title: Regulatory phosphorylation of FXYD2 by PKC and cross interactions between FXYD2, plasmalemmal Ca-ATPase and Na,K-ATPase.
abstract: FXYD2 is a regulatory peptide associated with the α-subunit of the kidney Na,K-ATPase. FXYD2 can be phosphorylated by PKA, and its phosphorylation activates Na,K-ATPase. Here we show that FXYD2 is phosphorylated by PKC (PKC-FXYD2-P), by PKA (PKA-FXYD2-P) or by PKA and PKC simultaneously (FXYD2-P(2)) modulating both the erythrocyte Na,K-ATPase and the plasma membrane Ca(2+)-ATPase (PMCA). In erythrocyte ghosts, the addition of PKA-FXYD2-P activated Na,K-ATPase by 80%, while non-phosphorylated FXYD2 (np) activated only 55%. The addition of np FXYD2 did not affect PMCA basal activity, but FXYD2-P(2) increased the basal PMCA activity by up to 200%. Calmodulin-activated PMCA activity was increased by np FXYD2 (3-fold) or FXYD2-P(2) (2.5-fold). However, PKC-FXYD2-P increased PMCA activity only by 50%. In contrast, when PMCA was treated with PKA-FXYD2-P, the ATPase activity was inhibited by 50%. The effect of all forms of FXYD2-P on calcium uptake from PMCA resembled the pattern observed in ATP hydrolysis. Our results suggest that the FXYD2 anchoring site could be conserved among the P-ATPase family permitting cross regulation. The effects of FXYD2 on calcium uptake and calcium-stimulated ATP hydrolysis suggest a novel role for FXYD2 on PMCA.
authors.affiliation: Laboratório de Estrutura e Regulação de Proteínas e ATPases, Instituto de Bioquímica Médica, Universidade Federal do Rio de Janeiro, Brazil.
authors.forename: Vanessa Faria
authors.initials: VF
authors.lastname: Cortes
authors.forename: Izabela Matos
authors.initials: IM
authors.lastname: Ribeiro
authors.forename: Hector
authors.initials: H
authors.lastname: Barrabin
authors.forename: Marcelo
authors.initials: M
authors.lastname: Alves-Ferreira
authors.forename: Carlos Frederico Leite
authors.initials: CF
authors.lastname: Fontes
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004912:Erythrocytes / Q000201:enzymology; D007679:Kidney Medulla / Q000201:enzymology; D010766:Phosphorylation; D053499:Plasma Membrane Calcium-Transporting ATPases / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D013552:Swine
chemical_list: D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D053499:Plasma Membrane Calcium-Transporting ATPases; D000254:Sodium-Potassium-Exchanging ATPase; D002118:Calcium