WAVELENGTH-SPECIFIC UP-REGULATION OF KERATIN MESSENGER-RNA EXPRESSIONIN RESPONSE TO ULTRAVIOLET-RADIATION

Keratin intermediate filaments are heteropolymers of coexpressed type I and type II protein chains, whose expression is tightly linked to th e differentiation status of the keratinocyte. Epidermal basal keratino cytes coexpress keratins K5 and K14, whereas suprabasal keratinocytes downregulate K5 and K14 and begin to coexpress keratins K1 and K10. Us ing both isotopic and non-isotopic in situ hybridization, we have inve stigated the changes in expression of the messenger RNA species encodi ng the K5/K14 and K1/K10 keratin pairs in response to ultraviolet radi ation. Here we report that following irradiation, the mRNA species enc oding both keratin pairs is upregulated in a wavelength-specific manne r, and that the link between the pattern of keratin mRNA expression an d the differentiation status of the keratinocyte is disrupted. Forty-e ight hours following ultraviolet B exposure, the amount of detectable mRNA encoding all four keratins studied had increased. Following UVA i rradiation, the K1 and K10 signal increased to a much lesser extent th an following ultraviolet B, whereas no change in the amount of mRNA en coding the K5/K14 pair was observed. Only two samples were examined fo llowing ultraviolet C exposure, but in both, increased K5/K14 signal, but not suprabasal K1/K10 signal, was observed. We suggest that the ob servations reported here may reflect important qualitative changes inv olved in photoadaptation of the epidermis, and provide further molecul ar markers of the different biological effects of ultraviolet radiatio n of different wavelengths.