Role of GRAIL in B cell tolerance and B-cell mediated inflammation

PROJECT SUMMARY/ABSTRACT B cells are the master regulators of humoral immune responses, and many autoimmune diseases arise due to the breakdown of self-tolerance in B cells. Understanding the signaling and genetic control of B cell tolerance will lead to the development of new tools for the early detection and treatment of B cell mediated autoimmunity. There is increased evidence on the potential contribution of the E3 ubiquitin ligase gene related to anergy in lymphocyte (GRAIL) in B cell mediated autoimmune diseases; however, to date, GRAIL expression in B cells and its role in B cell mediated immunity and inflammation remains undefined. Our data provides the first evidence of GRAIL expression in both mouse and human B cells, with higher expression particularly in anergic B cells, suggesting that GRAIL may contribute to establishment of B cell tolerance. In fact, GRAIL deficient B cells were hyper-responsive in terms of proliferation upon antigenic stimulation. In addition, aged GRAIL B cell conditional knockout (BcKO) mice developed lupus-like symptoms characterized by high titers of anti-double stranded DNA in the sera, accumulation of T follicular helper and B cells in the lymphoid tissues and spontaneous germinal center formation. Moreover, GRAIL BcKO mice are more susceptible to autoimmune diseases such as lupus and rheumatoid arthritis (RA). Importantly, we detected significantly reduced GRAIL expression in B cells from patients with RA, lupus, and immune checkpoint inhibitor (ICI)-induced arthritis compared to healthy donors, further indicating that GRAIL down-regulation could serve as a marker for onset of B cell mediated autoimmunity. Based on these findings, we hypothesize that regulation of B cell activation and tolerance by GRAIL may be an important checkpoint in censoring and elimination of autoreactive B cells; thus, GRAIL function is crucial to control the onset and development of B-cell mediated autoimmunity. Here in Aim 1, we propose to determine the molecular mechanisms responsible for regulation and function of GRAIL in B cell tolerance by utilizing conditional gene knockdown approaches and in vivo B cell tolerance models. We will identify the exact target(s) of GRAIL, which will determine its function in B cell activation and tolerance. In Aim 2, we will determine the role of GRAIL in antibody-dependent and - independent functions of B cells. The physiological significance of this finding will be assessed in a novel ICI- arthritis model. By utilizing B cell specific GRAIL targeting approach, we will assess whether GRAIL functions in B cells to control ICI-arthritis at the onset and/or progressive stages. In addition, cellular, global transcriptomic, and genome-wide analysis of biospecimens from cancer patients with ICI-arthritis will help to unmask B cell specific role of GRAIL in immune-related adverse event pathogenesis. The proposed research will provide new significant insight into mechanisms underlying B cell tolerance that will lead to development of pharmacological approaches in controlling B cell mediated autoimmunity.