Modular domains of focal adhesion-associated proteins.

Abstract

Attachment of cells to the extracellular matrix is mediated by structures called “focal adhesions.” Focal adhesions can be readily visualized by reflection contrast microscopy in cells grown in culture either on plastic or a defined extracellular matrix (ECM; e.g., fibronectin, collagen), appearing as spear tip-like structures connecting the extracellular matrix with the ventral plasma membrane (Jockusch et al. 1995). The cytoplasmic face of such structures is decorated with the termini of numerous actin stress filaments, indicating a direct linkage with the actin cytoskeletal network. Focal adhesions not only provide the cell with a point of adhesive contact with the extracellular matrix, but also function to mediate signals that regulate cell growth, migration and apoptosis (Burridge and Chrzanowska-Wodnicka 1996; Hynes 1992; Jockusch et al. 1995). The regulated assembly of focal adhesions at the leading edge of the cell is a central step in cell migration and more specialized processes such as axonal growth (Hynes 1992; Lauffenberger and Horwitz 1996). Loss of adhesion to the ECM can lead to cell cycle arrest or in some cells the induction of programmed cell death (Rouslahti and Reed 1994). Thus, adhesive interactions with the ECM play a critical role in regulating a variety of intracellular signaling pathways.