HPV16 E6 confers p53-dependent and p53-independent phenotypes in the epidermis of mice deficient for E6AP

Shai, Anny; Ml, Nguyen; Wagstaff, Joseph; Jiang, Y-H; Pf, Lambert

doi:10.1038/sj.onc.1210130

Cited by 27 publications

(31 citation statements)

References 57 publications

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“…Our data demonstrate that E6AP is not required for hTERT activation and therefore suggest that NFX1-91 destabilization is not necessary or that another E6-dependent pathway may specifically target NFX1-91. This is consistent with recent observations that E6-induced p53 degradation in vivo may occur through E6AP-dependent and E6AP-independent mechanisms (6,7,40).…”

Section: Resultssupporting

confidence: 81%

Binding of Human Papillomavirus Type 16 E6 to E6AP Is Not Required for Activation of hTERT

Šekaric

Cherry

Androphy

2008

J Virol

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The human papillomavirus (HPV) type 16 (HPV16) E6 protein stimulates transcription of the catalytic subunit of telomerase, hTERT, in epithelial cells. It has been reported that binding to the ubiquitin ligase E6AP is required for this E6 activity, with E6 directing E6AP to the hTERT promoter. We previously reported two E6AP binding-defective HPV16 E6 mutations that induced immortalization of human mammary epithelial cells. Because activation of hTERT is proposed to be necessary for epithelial cell immortalization, we sought to further characterize the relationship between E6/E6AP association and telomerase induction. We demonstrate that while these E6 mutants do not bind E6AP, they retain the capability to stimulate the expression of hTERT. Chromatin immunoprecipitation assays confirmed the presence of Myc, wild-type E6, and the E6AP binding-defective E6 mutants, but not E6AP itself, at the endogenous hTERT promoter. Interestingly, an immortalization-defective E6 mutant localized to the hTERT promoter but failed to increase transcription. We conclude that binding to E6AP is not necessary for E6 localization to or activation of the hTERT promoter and that another activity of E6 is involved in hTERT activation.The best-characterized property of the E6 protein of the cancer-associated human papillomavirus (HPV) is the degradation of p53 mediated by the ubiquitin ligase E6AP (20, 38). Additionally, E6 has several p53-independent activities. HPV type 16 (HPV16) E6 binds to and inhibits the transactivation functions of histone acetyltransferase (HAT) proteins CBP and p300 (36, 51). E6 also interacts with the calcium binding protein E6BP/ERC-55, the Rap GTPase-activating protein E6TP1, and the p53 coactivator hAda3 (8,15,27). An important activity of E6 thought to be necessary for epithelial cell immortalization is its ability to increase telomerase activity (16,26,35).Telomerase is a ribonucleoprotein complex that maintains telomere length. Its RNA subunit serves as a template for the synthesis of telomeric DNA, and its catalytic subunit has been shown to be necessary for telomerase enzymatic activity (49). Most somatic cells have no or very low telomerase activity (4). Senescence can be bypassed, and several primary human cell types can be immortalized, by forced expression of the telomerase catalytic subunit hTERT (4, 24, 44). Cellular oncogenes, as well as HPV16 E6, are known to induce hTERT transcription (10,26,28,47). The hTERT core promoter region contains E and GC boxes with recognition sites for transcription factors including Myc, SP-1, and USF (9, 17, 18, 42). Myc activates hTERT, while other factors, such as Mad, Sip1, and Menin, repress hTERT expression (19,28,34). Myc and Mad are highly unstable proteins and function by forming dimers with the stable protein Max (3, 12). It has been suggested that the hTERT promoter is differentially regulated by switching binding between Myc/Max and Mad/Max dimers (48). This is supported by the finding that Myc/Max complexes were dominant in immortal cells with high telo...

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Section: Resultssupporting

confidence: 81%

Binding of Human Papillomavirus Type 16 E6 to E6AP Is Not Required for Activation of hTERT

Šekaric

Cherry

Androphy

2008

J Virol

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“…While E6AP is required for in vitro degradation systems (9) and immortalized mouse fibroblasts (5), E6AP-null mice that express 16E6 in the skin do not accumulate p53 when irradiated, and mouse embryo kidney cells from those E6AP-null mice are reported to lose p53 upon overexpression of 16E6 (12,22). Further, ubiquitin-independent degradation of p53 by E6 has been described (2).…”

mentioning

confidence: 99%

Peptide Interactions Stabilize and Restructure Human Papillomavirus Type 16 E6 To Interact with p53

