Distinct processing of the pre-B cell receptor and the B cell receptor

Area of Science:

• Immunology
• Cell Biology
• Glycobiology

Background:

• B-cell receptor (BCR) μ heavy chains typically have complex oligosaccharides.
• Pre-BCR μ heavy chains uniquely possess high-mannose type oligosaccharides.
• High-mannose glycans are usually confined to the endoplasmic reticulum.

Purpose of the Study:

• Investigate the processing and cell surface expression of pre-BCR in pre-B cells.
• Determine the transport pathway and stability of pre-BCR complexes.
• Identify factors contributing to the low surface abundance of pre-BCR.

Main Methods:

• Analysis of oligosaccharide types on pre-BCR μ heavy chains.
• Assessment of pre-BCR transport using brefeldin A and monensin.
• Measurement of pre-BCR turnover rates and surface expression levels.
• Evaluation of surrogate light chain production.

Main Results:

• Pre-BCR μ heavy chains exhibit high-mannose, not complex, oligosaccharides.
• Pre-BCR utilizes a non-conventional, brefeldin A-sensitive, monensin-insensitive transport pathway.
• Pre-BCR is stably expressed at the plasma membrane with BCR-like turnover rates.
• Low pre-BCR surface expression is partly due to insufficient surrogate light chain production.

Conclusions:

• Pre-BCR glycosylation is distinct from BCR, featuring high-mannose structures.
• Pre-BCR transport to the cell surface is unconventional but stable.
• Surrogate light chain availability is a key limiting factor for pre-BCR surface expression.