Epidermal growth factor (EGF) elicits down-regulation of human papillomavirus type 16 (HPV-16) E6/E7 mRNA at the transcriptional level in an EGF-stimulated human keratinocyte cell line: functional role of EGF-responsive silencer in the HPV-16 long control region.
We have found that epidermal growth factor (EGF) elicits negative regulation of human papillomavirus type 16 (HPV-16) E6/E7 at the mRNA level in the HPV-16-immortalized human keratinocyte cell line (PHK160b). This down-regulation of HPV-16 E6/E7 expression was achieved when the cells were stimulated to proliferate with the concomitantly enhanced c-myc expression by EGF in a dose-dependent manner. By using partly synchronized PHK160b cells, negative and positive regulations of the HPV-16 E6/E7 expression was correlated to EGF-linked cell cycle events in this particular human keratinocyte cell line. In order to study transcriptional control mechanisms of the HPV-16 E6/E7, transient expression assays were performed with CAT expression plasmids that the transcription could be directed by the 5'-deleted HPV-16 long control region (LCR) including the virus P97 promoter. We demonstrated that the HPV-16 LCR contained EGF-responsive elements and that a predominant silencer activity was mapped in the proximal 124-bp region (EGFRE) of the LCR. This restricted LCR region had significant influence on HPV-16-homologous promoters in lowering the CAT expression in the presence and absence of EGF. EGFRE was thus considered to be a conditional transcription-controlling element on HPV-16 E6/E7 expression in this EGF-responsive human keratinocyte cell line. This suggests that specific sequences in the LCR play a critical part in the EGF-induced down-regulation of E6/E7 expression at the transcriptional level. Since the results obtained from the transient expression assay agreed with the mode of expression of the endogenous HPV-16 E6/E7, the present study strongly suggests that the transcriptional regulation of the HPV-16 E6/E7 oncogene is mediated by growth-related specific cellular factors interacting with HPV-16 LCR elements.
Yasumoto
S
S
Laboratory of Molecular and Cell Biology, Kanagawa Cancer Center Research Institute, Yokohama, Japan.
Taniguchi
A
A
Sohma
K
K
D002453:Cell Cycle / Q000235:genetics; D002460:Cell Line; D015500:Chloramphenicol O-Acetyltransferase / Q000096:biosynthesis / Q000235:genetics; D015536:Down-Regulation; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D015967:Gene Expression Regulation, Viral; D006801:Humans; D015603:Keratinocytes / Q000187:drug effects / Q000382:microbiology*; D027383:Papillomaviridae / Q000187:drug effects / Q000235:genetics* / Q000254:growth & development; D011401:Promoter Regions, Genetic; D016271:Proto-Oncogene Proteins c-myc / Q000096:biosynthesis / Q000235:genetics*; D012333:RNA, Messenger / Q000378:metabolism*; D012045:Regulatory Sequences, Nucleic Acid; D014158:Transcription, Genetic; D014779:Virus Replication
D016271:Proto-Oncogene Proteins c-myc; D012333:RNA, Messenger; D004815:Epidermal Growth Factor; D015500:Chloramphenicol O-Acetyltransferase