Regulation of Na,K-ATPase transport activity by protein kinase C.
Considerable evidence indicates that the renal Na+,K+-ATPase is regulated through phosphorylation/dephosphorylation reactions by kinases and phosphatases stimulated by hormones and second messengers. Recently, it has been reported that amino acids close to the NH2-terminal end of the Na+,K+-ATPase alpha-subunit are phosphorylated by protein kinase C (PKC) without apparent effect of this phosphorylation on Na+,K+-ATPase activity. To determine whether the alpha-subunit NH2-terminus is involved in the regulation of Na+, K+-ATPase activity by PKC, we have expressed the wild-type rodent Na+,K+-ATPase alpha-subunit and a mutant of this protein that lacks the first thirty-one amino acids at the NH2-terminal end in opossum kidney (OK) cells. Transfected cells expressed the ouabain-resistant phenotype characteristic of rodent kidney cells. The presence of the alpha-subunit NH2-terminal segment was not necessary to express the maximal Na+,K+-ATPase activity in cell membranes, and the sensitivity to ouabain and level of ouabain-sensitive Rb+-transport in intact cells were the same in cells transfected with the wild-type rodent alpha1 and the NH2-deletion mutant cDNAs. Activation of PKC by phorbol 12-myristate 13-acetate increased the Na+,K+-ATPase mediated Rb+-uptake and reduced the intracellular Na+ concentration of cells transfected with wild-type alpha1 cDNA. In contrast, these effects were not observed in cells expressing the NH2-deletion mutant of the alpha-subunit. Treatment with phorbol ester appears to affect specifically the Na+,K+-ATPase activity and no evidence was observed that other proteins involved in Na+-transport were affected. These results indicate that amino acid(s) located at the alpha-subunit NH2-terminus participate in the regulation of the Na+,K+-ATPase activity by PKC.
Pedemonte
C H
CH
College of Pharmacy, University of Houston, Houston, TX 77204-5515, USA.
Pressley
T A
TA
Lokhandwala
M F
MF
Cinelli
A R
AR
D000818:Animals; D001692:Biological Transport; D002478:Cells, Cultured; D018076:DNA, Complementary / Q000096:biosynthesis; D004847:Epithelial Cells; D004848:Epithelium / Q000201:enzymology; D007668:Kidney / Q000201:enzymology*; D011493:Protein Kinase C / Q000378:metabolism*; D012377:Rodentia; D017384:Sequence Deletion; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
D018076:DNA, Complementary; D011493:Protein Kinase C; D000254:Sodium-Potassium-Exchanging ATPase