Regulation of the Na/H exchanger regulatory factor in OK cells

The Na/H exchanger regulatory factor (NHE-RE), a recently cloned renal prot ein, is a necessary cofactor in protein kinase A-mediated inhibition of the renal brush border membrane Na/H exchanger. No studies to date, however, h ave examined the regulation of NHE-RF itself. The rabbit NHE-RF cDNA and an antibody to rabbit NHE-RF were used to study the effects of serum and cycl ic adenosine monophosphate (cAMP) on the steady-state levels of NHE-RF mRNA and on the abundance and intracellular distribution of the protein in OK c ells. Incubation of quiescent cells with serum was associated with a signif icant decrease in steady-state NHE-RF mRNA and protein abundance in the cyt osolic and membrane fractions. incubation of cells with cAMP for 6 h was as sociated with no change in NHE-mRNA at 24 h. There was, however, a 46% incr ease in protein abundance in the cytosolic fraction of the cell and a 43% d ecrease in the membrane fraction. Despite the decrease in membrane-associat ed NHE-RF in quiescent cells treated with serum of cAMP, there were no diff erences in either the basal rate of Na/H exchange transport or the inhibito ry effect of the acute addition of cAMP on the transporter between experime ntal and control cells. These studies provide the first description of the regulation of NHE-RF. The results indicate that serum is associated with a decrease in NHE-RF mRNA and protein, while chronic exposure to cAMP is asso ciated with an altered distribution of NHE-RF between the cytosolic and mem brane fractions of OK cells.