Title: Interaction of plasma membrane fibronectin receptor with talin—a transmembrane linkage
Abstract: Many observations suggest the presence of transmembrane linkages between the cytoskeleton and the extracellular matrix. In fibroblasts both light and electron microscopic observations reveal a co-alignment between actin filaments at the cell surface and extracellular fibronectin1–3. These associations are seen at sites of cell matrix interaction, frequently along stress fibres and sometimes where these bundles of microfilaments terminate at adhesion plaques (focal contacts). Non-morphological evidence also indicates a functional linkage between the cytoskeleton and extracellular matrix. Addition of fibronectin to transformed cells induces flattening of the cells and a reorganization of the actin cytoskeleton, with the concomitant appearance of arrays of stress fibres4–6. Conversely, disruption of the actin cytoskeleton by treatment with cytochalasin B leads to release of fibronectin from the cell surface7. As yet, there is no detailed knowledge of the molecules involved in this transmembrane linkage, although several proteins have been suggested as candidates in the chain of attachment between bundles of actin filaments and the cytoplasmic face of the plasma membrane: these include vinculin8, α-actinin9 and talin10, each one having been identified at regions where bundles of actin filaments interact with the plasma membrane and underlying cell-surface fibronectin10–13. Recently, the cell-substrate attachment (CSAT) antigen14 has been identified as a plasma membrane receptor for fibronectin15, raising the possibility that this glycoprotein complex may serve as a bridge between fibronectin and one or more of the underlying cytoskeletal components mentioned. Here we have investigated the interaction of the purified CSAT antigen with these cytoskeletal components, and we demonstrate an interaction specifically between the CSAT antigen and talin.