Sánchez-Mateos P, Campanero M R, Balboa M A, Sánchez-Madrid F
Sección de Inmunología, Hospital de la Princesa, Universidad Autónoma de Madrid, Spain.
J Immunol. 1993 Oct 1;151(7):3817-28.
The involvement of the VLA-4 integrin in an alternative leukocyte homotypic adhesion mechanism that is LFA-1/ICAM-1 independent, has been previously reported. We describe here the localization of beta 1 and alpha 4 integrin subunits at sites of cell-cell contact, on both beta 1- and alpha 4-induced aggregates of B lymphoblastoid Ramos cells. Moreover, the distribution of different VLA-alpha subunits was also examined on beta 1-induced cell aggregates of alpha 2- and alpha 4-transfected K-562 cells. Both alpha 2 and alpha 4 integrin subunits were mainly localized at sites of intercellular boundaries, suggesting a possible role for these integrins in leukocyte intercellular adhesion. The fibronectin receptor alpha 5 subunit was either diffuse throughout the plasma membrane, or displayed some accumulation at sites of cell-cell contact. Even though homotypic aggregation of U-937 cells was induced with the anti-alpha 5 P1D6 mAb, the alpha 5 subunit showed only partial redistribution to regions of cell-cell contact, compared with the complete redistribution of the alpha 4 subunit in the alpha 4-induced aggregates. The reorganization of the actin-cytoskeleton was observed at sites of intercellular boundaries in both the anti-beta 1- and anti-alpha 4-induced cell aggregates. Hence, F-actin and the cytoskeletal protein talin co-localized with beta 1 and alpha 4 integrin clusters at sites of cell-cell contact. Signal transduction during VLA-mediated homotypic cell adhesion has also been investigated. We found co-localization of beta 1 and alpha 4 subunits with tyrosine-phosphorylated proteins at cell-cell contact regions during cell aggregation. These data indicate that VLA integrin-mediated leukocyte aggregation results in clustering of beta 1-integrins at sites of cell-cell contact, together with co-localization of cytoskeletal proteins. These results also suggest that protein tyrosine phosphorylation is an important signal transduction mechanism when VLA integrins participate in intercellular contacts.
先前已有报道称，VLA - 4整合素参与了一种不依赖LFA - 1/ICAM - 1的替代性白细胞同型黏附机制。我们在此描述β1和α4整合素亚基在细胞 - 细胞接触位点的定位情况，这些位点存在于β1诱导的和α4诱导的B淋巴母细胞系Ramos细胞聚集体上。此外，还检测了不同VLA - α亚基在α2和α4转染的K - 562细胞的β1诱导细胞聚集体上的分布。α2和α4整合素亚基主要定位于细胞间边界位点，表明这些整合素在白细胞细胞间黏附中可能发挥作用。纤连蛋白受体α5亚基要么在整个质膜中呈弥散分布，要么在细胞 - 细胞接触位点有一些聚集。尽管用抗α5 P1D6单克隆抗体诱导了U - 937细胞的同型聚集，但与α4诱导聚集体中α4亚基的完全重新分布相比，α5亚基仅部分重新分布到细胞 - 细胞接触区域。在抗β1和抗α4诱导的细胞聚集体的细胞间边界位点均观察到肌动蛋白细胞骨架的重组。因此，F - 肌动蛋白和细胞骨架蛋白踝蛋白在细胞 - 细胞接触位点与β1和α4整合素簇共定位。还研究了VLA介导的同型细胞黏附过程中的信号转导。我们发现在细胞聚集过程中，β1和α4亚基与细胞 - 细胞接触区域的酪氨酸磷酸化蛋白共定位。这些数据表明，VLA整合素介导的白细胞聚集导致β1整合素在细胞 - 细胞接触位点聚集，同时细胞骨架蛋白也共定位。这些结果还表明，当VLA整合素参与细胞间接触时，蛋白酪氨酸磷酸化是一种重要的信号转导机制。
