Calreticulin controls the rate of assembly of CD1d molecules in the endoplasmic reticulum

Area of Science:

• Immunology
• Molecular Biology
• Cell Biology

Background:

• CD1d is an MHC class I-like molecule presenting lipid antigens to NKT cells.
• CD1d heavy chain folding involves calreticulin (CRT), calnexin (CNX), and ERp57.
• Beta(2)-microglobulin (β(2)m) association is required for CD1d heterodimer formation.

Purpose of the Study:

• To investigate the role of CRT in CD1d folding, assembly, and cell surface expression.
• To determine the impact of CRT deficiency on CD1d antigen presentation and stability.
• To identify alternative chaperones involved in CD1d processing in the absence of CRT.

Main Methods:

• Analysis of CD1d heavy chain folding and assembly rates in CRT-deficient cells.
• Assessment of CD1d intracellular transport and cell surface expression levels.
• Investigation of CD1d association with ER chaperones like Grp94 and Bip.

Main Results:

• CRT deficiency accelerated CD1d heavy chain folding and heterodimer formation.
• Absence of CRT did not impair CD1d antigen presentation but increased stable cell surface CD1d.
• Grp94 and Bip chaperones associated with CD1d in CRT-deficient cells, potentially replacing CRT's function.
• Impaired ER retention of free CD1d heavy chains in CRT-deficient cells led to increased plasma membrane expression.
• β(2)m association was essential for CD1d resistance to lysosomal degradation.

Conclusions:

• CRT plays a significant role in regulating CD1d heavy chain folding and ER retention.
• Alternative chaperones can mediate CD1d folding in the absence of CRT.
• β(2)m association is critical for CD1d stability and cell surface longevity.