The ERR-1 Orphan Receptor Is a Transcriptional Activator Expressed During Bone Development

Abstract

We studied the expression of estrogen-related receptor ERR-1 during mouse embryonic development. ERR-1 mRNA is present in bones formed by both the endochondral and intramembranous routes, and the onset of its expression coincides with bone formation. By RT-PCR experiments, we found that ERR-1, but not the related receptor ERR-2, is expressed in osteoblastic osteosarcoma cell lines as well as in primary osteoblastic cell populations derived from normal human bone. By gel shift analysis we found that ERR-1 binds as a monomer specifically to the SFRE sequence (SF-1-responsive-element; TCAAGGTCA). Mutation analysis revealed that both the core AGGTCA motif and the TCA 5'-extension are required for efficient ERR-1 binding. In transient transfection assays, ERR-1 acts as a potent transactivator through the SFRE sequence. This effect is cell-specific since ERR-1 activates transcription in the rat osteosarcoma cell line ROS 17.2/8 as well as in HeLa, NB-E, and FREJ4 cells but not in COS1 and HepG2 cells. Notably, the osteopontin (a protein expressed by osteoblasts and released in the bone matrix) gene promoter is a target for ERR-1 transcriptional regulation. Our findings suggest a role for ERR-1 in bone development and metabolism.

Activation of the thyroid hormone receptor α gene promoter by the orphan nuclear receptor ERRα

“…ERRa also down regulates the SV40 major late promoter (Wiley et al, 1993;Johnston et al, 1997). In contrast, we have demonstrated that ERRadependent transactivation through the SFRE is cellspeci®c (Bonnelye et al, 1997a). Indeed, cell lines such as HeLa or NB-E support ERRa-induced SFREdependent transcriptional regulation whereas others like HepG2 or COS1 do not.…”

“…Analysis of the sequence of this promoter reveals the existence of a perfect consensus SF-1 responsive element (SFRE; Wilson et al, 1993). As we have recently demonstrated, this site is also responsible for binding and activation by another nuclear orphan receptor, namely ERRa (Bonnelye et al, 1997a). As a ®rst step in evaluation of the signi®cance of this site, we decided to compare the sequence of the human version of the TRa promoter with the rat version isolated by Lazar et al (1994).…”

“…We have previously shown that ERRa exerts a cell-speci®c transactivation via the SFRE consensus site (Bonnelye et al, 1997a). We thus cotransfected two di erent cell lines that were demonstrated to support ERRa-induced activation, namely human HeLa and ras-transformed rat FREJ4 ®broblasts.…”

“…In contrast, ERRa has been shown to enhance the positive e ect of the estrogen receptor (ER) on the lactoferrin promoter through a consensus SFRE site but without having any autonomous e ect (Yang et al, 1996). We have identi®ed a ®rst direct positive target of ERRa with the osteopontin gene (Bonnelye et al, 1997a;Vanacker et al, submitted). Moreover, we have shown that ERRainduced transactivation is cell-speci®c and promoterspeci®c.…”

“…This e ect is mediated by a consensus SF-1 (Steroidogenic Factor 1) responsive element (SFRE) located 7443 bp relative to the major transcription start site of the human promoter (Vanacker et al, 1996). Moreover, we have shown that, in addition to mediating the e ect of SF-1 (Wilson et al, 1993), the SFRE is also the preferential binding site for another orphan nuclear receptor, namely the estrogen receptor related receptor, ERRa (Bonnelye et al, 1997a). Together with ERRb, this product has been identi®ed on the basis of its structural homology to the estrogen receptor (GigueÁ re et al, 1988).…”