Hasson T, Mooseker M S
Department of Biology, Yale University, New Haven, Connecticut 06520.
J Cell Biol. 1994 Oct;127(2):425-40. doi: 10.1083/jcb.127.2.425.
We have cloned a new mammalian unconventional myosin, porcine myosin-VI from the proximal tubule cell line, LLC-PK1 (CL4). Porcine myosin-VI is highly homologous to Drosophila 95F myosin heavy chain, and together these two myosins comprise a sixth class of myosin motors. Myosin-VI exhibits ATP-sensitive actin-binding activities characteristic of myosins, and it is associated with a calmodulin light chain. Within LLC-PK1 cells, myosin-VI is soluble and does not associate with the major actin-containing domains. Within the kidney, however, myosin-VI is associated with sedimentable structures and specifically locates to the actin- and membrane-rich apical brush border domain of the proximal tubule cells. This motor was not enriched within the glomerulus, capillaries, or distal tubules. Myosin-VI associates with the proximal tubule cytoskeleton in an ATP-sensitive fashion, suggesting that this motor is associated with the actin cytoskeleton within the proximal tubule cells. Given the difference in association of myosin-VI with the apical cytoskeleton between LLC-PK1 cells and adult kidney, it is likely that this cell line does not fully differentiate to form functional proximal tubule cells. Myosin-VI may require the presence of additional elements, only found in vivo in proximal tubule cells, to properly locate to the apical domain.
我们从近端肾小管细胞系LLC-PK1（CL4）中克隆了一种新的哺乳动物非常规肌球蛋白——猪肌球蛋白-VI。猪肌球蛋白-VI与果蝇95F肌球蛋白重链高度同源，这两种肌球蛋白共同构成了肌球蛋白马达的第六类。肌球蛋白-VI表现出肌球蛋白特有的ATP敏感型肌动蛋白结合活性，并且与钙调蛋白轻链相关联。在LLC-PK1细胞内，肌球蛋白-VI是可溶的，且不与主要的含肌动蛋白结构域相关联。然而，在肾脏中，肌球蛋白-VI与可沉降结构相关联，并特异性定位于近端肾小管细胞富含肌动蛋白和膜的顶端刷状缘结构域。这种马达在肾小球、毛细血管或远端肾小管中没有富集。肌球蛋白-VI以ATP敏感的方式与近端肾小管细胞骨架相关联，表明这种马达与近端肾小管细胞内的肌动蛋白细胞骨架相关。鉴于LLC-PK1细胞和成年肾脏中肌球蛋白-VI与顶端细胞骨架的关联存在差异，很可能这种细胞系不能完全分化形成功能性近端肾小管细胞。肌球蛋白-VI可能需要额外元素的存在才能正确定位于顶端结构域，而这些元素仅在近端肾小管细胞的体内环境中才能找到。
