Interactions between cells responsible for cell to cell adhesion also can communicate signals into the cellular interior, often involving interactions with cytoskeletal elements to produce changes in cell motility, migration, proliferation and shape. The cadherins are cell surface adhesion molecules that help form tight junctions between cells such as formation of epithelial cell layers. E-cadherin inactivation has been implicated in cancer development. In addition to mediating adhesion with other cells, cadherins transduce signals into cells through interactions with the catenins. Catenins probably affect actin cytoskeletal function through interactions with proteins like actinin and vinculin. Catenins also probably trigger changes in cell shape and motility with signals through the Rho small GTPases. Another important cell adhesion molecule is CD-31, or PECAM-1, involved in the formation of junctions between endothelial cells, cell migration, migration of lymphocytes, and regulation of lymphocyte activation. Src phosphorylates PECAM-1 on tyrosine residues causing SHP-2 association with PECAM-1. Paxillin acts as an adaptor protein between proteins involved in adhesion signaling like FAK and src and cytoskeletal elements. In addition to signals created by adhesion molecules to alter cellular responses, other signaling pathways can alter adhesion through components of the focal adhesion complex.
