Masilamani Madhan, Narayanan Sriram, Prieto Martha, Borrego Francisco, Coligan John E
Receptor Cell Biology Section, Laboratory of Immunogenetics, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, MD 20852, USA.
Traffic. 2008 Jun;9(6):1019-34. doi: 10.1111/j.1600-0854.2008.00738.x. Epub 2008 Mar 19.
The CD94/NKG2A inhibitory receptor, expressed by natural killer and T cells, is constantly exposed to its HLA-E ligand expressed by surrounding cells. Ligand exposure often induces receptor downregulation. For CD94/NKG2A, this could potentiate activation receptor(s) induced responses to normal bystander cells. We investigated CD94/NKG2A endocytosis and found that it occurs by an amiloride-sensitive, Rac1-dependent macropinocytic-like process; however, it does not require clathrin, dynamin, ADP ribosylation factor-6, phosphoinositide-3 kinase or the actin cytoskeleton. Once endocytosed, CD94/NKG2A traffics to early endosomal antigen 1(+), Rab5(+) early endosomes. It does appear in Rab4(+) early/sorting endosome, but, in the time period examined, fails to reach Rab11(+) recycling or Rab7(+) late endosomes or lysosome-associated membrane protein-1(+) lysosomes. These results indicate that CD94/NKG2A utilizes a previously undescribed endocytic mechanism coupled with an abbreviated trafficking pattern, perhaps to insure surface expression.
自然杀伤细胞和T细胞表达的CD94/NKG2A抑制性受体持续暴露于周围细胞表达的HLA-E配体。配体暴露常诱导受体下调。对于CD94/NKG2A而言,这可能增强激活受体诱导的对正常旁观者细胞的反应。我们研究了CD94/NKG2A的内吞作用,发现其通过一种对amiloride敏感、Rac1依赖性的巨胞饮样过程发生;然而,它不需要网格蛋白、发动蛋白、ADP核糖基化因子6、磷酸肌醇-3激酶或肌动蛋白细胞骨架。一旦被内吞,CD94/NKG2A转运至早期内体抗原1(+)、Rab5(+)早期内体。它确实出现在Rab4(+)早期/分拣内体中,但在所检测的时间段内,未能到达Rab11(+)再循环内体或Rab7(+)晚期内体或溶酶体相关膜蛋白-1(+)溶酶体。这些结果表明,CD94/NKG2A利用了一种先前未描述的内吞机制以及一种简化的转运模式,这可能是为了确保其表面表达。