FK614, a novel peroxisome proliferator-activated receptor gamma modulator, induces differential transactivation through a unique ligand-specific interaction with transcriptional coactivators.

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a ligand-dependent transcriptional factor implicated in regulating adipogenesis, glucose homeostasis, and in mediating the action of the insulin sensitizing anti-diabetic thiazolidinedione (TZD) compounds. [3-(2,4-Dichlorobenzyl)-2-methyl-N-(pentylsulfonyl)-3-H-benzimidazole-5-carboxamide] (FK614) is a structurally novel PPARgamma agonist that demonstrates potent anti-diabetic activity in vivo. Herein, we describe that FK614 is a selective PPARgamma ligand with specific transactivation properties that are dependent upon the context of coactivators. FK614 dissociates the corepressors NCoR (nuclear receptor corepressor) and SMRT (silencing mediator of retinoid and thyroid hormone receptors) from PPARgamma as effectively as rosiglitazone and pioglitazone, but can also differentially induce a ligand specific interaction of PPARgamma with coactivators. The amount of CBP (CREB-binding protein) and SRC-1 (steroid receptor coactivator-1) recruited by FK614 was less than that induced by rosiglitazone and pioglitazone, but FK614 caused similar PGC-1alpha (PPARgamma coactivator-1alpha) recruitment as these compounds. As a consequence of these ligand-specific differences in the strength of ligand-type specific interactions of PPARgamma and coactivators, FK614 functions as a partial or full agonist for transcriptional activation depending upon the amount of specific coactivators in cells following overexpression. In conclusion, FK614 is a novel, non-TZD type, and selective PPARgamma modulator whose pharmacological properties are distinct from rosiglitazone and pioglitazone.

Mechanisms of drug/H+ antiport: complete cysteine-scanning mutagenesis and the protein engineering approach.

The notorious difficulty of elucidating structures of membrane transporters by crystallography has long prevented our understanding of active transport mechanism coupled with ion/proton transport. The determination of the first crystal structure of the drug/H+ antiporter AcrB was a breakthrough for structure-based understanding of drug/H+ antiport. However, although AcrB is a major multidrug exporter in Gram-negative organisms, the majority of bacterial drug exporters are major facilitator superfamily (MFS) drug transporters. As no crystal structures have been solved for MFS transporters, the alternative protein-engineering methods are still very useful for estimating structures and functions of drug/H+ antiporters. This review describes this alternative approach for investigating the structure and function of tetracycline/H+ antiporters.