title: Transcriptional activation of insulin-like growth factor binding protein 6 by 17beta-estradiol in SaOS-2 cells.
abstract: Osteoblasts can synthesize the insulin-like growth factors (IGFs) and the IGF-binding proteins (IGFBPs), which may either enhance or attenuate IGF-stimulated bone cell proliferation. Since estrogen induced osteoblastic differentiation and proliferation through an estrogen-responsive gene in target cells, we investigated the effects of estrogen on IGFBP-6 expression in the human osteoblastic-like cell line SaOS-2. Expressions of IGFBP-6 protein and mRNA increased 2.8 and 2-fold, respectively, in the presence of 17-beta-estradiol (E2) (0.01 to 1 micronM) and estrogen receptor (ER) in SaOS-2 cells. On the other hand, E2 induced a 2-fold increase in SaOS-2 cell proliferation. To identify genomic sequences associated with estrogen responsiveness, the 5'-promoter region (-44 to +118) of the IGFBP-6 gene was cloned into a chloramphenicol acetyltransferase (CAT) reporter vector. E2 induced a 3-fold increase in CAT activity in SaOS-2 cells transiently transfected with this construct. Identification of the estrogen-responsive element (ERE) [5-CCTTCA CCTG-3] (-9 to +1) in this IGFBP-6 gene promoter region was confirmed using electromobility shift assays and deletion analysis. This functional ERE was important for E2-induced trans-activation of the IGFBP-6 gene. These results demonstrate that E2 exhibits a positive effect on IGFBP-6 gene transcription through estrogen-liganded ER binding to the functional ERE in the IGFBP-6 gene promoter in SaOS-2 cells.
authors.affiliation: Department of Endocrinology, First Affiliated Hospital, China Medical University, Shenyang 110001, China. g572@sina.com
authors.forename: Yu-yan
authors.initials: YY
authors.lastname: Zhao
authors.forename: Lei
authors.initials: L
authors.lastname: Guo
authors.forename: Xiao-juan
authors.initials: XJ
authors.lastname: Zhao
authors.forename: Hong
authors.initials: H
authors.lastname: Liu
authors.forename: Tian
authors.initials: T
authors.lastname: Lei
authors.forename: Dong-jie
authors.initials: DJ
authors.lastname: Ma
authors.forename: Xiao-yu
authors.initials: XY
authors.lastname: Gao