SUMOylation: A new modulator in sarcomere organization

• Applicant: Dr. Arnab Nayak, Ph.D.
• Subject Area: Cell Biology ; Anatomy and Physiology ; Biochemistry
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 434371414

SUMOylation (addition of Small Ubiquitin-like Modifier) is a reversible posttranslational modification of proteins, crucial for diverse physiological functions. Studies from the yeast, fruit fly, and mammalian systems have revealed the evolutionary conserved SUMO pathway as a major regulator of various cellular processes, ranging from chromatin modifications, transcription, cell cycle, DNA repair, and ribosome biogenesis. The perturbation of the SUMO pathway is embryonic lethal, and thus, underlines the imperative nature of SUMO signaling in metazoan development. Due to its significance in fundamental biological processes, the SUMO pathway is being increasingly linked with various human diseases, including acute myeloid leukemia (AML) and cardiomyopathies.The SUMO pathway is essential for gene expression and modulates higher order protein assembly. The contractile unit of myofibrils in skeletal and cardiac muscle, i.e., the sarcomere, is an example of a highly organized protein ensemble. The sarcomere consists of contractile proteins organized in a defined assemblage of thick (myosin) and thin (actin) filaments, crucial for force generation during muscle contraction. Precise assembly and maintenance of sarcomeric structures is critical for proper functioning of muscle cells and cardiomyocytes. Disorganized sarcomere structure is a hallmark of myopathies, including skeletal- and cardio-myopathies, as well as cachexia (muscle wasting). These conditions lead to defective muscle function characterized by myofibrillar disarray as a result of either altered turnover of major sarcomeric proteins (such as myosin heavy chain) and or by improper assembly of the sarcomeric structure. Understanding of how the specialized, coherent sarcomeric structure is modulated and maintained could serve as an important step forward to gain knowledge of the altered muscle function in diseased conditions.A detailed understanding of the SUMO pathway concerning the regulation of sarcomere function is lacking. As the SUMO pathway is critical for gene expression and modulation of higher order protein assembly, we hypothesized that SUMOylation might regulate either or both the transcriptional status of genes for sarcomeric contractile proteins, and the higher-order structure of sarcomere assembly. The primary goal of this proposal is to understand the basic mechanisms that operate in maintenance of sarcomere assembly and turn-over of sarcomeric proteins. To address our objectives, we employ combination of various methodologies including CRISPR/Cas9 gene editing tools, quantitative mass spectrometry and gene expression analysis. By establishing the role of SUMOylation in contractile function of muscle, this proposal will enable us to gain insights into the relevance of the SUMO pathway in muscle disorder such as cachexia. For this purpose, we use amyotrophic lateral sclerosis (ALS)-induced mouse cachexia model to understand a direct role of SUMO pathway in cachexia.

• DFG Programme: Research Grants