Ultraviolet B irradiation increases keratin 5 and keratin 14 expression through epidermal growth factor receptor of SV40-transformed human keratinocytes.

Abstract

Keratin intermediate filaments are heteropolymers composed of type I and type II keratins. Ultraviolet B (UVB) irradiation induces keratin expression by keratinocytes. Using SV40-transformed human keratinocytes (SVHK), we investigated the effect of UVB irradiation on keratin expression. UVB irradiation (10 mJ/cm(2)) increased keratin 5 and keratin 14 mRNAs and proteins without affecting cell viability. Upregulation of keratin 5 and keratin 14 was dependent on the dose of radiation: the effect was observed at 5 mJ/cm(2) and the maximal effect was observed at 10 mJ/cm(2). Higher UVB doses (more than 10 mJ/cm(2)) were cytotoxic. Expression of keratin 1 and keratin 10 was marginal in SVHK and was not affected at either the mRNA or protein level by UVB. The stimulatory effects on keratin 5 and keratin 14 expression were also observed in cultured normal human keratinocytes (NHK) and HaCaT keratinocytes. The tyrosine kinase inhibitor, genistein, and the epidermal growth factor (EGF) receptor inhibitor, AG1429, significantly suppressed the increase in expression of keratin 5 and keratin 14 by SVHK. In contrast, the suppressive effect was not observed with the protein kinase C inhibitor, H-7. Furthermore, pretreatment with neutralizing anti-EGF receptor antibody also suppressed UVB-induced keratin 5 and keratin 14 expression by SVHK, NHK and HaCaT cells. UVB irradiation did not affect the steady-state expression of TGF-alpha by SVHK. Immunoprecipitation and immunohistochemical studies revealed that UVB irradiation induced EGF receptor activation in the absence of EGF and TGF-alpha. These results indicate that UVB increases keratin 5 and keratin 14 expression through direct activation of the EGF receptor in SVHK.