Up-regulation of vascular endothelial growth factor in stromal cells of hemangioblastomas is correlated with up-regulation of the transcription factor HRF/HIF-2alpha

Abstract

Hemangioblastomas, the most frequent manifestation of the hereditary von Hippel-Lindau disease (VHL), are highly vascularized tumors of the central nervous system. In previous studies, the endothelial-specific mitogen vascular endothelial growth factor (VEGF) was shown to be up-regulated in the stromal cells, the putative neoplastic cells in hemangioblastomas. Therefore, it was suggested that secretion of VEGF by stromal cells is the pathogenetic cause of the vascular lesions in hemangioblastomas. The novel basic helix loop helix transcription factor HRF/HIF-2alpha is a candidate regulator of VEGF expression during development. We therefore investigated expression of HRF/HIF-2alpha in hemangioblastomas and found the overexpression of VEGF mRNA in stromal cells to be highly correlated with elevated expression levels of HRF/HIF-2alpha mRNA. This finding is suggestive for a role of HRF in VEGF-dependent vascular growth in hemangioblastomas and could provide a link between transcriptional activation of the VEGF gene and loss of function of the VHL gene product.

Figure 1.

Expression of VEGF in stromal cells of capillary hemangioblastomas is correlated with expression of the transcription factor HRF/HIF-2α as shown by in situ hybridization. Parallel sections of a representative capillary hemangioblastoma were hybridized with ³⁵S-labeled VEGF antisense RNA probe (A, dark-field illumination; B, bright-field view), ³⁵S-labeled HRF/HIF-2α antisense RNA probe (C), or ³⁵S-labeled sense control RNA probe (D). Whereas VEGF is expressed exclusively by stromal cells E, HRF/HIF-2α mRNA is detected on both stromal and endothelial cells (F). Endothelial cells are distinguished from stromal cells by the shape of their nuclei and positive staining for CD31 (G), bv, large blood vessel. Scale bars, 100 μm (A–D) and 50 μm (E–G).

Figure 2.

Northern blot analysis of total RNA from different human tissues. Lane 1, normal cerebrum; lane 2, normal cerebellum; lane 3 to 9, seven different capillary hemangioblastomas; lanes 10 to 13, four different glioblastomas. The membrane was hybridized with a ³²P-labeled human VEGF cDNA and reprobed with a mouse HRF/HIF-2α probe, a human HIF-1α probe, and a β-actin cDNA as loading control.