An analysis of growth and differentiation of human neuroblastoma, identification of HMG-CoA reductase and a novel zinc finger gene as potential mediators

grantor: University of TorontoSeveral biological and clinical features of neuroblastoma suggest that this neural crest derived tumor retains the potential for further differentiation. Delineating these events may provide insights for eventual clinical management of this chemorefractory disease. The NUB-7 human neuroblastoma derived cell line, established in our laboratory, uniquely displayed features of both primitive neuronal and Schwannian cells and was further inducible along both cell lineages with dibutyryl cyclic AMP and retinoic acid respectively. This differentiation potential mimics the in vivo differentiation patterns of neuroblastoma. Using the novel molecular technique of differential display, we identified 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase and a novel zinc finger gene as potential differentiation responsive genes in NUB-7. HMG-CoA reductase functions as the rate limiting enzyme of the mevalonate pathway involved in de novo cholesterol synthesis and cell cycle progression. Its expression and modulation during neuroblastoma induced differentiation implicated HMG-CoA reductase as a key regulator of neuroblastoma growth and a mediator of the biological effects of retinoic acid. Lovastatin, a non-reversible competitive inhibitor of HMG-CoA reductase induced marked cytotoxicity in neuroblastoma cell lines expressing P-glycoprotein, a well recognized drug efflux pump involved in chemoresistance. Moreover, this cytotoxicity was enhanced by the addition of dibutyryl cyclic AMP but not retinoic acid. These observations support the possible clinical utility of HMG-CoA reductase inhibitors in combination with differentiating agents in the treatment of neuroblastoma. A second novel clone, designated zf5-3, was localized to chromosome 19 and possessed 4 zinc finger DNA binding motifs characteristic of a wide variety of transcriptional regulators. The expression of zf5-3 was restricted to fetal neuronal, hepatic and renal tissues and their tumor derived cell lines. The expression of zf5-3 was downregulated during nervous tissue maturation as well as induced neuronal maturation of various neuroblastoma cell lines. These observations implicate zf5-3 as a potential mediator of differentiation in fetal neuronal tissues and their derived tumors including neuroblastoma through the maintenance of the undifferentiated state.Ph.D