The full-length E6 protein of human papillomavirus type 16 has transforming and trans-activating activities and cooperates with E7 to immortalize keratinocytes in culture

Abstract

The wild-type E6 and E7 genes of human papillomavirus type 16 (HPV16) can cooperate to immortalize normal human keratinocytes in culture. The E6 open reading frame of HPV16 and other HPV types highly associated with cervical cancer has the potential of encoding both full-length E6 and two truncated E6* proteins, the latter being generated via splicing within the E6 open reading frame portion of the E6-E7 polycistronic transcript. Those types, such as HPV6, that are infrequently associated with cervical carcinoma lack the splice site and encode only a full-length E6. We have now found that, in addition to cooperating with E7 to immortalize keratinocytes, HPV16 E6 can induce anchorage-independent growth in NIH 3T3 cells and trans-activate the adenovirus E2 promoter. HPV6 E6 was also able to trans-activate the adenovirus E2 promoter, although it was inactive in both cell transformation assays. An HPV16 splice site mutant which expressed only the full-length HPV16 E6 was active in all three assays, indicating that the E6* proteins are not required for these activities. The plasmid which encodes the E6* proteins was inactive and did not potentiate the activity of the HPV16 splice site mutant. The mutation that prevented splicing in E6-E7 mRNA severely reduced the level of E7 protein and increased E6 protein. Taken together, the results suggest that the primary function of the splice within E6 is to facilitate the translation of E7 and reduce translation of full-length E6, rather than to generate biologically active E6* proteins.

E6* oncoprotein expression of human papillomavirus type‐16 determines different ultraviolet sensitivity related to glutathione and glutathione peroxidase antioxidant defence

“…The potential to encode E6* proteins is an exclusive property of high-risk HPV types, but attempts to demonstrate that these oncoproteins possess transforming activity were unsuccessful (35). Pim and Banks have shown that HPV18 E6* protein was able to interact with both the full-length E6 and the E6-AP proteins in vitro and thereby to block the association of E6 with p53 (36).…”

DNA vaccines: an historical perspective and view to the future

“…Moreover, for some pathogens, even an attenuated version may contain proteins whose function is deleterious, e.g. human papilloma virus (HPV) E6, which can cause transformation of infected cells, part of the pathophysiologic process whereby HPV causes cancer (15). A vector thus has the advantage of encoding only those proteins of the pathogen specifically desired for the immune response (and possibly proteins necessary for the vector, which can augment or detract from the desired immune response, as discussed below).…”

Differential p53‐mediated responses to solar‐simulated radiation in human papillomavirus type 16‐infected keratinocytes

“…These high-risk mucosal HPV types also express a series of alternatively spliced transcripts in addition to the full-length E6 mRNA which encode truncated forms of E6 and are termed E6*. However, to date, attempts to demonstrate that these oncoproteins possess transforming activity were unsuccessful (9). For E6 and E7 oncoproteins, transforming activities are correlated, at least in part, with inactivation of p53 and pRb.…”