Parathyroid hormone stimulates translocation of protein kinase C isozymes in UMR-106 osteoblastic osteosarcoma cells

Studies with antagonists have provided evidence that protein kinase C (PKC) is involved in several of the actions of parathyroid hormone (PTH) on bone . PTH increases total PKC activity in bone and bone cells. The current stud ies investigated whether PTH can activate specific PKC isozymes, as demonst rated by translocation of these isozymes from cytosolic to membrane fractio ns. The isozymes selected for study, alpha, betaI, delta, epsilon, and zeta , were shown previously by us to be present in normal osteoblasts. and seve ral osteosarcoma-derived osteoblastic cells. UMR-106 cells, a widely used o steoblastic cell line, were selected for the current study. PKC isozymes in whole cell lysates and cell fractions were visualized by western blotting; isozyme distribution was also visualized by immunofluorescence. The total amounts of the isozymes and their relative distribution between membrane an d cytosolic fractions in untreated cells were stable over a range of passag es (5-20 from initial plating). In untreated cells, the concentrations of P KC alpha, betaI, and zeta were higher in the cytosol, and PKC delta and eps ilon were higher in the membrane fraction. Treatment with 1 or 10 nmol/L PT H for 1 or 5 min stimulated translocation of PKC alpha and betaI, with vari able effects on the other isozymes. Treatment with phorbol-12,13-dibutyrate (PDBu), 1 mu mol/L for 5 min, elicited similar effects to those of PTH on PKC alpha and betaI. Treatment with PDBu for 48 h resulted in a downregulat ion of PKC alpha, whereas a 48 h treatment with PTH did not cause downregul ation. The results indicate that PTH can affect specific PKC isozymes, prov iding a mechanism for differential regulation of cellular actions through t his pathway. (Bone 29:223-230; 2001) (C) 2001 by Elsevier Science Inc. All rights reserved.