Interactions of prostaglandin A2 with the glutathione-mediated biotransformation system.
The cyclopentenone prostaglandin A2 (PGA2) is known to inhibit cell proliferation, and metabolism of this compound thus might be important in controlling its ultimate function. The glutathione-related metabolism of PGA2 was therefore investigated both with purified glutathione S-transferase P1-1 (GSTP1-1) and with IGR-39 human melanoma cells. Firstly, the irreversible inhibition of human GSTP1-1 and its mutants C47S, C101S, and C47S/C101S was studied. PGA2 appeared to inhibit GSTP1-1 mainly by binding to the cysteine 47 moiety of the enzyme. This binding was reversed by a molar excess of GSH, indicating that retro-Michael cleavage occurs. Secondly, after exposing IGR-39 human melanoma cells to PGA2, both diastereoisomers of the PGA2-glutathione conjugate are excreted into the medium, although with a clear excess of the S-form, due to its preferential formation by the GSTP1-1 present in the cells. Thirdly, the effect of PGA2 on intracellular GST activity was determined by quantification of the excreted glutathione conjugate S-(2,4-dinitrophenyl)glutathione (DNPSG) after exposure to 1-chloro-2,4-dinitrobenzene. DNPSG excretion was inhibited after incubation with 10 or 20 microM PGA2 for 1 or 4 hr, as a result of glutathione depletion, reversible GST inhibition, and covalent modification of intracellular GST. Furthermore, PGA2 also inhibited transport of DNPSG by the multidrug resistance-associated protein, an effect that was reversible and competitive. In conclusion, PGA2 modulates all three aspects of the glutathione-mediated biotransformation system, i.e. GSH levels, GSTP1-1 activity, and transport of GSH conjugates. A role for GSTP1-1 as a specific transport protein inside the cell is indicated.
van Iersel
M L
ML
Department of Food Technology and Nutritional Sciences, Wageningen Agricultural University, The Netherlands.
Cnubben
N H
NH
Smink
N
N
Koeman
J H
JH
van Bladeren
P J
PJ
D001711:Biotransformation; D005978:Glutathione / Q000378:metabolism*; D051549:Glutathione S-Transferase pi; D005982:Glutathione Transferase / Q000037:antagonists & inhibitors / Q000378:metabolism; D006801:Humans; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000378:metabolism; D008545:Melanoma; D011454:Prostaglandins A / Q000378:metabolism*; D014407:Tumor Cells, Cultured
D007527:Isoenzymes; D011454:Prostaglandins A; C496556:GSTP1 protein, human; D051549:Glutathione S-Transferase pi; D005982:Glutathione Transferase; D005978:Glutathione; C100008:prostaglandin A2