An epitope-tagging system for studying regulation of the peroxisome proliferator activated receptor alpha (PPAR alpha).

Abstract

Peroxisome proliferators (PPs) are a group of compounds which cause peroxisome proliferation and hepatocellular carcinomas in rodents, and form a class of non-genotoxic carcinogens. It is thought that PPs act via a receptor similar to members of the nuclear hormone superfamily termed the peroxisome proliferator activated receptor (PPAR). Multiple subtypes (alpha, beta, delta and gamma) of the receptor exist and are differentially expressed between tissues and species. PPAR alpha has been shown to activate transcription by binding to response elements upstream of peroxisome proliferator responsive genes. However, despite the isolation of transcriptionally active human subtypes of the receptor, hPPAR alpha and hNUC1, humans are thought to be non-responsive to PPs. This is possibly due to regulation of PPAR, and it has been recently reported that PPAR alpha is a phosphoprotein in vivo and insulin regulates its phosphorylation. A system employing epitope-tagged receptors has been developed to study this further, with the aim of establishing stably transfected cell lines expressing high levels of epitope-tagged mouse and human PPAR alpha. Our experiments clearly demonstrate that an epitope-tagged mPPAR alpha receptor has an equal ability to modulate transcription as the native receptor in transactivation assays and will be further used to examine the molecular mechanisms of peroxisome proliferation.