Phosphorylation of phospholemman (FXYD1) by protein kinases A and C modulates distinct Na,K-ATPase isozymes.
Phospholemman (FXYD1), mainly expressed in heart and skeletal muscle, is a member of the FXYD protein family, which has been shown to decrease the apparent K(+) and Na(+) affinity of Na,K-ATPase ( Crambert, G., Fuzesi, M., Garty, H., Karlish, S., and Geering, K. (2002) Proc. Natl. Acad. Sci. U. S. A. 99, 11476-11481 ). In this study, we use the Xenopus oocyte expression system to study the role of phospholemman phosphorylation by protein kinases A and C in the modulation of different Na,K-ATPase isozymes present in the heart. Phosphorylation of phospholemman by protein kinase A has no effect on the maximal transport activity or on the apparent K(+) affinity of Na,K-ATPase alpha1/beta1 and alpha2/beta1 isozymes but increases their apparent Na(+) affinity, dependent on phospholemman phosphorylation at Ser(68). Phosphorylation of phospholemman by protein kinase C affects neither the maximal transport activity of alpha1/beta1 isozymes nor the K(+) affinity of alpha1/beta1 and alpha2/beta1 isozymes. However, protein kinase C phosphorylation of phospholemman increases the maximal Na,K-pump current of alpha2/beta1 isozymes by an increase in their turnover number. Thus, our results indicate that protein kinase A phosphorylation of phospholemman has similar functional effects on Na,K-ATPase alpha1/beta and alpha2/beta isozymes and increases their apparent Na(+) affinity, whereas protein kinase C phosphorylation of phospholemman modulates the transport activity of Na,K-ATPase alpha2/beta but not of alpha1/beta isozymes. The complex and distinct regulation of Na,K-ATPase isozymes by phosphorylation of phospholemman may be important for the efficient control of heart contractility and excitability.
Bibert
Stéphanie
S
Department of Pharmacology and Toxicology, University of Lausanne, 27 Rue du Bugnon, 1005 Lausanne, Switzerland.
Roy
Sophie
S
Department of Pharmacology and Toxicology, University of Lausanne, 27 Rue du Bugnon, 1005 Lausanne, Switzerland.
Schaer
Danièle
D
Department of Pharmacology and Toxicology, University of Lausanne, 27 Rue du Bugnon, 1005 Lausanne, Switzerland.
Horisberger
Jean-Daniel
JD
Department of Pharmacology and Toxicology, University of Lausanne, 27 Rue du Bugnon, 1005 Lausanne, Switzerland.
Geering
Käthi
K
Department of Pharmacology and Toxicology, University of Lausanne, 27 Rue du Bugnon, 1005 Lausanne, Switzerland. Electronic address: Kaethi.Geering@unil.ch.
D000818:Animals; D001667:Binding, Competitive; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D004285:Dogs; D005260:Female; D007527:Isoenzymes / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D009865:Oocytes / Q000378:metabolism; D010042:Ouabain / Q000378:metabolism; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D011188:Potassium / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D014981:Xenopus
D007527:Isoenzymes; D008565:Membrane Proteins; D010750:Phosphoproteins; C069141:phospholemman; D010042:Ouabain; D012964:Sodium; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium