Whereas the development of hemangioblastomas and renal cell carcinomas has been attributed to impaired HIF-1/2alpha down-regulation by pVHL mutant proteins, the molecular defects underlying the development of pheochromocytomas are still unknown.
We show here by immunohistochemical analysis that HB lesions display highly increased levels of VEGF expression and macrophage/microglia infiltration compared with those in normal brain tissues.
However, the finding of dramatic up-regulation of vascular endothelial growth factor (VEGF), a potent endothelial cell growth factor with vascular permeability-inducing activity, in stromal cells and the corresponding receptors, VEGFR-1 and VEGFR-2, in tumor endothelial cells suggests that angiogenesis and cyst formation in hemangioblastomas may be regulated by this signaling pathway via a paracrine mechanism.
In a previous study of hemangioblastomas, the most frequent manifestation of hereditary von Hippel-Lindau disease (VHL), we found elevated levels of vascular endothelial growth factor and HIF-2alpha mRNA in stromal cells of the tumors.
It has also been documented that higher levels of vascular endothelial growth factor (VEGF), hypoxia induced factor (HIF), and ubiquitin are found in ocular hemangioblastomas.
As stromal cells of capillary hemangioblastoma express high levels of vascular endothelial growth factor (VEGF) and placental growth factor (P1GF) mRNA, we studied the distribution of the corresponding VEGF and P1GF proteins.
Northern blot and in situ hybridization analysis revealed significant up-regulation of VEGF and VEGF receptor expression in VHL disease-associated and sporadic hemangioblastomas compared to normal brain and tumor stromal cells as sites of abundant VEGF transcription.
Similar to prior reports in infantile hemangiomas, propranolol induced apoptosis and paradoxically increased VEGF-A mRNA expression in patient-derived VHL-HBs and 786-O cells.
We demonstrated a massive upregulation of mRNA levels of VEGF and VEGFR2, CXCR4 and SDF1α, EphB4 and EphrinB2, as well as the main components of Dll4-Notch signaling in HB.
Our observations suggest that VHL mutations affect stromal cells in hemangioblastomas and that VEGF is upregulated in stromal cells as a consequence of mutations in the VHL gene.