Evidence for Ligand-independent Transcriptional Activation of the Human Estrogen-related Receptor α (ERRα)

Hepatocyte nuclear factor 4␣ (HNF4␣) is a novel nuclear receptor that participates in a hierarchical network of transcription factors regulating the development and physiology of such vital organs as the liver, pancreas, and kidney. Among the various transcriptional coregulators with which HNF4␣ interacts, peroxisome proliferation-activated receptor ␥ (PPAR␥) coactivator 1␣ (PGC-1␣) represents a novel coactivator whose activation is unusually robust and whose binding mode appears to be distinct from that of canonical coactivators such as NCoA/SRC/ p160 family members. To elucidate the potentially unique molecular mechanism of PGC-1␣ recruitment, we have determined the crystal structure of HNF4␣ in complex with a fragment of PGC-1␣ containing all three of its LXXLL motifs. Despite the presence of all three LXXLL motifs available for interactions, only one is bound at the canonical binding site, with no additional contacts observed between the two proteins. However, a close inspection of the electron density map indicates that the bound LXXLL motif is not a selected one but an averaged structure of more than one LXXLL motif. Further biochemical and functional studies show that the individual LXXLL motifs can bind but drive only minimal transactivation. Only when more than one LXXLL motif is involved can significant transcriptional activity be measured, and full activation requires all three LXXLL motifs. These findings led us to propose a model wherein each LXXLL motif has an additive effect, and the multiple binding modes by HNF4␣ toward the LXXLL motifs of PGC-1␣ could account for the apparent robust activation by providing a flexible mechanism for combinatorial recruitment of additional coactivators and mediators.

Section: Biochemical and Biological Evidence Of Multiple Binding Modesupporting

confidence: 57%

Section: Hepatocyte Nuclear Factor 4␣ (Hnf4␣)mentioning

confidence: 78%

Section: Discussionmentioning

confidence: 99%

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Multiple Binding Modes between HNF4α and the LXXLL Motifs of PGC-1α Lead to Full Activation

Rha

Shoelson

et al. 2009

“…Reflecting the physio-logic role of ERR␣, a number of ERR␣ target genes have been identified (15), and transcriptional function was shown to depend on chromatin environment of the promoters. Although no endogenous ligand has yet been found, synthetic ERR␣ ligands appear to modulate ERR␣ transcriptional activity as inverse antagonists (16,17). Although these findings suggest that ERR␣ is a potential interactant for co-activators and corepressors of transcription, only a few co-activators have been shown to support ERR␣ function (18 -20).…”

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confidence: 91%

Double PHD Fingers Protein DPF2 Recognizes Acetylated Histones and Suppresses the Function of Estrogen-related Receptor α through Histone Deacetylase 1

Matsuyama

Takada

Yokoyama

et al. 2010

Estrogen-related receptor ␣ (ERR␣) is a member of the nuclear receptor superfamily and regulates many physiological functions, including mitochondrial biogenesis and lipid metabolism. ERR␣ enhances the transactivation function without endogenous ligand by associating with coactivators such as peroxisome proliferator-activated receptor ␥ coactivator 1 ␣ and ␤ (PGC-1␣ and -␤) and members of the steroid receptor coactivator family. However, the molecular mechanism by which the transactivation function of ERR␣ is converted from a repressive state to an active state is poorly understood. Here we used biochemical purification techniques to identify ERR␣-associated proteins in HeLa cells stably expressing ERR␣. Interestingly, we found that double PHD fingers protein DPF2/BAF45d suppressed PGC-1␣-dependent transactivation of ERR␣ by recognizing acetylated histone H3 and associating with HDAC1. DPF2 directly bound to ERR␣ and suppressed the transactivation function of nuclear receptors such as androgen receptor. DPF2 was recruited to ERR target gene promoters in myoblast cells, and knockdown of DPF2 derepressed the level of mRNA expressed by target genes of ERR␣. These results show that DPF2 acts as a nuclear receptor-selective co-repressor for ERR␣ by associating with both acetylated histone H3 and HDAC1.Nuclear receptors (NRs) 3 play pivotal roles during the development of vertebrates and in diverse physiological events in adults (1, 2). NRs constitute a gene superfamily and act as transcription factors. For most members of the NR superfamily, the transcriptional function is dependent on binding of lipophilic ligands such as steroid hormones and fat-soluble vitamins. The other subset of NRs is considered an orphan receptor, as physiologically relevant ligands remain to be identified. Orphan receptors are constitutively active or repressive transcription factors; however, their potency in transcriptional regulation appears to be dependent on cell types and the promoter context (3).For ligand-dependent transcriptional controls by nuclear steroid/vitamin receptors, several distinct classes of transcriptional co-regulators-co-regulator complexes are indispensable in addition to basic transcription machinery to reorganize chromatin state (4). Transcriptional co-regulators for NRs can be divided into two classes in terms of chromatin reorganization (5-7). One class consists of histone-modifying enzymes that reversibly modify the N-terminal tails of histone proteins (8, 9). For example, acetylation and methylation at histone H3K4 and H3K36 are chromatin-activating modifications and support transcriptional activation by NRs (8, 10, 11). In contrast, transcriptional repression by NRs is coupled with inactivating modifications like deacetylation and methylation at histone H3K9 and H3K27. Accordingly, cognate histone modifying enzymes serve as NR co-regulators.The other class of transcriptional co-regulators are chromatin remodeling factors that directly reorganize nucleosomal arrays through ATP hydrolysis (11). Chromatin remod...