Ansari

Brimer

Pol

2012

J Virol

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). Here we show that minimal 16E6-binding LXXLL peptides reshape 16E6 to confer p53 interaction and stabilize 16E6 in vivo but that degradation of p53 by 16E6 requires E6AP expression. These experiments establish a general mechanism for how papillomavirus E6 binding to LXXLL peptides reshapes E6 to then act as an adapter molecule. P apillomavirus E6 oncoproteins interact with target cellular proteins through docking on short peptides often containing the sequence LXXLL (4, 6, 26). The cancer-associated human papillomavirus type 16 (HPV-16) protein E6 (16E6) binds to an LXXLL motif (LQELL) on the cellular E3 ubiquitin ligase E6AP (10); 16E6-E6AP recruits and ubiquitinates p53. Neither 16E6 nor E6AP interacts alone with p53 (8-10, 17, 18) (20). A form of E6AP with a C833A mutation still binds E6 and p53 but fails to ubiquitinate or degrade p53 (19).The necessity of E6AP for p53 degradation by 16E6 is controversial. While E6AP is required for in vitro degradation systems (9) and immortalized mouse fibroblasts (5), E6AP-null mice that express 16E6 in the skin do not accumulate p53 when irradiated, and mouse embryo kidney cells from those E6AP-null mice are reported to lose p53 upon overexpression of 16E6 (12,22). Further, ubiquitin-independent degradation of p53 by E6 has been described (2). These disparate observations raise the questions of whether of E6AP is necessary for degradation and how the specificity of 16E6 for p53 is determined.16E6 binding to the LQELL peptide alone recruits p53 to 16E6 in the absence of full-length E6AP. Our previous studies in yeast (Saccharomyces cerevisiae) had shown that p53 was very weakly recruited by LexA fusions to 16E6, but coexpression of LexA_16E6 with the E6AP C833A mutant (here termed E6AP-Ub Ϫ , for ubiquitin ligase negative) strongly recruited p53 to 16E6 (5). We reasoned that the binding of 16E6 solely to the minimal LQELL peptide of E6AP or similar LXXLL peptides might be sufficient to induce a p53-binding conformation of 16E6. To test this, we fused the 10-residue E6AP LQELL peptide between LexA and 16E6 to provide 16E6 with an LQELL docking site in cis; we similarly fused a mutated LXXLL peptide (LQEAS) between LexA and 16E6 (Fig. 1A). We tested interactions of these LexA fusions by yeast two-hybrid assays with a B42 transactivator-tagged LQELL peptide, B42_E6AP-Ub Ϫ , or with B42_E6AP-Ub Ϫ molecules where LQELL was progressively mutated from LQELL to LQELS or LQEAS. Fusion of the LQELL peptide in cis to 16E6 blocked interaction with B42_LQELL peptide in trans as expected, and mutation of LexA_LQELL_16E6 to LexA_LQEAS_16E6 restored interactions in trans (Fig. 1B, spots 4C and 4D). This is consistent with the LQELL peptide binding in cis to the 16E6 portion of the fusion protein and blocking trans interaction with the B42-fused peptide. Interaction of LQELL_16E6 with B42_E6AP-Ub Ϫ in trans was not blocked, indicating that the interaction of 16E6 with the full E6AP protein is more robust than the interaction with the free LQELL peptide but is still dependent upon an in...

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“…Therefore any radiation damage would not be sufficiently repaired, and damaged cells would be more likely to die during mitosis as they progress through the cell cycle. E6 has previously been shown to sensitize mammary epithelial cells, fibroblasts and keratinocytes to chemically induced death (Xu, Meikrantz et al 1995, Hawkins, Demers et al 1996, Liu, McKalip et al 2000, Liu, Zhao et al 2007), but has been reported to have the opposite effect or no effect in other cell types exposed to ionizing radiation or DNA-damaging chemicals (DeWeese, Walsh et al 1997, Hampson, El Hady et al 2001, Shai, Nguyen et al 2007). Thus, the radiosensitizing effect might be specific to a few cell types, including keratinocytes, the natural hosts for HPVs, and be dependent on the E6*I isoform.…”

Section: Discussionmentioning

confidence: 99%

The Effect of Human Papillomavirus E6 Oncogene on the Radiosensitivity of Non-Oropharyngeal Cancer Cells

Hong¹,

Zhang²,

Zhang³

et al. 2017

CCO

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Background:We have previously shown that stable transfection of the human papillomavirus (HPV) E6*I oncogene can sensitize two HPV negative oropharyngeal cancer (OSCC) cell lines to radiation. In the current study, we extended our work on OSCC to determine whether the HPV E6 oncogene can enhance the radiosensitivity of non-OSCC cell lines. Methods:Three non-OSCC cell lines (melanoma, colorectal adenocarcinoma and large cell lung cancer) were stably transfection with the HPV E6 oncogene (E6 total, E6*I and E6*II) and treated with different doses of radiation. Clonogenic assays were used to measure the radiation survival. Results:Following transfection, there was a reduction in the survival of the melanoma cell line after 2 Gy (SF2) from 0.401 (untransfected) to 0.219 (Melanoma-E6 total). This reduction was not evident at higher doses of radiation. There was no significant change in the SF2 of melanoma-E6*I (0.303) and melanoma-E6*II (0.414). The SF2 colorectal adenocarcinoma and large cell lung cancer cell lines did not change significantly after transfection. Conclusions:The radiosensitizing effect of HPV E6 oncogene is cell line specific. We found no clear evidence of a radiosensitising effect of E6 in these three non-OSCC cancer cell lines.

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HPV16 E6 confers p53-dependent and p53-independent phenotypes in the epidermis of mice deficient for E6AP

Cited by 27 publications

References 57 publications

Binding of Human Papillomavirus Type 16 E6 to E6AP Is Not Required for Activation of hTERT

Binding of Human Papillomavirus Type 16 E6 to E6AP Is Not Required for Activation of hTERT

Peptide Interactions Stabilize and Restructure Human Papillomavirus Type 16 E6 To Interact with p53

The Effect of Human Papillomavirus E6 Oncogene on the Radiosensitivity of Non-Oropharyngeal Cancer Cells

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