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Curr Opin Immunol. 2008 Apr;20(2):192-6. doi: 10.1016/j.coi.2008.03.002. Epub 2008 Apr 9.

Thymoproteasome: probable role in generating positively selecting peptides.

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Laboratory of Protein Metabolism, Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo 113-0033, Japan.


The proteasome is the protein destroying machinery conserved in all eukaryotes and plays essential roles in various cellular processes. Apart from the conserved 'standard' proteasome, a special type of proteasome called 'immunoproteasome' exists in vertebrates for better presentation of antigenic peptides on MHC class I molecules. Recently, another vertebrate-specific proteasome was discovered in the thymus. This 'thymoproteasome' has a novel catalytic subunit 'beta5t' with unusual enzymatic activity and is expressed exclusively in cortical thymic epithelial cells (cTECs), which catalyze positive selection of developing thymocytes. beta5t-deficient mice exhibit severe impairment in CD8(+) T cell development. These findings suggest that cTECs are quite unique cells capable of presenting a unique set of self-peptides that are not seen in other cells and are required for positive selection of CD8(+) T cells.

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