“…However, no natural ligand has been identified for the ERRs, which are therefore considered as orphan receptors. Crystallographic studies have shown that ERR␣ and -␥ spontaneously adopt active conformations (9,10). Although ERR␣ regulates transcription in a constitutive manner, some of its activities (DNA binding and contact with coactivators) can be regulated by phosphorylation (11).…”

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confidence: 99%

Modulating Estrogen Receptor-related Receptor-α Activity Inhibits Cell Proliferation

Bianco

Lanvin

Tribollet

et al. 2009

High expression of the estrogen receptor-related receptor (ERR)-␣ in human tumors is correlated to a poor prognosis, suggesting an involvement of the receptor in cell proliferation. In this study, we show that a synthetic compound (XCT790) that modulates the activity of ERR␣ reduces the proliferation of various cell lines and blocks the G 1 /S transition of the cell cycle in an ERR␣-dependent manner. XCT790 induces, in a p53-independent manner, the expression of the cell cycle inhibitor p21waf/cip1 at the protein, mRNA, and promoter level, leading to an accumulation of hypophosphorylated Rb. Finally, XCT790 reduces cell tumorigenicity in Nude mice.Breast cancer is the most common malignancy in women (1). In the initial phases, these tumors often depend on estrogens for their growth. At the molecular level, 17␤-estradiol (E2, 3 the main estrogen in the adult) acts by up-regulating the expression of cyclin D1, which regulates the activity of cyclin-dependent kinases (cdks) 4 and 6 (2, 3). These cdks facilitate the transition from the G 1 to the S phase of the cell cycle by hyperphosphorylating Rb (4). Adjuvant therapies aimed at counteracting the effects of estrogens are widely used (5). Anti-estrogens such as tamoxifen down-regulate the expression of cyclin D1 (3), whereas ICI182,780 (fulvestrant and faslodex) stimulates the expression of p21 waf/cip1 (hereafter referred to as p21) (6). This protein blocks the activity of the cyclin D-cdk complexes leading to hypophosphorylation of Rb and arrest in the G 1 phase of the cell cycle (4). However, a large proportion of breast cancers evolve so as to become resistant to anti-hormonal treatments through mechanisms that are not clearly characterized (1,5). This illustrates the need of new targets against which to develop innovative anti-cancer therapies.The effects of estrogens are mediated by two specific nuclear receptors (ER␣ and ER␤), which act as ligand-dependent transcription factors (7). Estrogen receptor-related receptors (ERR␣, -␤, and -␥) are other members of the nuclear receptor superfamily that share a high level of sequence identity with the ERs (8). However, no natural ligand has been identified for the ERRs, which are therefore considered as orphan receptors. Crystallographic studies have shown that ERR␣ and -␥ spontaneously adopt active conformations (9, 10). Although ERR␣ regulates transcription in a constitutive manner, some of its activities (DNA binding and contact with coactivators) can be regulated by phosphorylation (11). Furthermore, compounds such as the phytoestrogen genistein can inhibit the transcriptional activities of ERR␣ (12). In addition, based on its capacity to disrupt the interactions between ERR␣ and the PGC-1␣ coactivator, the synthetic molecule XCT790 has been identified as an ERR␣-specific inverse agonist (13). This compound down-regulates the expression of ERR␣ target genes probably by inducing an actively repressing conformation (14). At the same time, XCT790 promotes the proteasomedependent degradation of its receptor (15). ERR...