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).
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.
Paumi
Christian M
CM
Department of Biochemistry, Wake Forest University School of Medicine, Medical Center Boulevard, Winston-Salem, North Carolina 27157, USA.
Smitherman
Pamela K
PK
Townsend
Alan J
AJ
Morrow
Charles S
CS
D002384:Catalysis; D016923:Cell Death / Q000187:drug effects; D045744:Cell Line, Tumor; D005822:Genetic Vectors; D005978:Glutathione / Q000737:chemistry / Q000378:metabolism; D005982:Glutathione Transferase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006131:Growth Inhibitors / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism / Q000633:toxicity; D006801:Humans; D007527:Isoenzymes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D015230:Prostaglandin D2 / Q000031:analogs & derivatives / Q000037:antagonists & inhibitors* / Q000737:chemistry* / Q000378:metabolism / Q000633:toxicity; D018160:Receptors, Cytoplasmic and Nuclear / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism*; D015534:Trans-Activators / Q000037:antagonists & inhibitors* / Q000737:chemistry* / Q000378:metabolism / Q000633:toxicity; D014157:Transcription Factors / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism*; D015533:Transcriptional Activation; D014161:Transduction, Genetic
C097240:15-deoxy-delta(12,14)-prostaglandin J2; D006131:Growth Inhibitors; D007527:Isoenzymes; D018160:Receptors, Cytoplasmic and Nuclear; D015534:Trans-Activators; D014157:Transcription Factors; D005982:Glutathione Transferase; D005978:Glutathione; D015230:Prostaglandin D2