The ubiquitin ligase Itch limits mTORC1 nutrient sensing in B cells

PROJECT SUMMARY/ABSTRACT Severe immune dysregulation occurs in rare patients with loss-of-function mutations in the gene encoding the ubiquitin ligase Itch. 14 patients have been identified, presenting with chronic lung disease, various forms of organ-specific autoimmune diseases, and high levels of autoantibodies. One patient was successfully treated with a bone marrow transplant, showing that disease is caused by malfunctioning immune cells. Murine studies have enabled mechanistic dissection of Itch function in T cells, but these roles do not adequately explain why patients develop autoimmunity, particularly autoantibodies. Recent evidence shows that Itch directly restrains B cells to limit antibody production. In activated B cells, Itch prevents aberrantly high levels of the master metabolic regulator, mechanistic Target of Rapamycin Complex 1 (mTORC1) activity, a hallmark of lymphocytes in patients with more common autoimmune diseases such as lupus. Despite the evidence that Itch functions within B cells to restrain mTORC1 activity and antibody responses, where Itch functions within the mTORC1 activation pathway is unknown. These mechanisms are germane to understanding formation of autoimmunity in Itch deficient patients. The objective of this proposal is to determine how Itch limits aberrant mTORC1 activity in B cells. Our central hypothesis is that Itch regulates mTORC1 nutrient sensing to limit mitochondrial activity. Using primary mouse B cells and patient-derived lympoblastoid cell lines that are Itch-deficient or Itch-sufficient, we will 1) define the nutrient-sensing mTORC1 activation pathways regulated by Itch in B cells, and 2) determine how Itch inhibits purine nucleotide-mediated mTORC1 activity. This work will determine if Itch exerts regulatory control over mTORC1, providing a new target for the design of therapies that can treat rare patients with Itch mutations and those with mTORC1-associated autoimmune diseases.