Immunolocalization of protein kinase C isoenzymes α, βI and βII in rat kidney

Protein kinase C (PKC) significantly contributes to the control of renal function, but little is known about the renal function or localization of PKC isoenzymes. Therefore, the localization of PKC isoenzymes alpha, beta I, and beta II was studied in rat kidney. Immunoblot analysis identified immunoreactive bands corresponding to PKC alpha, beta I, and beta II in total cell extracts of both renal cortex and medulla. Immunohistochemistry using confocal laser scanning microscopy revealed immunostaining for PKC alpha within the glomerulus including podocytes and mesangial cells. PKC beta I was detected in mesangial cells, whereas anti-PKC beta II labeled neither podocytes nor mesangial cells. PKC beta II, however, was detected in cells within the mesangial area, which expressed MHC II, a marker for antigen-presenting cells. None of the three isoforms was detected in glomerular endothelial cells. A prominent immunostaining with anti-PKC alpha and beta I was localized to the brush border of S2 and S3 segments of proximal tubule, whereas S1 segments were not stained. Along the loop of Henle, both PKC alpha and PKC beta I were found in the luminal membrane of cortical and medullary thick ascending limb. In addition, anti-PKC beta I labeled the luminal membrane of thin limbs. In the cortical collecting duct (CCD), immunofluorescence for PKC alpha was observed at the apical membrane of both peanut agglutinin (PNA)-negative cells and part of PNA-positive cells, whereas in the medullary collecting duct (MCD), PKC alpha was detected at the basolateral membrane. In comparison, PKC beta I was localized at the luminal membrane of PNA-positive cells only in CCD and at the luminal membrane of MCD. Unlike PKC alpha or beta I, there was (I) no detectable immunostaining with anti-PKC beta II in the proximal tubule, the loop of Henle, or the CCD and (2) a distinct staining for PKC beta II of interstitial cells in cortex and medulla (including MHC II-positive dendritic cells). Furthermore, PKC beta II was detected in the luminal membrane of MCD. In summary, a distinct and differential expression pattern for PKC alpha, beta I, and beta II was shown in rat kidney, which may contribute to a better understanding of the specific role of these isoenzymes in the control of renal function.