The Integrin α7 Cytoplasmic Domain Regulates Cell Migration, Lamellipodia Formation, and p130CAS/Crk Coupling

Abstract

The integrin ␣ 7 ␤ 1 is the major laminin-binding integrin in skeletal, heart, and smooth muscle and is a receptor for laminin-1 and -2. It mediates myoblast migration on laminin-1 and -2 and thus might be involved in muscle development and repair. Previously we have shown that ␣ 7 B as well as the ␣ 7 A and -C splice variants induce cell motility on laminin when transfected into nonmotile HEK293 cells. In this study we have investigated the role of the cytoplasmic domain of ␣ 7 in the laminin-induced signal transduction of ␣ 7 ␤ 1 integrin regulating cell adhesion and migration. Deletion of the cytoplasmic domain did not affect assembly of the mutated ␣ 7 ⌬cyt/␤ 1 heterodimer on the cell surface or adhesion of ␣ 7 ⌬cyt-transfected cells to laminin. The motility of these cells on the laminin-1/E8 fragment, however, was significantly reduced to the level of mock-transfected cells; lamellipodia formation and polarization of the cells were also impaired. Adhesion to the laminin-1/E8 fragment induced tyrosine phosphorylation of the focal adhesion kinase, paxillin, and p130 CAS as well as the formation of a p130 CAS -Crk complex in wild-type ␣ 7 B-transfected cells. In ␣ 7 B⌬cyt cells, however, the extent of p130 CAS tyrosine formation was reduced and formation of the p130 CAS -Crk complex was impaired, with unaltered levels of p130 CAS and Crk protein levels. These findings indicate adhesion-dependent regulation of p130 CAS /Crk complex formation by the cytoplasmic domain of ␣ 7 B integrin after cell adhesion to laminin-1/E8 and imply ␣ 7 B-controlled lamellipodia formation and cell migration through the p130 CAS /Crk protein complex.During muscle repair, undifferentiated muscle precursor cells, so-called satellite cells, are activated and migrate to sites of damaged muscle along the basement membranes of preexisting muscle fibers to close the wound by proliferating and fusing (1, 2). In vitro, skeletal myoblasts have been shown to migrate on laminin (LN) 1 1 (3), the laminin-1-E8 fragment that is derived from laminin-1 by elastase digestion (4), and on laminin-2 (5), but not on fibronectin (4). The major component of muscle basement membranes supporting muscle cell migration is laminin-2 (6). The migration of fibroblast-like cells in culture involves polarization of cells, formation of filopodia, lamellipodia, stress fibers, and myosin-based contractility (7). Filopodia, lamellipodia and stress fiber formation are mediated by Cdc42, Rac, and Rho, respectively, which are members of the Rho family of small GTPases (8). Cdc42, Rac, and Rho can either be activated by soluble factors like growth factors, bioactive peptides, and hormones (8) or by integrins (9, 10), which can transduce signals from the extracellular matrix after clustering and ligand-induced conformational changes (11) in a hierarchical fashion (12). Several proteins become tyrosine-phosphorylated after integrin-mediated cell attachment. Those are, among others, the focal adhesion kinase (FAK) (13), the adaptor protein p130 CAS (Crk-associated Src substr...

Expression levels of the focal adhesion-associated proteins paxillin and p130CAS in canine and feline mammary tumors

“…p130 CAS -Crk signaling also appears to be important for haptotaxis involving ECM components other than vitronectin. For example, cells expressing a mutant of the α 7 integrin subunit exhibit diminished p130 CAS phosphorylation and p130 CASCrk association resulting in a decreased migration on laminin [13]. p130 CAS -deficient fibroblasts show decreased haptotaxis toward fibronectin, a decreased ability to migrate into the gap in a wound healing assay, and a decreased basal and serum-induced invasion through a 3-dimensional collagen matrix [4,8].…”

Crk1/2-dependent signaling is necessary for podocyte foot process spreading in mouse models of glomerular disease

“…Crk1/2 in other model systems functions in complex with the focal adhesion complex protein Cas to transduce signals necessary for lamellipodial protrusive activity (34). For this reason, we considered the possibility that recruitment of Crk1/2 to nephrin observed in the above-described models occurs via intermediary proteins, rather than by direct interaction.…”

Alternative Splice Variants of α7β1Integrin Selectively Recognize Different Laminin Isoforms

“…The cytoplasmic domains of ␣-subunits are involved in the transduction of extracellular signals to the cytoskeleton and intracellular signaling pathways regulating cellular responses (48 -51). Deletion of the entire cytoplasmic domain of ␣ 7 integrin has been shown to have no effect on the adhesion of transfected HEK293 cells to laminins-1 or -2, but it does alter cell migration and phosphorylation reactions (52). It remains to be elucidated whether the laminin isoform-specific interactions of the soluble ␣ 7X1 ␤ 1 and ␣ 7X2 ␤ 1 variants reflect their affinities in vivo or whether they are modulated in vivo depending on the cell type in which they are expressed, similar to the cases of ␣ 7 ␤ 1 (17) or ␣ 2 ␤ 1 (53).…”