IMMUNOCYTOCHEMICAL LOCALIZATION OF PROTEIN-KINASE-C SUBTYPES IN ANTERIOR-PITUITARY-CELLS - COLOCALIZATION IN HORMONE-CONTAINING CELLS REVEALS HETEROGENEITY

We have examined the distribution and colocalization of protein kinase-C (PKC) in cultured rat anterior pituitary cells by light microscopic immunocytochemistry using monoclonal antibodies to group A rat brain PKC subspecies. Type I (PKC-gamma) was not detected in the cells, in line with the assertion that the gamma-enzyme is expressed specifically in central nervous tissues. The other subspecies recognized by the antibodies (PKC-beta and PKC-alpha) were present throughout the cytoplasm in a diffused pattern, while the nuclei were apparently unstained. The number of cells stained with the antibodies in juvenile animals (12 days old) increased rapidly with age and reached a plateau between adult (5-month-old) and older (1-yr-old) rats. Type II (PKC-beta) was the predominant subspecies detected in anterior pituitary cells. Double immunofluorescence staining techniques enabled the colocalization of PKC with various anterior pituitary cell types. Surprisingly, not all of the hormone-producing cells were stained with the PKC antibodies. Moreover, within the different pituitary cell types, the percentage of PKC-stained cells varied, revealing heterogeneity among the various cell populations. Thus, among somatrophs, mammotrophs, thyrotrophs, ACTH-containing cells, and gonadotrophs, only 9%, 22%, 13%, 44%, and 26%, respectively, reacted with the PKC antibodies. We suggest that activation of pituitary PKC might mobilize only a fraction of the hormone-containing cells.