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1Genzyme Corporation, Framingham, Massachusetts 01701; and 2Graduate School of Medicine, Chiba University, Chiba 280, Japan
Submitted 30 January 2004 ; accepted in final form 7 June 2004
The hereditary von Hippel-Lindau (VHL) syndrome predisposes sufferers to highly vascularized tumors such as renal clear cell carcinoma (RCC) and central nervous system hemangioblastoma. In RCC4 and RCC7860 VHL cells with VHL mutations, the protein of hypoxia-inducible factor-1
(HIF-1
) is constitutively stabilized and the mRNA levels of HIF target genes, including vascular endothelial growth factor (VEGF), are elevated. However, the expression of angiopoietins in these cells and their involvement in angiogenesis are not well known. In this study, we compared the mRNA levels of angiopoietins in human kidney proximal tubule epithelial (RPTE) and RCC4 and RCC7860 VHL cells. In RPTE cells, angiopoietin-4 (Ang-4) expression was selectively induced by hypoxia or by expression of a hybrid form of HIF-1
. Under normoxic conditions, the mRNA levels of Ang-4 were higher in RCC4 and RCC7860 VHL than RPTE cells. Angiopoietin-1 expression was detectable in RCC4 and RCC7860 VHL cells but not RPTE cells. In RCC7860 VHL+ cells, which were stably transfected with a wild-type copy of VHL, the mRNA levels of VEGF and Ang-4 were suppressed and the hypoxic response was restored. We also demonstrated that stimulation of endothelial tube formation by conditioned medium harvested from RCC4 cells was inhibited by a soluble Tie-2 receptor. These results suggest that the angiopoietin/Tie-2 system may participate in the angiogenic response to hypoxia in renal tissues and in tumor angiogenesis in renal carcinoma.
hypoxia-inducible factor-
; von Hippel-Lindau; vascular endothelial growth factor; Tie-2 receptor
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