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Structural mutation affecting intracellular transport and cell surface expression of murine class II molecules
I J Griffith1, N Nabavi, Z Ghogawala
1Department of Cancer Biology, Harvard School of Public Health, Boston, Massachusetts 02115.
The Journal of Experimental Medicine
|February 1, 1988
Summary
Researchers identified mutations in the beta chains of I-A and I-E molecules in M12 B cell lines. These mutations prevent the proper cell surface expression of these important immune system components.
Area of Science:
- Immunology
- Molecular Biology
- Cell Biology
Background:
- MHC class II (Ia) molecules are crucial for T cell activation.
- B cell lymphomas like M12.4.1 provide a model for studying Ia expression.
- Ia variants lacking surface expression were selected for molecular analysis.
Purpose of the Study:
- To identify the molecular basis of Ia variants with absent surface expression.
- To understand the mechanisms regulating Ia molecule transport and cell surface presentation.
Main Methods:
- Selection of Ia-negative variants from M12.4.1 B cell lymphoma.
- Molecular analysis of selected cell lines (M12.A2 and M12.C3).
- DNA sequencing to identify mutations in Ia beta chain genes.
Main Results:
- Identical single-nucleotide transitions were found in the Ad beta and Ed beta genes.
- These mutations resulted in a Ser for Asn substitution at residue 82/83 in the beta 1 domain.
- Mutant Ia molecules accumulated in the cytoplasm, not reaching the cell surface.
Conclusions:
- A specific mutation in the Ia beta chain (Asn82/83Ser) disrupts proper protein transport.
- This mutation likely interferes with signals required for Ia molecule trafficking to the cell surface.
- Understanding these transport mechanisms is key for immune system regulation and potential therapeutic targets.