Abstract 18472: SUMO2 is a Novel Regulator of Calcineurin/NFAT Signaling and Cardiomyocyte Hypertrophy
Background: The calcineurin (Cn)/NFAT axis is a pivotal pathway in cardiomyocyte signaling in general and in the pathogenesis of cardiac hypertrophy and remodeling in particular.
Methods & Results: The objective of this study was to systematically identify yet unknown modulators of the Cn/NFAT pathway. We thus screened a human cardiac cDNA-library (107 primary clones) using an NFAT-dependent luciferase (luc) reporter assay in C2C12 cells. Through several rounds of confirmation we identified SUMO2 as a novel strong activator of Cn/NFAT signaling. Moreover, we found SUMO2 to be a direct interaction partner of a nuclear calcineurin A pool. Further experiments in C2C12 cells indicated that SUMO2 mediates NFAT activation through Cn as shown by exaggerated NFAT activation even in the presence of constitutively active CnA (NFAT-luc: ΔCnA; 3.85-fold, p<0.001). Likewise, wild-type Cn was “super”-activated in the presence of SUMO2 through addition of Ionomycin/PMA (NFAT-luc: 2.5-fold, p<0.001). In contrast, siRNA-mediated SUMO2 knockdown reduced NFAT activation via Cn (NFAT-luc: 20% reduction, p<0.05). Similar results, that is activation or inhibition of Cn-mediated NFAT signaling were obtained upon SUMO2 overexpression and knockdown in neonatal rat ventricular cardiomyocytes (NRVCM), respectively. We next studied the phenotypic and molecular effects of SUMO2 in NRVCM. As predicted, SUMO2 induced NRVCM hypertrophy, which was further exaggerated in the presence of ΔCnA (Cell size: SUMO2: 120%; ΔCnA: 115%; SUMO2+ ΔCnA: 128%, n>1000 cells; all p<0.001). Conversely, SUMO2 induced hypertrophy was abrogated in the presence of CnA inhibitors.
Finally we studied the effect of a sumoylation-deficient mutant of SUMO2 (SUMO2ΔGG). Surprisingly, induction of Cn/NFAT and NRVCM hypertrophy was comparable to sumoylation-competent SUMO2 (ΔCnA+SUMO2ΔGG: 1.7-fold NFAT-luc, p<0.01; Cell size: 125%, p<0.001), consistent with a sumoylation independent mechanism for activation of Cn/NFAT.
Conclusions: In conclusion, we identified SUMO2 as a novel positive regulator of Cn/NFAT signaling and cardiomyocyte hypertrophy. Interestingly, these effects are independent of sumoylation, but rather mediated by retaining/tethering activated CnA in the nucleus.
Author Disclosures: A. Bernt: None. A.Y. Rangrez: None. C. Rohr: None. S. Katz: None. D. Frank: None. N. Frey: None.
- © 2014 by American Heart Association, Inc.