c-fos is unaffected, and (e) optimal regulation of each gene is achieved at environmentally relevant fluences (25-100 J/m² for UVB and 2500-10000 J/m² for UVA). Thus, distinct sets of genes are activated (or repressed) by UVB and UVA irradiation. Treatment with organic hydrogen peroxides mimicked UVB radiation in upregulating c-jun expression, suggesting the participation of reactive oxygen intermediates in the UVB-signaling pathway. We propose that wavelength-specific regulation of nuclear mediator genes accounts for the development of at least some of the wavelength-specific cutaneous manifestations of ultraviolet radiation.