Loss of ERE binding activity by estrogen receptor-alpha alters basal and estrogen-stimulated bone-related gene expression by osteoblastic cells.
Estrogen receptor (ER)-alpha 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-alpha 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-alpha or the NERKI receptor. Compared to cells transfected with the control vector, stable expression of ER-alpha, 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-alpha 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.
Rudnik
Volha
V
Endocrine Research Unit, Rochester, Mayo Clinic and Mayo Foundation, Rochester, Minnesota 55905, USA.
Sanyal
Arunik
A
Syed
Farhan A
FA
Monroe
David G
DG
Spelsberg
Thomas C
TC
Oursler
Merry Jo
MJ
Khosla
Sundeep
S
D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D001846:Bone Development / Q000187:drug effects / Q000235:genetics*; D001842:Bone and Bones / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D003094:Collagen / Q000378:metabolism; D004958:Estradiol / Q000494:pharmacology; D047628:Estrogen Receptor alpha / Q000172:deficiency / Q000187:drug effects / Q000378:metabolism*; D004967:Estrogens / Q000502:physiology*; D005260:Female; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D051379:Mice; D010006:Osteoblasts / Q000187:drug effects / Q000378:metabolism*; D015675:Osteocalcin / Q000378:metabolism; D012333:RNA, Messenger / Q000096:biosynthesis; D020218:Response Elements / Q000187:drug effects / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology; D014158:Transcription, Genetic / Q000235:genetics*
C506487:ESR1 protein, human; D047628:Estrogen Receptor alpha; D004967:Estrogens; D012333:RNA, Messenger; D015675:Osteocalcin; D004958:Estradiol; D007334:Insulin-Like Growth Factor I; D003094:Collagen; D000469:Alkaline Phosphatase