UP-REGULATION OF VASCULAR ENDOTHELIAL GROWTH-FACTOR VASCULAR-PERMEABILITY FACTOR IN MOUSE SKIN CARCINOGENESIS CORRELATES WITH MALIGNANT PROGRESSION STATE AND ACTIVATED H-RAS EXPRESSION LEVELS

Angiogenesis is a crucial process for tumor growth and metastasis regu lated by the balance of positive and negative factors. Vascular endoth elial growth factor (VEGF/VPF) is a specific mitogen for endothelial c ells that has been shown to be overexpressed in a variety of tumors an d other inflammatory diseases. To analyze the implication of VEGF/VPF during tumorigenesis, we have studied its expression at different stag es of tumor development using the mouse skin carcinogenesis model. VEG F/VPF mRNA was induced in skin in vivo after 12-O-tetradecanoylphorbol -13-acetate treatment. Constitutive up-regulation of VEGF/VPF at the m RNA and protein levels was also observed in premalignant papillomas an d, at a higher level, in squamous carcinomas, suggesting a correlation between VEGF/VPF expression and tumor progression. A direct positive correlation between VEGF/VPF mRNA expression and the level of activate d H-ras gene was found in a series of cell lines representing differen t stages of epidermal tumor development. Consequently, a clone of one of these cell lines, HaCa4, which has lost most of its v-ras expressio n, down-regulated VEGF mRNA expression concomitantly with its metastat ic potential. Direct evidence of H-ras involvement in VEGF induction w as obtained when an immortalized mouse keratinocyte cell line transduc ed with a retrovirus carrying v-a-ras showed highly increased VEGF/VPF mRNA levels. These data show that in mouse skin carcinogenesis, the V EGF/VPF angiogenic stimulus occurs early during premalignant papilloma development and further increases at later stages. Moreover, we demon strate that increasing the activated H-ras dose, a phenomenon that tak es place sequentially throughout mouse skin tumor development, may pla y an additional role by facilitating malignant in vivo progression thr ough the modulation of VEGF/VPF-mediated angiogenesis.