Abstract

Glutathione transferase P1-1 (GSTP1-1) plays crucial roles in cancer chemoprevention and chemoresistance and is a key target for anticancer drug development. Oxidative stress or inhibitor-induced GSTP1-1 oligomerization leads to the activation of stress cascades and apoptosis in various tumor cells. Therefore, bivalent glutathione transferase (GST) inhibitors with the potential to interact with GST dimers are been sought as pharmacological and/or therapeutic agents. Here we have characterized GSTP1-1 oligomerization in response to various endogenous and exogenous agents. Ethacrynic acid, a classic GSTP1-1 inhibitor, 4-hydroxy-nonenal, hydrogen peroxide, and diamide all induced reversible GSTP1-1 oligomerization in Jurkat leukemia cells through the formation of disulphide bonds involving Cys47 and/or Cys101, as suggested by reducing and nonreducing SDS-polyacrylamide gel electrophoresis analysis of cysteine to serine mutants. Remarkably, the electrophilic prostanoid 15-deoxy-Δ^12,14-prostaglandin J₂ (15d-PGJ₂) induced irreversible GSTP1-1 oligomerization, specifically involving Cys101, a residue present in the human but not in the murine enzyme. 15d-PGJ₂-induced GSTP1-1 cross-linking required the prostaglandin (PG) dienone structure and was associated with sustained c-Jun NH₂-terminal kinase activation and induction of apoptosis. It is noteworthy that 15d-PGJ₂ elicited GSTP1-1 cross-linking in vitro, a process that could be mimicked by other dienone cyclopentenone PG, such as Δ¹²-PGJ₂, and by the bifunctional thiol reagent dibromobimane, suggesting that cyclopentenone PG may be directly involved in oligomer formation. Remarkably, Δ¹²-PGJ₂-induced oligomeric species were clearly observed by electron microscopy showing dimensions compatible with GSTP1-1 tetramers. These results provide the first direct visualization of GSTP1-1 oligomeric species. Moreover, they offer novel strategies for the modulation of GSTP1-1 cellular functions, which could be exploited to overcome its role in cancer chemoresistance.