Cells secrete materials into the regions outside the plasma membrane which form extra cellular structures, collectively called the extracellular matrix (ECM) which primarily functions as support to cells1. The ECM also regulates additional functions such as cell division, adhesion, motility, migration and differentiation. Cell adhesion is the binding of cells to ECM and other cells1. The ECM consists of polymeric proteins, glycoproteins and glycosaminoglycans2. Major components of the ECM are laminin, collagen, fibronectin, proteoglycan, and elastin. The cell – matrix adhesion regulates the shape and activity of the cell like cell migration, growth, and differentiation. It also determines 3D organization of tissues during embryonic development3. To perform these functions the cells must be able to interact with the ECM efficiently. Cell-matrix adhesion can occur in two ways; by focal adhesions and hemidesmosomes4. .
These interactions are mediated by cell receptors called integrins. Integrins are a large family of heterodimeric proteins that exist as alpha and beta heterodimers2. 19 alpha and 8 beta integrins have been characterised in mammals5. Integrins can bind to other cells surface integrins and also to substrates like collagen and laminin. Different integrins are specific to their substrates. For example collagen, laminin and fibronectin bind to α2β1, α6β1 and α5β1 respectively. Collagen is the most abundant protein in mammals6. It makes up to about 25 – 35 % of the whole protein content2. It is made up of three polypeptide chains wound into a triple helix2. Laminins are proteins and are a major component of the basal lamina which is a layer of extracellular matrix secreted by the epithelial cells7. They interact with integrin receptors and are so involved in cell-matrix interactions. Fibrinogen is a glycoprotein synthesised in the liver which is involved in blood coagulation.
