IMPACT OF ONCOGENES IN TUMOR ANGIOGENESIS - MUTANT K-RAS UP-REGULATION OF VASCULAR ENDOTHELIAL GROWTH-FACTOR VASCULAR-PERMEABILITY FACTOR IS NECESSARY, BUT NOT SUFFICIENT FOR TUMORIGENICITY OF HUMAN COLORECTAL-CARCINOMA CELLS

Targeted disruption of the single mutant K-ras allele in two human col orectal carcinoma cell lines (DLD-1 and HCT-116) leads to loss of tumo rigenic competence in nude mice with retention of ability to grow inde finitely in monolayer culture, Because expression of the mutant K-ras oncogene in these cell lines is associated with marked up regulation o f vascular endothelial growth factor/vascular permeability factor (VEG F/VPF), we sought to determine whether this potent angiogenesis induce r plays a role in K-ras-dependent tumorigenic competence, Transfection of a VEGF(121) antisense expression vector into DLD-1 and HCT-116 cel ls resulted in suppression of VEGF/VPF production by a factor of 3- to 4-fold, The VEGF/VPF-deficient sublines, unlike the parental populati on or vector controls, were profoundly suppressed in their ability to form tumors in nude mice for as long as 6 months after cell injection, In contrast, in vitro growth of these sublines was unaffected, thus d emonstrating the critical importance of VEGF/VPF as an angiogenic fact or for HCT-116 and DLD-1 cells, Transfection of a full-length VEGF(121 ) cDNA into two nontumorigenic mutant K-ras knockout sublines resulted in a weak but detectable restoration of tumorigenic ability in vivo i n a subset of the transfectants, with no consistent change in growth p roperties in vitro, The findings indicate that mutant ras-oncogene-dep endent VEGF/VPF expression is necessary, but not sufficient for progre ssive tumor growth in vivo and highlight the relative contribution of oncogenes, such as mutant K-ras, to the process of tumor angiogenesis.