Oncogenes and tumor angiogenesis: the HPV-16 E6 oncoprotein activates the vascular endothelial growth factor (VEGF) gene promoter in a p53 independent manner

Like other types of pre-malignant lesions and carcinoma, angiogenesis is as sociated with high-grade cervical dysplasia and with invasive squamous carc inoma of the cervix, Vascular endothelial cell growth factor (VEGF) is know n to be one of the most important inducers of angiogenesis and is upregulat ed in carcinoma of the cervix, Human Papilloma Virus 16 (HPV-16) has been e tiologically linked to human cervical cancer, and the major oncogenic prote ins encoded by the viral genome, E6 and E7, are involved in the immortaliza tion of target cells, Because several oncogenes including mutant ras, EGF r eceptor, ErbB2/Her2, c-myc and v-src upregulate VEGF expression, we asked w hether HVP-16 E6 oncoprotein could act in a similar fashion. We found that HPV-16 E6-positive cells generally express high levels of VEGF message. Fur thermore, co-expression of the VEGF promoter-Luc (luciferase) reporter gene with E6 in both human keratinocytes and mouse fibroblast showed that E6 on coprotein upregulates VEGF promoter activity, and does so in a p53 independ ent manner. An E6 responsive region which comprises four Sp-1 sites, betwee n -194 and -50 bp of the VEGF promoter, is also necessary for constitutive VEGF transcription, Taken together, our results suggest the possibility tha t the HPV oncoprotein E6 may contribute to tumor angiogenesis by direct sti mulation of the VEGF gene.