HPV16 E6 and E7 proteins induce a chronic oxidative stress response via NOX2 that causes genomic instability and increased susceptibility to DNA damage in head and neck cancer cells.
Human papillomavirus (HPV) is the causative agent of a subgroup of head and neck cancer characterized by an intrinsic radiosensitivity. HPV initiates cellular transformation through the activity of E6 and E7 proteins. E6 and E7 expression is necessary but not sufficient to transform the host cell, as genomic instability is required to acquire the malignant phenotype in HPV-initiated cells. This study reveals a key role played by oxidative stress in promoting genomic instability and radiosensitivity in HPV-positive head and neck cancer. By employing an isogenic human cell model, we observed that expression of E6 and E7 is sufficient to induce reactive oxygen species (ROS) generation in head and neck cancer cells. E6/E7-induced oxidative stress is mediated by nicotinamide adenine dinucleotide phosphate oxidases (NOXs) and causes DNA damage and chromosomal aberrations. This mechanism for genomic instability distinguishes HPV-positive from HPV-negative tumors, as we observed NOX-induced oxidative stress in HPV-positive but not HPV-negative head and neck cancer cells. We identified NOX2 as the source of HPV-induced oxidative stress as NOX2 silencing significantly reduced ROS generation, DNA damage and chromosomal aberrations in HPV-positive cells. Due to their state of chronic oxidative stress, HPV-positive cells are more susceptible to DNA damage induced by ROS and ionizing radiation (IR). Furthermore, exposure to IR results in the formation of complex lesions in HPV-positive cells as indicated by the higher amount of chromosomal breakage observed in this group of cells. These results reveal a novel mechanism for sustaining genomic instability in HPV-positive head and neck tumors and elucidate its contribution to their intrinsic radiosensitivity.
Department of Hematology and Medical Oncology, Winship Cancer Institute.
Rossella
R
Marullo
Department of Biochemistry and.
Erica
E
Werner
Department of Hematology and Medical Oncology, Winship Cancer Institute.
Hongzheng
H
Zhang
Department of Hematology and Medical Oncology, Winship Cancer Institute.
Georgia Z
GZ
Chen
Department of Hematology and Medical Oncology, Winship Cancer Institute.
Dong M
DM
Shin
Department of Hematology and Medical Oncology, Winship Cancer Institute, Department of Biochemistry and Department of Radiation Oncology, Winship Cancer Institute, Emory University, Atlanta, GA 30322, USA medpwd@emory.edu.
Paul W
PW
Doetsch
D063646:Carcinogenesis / Q000378:metabolism; D045744:Cell Line, Tumor; D004249:DNA Damage; D004198:Disease Susceptibility; D042822:Genomic Instability; D006258:Head and Neck Neoplasms / Q000235:genetics / Q000821:virology*; D006801:Humans; D008562:Membrane Glycoproteins / Q000502:physiology*; D000074662:NADPH Oxidase 2; D019255:NADPH Oxidases / Q000502:physiology*; D009856:Oncogene Proteins, Viral / Q000502:physiology*; D018384:Oxidative Stress; D050725:Papillomavirus E7 Proteins / Q000502:physiology*; D017382:Reactive Oxygen Species / Q000378:metabolism; D012097:Repressor Proteins / Q000502:physiology*
C068651:E6 protein, Human papillomavirus type 16; D008562:Membrane Glycoproteins; D009856:Oncogene Proteins, Viral; D050725:Papillomavirus E7 Proteins; D017382:Reactive Oxygen Species; D012097:Repressor Proteins; C059731:oncogene protein E7, Human papillomavirus type 16; C056558:CYBB protein, human; D000074662:NADPH Oxidase 2; D019255:NADPH Oxidases