Neural cell adhesion molecule (cluster of differentiation 56) in health and disease

Abstract

Cluster of differentiation (CD) 56, a member of the immunoglobulin superfamily, and an isoform of neural cell adhesion molecule (NCAM), was the first cell adhesion molecule to be identified. NCAM (CD56) plays an important role both in human health and in disease. Human NCAM gene is located on chromosome 11q23. CD56 antigen is a 175–185-kD cell surface glycoprotein expressed on all subsets of human natural killer (NK) cells except a small minority of CD56− NK-cell, on subsets of CD4+/CD8+ T-cells, interleukin-2-activated thymocytes, bone marrow macrophages, osteoclasts, and on adrenal gland and neural tissues. NCAM is important in calcium independent cell-cell interactions that mediate homotypic and heterotypic cell-cell and cell-matrix adhesions. At least 27 alternatively spliced NCAM mRNAs are produced giving a wide diversity to NCAM isoforms sharing a similar structural organization. NCAM in the cerebellum and cerebral cortex mediates homophilic adhesion of neural cells, and plays an important role in brain development, emotions, and memory functions. While CD56+ NK-cells play an important role in defense against infections, tumor remission, normal pregnancy and graft rejection. Malignancies expressing CD56 are usually aggressive, with more potential for metastasis and extramedullary/central nervous system involvement, and may respond to new CD56-linked targeted therapies.