Proximity-Based Labeling Identifies MHC Class II and CD37 as B Cell Receptor-Proximal Proteins with Immunological...

Area of Science:

• Immunology
• Cell Biology
• Molecular Biology

Background:

• The B cell receptor (BCR) is crucial for B cell activation, antigen processing, and presentation to T cells.
• BCR signaling and endocytosis are primarily driven by cytoplasmic tail motifs, but modulated by other cellular elements like CD20 and lipid microdomains.

Purpose of the Study:

• To identify novel proteins that interact with and modulate the function of the murine IgM B cell receptor (BCR).

Main Methods:

• Employed proximity-based biotinylation coupled with mass spectrometry to identify molecular neighbors of the BCR.
• Utilized CRISPR-based knockout of CD37 in a B cell line to assess its functional impact on BCR signaling and endocytosis.

Main Results:

• Identified MHC class II molecules, integrins, transporters, and membrane microdomain proteins as BCR neighbors.
• Discovered CD37, a tetraspanin protein, as a BCR neighbor, with its absence leading to heightened BCR signaling and slower endocytosis.
• Observed that CD37 knockout tempered the formation of peptide-class II complexes.

Conclusions:

• BCR molecular neighbors significantly influence membrane-mediated BCR functions.
• The tetraspanin CD37 is a novel modulator of BCR signaling, endocytosis, and antigen processing complex formation.
• Proximity-based labeling is an effective technique for discovering previously unknown BCR-interacting proteins.