Kim H S, Garcia J, Exley M, Johnson K W, Balk S P, Blumberg R S
Division of Gastroenterology, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA.
J Biol Chem. 1999 Apr 2;274(14):9289-95. doi: 10.1074/jbc.274.14.9289.
CD1d is a major histocompatibility complex class I-like molecule that exhibits a distinct antigen processing pathway that functions in the presentation of hydrophobic antigens to T cells. CD1d has been previously shown to be expressed on the cell surface of human intestinal epithelial cell lines in vivo and a transfected cell line in vitro independently of beta2-microglobulin (beta2m). To define the relationship between CD1d and beta2m and characterize the biochemical structure of CD1d in the absence of beta2m, we have used a newly generated series of CD1d transfectants and CD1d-specific antibodies. These studies show that in the absence of beta2m, CD1d is expressed on the cell surface as a 45-kDa glycoprotein that is sensitive to endoglycosidase-H and is reduced to 37-kDa after N-glycanase digestion. In contrast, in the presence of beta2m, CD1d is expressed on the cell surface as a 48-kDa endoglycosidase-H-resistant glycoprotein. Pulse-chase metabolic labeling studies demonstrate that acquisition of endoglycosidase-H resistance of CD1d is observed in the presence of beta2m but not in the absence of beta2m even after a 24-h chase period. Thus, CD1d is able to be transported to the cell surface independently of beta2m; however, in the absence of beta2m, the glycosylation pattern of CD1d is altered and consistent with an immature glycoprotein.
CD1d是一种主要组织相容性复合体I类样分子，它展现出独特的抗原加工途径，在向T细胞呈递疏水性抗原过程中发挥作用。先前研究表明，CD1d在体内人肠道上皮细胞系的细胞表面以及体外转染细胞系中表达，且不依赖于β2-微球蛋白（β2m）。为了确定CD1d与β2m之间的关系，并在不存在β2m的情况下表征CD1d的生化结构，我们使用了一系列新产生的CD1d转染子和CD1d特异性抗体。这些研究表明，在不存在β2m的情况下，CD1d作为一种45 kDa的糖蛋白在细胞表面表达，该糖蛋白对内切糖苷酶-H敏感，经N-糖苷酶消化后降至37 kDa。相比之下，在存在β2m的情况下，CD1d作为一种48 kDa的耐内切糖苷酶-H糖蛋白在细胞表面表达。脉冲追踪代谢标记研究表明，即使在24小时追踪期后，在存在β2m的情况下可观察到CD1d获得耐内切糖苷酶-H特性，而在不存在β2m的情况下则未观察到。因此，CD1d能够不依赖于β2m转运至细胞表面；然而，在不存在β2m的情况下，CD1d的糖基化模式发生改变，与未成熟糖蛋白一致。
