Boll W, Partin J S, Katz A I, Caplan M J, Jamieson J D
Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06510-8002.
Proc Natl Acad Sci U S A. 1991 Oct 1;88(19):8592-6. doi: 10.1073/pnas.88.19.8592.
Polarized epithelial cells target distinct sets of membrane and secretory proteins to their apical and basolateral domains. Here we examine whether constitutively secreted and membrane proteins that are bound for the same domain share the same carrier vesicles. To address the issue, differential effects of microtubule depolymerization on basolateral protein targeting in the polarized Madin-Darby canine kidney II cell line were studied. We find that the basolateral insertion of the active, ouabain-binding Na+,K(+)-ATPase and of a set of very late antigen integrins is little affected by microtubule disruption. Under equivalent conditions, the basolateral secretion of the basement membrane protein laminin is strongly suppressed. More specifically, it is demonstrated that microtubules are involved in targeting laminin, but not integrins, from the compartment related to the accumulation of newly synthesized proteins at 20 degrees C (trans-Golgi network) to the basolateral domain. Our study also reveals that laminin associated with basolateral binding sites interacts with those sites only secondarily to secretion. The data provide evidence for a branch in the basolateral targeting pathway, with secreted and membrane proteins loaded into distinct carrier vesicles.
极化上皮细胞将不同的膜蛋白和分泌蛋白靶向运输到其顶端和基底外侧结构域。在此，我们研究了运往同一结构域的组成型分泌蛋白和膜蛋白是否共享相同的载体囊泡。为解决该问题，我们研究了微管解聚对极化的Madin-Darby犬肾II细胞系中基底外侧蛋白靶向运输的不同影响。我们发现，活性的、结合哇巴因的Na⁺,K⁺-ATP酶以及一组极晚期抗原整合素向基底外侧的插入受微管破坏的影响很小。在相同条件下，基底膜蛋白层粘连蛋白的基底外侧分泌受到强烈抑制。更具体地说，已证明微管参与将层粘连蛋白（而非整合素）从与20℃时新合成蛋白积累相关的区室（反式高尔基体网络）靶向运输到基底外侧结构域。我们的研究还表明，与基底外侧结合位点相关的层粘连蛋白仅在分泌后才与这些位点相互作用。这些数据为基底外侧靶向运输途径中的一个分支提供了证据，即分泌蛋白和膜蛋白被装载到不同的载体囊泡中。
