Parathyroid hormone activates PKC-δ and regulates osteoblastic differentiation via a PLC-independent pathway

• Published in: Bone (New York, N.Y.) N.Y.), 2006-04, Vol.38 (4), p.485-496
• Main Authors: Yang, Dehong, Guo, Jun, Divieti, Paola, Bringhurst, F. Richard
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; Cell Differentiation - drug effects; Cell Line, Transformed; Enzyme Activation; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation - drug effects; Osteoblastic differentiation; Osteoblasts - cytology; Osteoblasts - drug effects; Parathyroid hormone; Parathyroid Hormone - pharmacology; Parathyroid hormone receptor; Phosphorylation; Protein kinase C; Protein Kinase C-delta - metabolism; Signal Transduction; Type C Phospholipases - metabolism; Vertebrates: anatomy and physiology, studies on body, several organs or systems
• ISSN: 8756-3282; 1873-2763
• DOI: 10.1016/j.bone.2005.10.009

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, [G 1,R 19]hPTH(1–28) and [G 1,R 19]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 [G 1,R 19]hPTH(1–34), but not [G 1,R 19]hPTH(1–28), increased differentiation of Wt9 cells during a 16-day alternate-daily treatment protocol. Wt9 cells expressed PKC-βI, -δ, -ε and -ζ, 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-δ, however, and a time- and concentration-dependent increase in cytosolic [phospho-Thr 505]PKC-δ which was maximal within 40 s at 100 nM in both Wt9 cells and primary osteoblasts. This response was mimicked by [G 1,R 19]hPTH(1–34) but not by [G 1,R 19]hPTH(1–28). Increased expression of bone sialoprotein (BSP) and osteocalcin (OC) mRNAs induced by PTH(1–34) and [G 1,R 19]hPTH(1–34) in Wt9 cells was blocked by rottlerin, a PKC-δ inhibitor. We conclude that PTH1Rs activate PKC-δ by a PLC-independent, PTH(29–34)-dependent mechanism that promotes osteoblastic differentiation.