Dogic D, Rousselle P, Aumailley M
Institut de Biologie et Chimie des Protéines, CNRS UPR 412, Lyon, France.
J Cell Sci. 1998 Mar;111 ( Pt 6):793-802. doi: 10.1242/jcs.111.6.793.
Laminin 1 (alpha1beta1gamma1) and laminin 5 (alpha3beta3gamma2) induce cell adhesion with different involvement of integrins: both are ligands for the alpha6beta1 integrin, while alpha3beta1 integrin has affinity for laminin 5 only. These two laminin isoforms therefore provide good models to investigate whether alpha3beta1 and alpha6beta1 integrins play different roles in signal transduction and in focal adhesion formation. Laminin 1 or 5 induced adhesion of normal human skin fibroblasts to a similar extent but promoted different overall cell shapes. On laminin 1 the fibroblasts formed mainly filopodia-like structures, while on laminin 5 they developed lamellipodias. Staining of fibrillar actin with fluorescein-phalloidin revealed a similar organisation of the actin cytoskeleton on both substrates. However, integrin subunits and several cytoskeletal linker proteins, including vinculin, talin, and paxillin, showed an isoform-specific arrangement into focal adhesions. On laminin 1 they were recruited into thick and short aggregates localized at the termini of actin stress fibers, while on laminin 5 they appeared as dots or streaks clustered on a long portion of actin microfilaments. To test whether the differing affinity of laminin 1 or 5 for alpha3beta1 integrin would explain the formation of morphologically different focal adhesions, cells were seeded on laminin 1 under conditions in which alpha3beta1 integrins were occupied by a function-blocking antibody. This resulted in the formation of focal adhesions similar to that observed on laminin 5, where the integrin is occupied by its natural ligand. These results provide the first evidence for a cross-talk between alpha3beta1 and alpha6beta1 integrins and indicate that occupancy of alpha3beta1 integrins results in a trans-dominant regulation of alpha6beta1 integrin clustering and of focal adhesions. It suggests that recruitment of integrins and cytoskeletal linker proteins are laminin isoform-specific and that tissue specific expression of laminin isoforms might modulate cell behavior by the activation of distinct sets of integrins and by the induction of distinct molecular assemblies within the cell adhesion signaling complexes.
层粘连蛋白1（α1β1γ1）和层粘连蛋白5（α3β3γ2）诱导细胞黏附时整合素的参与情况不同：二者都是α6β1整合素的配体，而α3β1整合素仅对层粘连蛋白5有亲和力。因此，这两种层粘连蛋白异构体为研究α3β1和α6β1整合素在信号转导和黏着斑形成中是否发挥不同作用提供了良好模型。层粘连蛋白1或5诱导正常人皮肤成纤维细胞黏附的程度相似，但促进形成了不同的整体细胞形态。在层粘连蛋白1上，成纤维细胞主要形成丝状伪足样结构，而在层粘连蛋白5上，它们形成片状伪足。用荧光素 - 鬼笔环肽对纤维状肌动蛋白进行染色显示，两种底物上肌动蛋白细胞骨架的组织方式相似。然而，整合素亚基和几种细胞骨架连接蛋白，包括纽蛋白、踝蛋白和桩蛋白，在黏着斑中呈现出异构体特异性的排列。在层粘连蛋白1上，它们被募集到位于肌动蛋白应力纤维末端的粗大且短小的聚集体中，而在层粘连蛋白5上，它们表现为聚集在肌动蛋白微丝长段上的点状或条纹状。为了测试层粘连蛋白1或5对α3β1整合素的不同亲和力是否能解释形态上不同的黏着斑的形成，将细胞接种在层粘连蛋白1上，此时α3β1整合素被功能阻断抗体占据。这导致形成了与在层粘连蛋白5上观察到的相似的黏着斑，在层粘连蛋白5上整合素被其天然配体占据。这些结果为α3β1和α6β1整合素之间的相互作用提供了首个证据，并表明α3β1整合素的占据导致对α6β1整合素聚集和黏着斑的反式显性调节。这表明整合素和细胞骨架连接蛋白的募集是层粘连蛋白异构体特异性的，并且层粘连蛋白异构体的组织特异性表达可能通过激活不同组的整合素以及诱导细胞黏附信号复合物内不同的分子组装来调节细胞行为。
