Regulatory phosphorylation of FXYD2 by PKC and cross interactions between FXYD2, plasmalemmal Ca-ATPase and Na,K-ATPase.

FXYD2 is a regulatory peptide associated with the α-subunit of the kidney Na,K-ATPase. FXYD2 can be phosphorylated by and its phosphorylation activates Na,K-ATPase. Here we show that FXYD2 is phosphorylated by by or by duanyu1529 and duanyu1531 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 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, increased PMCA activity only by 50%. In contrast, when PMCA was treated with 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.

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