Lag3-KIEELE domain plays a key role in Lag3-dependent Treg function 2267565

Abstract Introduction Lymphocyte activation gene 3 (Lag3) is a co-inhibitory receptor expressed on activated T cells and Foxp3+ regulatory T cells (Tregs). However, the mechanisms underlying its inhibitory function remain largely unclear. We previously demonstrated that Lag3 expression in Tregs constrains glycolytic activity by limiting Myc-PI3K-LDHA pathway activation, thereby supporting Treg-mediated suppression of autoimmune inflammation. Here, we report that the conserved intracellular KIEELE motif of the Lag3 is critical for its ability to regulate Treg suppressive function and metabolic programming. Methods We utilized a novel Treg-specific Lag3-KIEELE motif—deficient mouse model to test the importance of Lag3’s highly conserved KIEELE motif and Lag3 immunoprecipitation—mass spectrometry analysis to identify potential cytosolic proteins potentially mediating the Lag3 functions. Results We found that loss of this KIEELE motif specifically in Tregs significantly impairs their suppressive function and alters their metabolic profiles. Lag3-deficient Tregs displayed elevated glycolysis with Myc expression, phenotypes similar to Lag3-deficient Tregs. Lag3 IP-MS experiment further identified cytosolic proteins interacting with the KIEELE motif, suggesting potential mediators of Lag3 signaling. Conclusion Collectively, these findings provide the first mechanistic insight into how Lag3 modulates intracellular pathways to control both Treg suppressive activity and effector T cell responses. Funding Source NIAID Topic Categories Immune Response Regulation: Cellular Mechanisms (IRC)