| Nectins are a small family of Ca++-independent immunoglobulin (Ig)-like cell adhesion molecules (CAMs) that organize intercellular junctions (1, 2, 3, 4). The Nectin family has at least four members (Nectin-1-4), all of which show alternate splicing, a transmembrane (TM) region (except for Nectin-1gamma), and three extracellular Ig-domains. Nectins are highly homologous to the human receptor for poliovirus, and as such, have been alternatively-named poliovirus receptor-related proteins. They do not, however, appear to bind poliovirus (1). Nectin-3 (also PRR3, CD113 and PVRL3) is an 83kD, type I TM glycoprotein. Its precursor is 549 amino acids (aa) in length. It contains an extended signal sequence of 57 aa, an extracellular domain (ECD) of 347 aa, a transmembrane segment of 21 aa (aa 405-425), and a cytoplasmic region of 124 amino acids. The ECD shows three Ig-like domains, one N-terminal V-type and two membrane-proximal C2-type. The cytoplasmic region shows a Glu-Trp-Tyr-Val motif that binds afadin (3, 5, 6). The ECD of human Nectin-3 is 94% aa identical to mouse Nectin-3 ECD (5, 6). Nectin-3 has a diverse expression pattern. It has been found in junctions between small intestinal columnar epithelial cells (6), pigmented and nonpigmented epithelium in the ciliary body (7), spermatids and Sertoli cells in the seminiferous tubules (8), and on spinal cord motor neurons and axons, plus Schwann cells of the peripheral nervous system (9). As with mouse, human Nectin-3 has three potential isoforms. It does not appear that they are strict orthologs. In addition to the full length isoform, a second human isoform has a 31 aa substitution for the first 54 aa of the signal sequence, followed by a deletion of aa 291-549 (10). The third human isoform shows a 10 aa substitution for aa 357-549 (11). Nectin-3 is proposed to promote cell adhesion by initiating cell-to-cell adhesion, allowing for subsequent JAM and cadherin-based intercellular junction formation. It does so by first forming same cell (cis-) heterodimers with avb3 and PDGFR (an anti-apoptotic interaction) (2, 4). This results in actin reorganization and recruitment of adherens and occludins adhesion molecules. Subsequent Nectin-3 activity adds strength to the junction through trans-interactions with a variety of molecules, including Nectin-3 itself, as well as Nectins-1 and 2 plus Necl-1, 2 and 5 (3, 4). A DNA sequence encoding the extracellular domain of human Nectin-3 (Leu 56-Asp 400, Accession NP_056295) was fused to a six-histidine tag at the C-terminus. The protein was expressed in a mouse myeloma cell line, NS0. Calculated molecular mass of 38.7kD. A minor sequence starting at Gly 58 is also present. As a result of glycosylation, the recombinant monomer migrates as an ~ 66-85kD protein in SDS-PAGE under reducing conditions. Activity: Measured by its ability to bind rhNectin-1. Storage and Stability: Lyophilized and reconstituted products are stable for 6 months after receipt at -20C. Reconstitute with sterile PBS. Aliquot to avoid repeated freezing and thawing. Store at -20C. For maximum recovery of product, centrifuge the original vial after thawing and prior to removing the cap. |
