Regulation of the Na,K-ATPase in MDCK cells by prostaglandin E₁: A role for calcium as well as cAMP

Prostaglandins (PGs) play a significant role in the regulation of sodium reabsorption by the kidney, in addition to accumulating during inflammation as well as in several solid tumors. Previously, we presented evidence indicating that prostaglandin E₁ (PGE₁), a supplement in the serum-free medium for MDCK cells, increases the activity of the Na,K-ATPase in MDCK cells, in addition to its growth stimulatory effect [J. Cell. Physiol. 151 (1992) 337]. This report defines the molecular mechanisms, and signaling pathways responsible for the increased Na,K-ATPase activity. Our results indicate that the increased activity of the Na,K-ATPase in MDCK monolayers treated with either PGE₁ or 8Bromocyclic AMP (8Br-cAMP) can be attributed to an increase in the rate of biosynthesis of the Na,K-ATPase, and an increase in the levels of Na,K-ATPase α and β subunit mRNAs. As β subunit mRNA increased to a larger extent than α subunit mRNA, transient transfection studies were conducted using a human β1 promoter/luciferase construct [Nucleic Acids Res. 21 (1993) 2619]. While an 8Br-cAMP stimulation was observed (suggesting the involvement of cAMP), our results also suggest that the observed PGE₁ stimulation could be explained by the involvement of Ca²⁺ as well protein kinase C (PKC). Consistent with the involvement of Ca²⁺, TMB-8 (which inhibits Ca²⁺ efflux from intracellular stores) inhibited the PGE₁ stimulation. Moreover, PGE₁ was observed to stimulate the translocation of PKC β1 from the soluble to the particulate fraction. The translocation of PKC, the PGE₁ stimulation of transcription, and the PGE₁-mediated increase in the β subunit mRNA level were all inhibited by the PKC inhibitor Gö6989. These results can be explained by the involvement of two classes of cell surface receptors in mediating the PGE₁ stimulation, including the EP1subtype (which activates phospholipase C), as well as the EP2 subtype (which activates adenylate cyclase).