Identification and regulation of novel PPAR-γ splice variants in human THP-1 macrophages
We have previously identified four novel isoforms of PPAR-γ transcripts in monkey macrophages (J. Zhou, K.M. Wilson, J.D. Medh, Genetic analysis of four novel peroxisome proliferator receptor-γ splice variants in monkey macrophages. Biochem. Biophys. Res. Commun., 293 (2002) 274-283). The purpose of this study was to ascertain that these isoforms are also present in humans. Specific primers were designed to amplify individual isoform transcripts. The presence of PPAR-γ4, PPAR-γ5, and PPAR-γ7 transcripts in human THP-1 macrophages was confirmed by RT-PCR and sequencing. A transcript corresponding to PPAR-γ6 was not detected. The presence of novel full-length transcripts and protein was also ascertained by Northern and Western blot analysis. Treatment of THP-1 cells with 15-deoxy-Δ12,14-prostaglandin J2 (15d-PGJ2) resulted in more than 20% induction in the expression of PPAR-γ5 and PPAR-γ7 transcripts by both Northern blot analysis and RT-PCR. Another PPAR-γ ligand, troglitazone, induced expression of only PPAR-γ5. Both ligands inhibited the expression of PPAR-γ1 and PPAR-γ2. Additionally, 15d-PGJ2 and troglitazone increased the level of apolipoprotein E transcript by 60% but decreased lipoprotein lipase expression by 15% in THP-1 cells. The differential regulation of PPAR-γ transcripts suggests that each transcript isoform may contribute to macrophage function.