The role of human papillomavirus 16 E6 in anchorage-independent and invasive growth of mouse tonsil epithelium

Objective: To provide a manipulatable system to study the mechanism of human papillomavirus 16 (HPV16) E6-related transformation of an epithelial cell type affected by HPV16 in humans. Design: Biochemical and physiological studies of mouse tonsil epithelial cells (MTECs) transformed with HPV16 oncogenes plus H-ras in vitro and in vivo. Setting: Basic research laboratory. Participants: C57BL/6 mice. Interventions: Transduction of the HPV16 oncogenes E6 and E7 in retroviral vectors into MTECs with isolation of multiple individual clones that expressed E6, E7, or both alone or in conjunction with H-ras. Main Outcome Measures: Growth in culture, anchorage-independent growth, and growth in immune competent, syngeneic mice. Results: The MTECs that expressed E6 degraded p53 by a mechanism that is inhibited by proteasomal blockade. Although normal MTECs senesced after 20 population doublings, E6 alone or in combination with E7 was sufficient to immortalize MTECs beyond 25 population doublings, lower their population-doubling time, and permit anchorage-independent growth. However, only MTECs that express E6 plus H-ras or E6/E7 plus H-ras formed invasive tumors in immune competent, syngeneic mice at orthotopic intraoral and subdermal sites. Conclusions: We found that HPV16 E6 and E7 alone are not sufficient for invasive growth. However, the synergistic activity of H-ras and E6 was sufficient to result in invasive growth.