Regulation of Na,K-ATPase Transport Activity by Protein Kinase C |
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Authors: | CH Pedemonte TA Pressley MF Lokhandwala AR Cinelli |
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Institution: | (1) College of Pharmacy, University of Houston, Houston, TX 77204-5515, USA, US;(2) Dept. of Physiology, Texas Tech University, Health Sciences Center, Lubbock, TX 79430, USA, US;(3) Dept. of Anatomy and Cell Biology, SUNY at Brooklyn, NY 11203, USA, US |
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Abstract: | 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 α-subunit are phosphorylated by protein kinase C (PKC) without apparent effect of this phosphorylation on Na+,K+-ATPase activity. To determine whether the α-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 α-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 α-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 α1 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 α1 cDNA. In contrast, these effects were not observed in cells expressing
the NH2-deletion mutant of the α-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 α-subunit NH2-terminus participate in the regulation of the Na+,K+-ATPase activity by PKC.
Received: 10 July 1996/Revised: 19 September 1996 |
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Keywords: | : Na+ K+-ATPase — Na+-pump — Na+-transport |
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