Transcriptional Corepressor SMILE Recruits SIRT1 to Inhibit Nuclear Receptor Estrogen Receptor-related Receptor γ Transactivation

Abstract

SMILE (small heterodimer partner interacting leucine zipper protein) has been identified as a corepressor of the glucocorticoid receptor, constitutive androstane receptor, and hepatocyte nuclear factor 4␣. Here we show that SMILE also represses estrogen receptor-related receptor ␥ (ERR␥) transactivation. Knockdown of SMILE gene expression increases ERR␥ activity. SMILE directly interacts with ERR␥ in vitro and in vivo. Domain mapping analysis showed that SMILE binds to the AF2 domain of ERR␥. SMILE represses ERR␥ transactivation partially through competition with coactivators PGC-1␣, PGC-1␤, and GRIP1. Interestingly, the repression of SMILE on ERR␥ is released by SIRT1 inhibitors, a catalytically inactive SIRT1 mutant, and SIRT1 small interfering RNA but not by histone protein deacetylase inhibitor. In vivo glutathione S-transferase pulldown and coimmunoprecipitation assays validated that SMILE physically interacts with SIRT1. Furthermore, the ERR␥ inverse agonist GSK5182 enhances the interaction of SMILE with ERR␥ and SMILE-mediated repression. Knockdown of SMILE or SIRT1 blocks the repressive effect of GSK5182. Moreover, chromatin immunoprecipitation assays revealed that GSK5182 augments the association of SMILE and SIRT1 on the promoter of the ERR␥ target PDK4. GSK5182 and adenoviral overexpression of SMILE cooperate to repress ERR␥-induced PDK4 gene expression, and this repression is released by overexpression of a catalytically defective SIRT1 mutant. Finally, we demonstrated that ERR␥ regulates SMILE gene expression, which in turn inhibits ERR␥. Overall, these findings implicate SMILE as a novel corepressor of ERR␥ and recruitment of SIRT1 as a novel repressive mechanism for SMILE and ERR␥ inverse agonist.

Estrogen-related Receptor γ (ERRγ) Is a Novel Transcriptional Regulator of Phosphatidic Acid Phosphatase, LIPIN1, and Inhibits Hepatic Insulin Signaling

“…Expression vectors for FLAG-ERR␣, HA-ERR␤, and FLAG-ERR␥ were described previously (30). The ERR response element (ERRE)-mutated mLIPIN1 promoter was generated via site-directed mutagenesis (Stratagene), and the construct was confirmed by DNA sequencing.…”

“…RNA Isolation and Analysis-Total RNAs were isolated from cell lines or primary hepatocytes using TRIzol reagent (Invitrogen), in accordance with the manufacturer's instructions, and semi-quantitative and real time quantitative PCR analysis were conducted using primers for ERR␣, ERR␥, LIPIN1, LIPIN2, SHP, PGC-1␣ and PDK4 as described previously (4,30,32). All data were normalized to ribosomal L32 expression.…”

Insulin-Inducible SMILE Inhibits Hepatic Gluconeogenesis

“…SMILE has also been reported to function as a coactivator of activating transcription factor 4 or as a corepressor of host cell factor-binding transcription factor (13,14). Previously, we have reported that SMILE is a corepressor of the estrogen receptor-related receptor g, glucocorticoid receptor (GR), constitutive androstane receptor, hepatocyte nuclear factor 4a (HNF4a), and CREBH (15)(16)(17). A recent study demonstrated that SMILE activates tumor suppressor p53 and inhibits the function of bone morphogenetic protein 6 by interacting with Smads (18,19).…”

SMILE Is an Insulin-Inducible Transcriptional Corepressor of Hepatic Gluconeogenic Gene Programs

“…1). In addition to HNF4a, other transcription factors interacting with SMILE, including ERRg, GR, CREBH, and/or FOXO1 (6)(7)(8), might mediate the inhibitory effects of insulin on gluconeogenic gene expression (9,11,12). To summarize, the article by Lee et al (5) demonstrates that the nuclear orphan receptor SMILE plays a large role in the homeostatic regulation of hepatic gluconeogenesis and that correction of its aberrant activity (possibly via pharmacological agents) represents a promising avenue for the therapy of metabolic disease.…”

“…However, in this issue of Diabetes, Lee et al (5) dissect the role of the small heterodimer partnerinteracting leucine zipper protein (SMILE) in insulinmediated hepatic glucose metabolism. SMILE is a member of the CREB/ATF family of basic-region leucine zipper (bZIP) transcription factors and has been reported to function as a corepressor of nuclear receptor superfamily genes, including estrogen-related receptor g (ERRg), glucocorticoid receptor (GR), hepatocyte nuclear factor 4a (HNF4a), and cAMP-responsive element-binding protein H (CREBH) (6)(7)(8). In fact, ERRg, GR, HNF4a, and CREBH have all been implicated in upregulating gluconeogenic gene expression (9-12).…”