Abstract 390: Dysregulation of ATF2 in Dilated Cardiomyopathy Caused by FBXO32 Mutation

Background: Dilated cardiomyopathy (DCM) is a common form of cardiomyopathy causing systolic dysfunction and heart failure. Rare variants in more than 30 genes mostly encoding sarcomeric proteins and proteins of the extracellular matrix have been implicated in familial DCM to date. We recently identified a novel mutation (Gly243Arg) in FBXO32 causing familial DCM through abnormal SKP1/CUL/F-BOX (SCF) complex formation and defects in proteins regulating the autophagy/lysosome machinery (Al-Yacoub, Genome Biology, 2016). Objective: To explore in more details the mechanisms by which the defective SCF FBXO32 complex leads to the development of DCM. Methodology: Using a PCR-based microarray, we screened for mRNAs significantly dysregulated in the heart of the patient carrying the FBXO32 mutation compared to control and idiopathic human hearts. Subsequently, we validated dysregulation of a candidate gene using immunoblot analysis and tested the effect of the mutant or wild-type FBXO32 on the novel candidate identified in primary neonatal rat cardiomyocytes. Results: We found a robust up-regulation in mRNA expression of the Activating transcription Factor 2 (ATF2), a member of the leucine zipper family of DNA binding proteins, which plays a critical role in cardiac development. ATF2 protein level was also strongly increased in the heart with the FBXO32 mutation compared to control hearts and to hearts of idiopathic origin. Expression of the mutant FBXO32 protein in primary cardiomyocytes enhanced ATF2 protein expression compared to cells expressing the wild-type FBXO32 protein. Since FBXO32 is member of the SCF complex and has ubiquitin ligase activity, experiments are now investigating whether FBXO32 directly regulates ATF2 protein stability and the role of ATF2 in autophagy flux regulation in dilated cardiomyopathy. Conclusion: Our results indicate that abnormal SCF activity due to the FBXO32 mutation stabilizes the AFT2 transcription factor and suggest a new mechanism by aberrant SCF activity causes DCM in human.