Vitamin D and dexamethasone inversely regulate parathyroid hormone-induced regulator of G protein signaling-2 expression in osteoblast-like cells

Endocrinology. 2003 Jun;144(6):2496-504. doi: 10.1210/en.2002-0160.

Abstract

The PTH/PTHrP receptor stimulates both adenylate cyclase- and phospholipase C-dependent signaling pathways via different G proteins. The biological actions of PTH on bone are modified by steroid hormones. PTH induces expression of regulator of G protein signaling (RGS)-2, a putative preferential inhibitor of G(q)-mediated phospholipase C activation. We investigated whether steroid hormones interfere with PTH signaling by modulating PTH-induced RGS-2 expression in osteoblast-like UMR 106-01 cells. PTH (1-34) rapidly and transiently induced expression of RGS-2 mRNA and protein via the cAMP/protein kinase A pathway within 30 min, with maximal protein abundance after 2 h. PTH-induced RGS-2 preferentially bound to Galpha(q), compared with Galpha(s) protein. 1,25-(OH)(2)D(3) pretreatment enhanced PTH-induced RGS-2 mRNA and protein accumulation, whereas dexamethasone preincubation had an attenuating effect. These effects were due to modulation of the RGS-2 gene transcription rate, which increased by 35% with 1,25-(OH)(2)D(3) and decreased by 63% with dexamethasone pretreatment. RGS-2 mRNA half-life was not affected by either steroid. The transcriptional effects of dexamethasone and 1,25-(OH)(2)D(3) were independent of PTH/PTHrP receptor activation and were not explained by effects on cAMP accumulation, cAMP response element-binding protein expression or phosphorylation, or the abundance of the osteoblast-specific transcription factor core-binding factor alpha (CBFa1/Runx2), a known activator of RGS-2 expression. In conclusion, glucocorticoids and 1,25-(OH)(2)D(3) inversely modulate PTH-induced RGS-2 gene transcription. Regulation of RGS-2 may constitute a novel mechanism by which steroids modulate signaling via the PTH/PTHrP receptor and other G protein-coupled receptors in bone.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Bone and Bones / cytology
  • Bone and Bones / metabolism
  • Calcitriol / pharmacology*
  • Calcium Channel Agonists / pharmacology*
  • Colforsin / pharmacology
  • Core Binding Factor Alpha 1 Subunit
  • Core Binding Factors
  • Cyclic AMP / metabolism
  • Cyclic AMP Response Element-Binding Protein / metabolism
  • Cyclic AMP-Dependent Protein Kinases / metabolism
  • Dexamethasone / pharmacology*
  • GTP-Binding Protein alpha Subunits, Gq-G11
  • Gene Expression / drug effects
  • Gene Expression / physiology
  • Glucocorticoids / pharmacology*
  • Heterotrimeric GTP-Binding Proteins / metabolism
  • Neoplasm Proteins*
  • Osteoblasts / cytology
  • Osteoblasts / physiology*
  • Osteosarcoma
  • Parathyroid Hormone / pharmacology
  • RGS Proteins / genetics*
  • RGS Proteins / metabolism
  • RNA, Messenger / analysis
  • Rats
  • Signal Transduction / drug effects
  • Signal Transduction / physiology
  • Transcription Factors / metabolism
  • Tumor Cells, Cultured

Substances

  • Calcium Channel Agonists
  • Core Binding Factor Alpha 1 Subunit
  • Core Binding Factors
  • Cyclic AMP Response Element-Binding Protein
  • Glucocorticoids
  • Neoplasm Proteins
  • Parathyroid Hormone
  • RGS Proteins
  • RNA, Messenger
  • Rgs2 protein, mouse
  • Transcription Factors
  • Colforsin
  • Dexamethasone
  • Cyclic AMP
  • Cyclic AMP-Dependent Protein Kinases
  • GTP-Binding Protein alpha Subunits, Gq-G11
  • Heterotrimeric GTP-Binding Proteins
  • Calcitriol