VEGF165b, an inhibitory vascular endothelial growth factor splice variant: mechanism of action, in vivo effect on angiogenesis and endogenous protein expression.

Growth of new blood vessels (angiogenesis), required for all tumor growth, is stimulated by the expression of vascular endothelial growth factor (VEGF). VEGF is up-regulated in all known solid tumors but also in atherosclerosis, diabetic retinopathy, arthritis, and many other conditions. Conventional VEGF isoforms have been universally described as proangiogenic cytokines. Here, we show that an endogenous splice variant, VEGF(165)b, is expressed as protein in normal cells and tissues and is circulating in human plasma. We also present evidence for a sister family of presumably inhibitory splice variants. Moreover, these isoforms are down-regulated in prostate cancer. We also show that VEGF(165)b binds VEGF receptor 2 with the same affinity as VEGF(165) but does not activate it or stimulate downstream signaling pathways. Moreover, it prevents VEGF(165)-mediated VEGF receptor 2 phosphorylation and signaling in cultured cells. Furthermore, we show, with two different in vivo angiogenesis models, that VEGF(165)b is not angiogenic and that it inhibits VEGF(165)-mediated angiogenesis in rabbit cornea and rat mesentery. Finally, we show that VEGF(165)b expressing tumors grow significantly more slowly than VEGF(165)-expressing tumors, indicating that a switch in splicing from VEGF(165) to VEGF(165)b can inhibit tumor growth. These results suggest that regulation of VEGF splicing may be a critical switch from an antiangiogenic to a proangiogenic phenotype.

Relative expression of vascular endothelial growth factor isoforms in squamous cell carcinoma of the head and neck.

BACKGROUND: Alternative splicing of the vascular endothelial growth factor (VEGF) gene results in a family of antiangiogenic isoforms (VEGFxxx b), not yet investigated in squamous cell carcinoma of the head and neck (SCCHN). We examined, therefore, the prognostic value of the relative expression of VEGF isoforms in SCCHN. METHODS: A tissue microarray comprising 187 SCCHNs was studied by immunohistochemistry with total VEGF (panVEGF) and VEGFxxx b-specific antibodies, and scored by 2 assessors for intensity and proportion. Scores were combined and expression ratios calculated. RESULTS: No meaningful significant differences were observed between panVEGF, VEGFxxx b, or expression ratio, and presence of lymphatic metastasis, or overall survival. This held true when tumor subsites were analyzed independently and when human papillomavirus (HPV) was accounted for in the oropharyngeal subgroup. CONCLUSION: Differential VEGF isoform expression is not a reliable prognostic biomarker for either the clinically node negative/pathologically node-positive neck or overall survival in pharyngeal and laryngeal SCCHNs.