HUMAN NEUROBLASTOMA CELL TRANSDIFFERENTIATION: BIOCHEMICAL CHARACTERISTICS OF CLONED CELL VARIANTS

Neuroblastomas are tumors of neural crest origin which histologically may exhibit multiple cellular phenotypes. Many neuroblastoma cell lines comprise morphologically distinct but karyotypically identical types of cells. One cell type (N) is neuroblastic and poorly substrate-attached whereas the other cell type (S) is large, flat and strongly adherent. N and S cells can undergo bidirectional, morphological interconversion. Biochemical studies have shown that N-type cells from the cell line SK-N-SH express activities for neurotransmitter enzymes whereas S counterparts do not. By contrast, the S cells express tyrosinase, a melanocyte marker. This morphological and biochemical interconversion between two phenotypes is termed transdifferentiation. A third cell type observed in several neuroblastoma cell lines has a morphology intermediate between that of the N and S cells and is termed I. To further characterize these three cell types, N, S and I cells from six human neuroblastoma cell lines were analyzed for expression of phenotypic marker enzymes, intermediate filament proteins, fibronectin, EGF receptor and N-myc. N cells have properties of neuroblastic cells, as indicated by their morphology, neurotransmitter-synthesizing enzyme activity, norepinephrine uptake, and expression of neurofilament proteins. S cells may represent one or more non-neuronal neural crest derivatives, e.g., Schwann cells, melanocytes, or mesectodermal cells, as indicated by their lack of neurotransmitter enzymes, and their expression of vimentin, fibronectin, and tyrosinase activity. I cells express both vimentin and neurofilament proteins and thus share properties of both N and S cells. I cells may be pluripotent stem cells capable of differentiating either into neuroblasts or other neural crest derivatives. Alternatively, the I cells may represent a transitional form in the N and S transdifferentiation process. N and S cells may be regulated by different control mechanisms as indicated by their differential expression of EGF receptor and by possible differences in N-myc expression. Several conclusions can be drawn. First, the occurrence of N, S and I cell types is prevalent among neuroblastoma cell lines. Second, human neuroblastoma cells may undergo transdifferentiation between two neuroectodermal differentiation programs. This phenotypic interconversion in culture may reflect the cellular heterogeneity observed in neuroblastoma tumors. The capacity of human neuroblastoma cells to undergo phenotypic interconversion in culture may be closely linked to the ability of some tumors to undergo differentiation and spontaneous regression in the patient