Nectins are type I transmembrane glycoproteins that are calcium-independent immunoglobulin (Ig)-like cell adhesion molecules (CAMs). Homology has led to their designation as poliovirus receptor-related (PRR) proteins, but nectins do not bind poliovirus. The extracellular domains of the nectin family form cis-homodimers (same cell), followed by homophilic or heterophilic trans-dimers (across cells) that organize intercellular junctions. Nectin-1, also known as CD111, PRR1 and herpes virus entry mediator C (HVEC) has a secreted splice variant. Nectin-1, Nectin-2 (CD112, PRR2, HVEB) and Nectin-3 (PRR3) are concentrated in adherens junctions and exist on neurons, endothelial cells, epithelial cells and fibroblasts.
Nectin-4 is a type I transmembrane glycoprotein belonging to the Nectin family of Ig superfamily proteins. It is both a homophilic and heterophilic (with Nectin-1) cell adhesion molecule that is expressed in the placenta, the embryo, and in breast carcinoma. A soluble form of Nectin-4 is generated from the membrane protein via the action of TACE/ADAM-17.