Distinct role of the N-terminal tail of the Na,K-ATPase catalytic subunit as a signal transducer

Mounting evidence suggests that the ion pump, Na, K-ATPase, can, in the presence of ouabain, act as a signal transducer. A prominent binding motif linking the Na, K-ATPase to intracellular signaling effectors has, however, not yet been identified. Here we report that the N-terminal tail of the Na, K-ATPase catalytic alpha-subunit (alpha NT-t) binds directly to the N terminus of the inositol 1,4,5-trisphosphate receptor. Three amino acid residues, LKK, conserved in most species and most alpha-isoforms, are essential for the binding to occur. In wild-type cells, low concentrations of ouabain trigger low frequency calcium oscillations that activate NF-kappa B and protect from apoptosis. All of these effects are suppressed in cells overexpressing a peptide corresponding to alpha NT-t but not in cells overexpressing a peptide corresponding to alpha NT- t Delta LKK. Thus we have identified a well conserved Na, K-ATPase motif that binds to the inositol 1,4,5-trisphosphate receptor and can trigger an anti-apoptotic calcium signal.