Transcriptional inactivation of STAT3 by PPARgamma suppresses IL-6-responsive multiple myeloma cells.

Multiple myeloma (MM) remains largely incurable despite conventional and high-dose therapies. Therefore, novel biologically based treatment approaches are urgently required. Here we demonstrate that expression of peroxisome proliferator-activated receptor gamma (PPARgamma) in MM cells and its agonists 15-d-PGJ2 and troglitazone completely abolished IL-6-inducible MM cell proliferation and induced apoptosis through affecting expression of multiple cell cycle or apoptosis genes, whereas PPARgamma antagonist GW9662 and PPARalpha agonist WY14643 did not display this inhibitory effect. These PPARgamma agonists significantly inhibited DNA binding and transactivation of STAT3 bound to the promoter of target genes in chromatin, but did not affect the expression of IL-6 receptor and phosphorylation of JAK/STAT3, MAPK, and PI3K/Akt. Interestingly, although inactivation of STAT3 by PPARgamma agonists is in a PPARgamma-dependent manner, the molecular mechanism by which two structurally distinct PPARgamma agonists suppress IL-6-activated STAT3 shows the divergent interactions between PPARgamma and STAT3 including direct or SMRT-mediated association.