An ERRβ/γ agonist modulates GRα expression, and glucocorticoid responsive gene expression in skeletal muscle cells

Estrogen-related receptors (ERRs) are constitutively active orphan nuclear receptors. Natural ligands have not been identified, however, recent reports have demonstrated the synthetic phenolic acyl hydrazone, GSK4716, functions as a selective ERRβ/γ agonist. We demonstrate that ERRβ is transiently induced, and ERRγ is dramatically induced (and accumulates) in a differentiation-dependent manner in skeletal muscle cells. Treatment of differentiated skeletal muscle cells with the ERRβ/γ agonist (GSK4716) produced a significant increase in the expression of GRα (isoform D) protein. Quantitative RT-PCR (Q-RT-PCR) analysis after treatment with GSK4716, revealed induction of the mRNAs encoding the glucocorticoid receptor (GR), 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1), the enzyme that converts inactive cortisone to cortisol and hexose-6-phosphate dehydrogenase expression (H6PDH) that stimulates oxoreduction by 11β-HSD1. Candidate based expression profiling also demonstrated the mRNAs encoding characterized GR target genes, including C/EBP, ApoD and Monoamine oxidase-A (MAO-A) are induced in GSK4716 treated cells. In concordance with these observations, siRNA-mediated suppression of the mRNA encoding ERRγ (but not ERRα and β) attenuated the expression of mRNAs encoding GR, 11βHSD1 and GR target gene(s). Similarly, treatment with the ERRγ (and ERα) antagonist diethylstilbestrol (DES) suppressed glucocorticoid responsive gene expression in skeletal muscle cells. Interestingly, we observed that GSK4716 trans-activated GRE-TK-LUC in a GR-dependent manner. This study highlights the regulatory crosstalk between ERRγ and GR signaling in skeletal muscle cells, and suggests the ERRγ agonist modulates the expression of critical genes that control GR signaling and glucocorticoid sensitive gene expression.