Towndrow K M, Mertens J J, Jeong J K, Weber T J, Monks T J, Lau S S
Division of Pharmacology, College of Pharmacy, The University of Texas at Austin, Austin, Texas 78712, USA.
Chem Res Toxicol. 2000 Feb;13(2):111-7. doi: 10.1021/tx990160s.
Cellular stress can initiate prostaglandin (PG) biosynthesis which, through changes in gene expression, can modulate cellular functions, including cell growth. PGA(2), a metabolite of PGE(2), 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 PGE(2) synthesis and gene expression in a renal proximal tubular epithelial cell line (LLC-PK(1)). TGHQ (200 microM, 2 h) increases PGE(2) synthesis (2-3-fold) in LLC-PK(1) 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 PGE(2) 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-PK(1) cells from TGHQ-mediated cytotoxicity. Only catalase, however, completely blocks TGHQ-mediated PGE(2) 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 PGE(2) synthesis, it does not affect TGHQ-mediated induction of gadd153 or hsp70 expression. In contrast, a stable PGE(2) analogue, 11-deoxy-16, 16-dimethyl-PGE(2) (DDM-PGE(2)), which protects LLC-PK(1) 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 PGE(2) synthesis and stress gene expression, acute TGHQ-mediated increases in gadd153 and hsp70 mRNA levels are independent of PGE(2) synthesis.
细胞应激可启动前列腺素（PG）生物合成，通过基因表达变化，可调节细胞功能，包括细胞生长。PGA(2)是PGE(2)的一种代谢产物，可诱导HeLa细胞和人二倍体成纤维细胞中应激反应基因的表达，包括gadd153和hsp70。PG、gadd153和hsp70的表达也受细胞氧化还原状态的影响。多酚类谷胱甘肽缀合物保留了氧化还原循环的能力，同时产生活性氧。一种这样的缀合物，2,3,5-三（谷胱甘肽-S-基）对苯二酚（TGHQ），是肾致癌物对苯二酚的一种强效肾毒性和肾致癌代谢产物。因此，我们研究了TGHQ对肾近端小管上皮细胞系（LLC-PK(1)）中PGE(2)合成和基因表达的影响。TGHQ（200 microM，2小时）可使LLC-PK(1)细胞中PGE(2)合成增加（2-3倍），而细胞活力仅轻微降低（5%）。这种反应具有毒物特异性，因为另一种近端小管毒物S-（1,2-二氯乙烯基）-L-半胱氨酸（DCVC）仅在细胞活力大幅降低（68%）后才刺激PGE(2)合成。与TGHQ产生氧化应激的能力一致，甲磺酸去铁胺和过氧化氢酶均可保护LLC-PK(1)细胞免受TGHQ介导的细胞毒性。然而，只有过氧化氢酶能完全阻断TGHQ介导的PGE(2)合成，这意味着过氧化氢在该反应中起主要作用。TGHQ可诱导gadd153和hsp70的早期（60分钟）表达。然而，虽然用阿司匹林抑制环氧化酶可阻止TGHQ诱导的PGE(2)合成，但并不影响TGHQ介导的gadd153或hsp70表达的诱导。相反，一种稳定的PGE(2)类似物11-脱氧-16,16-二甲基-PGE(2)（DDM-PGE(2)）可保护LLC-PK(1)细胞免受TGHQ介导的细胞毒性，并适度提高gadd153和hsp70的表达水平。此外，过氧化氢酶以及程度较轻的甲磺酸去铁胺可阻断TGHQ诱导的基因表达。因此，虽然TGHQ诱导的活性氧生成是PGE(2)合成和应激基因表达所必需的，但TGHQ急性介导的gadd153和hsp70 mRNA水平升高与PGE(2)合成无关。
