Interaction of protein kinase C and cAMP-dependent pathways in the phosphorylation of the Na,K-ATPase.
To test the hypothesis that there is cross-talk between the protein kinase C (PKC) and protein kinase A (PKA) pathways in the regulation of the Na,K-ATPase, we measured its phosphorylation in mammalian cell cultures. Phosphorylation of the PKC site, Ser-18, appeared to be due to the activation of the alpha isoform of the kinase. In NRK-52E and L6 cells, this phosphorylation was reduced by prior activation of a cAMP-dependent signaling pathway with forskolin. In principle this would be consistent with direct interaction between the two phosphorylation sites, but further investigation suggested a more indirect mechanism. First, phosphorylation of Ser-938, the PKA site, could not be detected despite the presence of active PKA. Second, there was a major reduction in the phosphorylation of unrelated phosphoproteins as a consequence of elevation of cAMP, suggesting generalized reduction of kinase activity or activation of phosphatase activity. In NRK-52E and L6, phosphorylation of the Na, K-ATPase at Ser-18 paralleled this global change. In C6 cells, in contrast, there was no cAMP effect on Na,K-ATPase phosphorylation at Ser-18 and no global cAMP effect on other phosphoproteins. The cross-talk is evidently mediated by events occurring at the cellular level.
Laboratory of Membrane Biology, Neuroscience Center, Massachusetts General Hospital, Charlestown, Massachusetts 02129, USA.
M S
MS
Feschenko
E
E
Stevenson
K J
KJ
Sweadner
D000818:Animals; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism*; D051381:Rats; D012694:Serine / Q000737:chemistry / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000737:chemistry / Q000378:metabolism*
D012694:Serine; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D000254:Sodium-Potassium-Exchanging ATPase