Encyclopedia of Signaling Molecules

2018 Edition
| Editors: Sangdun Choi


Reference work entry
DOI: https://doi.org/10.1007/978-3-319-67199-4_429


 CD56;  D2;  N-CAM;  NCAM

Historical Background

Cell–cell interactions via cell adhesion are the basis for the evolution of all multicellular organisms. The first experiments to understand cell adhesion were performed at the beginning of the last century by Wilson (1907), who dissociated sponges and allowed them to fuse and to reconstitute. Fifty years later, Townes and Holtfreter (1955) demonstrated that dissociated cells from amphibian embryos adhere to form random aggregates of their origin, with ectoderm forming an outer surface layer, endoderm forming a compact central ball, and mesoderm producing a loose array of cells. In 1963, Roger Sperry (1963) proposed that different cells bear distinct cell surface proteins that serve as markers or tags. One of these markers, the Neural Cell Adhesion Molecule (NCAM) was first described in 1974 by Elizabeth Bock (Jacque et al. 1974) and designated as D2 antigen. Three years later, the group of Edelman (Thiery et al. 1977) approved that NCAM mediates cell–cell adhesion and established it as one of the first cell adhesion molecules. When NCAM was sequenced and cloned during the mid-1980s, it became obvious that NCAM belongs to the immunoglobulin superfamily (Barthels et al. 1987) and that NCAM is not only responsible for static adhesion, but also transmits signals across the cell membrane. With the help of transgenic knockout techniques, Cremer and colleagues could demonstrate 1994 (Cremer et al. 1994) that NCAM is involved in learning and memory.

Structure and Function

NCAM is a glycoprotein belonging to the immunoglobulin superfamily. All members of this protein superfamily have in common the presence of at least one immunoglobulin-like domain, which received their name from immunoglobulins (antibodies). There are more than 750 proteins known with immunoglobulin-like domains. An immunoglobulin-like domain usually consists of 70–110 amino acids with a defined secondary structure including one disulfide bridge. NCAM consists of five immunoglobulin domains in its extracellular domain. Furthermore NCAM has two membrane proximal fibronectin type III (F3) homologous repeats. There exist three major isoforms of NCAM, which are generated by alternative splicing from one single gene (Barbas et al. 1988). The isoforms are named according their apparent molecular weight as NCAM120 (gylcosylphosphatidyl inositol anchor = GPI-anchored) or NCAM140 and NCAM180 (transmembrane-anchored). NCAM140 and NCAM180 differ in the intracellular domain in that NCAM180 has an additional insert of 267 amino acids (see Fig. 1). Although identified in the nervous system, NCAM is expressed in many other cell types or tissues, such as muscle cells or immune cells. This is underlined by the fact that NCAM corresponds to CD56 and is a marker of natural killer cells.
NCAM1, Fig. 1

Schematic representation of the three major isoforms of NCAM

NCAM mediates preferentially homophilic NCAM–NCAM interactions, which are Ca2+-independent. The homophilic NCAM–NCAM interactions mediate adhesion between neurons and neurons, neurons and glia cells, and between glia cells and glia cells. NCAM140 is known to be responsible for the fasciculation of axons or neurites and for promotion of axonal regeneration after injury. NCAM-deficient mice have defects in learning and memory and have a smaller brain compared to wild-type animals. Furthermore, the nervous system–specific NCAM180 is thought to stabilize cell–cell contacts at synapses. A recent model of NCAM–NCAM interaction suggests that two NCAMs form dimers on the cell curface (cis-interaction) and that these dimers bind to existing dimers on opposing cells (trans-interaction) via their Ig-domains 2 and 3 in antiparallel orientation (“zipper”-like) (Soroka et al. 2003).

Posttranslational Modification

NCAM is notable for several posttranslational modifications. Like many other proteins involved in signal transduction, NCAM was demonstrated to be phosphorylated. NCAM contains numerous (depending on its isoform) potential phosphorylation sites on Serine or Threonine residues but only one on a Thyrosine residue. In addition, NCAM has five N-glycosylation sites and nearly 30% of its apparent molecular weight is represented by glycans. It is of special interest that NCAM bears a very unique type of glycosylation, namely, polysialylation (Finne et al. 1983). Polysialylation is characterized by the presence of up to 150 monomers of sialic acid on the outer chains of the N-glycans of the fifth immunoglobulin-like domain (see Fig. 2). Polysialylation on NCAM represents more than 95% of all polysialylation of a specific organism. The addition of polysialic acids introduce one negative charge per sialic acid and alter dramatically the function of NCAM. Polysialylated NCAM is much less adhesive compared to non-polysialylated NCAM. The expression of polysialic acid is strongly regulated. It is high during development and drops during lifetime. Adult mammals (including humans) express high levels of polysialylated NCAM only at sites of plasticity, such as hippocampus, the place of learning and memory.
NCAM1, Fig. 2

Polysialylation of NCAM. Note that polysialylation of NCAM results in the introduction of more than 100 negatively charged sialic acids on a classical Aspargine-linked glycan structure

Please note that there are several and sometimes confusing abbreviations for polysialic acid or polysialylated NCAM used in the literature (PSA = polysialic acid; E-NCAM = embryonic NCAM; polySia = polysialic acid).


