Nabi I R, Le Bivic A, Fambrough D, Rodriguez-Boulan E
Department of Cell Biology and Anatomy, Cornell University Medical College, New York 10021.
J Cell Biol. 1991 Dec;115(6):1573-84. doi: 10.1083/jcb.115.6.1573.
Using surface immunoprecipitation at 37 degrees C to "catch" the transient apical or basolateral appearance of an endogenous MDCK lysosomal membrane glycoprotein, the AC17 antigen, we demonstrate that the bulk of newly synthesized AC17 antigen is polarly targeted from the Golgi apparatus to the basolateral plasma membrane or early endosomes and is then transported to lysosomes via the endocytic pathway. The AC17 antigen exhibits very similar properties to members of the family of lysosomal-associated membrane glycoproteins (LAMPs). Parallel studies of an avian LAMP, LEP100, transfected into MDCK cells revealed colocalization of the two proteins to lysosomes, identical biosynthetic and degradation rates, and similar low levels of steady-state expression on both the apical (0.8%) and basolateral (2.1%) membranes. After treatment of the cells with chloroquine, newly synthesized AC17 antigen, while still initially targeted basolaterally, appears stably in both the apical and basolateral domains, consistent with the depletion of the AC17 antigen from lysosomes and its recycling in a nonpolar fashion to the cell surface.
利用37摄氏度下的表面免疫沉淀法“捕获”内源性MDCK溶酶体膜糖蛋白AC17抗原的瞬时顶端或基底外侧出现情况，我们证明，新合成的AC17抗原大部分从高尔基体极性靶向至基底外侧质膜或早期内体，然后通过内吞途径转运至溶酶体。AC17抗原表现出与溶酶体相关膜糖蛋白（LAMP）家族成员非常相似的特性。对转染到MDCK细胞中的一种禽类LAMP即LEP100的平行研究表明，这两种蛋白共定位于溶酶体，具有相同的生物合成和降解速率，并且在顶端（0.8%）和基底外侧（2.1%）膜上的稳态表达水平相似且较低。在用氯喹处理细胞后，新合成的AC17抗原虽然最初仍靶向基底外侧，但在顶端和基底外侧结构域均稳定出现，这与AC17抗原从溶酶体中耗尽并以非极性方式循环至细胞表面一致。
