Unliganded estrogen receptor α stimulates bone sialoprotein gene expression.
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.
Department of Periodontology, Nihon University School of Dentistry at Matsudo, Chiba 271-8587, Japan; Research Institute of Oral Science, Nihon University School of Dentistry at Matsudo, Chiba 271-8587, Japan.
Hideki
H
Takai
Department of Periodontology, Nihon University School of Dentistry at Matsudo, Chiba 271-8587, Japan.
Hiroyoshi
H
Matsumura
Department of Periodontology, Nihon University School of Dentistry at Matsudo, Chiba 271-8587, Japan.
Sari
S
Matsui
Department of Periodontology, Nihon University School of Dentistry at Matsudo, Chiba 271-8587, Japan.
Kyung Mi
KM
Kim
Department of Periodontology, Nihon University School of Dentistry at Matsudo, Chiba 271-8587, Japan; Research Institute of Oral Science, Nihon University School of Dentistry at Matsudo, Chiba 271-8587, Japan.
Masaru
M
Mezawa
Department of Periodontology, Nihon University School of Dentistry at Matsudo, Chiba 271-8587, Japan; Research Institute of Oral Science, Nihon University School of Dentistry at Matsudo, Chiba 271-8587, Japan.
Yohei
Y
Nakayama
Department of Periodontology, Nihon University School of Dentistry at Matsudo, Chiba 271-8587, Japan; Research Institute of Oral Science, Nihon University School of Dentistry at Matsudo, Chiba 271-8587, Japan. Electronic address: ogata.yorimasa@nihon-u.ac.jp.
Yorimasa
Y
Ogata
D000818:Animals; D001846:Bone Development / Q000235:genetics; D001842:Bone and Bones; D002460:Cell Line; D017362:Cyclic AMP Response Element-Binding Protein / Q000235:genetics* / Q000276:immunology; D004958:Estradiol / Q000378:metabolism; D047628:Estrogen Receptor alpha / Q000096:biosynthesis / Q000276:immunology / Q000378:metabolism*; D015870:Gene Expression; D058574:Integrin-Binding Sialoprotein / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D010006:Osteoblasts / Q000378:metabolism*; D011401:Promoter Regions, Genetic / Q000235:genetics; D016760:Proto-Oncogene Proteins c-fos / Q000276:immunology; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D050436:Regulatory Elements, Transcriptional / Q000235:genetics; D018808:Transcription Factor AP-1 / Q000235:genetics* / Q000276:immunology / Q000378:metabolism; D014158:Transcription, Genetic; D014162:Transfection
D017362:Cyclic AMP Response Element-Binding Protein; D047628:Estrogen Receptor alpha; D058574:Integrin-Binding Sialoprotein; D016760:Proto-Oncogene Proteins c-fos; D012333:RNA, Messenger; D018808:Transcription Factor AP-1; D004958:Estradiol
Activator protein 1; Bone sialoprotein; Estrogen; Estrogen receptor; Osteoblasts; Transcription; cAMP response element