Unliganded estrogen receptor α stimulates bone sialoprotein gene expression

• Published in: Gene Vol. 539; no. 1; pp. 50 - 57
• Main Authors: Takai, Hideki, Matsumura, Hiroyoshi, Matsui, Sari, Kim, Kyung Mi, Mezawa, Masaru, Nakayama, Yohei, Ogata, Yorimasa
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 10.04.2014
• Subjects: Activator protein 1; Animals; Bone and Bones; Bone Development - genetics; Bone sialoprotein; cAMP response element; Cell Line; Cyclic AMP Response Element-Binding Protein - genetics; Cyclic AMP Response Element-Binding Protein - immunology; Estradiol - metabolism; Estrogen; Estrogen receptor; 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; Osteoblasts - metabolism; Promoter Regions, Genetic - genetics; Proto-Oncogene Proteins c-fos - immunology; Rats; Regulatory Elements, Transcriptional - genetics; RNA, Messenger - biosynthesis; Transcription; Transcription Factor AP-1 - genetics; Transcription Factor AP-1 - immunology; Transcription Factor AP-1 - metabolism; Transcription, Genetic; Transfection; cAMP response element; Estrogen receptor; AP1; FGF; Transcription; ERα; Estrogen; Activator protein 1; Bone sialoprotein; nts; Osteoblasts; bp; MEM; CRE; FCS; FRE; LUC; GAPDH; BSP
• ISSN: 0378-1119; 1879-0038
• DOI: 10.1016/j.gene.2014.01.063

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 (10−8M, 24h). 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 2bp 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. •ERα stimulates BSP gene transcription in a ligand-independent manner.•ERα increases BSP transcription without estrogen in osteoblast-like cells.•Targets of ERα are CRE and AP1/GRE elements in the rat BSP gene promoter.•CRE binding proteins in the rat BSP gene promoter are CREB and ERα.•AP1/GRE binding proteins in the rat BSP gene promoter are c-Fos and ERα.