Grant E P, Michalek M T, Goldberg A L, Rock K L
Department of Pathology, Harvard Medical School, Boston, MA 02115, USA.
J Immunol. 1995 Oct 15;155(8):3750-8.
The effect on MHC class I Ag presentation of enhancing a protein's rate of degradation by the ubiquitin-proteasome pathway was investigated. In extracts of mouse B-lymphoblasts and reticulocytes, as in rabbit reticulocytes, proteins with acidic or basic N-termini are conjugated to ubiquitin and degraded by the 26S proteasome very rapidly. We found that the rate of MHC class I presentation of microinjected beta-galactosidase was enhanced when this antigenic protein was modified with such a destabilizing amino-terminal residue. This enhanced presentation was inhibited by blocking potential ubiquitination sites on the protein through methylation of amino groups and by peptide aldehyde inhibitors of the proteasome. Furthermore, in B lymphoblast cell extracts, the rapid degradation of these beta-galactosidase constructs required ATP and ubiquitin and was blocked by inhibitors of proteasomes. Their rates of degradation in extracts correlated with their rates of class I Ag presentation in vivo. These results indicate that ubiquitin conjugation is a key rate-limiting step in Ag presentation and provide further evidence for a critical role of ubiquitin and the 26S proteasome in generating MHC class I-presented peptides.
研究了通过泛素 - 蛋白酶体途径提高蛋白质降解速率对MHC I类抗原呈递的影响。在小鼠B淋巴细胞和成红细胞提取物中，如同在兔网织红细胞中一样，具有酸性或碱性N末端的蛋白质会与泛素结合，并被26S蛋白酶体非常迅速地降解。我们发现，当这种抗原性蛋白质用这种不稳定的氨基末端残基修饰时，显微注射的β - 半乳糖苷酶的MHC I类呈递速率会提高。通过对氨基进行甲基化来阻断蛋白质上潜在的泛素化位点以及使用蛋白酶体的肽醛抑制剂可抑制这种增强的呈递。此外，在B淋巴细胞提取物中，这些β - 半乳糖苷酶构建体的快速降解需要ATP和泛素，并被蛋白酶体抑制剂阻断。它们在提取物中的降解速率与它们在体内的I类抗原呈递速率相关。这些结果表明，泛素结合是抗原呈递中的关键限速步骤，并为泛素和26S蛋白酶体在产生MHC I类呈递肽中的关键作用提供了进一步的证据。