The last two decades of research on NCAM-mediated signal transduction focuses mainly on NCAM-mediated promotion of neurite outgrowth, which will be discussed in the following. One central pathway of the NCAM-mediated signal transduction is the mitogen-activated protein kinase pathway (MAPK pathway). The MAPK pathway can be activated by two mechanisms: First, via the Fibroblast Growth Factor Receptor (FGF-receptor) (Doherty and Walsh 1996) and second via non-receptor kinases such as FAK and Fyn (Beggs et al. 1997).

The Mitogen-Activated Protein Kinase Pathway

It has been demonstrated that NCAM interacts directly with the FGF-receptor on one cell membrane (cis-interaction) via the F3 modules 1 and 2 (Kiselyov et al. 2003). NCAM binding is capable of activating the FGF-receptor upon NCAM–NCAM interaction. The FGF-receptor activation leads to recruitment of the adaptor proteins Shc and Grb-2, which then activate Ras as key enzyme of the MAPK pathway. Final target of the MAPK pathway is the transcription factor  CREB (Jessen et al. 2001), which activates transcription of genes, which are responsible for neurite outgrowth. The NCAM-mediated FGF-receptor activation and neurite outgrowth can be inhibited by ATP, which could be explained by an overlapping ATP and FGF-receptor binding sites in the second F3 module of NCAM (Skladchikova et al. 1999). However, the also close polysialylation at the Ig module 5 of NCAM is essential for NCAM-dependent neurite outgrowth (Doherty et al. 1990). Another possibility to activate the MAPK pathway is via the recruitment of the non-receptor kinases FAK and Fyn. It has been demonstrated in several studies that NCAM is also associated with the receptor protein tyrosine phosphatase-alpha (RPTP-alpha). NCAM–NACM interaction leads to the activation of RPTP-alpha and to recruitment of Fyn and FAK, which then are responsible for further activation of the MAPK pathway (see Fig. 3).
NCAM1, Fig. 3

Simplified scheme of the NCAM-mediated signal transduction (For details see text or for review see Maness and Schachner (2007))

Phospholipase C and Calcium

NCAM-mediated signaling has been demonstrated to involve an increase in intracellular Ca2+-concentration (Kolkova et al. 2000). Several studies suggested that phospholipase Cγ (PLCγ) is responsible for the NCAM-mediated increase in Ca2+-concentration. Upon NCAM–NCAM interaction, PLCγ cleaves PIP2 into inositol trisphosphate (IP3) and diacylglycerol (DAG).  IP3 Receptors binds to its intracellular receptor at the ER-membrane and releases Ca2+ from the ER store. Furthermore  arachidonic acid (AA) might be released from DAG by the DAG lipase, which further activates Ca2+-channels at the plasma membrane. All this leads to an increase of intracellular Ca2+. The increased Ca2+ binds to calmodulin and this leads to the activation of the Ca2+-calmodulin-dependent protein kinase II. Ca2+-calmodulin-dependent protein kinase II phosphorylates several target proteins, which are involved in neurite outgrowth (see Fig. 3).

Cyclic Adenosine Monophosphate and Cyclic Guanosine Monophosphate

The involvement of the two second messengers cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) in NCAM signaling has been demonstrated in several studies by the use of specific inhibitors (Shimomura et al. 1998). However, the exact role of the respective heterotrimeric G-proteins (in the case of cAMP) or nitric oxid synthases (in the case of cGMP) is not clear yet.


NCAM may transmit signals into the cell by several mechanisms. This is, like in many other cases, a complex network of signal transduction pathways. The MAPK pathway seems to be very crucial for NCAM-mediated signal transduction. However, little is known about relative roles of the individual players and further research is necessary to elucidate the total network of NCAM signaling.


