Fabre-Jonca N, Viard I, French L E, Masson D
Epithelial Network, University of Geneva, Medical School, Switzerland.
J Invest Dermatol. 1999 Feb;112(2):216-25. doi: 10.1046/j.1523-1747.1999.00500.x.
Microtubules are involved in the positioning and movement of organelles and vesicles and therefore play fundamental roles in cell polarization and differentiation. Their organization and properties are cell-type specific and are controlled by microtubule-associated proteins (MAP). E-MAP-115 (epithelial microtubule-associated protein of 115 kDa) has been identified as a microtubule-stabilizing protein predominantly expressed in epithelial cells. We have used human skin and primary keratinocytes as a model to assess a putative function of E-MAP-115 in stabilizing and reorganizing the microtubule network during epithelial cell differentiation. Immunolabeling of skin sections indicated that E-MAP-115 is predominantly expressed in the suprabasal layers of the normal epidermis and, in agreement with this observation, is relatively abundant in squamous cell carcinomas but barely detectable in basal cell carcinomas. In primary keratinocytes whose terminal differentiation was induced by increasing the Ca2+ concentration of the medium, E-MAP-115 expression significantly increased during the first day, as observed by northern and western blot analysis. Parallel immunofluorescence studies showed an early redistribution of E-MAP-115 from microtubules with a paranuclear localization to cortical microtubules organized in spike-like bundles facing intercellular contacts. This phenomenon is transient and can be reversed by Ca2+ depletion. Treatment of cells with cytoskeleton-active drugs after raising the Ca2+ concentration indicated that E-MAP-115 is associated with a subset of stable microtubules and that the cortical localization of these microtubules is dependent on other microtubules but not on strong interactions with the actin cytoskeleton or the plasma membrane. The mechanism whereby E-MAP-115 would redistribute to and stabilize cortical microtubules used for the polarized transport of vesicles towards the plasma membrane, where important reorganizations take place upon stratification, is discussed.
微管参与细胞器和囊泡的定位与移动，因此在细胞极化和分化中发挥着重要作用。它们的组织和特性具有细胞类型特异性，并受微管相关蛋白（MAP）调控。E-MAP-115（115 kDa的上皮微管相关蛋白）已被鉴定为一种主要在上皮细胞中表达的微管稳定蛋白。我们以人皮肤和原代角质形成细胞为模型，评估E-MAP-115在表皮细胞分化过程中稳定和重组微管网络的假定功能。皮肤切片的免疫标记表明，E-MAP-115主要在正常表皮的基上层表达，与此观察结果一致，其在鳞状细胞癌中相对丰富，而在基底细胞癌中几乎检测不到。在通过提高培养基中Ca2+浓度诱导终末分化的原代角质形成细胞中，通过Northern和Western印迹分析观察到，E-MAP-115表达在第一天显著增加。平行免疫荧光研究显示，E-MAP-115早期从具有核旁定位的微管重新分布到面向细胞间接触的呈穗状束状排列的皮质微管。这种现象是短暂的，可通过Ca2+耗竭逆转。提高Ca2+浓度后用细胞骨架活性药物处理细胞表明，E-MAP-115与一部分稳定的微管相关，这些微管的皮质定位依赖于其他微管，但不依赖于与肌动蛋白细胞骨架或质膜的强相互作用。本文讨论了E-MAP-115重新分布并稳定用于囊泡向质膜极化运输的皮质微管的机制，囊泡向质膜的极化运输在分层时会发生重要的重组。
