Title: Glutathione S-transferases (GSTs) inhibit transcriptional activation by the peroxisomal proliferator-activated receptor gamma (PPAR gamma) ligand, 15-deoxy-delta 12,14prostaglandin J2 (15-d-PGJ2).

Authors: Paumi, Christian M; Smitherman, Pamela K; Townsend, Alan J; Morrow, Charles S

Published In Biochemistry, (2004 Mar 2)

Abstract: 15-Deoxy-Delta(12,14)prostaglandin J(2) (15-d-PGJ(2)), a terminal metabolite of the J-series cyclopentenone prostaglandins, influences a variety of cellular processes including gene expression, differentiation, growth, and apoptosis. As a ligand of peroxisomal proliferator-activated receptor gamma (PPAR gamma), 15-d-PGJ(2) can transactivate PPAR gamma-responsive promoters. Previously, we showed that multidrug resistance proteins MRP1 and MRP3 attenuate cytotoxic and transactivating activities of 15-d-PGJ(2) in MCF7 breast cancer cells. Attenuation was glutathione-dependent and was associated with formation of the glutathione conjugate of 15-d-PGJ(2), 15-d-PGJ(2)-SG, and its active efflux by MRP. Here we have investigated whether the glutathione S-transferases (GST) can influence biological activities of 15-d-PGJ(2). MCF7 cells were stably transduced with human cytosolic GST isozymes M1a, A1, or P1a. These GSTs had no effect on 15-d-PGJ(2) cytotoxicity when expressed either alone or in combination with MRP1. However, expression of any of the three GSTs significantly inhibited 15-d-PGJ(2)-dependent transactivation of a PPAR gamma-responsive reporter gene. The degree of inhibition correlated with the level of GST expressed. Under physiologic conditions, the nonenzymatic rate of 15-d-PGJ(2) conjugation with glutathione was significant. Of the three GST isozymes, only GSTM1a-1a further stimulated the rate of 15-d-PGJ(2)-SG formation. Moreover, GSTM1a-1a rate enhancement was only a transient burst that was complete within 15 s. Hence, catalysis plays little, if any, role in GST inhibition of 15-d-PGJ(2)-dependent transactivation. In contrast, inhibition of transactivation was associated with strong GST/15-d-PGJ(2) interactions. Potent inhibition by 15-d-PGJ(2) and 15-d-PGJ(2)-SG of GST activity was observed with K(i) in the 0.15-2.0 microM range for the three GST isozymes, results suggesting avid associations between GST and 15-d-PGJ(2) or 15-d-PGJ(2)-SG. Electrospray ionization mass spectrometry (ESI/MS) studies revealed no stable adducts of GST and 15-d-PGJ(2) indicating that GST/15-d-PGJ(2) interactions are primarily noncovalent. These results are consistent with a mechanism of GST-mediated inhibition of transactivation in which GST binds 15-d-PGJ(2) and 15-d-PGJ(2)-SG thereby sequestering the ligands in the cytosol away from their nuclear target, PPAR gamma.

PubMed ID: 14979731

MeSH Terms: Catalysis; Cell Death/drug effects; Cell Line, Tumor; Genetic Vectors; Glutathione Transferase/chemistry*; Glutathione Transferase/genetics; Glutathione Transferase/metabolism; Glutathione/chemistry; Glutathione/metabolism; Growth Inhibitors/antagonists & inhibitors; Growth Inhibitors/chemistry; Growth Inhibitors/metabolism; Growth Inhibitors/toxicity; Humans; Isoenzymes/chemistry; Isoenzymes/genetics; Isoenzymes/metabolism; Prostaglandin D2/analogs & derivatives; Prostaglandin D2/antagonists & inhibitors*; Prostaglandin D2/chemistry*; Prostaglandin D2/metabolism; Prostaglandin D2/toxicity; Receptors, Cytoplasmic and Nuclear/antagonists & inhibitors; Receptors, Cytoplasmic and Nuclear/chemistry; Receptors, Cytoplasmic and Nuclear/metabolism*; Research Support, U.S. Gov't, P.H.S.; Trans-Activation (Genetics)*; Trans-Activators/antagonists & inhibitors*; Trans-Activators/chemistry*; Trans-Activators/metabolism; Trans-Activators/toxicity; Transcription Factors/antagonists & inhibitors; Transcription Factors/chemistry; Transcription Factors/metabolism*; Transduction, Genetic