Effect of BPV1 E2-mediated inhibition of E6/E7 expression in HPV16-positive cervical carcinoma cells.
OBJECTIVE
E6 and E7 proteins of high-risk-type human papillomavirus are major etiological agents for cervical carcinomas and are continuously expressed in those cancer cells. They inhibit cell cycle control functions by inactivating p53 and Rb proteins and also immortalize cells through the induction of telomerase activity. Expression of E6 and E7 genes in HeLa, an HPV18-positive cell line, has been shown to be inhibited by the E2 protein of bovine papillomavirus (BPV1), and this resulted in the activation of the p53-mediated growth inhibitory pathway followed by an inhibition of cell proliferation. In this study, the effect of BPV1 E2-mediated inhibition of E6 and E7 expression was examined in HPV16-positive cervical carcinoma cell lines recently established from Korean patients.


METHODS
BPV1 E2 was expressed in the test cells through acute infection of an SV40-BPV1 recombinant virus. Its effect on cell proliferation was assessed through MTT and DNA synthesis assays, and the status of factors involved in cell cycle control was examined through Western blotting and reverse transcription-polymerase chain reaction.


RESULTS
BPV1 E2 expression caused a significant decrease in E6/E7 transcription in all three cell lines. This was accompanied by an increase in the levels of p53 protein and activity and a decrease in the expression of Cdc25A, a Cdk2-activating phosphatase. Concomitantly, E2F1 activity and cellular DNA synthesis capacity were significantly reduced.


CONCLUSIONS
These results indicate that inhibition of E6/E7 gene expression in the HPV16-positive cervical carcinoma cells induces suppression in cell proliferation by activating the growth inhibitory factors, p53 and Rb, and also by downregulating the cell cycle stimulatory factor, Cdc25A.
Moon
M S
MS
Department of Life Science, Sogang University, Seoul, Korea.
Lee
C J
CJ
Um
S J
SJ
Park
J S
JS
Yang
J M
JM
Hwang
E S
ES
D000818:Animals; D052688:Bovine papillomavirus 1 / Q000235:genetics; D019556:COS Cells; D002352:Carrier Proteins; D002417:Cattle; D002453:Cell Cycle / Q000502:physiology; D018797:Cell Cycle Proteins; D002455:Cell Division / Q000502:physiology; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D015536:Down-Regulation; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D005260:Female; D006131:Growth Inhibitors / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology; D006801:Humans; D009856:Oncogene Proteins, Viral / Q000037:antagonists & inhibitors* / Q000096:biosynthesis; D027383:Papillomaviridae / Q000235:genetics / Q000378:metabolism; D050725:Papillomavirus E7 Proteins; D012097:Repressor Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology; D016160:Retinoblastoma Protein / Q000378:metabolism / Q000502:physiology; D056465:Retinoblastoma-Binding Protein 1; D015398:Signal Transduction / Q000502:physiology; D050680:Transcription Factor DP1; D014157:Transcription Factors / Q000502:physiology; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism / Q000502:physiology; D002583:Uterine Cervical Neoplasms / Q000378:metabolism / Q000473:pathology / Q000821:virology*; D014764:Viral Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D020687:cdc25 Phosphatases / Q000096:biosynthesis / Q000235:genetics
D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; C051550:E2 protein, Bovine papillomavirus; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; C493753:E2F1 protein, human; C068651:E6 protein, Human papillomavirus type 16; D006131:Growth Inhibitors; D009856:Oncogene Proteins, Viral; D050725:Papillomavirus E7 Proteins; D012097:Repressor Proteins; D016160:Retinoblastoma Protein; D056465:Retinoblastoma-Binding Protein 1; D050680:Transcription Factor DP1; D014157:Transcription Factors; D016159:Tumor Suppressor Protein p53; D014764:Viral Proteins; C059731:oncogene protein E7, Human papillomavirus type 16; C517004:CDC25A protein, human; D020687:cdc25 Phosphatases