Cytokines and sodium induce protein kinase A-dependent cell-surface Na,K-ATPase recruitment via dissociation of NF-kappaB/IkappaB/protein kinase A catalytic subunit complex in collecting duct principal cells.

Abstract

Collecting duct (CD) principal cells are exposed to large physiologic variations of apical Na+ influx as a result of variations of Na(+) intake and extrarenal losses. It was shown previously that increasing intracellular [Na+] induces recruitment of Na,K-ATPase to the cell surface in a protein kinase A (PKA)-dependent manner in both native and cultured renal CD principal cells. As described previously in response to cytokines in nonrenal cells, PKA activation in response to increased intracellular [Na+] was independent of cAMP and required proteasomal activity. With the use of cultured mpkCCD(cL4) cells as a model of CD principal cells, whether cytokines and increased intracellular [Na+] share a common signaling pathway leading to cell-surface Na,K-ATPase recruitment was investigated. Results showed that two potent inducers of NF-kappaB, LPS and TNF-alpha, enhance Na+ transport and induce cell-surface Na,K-ATPase recruitment in mpkCCD(cL4) cells via cAMP-independent PKA activation. In addition, increased intracellular [Na+] after selective plasma membrane permeabilization by a low concentration of the Na+ ionophore amphotericin B (1 microg/ml) induced dissociation of the PKA catalytic subunit from p65-NF-kappaB and IkappaBalpha. Moreover, inhibitors of NF-kappaB/IkappaB dissociation prevented both Na+-dependent stimulation of PKA activity and cell-surface Na,K-ATPase recruitment. Altogether, these results revealed the presence of a novel Na+-dependent intracellular signaling pathway leading to Na,K-ATPase cell-surface recruitment via dissociation of the PKA catalytic subunit from a macromolecular complex that contains NF-kappaB and IkappaBalpha in CD epithelial cells.