Sodium/Calcium Exchanger (NCX1) Macromolecular Complex

The sodium-calcium exchanger, NCX1, is a ubiquitously expressed membrane protein essential in calcium homeostasis for many cells including those in mammalian heart and brain. The function of NCX1 depends on subcellular (“local”) factors, the phosphorylation state of NCX1, and the subcellular locatio...

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Bibliographic Details
Published in:The Journal of biological chemistry 2003-08, Vol.278 (31), p.28849-28855
Main Authors: Schulze, Dan H., Muqhal, Muqeem, Lederer, W.Jon, Ruknudin, Abdul M.
Format: Article
Language:English
Subjects:
Animals
Cyclic AMP-Dependent Protein Kinases - analysis
Cyclic AMP-Dependent Protein Kinases - metabolism
Immunohistochemistry
Immunosorbent Techniques
Macromolecular Substances
Membrane Proteins - analysis
Membrane Proteins - metabolism
Myocardium - chemistry
Myocardium - enzymology
Phosphoric Monoester Hydrolases - metabolism
Phosphorylation
Protein Kinase C - metabolism
Rats
Rats, Inbred F344
Sodium-Calcium Exchanger - analysis
Sodium-Calcium Exchanger - chemistry
Sodium-Calcium Exchanger - metabolism
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Summary:The sodium-calcium exchanger, NCX1, is a ubiquitously expressed membrane protein essential in calcium homeostasis for many cells including those in mammalian heart and brain. The function of NCX1 depends on subcellular (“local”) factors, the phosphorylation state of NCX1, and the subcellular location of NCX1 within the cell. Here we investigate the molecular organization of NCX1 within the cardiac myocyte. We show that NCX1 is dynamically phosphorylated by protein kinase A (PKA)-dependent phosphorylation in vitro. We also provide evidence that the regulation of this phosphorylation is attributed to the existence of an NCX1 macromolecular complex. Specifically, we show that the macromolecular complex includes both the catalytic and regulatory subunits of PKA. However, only the RI regulatory subunit is found in this macromolecular complex, not RII. Other critical regulatory enzymes are also associated with NCX1, including protein kinase C (PKC) and two serine/threonine protein phosphatases, PP1 and PP2A. Importantly, the protein kinase A-anchoring protein, mAKAP, is found and its presence in the macromolecular complex suggests that these regulatory enzymes are coordinately positioned to regulate NCX1 as has been found in diverse cells for a number of channel proteins. Dual immunocytochemical staining showed the colocalization of NCX1 protein with mAKAP and PKA-RI proteins in cardiomyocytes. Finally, leucine/isoleucine zipper motifs have been identified as possible sites of interaction. Our finding of an NCX1 macromolecular complex in heart suggests how NCX1 regulation is achieved in heart and other cells. The existence of the NCX1 macromolecular complex may also provide an explanation for recent controversial findings.
ISSN:0021-9258
1083-351X
DOI:10.1074/jbc.M300754200