Cell-specific signaling and structure-activity relations of parathyroid hormone analogs in mouse kidney cells

PTH is an 84-amino acid protein. Occupancy of its cognate receptor generall y results in activation of adenylyl cyclase and/or phosphoinositide-specifi c phospholipase C beta (PLC beta). In the kidney, PTH receptors are present on proximal and distal tubule cells. In proximal tubules, PTH induces calc ium signaling, typified by a transient rise in intracellular calcium ([Ca2](i)) and inositol trisphosphate formation, but does not affect calcium abs orption. By contrast, in distal tubules, PTH increases calcium absorption t hat is associated with a slow and sustained rise in [Ca2+](i), but does not stimulate phospholipase C (PLC) or cause inositol trisphosphate accumulati on. Nonetheless, stimulation of distal calcium transport requires activatio n of protein kinase C (PKC) and protein kinase A. We now characterize the o rigin of the differential effects of ligand occupancy by using synthetic hu man PTH analogs that preferentially activate adenylyl cyclase and/or PLC be ta. We further tested the hypothesis that phospholipase D is responsible fo r PKC activation in distal tubule cells. PTH-(1-31) increased [Ca2+](i) in distal tubule but not in proximal tubule cells, whereas PTH-(3-34) caused a partial increase in [Ca2+](i) in proximal cells, but had no effect in dist al cells. PTH-(7-34) blocked increases in [Ca2+](i) in distal tubule cells stimulated by PTH-(1-34) and PTH(1-31). The PLC inhibitor U73122 abolished the PTH-induced rise in [Ca2+](i) and inositol trisphosphate formation by p roximal tubule cells, but had no effect on PTH-stimulated Ca2+ uptake by di stal tubule cells. These results support the view that activation of PKC by PTH in distal tubule cells does not involve PLC beta. PTH did, however, ac tivate phospholipase D with attendant formation of diacylglycerol in distal cells. As activation of PKC is required for induction of calcium transport by PTH, we conclude that PTH receptors are capable of activating multiple phospholipases and that the structural requirements for such activation dif fer in proximal and distal tubule cells.