Loss of ERE Binding Activity by Estrogen Receptor-Alpha Alters Basal and Estrogen-Stimulated Bone-Related Gene Expression by Osteoblastic Cells

J Cell Biochem. 2008 Feb 15;103(3):896-907. doi: 10.1002/jcb.21459.

Abstract

Estrogen receptor (ER)-alpha can signal either via estrogen response element (ERE)-mediated pathways or via alternate pathways involving protein-protein or membrane signaling. We previously demonstrated that, as compared to wild type (WT) controls, mice expressing a mutant ER-alpha lacking the ability to bind EREs (non-classical estrogen receptor knock-in (NERKI)) display significant impairments in the skeletal response to estrogen. To elucidate the mechanism(s) underlying these in vivo deficits, we generated U2OS cells stably expressing either WT ER-alpha or the NERKI receptor. Compared to cells transfected with the control vector, stable expression of ER-alpha, even in the absence of E2, resulted in an increase in mRNA levels for alkaline phosphatase (AP, by 400%, P < 0.01) and a decrease in mRNA levels for insulin growth factor-I (IGF-I) (by 65%, P < 0.001), with no effects on collagen I (col I) or osteocalcin (OCN) mRNA levels. By contrast, stable expression of the NERKI receptor resulted in the suppression of mRNA levels for AP, col I, OCN, and IGF-I (by 62, 89, 60, and 70%, P < 0.001). While E2 increased mRNA levels of AP, OCN, col I, and IGF-I in ER-alpha cells, E2 effects in the NERKI cells on AP and OCN mRNA levels were attenuated, with a trend for E2 to inhibit col I mRNA levels. In addition, E2 had no effects on IGF-I mRNA levels in NERKI cells. Collectively, these findings indicate that ERE signaling plays a significant role in mediating effects of estrogen on osteoblastic differentiation markers and on IGF-I mRNA levels.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Alkaline Phosphatase / metabolism
  • Animals
  • Bone Development / drug effects
  • Bone Development / genetics*
  • Bone and Bones / drug effects
  • Bone and Bones / metabolism
  • Bone and Bones / physiology*
  • Collagen / metabolism
  • Estradiol / pharmacology
  • Estrogen Receptor alpha / deficiency
  • Estrogen Receptor alpha / drug effects
  • Estrogen Receptor alpha / metabolism*
  • Estrogens / physiology*
  • Female
  • Gene Expression Regulation, Developmental / drug effects
  • Gene Expression Regulation, Developmental / physiology*
  • Humans
  • Insulin-Like Growth Factor I / metabolism
  • Mice
  • Osteoblasts / drug effects
  • Osteoblasts / metabolism*
  • Osteocalcin / metabolism
  • RNA, Messenger / biosynthesis
  • Response Elements / drug effects
  • Response Elements / physiology
  • Signal Transduction / physiology
  • Transcription, Genetic / genetics*

Substances

  • Estrogen Receptor alpha
  • Estrogens
  • RNA, Messenger
  • estrogen receptor alpha, human
  • Osteocalcin
  • Estradiol
  • Insulin-Like Growth Factor I
  • Collagen
  • Alkaline Phosphatase