The human papillomavirus confers radiosensitivity in oropharyngeal cancer cells by enhancing DNA double strand break
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Mei Zhang1,2 and Angela M. Hong1,2
1 Faculty of Medicine and Health, Central Clinical School, The University of Sydney, NSW, Australia
2 Department of Radiation Oncology, Chris O’Brien Lifehouse, NSW, Australia
Keywords: radiosensitivity; oropharyngeal cancer; human papillomavirus; double-strand break; radiobiology
Received: December 24, 2019 Accepted: February 17, 2020 Published: April 21, 2020
Background: Patients with Human papillomavirus (HPV)-positive oropharyngeal squamous cell carcinoma (OPSCC) has better outcomes than those with HPV-negative OPSCC. This may be related to its enhanced radiosensitivity. This study examined the effect of HPV and its E6 oncoprotein on the morphology, radiosensitivity, and repair of radiation-induced DNA damage.
Materials and Methods: HPV-negative UM-SCC4 with and without transfection of HPV E6 oncoprotein, HPV-negative UPCI-SCC-089 and HPV-positive UPCI-SCC-099 cell lines were used in this study. The radiosensitivity and morphological changes after radiation were determined by clonogenic assay. Radiation-induced double-strand breaks in the DNA was measured by γ-H2AX foci immunofluorescent assay.
Results: The survival fraction after 10 Gy was significantly lower for the HPV-positive SCC-099 cells than for the HPV-negative cells (p = 0.03). The levels of γ-H2AX foci formation and retention were time and cell line-dependent. The γ-H2AX level started to increase at 1 hour and peaked at 4 hours after 10 Gy radiation in the HPV-negative SCC-089 and UM-SCC4 cells before reducing to negligible level (p = 0.0001). In contrast, the HPV-positive UPCI-SCC-099 cells displayed persistent γ-H2AX activity; the expression of γ-H2AX remained high at 48 hours post radiation (p = 0.001). Transfection with the E6 oncoprotein prolonged γ-H2AX formation up to 24 hours in HPV-negative SCC4 cells. HPV-positive SCC-099 cells were more likely to show the classical apoptotic changes of increased cell thickness and increased motility after radiation.
Conclusions: This in vitro study confirmed that HPV-positive OPSCC was more radiosensitive. Transfection with the E6 oncoprotein enhanced the radiosensitivity in HPV-negative OPSCC by impairing the DNA repair mechanism and enhancing apoptotic cell death.
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