Unliganded estrogen receptor α stimulates bone sialoprotein gene expression

Gene. 2014 Apr 10;539(1):50-7. doi: 10.1016/j.gene.2014.01.063. Epub 2014 Feb 2.

Abstract

Estrogen is one of the steroid hormones essential for skeletal development. The estrogen receptor (ER) is a transcription factor and a member of the steroid receptor superfamily. There are two different forms of the ER, usually referred to as α and β, each encoded by a separate gene. Hormone-activated ERs form dimers, since the two forms are coexpressed in many cell types. Bone sialoprotein (BSP) is a tissue-specific acidic glycoprotein that is expressed by differentiated osteoblasts, odontoblasts and cementoblasts during the initial formation of mineralized tissue. To determine the molecular basis of the tissue-specific expression of BSP and its regulation by estrogen and the ER, we have analyzed the effects of β-estradiol and ERα on BSP gene transcription. ERα protein levels were increased after ERα overexpression in ROS17/2.8 cells. While BSP mRNA levels were increased by ERα overexpression, the endogenous and overexpressed BSP mRNA levels were not changed by β-estradiol (10(-8)M, 24 h). Luciferase activities of different sized BSP promoter constructs (pLUC3~6) were increased by ERα overexpression, whereas basal and induced luciferase activities by ERα overexpression were not influenced by β-estradiol. Effects of ERα overexpression were abrogated by 2 bp mutations in either the cAMP response element (CRE) or activator protein 1 (AP1)/glucocorticoid response element (GRE). Gel shift analyses showed that ERα overexpression increased binding to the CRE and AP1/GRE elements. Notably, the CRE-protein complexes were disrupted by ERα, CREB and phospho-CREB antibodies. The AP1/GRE-protein complexes were supershifted by the c-Fos antibody. These studies demonstrate that ERα stimulates BSP gene transcription in a ligand-independent manner by targeting the CRE and AP1/GRE elements in the rat BSP gene promoter.

Keywords: Activator protein 1; Bone sialoprotein; Estrogen; Estrogen receptor; Osteoblasts; Transcription; cAMP response element.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Bone Development / genetics
  • Bone and Bones
  • Cell Line
  • Cyclic AMP Response Element-Binding Protein / genetics*
  • Cyclic AMP Response Element-Binding Protein / immunology
  • Estradiol / metabolism
  • Estrogen Receptor alpha / biosynthesis
  • Estrogen Receptor alpha / immunology
  • Estrogen Receptor alpha / metabolism*
  • Gene Expression
  • Integrin-Binding Sialoprotein / biosynthesis
  • Integrin-Binding Sialoprotein / genetics*
  • Integrin-Binding Sialoprotein / metabolism
  • Osteoblasts / metabolism*
  • Promoter Regions, Genetic / genetics
  • Proto-Oncogene Proteins c-fos / immunology
  • RNA, Messenger / biosynthesis
  • Rats
  • Regulatory Elements, Transcriptional / genetics
  • Transcription Factor AP-1 / genetics*
  • Transcription Factor AP-1 / immunology
  • Transcription Factor AP-1 / metabolism
  • Transcription, Genetic
  • Transfection

Substances

  • Cyclic AMP Response Element-Binding Protein
  • Estrogen Receptor alpha
  • Integrin-Binding Sialoprotein
  • Proto-Oncogene Proteins c-fos
  • RNA, Messenger
  • Transcription Factor AP-1
  • Estradiol