Induction of osteoblast differentiation indexes by PTHrP in MG-63 cells involves multiple signaling pathways

Abstract

Parathyroid hormone (PTH)-related peptide (PTHrP) can modulate the proliferation and differentiation of a number of cell types including osteoblasts. PTHrP can activate a G protein-coupled PTH/PTHrP receptor, which can interface with several second-messenger systems. In the current study, we have examined the signaling pathways involved in stimulated type I collagen and alkaline phosphatase expression in the human osteoblast-derived osteosarcoma cells, MG-63. By use of Northern blotting and histochemical analysis, maximum induction of these two markers of osteoblast differentiation occurred after 8 h of treatment with 100 nM PTHrP-(1-34). Chemical inhibitors of adenylate cyclase (H-89) or of protein kinase C (chelerythrine chloride) each diminished PTHrP-mediated type I collagen and alkaline phosphatase stimulation in a dose-dependent manner. These effects of PTHrP could also be blocked by inhibiting the Ras-mitogen-activated protein kinase (MAPK) pathway with a Ras farnesylation inhibitor, B1086, or with a MAPK inhibitor, PD-98059. Transient transfection of MG-63 cells with a mutant form of Galpha, which can sequester betagamma-subunits, showed significant downregulation of PTHrP-stimulated type I collagen expression, as did inhibition of phosphatidylinositol 3-kinase (PI 3-kinase) by wortmannin. Consequently, the betagamma-PI 3-kinase pathway may be involved in PTHrP stimulation of Ras. Collectively, these results demonstrate that, acting via its G protein-coupled receptor, PTHrP can induce indexes of osteoblast differentiation by utilizing multiple, perhaps parallel, signaling pathways.

Multiple signaling pathways involved in stimulation of osteoblast differentiation by N-methyl-D-aspartate receptors activation in vitro

“…The MAPK, PKC, PKA and PI3K signaling pathways can all be directly activated downstream of calcium influx [61] . The activation of protein kinase C (PKC) and/or protein kinase A (PKA) plays an essential role in osteoblast differentiation [62] . In our previous study, we have observed activation of the ERK1/2 signaling pathway when osteoblasts were treated with NMDA [12] .…”

Osteogenic BMPs promote tumor growth of human osteosarcomas that harbor differentiation defects

“…32 Human OS tumors usually exhibit osteoblast-like features. 3,[33][34][35][36][37][38][39] We demonstrated that differentiation-promoting agents (eg, PPARg agonists and 9-cis retinoic acid) can induce osteoblast differentiation and inhibit OS cell proliferation. 3,40 Here, we investigate whether the disruption of osteoblast differentiation plays a role in OS development.…”

Parathyroid Hormone Induction of the Osteocalcin Gene

“…In vitro, PTH inhibits bone marker gene expression and mineralization in differentiated osteoblasts and cementoblasts (49,56). In contrast, PTH rapidly induces osteoblastspecific gene expression in undifferentiated, proliferating osteoblasts (8,16,57,58). Thus, PTH may preferentially stimulate osteoblast differentiation in immature cells while inhibiting it in more mature cells.…”

“…A number of signaling transduction pathways have been associated with PTH (8,9,(47)(48)(49)(50). For example, Boguslawski et al (16) showed that PKA and PKC pathways cooperatively interact in PTH-mediated OCN gene expression in rat and human osteoblast cell lines.…”

“…PTH functions through the PTH-1 receptor, a G protein-coupled receptor that is expressed in osteoblasts (5-7). Binding of PTH to its receptor activates multiple intracellular signaling pathways that involve cyclic cAMP, inositol phosphates, intracellular Ca 2ϩ , protein kinases A and C (2), and the extracellular signal-regulated kinase/ mitogen-activated protein kinase (MAPK) pathway (8,9).…”