Recruitment of HIF-1α and HIF-2α to common target genes is differentially regulated in neuroblastoma: HIF-2α promotes an aggressive phenotype

Abstract

In neuroblastoma specimens, HIF-2alpha but not HIF-1alpha is strongly expressed in well-vascularized areas. In vitro, HIF-2alpha protein was stabilized at 5% O2 (resembling end capillary oxygen conditions) and, in contrast to the low HIF-1alpha activity at this oxygen level, actively transcribed genes like VEGF. Under hypoxia (1% O2), HIF-1alpha was transiently stabilized and primarily mediated acute responses, whereas HIF-2alpha protein gradually accumulated and governed prolonged hypoxic gene activation. Knockdown of HIF-2alpha reduced growth of neuroblastoma tumors in athymic mice. Furthermore, high HIF-2alpha protein levels were correlated with advanced clinical stage and high VEGF expression and predicted poor prognosis in a clinical neuroblastoma material. Our results demonstrate the relevance of HIF-2alpha in neuroblastoma progression and have general tumor biological implications.

The TWIST1 oncogene is a direct target of hypoxia-inducible factor-2α

“…Interestingly, HIF-2a has been shown to enhance aggressive tumor behavior (Kondo et al, 2003;Holmquist-Mengelbier et al, 2006). This is consistent with HIF-2a-dependent regulation of TWIST1 as shown here.…”

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

“…With neuroblastoma as a model system, we showed that during hypoxia-driven VEGF expression there is a temporal shift in the usage of the HIFs; whereas the VEGF expression is HIF-1 dependent at an acute phase, the expression during prolonged hypoxia is primarily HIF-2 driven (Holmquist-Mengelbier et al 2006). In a follow-up study using a large clinical neuroblastoma tissue microarray material immunohistochemically stained for HIF-1α, HIF-2α, VEGF and blood vessel endothelial cells (CD31), tumor cells staining intensely for HIFs correlated to VEGF positivity, while the HIF-1α and HIF-2α staining did not fully correlate to each other ).…”

“…In tumor cell lines, with few exceptions both HIF-1α and HIF-2α are expressed, and we recently postulated that HIF-1α is involved in adaptation to acute, and HIF-2α to prolonged, hypoxia (Holmquist-Mengelbier et al 2006;Helczynska et al 2008). For historical reasons, HIF-1α is the isoform that has been most extensively studied in clinical tumor materials and frequently been correlated with aggressive tumor disease, but in recent years high tumor levels of HIF-2α rather than HIF-1α have been shown to associate with negative overall survival and metastatic disease.…”

“…By immunohistochemistry, we could further demonstrate HIF-2α protein in human SNS paraganglia at fetal week 8.5 (Nilsson et al 2005), which developmentally corresponds to mouse embryonal day E16, a time point when mouse SNS paraganglia express HIF-2α as determined by in situ hybridizations (Tian et al 1998;Jögi et al 2002). Using the same immunohistochemical protocol that detects HIF-2α in developing human paraganglia, staining of human neuroblastoma specimens highlights small subsets of cells intensely expressing HIF-2α protein, and the presence of such cells strongly correlates to disseminated disease (high clinical stage) and tumor-related death (Holmquist-Mengelbier et al 2006). Further immunohistochemical characterization of these cells reveals that they frequently are perivascularly located, lack the expression of SNS markers like TH and NSE found in the bulk of neuroblastoma tumor cells, but express neural crest and early SNS progenitor markers such as NOTCH-1, HES-1, Vimentin and HAND2 (Pietras et al 2008).…”

“…Importantly, and the reason for the focus on HIF-2α in this review, HIF-1α and HIF-2α are differently regulated in tumors such as neuroblastoma, breast cancer, non-small cell lung carcinoma (NSCLC) and glioma and seem to have different impact on tumor behavior and patient outcome in these tumors (Holmquist-Mengelbier et al 2006;Helczynska et al 2008;Heddleston et al 2009;Kim et al 2009b;Li et al 2009;Noguera et al 2009). …”