Loss of ERE binding activity by estrogen receptor-α alters basal and estrogen-stimulated bone-related gene expression by osteoblastic cells
✍ Scribed by Volha Rudnik; Arunik Sanyal; Farhan A. Syed; David G. Monroe; Thomas C. Spelsberg; Merry Jo Oursler; Sundeep Khosla
- Publisher
- John Wiley and Sons
- Year
- 2008
- Tongue
- English
- Weight
- 207 KB
- Volume
- 103
- Category
- Article
- ISSN
- 0730-2312
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✦ Synopsis
Abstract
Estrogen receptor (ER)‐α can signal either via estrogen response element (ERE)‐mediated pathways or via alternate pathways involving protein–protein or membrane signaling. We previously demonstrated that, as compared to wild type (WT) controls, mice expressing a mutant ER‐α lacking the ability to bind EREs (non‐classical estrogen receptor knock‐in (NERKI)) display significant impairments in the skeletal response to estrogen. To elucidate the mechanism(s) underlying these in vivo deficits, we generated U2OS cells stably expressing either WT ER‐α or the NERKI receptor. Compared to cells transfected with the control vector, stable expression of ER‐α, even in the absence of E2, resulted in an increase in mRNA levels for alkaline phosphatase (AP, by 400%, P < 0.01) and a decrease in mRNA levels for insulin growth factor‐I (IGF‐I) (by 65%, P < 0.001), with no effects on collagen I (col I) or osteocalcin (OCN) mRNA levels. By contrast, stable expression of the NERKI receptor resulted in the suppression of mRNA levels for AP, col I, OCN, and IGF‐I (by 62, 89, 60, and 70%, P < 0.001). While E2 increased mRNA levels of AP, OCN, col I, and IGF‐I in ER‐α cells, E2 effects in the NERKI cells on AP and OCN mRNA levels were attenuated, with a trend for E2 to inhibit col I mRNA levels. In addition, E2 had no effects on IGF‐I mRNA levels in NERKI cells. Collectively, these findings indicate that ERE signaling plays a significant role in mediating effects of estrogen on osteoblastic differentiation markers and on IGF‐I mRNA levels. J. Cell. Biochem. 103: 896–907, 2008. © 2007 Wiley‐Liss, Inc.