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