Biochemical and immunological characterization of renal protein kinase C

Protein kinase C (PKC) plays an important role in regulation of renal transport and metabolic function. To understand the role of a specific PKC isozyme in renal homeostasis, alpha-PKC content, regulation, and localization have been characterized. Immunoadsorption assays were used to determine that 34% of the total rat kidney PKC (measured as phorbol ester receptors) was alpha-PKC. Immunohistochemical staining with alpha-PKC-specific monoclonal antibodies determined that alpha-PKC was present throughout the nephron and was especially concentrated in proximal tubules and papillary collecting ducts. In general, the S3 segment of the proximal tubule stained more intensely than the S1-S2 segments. Cortical collecting ducts stained poorly for alpha-PKC. Interstitial cells of the papilla also stained for alpha-PKC. Subcellular distribution of alpha-PKC could not be determined in tissue sections; however, in cultured proximal tubule epithelial cells, alpha-PKC was localized not only in cytoplasm but also in cell-cell borders and focal contacts. Chromatography of rat kidney soluble fraction revealed two endogenous kinase inhibitors, one which is PKC specific and one which is a more general kinase inhibitor. The presence of negative regulators of PKC activity suggests that both activation and inactivation of PKC are important for normal renal function.