HIF-1alpha and HIF-2alpha Are Differentially Regulated in Vivo in Neuroblastoma: High HIF-1alpha 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.