Shurety W, Bright N A, Luzio J P
Department of Clinical Biochemistry, University of Cambridge, Addenbrooke's Hospital, UK.
J Cell Sci. 1996 Dec;109 ( Pt 12):2927-35. doi: 10.1242/jcs.109.12.2927.
Apical endocytosis of 125I-ricin in Caco-2 cells was inhibited > 95% by hypertonic and/or acid media, consistent with the major uptake route being clathrin-mediated. The presence of apical cell surface bound ricin-gold in clathrin coated pits and vesicles was observed by electron microscopy. An electron microscopic investigation in which ricin-gold bound to the apical surface was quantitated, showed that cytochalasin D, which inhibits apical but not basolateral endocytosis, prevented movement of ricin-gold along the microvillar surface. This was consistent with an actin bound mechanochemical motor within microvilli driving the movement of membranous components towards the cell body. Cytochalasin D also caused an increase in the number of coated pits observed at the apical cell surface relative to the number observed in untreated cells. Stimulation of apical endocytosis of ricin by phorbol 12-myristate 13-acetate showed the characteristics of being mediated by protein kinase C, was not due to an effect on ricin movement along the microvillar surface, and may be explained by increases in formation and pinching off of clathrin coated pits at the apical cell surface.
在Caco-2细胞中，高渗和/或酸性培养基可使125I-蓖麻毒素的顶端内吞作用受到>95%的抑制，这与主要摄取途径是网格蛋白介导的一致。通过电子显微镜观察到网格蛋白包被小窝和小泡中有顶端细胞表面结合的蓖麻毒素-金。一项对结合到顶端表面的蓖麻毒素-金进行定量的电子显微镜研究表明，抑制顶端而非基底外侧内吞作用的细胞松弛素D可阻止蓖麻毒素-金沿微绒毛表面移动。这与微绒毛内的肌动蛋白结合机械化学马达驱动膜性成分向细胞体移动是一致的。相对于未处理细胞中观察到的数量，细胞松弛素D还导致顶端细胞表面观察到的包被小窝数量增加。佛波酯12-肉豆蔻酸酯13-乙酸酯对蓖麻毒素顶端内吞作用的刺激表现出由蛋白激酶C介导的特征，这不是由于对蓖麻毒素沿微绒毛表面移动的影响，可能是由于顶端细胞表面网格蛋白包被小窝的形成和缢断增加所致。
