The cell adhesion molecules (CAMs) are Glycoproteins present on the external surface of the cell membrane. They recognize and interact either with other CAMs on adjacent cells or with the proteins of the extra–cellular matrix (ECM). These cell adhesion molecules play significant role in the process of development, morphogenesis, maintenance and regeneration of the form, structure and the organization of the organisms. Based on various criteria there are a number of classifications of CAMs. More recently they have been grouped into five super–families, which contain a number of smaller sub–families. The super–families include the cadherins, integrins, selectins, immunoglobulins and proteoglycans (including the syndecan sub–family of the adhesion molecules). There is an evidence of E–cadherin expression even at the one–cell stage of embryogenesis and its influence increases with cell compaction at the 8–16 cell stage. Implantation of the embryo in the uterine epithelium involves both E– and P–cadherins. Integrins participate in both Cell–matrix and cell–cell adhesion in a wide variety of physiologically important processes such as haemostasis and wound healing. Syndecans can mediate the activity of the ligands and enable the cells to become more or less responsive to their micro environment by binding to extra–cellular ligands. Although the immunoglobulins are able to bind to cells, their main role appears to be in the immune and inflammatory responses rather than the maintenance and regulation of the structural components of tissues and organs. CAMs also play a role in establishment of the blood– brain barrier and facilitate its penetration by immune cells. Selectins and integrins are the most important cell adhesion molecules in this process. It is now well established that alterations in the expression and function of cell-cell and cell-matrix adhesion molecules correlate with the progression to tumour malignancy. Functional experiments with cultured tumour cells and transgenic mouse models have indicated that the loss of the cell adhesion molecule E-cadherin is causally involved in the formation of epithelial cancers and carcinomas. Altered expression of integrins is correlated with several causes of infertility. Null mutations of several integrins leads to peri-implantation lethality and functional blockade of selected integrins reduces the number of implantation sites. E-selectins are synthesized only when they are required. They are involved in recruiting leukocytes such as neutrophils and macrophages to the inflammation sites. Gicerin is a novel cell adhesion molecule in the immunoglobulin super family and has both homophilic and heterophilic adhesive activity to neurite outgrowth factor (NOF), an extracellular matrix protein in the laminin family. Gicerin might play a role in oviductal development and regeneration and also in the metastasis of adenocarcinomas. Syndecans are involved in the maintenance of cell morphology. If syndecans are not expressed in epithelial cell, then the cells become rounded in shape.
Cell adhesion molecules (CAMs), cadherin, integrin, selectin, immunoglobulin, syndecan
