Aspects of the regulatory mechanisms of PPAR functions: Analysis of a bidirectional response element and regulation by sumoylation

Peroxisome proliferator-activated receptors (PPARs) constitute a subfamily of nuclear receptor superfamily. A wide variety of compounds including hypolipidemic agents, antidiabetic drugs, and long-chain fatty acids are the potential ligands of PPARs. To approach the regulatory mechanisms of PPARs, we studied on two subjects in this work. First, we identified a functional PPAR-binding site in the spacer region between the PEX11 alpha and perilipin genes, which are arranged in tandem on the mouse genome. By gene reporter assays and in vivo as well as in vitro binding assays, we show that these genes are regulated tissue-selectively through this common binding site: The PEX11 alpha gene is activated by PPAR alpha in the liver, whereas the perilipin gene by PPAR gamma in the adipose tissue. As the second subject, we found that PPAR gamma 2 is conjugated with small ubiquitin-related modifier (SUMO) at a specific lysine residue in the amino-terminal region. By site-directed mutagenesis combined with gene reporter assays and sumoylation analyses, we show that sumoylation represses the ligand-independent transactivating function carried by this region, and hence negatively regulates the whole transactivating competence of PPAR gamma 2. In addition, phosphorylation at a specific site in the amino-terminal region represses the transactivation by PPAR gamma 2 possibly through enhancing sumoylation.