Expression of proliferating cell nuclear antigen/cyclin in human keratinocytes

The expression of proliferating cell nuclear antigen (PCNA), also called cyclin, in human keratinocytes was examined by using the serum obtained from a SLE patient and a murine monoclonal antibody against PCNA/cyclin. In the normal epidermis, few of the nuclei were labeled with anti-PCNA/cyclin. This was in contrast to the positive nuclear staining seen in active lesions of psoriasis. In a primary culture of human keratinocytes growing as a monolayer, 20%-30% of cells expressed PCNA/cyclin. SV40-transformed human keratinocytes showed positive nuclear staining in about 40% of the cell population. In stratified keratinocytes cultured in a high Ca++ medium, PCNA/cyclin expression was decreased and only the cells in the basal and suprabasal layers showed positive staining. These results indicate that the expression of PCNA/cyclin correlates with the proliferating state in human keratinocytes and may not be associated with the mechanism of differentiation in keratinocytes.