Modulation of Na+-Ca2+ Exchanger Expression by Immunosuppressive Drugs Is Isoform-Specific

Department of Biochemistry, Hebrew University-Hadassah Medical School, P.O. Box 12272, Jerusalem 91120, Israel. .
Molecular pharmacology (Impact Factor: 4.13). 05/2008; 73(4):1254-63. DOI: 10.1124/mol.107.041582
Source: PubMed


The Na(+)-Ca(2+) exchanger (NCX) is a major Ca(2+)-regulating protein encoded by three genes: NCX1, NCX2, and NCX3. They share a sequence homology of approximately 65%. NCX1 protein is expressed ubiquitously, and NCX2 and NCX3 are expressed almost exclusively in the brain. We have shown previously (Kimchi-Sarfaty et al., 2002) that treatment of NCX1-transfected human embryonic kidney (HEK) 293 cells with the immunosuppressive cyclosporin A (CsA) and its nonimmunosuppressive analog PSC833 (valspodar) results in down-regulation of surface expression and transport activity of the protein without a decrease in expression of cell NCX1 protein. In this study, we show that cyclosporin A and PSC833 treatment of NCX2- and NCX3-transfected HEK 293 cells also resulted in dose-dependent down-regulation of surface expression and transport activity of the two brain NCX proteins; however, whereas CsA had no effect on total cell NCX protein expression, PSC833 reduced mRNA and cell protein expression of NCX2 and NCX3. Moreover, tacrolimus (FK506), which had no effect on NCX1 protein expression, down-regulated NCX2 and NCX3 surface expression and transport activity without any significant effect on cell protein expression. Sirolimus (rapamycin) had no effect on NCX2 and NCX3 protein expression, yet it reduced NCX2 and NCX3 transport activity. Because all of the experimental conditions in our studies were identical, presumably the different drug response is related to structural differences between NCX isoforms. Clinical studies suggested that immunosuppressive regimes of patients who have received transplants resulted in complications related to Ca(2+). Expression of NCX genes is tissue-specific. Hence, our results can potentially provide a tool for choosing the immunosuppressive protocol to be used.

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    ABSTRACT: The Na(+)-Ca(2+) exchanger (NCX) is a major Ca(2+) regulating protein. It is almost ubiquitously expressed. Cyclophilins (Cyps) make up a class of proteins that are involved in protein folding via their peptidyl prolyl cis-trans isomerase (PPIase) and chaperone domains. They are also the cellular receptors of cyclosporin A (CsA). Binding of CsA to cyclophilins inhibits both PPIase and chaperone activities. We have shown that treatment of transfected HEK 293 cells expressing the Na(+)-Ca(2+) exchanger NCX1 with CsA results in downregulation of surface expression and transport activity, without any reduction in the total level of cell NCX1 protein [Kimchi-Sarfaty, C., et al. (2002) J. Biol. Chem. 277 (4), 2505-2510]. In this work, we show that knockdown of cell CypA using targeting siRNA (without any CsA treatment) results in a reduction in the level of NCX1 surface expression, a decrease in the level of Na(+)-dependent Ca(2+) uptake, and no change in the total amount of cell NCX1 protein in NCX1.5-transfected HEK 293 cells and nontransfected H9c2 cells that express NCX1.1 naturally. It also reduced Na(+)-dependent Ca(2+) fluxes measured by changes in Fluo-4 AM fluorescence in single NCX1.5-transfected HEK 293 and single H9c2 cells. Knockdown of CypB had no significant effect on either transport activity, surface expression, NCX1 cell protein expression, or Ca(2+) fluxes. Overexpression of CypA or its R55A mutant, which exhibits a substantially reduced PPIase activity, alleviated the reduction of NCX1 surface expression caused by CsA treatment, suggesting that the PPIase domain was probably not mandatory for NCX1 functional expression. We suggest that CypA plays a role in the functional expression of NCX1 protein.
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    Preview · Article · Mar 2011 · Journal of Biological Chemistry
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