Associates with and regulates the activity of the sodium/potassium-transporting ATPase (NKA) which catalyzes the hydrolysis of ATP coupled with the exchange of Na(+) and K(+) ions across the plasma membrane (By similarity). May increase NKA activity by increasing the apparent affinity for Na(+) (PubMed:18263667). Involved in down-regulation of E-cadherin which results in reduced cell adhesion. Promotes metastasis (PubMed:11756660). {ECO:0000250|UniProtKB:P97808, ECO:0000269|PubMed:11756660, ECO:0000269|PubMed:18263667}. This is the function of FXYD5 (FXYD domain containing ion transport regulator 5, Ensembl gene identifier ENSG00000089327).