A plant lignan, 3'-O-methyl-nordihydroguaiaretic acid, suppresses papillomavirus E6 protein function, stabilizes p53 protein, and induces apoptosis in cervical tumor cells.
Persistent infection with oncogenic human papillomaviruses (HPVs) is the most important factor in the induction of uterine cervical cancer, a leading cause of cancer mortality in women worldwide. Upon cell transformation, continual expression of the viral oncogenes is required to maintain the transformed phenotype. The viral E6 protein forms a ternary complex with the cellular E6-AP protein and p53 protein which promotes the rapid degradation of p53. Recent studies have revealed that lignans from the creosote bush (3'-O-methyl-nordihydroguaiaretic acid) can repress the viral promoter responsible for E6 gene expression. Work reported here shows that the lignan can subvert viral oncogene function resulting in stabilized p53 protein within treated HPV-containing tumor cells. The stabilized p53 is transcriptionally active as demonstrated by a luciferase reporter vector and induction of genes for Bax and PUMA proteins. Apoptosis is detected by annexin V binding to treated cells as analyzed by flow cytometry. Programmed cell death is confirmed by the induction of active caspases and TUNEL assay. Initiator caspase-9 is activated first, followed later by the effector caspase-3 enzyme. The stabilization and induced apoptosis are not observed within treated HPV-negative cervical tumor cells. Quantitative real time RT-PCR analysis of endogenous E6 gene transcription from the integrated HPV 16 promoter shows at least a fivefold repression of expression as compared to untreated cells. These results indicate that the loss of E6 protein in treated cells could be, in part, responsible for the stabilization of p53 within the lignan treated cells.
Allen
Kristi L
KL
Department of Microbiology, Immunology and Biochemistry, Northeastern Ohio Universities College of Medicine, 4209 State Rt. 44, Rootstown, OH 44272, USA.
Tschantz
Deidra R
DR
Awad
Keytam S
KS
Lynch
William P
WP
DeLucia
Angelo L
AL
D017209:Apoptosis / Q000187:drug effects*; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism; D053148:Caspase 3 / Q000378:metabolism; D053453:Caspase 9 / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D005260:Female; D006801:Humans; D008156:Luciferases; D009637:Masoprocol / Q000031:analogs & derivatives* / Q000627:therapeutic use; D009856:Oncogene Proteins, Viral / Q000378:metabolism*; D010944:Plants / Q000737:chemistry; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D012097:Repressor Proteins / Q000378:metabolism*; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured / Q000187:drug effects; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism*; D002583:Uterine Cervical Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D051028:bcl-2-Associated X Protein / Q000378:metabolism
D051017:Apoptosis Regulatory Proteins; C438378:BBC3 protein, human; C068651:E6 protein, Human papillomavirus type 16; D009856:Oncogene Proteins, Viral; D011518:Proto-Oncogene Proteins; D012097:Repressor Proteins; D016159:Tumor Suppressor Protein p53; D051028:bcl-2-Associated X Protein; C042349:heminordihydroguaiaretic acid; D009637:Masoprocol; D008156:Luciferases; D053148:Caspase 3; D053453:Caspase 9