Regulation of Peroxisome Proliferator–Activated Receptor-α by MDM2

Abstract

Peroxisome proliferator-activated receptor-alpha (PPARalpha) belongs to the nuclear receptor (NR) family of transcription factors and regulates lipid and glucose metabolism. Like other NRs, the regulation of gene expression by PPARalpha depends on cofactor recruitment to the transcription complex and multiple protein-protein interactions. In this study, Murine Double Minute 2 (MDM2), an E3 ubiquitin ligase, is identified as a PPARalpha-interacting protein that regulates PPARalpha transcriptional activity. MDM2 modulated the transcriptional activity of PPARalpha and PPARbeta/delta, but not PPARgamma in reporter assays. Knockdown of MDM2 by small interfering RNA in rat hepatoma cells inhibited ligand-induced mRNA levels of several PPARalpha target genes involved in lipid metabolism. MDM2 associated with PPARalpha on target gene promoters, and this association increased in response to Wy14,643 treatment. MDM2 interacted with PPARalpha and this interaction occurred with the A/B domain of PPARalpha. Coexpression of MDM2 increased PPARalpha ubiquitination and the E3 ubiquitin ligase activity of MDM2 affected PPARalpha protein expression and transcriptional activity. MDM2 expression was decreased in response to clofibrate in wild-type (WT), but not in PPARalpha null mice, indicating a PPARalpha-dependent regulation. These studies identify a role for MDM2 in regulating PPARalpha-mediated pathways of lipid metabolism.

The ubiquitin ligase MuRF1 regulates PPARα activity in the heart by enhancing nuclear export via monoubiquitination

“…The regulation of PPARα by post-translational modification with ubiquitin has been demonstrated in rat hepatoma and the HepG2 cell lines (Gopinathan et al, 2009). The E3 MDM2 has been associated with increased poly-ubiquitination of PPARα; interestingly, the MDM2 to PPARα ratio determined if MDM2 activated (MDM2: PPARα <1) or inhibited (MDM2: PPARα >1) (Gopinathan et al, 2009).…”

“…Recent studies have provocatively suggested that post-translational modifications can be found on all three PPAR isoforms. For example, polyubiquitination of PPARβ/δ and PPARγ1/2 in cancer and adipo-cytes cells, respectively, has been identified, but the effects of polyubiquitination on the activity of these PPAR isoforms and whether degradation occurs are not known (Gareau and Lima, 2010; Gopinathan et al, 2009; Wadosky and Willis, 2012). These studies suggest that ubiquitin ligases, proteins that direct specific ubiquitination of substrates (PPARs in this case), may be regulating PPAR activity in some yet to be determined manner.…”

The story so far: post-translational regulation of peroxisome proliferator-activated receptors by ubiquitination and SUMOylation

“…Increasing MDM2 levels relative to PPAR␣ and PPAR␤/␦, but not PPAR␥, leads to a decrease in PPAR activity (34), whereas knocking down MDM2 expression levels with small interfering RNA in rat hepatoma cells inhibits mRNA expression of several PPAR␣ targets (34). Increasing MDM2 levels in the presence of Wy-14643 (a PPAR␣ selective agonist) leads to enhanced PPAR␣ activity up to a ratio of MDM2 to PPAR␣ Ͻ0.5 to 1; however, ratios of MDM2 to PPAR␣ Ն 1 inhibits PPAR␣ activity (34). In summary, these studies demonstrate the ubiquitination of PPAR␣ in a ligand-dependent manner and that effect of ubiquitination on PPAR␣ activity depends on the systems studied (Table 1).…”

“…MDM2 associates with PPAR␣ through the A/B domain of PPAR␣ ( Fig. 2A) and the coexpression of MDM2 increases PPAR␣ ubiquitination (34). Increasing MDM2 levels relative to PPAR␣ and PPAR␤/␦, but not PPAR␥, leads to a decrease in PPAR activity (34), whereas knocking down MDM2 expression levels with small interfering RNA in rat hepatoma cells inhibits mRNA expression of several PPAR␣ targets (34).…”

“…2A) and the coexpression of MDM2 increases PPAR␣ ubiquitination (34). Increasing MDM2 levels relative to PPAR␣ and PPAR␤/␦, but not PPAR␥, leads to a decrease in PPAR activity (34), whereas knocking down MDM2 expression levels with small interfering RNA in rat hepatoma cells inhibits mRNA expression of several PPAR␣ targets (34). Increasing MDM2 levels in the presence of Wy-14643 (a PPAR␣ selective agonist) leads to enhanced PPAR␣ activity up to a ratio of MDM2 to PPAR␣ Ͻ0.5 to 1; however, ratios of MDM2 to PPAR␣ Ն 1 inhibits PPAR␣ activity (34).…”