Identification of Nck family genes, chromosomal localization, expression, and signaling specificity

Already a dozen molecules share binding to the Src homology (SH) 3 domains of human Nck, an SH3-SH3-SH3-SH2 adapter protein. We reason that there may be multiple gene members of Nck to accommodate the large binding repertoires. Here we report identification of novel human and mouse Nck genes and rename them as the Nck alpha and Nck beta genes (including the human Nck alpha, human Nck beta, mouse Nck alpha, and mouse Nck beta genes). Nck alpha and Nck beta share 68% amino acid identity, whereas the two Nck alpha and two Nck beta across the species show 96% identity to each other. The human Nck beta gene is mapped to 2q12, whereas the human Nck alpha gene has previously been mapped at 3q21. Antibodies specifically against Nck alpha and Nck beta detect Nck alpha and Nck beta with an identical molecular mass in the same cells of various origins. Ectopically expressed Nck beta, but not its SH2 domain mutant, strongly inhibits epidermal growth factor- and platelet-derived growth factor-stimulated DNA synthesis. Consistently, epidermal growth factor receptor and platelet-derived growth factor receptor preferentially interact with Nck beta over Nck alpha in vitro. This study indicates that Nck is a multiple gene family and that each gene may have its own signaling specificity. Because previous anti-Nck (human Nck alpha) antibodies cross-react with Nck beta, reassessment of those studies with specific Nck genes would be necessary.