Stress- and growth-related gene expression are independent of chemical- induced prostaglandin E₂ synthesis in renal epithelial cells

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.