Hypoxia alters gene expression in human neuroblastoma cells toward an immature and neural crest-like phenotype

Abstract

Insufficient oxygen and nutrient supply often restrain solid tumor growth, and the hypoxia-inducible factors (HIF) 1␣ and HIF-2␣ are key transcription regulators of phenotypic adaptation to low oxygen levels. Moreover, mouse gene disruption studies have implicated HIF-2␣ in embryonic regulation of tyrosine hydroxylase, a hallmark gene of the sympathetic nervous system. Neuroblastoma tumors originate from immature sympathetic cells, and therefore we investigated the effect of hypoxia on the differentiation status of human neuroblastoma cells. Hypoxia stabilized HIF-1␣ and HIF-2␣ proteins and activated the expression of known hypoxia-induced genes, such as vascular endothelial growth factor and tyrosine hydroxylase. These changes in gene expression also occurred in hypoxic regions of experimental neuroblastoma xenografts grown in mice. In contrast, hypoxia decreased the expression of several neuronal͞neuroendocrine marker genes but induced genes expressed in neural crest sympathetic progenitors, for instance c-kit and Notch-1. Thus, hypoxia apparently causes dedifferentiation both in vitro and in vivo. These findings suggest a novel mechanism for selection of highly malignant tumor cells with stem-cell characteristics.

Cellular differentiation determines the expression of the hypoxia-inducible protein NDRG1 in pancreatic cancer

“…The loss of ability to express NDRG1 would assist cells to dedifferentiate to a more aggressive phenotype with more metastatic potential. Recently, it has been suggested that hypoxia can induce dedifferentiation and genetic instability of tumour cells, which may account for the heterogeneity and aggressiveness of solid tumours (Reynolds et al, 1996;Jogi et al, 2002;Helczynska et al, 2003;Unruh et al, 2003).…”

The role of oxygen availability in embryonic development and stem cell function

“…O 2 effects on the function of stem and progenitor cells might also be important in pathophysiological settings, as suggested by recent investigations of neuroblastoma 62 . The sympathetic nervous system (SNS) develops from the neural crest and is composed of both neurons and neuroendocrine (chromaffin) cells.…”

“…Some neuroblastomas contain both neuroblastic and neuroendocrine cell types, with spontaneous changes in cell differentiation status clearly affected by O 2 availability within these tumours. Pahlman and colleagues showed that hypoxia (1-5% O 2 ) induced the expression of markers associated with neural crest sympathetic progenitors, such as c-Kit and Notch, in cultured neuroblastoma cells, whereas it decreased the expression of SNS transcription factors HASH-1 and dHAND 62 . Similar changes in gene expression were also noted in O 2 -starved regions of neuroblastoma xenografts grown in mice.…”

The HIF-2α-Driven Pseudo-Hypoxic Phenotype in Tumor Aggressiveness, Differentiation, and Vascularization

“…proteins are expressed and become stabilized at hypoxia in neuroblastoma cell lines (Jögi et al 2002). There is, however, a distinct difference in stabilization kinetics suggesting that HIF-1 is responsible for the acute and HIF-2 for the prolonged response to hypoxia (HolmquistMengelbier et al 2006).…”

“…One aspect of adaptation to hypoxia, which is of particular importance in tumor cells, is the effect on the tumor cell differentiation status and newly discovered links between HIF-2α expression and tumor initiating/stem cells. Initially described in cultured neuroblastoma and breast cancer cells and in breast tumor specimens, hypoxia can push tumor cells towards an immature, stem cell-like phenotype (Jögi et al 2002;Helczynska et al 2003). The phenomenon has recently also been observed in glioma (Heddleston et al 2009) suggesting that the dedifferentiating effect of hypoxia could be general and not restricted to specific tumor forms.…”