Inhibitory interaction of the 14-3-3 proteins with ubiquitous (PMCA1) and tissue-specific (PMCA3) isoforms of the plasma membrane Ca2+ pump

A previous study has demonstrated that the ubiquitous plasma membrane CA(2+) pump PMCA4 interacted with isoform epsilon of the 14-3-3 protein, whereas the nervous tissue-specific PMCA2 did not. The 14-3-3 proteins are widely expressed small acidic proteins, which modulate cell signaling, intracellular trafficking, transcription and Apoptosis. The investigation has been extended to the other tissue-restricted pump (PMCA3) and to the other ubiquitous pump (PMCA1). At variance with PMCA2, PMCA3 interacted with the 14-3-3epsilon protein in a two-hybrid system assay, which could not be used for PMCA1. The 14-3-3epsilon protein immunoprecipitated with both PMCA3 and PMCA1 when expressed in HeLa cells. Pull-down experiments using GST-PMCA1 and GST-PMCA3 fusion products confirmed the interaction of both pumps with the 14-3-3epsilon protein. The binding was phosphorylation-independent with both PMCA3 and PMCA1. The 14-3-3zeta isoform also interacted with PMCA3; however, it did not interact with PMCA1. The effect of the interaction on the activity of the two pumps, and thus on the homeostasis of CA(2+), was investigated by co-expressing the 14-3-3epsilon protein and PMCA3 or PMCA1 in CHO cells together with the recombinant CA(2+) indicator aequorin: the ability of cells to re-establish the basal CA(2+) concentration following a CA(2+) transient induced by an InsP(3)-producing agonist was substantially decreased with both pumps, indicating that the interaction with the 14-3-3 protein inhibited the activity of both PMCA3 and PMCA1.