A study of protein kinase C isozyme distribution in relation to Bcl-2 expression during apoptosis of epithelial cells in vivo.

The steady-state population of stratified squamous epithelium is maintained by balanced cell proliferation and apoptosis. Protein kinase C (PKC) is intimately involved in the regulation of cell proliferation and cell survival. In order to gain insight into the mechanisms regulating apoptosis, the immunocytochemical localization of six PKC isozymes (PKC-alpha, -beta, -delta, -epsilon, -gamma, and -zeta) were studied in the surface epithelium of the human tonsil by immunofluorescence staining and confocal laser scanning microscopy. All cells expressed cytoplasmic PKC-alpha, -beta, -delta, -epsilon, and -zeta; PKC-delta and -epsilon were most abundant in viable epithelial cells while PKC-alpha and -beta expression was most intense in cells undergoing apoptosis. PKC-beta and -delta were also present in the nucleus of viable epithelial cells coexpressing cytoplasmic Bcl-2, an oncogene product which protects from apoptosis. Nuclear expression of these isozymes did not correlate with epithelial cell mitosis, as defined by proliferating cell nuclear antigen. Thus, differential subcellular localization of PKC isoforms is associated with the regulation of epithelial cell apoptosis in situ.