Increased expression of G₁₁α in osteoblastic cells enhances parathyroid hormone activation of phospholipase C and AP‐1 regulation of matrix metalloproteinase‐13 mRNA

Abstract

In osteoblasts parathyroid hormone (PTH) stimulates the PTH/PTH-related peptide (PTHrP) receptor (PTH1R) that couples via G(s) to adenylyl cyclase stimulation and via G(11) to phospholipase C (PLC) stimulation. We have investigated the effect of increasing G(11)alpha levels in UMR 106-01 osteoblastic cells by transient transfection with cDNA encoding G(11)alpha on PTH stimulation of PLC and protein kinase C (PKC) as well as PTH regulation of mRNA encoding matrix metalloproteinase-13 (MMP-13). Transfection with G(11)alpha cDNA resulted in a 5-fold increase in PTH-stimulated PLC activity with no change in PTH-stimulated adenylyl cyclase. PTH-induced translocation of PKC-betaI, -delta, and -zeta to the cell membrane and PKC-zeta to the nucleus was also increased. Increased G(11)alpha protein resulted in increased stimulation of MMP-13 mRNA levels at all doses of PTH. There was a 2.5 +/- 0.35 fold increase in maximal PTH-stimulation of c-jun mRNA and smaller but significant increases in c-fos accompanied by increased basal and PTH-stimulated AP-1 binding in cells expressing increased G(11)alpha. Runx-2 mRNA and protein levels were not significantly increased by increased G(11)alpha expression. The increase in PTH stimulation of c-jun, c-fos, and MMP-13 in G(11)alpha-transfected cells were all blocked by bisindolylmaleimide I, a selective inhibitor of PKC. These results demonstrate that regulation of the PLC pathway through the PTH1R is significantly increased by elevating expression of G(11)alpha in osteoblastic cells. This leads to increased PTH stimulation of MMP-13 expression by increased stimulation of AP-1 factors c-jun and c-fos.

Elevated Gα11expression in osteoblast lineage cells promotes osteoclastogenesis and leads to enhanced trabecular bone accrual in response to pamidronate

“…To determine whether variation in G protein expression in osteoblasts can govern bone turnover, we demonstrated previously that UMR 106-01 cells transfected with Gna11, which encodes for G␣ 11 , enhances the cellular PLC response to PTH stimulation (5). More recently, we showed that mice with overexpression of G␣ 11 in osteoblast lineage cells (G 11 -Tg) have an osteopenic phenotype with decreased bone formation, increased osteoclasts, and elevated expression of genes that encode RANKL and M-CSF (6).…”

Role and Function of Matrix Metalloproteinases in the Differentiation and Biological Characterization of Mesenchymal Stem Cells

“…Activation of parathyroid hormone receptors in osteoblasts has been shown to increase the expression levels of several MMPs (MMP‐9, MMP‐13) through increased stimulation of the phospholipase C pathway, leading to upregulated expression of the AP‐1 factors c‐jun and c‐fos [59]. MMPs are thought to also play a role in the bone remodeling and transdifferentiation balance.…”

Expression pattern of matrix metalloproteinase and TIMP genes in fibroblasts derived from Ets-1 knock-out mice compared to wild-type mouse fibroblasts

“…Expression and activity of these enzymes are controlled by a fine balance between induction by different growth factors and cytokines, proteolytic activation through the plasminogen/ plasmin system and inhibition by several tissue inhibitors of metalloproteinases (TIMPs) (8)(9)(10)(11)(12)(13)(14)(15)(16)(17). An important level of regulation of MMPs is transcription and several transcription factors, such as AP-1, SP-1 and members of the ETS-family, have been shown to transactivate or transrepress different protease genes alone or in combination (18)(19)(20)(21)(22)(23)(24)(25). Several lines of evidence point to major roles of the Ets-1 transcription factor for this level of regulation (26)(27)(28).…”