Vascular endothelial growth factor-B and vascular endothelial growth factor-C expression in renal cell carcinomas: Regulation by the von Hippel-Lindau gene and hypoxia

Angiogenesis is essential for tumor growth and metastasis. It is regulated by numerous angiogenic factors, one of the most important being vascular en dothdial growth factor (VEGF), Recently VEGF-B and VEGF-C, two new VEGF fam ily members, have been identified that bind to the tyrosine kinase receptor s flt-1 (VEGFR1), KDR (VEGFR2), and flt-4 (VEGFR3), Although the importance of VEGF-A has been shown in renal carcinomas, the contribution of these ne w ligands in kidney tumors is not clear. We have, therefore, measured the m RNA level of VE GF-B and VEGF-C together with their receptors by RNase prot ection assay (RPA) in 26 normal kidney samples and 45 renal cell cancers. W e observed a significant up-regulation of VEGF-B (P = 0.002) but not YEGF-C (P = 0.3) in neoplastic kidney compared with normal tissues. In addition, although VEGF receptors were higher in tumors than normal kidney, there was a significant up-regulation of only flt-1 (P = 0.003) but not KDR (P = 0.1 2) or flt-4 (P = 0.09), There was also a significant correlation between VE GF-C and both of its receptors flt-4 (P = 0.006) and KDR (P = 0.03) hut no association between VEGF-B and its receptor flt-1 (P = 0.23). A significant increase was observed in flt-1 (P < 0.001), KDR (P = 0.02), and flt-4 (P = 0.01) but not VEGF-B (P = 0.82) or VEGF-C (P = 0.52) expression in clear c ell compared with chromophil (papillary) carcinomas. No significant associa tion was demonstrated between VEGF-B, VEGF-C, flt-1, KDR, and flt-4 with pa tient sex, patient age, or tumor size (P > 0.05), The effect of von Hippel- Lindau (VHL) gene and hypoxia on VEGF-B and VEGF-C expression in the renal carcinoma cell line 786-0 transfected with wild-type and mutant VHL was det ermined by growing cells under 21% O2- and 0.1% O-2. In wild-type VHL cells , whereas VEGF-A was significantly up-regulated under hypoxic compared with normoxic conditions (P < 0.001), expression of VEGF-C was reduced (P < 0.0 02), Nevertheless, the repression of VEGF-C was lost in mutant VHL cell lin es under hypoxia, In contrast VEGF-B was not regulated by VHL despite clear up-regulation in vivo. These findings strongly support an enhanced role fo r this pathway in clear cell carcinomas by regulating angiogenesis and/or l ymphangiogenesis. The study shows that clear cell tumors are able to up-reg ulate angiogenic growth factor receptors more efficiently than chromophil ( papillary), that clear cell tumors can use pathways independent of VHL to r egulate angiogenesis, and that this combined regulation may account for the ir more aggressive phenotype, which suggests that targeting VEGFR1 (flt-1) may be particularly effective in these tumor types.