Orphan nuclear receptor ERRalpha (NR3B1) is recognized as a key regulator of mitochondrial biogenesis, but it is not known whether ERRalpha and other ERR isoforms play a broader role in cardiac energetics and function. We used genome-wide location analysis and expression profiling to appraise the role of ERRalpha and gamma (NR3B3) in the adult heart. Our data indicate that the two receptors, acting as nonobligatory heterodimers, target a common set of promoters involved in the uptake of energy substrates, production and transport of ATP across the mitochondrial membranes, and intracellular fuel sensing, as well as Ca(2+) handling and contractile work. Motif-finding algorithms assisted by functional studies indicated that ERR target promoters are enriched for NRF-1, CREB, and STAT3 binding sites. Our study thus reveals that the ERRs orchestrate a comprehensive cardiac transcriptional program and further suggests that modulation of ERR activities could be used to manage cardiomyopathies.

At birth, the heart undergoes a critical metabolic switch from a predominant dependence on carbohydrates during fetal life to a greater dependence on postnatal oxidative metabolism. This remains the principle metabolic state throughout life, although pathologic conditions such as heart failure and cardiac hypertrophy reactivate components of the fetal genetic program to increase carbohydrate utilization. Disruption of the ERRgamma gene (Esrrg), which is expressed at high levels in the fetal and postnatal mouse heart, blocks this switch, resulting in lactatemia, electrocardiographic abnormalities, and death during the first week of life. Genomic ChIP-on-chip and expression analysis identifies ERRgamma as both a direct and an indirect regulator of a nuclear-encoded mitochondrial genetic network that coordinates the postnatal metabolic transition. These findings reveal an unexpected and essential molecular genetic component of the oxidative metabolic gene program in the heart and highlight ERRgamma in the study of cardiac hypertrophy and failure.

Cancer cell metabolism is often characterized by a shift from an oxidative to a glycolytic bioenergetics pathway, a phenomenon known as the Warburg effect. miR-378(∗) is embedded within PPARGC1b which encodes PGC-1β, a transcriptional regulator of oxidative energy metabolism. Here we show that miR-378(∗) expression is regulated by ERBB2 and induces a metabolic shift in breast cancer cells. miR-378(∗) performs this function by inhibiting the expression of two PGC-1β partners, ERRγ and GABPA, leading to a reduction in tricarboxylic acid cycle gene expression and oxygen consumption as well as an increase in lactate production and in cell proliferation. In situ hybridization experiments show that miR-378(∗) expression correlates with progression of human breast cancer. These results identify miR-378(∗) as a molecular switch involved in the orchestration of the Warburg effect in breast cancer cells via interference with a well-integrated bioenergetics transcriptional pathway.

Downregulation and functional deactivation of the transcriptional coactivator PGC-1alpha has been implicated in heart failure pathogenesis. We hypothesized that the estrogen-related receptor alpha (ERRalpha), which recruits PGC-1alpha to metabolic target genes in heart, exerts protective effects in the context of stressors known to cause heart failure. ERRalpha(-/-) mice subjected to left ventricular (LV) pressure overload developed signatures of heart failure including chamber dilatation and reduced LV fractional shortening. (31)P-NMR studies revealed abnormal phosphocreatine depletion in ERRalpha(-/-) hearts subjected to hemodynamic stress, indicative of a defect in ATP reserve. Mitochondrial respiration studies demonstrated reduced maximal ATP synthesis rates in ERRalpha(-/-) hearts. Cardiac ERRalpha target genes involved in energy substrate oxidation, ATP synthesis, and phosphate transfer were downregulated in ERRalpha(-/-) mice at baseline or with pressure overload. These results demonstrate that the nuclear receptor ERRalpha is required for the adaptive bioenergetic response to hemodynamic stressors known to cause heart failure.

mTOR and ERRα are key regulators of common metabolic processes, including lipid homeostasis. However, it is currently unknown whether these factors cooperate in the control of metabolism. ChIP-sequencing analyses of mouse liver reveal that mTOR occupies regulatory regions of genes on a genome-wide scale including enrichment at genes shared with ERRα that are involved in the TCA cycle and lipid biosynthesis. Genetic ablation of ERRα and rapamycin treatment, alone or in combination, alter the expression of these genes and induce the accumulation of TCA metabolites. As a consequence, both genetic and pharmacological inhibition of ERRα activity exacerbates hepatic hyperlipidemia observed in rapamycin-treated mice. We further show that mTOR regulates ERRα activity through ubiquitin-mediated degradation via transcriptional control of the ubiquitin-proteasome pathway. Our work expands the role of mTOR action in metabolism and highlights the existence of a potent mTOR/ERRα regulatory axis with significant clinical impact.

