A VITAMIN-D ANALOG KH 1060 ACTIVATES THE PROTEIN-KINASE C-C-FOS SIGNALING PATHWAY TO STIMULATE EPIDERMAL PROLIFERATION IN MURINE SKIN

The cellular signalling pathways of a potent 20-epi-22-oxa vitamin D-3 analogue (KH 1060) were examined in vivo in a hairless mouse model. Seventy two hours after a single topical application of KH 1060 a thickening of the epidermis (from 24.8+/-1.2 mu m at 0.01 pmol/cm(2) KH 1060 to 124.2+/-6 mu m at 5 pmol/cm(2) KH 1060, P<0.001) was elicited due to epidermal hyperproliferation. This effect could be blocked by topical 2.5 mu mol/cm(2) sphingosine, an inhibitor of protein kinase C. Two hours after topical application of 2.5 pmol/cm(2) KH 1060 a translocation of protein kinase C activity from cytoplasm to the membrane fractions was observed. Moreover, using a reverse-transcription polymerase chain reaction technique, a transient upregulation of c-fos gene expression was seen 2 hours after topical treatment with KH 1060. The expression of c-fos was dependent on protein kinase C activation, since after pretreatment with the protein kinase C blocker sphingosine, c-fos messenger RNA was not detected. These findings strongly suggest that KH 1060 stimulates epidermal growth through activation of the protein kinase C - c-fos signalling axis in vivo.