Human fetal neuroblast and neuroblastoma transcriptome analysis confirms neuroblast origin and highlights neuroblastoma candidate genes

BACKGROUND: Neuroblastoma tumor cells are assumed to originate from primitive neuroblasts giving rise to the sympathetic nervous system. Because these precursor cells are not detectable in postnatal life, their transcription profile has remained inaccessible for comparative data mining strategies in neuroblastoma. This study provides the first genome-wide mRNA expression profile of these human fetal sympathetic neuroblasts. To this purpose, small islets of normal neuroblasts were isolated by laser microdissection from human fetal adrenal glands. RESULTS: Expression of catecholamine metabolism genes, and neuronal and neuroendocrine markers in the neuroblasts indicated that the proper cells were microdissected. The similarities in expression profile between normal neuroblasts and malignant neuroblastomas provided strong evidence for the neuroblast origin hypothesis of neuroblastoma. Next, supervised feature selection was used to identify the genes that are differentially expressed in normal neuroblasts versus neuroblastoma tumors. This approach efficiently sifted out genes previously reported in neuroblastoma expression profiling studies; most importantly, it also highlighted a series of genes and pathways previously not mentioned in neuroblastoma biology but that were assumed to be involved in neuroblastoma pathogenesis. CONCLUSION: This unique dataset adds power to ongoing and future gene expression studies in neuroblastoma and will facilitate the identification of molecular targets for novel therapies. In addition, this neuroblast transcriptome resource could prove useful for the further study of human sympathoadrenal biogenesis

Arsenic trioxide-induced neuroblastoma cell death is accompanied by proteolytic activation of nuclear Bax.

Arsenic trioxide (As2O3) is toxic to multidrug-resistant neuroblastoma cells in vivo and in vitro. In neuroblastoma, As2O3 does not exert its cell death-promoting effects via a classical apoptotic pathway. A death mechanism involving proteolytic cleavage of Bax to a p18 form seems to be of importance, because inhibition of Bax cleavage coincides with diminished cell death. As existing models of cell death implicate Bax in the intrinsic apoptotic pathway, triggering death after Bax translocation to the mitochondria, we investigated the cellular localization of p18 Bax by subcellular fractionation. After As2O3 treatment, p18 Bax was only present in nuclei-enriched, mitochondria-depleted fractions. Cytoplasmic p21 Bax levels decreased, whereas total (p21 and p18) nuclear Bax increased. Overexpressed p21 Bax localized to the cytoplasm and nuclei, whereas overexpressed p18 Bax localized to extra-nuclear structures only. The inability of overexpressed p18 Bax to locate to the nucleus, and the As2O3-induced reduction of p21 Bax in the cytosol, suggest an As2O3-induced mechanism where p18 Bax gets cleaved and 'trapped' in the nucleus. This model is strengthened by the observation that calpain, the protease responsible for p18 Bax generation, is present in the nuclei, and that nuclear calpain is induced by increasing As2O3 and Ca2+ levels

HIF-1{alpha} and HIF-2{alpha} Are Differentially Regulated In vivo in Neuroblastoma: High HIF-1{alpha} Correlates Negatively to Advanced Clinical Stage and Tumor Vascularization.

PURPOSE: Hypoxia is considered to be a major driving force behind tumor angiogenesis. The stabilization and activation at hypoxia of the hypoxia-inducible factors HIF-1alpha and HIF-2alpha and the concomitant induction of expression of vascular endothelial growth factor (VEGF) and other proangiogenic factors provide a molecular frame for hypoxia-driven tumor angiogenesis. This study has investigated how HIF and VEGF protein levels relate to each other with regard to vascularization, tumor stage, and overall survival in neuroblastoma. EXPERIMENTAL DESIGN: Tissue cores taken from tumor specimens representing 93 children with neuroblastoma were arranged on a microarray and stained for HIF-1alpha, HIF-2alpha, VEGF, and CD31 proteins. Both fraction of positive cells and staining intensity were evaluated and protein levels were correlated with each other and with clinical variables. RESULTS: Although high levels of both HIF-1alpha (P < 0.001) and HIF-2alpha (P < 0.001) correlated positively to VEGF expression, they did not fully correlate with each other. Moreover, HIF-1alpha (P = 0.002) and VEGF (P < 0.001), but not HIF-2alpha, correlated negatively to vascularization as determined by CD31 staining abundance. VEGF expression or degree of vascularization did not correlate with tumor stage or overall survival. High HIF-1alpha levels correlated with low tumor stage (P < 0.001) and were associated with a favorable patient prognosis (P = 0.08). CONCLUSIONS: The discordant results on expression of HIF-1alpha and HIF-2alpha suggest that these two proteins are differentially regulated in vivo, thus reflecting distinctive protein expression/stabilization mechanisms. The association between HIF-1alpha and favorable outcome stresses the importance of discriminating HIF-2alpha from HIF-1alpha expression and has implications for using HIFs as treatment targets. (Clin Cancer Res 2009;15(23):OF1-7)

High levels of HIF-2alpha highlight an immature neural crest-like neuroblastoma cell cohort located in a perivascular niche.

