Suppression of keratin 15 expression by transforming growth factor beta invitro and by cutaneous injury in vivo

Transforming growth factor beta (TGF-beta) is a multifunctional cytokine wh ich plays an important role in cutaneous wound repair. To gain insight into the mechanisms of action of this growth and differentiation factor in the skin, we searched for genes which are regulated by TGF-beta 1 in cultured H aCaT keratinocytes. Using the differential display RT-PCR technology we ide ntified a gene which was strongly downregulated by TGF-beta 1. The identifi ed cDNA includes sequences of the keratin 15 (K15) gene which encodes a com ponent of the cytoskeleton of basal cells in stratified epithelia, Surprisi ngly, our cDNA also included an unknown sequence. Since this cDNA lacks an open reading frame, the corresponding mRNA is likely to be nonfunctional. H owever, we also demonstrate a strong negative regulation of the expression of the published, functional K15 variant. Expression of K15 was also suppre ssed by tumor necrosis factor alpha (TNF-alpha) and to a lesser extent by e pidermal growth factor (EGF) and keratinocyte growth factor (KGF). By contr ast, the major basal type I keratin, K14, was upregulated by TGF-beta 1, wh ereas TNF-alpha EGF, and KGF had no effect. Consistent with the in vitro da ta, we found a significant reduction of the K15 mRNA levels after skin inju ry, whereas K14 expression increased during the wound healing process. Immu nostaining revealed the presence of K15 in all basal cells of the epidermis adjacent to the wound, but not in the hyperproliferative epithelium above the granulation tissue. These data demonstrate that K15 is excluded from th e activated keratinocytes of the hyperthickened wound epidermis, possibly a s a result of increased growth factor expression in injured skin. (C) 2000 Academic Press.