Nucleoside Diphosphate Kinase-C Suppresses cAMP Formation in Human Heart Failure

Background: Chronic heart failure (HF) is associated with altered signal transduction via β-adrenoceptors and G proteins, and with reduced cAMP formation. Nucleoside diphosphate kinases (NDPKs) are enriched at the plasma membrane of end-stage HF patients, but the functional consequences of this are largely unknown, particularly for NDPK-C. Here, we investigated the potential role of NDPK-C in cardiac cAMP formation and contractility. Methods: Real-time PCR, (Far) Western blot, immunoprecipitation, and immunocytochemistry were used to study the expression, interaction with G proteins, and localization of NDPKs. cAMP levels were determined using immunoassays or fluorescent resonance energy transfer, and contractility was determined in cardiomyocytes (cell shortening) and in vivo (fractional shortening). Results: NDPK-C was essential for the formation of a NDPK-B/G proteins complex. Protein and mRNA levels of NDPK-C were up-regulated in end-stage human HF, in rats following chronic isoprenaline (ISO) stimulation through osmotic minipumps, and after incubation of rat neonatal cardiomyocytes with ISO. ISO also promoted translocation of NDPK-C to the plasma membrane. Overexpression of NDPK-C in cardiomyocytes increased cAMP levels and sensitized cardiomyocytes to ISO-induced augmentation of contractility, whereas NDPK-C knockdown decreased cAMP levels. In vivo, depletion of NDPK-C in zebrafish embryos caused cardiac edema and ventricular dysfunction. NDPK-B knockout mice had unaltered NDPK-C expression, but showed contractile dysfunction and exacerbated cardiac remodeling during chronic ISO stimulation. In human end-stage HF, the complex formation between NDPK-C and Gαi2 was increased, whereas NDPK-C/Gαs interaction was decreased, producing a switch that may contribute to an NDPK-C-dependent cAMP-reduction in HF. Conclusions: Our findings identify NDPK-C as an essential requirement for both the interaction between NDPK isoforms and with G proteins. NDPK-C is a novel critical regulator of β-adrenoceptor/cAMP signaling and cardiac contractility. By switching from Gαs to Gαi2 activation, NDPK-C may contribute to lower cAMP levels and the related contractile dysfunction in HF.