Cyclosporin-A affects the organization of cytoskeleton of normal human keratinocytes in culture.

Cyclosporin-A (CsA) is a potent immunoregulatory molecule which has been widely used in many immunomediated and inflammatory skin diseases. It inhibits the proliferation of keratinocytes, but its possible effects(s) on cell differentiation are poorly known. To address this issue, we have studied the influence of CsA on the assembly of intermediate filaments by normal human keratinocytes in culture. Control keratinocytes were flat; the cells which had not reached confluence stained intensely for vimentin and weakly for cytokeratins; confluent cells stained with intermediate intensity for both types of proteins and the cells adhering on the top of others, interpreted as the best differentiated ones, stained for cytokeratins but not for vimentin. CsA (1.6 micrograms/ml for 10 days) inhibited the growth of keratinocytes, which never reached confluence; most cells appeared small and roundish, only some stained for cytokeratins and few for vimentin. By electron microscopy, a well organized meshwork of tonofibrils was recognized in many control keratinocytes, but never in CsA-treated keratinocytes. We propose that the cytoskeleton could be a target of CsA and that its alteration mediates other effects of CsA on keratinocytes, including those on cell growth.