Murata Shigeo, Takahama Yousuke, Tanaka Keiji
Laboratory of Protein Metabolism, Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo 113-0033, Japan.
Curr Opin Immunol. 2008 Apr;20(2):192-6. doi: 10.1016/j.coi.2008.03.002. Epub 2008 Apr 9.
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.
蛋白酶体是所有真核生物中保守的蛋白质破坏机制，在各种细胞过程中发挥着重要作用。除了保守的“标准”蛋白酶体之外，脊椎动物中还存在一种特殊类型的蛋白酶体，称为“免疫蛋白酶体”，用于更好地在MHC I类分子上呈递抗原肽。最近，在胸腺中发现了另一种脊椎动物特有的蛋白酶体。这种“胸腺蛋白酶体”具有一种新型催化亚基“β5t”，具有不寻常的酶活性，并且仅在皮质胸腺上皮细胞（cTEC）中表达，后者催化发育中的胸腺细胞的阳性选择。β5t缺陷小鼠在CD8(+) T细胞发育中表现出严重受损。这些发现表明，cTEC是相当独特的细胞，能够呈递一组在其他细胞中未见的独特自身肽，这些肽是CD8(+) T细胞阳性选择所必需的。
