β-arrestin2 regulates parathyroid hormone effects on a p38 MAPK and NFκB gene expression network in osteoblasts

Interaction of the cytoplasmic adaptor molecule beta-arrestin2 with the activated parathyroid hormone (PTH)/PTHrP receptor inhibits G protein mediated signaling and triggers MAPKs signaling. In turn, the effects of both intermittent (i.) and continuous (c.) PTH on bone are altered in beta-arrestin2-deficient (Arrb2(-/-)) mice. To elucidate the expression profile of bone genes responsive to PTH and targeted for regulation by beta-arrestin2, we performed microarray analysis using total RNA from primary osteoblastic cells isolated from wild-type (WT) and Arrb2(-/-) mice. By comparing gene expression profiles in cells exposed to i.PTH, c.PTH or vehicle (Veh) for 2 weeks, we found that i.PTH specifically up-regulated 215 sequences (including beta-arrestin2) and down-regulated 200 sequences in WT cells, about two-thirds of thern being under the control of beta-arrestin2. In addition, beta-arrestin2 appeared necessary to the down-regulation of a genomic cluster coding for small leucin-rich Proteins (SLRPs) including osteoglycin, osteomodulin and asporin. Pathway analyses identified a main gene network centered on p38 MAPK and NF kappa B that requires beta-arrestin2 for up- or down-regulation by i.PTH, and a smaller network of PTH-regulated genes centered on TGFBI, that is normally repressed by beta-arrestin2. In contrast the expression of some known PTH gene targets regulated by the cAMP/PKA pathway was not affected by the presence or absence of beta-arrestin2 in osteoblasts. These results indicate that beta-arrestin2 targets prominently p38 MAPK- and NF kappa B-dependent expression in osteoblasts exposed to i. PTH, and delineates new molecular mechanisms to explain the anabolic and catabolic effects of PTH on bone. (c) 2009 Elsevier Inc. All rights reserved.