Laminin responsiveness is associated with changes in fibroblast morphology, motility, and anchorage‐independent growth: Cell system for examining the interaction between laminin and EGF signaling pathways

Abstract

Laminin can influence the adhesion, differentiation, and motility of several cell types, including epithelial and neural cells. In addition, laminin, which contains an epidermal growth factor (EGF)-like motif, can stimulate DNA synthesis in fibroblasts possessing the EGF receptor, but laminin does not compete for EGF binding. To further investigate laminin action in fibroblasts, and the relationship between laminin and EGF receptor function, we have developed a system wherein cells containing laminin-binding activity were cloned from a mouse fibroblast cell line (B82L-wt) that cannot adhere to laminin but that have been transfected with the wild-type human EGF receptor. Although only the isolated clones can efficiently attach to laminin-coated plates, all the cells can adhere to plastic, fibronectin, and collagen l, and all exhibit comparable levels of cell surface-associated laminin. Ligand-binding assays showed that the cells with laminin attachment activity possess high-affinity EGF binding (Kd approximately 0.4 nM), and all express a similar level of the human EGF receptor. However, when compared to the B82L-wt cells, the cells with laminin-binding activity exhibit altered morphology, anchorage-independent growth, and motility. Specifically, the morphology of the fibroblasts possessing laminin binding activity appears more elongated and they spread more extensively on plastic plates. Analysis of their growth in soft agar revealed that the clones have a 2-5-fold increase in colony formation in comparison to the B82L-wt cells. The cells possessing laminin attachment ability also exhibit laminin-induced motility, and this movement is directional (chemotaxis) rather than random (chemokinesis), indicating functional laminin receptors and signaling pathways. To examine the specific laminin receptors involved in these effects, the influence of anti-integrin subunit antibodies on cell adhesion and migration was evaluated. These studies showed that an anti-alpha 6 integrin antibody can completely inhibit the clonal cells' attachment and migration to laminin, and anti-alpha 6 immunoblots revealed that only the clones express measurable levels of alpha 6. These data indicate that alpha 6-containing integrins contribute to the laminin-mediated attachment and motility of these clones and that this system may also influence the morphology and anchorage-independent growth of these fibroblasts. In addition, these cells provide a unique system for examining the interaction between EGF and laminin receptor action.