Cytokines and Sodium Induce Protein Kinase A-Dependent Cell-Surface Na,K-ATPase Recruitment via Dissociation of NF-B/IB/Protein Kinase A Catalytic Subunit Complex in Collecting Duct Principal Cells

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*Service of Nephrology, Foundation for Medical Research, Geneva, Switzerland; and Dulbecco Telethon Institute, Laboratory of Medical Genetics, S. Orsola-Malpighi Hospital, Bologna, Italy

	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-B, LPS and TNF-, 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 µg/ml) induced dissociation of the PKA catalytic subunit from p65-NF-B and IB. Moreover, inhibitors of NF-B/IB 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-B and IB in CD epithelial cells.