Hotchin N A, Hall A
CRC Oncogene and Signal Transduction Group, MRC Laboratory for Molecular Cell Biology, University College London.
J Cell Biol. 1995 Dec;131(6 Pt 2):1857-65. doi: 10.1083/jcb.131.6.1857.
Interaction of cells with extracellular matrix via integrin adhesion receptors plays an important role in a wide range of cellular: functions, for example cell growth, movement, and differentiation. Upon interaction with substrate, integrins cluster and associate with a variety of cytoplasmic proteins to form focal complexes and with the actin cytoskeleton. Although the intracellular signals induced by integrins are at present undefined, it is thought that they are mediated by proteins recruited to the focal complexes. It has been suggested, for example, that after recruitment to focal adhesions p125FAK can activate the ERK1/2 MAP kinase cascade. We have previously reported that members of the rho family of small GTPases can trigger the assembly of focal complexes when activated in cells. Using microinjection techniques, we have now examined the role of the extracellular matrix and of the two GTP-binding proteins, rac and rho, in the assembly of integrin complexes in both mouse and human fibroblasts. We find that the interaction of integrins with extracellular matrix alone is not sufficient to induce integrin clustering and focal complex formation. Similarly, activation of rho or rac by extracellular growth factors does not lead to focal complex formation in the absence of matrix. Focal complexes are only assembled in the presence of both matrix and functionally active members of the rho family. In agreement with this, the interaction of integrins with matrix in the absence of rho/rac activity is unable to activate the ERK1/2 kinases in Swiss 3T3 cells. In fact, ERK1/2 can be activated fully by growth factors in the absence of matrix and it seems unlikely, therefore, that the adhesion dependence of fibroblast growth is mediated through the ras/MAP kinase pathway. We conclude that extracellular matrix is not sufficient to trigger focal complex assembly and subsequent integrin-dependent signal transduction in the absence of functionally active members of the rho family of GTPases.
细胞通过整合素黏附受体与细胞外基质的相互作用在广泛的细胞功能中发挥重要作用，例如细胞生长、运动和分化。与底物相互作用时，整合素聚集并与多种细胞质蛋白结合形成黏着斑复合体，并与肌动蛋白细胞骨架结合。尽管目前整合素诱导的细胞内信号尚不清楚，但认为它们是由募集到黏着斑复合体的蛋白质介导的。例如，有人提出，募集到黏着斑后，p125FAK可以激活ERK1/2丝裂原活化蛋白激酶级联反应。我们之前报道过，小GTP酶rho家族的成员在细胞中被激活时可以触发黏着斑复合体的组装。利用显微注射技术，我们现在研究了细胞外基质以及两种GTP结合蛋白rac和rho在小鼠和人成纤维细胞整合素复合体组装中的作用。我们发现，仅整合素与细胞外基质的相互作用不足以诱导整合素聚集和黏着斑复合体形成。同样，在没有基质的情况下，细胞外生长因子对rho或rac的激活不会导致黏着斑复合体形成。黏着斑复合体仅在同时存在基质和rho家族功能活跃成员的情况下组装。与此一致的是，在没有rho/rac活性的情况下，整合素与基质的相互作用无法激活瑞士3T3细胞中的ERK1/2激酶。事实上，在没有基质的情况下，生长因子可以完全激活ERK1/2，因此，成纤维细胞生长的黏附依赖性似乎不太可能通过ras/丝裂原活化蛋白激酶途径介导。我们得出结论，在没有GTP酶rho家族功能活跃成员的情况下，细胞外基质不足以触发黏着斑复合体组装和随后依赖整合素的信号转导。
