MYSM1-dependent DNA damage responses in early B cell development

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PROJECT SUMMARY Inborn errors of immunity provide unique opportunities to investigate the role of identified genes in the development and function of the immune system. Investigation of these immune disorders has provided important insights into human immunity and has established fundamental principles of basic and clinical immunology. In this regard, germline variants in MYSM1 have recently been identified in patients with primary immune deficiency characterized by low T cells, near complete absence of B cells, hypogammaglobulinemia, and increased sensitivity to genotoxic agents. The role of MYSM1 in immune development and in cellular response to DNA damage remain a critical knowledge gap. Deficiency of MYSM1 results in increased DNA damage signals, particularly in B cells, in the absence of exposure to DNA damaging agents. During early development, B cells (and T cells) generate DNA breaks to assembly the genes that encode their antibody receptors. These DNA breaks are essential for creating the diversity of the immune system to recognize various pathogens. In preliminary experiments, we find that, in response to these programmed DNA breaks, loss of MYSM1 results in persistent DNA damage signaling, including activation of cell death programs, which impairs B cell maturation. Our goal is to determine the mechanism of MYSM1 in regulation of cellular responses to DNA damage and in coordination of B cell development. We propose that MYSM1 functions to terminate DNA damage responses after DNA break repair and that this activity is critical for suppressing cell death pathways to promote continued B cell development. We will define the role of MYSM1 in DNA damage signaling in early B cells and will determine the mechanisms that regulate MYSM1 activity. Understanding the signals that direct DNA damage programs in immune cells is essential for elucidating mechanisms of primary immune deficiency and for optimizing treatment approaches. These studies will establish a new paradigm for inactivating DNA damage responses and will reveal new opportunities to improve clinical management of patients with MYSM1 deficiency as well as patients with abnormalities in other DNA damage pathways.