  1. Barbas JA, Chaix JC, Steinmetz M, Goridis C. Differential splicing and alternative polyadenylation generates distinct N-CAM transcripts and proteins in the mouse. EMBO J. 1988;7:625–32.PubMedPubMedCentralGoogle Scholar
  2. Barthels D, Santoni MJ, Wille W, Ruppert C, Chaix JC, Hirsch MR, Fontecilla-Camps JC, Goridis C. Isolation and nucleotide sequence of mouse NCAM cDNA that codes for a Mr 79,000 polypeptide without a membrane-spanning region. EMBO J. 1987;6:907–14.PubMedPubMedCentralGoogle Scholar
  3. Beggs HE, Baragona SC, Hemperly JJ, Maness PF. NCAM140 interacts with the focal adhesion kinase p125(fak) and the SRC-related tyrosine kinase p59(fyn). J Biol Chem. 1997;272:8310–9.PubMedCrossRefGoogle Scholar
  4. Cremer H, Lange R, Christoph A, Plomann M, Vopper G, Roes J, Brown R, Baldwin S, Kraemer P, Scheff S, et al. Inactivation of the N-CAM gene in mice results in size reduction of the olfactory bulb and deficits in spatial learning. Nature. 1994;367:455–9.PubMedCrossRefGoogle Scholar
  5. Doherty P, Walsh FS. CAM-FGF receptor interactions: a model for axonal growth. Mol Cell Neurosci. 1996;8:99–111.CrossRefGoogle Scholar
  6. Doherty P, Cohen J, Walsh FS. Neurite outgrowth in response to transfected N-CAM changes during development and is modulated by polysialic acid. Neuron. 1990;5(2):209–19.PubMedCrossRefGoogle Scholar
  7. Finne J, Finne U, Deagostini-Bazin H, Goridis C. Occurrence of alpha 2–8 linked polysialosyl units in a neural cell adhesion molecule. Biochem Biophys Res Commun. 1983;112:482–7.PubMedCrossRefGoogle Scholar
  8. Jacque CM, Jorgensen OS, Bock E. Quantitative studies on the brain specific antigens S-100, GFA, 14-3-2, D1, D2, D3 and C1 in Quaking mouse. FEBS Lett. 1974;49:264–6.PubMedCrossRefGoogle Scholar
  9. Jessen U, Novitskaya V, Pedersen N, Serup P, Berezin V, Bock E. The transcription factors CREB and c-Fos play key roles in NCAM-mediated neuritogenesis in PC12-E2 cells. J Neurochem. 2001;79:1149–60.PubMedCrossRefGoogle Scholar
  10. Kiselyov VV, Skladchikova G, Hinsby AM, Jensen PH, Kulahin N, Soroka V, Pedersen N, Tsetlin V, Poulsen FM, Berezin V, Bock E. Structural basis for a direct interaction between FGFR1 and NCAM and evidence for a regulatory role of ATP. Structure. 2003;11(6):691–701.PubMedCrossRefGoogle Scholar
  11. Kolkova K, Novitskaya V, Pedersen N, Berezin V, Bock E. Neural cell adhesion molecule-stimulated neurite outgrowth depends on activation of protein kinase C and the Ras-mitogen-activated protein kinase pathway. J Neurosci. 2000;20:2238–46.PubMedGoogle Scholar
  12. Maness PF, Schachner M. Neural recognition molecules of the immunoglobulin superfamily: signaling transducers of axon guidance and neuronal migration. Nat Neurosci. 2007;10:19–26.PubMedCrossRefGoogle Scholar
  13. Shimomura A, Okamoto Y, Hirata Y, Kobayashi M, Kawakami K, Kiuchi K, Wakabayashi T, Hagiwara M. Dominant negative ATF1 blocks cyclic AMP-induced neurite outgrowth in PC12D cells. J Neurochem. 1998;70:1029–34.PubMedCrossRefGoogle Scholar
  14. Skladchikova G, Ronn LC, Berezin V, Bock E. Extracellular adenosine triphosphate affects neural cell adhesion molecule (NCAM)-mediated cell adhesion and neurite outgrowth. J Neurosci Res. 1999;57(2):207–18.PubMedCrossRefGoogle Scholar
  15. Soroka V, Kolkova K, Kastrup JS, Diederichs K, Breed J, Kiselyov VV, Poulsen FM, Larsen IK, Welte W, Berezin V, Bock E, Kasper C. Structure and interactions of NCAM Ig1-2-3 suggest a novel zipper mechanism for homophilic adhesion. Structure. 2003;11:1291–301.PubMedCrossRefGoogle Scholar
  16. Sperry RW. Chemoaffinity in the orderly growth of nerve fiber patterns and connections. Proc Natl Acad Sci U S A. 1963;50:703–10.PubMedPubMedCentralCrossRefGoogle Scholar
  17. Thiery JP, Brackenbury R, Rutishauser U, Edelman GM. Adhesion among neural cells of the chick embryo. II. Purification and characterization of a cell adhesion molecule from neural retina. J Biol Chem. 1977;252:6841–5.PubMedGoogle Scholar
  18. Townes PL, Holtfreter J. Directed movements and selective adhesion of embryonic amphibian cells. J Exp Zool. 1955;128:53–120.CrossRefGoogle Scholar
  19. Wilson HVP. On some phenomena of coalescence and regeneration in sponges. J Exp Zool. 1907;5:245–58.CrossRefGoogle Scholar

Copyright information

© Springer International Publishing AG 2018

Authors and Affiliations

  • Rüdiger Horstkorte
    • 1
  • Bettina Büttner
    • 1
  • Kaya Bork
    • 1
  1. 1.Institute for Physiological ChemistryMartin-Luther-University Halle-WittenbergHalle (Saale)Germany