Immunohistochemical localization of proliferating cell nuclear antigen/cyclin in human skin

Expression of proliferating cell nuclear antigen/cyclin (PCNA/cyclin) in skin tissue specimens and cultured keratinocytes was studied using a monospecific antibody, obtained from a patient with systemic lupus erythematosus, and a monoclonal antibody. Indirect immunofluorescent staining revealed that cultured keratinocytes obtained from human foreskins expressed PCNA/cyclin as variable nuclear patterns in 15-30% of the cells. In normal human skin tissue specimens, PCNA/cyclin was demonstrated in only a few basal cells. Interestingly, PCNA/cyclin was expressed strongly in almost all the cells of the lowest layer of the epidermis adjacent to squamous cell carcinomas, whereas the tumor aggregates themselves had no positive staining. In contrast, no such characteristic staining was demonstrated in specimens of basal cell carcinoma. The staining pattern of PCNA/cyclin was different from that of Ki-67 in the skin tissue specimens. Our results suggest that PCNA/cyclin could be a useful marker of cell proliferation.