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Abstract 304: Crystal Structure Of Fak/mef2 Complex Reveals The Role Of Fak In The Regulation Of Mef2 Transcription Factor.

Members of MEF2 (Myocyte Enhancer Factor 2) family of transcription factors are major regulators of cardiac development and homeostasis. Their functions are regulated at several levels, including the association with a variety of protein partners. We have previously shown that FAK (Focal Adhesion Kinase) regulates the stretch-induced activation of MEF2 in cardiomyocytes. But, the molecular mechanisms, involved in this process, are unclear. Here, we integrated biochemical, imaging and structural analyses to characterize a novel interaction between MEF2 and FAK. An association between MEF2 and FAK was detected by co-immunoprecipitation in the extracts of stretched cardiomyocytes (10%, 60Hz, 2 hours). MEF2 and FAK staining were co-localized in the nuclei of stretched cells. Pull down assays indicated that the Focal Adhesion Targeting (FAT) domain is sufficient to confer FAK interaction with MEF2. Gene reporter assays indicated that the interaction with FAK enhances the MEF2C transcriptional activity in cultured cardiomyocytes. Also, we present a 2.9-A X-ray crystal structure for the FAK_FAT domain bound to MEF2C (1-95), comprised by the MADS box/MEF2 domain. The structural information, when used in combination with biochemical studies, small-angle X-ray scattering (SAXS) data and reporter gene assay, lead to a mechanistic model describing how FAK binds to MEF2C and stimulates its transcription function in cardiomyocytes. We further validated this model by showing that the binding of FAK to MEF2C is essential for the hypertrophy of cardiomyocyte in response to mechanical stress. Our results present FAK as a new positive regulator of MEF2, implicated in the fine control of the signal transduction between focal adhesions and the nucleus of cardiac myocytes during mechanical stress.