Proliferating cell nuclear antigen/cyclin in cultured human keratinocytes

Expression of proliferating cell nuclear antigen (PCNA)/cyclin in cultured human keratinocytes was studied using an antibody from an SLE patient as the reagent. By indirect immunofluorescence staining, SV40-transformed human keratinocytes expressed PCNA/cyclin in 40-45% of the cells as a nulcear granular fluorescence. After synchronization of these cells, their nuclear distribution pattern during the S phase was sequential and showed a clear correlation with DNA synthesis. Primary cultured keratinocytes grown in high Ca+ medium expressed PCNA/cyclin in 10-15% of the cells with a similar staining pattern. These positively stained cells were confined to the basal and immediate suprabasal layers of the stratified culture sheet. The keratinocytes disaggregated by trypsin were separated according to cell size through a screen of Nitex monofilament cloth. The cells smaller than 15 microns in diameter synthesized abundant PCNA/cyclin, while the larger cells expressed very low levels. These results indicate that the expression of PCNA/cyclin correlates with DNA synthesis in cultured keratinocytes, but is not associated with their differentiation process.