Abstract
Earlier reports showed that hyperplasia of sympathoadrenal cell precursors during embryogenesis in Nf1-deficient mice is independent of Nf1's role in down-modulating RAS-MAPK signaling. We demonstrate in zebrafish that nf1 loss leads to aberrant activation of RAS signaling in MYCN-induced neuroblastomas that arise in these precursors, and that the GTPase-activating protein (GAP)-related domain (GRD) is sufficient to suppress the acceleration of neuroblastoma in nf1-deficient fish, but not the hypertrophy of sympathoadrenal cells in nf1 mutant embryos. Thus, even though neuroblastoma is a classical "developmental tumor", NF1 relies on a very different mechanism to suppress malignant transformation than it does to modulate normal neural crest cell growth. We also show marked synergy in tumor cell killing between MEK inhibitors (trametinib) and retinoids (isotretinoin) in primary nf1a-/- zebrafish neuroblastomas. Thus, our model system has considerable translational potential for investigating new strategies to improve the treatment of very high-risk neuroblastomas with aberrant RAS-MAPK activation.
Highlights
Neuroblastoma, a malignant embryonic tumor of childhood, arises in neural crest-derived dopaminergic neuroblasts that generate the peripheral sympathetic nervous system (PSNS)
We show that the very aggressive growth properties of MYCN-induced neuroblastomas with loss of nf1 are due to aberrant activation of RAS signaling, because the increased penetrance and rapid growth could be suppressed by overexpressing the intact NF1 GTPase-activating protein-related domain (GRD) domain
We use a zebrafish model to demonstrate that NF1 loss can potentiate the tumorigenic effects of MYCN-overexpression in high-risk neuroblastoma
Summary
Neuroblastoma, a malignant embryonic tumor of childhood, arises in neural crest-derived dopaminergic neuroblasts that generate the peripheral sympathetic nervous system (PSNS). These experiments show that NF1 uses different domains and signalling pathways to regulate the normal development of part of the nervous system and to prevent formation of neuroblastoma These engineered zebrafish represent an animal model of neuroblastoma that mimics the human disease in many ways. Studies showed identical or only modestly elevated RAS-GTP levels in NF1-deficient human neuroblastoma cells, in contrast to highly elevated RAS-GTP levels in NF1-deficient Schwannoma tumor cells (Johnson et al, 1993; The et al, 1993) These results, coupled with the numerous mutations of NF1 that cause the disease neurofibromatosis type 1, but do not appear to affect protein stability or GAP function (Abernathy et al, 1997; Fahsold et al, 2000), argue that functional domains outside the GRD may mediate important aspects of neurofibromin function in neuroblastoma tumor suppression. The wild-type GRD domain failed to rescue the hypertrophy of sympathoadrenal cells in nf mutant embryos, indicating that the role of NF1 in suppressing neuroblastoma tumorigenesis differs from the mechanism that prevents PSNS hyperplasia during normal development
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