DIFFERENTIAL EXPRESSION OF CYCLOPHILIN ISOFORMS DURING KERATINOCYTE DIFFERENTIATION

Cyclophilin A, the major intracellular binding protein for the immunos uppressive drug cyclosporin A (CsA), was studied in human keratinocyte s during differentiation both in vivo and in vitro. Analysis of cyclop hilin by gel-filtration radiobinding-assay with tritiated CsA showed o ne specific radioactive peak at 17 kDa. By this technique, the levels of cyclophilin (mean 55.23 +/- 8.43 pmol/mg protein) did not significa ntly differ during keratinocyte differentiation. When the protein extr acts from calcium-induced differentiating keratinocytes and normal hum an skin were analysed by PAGE radiobinding-assay, two specific radioac tive CsA-binding peaks were detected. The major peak (R(F) 0.13) was e xpressed in all samples (mean 47.32 +/- 17.53 pmol/mg protein) whereas the minor peak (R(F) 0.23) was dramatically decreased about 6-fold in abnormally differentiated skin (psoriasis) as well as in non-differen tiated keratinocytes. At least six [H-3]CsA-binding isoforms with pi v alues ranging from 5.58 to 7.75 were detected by isoelectrofocusing au toradio-blotting-assay in normal human skin; three of them immuno-reac ted with antibodies to cyclophilin. These results demonstrated the pre sence of several cyclophilin isoforms in human epidermal cells and an expression which correlated with the differentiation of human keratino cytes both in vivo and in vitro.