Expression of Human Papillomavirus Type 16 E7 Is Sufficient To Significantly Increase Expression of Angiogenic Factors But Is Not Sufficient To Induce Endothelial Cell Migration

Abstract

Human papillomavirus 16 (HPV 16) causes cancer. Two viral oncoproteins of HPV 16, E6 and E7, are consistently expressed in these cancers. HPV 16 E6 and E7 proteins target p53 and Rb family members, respectively, for degradation thus inactivating the functiond of these tumor suppressor proteins. Tumor development requires the acquisition of a blood supply, a process known as angiogenesis. Tumor suppressors negatively regulate angigogenesis. Expression of HPV 16 E6 and E7 together in human foreskin keratinocytes (HFKs) increases the level of angiogenic inducers vascular endothelial growth factor (VEGF) and interleukin-8 (IL-8). Further, conditioned media from such cells are sufficient to alter endothelial cell behavior both in vitro and in vivo. To determine the individual contributions of HPV E6 and E7 to angiogenesis, translational termination linkers (TTLs) were inserted into the coding region of E6 or E7. Following retroviral transduction of the mutated cassette into HFKs, the ability of E7 in the context of the E6TTL mutation (E6TTLE7) and E6 in the context of the E7TTL mutation (E6E7TTL) to induce VEGF and IL-8 was compared to the LXSN control retrovirus. E7 and, to a lesser extent E6, increased the expression of VEGF and IL-8. Migration of human microvascular endothelial cells was not induced using conditioned media from either E6 or E7 expressing cells. Since the increased levels of VEGF and IL-8 induced by HPV 16E6ETTLE7 were not sufficient to alter endothelial cell behavior, immunological depletion experiments were used to determine whether either angiogenic factor was required for HPV 16E6 and E7 together to induce HMVEC migration. Only VEGF was required. Preliminary data suggest that the ability of HPV 16 E7 to induce angiogenic factors is dependent upon degradation of a specific Rb family member.