Mechanistic impact of oligomer poisoning by dominant-negative CARD11 variants

Area of Science:

• Immunology
• Molecular Cell Biology

Background:

• CARD11 is a crucial scaffold protein regulating antigen receptor signaling pathways.
• Germline CARD11 mutations lead to Primary Immunodeficiency (PID) through various mechanisms, including loss-of-function (LOF) and gain-of-function (GOF).
• Three distinct PID classes arise from CARD11 mutations: CARD11 deficiency (homozygous LOF), BENTA disease (heterozygous GOF), and CADINS (heterozygous dominant-negative LOF).

Purpose of the Study:

• To investigate the mechanistic basis of dominant-negative effects in heterozygous LOF CARD11 mutants.
• To identify specific steps in the CARD11 signaling pathway affected by dominant-negative variants.
• To elucidate how varying dominant-negative activities of CARD11 mutants influence disease inheritance patterns.

Main Methods:

• Characterization of CARD11 loss-of-function mutants with diverse dominant-negative activities.
• Analysis of CARD11 oligomerization and signaling in mixed wild-type:mutant complexes.
• Identification of critical steps in the CARD11 signaling cycle impacted by mutant variants.

Main Results:

• Strong dominant-negative CARD11 mutants were found to inhibit signaling from mixed wild-type:mutant oligomers.
• These mutants interfere with at least two key steps: the Opening Step and the Cofactor Association Step.
• Evidence suggests cooperative function of CARD11 oligomer subunits in multiple signaling stages.

Conclusions:

• CARD11 oligomer subunits cooperate during antigen receptor signaling at multiple steps.
• The degree of dominant-negative activity in LOF CARD11 mutants dictates their impact on signaling.
• Understanding these mechanisms explains how different heterozygous LOF mutations in CARD11 lead to distinct disease phenotypes and inheritance patterns.