VEGF Isoforms and Mutations in Human Colorectal Cancer

We wished to demonstrate vascular endothelial growth factor (VEGF) transcript polymorphism in human colon cancer. RNA was extracted from 25 primary human colorectal adenocarcinomas followed by VEGF transcript amplification, fragment elution, subcloning, positive selection via insert analysis and sequencing. Four distinct splice variants were consistently expressed in cancer, including VEGF121, VEGF165, VEGF189 and the newly identified truncated splice variant VEGF145. Six novel mutations were characterized, all of which occurred within the conserved expression site of the gene and which consequently were present in all splice forms. Five cancers exhibited single nucleotide changes and 1 cancer a 2-nucleotide deletion. A silent mutation was observed in exon 1 at position +70 relative to the amplification start site, a 1- and 2-base deletion with frameshift and protein truncation in exon 3 at positions +172 and +171/172, respectively, a transition mutation in exon 3 at position +248 and 2 transition mutations in exon 4 at positions +398 and +403. All of these sense mutations should alter protein conformation. To our knowledge, this is the first report of VEGF145 in solid malignancy. Its biologic activity remains to be determined. We have demonstrated a variety of sporadic mutations within human colorectal cancer VEGF mRNA. Mutant angiogenic VEGF may provide a genomic basis for the diversity of tumor-host response and may prove to be important in antisense oligonucleotide targeting, since all the different VEGF isoforms would have to be neutralized to prevent angiogenesis.