Neuronal ‘differentiation’ of murine neuroblastoma cells induced by neocarzinostatin: neural cell adhesion molecules

Abstract

Neural crest tumor cells which have been pharmacologically induced in culture to undergo neuronal ‘differentiation’ have been proposed as a model for normal neural crest cell differentiation. We have previously reported that murine neuroblastoma cells treated with the antineoplastic agent neocarzinostatin (NCS) adopt the light microscopic appearance of differentiated neurons. After undergoing morphologic change, the cells no longer divide. As part of an effort to compare the process of differentiation in these cells with what is known about normal neural crest cells, we have examined the cellular distribution and isoform complement of neural cell adhesion molecules (NCAMs) in native and NCS-treated neuroblastoma cells. Our studies show that NCS induces profound changes in NCAM distribution. Immunohistochemical staining indicates that, in contrast to native neuroblastoma cells, more than 80% of treated cells display surface NCAM by 4 days following treatment. Unlike the case for normal neurons, NCAM is uniformly distributed over the treated cell surface. Neuroblastoma cells treated with NCS are more avidly adherent to culture plates coated with NCAM than are control neuroblastoma cells, reflecting the homophilic binding characteristics of NCAM. Interestingly, Western blot analysis for NCAM demonstrates similar total cellular content of a single NCAM species in both control and treated neuroblastoma cells. Furthermore, this 120 kDa mol. wt. NCAM is an isoform of NCAM not found on normally differentiated cerebellar neurons. While the presence of NCAM on these treated murine neuroblastoma cells is evidence for ‘differentiation’ along neuronal lines, the isoform complement and cell surface distribution of NCAM in treated cells are not normal. The change in surface staining for NCAM without a change in the total amount of NCAM suggests a redistribution of NCAM within the cell. This is supported by our finding that, while untreated cells do not stain superficially for NCAM, permeabilization of these cells leads to marked staining, implying that, upon treatment, cytoplasmic NCAM is translocated to the membrane.