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The cytoplasmic tail of CD4 targets chimeric molecules to a degradative pathway
J W Baenziger1, A Okamoto, E Hall
1Howard Hughes Medical Institute, Department of Medicine, University of California, San Francisco 94143.
Abstract:
Many different cell surface receptors undergo endocytosis via coated pits. Once having entered the cell, the receptors are sorted into diverse pathways. Which path a given receptor will follow is determined by signals inherent in the receptor's structure. The nature of these structural features is not yet known. In this study, we have taken the approach of constructing chimeric molecules to localize the domain of the T-cell surface molecule CD4 which is responsible for targeting it for degradation. Chimeric molecules bearing the cytoplasmic domain of CD4 and the extracellular domain of either the low-density lipoprotein receptor or a major histocompatibility complex (MHC) class I molecule were both internalized in response to phorbol 12-myristate 13-acetate and were subsequently degraded, indicating that the cytoplasmic tail of CD4 contains all the information required for both processes. The ability to modulate the level of MHC class I molecules on the cell surface offers an approach to investigating quantitative aspects of antigen presentation, the initial possibilities of which are explored herein.
Insights
The cytoplasmic tail of the T-cell molecule CD4 directs its internalization and degradation. This finding reveals key structural signals for receptor sorting and degradation pathways.
Area of Science:
- Cell biology
- Immunology
- Molecular biology
Background:
- Cell surface receptors are internalized via endocytosis through coated pits.
- Receptor sorting into intracellular pathways depends on structural signals, which remain largely unknown.
- Understanding these signals is crucial for modulating cellular processes.
Purpose of the Study:
- To identify the specific domain of the T-cell surface molecule CD4 responsible for targeting it for degradation.
- To investigate the role of CD4's cytoplasmic domain in receptor internalization and degradation pathways.
Main Methods:
- Construction of chimeric molecules by combining the cytoplasmic domain of CD4 with extracellular domains of other receptors (low-density lipoprotein receptor, MHC class I).
- Internalization and degradation assays using phorbol 12-myristate 13-acetate stimulation.
- Analysis of receptor trafficking and degradation pathways.
Main Results:
- Chimeric molecules containing the CD4 cytoplasmic domain were internalized and subsequently degraded.
- These results indicate that the cytoplasmic tail of CD4 possesses the necessary information for both internalization and degradation.
- The study provides insights into the structural basis of receptor sorting.
Conclusions:
- The cytoplasmic tail of CD4 contains all essential information for its targeting to degradation pathways.
- This finding has implications for understanding receptor trafficking and potentially modulating antigen presentation via MHC class I molecules.