Maratos-Flier E, Kao C Y, Verdin E M, King G L
Elliott P. Joslin Research Laboratory, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02215.
J Cell Biol. 1987 Oct;105(4):1595-601. doi: 10.1083/jcb.105.4.1595.
Transcellular transport of a variety of ligands may be an important mechanism by which regulatory substances reach their site of action. We have studied the transcellular transport of two 6,000-mol-wt proteins, epidermal growth factor (EGF) and insulin, across polarized Madin-Darby canine kidney (MDCK) cells grown on dual-sided chambers on a nitrocellulose filter substrate. When grown on these chambers, MDCK cells are polarized and express distinct basal and apical surfaces. MDCK cells are capable of unidirectional transport of EGF from the basal-to-apical direction, 50% of bound EGF transported in 2 h. Transport was inhibited by the addition of unlabeled EGF in a dose-dependent manner. Anti-EGF receptor Ab, which inhibited binding, also inhibited transport. No transport in the apical-to-basal direction is noted. Insulin transport is not observed in either direction. Transport correlates with the presence of ligand-specific receptors on the cell surface. Hence, EGF receptors (Ro = 48,000, Kd = 3.5 X 10(-10) M) are found only on the basal surface of the MDCK cells and neither surface expresses insulin receptors. Characterization of the EGF receptors on MDCK cells, as assessed by affinity, molecular mass, and anti-receptor antibody binding reveals that this receptor has similar characteristics to EGF receptors previously described on a variety of cells. Hence, the EGF receptor can function as a transporter of EGF across an epithelial cell barrier.
多种配体的跨细胞转运可能是调节物质到达其作用位点的重要机制。我们研究了两种分子量为6000道尔顿的蛋白质——表皮生长因子（EGF）和胰岛素，在硝酸纤维素滤膜基质上双面培养的极化的麦氏犬肾（MDCK）细胞中的跨细胞转运。当在这些培养皿上生长时，MDCK细胞呈极化状态，并表现出明显的基底表面和顶端表面。MDCK细胞能够将EGF从基底向顶端单向转运，2小时内转运50%结合的EGF。添加未标记的EGF以剂量依赖性方式抑制转运。抑制结合的抗EGF受体抗体也抑制转运。未观察到从顶端向基底方向的转运。在两个方向上均未观察到胰岛素转运。转运与细胞表面存在配体特异性受体相关。因此，EGF受体（Ro = 48,000，Kd = 3.5×10⁻¹⁰ M）仅在MDCK细胞的基底表面发现，且两个表面均不表达胰岛素受体。通过亲和力、分子量和抗受体抗体结合评估的MDCK细胞上EGF受体的特征表明，该受体具有与先前在多种细胞上描述的EGF受体相似的特征。因此，EGF受体可以作为EGF跨上皮细胞屏障的转运体发挥作用。
