Sanger J M, Chang R, Ashton F, Kaper J B, Sanger J W
Department of Cell and Developmental Biology, University of Pennsylvania School of Medicine, Philadelphia 19104-6058, USA.
Cell Motil Cytoskeleton. 1996;34(4):279-87. doi: 10.1002/(SICI)1097-0169(1996)34:4<279::AID-CM3>3.0.CO;2-3.
Enteropathogenic Escherichia coli (EPEC) attach to cells (attachment) lining the intestine and induce a decrease in the number of the cells' microvilli (effacement). This attachment and effacement is followed by diarrhea, which may be explained, at least in part, to the loss of microvilli and the decreased ability of the infected cells to absorb fluids. EPEC also attach to the surfaces of a number of cultured cells including CaCo-2, LLC-PK, and PtK2 cells. The extracellular, attached EPEC induce filaments of actin to form in the cytoplasm just underneath the EPEC surface attachment sites. Beneath some of the attached EPEC, the actin filaments become organized into membrane encased columns that extend up to 6 micrometers above the cell surface creating "pedestals" on which the EPEC rest. The raised pedestals can be readily observed in stereo pairs taken using the Intermediate Voltage Electron Microscope. The concentration of non-muscle isoforms of myosin II and tropomyosin near the base of the pedestals suggests a similarity of these structures to brush border microvilli. Video microscopy indicates that these EPEC pedestals can bend and undulate, alternately growing longer and shorter while remaining tethered in place on the cell surface. Some of the attached EPEC also translocate along the cell surface, reaching speeds up to 0.07 micrometers/sec. Both types of movement are inhibited by cytochalasin D, indicating that actin polymerization in the pedestals is required for the motility of EPEC on the host cell surface. In this respect, EPEC motility on host cells resembles the intracellular motility of Listeria, but there are differences in the actin filament bundles induced by the two different bacteria. The most obvious one is the interposition of the cell membrane between EPEC and the actin filaments in the pedestal in contrast to the close apposition of actin filaments to Listeria. The intensity of fluorescence of rhodamine phalloidin is nearly uniform along most of the length of the pedestals indicating a constant number of actin filaments, whereas the fluorescence intensity decreases along the length of Listeria tails reflecting the disassembly that occurs all along the tails. Epec's movements may be a hybrid of Listeria filopodia and Aplysia inductopodia movements. This paper is the first report of a microbe attached to the extracellular surface of an infected cell propelled by an intracellular actin polymerization-dependent mechanism.
肠致病性大肠杆菌（EPEC）附着于肠道内壁的细胞（附着作用），并导致这些细胞的微绒毛数量减少（刷状缘缺失）。这种附着和刷状缘缺失之后会出现腹泻，这至少部分可以解释为微绒毛的丧失以及受感染细胞吸收液体能力的下降。EPEC还能附着于多种培养细胞的表面，包括CaCo-2、LLC-PK和PtK2细胞。附着在细胞外的EPEC会诱导肌动蛋白丝在其表面附着位点正下方的细胞质中形成。在一些附着的EPEC下方，肌动蛋白丝会组织成被膜包裹的柱状结构，这些柱状结构在细胞表面上方延伸达6微米，形成EPEC赖以附着的“基座”。使用中压电子显微镜拍摄的立体图像中可以很容易地观察到这些凸起的基座。肌球蛋白II和原肌球蛋白的非肌肉异构体在基座底部附近的聚集表明这些结构与刷状缘微绒毛相似。视频显微镜观察表明，这些EPEC基座可以弯曲和起伏，交替变长和变短，同时仍固定在细胞表面的原位。一些附着在细胞上的EPEC还会沿着细胞表面移动，速度可达0.07微米/秒。这两种类型的运动都受到细胞松弛素D的抑制，这表明基座中的肌动蛋白聚合是EPEC在宿主细胞表面运动所必需的。在这方面，EPEC在宿主细胞上的运动类似于李斯特菌的细胞内运动，但两种不同细菌诱导形成的肌动蛋白丝束存在差异。最明显的差异是，与肌动蛋白丝与李斯特菌紧密贴合不同，在基座中EPEC与肌动蛋白丝之间隔着细胞膜。罗丹明鬼笔环肽的荧光强度在基座的大部分长度上几乎是均匀的，这表明肌动蛋白丝的数量恒定，而沿着李斯特菌尾部的荧光强度则随着尾部各处发生的解聚而降低。EPEC的运动可能是李斯特菌丝状伪足运动和海兔诱导伪足运动的混合形式。本文首次报道了一种微生物通过细胞内肌动蛋白聚合依赖机制在受感染细胞的细胞外表面推动下进行移动。
