Functional analysis of the fiber type-specific gene regulation in skeletal muscle: Modulation of NFAT function by post-translational modifications

点击翻译按钮获取中文摘要

One of the major characteristics of the skeletal muscle is its plasticity. Muscle fibers can be altered in response to physiological demands e.g. endurance activity, but also inactivity, age-dependent atrophy or muscle dystrophies. This involves the alteration of concerted gene programs resulting in the different contractile and metabolic features of fibre types. The slow and fast isoforms of the motor protein myosin heavy chain (MyHC) are a main characteristic of each fiber type. A shift from fast to slow fibers (fast-to-slow transformation) is mediated by the calcineurin/NFATc (nuclear factor of activated T cells)-signaling pathway and can be induced in cultured cells by addition of Ca2+-Ionophore. This renewal proposal investigates an additional regulatory pathway of proteins 1-4, including the C-terminal variants of c1, downstream of calcineurin by post-translational modifications (PTMs) and focus on the fine-tuning of NFATc signaling by acetylation or SUMOylation of proteins in skeletal muscle. In other cell models, e.g. immune response of T-cells, a modification by acetylation or SUMOylation of transcription factors can induce or repress transcriptional activation of their target genes depending on the promoter context. Here, a possible regulatory mechanism by acetylation or SUMOylation of proteins leading to the activation of the slow and inhibition of the fast fiber type gene program in slow fibers will be investigated. This includes the identification of functional acetylation/SUMOylation acceptor sites in the proteins 1-4 and c1 Isoforms and the investigation of a modification in a promoter-dependant manner. Preliminary data indicate a correlation of gene activation and repression by acetylated and SUMOylated NFATc, respectively. Furthermore, we will search for binding sites adjacent to NFATc response elements and for transcriptional cofactors. The initial experiments in cell culture will be completed by the analysis of a fast-to-slow transformation in a human model system.The objectives are a better understanding of the highly efficient regulatory mechanisms in skeletal muscle fibers with their alternating activation and inhibition of fiber type-specific gene programs. Additional regulatory mechanisms of proteins could further elucidate fiber type-specific gene regulations with clinical implications, in respect to e.g. neuromuscular diseases. In addition, it might also have a broader impact on the regulation of NFATc signaling pathway in the cross-striated cardiac muscle.