title: 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.
abstract: Targeted disruption of the single mutant K-ras allele in two human colorectal carcinoma cell lines (DLD-1 and HCT-116) leads to loss of tumorigenic competence in nude mice with retention of ability to grow indefinitely in monolayer culture. Because expression of the mutant K-ras oncogene in these cell lines is associated with marked up-regulation of vascular endothelial growth factor/vascular permeability factor (VEGF/VPF), we sought to determine whether this potent angiogenesis inducer plays a role in K-ras-dependent tumorigenic competence. Transfection of a VEGF121 antisense expression vector into DLD-1 and HCT-116 cells resulted in suppression of VEGF/VPF production by a factor of 3- to 4-fold. The VEGF/VPF-deficient sublines, unlike the parental population 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 demonstrating the critical importance of VEGF/VPF as an angiogenic factor for HCT-116 and DLD-1 cells. Transfection of a full-length VEGF121 cDNA into two nontumorigenic mutant K-ras knockout sublines resulted in a weak but detectable restoration of tumorigenic ability in vivo in a subset of the transfectants, with no consistent change in growth properties in vitro. The findings indicate that mutant ras-oncogene-dependent VEGF/VPF expression is necessary, but not sufficient, for progressive tumor growth in vivo and highlight the relative contribution of oncogenes, such as mutant K-ras, to the process of tumor angiogenesis.
authors.affiliation: Division of Cancer Biology Research, Sunnybrook Health Science Centre, Toronto, Ontario, M4N 3M5, Canada.
authors.forename: F
authors.initials: F
authors.lastname: Okada
authors.forename: J W
authors.initials: JW
authors.lastname: Rak
authors.forename: B S
authors.initials: BS
authors.lastname: Croix
authors.forename: B
authors.initials: B
authors.lastname: Lieubeau
authors.forename: M
authors.initials: M
authors.lastname: Kaya
authors.forename: L
authors.initials: L
authors.lastname: Roncari
authors.forename: S
authors.initials: S
authors.lastname: Shirasawa
authors.forename: T
authors.initials: T
authors.lastname: Sasazuki
authors.forename: R S
authors.initials: RS
authors.lastname: Kerbel
mesh_terms: D000818:Animals; D002277:Carcinoma / Q000098:blood supply* / Q000235:genetics*; D015179:Colorectal Neoplasms / Q000098:blood supply* / Q000235:genetics*; D016228:Endothelial Growth Factors / Q000235:genetics*; D015972:Gene Expression Regulation, Neoplastic; D011905:Genes, ras; D006801:Humans; D008222:Lymphokines / Q000235:genetics*; D051379:Mice; D009154:Mutation; D009389:Neovascularization, Pathologic / Q000235:genetics*; D014407:Tumor Cells, Cultured; D015854:Up-Regulation; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors
chemical_list: D016228:Endothelial Growth Factors; D008222:Lymphokines; C467484:VEGFA protein, human; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors