The large cytoplasmic domain is not required for concentration of N-CAM at cell-cell contacts in transfected mouse neuroblastoma cells

The neural cell adhesion molecule NCAM regulates neuritogenesis by multiple mechanisms of interaction

The neural cell adhesion molecule NCAM and its glycosylation with polysialic acid (polySia) are crucially involved in proliferation, migration and differentiation of neural progenitors. Modification with polySia, homophilic and heterophilic interactions set the function of NCAM, but little is known on their interplay. We have shown recently that removal of polySia induces neuronal differentiation via heterophilic NCAM interactions at cell contacts between SH-SY5Y neuroblastoma cells. Here we analyze the additional impact of NCAM-positive fibroblasts as a ligand-presenting cellular environment, a model often used to demonstrate the neuritogenic effect of homophilic NCAM interactions. Native SH-SY5Y cells did not respond to interactions with fibroblast NCAM. However, after induction of neuronal differentiation by retinoic acid the previously ineffective NCAM signals activated extracellular signal-regulated kinase (ERK) and promoted neuritogenesis. Removal of polySia increased neuritogenesis in retinoic acid-treated cells additive to the NCAM substrate effect. The change in responsiveness to substrate NCAM was associated with a rearrangement of polysialylated NCAM away from its enrichment at homotypic cell-cell contacts and with the appearance of non-polysialylated NCAM, i.e. changes facilitating NCAM interactions with the substrate. Thus, heterophilic and homophilic NCAM interactions are integrated into the cell's response yet they have the capacity to independently trigger neuritogenesis. The actual occurrence of each of these interactions, however, depends on the cellular context, targeted cell surface presentation of NCAM and the dynamic regulation of its modification by polysialic acid. In summary, this study reveals how the complex interplay of NCAM interactions and polysialylation provides an elaborate system to regulate neuritogenesis.

Nerve cell adhesion molecule expression in squamous cell carcinoma of the head and neck: a predictor of propensity toward perineural spread

OBJECTIVE

To evaluate head and neck squamous cell carcinomas (SCCAs) for the expression of nerve cell adhesion molecule (N-CAM). We propose that expression of N-CAM by tumor cells may be associated with perineural invasion in SCCA of the head and neck.

METHODS

Seventy-six archived specimens of histologically proven SCCA were analyzed by immunohistochemistry for the expression of N-CAM. Positive and negative controls were used to assess staining. Two sections of each specimen were reviewed for the presence of perineural invasion. A retrospective chart review was performed for each patient that corresponded to the above specimens.

RESULTS

Perineural invasion was present in 28 (37%) of the 76 patients evaluated for the expression of N-CAM. N-CAM expression was demonstrated in 38 (50%) of the 76 specimens. The incidence of N-CAM expression was significantly associated with perineural invasion (P = .002). There was no significant association between the presence of staining or the presence of perineural invasion and the incidence of locoregional recurrence, distant metastasis, or survival status; however, the mean follow-up was only 13.6 months (range, 1-49 mo).

CONCLUSION

There is a positive correlation between the presence of N-CAM expression and perineural invasion in SCCA of the head and neck. The expression of this adhesion molecule by tumor cells may facilitate both homophilic cell-to-cell and heterophilic cell-to-substrate adhesion, thereby enabling the tumor cells to use the perineural tissues or neural cells, or both as a conduit for perineural spread.

Intracellular signaling is changed after clustering of the neural cell adhesion molecules axonin-1 and NgCAM during neurite fasciculation

Neural cell adhesion molecules of the immunoglobulin/fibronectin type III family on axons have been implicated in promotion of neurite outgrowth, fasciculation, and the mediation of specific cell adhesion. The present study demonstrates that two of these molecules on dorsal root ganglion neurons are associated with distinct protein kinases, axonin-1 with the src-related nonreceptor tyrosine kinase fyn and NgCAM with a casein kinase II-related activity and a serine/ threonine kinase related to S6 kinase. When neurites grew without contacts involving axonin-1 and NgCAM, strong fyn kinase activity was associated with axonin-1, whereas the NgCAM-associated kinase activities were low. Clustering of axonin-1 with NgCAM induced by the formation of cell-cell contacts correlated with a reduction of the axonin-1-associated fyn activity and an increased phosphorylation of NgCAM by the associated casein kinase II-related activity. Thus, axonin-1 and NgCAM trigger distinctive intracellular signals during in vitro differentiation depending on their state of association.

Integrity of the homophilic binding site is required for the preferential localization of NCAM in intercellular contacts

The neural cell adhesion molecule NCAM is a member of the immunoglobulin (Ig) superfamily. NCAM can undergo homophilic binding and heterophilic interactions with cell surface components and is often concentrated at sites of intercellular contact. To investigate the molecular basis of this biased surface distribution, we examined L cell transfectants expressing wild-type or mutant forms of chick NCAM-140 by laser scanning confocal microscopy. Mutant NCAMs that lacked Ig-like domains 1, 2, 4, or 5 were preferentially localized in contact regions. However, the relative concentration of these mutant NCAMs in contact sites was substantially reduced compared with wild-type NCAM. In contrast, NCAM redistribution to intercellular contacts was abolished in cells expressing mutant NCAMs that either lacked Ig-like domain 3 or contained mutations in the homophilic binding site in this domain. In heterotypic contacts between PC12 cells and L cell transfectants, colocalization of rat NCAM and chick NCAM was again dependent on the integrity of the homophilic binding site of the NCAM expressed on L cells. These results provide evidence that homophilic binding is the main mechanism by which NCAM becomes redistributed to intercellular contacts. They also implicate a role for other Ig-like domains in the accumulation of NCAM at cell-cell contacts.

Solid-phase binding analysis of N-CAM interactions with brain fodrin

The large cytoplasmic domain form of the neural cell adhesion molecule N-CAM has been reported to interact specifically with fodrin, a submembranous cytoskeletal protein. We tested the abilities of fodrins from bovine brain and embryonic chicken brain to bind to N-CAM that had been isolated from differentiated or undifferentiated mouse N2A neuroblastoma cells or from the brains of embryonic day 11 or day 14 chickens. Labeled fodrin samples bound with immobilized fodrin at a minimum soluble fodrin concentration of 2.5 x 10(-8) M, but the labeled fodrin did not bind to the immobilized N-CAM when incubated at 20-fold higher fodrin concentrations.