Simonsen A, Bremnes B, Nordeng T W, Bakke O
Department of Biology, University of Oslo, Norway.
Eur J Cell Biol. 1998 May;76(1):25-32. doi: 10.1016/S0171-9335(98)80014-9.
The major histocompatibility complex (MHC) class II-associated invariant chain (Ii) contains signals for transport to endocytic compartments where the class II molecules bind antigenic peptides for presentation to CD4+ T cells. Two leucine-based signals in the Ii cytoplasmic tail can be independently recognized for endosomal sorting of Ii, and we have recently shown that each signal is sufficient for basolateral sorting and internalization of Ii in polarized Madine Darby Canine Kidney (MDCK) II cells. The recognition motif for endosomal sorting is complex and consists of two critical leucine-like residues as well as surrounding amino acids. Here, we have analyzed the importance of residues surrounding the membrane-distal leucine-based signal in basolateral sorting and internalization of Ii in MDCK II cells. We find that the DDQxxLI motif is involved in both sorting events indicating the presence of similar signal recognition components both at the TGN and at the plasma membrane. The identical motif is required for endosomal localization and internalization of Ii also in simian COS cells and the human HeLa and M1 cells.
主要组织相容性复合体（MHC）II类相关恒定链（Ii）含有转运至内吞小室的信号，在这些小室中，II类分子结合抗原肽以呈递给CD4 + T细胞。Ii细胞质尾部的两个基于亮氨酸的信号可被独立识别用于Ii的内体分选，并且我们最近表明，每个信号对于极化的犬肾（MDCK）II细胞中Ii的基底外侧分选和内化都是足够的。内体分选的识别基序很复杂，由两个关键的亮氨酸样残基以及周围的氨基酸组成。在这里，我们分析了MDCK II细胞中Ii的基底外侧分选和内化过程中，膜远端基于亮氨酸的信号周围残基的重要性。我们发现DDQxxLI基序参与了这两种分选事件，表明在反式高尔基体网络（TGN）和质膜处存在相似的信号识别成分。相同的基序对于猿猴COS细胞以及人HeLa和M1细胞中Ii的内体定位和内化也是必需的。
