Sijts A J, Standera S, Toes R E, Ruppert T, Beekman N J, van Veelen P A, Ossendorp F A, Melief C J, Kloetzel P M
Institute of Biochemistry, Charité, Humboldt University, Berlin, Germany.
J Immunol. 2000 May 1;164(9):4500-6. doi: 10.4049/jimmunol.164.9.4500.
Proteasomes are the major source for the generation of peptides bound by MHC class I molecules. To study the functional relevance of the IFN-gamma-inducible proteasome subunits low molecular mass protein 2 (LMP2), LMP7, and mouse embryonal cell (MEC) ligand 1 in Ag processing and concomitantly that of immunoproteasomes, we established the tetracycline-regulated mouse cell line MEC217, allowing the titrable formation of immunoproteasomes. Infection of MEC217 cells with Adenovirus type 5 (Ad5) and analysis of Ag presentation with Ad5-specific CTL showed that cells containing immunoproteasomes processed the viral early 1B protein (E1B)-derived epitope E1B192-200 with increased efficiency, thus allowing a faster detection of viral entry in induced cells. Importantly, optimal CTL activation was already achieved at submaximal immunosubunit expression. In contrast, digestion of E1B-polypeptide with purified proteasomes in vitro yielded E1B192-200 at quantities that were proportional to the relative contents of immunosubunits. Our data provide evidence that the IFN-gamma-inducible proteasome subunits, when present at relatively low levels as at initial stages of infection, already increase the efficiency of antigenic peptide generation and thereby enhance MHC class I Ag processing in infected cells.
蛋白酶体是与MHC I类分子结合的肽产生的主要来源。为了研究干扰素-γ诱导的蛋白酶体亚基低分子量蛋白2（LMP2）、LMP7和小鼠胚胎细胞（MEC）配体1在抗原加工中的功能相关性，以及免疫蛋白酶体的功能相关性，我们建立了四环素调控的小鼠细胞系MEC217，可滴定形成免疫蛋白酶体。用5型腺病毒（Ad5）感染MEC217细胞并用Ad5特异性CTL分析抗原呈递，结果表明含有免疫蛋白酶体的细胞能更高效地加工病毒早期1B蛋白（E1B）衍生的表位E1B192-200，从而能更快地检测到诱导细胞中的病毒进入。重要的是，在亚最大免疫亚基表达时就已实现最佳CTL激活。相比之下，在体外用纯化的蛋白酶体消化E1B多肽产生的E1B192-200的量与免疫亚基的相对含量成正比。我们的数据证明，干扰素-γ诱导的蛋白酶体亚基在感染初期以相对较低水平存在时，就已提高了抗原肽产生的效率，从而增强了感染细胞中MHC I类抗原的加工。
