Cellular stress can initiate prostaglandin (PG) biosynthesis which, through changes in gene expression, can modulate cellular functions, including cell growth. PGA2, a metabolite of PGE2, induces the expression of stress response genes, including gadd153 and hsp70, in HeLa cells and human diploid fibroblasts. PGs, gadd153, and hsp70 expression are also influenced by the cellular redox status. Polyphenolic glutathione conjugates retain the ability to redox cycle, with the concomitant generation of reactive oxygen species. One such conjugate, 2,3,5-tris(glutathion-S- yl)hydroquinone (TGHQ), is a potent nephrotoxic and nephrocarcinogenic metabolite of the nephrocarcinogen, hydroquinone. We therefore investigated the effects of TGHQ on PGE2 synthesis and gene expression in a renal proximal tubular epithelial cell line (LLC-PK1). TGHQ (200 μM, 2 h) increases PGE2 synthesis (2-3-fold) in LLC-PK1 cells with only minor (5%) reductions in cell viability. This response is toxicant-specific, since another proximal tubular toxicant, S-(1,2-dichlorovinyl)-L-cysteine (DCVC), stimulates PGE2 synthesis only after massive (68%) reductions in cell viability. Consistent with the ability of TGHQ to generate an oxidative stress, both deferoxamine mesylate and catalase protect LLC-PK1 cells from TGHQ-mediated cytotoxicity. Only catalase, however, completely blocks TGHQ- mediated PGE2 synthesis, implying a major role for hydrogen peroxide in this response. TGHQ induces the early (60 min) expression of gadd153 and hsp70. However, while inhibition of cyclooxygenase with aspirin prevents TGHQ- induced PGE2 synthesis, it does not affect TGHQ-mediated induction of gadd153 or hsp70 expression. In contrast, a stable PGE2 analogue, 11-deoxy- 16,-16-dimethyl-PGE2 (DDM-PGE2), which protects LLC-PK1 cells against TGHQ-mediated cytotoxicity, modestly elevates the levels of gadd153 and hsp70 expression. In addition, catalase and, to a lesser extent, deferoxamine mesylate block TGHQ-induced gene expression. Therefore, although TGHQ-induced generation of reactive oxygen species is required for PGE2 synthesis and stress gene expression, acute TGHQ-mediated increases in gadd153 and hsp70 mRNA levels are independent of PGE2 synthesis.
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