Fig. 9: calpain2a inhibits TRAF6-mediated ubiquitination of IRF7 and IRF3.
From: The protease calpain2a limits innate immunity by targeting TRAF6 in teleost fish
a, b HEK293 cells were cotransfected with IRF3-Myc, TRAF6-HA and WT-ubiquitin-His or K63O-ubiquitin-His (in which only lysine 63 is kept) together with calpain2a-Flag, calpain2a-ΔCysPc-Flag or empty vector. After 24 h post-transfection, the cells were lysed and purified with Ni-NTA agarose. c, d HEK293 cells were cotransfected with IRF7-Myc, TRAF6-HA and WT-ubiquitin-His or K63O-ubiquitin-His (in which only lysine 63 is kept) together with calpain2a-Flag, calpain2a-ΔCysPc-Flag or empty vector. After 24 h post-transfection, the cells were lysed and purified with Ni-NTA agarose. All the immunoprecipitates and input with anti-Myc, anti-Flag, anti-HA, and anti-Tubulin Abs. All experiments were performed in at least three independent experiments. e Model detailing the roles of calpain2a in TRAF6-mediated signaling pathways. Upon LPS and virus, TRAF6 could be activated, homo-oligomerization and auto-ubiquitination. BECN1, ECSIT, IRF7 and IRF3 are ubiquitinated by TRAF6 and trigger the activation of downstream signals. calpain2a as a negative regulator targets TRAF6 to inhibit TRAF6-mediated signaling pathways.
