Transcriptional activation of several heterologous promoters by the E6 protein of human papillomavirus type 16

Abstract

The E6 protein of human papillomavirus type 16 (HPV-16), along with E7, is responsible for the HPV-induced malignant transformation of the cervix. However, the mechanism of this transformation activity is not well understood. We investigated whether the entire E6 protein of HPV-16 could act as an activator of transcription. Experiments in which NIH 3T3 cells were cotransfected with an E6 expression vector together with the reporter chloramphenicol acetyltransferase (CAT) gene linked to various minimal promoters indicated that E6 could activate transcription from a series of viral TATA-containing promoters. Mutations or deletions that affected all upstream regulatory elements present in the thymidine kinase (TK) promoter, such as the GC and CAAT boxes, reduced the level of E6-induced transcription. However, compared with the basal level, these truncated promoters were still activated by E6. Although site-directed mutations of the TATA sequence present in the TK or human immunodeficiency virus long terminal repeat promoters reduced the level of basal transcription, they did not abolish the E6-mediated activation. Moreover, E6 could restore almost completely the full level of wild-type E6-induced transcription as long as the upstream regulatory elements (GC/CAAT in the TK promoter, NF-KcB in the human immunodeficiency virus long terminal repeat) were intact. This dual interaction of HPV-16 E6 is reminiscent of the activity of a coactivator.

Constitutive activation of transcription factor AP-1 in cervical cancer and suppression of human papillomavirus (HPV) transcription and AP-1 activity in HeLa cells by curcumin

“…The 2 transforming early genes E6 and E7 of high risk HPV16 and HPV18, possess an intrinsic transactivation capacity on their own homologous promoters,33, 34 but constitutive expression of E6 and E7 in immortalized or malignantly transformed human keratinocytes is mainly dependent on the availability of a defined set of transcription factors, such as AP‐1, derived from the infected host cells. Our results show that the AP‐1 binding activity is very high in cervical tumor tissues, whereas it is nil or negligible in normal cervical cells.…”

Extended effects of human papillomavirus 16 E6-specific short hairpin RNA on cervical carcinoma cells

“…In mice, it was also shown that expression of HPV16 E6 and E7 oncogenic proteins could cause metastatic conversion of mouse cells (37) . HPV16 E6 and E7 genes have been shown to be able to regulate transcription from heterologous promoters (38,39) , maybe this ability of the two genes leads to expression of some cellular genes that are correlated with invasion and metastasis. The results revealed that HPV16 E6A shRNA could play an important role in reducing the invasion and migration of HPV16‐related cervical cancer cells, thus could effectively block the progression of cervical cancer.…”

DNA vaccine encoding endosome‐targeted human papillomavirus type 16 E7 protein generates CD4+ T cell‐dependent protection

“…NIH‐3T3 cells were transfected with the different plasmids and the blue scribe plasmid, as carrier, using the calcium phosphate co‐precipitation method 32. Thirty‐six hours later, cells were harvested, counted and a same number of cells from each sample were used.…”