Parathyroid hormone activates PKC-delta and regulates osteoblastic differentiation via a PLC-independent pathway.
PTH exerts major effects upon bone by activating PTH/PTHrP receptors (PTH1Rs) expressed on osteoblasts. The PTH1R is capable of engaging multiple signaling pathways in parallel, including Gs/adenylyl cyclase (AC), Gq/phospholipase C/protein kinase C (PLC/PKC) and a distinct mechanism, involving activation of PKC via a PLC-independent pathway, that depends upon ligand determinants within the PTH(29-34) sequence. The involvement of PLC-dependent vs. PLC-independent PKC activation in PTH action was studied in clonal PTH1R-expressing murine calvarial osteoblasts ("Wt9") using two signal-selective analogs, [G1,R19]hPTH(1-28) and [G1,R19]hPTH(1-34). Both analogs lack PLC signaling but differ in their capacity to activate the PLC-independent PKC pathway. Both hPTH(1-34) and [G1,R19]hPTH(1-34), but not [G1,R19]hPTH(1-28), increased differentiation of Wt9 cells during a 16-day alternate-daily treatment protocol. Wt9 cells expressed PKC-betaI, -delta, -epsilon and -zeta, none of which exhibited net translocation to membranes in response to hPTH(1-34) or either analog. hPTH(1-34) induced activation of membrane-associated PKC-delta, however, and a time- and concentration-dependent increase in cytosolic [phospho-Thr505]PKC-delta which was maximal within 40 s at 100 nM in both Wt9 cells and primary osteoblasts. This response was mimicked by [G1,R19]hPTH(1-34) but not by [G1,R19]hPTH(1-28). Increased expression of bone sialoprotein (BSP) and osteocalcin (OC) mRNAs induced by PTH(1-34) and [G1,R19]hPTH(1-34) in Wt9 cells was blocked by rottlerin, a PKC-delta inhibitor. We conclude that PTH1Rs activate PKC-delta by a PLC-independent, PTH(29-34)-dependent mechanism that promotes osteoblastic differentiation.
Yang
Dehong
D
Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA.
Guo
Jun
J
Divieti
Paola
P
Bringhurst
F Richard
FR
D002454:Cell Differentiation / Q000187:drug effects*; D002461:Cell Line, Transformed; D004789:Enzyme Activation; D005786:Gene Expression Regulation / Q000187:drug effects; D010006:Osteoblasts / Q000166:cytology / Q000187:drug effects*; D010281:Parathyroid Hormone / Q000494:pharmacology*; D010766:Phosphorylation; D051745:Protein Kinase C-delta / Q000378:metabolism*; D015398:Signal Transduction; D010738:Type C Phospholipases / Q000378:metabolism*
D010281:Parathyroid Hormone; D051745:Protein Kinase C-delta; D010738:Type C Phospholipases