Bénaroch P, Yilla M, Raposo G, Ito K, Miwa K, Geuze H J, Ploegh H L
Department of Biology, Massachussetts Institute of Technology, Cambridge 02139.
EMBO J. 1995 Jan 3;14(1):37-49. doi: 10.1002/j.1460-2075.1995.tb06973.x.
We have examined trafficking of major histocompatibility complex (MHC) class II molecules in human B cells exposed to concanamycin B, a highly specific inhibitor of the vacuolar H(+)-ATPases required for acidification of the vacuolar system and for early to late endosomal transport. Neutralization of vacuolar compartments prevents breakdown of the invariant chain (Ii) and blocks conversion of MHC class II molecules to peptide-loaded, SDS-stable alpha beta dimers. Ii remains associated with alpha beta and this complex accumulates internally, as ascertained biochemically and by morphological methods. In concanamycin B-treated cells, a slow increase (> 20-fold) in surface expression of Ii, mostly complexed with alpha beta, is detected. This surface-disposed fraction of alpha beta Ii is nevertheless a minor population that reaches the cell surface directly, or is routed via early endosomes as intermediary stations. In inhibitor-treated cells, the bulk of newly synthesized alpha beta Ii is no longer accessible to fluid phase endocytic markers. It is concluded that the majority of alpha beta Ii is targeted directly from the trans-Golgi network to the compartment for peptide loading, bypassing the cell surface and early endosomes en route to the endocytic pathway.
我们研究了在暴露于 concanamycin B 的人 B 细胞中主要组织相容性复合体（MHC）II 类分子的运输情况，concanamycin B 是一种高度特异性的液泡 H(+)-ATP 酶抑制剂，液泡系统酸化以及早期到晚期内体运输都需要这种酶。液泡区室的中和作用可防止恒定链（Ii）的降解，并阻止 MHC II 类分子转化为肽负载的、SDS 稳定的αβ二聚体。Ii 仍然与αβ结合，并且这种复合物在细胞内积累，这已通过生化和形态学方法得以确定。在经 concanamycin B 处理的细胞中，检测到 Ii 的表面表达缓慢增加（>20 倍），其中大部分与αβ复合。然而，这种位于细胞表面的αβIi 部分是直接到达细胞表面或通过早期内体作为中间站转运的少数群体。在抑制剂处理的细胞中，新合成的大部分αβIi 不再可被液相内吞标记物识别。得出的结论是，大多数αβIi 直接从反式高尔基体网络靶向肽负载区室，在进入内吞途径的途中绕过细胞表面和早期内体。
