Role of protein kinase C in parathyroid hormone stimulation of renal 1,25-dihydroxyvitamin I)3 secretion

PTH is a major regulator of renal proximal tubule 1,25(OH)2D3 biosynthesis. However, the intracellular path-ways involved in PTH activation of the mitochondrial 25-hy-droxyvitamin D3-1 alpha-hydroxylase (1-OHase) remain un-known. PTH can activate both the adenylate cyclase/protein kinase A (PKA) and the plasma membrane phospholipase C/ protein kinase C (PKC) pathways. The present study was un-dertaken to determine whether PKC may mediate PTH activa-tion of renal 25-hydroxyvitamin D3-1 alpha-hydroxylase activ-ity. Rat PTH 1-34 fragment in vitro translocated PKC activity from cytosolic to soluble membrane fraction from freshly pre-pared rat proximal tubules. Physiologic concentrations (10-'-10-10 M) of rat PTH 1-34 fragment increased PKC transloca-tion three- to fourfold while PKA activity ratio increased at PTH i0- M. PTH stimulation ofPKC and PKA was reduced in the presence of staurosporine (10 nM) by 41 and 29%, re-spectively. Sangivamycin (10 and 50,M) also reduced PTH-stimulated PKC translocation, but did not alter PKA activity ratio. In vitro perifusion of renal proximal tubules with PTH (1011 M) increased 1,25(OH)2D3 steady-state secretion two-to fourfold. Sangivamycin at the same concentration that inhibited PKC translocation by 52 % completely inhibited PTH-stimulated 1,25(OH)2D3 secretion. The present studies indi-cate that the phospholipase C/PKC pathway may mediate PTH stimulation of mammalian renal proximal tubul