Estrogen-related receptor a (ERRa) and proliferatoractivated receptor g coactivator-1a (PGC-1a) play central roles in the transcriptional control of energy homeostasis, but little is known about factors regulating their activity. Here we identified the homeobox protein prospero-related homeobox 1 (Prox1) as one such factor. Prox1 interacts with ERRa and PGC-1a, occupies promoters of metabolic genes on a genome-wide scale, and inhibits the activity of the ERRa/PGC-1a complex. DNA motif analysis suggests that Prox1 interacts with the genome through tethering to ERRa and other factors. Importantly, ablation of Prox1 and ERRa have opposite effects on the respiratory capacity of liver cells, revealing an unexpected role for Prox1 in the control of energy homeostasis. Regulation of energy homeostasis involves elaborate biochemical pathways that have evolved to react to the metabolic needs of the organism in response to specific physiological states. While homeostatic regulation is generally under hormonal control and achieved through allosteric control and post-translational modifications of metabolic enzymes for immediate needs, organ-specific requirements and lasting adaptation require regulation of metabolic genes at the transcriptional level via the action of diverse classes of transcription factors and coregulatory proteins (Desvergne et al. 2006;Feige and Auwerx 2007). Among those factors, the orphan nuclear receptor estrogenrelated receptor a (ERRa, NR3B1) and the coregulator peroxisome proliferator-activated receptor g coactivator1a (PGC-1a) have been shown to play a predominant role in controlling several aspects of energy metabolism, most notably mitochondrial biogenesis and oxidative phosphorylation (Oxphos) (Lin et al. 2005;Giguè re 2008).

The orphan nuclear estrogen-related receptor ␣ (ERR␣) and transcriptional cofactor peroxisome proliferator-activated receptor ␥ coactivator-1␣ (PGC-1␣) are involved in the regulation of energy metabolism. Recently, extensive cross-talk between PGC-1␣ and ERR␣ has been demonstrated. The presence of PGC-1␣ is associated with an elevated expression of ERR␣, and the two proteins can influence the transcriptional activities of one another. Using a candidate gene approach to detect regulatory variants within genes encoding nuclear receptors, we have identified a 23-bp sequence (ESRRA23) containing two nuclear receptor recognition half-site motifs that is present in 1-4 copies within the promoter of the human ESRRA gene encoding ERR␣. The ES-RRA23 sequence contains a functional ERR response element that is specifically bound by ERR␣, and chromatin immunoprecipitation shows that endogenous ERR␣ occupies its own promoter in vivo. Strikingly, introduction of PGC-1␣ in HeLa cells by transient transfection induces the activity of the ESRRA promoter in a manner that is dependent on the presence of the ES-RRA23 element and on its dosage. Coexpression of ERR␣ and PGC-1␣ results in a synergistic activation of the ESRRA promoter. In experiments using ERR␣ null fibroblasts, the ability of PGC-1␣ to stimulate the ESRRA promoter is considerably reduced but can be restored by addition of ERR␣. Taken together, these results demonstrate that an interdependent ERR␣/PGC-1␣-based transcriptional pathway targets the ESRRA23 element to dictate the level of ERR␣ expression. This study further suggests that this regulatory polymorphism may provide differential responses to ERR␣/PGC-1␣-mediated metabolic cues in the human population.Nuclear hormone receptors are transcription factors that control essential developmental and physiological pathways (1). Although the transcriptional activity of nuclear receptors is primarily regulated by specific ligands, several members of the superfamily of nuclear receptors have no known natural ligands and are therefore referred to as orphan receptors (2). Estrogen-related receptor ␣ (ERR␣ 1 ; NR3B1) was the first orphan nuclear receptor to be identified on the basis of its similarity with estrogen receptor ␣ (ER␣; NR3A1) (3). Phylogenic tree reconstruction confirmed that ERR␣ belongs to the subgroup of receptors for steroid hormones (4), and ERR␣ was subsequently shown to share both structural and functional attributes with the ERs including binding to synthetic estrogenic ligands (reviewed in Ref. 5). ERR␣ also recognizes estrogen response elements (EREs), but characterization of its DNA binding properties demonstrated a preference for sites composed of a single half-site preceded by three nucleotides with the consensus sequence TNAAGGTCA, referred to as an ERRE (6 -10). The transcriptional activity of ERR␣ is independent of exogenously added ligand, and its relative potency as a transcriptional activator appears to be cell context-and promoterdependent (3,8,(11)(12)(13)(14)(15). ERR␣ has also been describ...

Androgen receptor (AR) signaling reprograms cellular metabolism to support prostate cancer (PCa) growth and survival. Another key regulator of cellular metabolism is mTOR, a kinase found in diverse protein complexes and cellular localizations, including the nucleus. However, whether nuclear mTOR plays a role in PCa progression and participates in direct transcriptional cross-talk with the AR is unknown. Here, via the intersection of gene expression, genomic, and metabolic studies, we reveal the existence of a nuclear mTOR-AR transcriptional axis integral to the metabolic rewiring of PCa cells. Androgens reprogram mTOR-chromatin associations in an AR-dependent manner in which activation of mTOR-dependent metabolic gene networks is essential for androgeninduced aerobic glycolysis and mitochondrial respiration. In models of castration-resistant PCa cells, mTOR was capable of transcriptionally regulating metabolic gene programs in the absence of androgens, highlighting a potential novel castration resistance mechanism to sustain cell metabolism even without a functional AR. Remarkably, we demonstrate that increased mTOR nuclear localization is indicative of poor prognosis in patients, with the highest levels detected in castration-resistant PCa tumors and metastases. Identification of a functional mTOR targeted multigene signature robustly discriminates between normal prostate tissues, primary tumors, and hormone refractory metastatic samples but is also predictive of cancer recurrence. This study thus underscores a paradigm shift from AR to nuclear mTOR as being the master transcriptional regulator of metabolism in PCa.