PGE₂-mediated cytoprotection in renal epithelial cells: Evidence for a pharmacologically distinct receptor

Although the exact mechanism of prostaglandin E₂ (PGE₂)-mediated cytoprotection has not been elucidated, its ability to induce cytoprotection in cell culture suggests this action occurs at the cellular level. The present studies were conducted to determine whether PGE₂ induces protection against 2,3,5-(trisglutathion-S-yl)-hydroquinone [2,3,5-(trisglutathion-S- yl)-HQ]-mediated cytotoxicity in a renal proximal tubule epithelial cell line (LLC-PK₁) and to delineate the cellular and molecular mechanisms associated with this response. Pretreatment of LLC-PK₁ cells with 0.01-40 μM PGE₂ for 24 h fully protects against a moderately toxic concentration of 2,3,5-(trisglutathion-S-yl)-HQ. PGE₂-mediated cytoprotection is observed in cells pretreated at pH 7.4 but not at pH 7.8. However, cytoprotection is observed in LLC-PK₁ cells pretreated with the PGE₂ analog, 11-deoxy- 16,16-dimethyl PGE₂ (DDM-PGE₂) but not with the PGE₂ receptor [E- prostanoid (EP)] agonists 17-phenyltrinor PGE₂ (EP₁), 11-deoxy PGE₁ (EP₂/EP₄), sulprostone (EP₁/EP₃), PGE₁, or PGA₂. 12-O- tetradecanoylphorbol-13-acetate (TPA), a potent activator of protein kinase C (PKC), also induces cytoprotection, supporting a role for this pathway in the cytoprotective response. PGE₂, DDM-PGE₂, and TPA all induce the binding of nuclear proteins to a TPA responsive element (TRE) whereas analogs that did not induce cytoprotection (PGE₁, 17-phenyltrinor PGE₂, sulprostone) were without effect. DDM-PGE₂- and TPA-mediated cytoprotection and TRE binding activity are inhibited by N-(2{[3-(4-bromophenyl)-2- propenyl]-amino}-ethyl)-5-isoquinolinesulfonamide (H-89) a PKC inhibiter. These data suggest that cytoprotection by PGE₂ and DDM-PGE₂ in LLC-PK₁ cells is mediated by a PKC-coupled receptor, which is pharmacologically distinct from the presently classified EP receptor subtypes.