Comparative expression of novel vascular endothelial growth factor/vascular permeability factor transcripts in skin, papillomas, and carcinomas of v-Ha-ras Tg.AC transgenic mice and FVB/N mice.

One of the most frequently detected changes in human solid tumors is the mutation of the ras oncogene, which has been associated with production of angiogenic growth factors such as vascular endothelial growth factor/vascular permeability factor (VEGF/VPF). Using the v-Ha-ras Tg-AC transgenic mice and the background FVB/N strain of inbred mice, the pattern of expression of specific VEGF/VPF transcripts was characterized in major organs and in skin, papillomas, and carcinomas during multi-stage skin carcinogenesis. Three VEGF/VPF transcripts were found to be constitutively expressed in skin as well as the major organs in both mouse strains, which corresponded in size and sequence to previously reported murine VEGF120 with a bp size of 331, VEGF164 with a bp size of 333, and VEGF188 with a bp size of 407. A previously unreported fourth murine transcript was also detected in skin and major tissues from both mouse strains which corresponded to rat VEGF144, with a bp size of 404. In addition, a unique 425 bp VEGF transcript which corresponded to human VEGF205 was present in highly vascularized tissues including heart, lung, liver, kidney, brain, as well in papillomas and carcinomas isolated from v-Ha-ras Tg.AC mice. In contrast, VEGF205 was present only in carcinomas derived from FVB/N mice. An antibody generated from a peptide sequence designed to detect each of the five VEGF/VPF peptides defined by RT-PCR analysis confirmed the existence of these five peptides and confirmed that the murine VEGF205 peptide was selectively expressed in papillomas and carcinomas derived from v-Ha-ras Tg.AC mice. These results demonstrate that there is significant alternative splicing of the murine VEGF/VPF gene during multi-stage carcinogenesis, which results in four commonly expressed VEGF transcripts. In addition, these studies identified a fifth VEGF transcript and peptide at the later stages of tumor promotion and in progression which appears to be linked to the presence of v-Ha-ras.