Increased expression of VEGF121/VEGF165-189 ratio results in a significant enhancement of human prostate tumor angiogenesis

Vascular endothelial growth factor (VEGF) is a proangiogenic factor upregulated in many tumors. The alternative splicing of VEGF mRNA renders 3 major isoforms of 121, 165 and 189 amino-acids in humans (1 less amino-acid for each mouse VEGF isoform). We have designed isoform specific real time QRT-PCR assays to quantitate VEGF transcripts in mouse and human normal and malignant prostates. In the human normal prostate, VEGF165 was the predominant isoform (62.8% ± 5.2%), followed by VEGF121 (22.5% ± 6.3%) and VEGF189 (p < 0.001) (14.6% ± 2.1%). Prostate tumors showed a significant increase in the percentage of VEGF121 and decreases in VEGF165 (p < 0.01) and VEGF189 (p < 0.05). However, the amount of total VEGF mRNA was similar between normal and malignant prostates. VEGF164 was the transcript with the highest expression in the mouse normal prostate. Unlike human prostate cancer, tumors from TRAMP mice demonstrated a significant increase in total VEGF mRNA levels and in each of the VEGF isoforms, without changes in the relative isoform ratios. Morpholino phosphorodiamide antisense oligonucleotide technology was used to increase the relative amount of VEGF121 while proportionally decreasing VEGF165 and VEGF189 levels in human prostate cell lines, through the modification of alternative splicing, without changing transcription levels and total amount of VEGF. The increase in the VEGF121/VEGF165–189 ratio in PC3 cells resulted in a dramatic increase in prostate tumor angiogenesis in vivo. Our results underscore the importance of VEGF121 in human prostate carcinoma and demonstrate that the relative expression of the different VEGF isoforms has an impact on prostate carcinogenesis. © 2007 Wiley-Liss, Inc.