Stress- and Growth-Related Gene Expression Are Independent of Chemical-Induced Prostaglandin E₂ Synthesis in Renal Epithelial Cells

Abstract

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.

Effect of Epidermal Growth Factor on Phosphate Uptake in Renal Proximal Tubule Cells: Involvement of PKC, MAPK, and cPLA₂

“…Burns et al [36] also reported that EGF dramatically increased endogenous epoxyeicosatrienoic acid levels in primary cultures of rabbit PTCs. Although the activity of cyclooxygenase is very low in proximal tubule [37], it may be sufficient to have conversion of AA into its metabolites, based upon several reports including our report [38,39]. Indeed, EGF increased PGE 2 , major metabolites of cyclooxygenase, production in this system [unpubl.…”

Action of EGF and PGE2on basolateral organic anion uptake in rabbit proximal renal tubules and hOAT1 expressed in human kidney epithelial cells

“…In inflammatory disease of the kidney, PGE 2 and its receptors are shown to be upregulated (26). In proximal tubule cells from pigs and humans, PGE 2 is generated by reactive oxygen species (27,54) induced by stress and may directly contribute to renal lesions and loss of kidney function. Inasmuch as basolateral uptake is the rate-limiting step of organic anion secretion, we expect that PGE 2 induces stimulation of organic anion secretion into the proximal tubular lumen.…”

Short-Term Regulation of Basolateral Organic Anion Uptake in Proximal Tubular OK cells

“…It is well known that renal cortex tissue (42), renal epithelial cell lines (43), and isolated proximal tubules (44) produce PGE 2 . The fact that inhibition of COX diminishes organic anion uptake in the OK cell system alone is, of course, not the final proof for EGF-stimulated PGE 2 formation.…”