Characterization of the perturbed differentiation in neuroblastoma, aided by the analysis of normal sympathetic nervous system development

Sammanfattning: Neuroblastoma is a pediatric tumor derived from cells in the sympathetic nervous system. In an attempt to explain the heterogeneous clinical behavior of neuroblastoma tumors, neuroblastomas have been characterized with regard to their degree of sympathetic differentiation. Their expression of genes and proteins that regulate normal sympathetic development and cell cycle/cell death regulators was assessed by in situ hybridization and immunohistochemistry. The cell types of the developing prenatal sympathetic nervous system were also characterized in order to identify marker genes that distinguish between neuronal and neuroendocrine sympathetic cell types. Principally two groups of neuroblastomas have been identified. Unfavorable prognosis, nondifferentiating neuroblastomas expressed marker genes of immature sympathetic neuroblasts. Differentiating neuroblastoma tumors, often with favorable prognosis, also expressed neuronal marker genes, but only in the immature, proliferating cells adjacent to the fibrovascular stroma. With increasing distance from the stroma, these tumor cells cease to proliferate, downregulate their expression of neuronal marker genes, differentiate, and upregulate their expression of neuroendocrine marker genes. Thus, it appears that in these tumors initially neuroblastic cells mature towards a neuroendocrine lineage. Also cell cycle and cell death regulators were expressed in a physiological context resembling normal cellular behavior in these tumors. Proliferating cells expressed Bcl-2. With differentiation, cells downregulate Bcl-2 and upregulate p53. Cells adjacent to the p53 expressing cells die by apoptosis. Karyorrhectic cells, as defined by the mitosis-karyorrhexis index, were identified to be either proliferating or apoptotic. Neuroblastoma cell lines, established from high stage tumors, were analyzed with regard to their inability to respond to nerve growth factor (NGF). These cell lines expressed the high-affinity NGF receptor TrkA and the low-affinity receptor, and yet they did not respond to NGF. By the introduction of exogenous TrkA, NGF-responsiveness was partly restored in these cell lines.