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

Abstract

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 transcriptioncontrolling 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.

Isolation of silencer‐containing sequences causing a tissue‐specific position effect on alcohol dehydrogenase expression in Drosophila melanogaster

“…A d h promoter. Most silencers that have been tested are able to repress expression from heterologous promoters (Cao et al, 1989;Larsen et al, 1986;Savagner et al, 1990;Goodbourn et al, 1986;Yasumoto et al, 1991;Petersen et aZ., 1991;Artelt et al, 1991), but at least two examples of silencer that appear to be promoter specific have been reported (Rippe et al, 1989;Borras et al, 1988). The specificity of the GC-1 silencer for A d h might arise in one of two general ways.…”

NF-IL6 represses early gene expression of human papillomavirus type 16 through binding to the noncoding region

“…A number of extracellular factors, such as transforming growth factor IB, epidermal growth factor, gamma interferon, and leukoregulin, have been reported to repress HPV16 early gene expression in HPV16-immortalized epithelial cells (51,52,55). Very little information has been obtained about the molecular mechanisms through which the down-regula- tion signals from these factors are transduced to transcriptional machinery.…”

“…Very little information has been obtained about the molecular mechanisms through which the down-regula- tion signals from these factors are transduced to transcriptional machinery. However, NF-I or AP1 sites have been thought to be essential in these down-regulations (12,52,55). Thus, NF-IL6, which was demonstrated to bind to sites fairly identical to the NF-I and AP1 sites and to repress early gene expression, may be involved in these regulations as a final mediator.…”

Development of anticancer gene vaccine interact with human papillomavirus oncoprotein inhibition

“…AAV Rep 78 protein has been known to disrupt binding of TATA‐binding protein to the p97 promoter of HPV 16 (12) . Therefore, Rep 78 gene has been an important target for the gene therapy in cervical cancer treatment (13–23) . However, so far only few relevant targets for the diverse Rep activities have been identified.…”

“…E6 and E7 play a critical role in inducing cervical cancer by interacting with p53 and pRb for inactivation of these cellular regulatory proteins, respectively. The expressions of E6 and E7 are regulated by long control region promoter–encoded gene Rep 78 (7–19) . The biochemical activities of Rep 78 have been described, but the effect of Rep proteins on the cervical cell lines has not been characterized.…”