Glucocorticoids induce neuroendocrine cell differentiation and increase expression of N-myc in N-type human...

Human neuroblastoma cell lines comprise cellular counterparts of normal differentiation phenotypes arising from the developing neural crest Three distinct cell types have been isolated from cell lines: N-type cells with properties of embryonic sympathoadrenoblasts, S-type cells resembling nonneuronal Schwannian/glial/melanoblastic precursors, and I-type stem cells that can differentiate into either N- or S-type cells. Sympathoadrenoblasts from the normal neural crest further differentiate into neuronal or neuroendocrine cells. In this study, we show that malignant N-type neuroblasts likewise can differentiate futher along these same pathways. Retinoic acid and forskolin induce a neuronalphenotype, denoted morphologically by cell aggregation and increased neurite formation and biochemically by increases in neurofilament proteins, tyrosine hydroxylase, and secretogranin II and decrease inchromogranin A. By contrast, dexamethasone, a synthetic glucocorticoid, induces a chromaffin cell phenotype characterized by increased cell flattening, loss of neuritic processes, increased chromogranin A and tyrosine hydroxylase proteins, and decreased amounts of secretogranin II and neurofilaments. N-myc gene expression is upregulated by glucocorticoids; dexamethasone-treated N-type cells show significant (2.3- to 7.8-fold) increases in N-myc mRNA and protein steady-state levels. This effect is specific for glucocorticosteroids, is blocked by addition of the steroid receptor antagonist RU486, and involves direct activation of the N-myc promoter. These findings are the first to show that glucocorticoids upregulate N-myc expression in human neuroblastoma cells.