Interferon-γ can stimulate post-proteasomal trimming of the N terminus of an antigenic peptide by inducing leucine aminopeptidase
Interferon-γ can stimulate post-proteasomal trimming of the N terminus of an antigenic peptide by inducing leucine aminopeptidase
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DOI：
10.1074/jbc.273.30.18734
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发表时间：
1998-07-24
影响因子：
4.8
通讯作者：
Goldberg, AL
中科院分区：
文献类型：
--
作者：
Beninga, J;Rock, KL;Goldberg, AL
大多数呈递在主要组织相容性复合物 I 类分子上的抗原肽是在蛋白酶体分解蛋白质过程中产生的，蛋白酶体的特异性会被干扰素-γ (IFN-γ) 改变。当卵清蛋白衍生表位 SIINFEKL 的延伸版本在体内表达时，正确的 C 末端由蛋白酶体切割生成，但不同的胞质蛋白酶生成其 N 末端。为了鉴定参与抗原加工的其他蛋白酶，我们将 HeLa 细胞的可溶性提取物与 11 聚体 QLESIINFEKL 一起孵育，QLESIINFEKL 在体内通过不依赖于蛋白酶体的途径加工成抗原性 8 聚体 (SIINFEKL)。通过连续去除 N 端残基，该 11 聚体转化为 9 聚体，但令人惊讶的是，提取物显示出很少或没有针对该前体的内肽酶或羧肽酶活性。用 IFN-γ 处理细胞后，这种 N 末端修剪速度加快了数倍，并继续形成抗原性 8 聚体。 IFN 处理的细胞还对许多模型荧光底物表现出更高的氨肽酶活性。提取物分级分离后，检测到三个对贝他汀敏感的氨肽酶峰，其中一个由 IFN-γ 诱导，经免疫学鉴定为亮氨酸氨肽酶 (LAP)。纯化的 LAP，就像 IFN-γ 处理的细胞的提取物一样，将 11 聚体肽加工成 SIINFEKL。因此，IFN-γ不仅促进决定抗原肽C末端的蛋白酶体裂解，而且还可以通过诱导LAP刺激其N末端的形成。该酶似乎催化该前体以及可能的其他蛋白酶体衍生前体的 N 末端的修剪。因此，对 LAP 的敏感性可能对免疫显性表位的产生具有重要影响。
Most antigenic peptides presented on major histocompatibility complex class I molecules are generated during protein breakdown by proteasomes, whose specificity is altered by interferon-gamma (IFN-gamma). When extended versions of the ovalbumin-derived epitope SIINFEKL are expressed in vivo, the correct C terminus is generated by proteasomal cleavage, but distinct cytosolic protease(s) generate its N terminus. To identify the other protease(s) involved in antigen processing, we incubated soluble extracts of HeLa cells with the 11-mer QLESIINFEKL, which in vivo is processed to the antigenic 8-mer (SIINFEKL) by a proteasome-independent pathway. This 11-mer was converted to the 9-mer by sequential removal of the N-terminal residues, but surprisingly the extract showed little or no endopeptidase or carboxypeptidase activity against this precursor. After treatment of cells with IFN-gamma, this N-terminal trimming was severalfold faster and proceeded to the antigenic 8-mer. The IFN-treated cells also showed greater aminopeptidase activity against many model fluorogenic substrates. Upon extract fractionation, three bestatin-sensitive aminopeptidase peaks were detected, One was induced by IFN-gamma and was identified immunologically as leucine aminopeptidase (LAP). Purified LAP, like the extracts of IFN-gamma-treated cells, processed the 11-mer peptide to SIINFEKL. Thus, IFN-gamma not only promotes proteasomal cleavages that determine the C termini of antigenic peptides, but also can stimulate formation of their N termini by inducing LAP. This enzyme appears to catalyze the trimming of the N terminus of this and presumably other proteasome-derived precursors. Thus, susceptibility to LAP may be an important influence on the generation on immunodominant epitopes.