Abstract
Prostaglandin E(2) (PGE(2)) contributes to cystogenesis in genetically nonorthologous models of autosomal dominant polycystic kidney disease (ADPKD). However, it remains unknown whether PGE(2) induces the classic features of cystic epithelia in genetically orthologous models of ADPKD. We hypothesized that, in ADPKD epithelia, PGE(2) induces proliferation and chloride (Cl(-)) secretion, two archetypal phenotypic features of ADPKD. To test this hypothesis, proliferation and Cl(-) secretion were measured in renal epithelial cells deficient in polycystin-1 (PC-1). PC-1-deficient cells increased in cell number (proliferated) faster than PC-1-replete cells, and this proliferative advantage was abrogated by cyclooxygenase inhibition, indicating a role for PGE(2) in cell proliferation. Exogenous administration of PGE(2) increased proliferation of PC-1-deficient cells by 38.8 ± 5.2% (P < 0.05) but inhibited the growth of PC-1-replete control cells by 49.4 ± 1.9% (P < 0.05). Next, we tested whether PGE(2)-specific E prostanoid (EP) receptor agonists induce intracellular cAMP and downstream β-catenin activation. PGE(2) and EP4 receptor agonism (TCS 2510) increased intracellular cAMP concentration and the abundance of active β-catenin in PC-1-deficient cells, suggesting a mechanism for PGE(2)-mediated proliferation. Consistent with this hypothesis, antagonizing EP4 receptors reverted the growth advantage of PC-1-deficient cells, implicating a central role for the EP4 receptor in proliferation. To test whether PGE(2)-dependent Cl(-) secretion is also enhanced in PC-1-deficient cells, we used an Ussing chamber to measure short-circuit current (I(sc)). Addition of PGE(2) induced a fivefold higher increase in I(sc) in PC-1-deficient cells compared with PC-1-replete cells. This PGE(2)-induced increase in I(sc) in PC-1-deficient cells was blocked by CFTR-172 and flufenamic acid, indicating that PGE(2) activates CFTR and calcium-activated Cl(-) channels. In conclusion, PGE(2) activates aberrant signaling pathways in PC-1-deficient epithelia that contribute to the proliferative and secretory phenotype characteristic of ADPKD and suggests a therapeutic role for PGE(2) inhibition and EP4 receptor antagonism.