Proteasomes can either generate or destroy MHC class I epitopes: evidence for nonproteasomal epitope generation in the cytosol.
Proteasomes can either generate or destroy MHC class I epitopes: evidence for nonproteasomal epitope generation in the cytosol.
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DOI：
10.4049/jimmunol.161.1.112
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发表时间：
1998-07
影响因子：
4.4
通讯作者：
C. J. Luckey;G. King;J. Marto;Sunita Venketeswaran;Bernhard Maier;Victoria L. Crotzer;T. Colella;J. Shabanowitz;Donald F. Hunt;V. Engelhard
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文献类型：
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作者：
C. J. Luckey;G. King;J. Marto;Sunita Venketeswaran;Bernhard Maier;Victoria L. Crotzer;T. Colella;J. Shabanowitz;Donald F. Hunt;V. Engelhard
蛋白酶体参与大多数与 MHC I 类分子相关的肽的产生。我们使用两种不同的蛋白酶体抑制剂，即肽醛 N-乙酰基-L-亮氨酰-L-亮氨酰-L-正亮氨酸 (LLnL) 和高度特异性抑制剂乳胞素，来检查蛋白酶体在生成与 HLA-A*0201 相关的肽表位中的作用。 LLnL 和乳胞素均不能完全阻断 HLA-A*0201 的表达。此外，还评估了 LLnL 和乳胞素对不同类别的特定表位、TAP 独立型与 TAP 依赖型以及源自胞质或膜蛋白的表达的影响。正如预测的那样，两个 TAP 依赖性表位的呈递被 LLnL 和乳胞素阻断，而在内质网中加工的 TAP 独立表位则不受任一抑制剂的影响。令人惊讶的是，LLnL 和乳胞素均增加而不是抑制甲型流感病毒 M1 蛋白的细胞质转录和 TAP 依赖性肽的表达。对含有该表位的合成 24 聚体的体外蛋白酶体消化物进行的质谱分析显示，没有任何长度的消化产物包含完整的表位。相反，主要物种是由表位内的切割位点产生的。尽管这些位点的切割可被 LLnL 和乳胞素抑制，但仍不会产生含有表位的物质。我们得出的结论是，在某些情况下，蛋白酶体实际上可能会破坏原本由 I 类分子呈递的表位。这些结果表明一些表位是由胞质溶胶中的非蛋白酶体蛋白酶产生的。
Proteasomes have been implicated in the production of the majority of peptides that associate with MHC class I molecules. We used two different proteasome inhibitors, the peptide aldehyde N-acetyl-L-leucyl-L-leucyl-L-norleucinal (LLnL) and the highly specific inhibitor lactacystin, to examine the role of proteasomes in generating peptide epitopes associated with HLA-A*0201. Neither LLnL nor lactacystin was able to completely block the expression of the HLA-A*0201. Furthermore, the effects of LLnL and lactacystin on the expression of different categories of specific epitopes, TAP independent vs TAP dependent and derived from either cytosolic or membrane proteins, were assessed. As predicted, presentation of two TAP-dependent epitopes was blocked by LLnL and lactacystin, while a TAP-independent epitope that is processed in the endoplasmic reticulum was unaffected by either inhibitor. Surprisingly, both LLnL and lactacystin increased rather than inhibited the expression of a cytosolically transcribed and TAP-dependent peptide from the influenza A virus M1 protein. Mass spectrometric analyses of in vitro proteasome digests of a synthetic 24 mer containing this epitope revealed no digestion products of any length that included the intact epitope. Instead, the major species resulted from cleavage sites within the epitope. Although cleavage at these sites was inhibitable by LLnL and lactacystin, epitope-containing species were still not produced. We conclude that proteasomes may in some cases actually destroy epitopes that would otherwise be destined for presentation by class I molecules. These results suggest that some epitopes are generated by nonproteasomal proteases in the cytosol.