VEGF-D is an x-linked/AP-1 regulated putative onco-angiogen in human glioblastoma multiforme

Background: Glioblastoma multiforme (GBM) is a hypervascularized and locall y infiltrating brain tumor of astroglial origin with a very poor prognosis. An X-linked c-fos oncogene-inducible mitogenic, morphogenic, and angiogeni c factor, endothelial growth factor-D (VEGF-D), is the newest mammalian mem ber of VEGF family. We analyzed VEGF-D in GBM because of its high angiogeni c potential and its linkage to the X chromosome. Materials and Methods: Nonmalignant brain and GBM tissue sections as well a s GBM cell lines were analyzed by immunofluorescence for the expression of VEGF-D, factor VIII (endothelial cell marker), glial-fibrillary acidic prot ein (GFAP) (astrocytic cell lineage cytoplasmic marker), and several Fos fa mily transcription factors, including c-Fos and Fra-1. The proteins were al so detected by Western blots. The differences between genotypes of normal b rain and GBM cells were examined by cDNA microarrays. Results and Conclusions: GBM expressed ubiquitously VEGF-D, which colocaliz ed with GFAP. Contrary to our expectations, low levels of c-Fos were detect ed in GBM cells. However, we identified another Fos family member, Fra-1, t ogether with its transcriptional activation partner, c-Jun, as being stably up-regulated in GBM cells. Furthermore, we demonstrated that a fra-1 trans gene induced VEGF-D expression in cultured cells and GBM cell stimulation e voked a sustained increase in both Fra-1 and VEGF-D levels. This study reve als that an up-regulation of AP-1 factors may be a hallmark of GBM. Because VEGF-D activates VEGF receptor 2 and 3, receptors important for tumor angi ogenesis, it may represent an X-linked/AP-1-regulated onco-angiogen in huma n GBM. The VEGF-D system and AP-1 activity appear to be very attractive tar gets for new molecular diagnostics and rational molecular anti-cancer thera pies.