Abstract 306: Targeting of Cdc42-Interacting Protein 4 - Calcineurin Aβ Complexes Ameliorates Pressure Overload-induced Cardiac Remodeling

Abstract

Pathological cardiac remodeling is the primary mechanism underlying the development of heart failure. The Ca 2+ /calmodulin-dependent protein phosphatase calcineurin is a key regulator of pathological myocyte hypertrophy. Previously, it was shown that the β-isoform of the calcineurin catalytic A-subunit (CaNAβ) was uniquely required for hypertrophy. In order to determine the mechanism of CaN A-subunit specificity, we performed a yeast two-hybrid screen using the CaNAβ-specific N-terminal polyproline domain. We now show that a new binding partner for CaNAβ is the F-Bar (Fes-CIP4 homology [ F CH] - B in/ A mphyphysin/ R vs) scaffold protein Cdc42-interacting protein 4 (CIP4/TRIP10). The CaNAβ polyproline domains binds the SH3 domain of CIP4. Using a new CIP4 conditional knock-out mouse, we show that CIP4 contributes to the hypertrophy induced in vivo by pressure overload. After induction of conditional gene deletion using tamoxifen, CIP4 fl/fl ;Tg(Myh6-cre/Esr1*) mice exhibited decreased hypertrophy and improved cardiac function over a period of 16 weeks following transverse aortic constriction survival surgery when compared to control tamoxifen-treated Tg(Myh6-cre/Esr1*) and CIP4 fl/fl mice. In order to show the relevance of CaNAβ-CIP4 binding, we also developed an adeno-associated virus (AAV) gene therapy vector that expresses a CaNAβ polyproline domain - GFP fusion protein under the control of the cardiac myocyte-specific troponin T promoter. Disruption of CIP4-CaNAβ binding in vivo by the AAV vector attenuates cardiac hypertrophy following two weeks of pressure overload and improved systolic function. Together these results both demonstrate the role of a F-Bar scaffold protein in cardiac remodeling and reveal a novel mechanism for specificity in calcineurin signaling. Identification of this new signaling pathway also suggests a new therapeutic approach to heart failure with reduced ejection fraction.