Unique properties of coactivator recruitment caused by differential binding of FK614, an anti-diabetic agent, to peroxisome proliferator-activated receptor γ

FK614 is a structurally novel class of peroxisome proliferator-activated receptor gamma (PPAR gamma) agonist, with the mechanism of its insulin-sensitizing action most likely due to activation of PPAR gamma. In this study, properties of FK614 for PPAR gamma binding, ability to induce conformational change, and coactivator recruitment were investigated. FK614, rosiglitazone, and pioglitazone competed specific binding of vertical bar H-3 vertical bar rosiglitazone to PPAR gamma with K-i values of 11 nm, 47 nm, and 1.3 mu m, respectively. Limited trypsin digestion of PPAR gamma with FK614 or rosiglitazone produced distinct patterns of digested polypeptides, suggesting that FK614 directly binds to PPAR gamma but induces specific alterations in receptor conformation. FK614 induced interaction of PPAR gamma with nuclear receptor coactivator CBP but of lower magnitude than rosiglitazone and pioglitazone. The estimated K-d values of FK614-, rosigiitazone-, and pioglitazone-PPAR gamma complex to CBP peptide were 1.8, 0.64, and 0.72 mu M, respectively, indicating FK614-PPAR gamma complex exhibits a lower affinity for CBP peptide compared to other agonist-PPAR gamma complexes. When tested the effect of FK614 on CBP recruitment induced by 9(S)-hydroxyoctadecadienoic acid, an endogenous ligand, FK614 negatively modulated PPAR gamma activation. The unique properties of FK614 may underlie the molecular basis of ligand-dependent transcriptional modulation mediated by PPAR gamma.