High HIF-2alpha protein levels in the sympathetic nervous system-derived childhood tumour neuroblastoma as well as immature phenotype correlate to unfavourable outcome. Here we show that a small subset of perivascularly located, strongly HIF-2alpha-positive tumour cells (MYCN amplified) lacks expression of differentiation markers, but expresses neural crest and early sympathetic progenitor marker genes such as Notch-1, HES-1, c-Kit, dHAND, and vimentin. HIF-2alpha- and CD68-positive tumour-associated macrophages were frequently found close to the immature and HIF-2alpha-positive neuroblastoma cells and as VEGF levels are high in the perivascular niche, we hypothesize that neuroblastoma neural crest-like cells and macrophages cooperate to facilitate angiogenesis and thereby contribute to the aggressive neuroblastoma phenotype. Copyright (c) 2008 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd

HIF-1alpha induces MXI1 by alternate promoter usage in human neuroblastoma cells.

Adaptation to low oxygen conditions is essential for maintaining homeostasis and viability in oxygen-consuming multi-cellular tissues, including solid tumors. Central in these processes are the hypoxia-inducible transcription factors, HIF-1 and HIF-2, controlling genes involved in e.g. glucose metabolism and neovascularization. Tumor hypoxia and HIF expression have also been associated with a dedifferentiated phenotype and increased aggressiveness. In this report we show that the MAX interactor-1 (MXI1) gene is directly regulated by HIF proteins in neuroblastoma and breast cancer cells. HIF-binding and transactivation were detected within MXI1 gene regulatory sequences in the vicinity of the MXI1-0 promoter, leading to rapid induction of the alternate MXI1-0 isoform followed by a long-term induction of both the MXI1-0 and MXI1 isoforms. Importantly, knock-down of MXI1 had limited effect on MYC/MYCN activity under hypoxia, an observation that might be related to the different functional attributes of the two MXI1 isoforms

Hypoxic conditions induce a cancer-like phenotype in human breast epithelial cells.

INTRODUCTION: Solid tumors are less oxygenated than their tissue of origin. Low intra-tumor oxygen levels are associated with worse outcome, increased metastatic potential and immature phenotype in breast cancer. We have reported that tumor hypoxia correlates to low differentiation status in breast cancer. Less is known about effects of hypoxia on non-malignant cells. Here we address whether hypoxia influences the differentiation stage of non-malignant breast epithelial cells and potentially have bearing on early stages of tumorigenesis. METHODS: Normal human primary breast epithelial cells and immortalized non-malignant mammary epithelial MCF-10A cells were grown in a three-dimensional overlay culture on laminin-rich extracellular matrix for up to 21 days at normoxic or hypoxic conditions. Acinar morphogenesis and expression of markers of epithelial differentiation and cell polarization were analyzed by immunofluorescence, immunohistochemistry, qPCR and immunoblot. RESULTS: In large ductal carcinoma in situ patient-specimens, we find that epithelial cells with high HIF-1α levels and multiple cell layers away from the vasculature are immature compared to well-oxygenated cells. We show that hypoxic conditions impaired acinar morphogenesis of primary and immortalized breast epithelial cells grown ex vivo on laminin-rich matrix. Normoxic cultures formed polarized acini-like spheres with the anticipated distribution of marker proteins associated with mammary epithelial polarization e.g. α6-integrin, laminin 5 and Human Milk Fat Globule/MUC1. At hypoxia, cells were not polarized and the sub-cellular distribution pattern of the marker proteins rather resembled that reported in vivo in breast cancer. The hypoxic cells remained in a mitotic state, whereas proliferation ceased with acinar morphogenesis at normoxia. We found induced expression of the differentiation repressor ID1 in the undifferentiated hypoxic MCF-10A cell structures. Acinar morphogenesis was associated with global histone deacetylation whereas the hypoxic breast epithelial cells showed sustained global histone acetylation, which is generally associated with active transcription and an undifferentiated proliferative state

HIF-2α Expression Is Suppressed in SCLC Cells, Which Survive in Moderate and Severe Hypoxia When HIF-1α Is Repressed.

Small cell lung carcinoma (SCLC) is extremely aggressive and frequently metastasizes widely in its early stage. Because tumor hypoxia is related to aggressive tumor behavior and the hypoxic adaptation of SCLC is poorly documented, we stained SCLC tumors arranged in a tissue microarray for hypoxia-inducible factor (HIF)-1α and HIF-2α proteins. We found an overall lack of HIF-2α protein expression, which was confirmed in large tumor sections. HIF-1α protein was strongly expressed in most tumors, frequently adjacent to necrotic regions. In concordance, cultured SCLC but not non-small cell lung carcinoma cells showed no or extremely low levels of HIF-2α mRNA and no HIF-2α protein at hypoxia. HIF-1α was stabilized after 4 hours at hypoxia, and its accumulation increased up to 96 hours. SCLC cells survived well and showed net proliferation and low cell death in modest (1% oxygen) and severe (0.1% oxygen) hypoxia. HIF-1α repression virtually did not influence cell death or viability despite reduced levels of hypoxia-inducible genes, such as BNIP3 and BNIP3L. At 1% oxygen no increased autophagy (LC3B-II activation) or NF-κB signaling were detected, whereas the unfolded protein response was activated at severe hypoxia. Our data indicate that HIFs are not exclusively required for SCLC cell survival at modest or severe hypoxia and that additional, yet uncharacterized, hypoxia-driven adaptation pathways may become activated