Estrogen receptor-related receptor α (ERRα) regulates osteopontin expression through a non-canonical ERRα response element in a cell context-dependent manner

Abstract

We previously demonstrated that the orphan nuclear receptor, estrogen receptor-related receptor a (ERRa) is highly expressed in osteoblasts and osteoclasts, regulates osteogenesis and expression of osteoblast-associated markers in the rat calvaria cell differentiation system, and is dysregulated in the rat ovariectomy model of postmenopausal osteoporosis. There are conflicting published data on the transcriptional regulation by ERRa of the gene for osteopontin (OPN), an extracellular matrix protein required in bone remodeling, and a potential direct target mediating ERRa effects in bone. We therefore readdressed OPN gene regulation by ERRa in both osteoblastic (rat osteosarcoma ROS17/2.8 cells) and non-osteoblastic (HeLa) cell lines using a mouse proximal 2 kb OPN promoter fragment. A minimal OPN promoter fragment spanning from K56 to C9 bp is activated in HeLa cells but repressed it in ROS17/2.8 cells. Adenine scanning mutagenesis revealed the presence of a non-canonical ERRa response element in this minimal promoter. Surprisingly, prototypical inactivating mutations in the activation function 2 (AF2) domain or a naturally occurring allelic variant of ERRa (ERRaH408) were all better activators than wild-type ERRa in HeLa cells, activities that were generally paralleled by repression in ROS17/2.8 cells. Finally, we found that the N-terminus of ERRa harbors a repressor domain that acts in a cell context-dependent manner. We conclude that OPN is an ERRa target gene whose promoter is regulated by ERRa in a cell context-dependent manner and that a predicted silencing mutation in AF2 or a more flexible helix 12 increases ERRa transcriptional activity, effects with implications for ERRa as a therapeutic target in bone.

Dual Function of ERRα in Breast Cancer and Bone Metastasis Formation: Implication of VEGF and Osteoprotegerin

“…ERRa is also highly expressed in skeletal tissues (21,22) and has been reported to regulate osteoblast, OC differentiation, and bone formation in vitro (21,22,23,24) and in vivo (25)(26)(27). Consistent with these observations, osteopontin (OPN) has been reported to be a direct target gene of ERRa in osteoblastic cell lines (28)(29)(30). The role of ERRa in bone metastasis formation is currently unknown.…”

Src is a major signaling component for CTGF induction by TGF‐β1 in osteoblasts

“…In this study we first examined whether CTGF could be induced by TGF-β1 in rat osteosarcoma osteoblast-like cells (ROS17/2.8). ROS osteoblast-like cells are a transformed osteoblast cell line that are widely used for studies of osteoblast differentiation and function and are considered as more differentiated osteoblasts relative to primary osteoblasts (Granet et al, 2002; Kartsogiannis and Ng, 2004; Majeska and Rodan, 1982; Noda, 1989; Rodan and Majeska, 1982; Takai et al, 2008; Zirngibl et al, 2008). The TGF-β1 dose of 5ng/ml was used for this and all subsequent experiments since we had previously demonstrated that this was the minimal dose required for maximal induction of CTGF (Arnott et al, 2007).…”

Estrogen-Related Receptor Alpha Confers Methotrexate Resistance via Attenuation of Reactive Oxygen Species Production and P53 Mediated Apoptosis in Osteosarcoma Cells

“…It may play a functional role in osteoblast differentiation and bone formation by regulating the expression of osteocalcin (OC), bone sialoprotein (BSP), Runx2, and alkaline phosphatase (ALP) [28, 29]. We and others have identified that osteopontin (OPN) and osteocalcin (OC) are ERR α direct target genes in bone [30, 31]. Interestingly, studies also showed that OPN and OC promote cancer progression in different cancer types [32, 33].…”