MyD88 determines T cell fate through BCAP-PI3K signaling

Area of Science:

• Immunology
• Molecular Biology
• Cell Signaling

Background:

• Effector T cell life cycles are governed by T cell receptor (TCR) signals, dictating activation, inflammation, or apoptosis for inflammation resolution.
• Myeloid differentiation primary response 88 (MyD88) typically promotes inflammation in myeloid cells via toll-like receptors (TLRs), but its role in T cells is distinct, dampening TCR activation and survival.

Purpose of the Study:

• To elucidate the molecular mechanism by which MyD88 regulates T cell apoptosis following TCR activation and Fas ligation.
• To investigate the interaction between MyD88 and B cell activating protein (BCAP) in controlling T cell fate.

Main Methods:

• Investigated the interaction between MyD88 and BCAP in T cells after TCR engagement and Fas ligation.
• Utilized MyD88 knockout (MyD88-/-) T cells and BCAP knockdown to assess their impact on T cell activation, survival, and signaling.
• Examined the effect of lipopolysaccharide (LPS) activation of TLR4 on MyD88-BCAP association and T cell survival.

Main Results:

• TCR engagement upregulates both MyD88 and BCAP, promoting their interaction and limiting BCAP's availability for TCR-BCAP-PI3K-AKT signaling, thus reducing T cell activation and survival.
• MyD88-/- T cells exhibit enhanced activation markers, pro-inflammatory signals, and survival.
• Lipopolysaccharide (LPS) activation of TLR4 disrupts MyD88-BCAP association, restoring T cell survival in wild-type cells; BCAP knockdown eliminates the enhanced T cell phenotype in MyD88-/- cells.

Conclusions:

• MyD88 acts downstream of the TCR to regulate T cell apoptosis and fate through its association with BCAP.
• This interaction represents a novel molecular mechanism controlling T cell biology.
• Targeting the MyD88-BCAP interaction could offer therapeutic strategies for fine-tuning T cell effector function and survival.