Fig. 2

Mutant ras oncogene regulates expression of VEGF mRNA.

(A) Northern blot of VEGF mRNA is shown of human HT 1080 human fibrosarcoma cells (as a positive control), nontumorigenic rat intestinal epithelial cell line-18 (IEC-18 cells), and two clones of IEC-18, Ras-7 and Ras-3, which were obtained by transfection of IEC-18 cells with a mutant human H-ras oncogene. These latter two lines are tumorigenic, and unlike IEC-18 cells, they express abundant VEGF transcripts. MT-ras is a clone of IEC-18 which expresses its transfected mutant H-ras oncogene only when exposed to heavy metals such as zinc and cadmium, as the gene is under the control of a metallothionein promotor. VEGF mRNA are not expressed in this clone unless they are exposed to these metals. (B) Northern blot for VEGF mRNA in human DLD-1 and HCT-116 human colorectal carcinoma cells, each of which contains a single mutant K-ras allele. DKS-8 and Hkh-2 are sublines obtained from DLD-1 and HCT-116, respectively, in which the mutant K-ras allele has been disrupted by gene targeting (55). The DLD-1 and HCT-116 cell lines are tumorigenic in nude mice, whereas DKS-8 and Hkh-2 are not. The suppression of VEGF mRNA is matched by a down-regulation in VEGF protein released by the cells into the conditioned medium. The results are taken from Rak et al. (38).