Exp Mol Med.  2009 Jul;41(7):478-486. 10.3858/emm.2009.41.7.053.

Transcriptional activation of insulin-like growth factor binding protein 6 by 17beta-estradiol in SaOS-2 cells

• Zhao YY
• Guo L
• Zhao XJ
• Liu H
• Lei T
• Ma DJ
• Gao XY

• KMID: 1058022
• DOI: http://doi.org/10.3858/emm.2009.41.7.053

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 micrometer) 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.

Keyword

estrogen; insulin-like growth factor binding protein 6; osteoblasts; receptors, estrogen; transcription, genetic

MeSH Terms

Blotting, Western
Cell Proliferation
Chloramphenicol O-Acetyltransferase/metabolism
Electrophoretic Mobility Shift Assay
Estradiol/*pharmacology
Estrogen Receptor alpha/genetics/metabolism
Estrogens/pharmacology
Humans
Insulin-Like Growth Factor Binding Protein 6/*genetics/metabolism
Osteoblasts/*drug effects/metabolism
Promoter Regions, Genetic/*genetics
RNA, Messenger/genetics/metabolism
Response Elements
Reverse Transcriptase Polymerase Chain Reaction
*Transcriptional Activation
Tumor Cells, Cultured