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

High-risk human papillomaviruses are the causative agents of cervical and other anogenital cancers. In these cancers, two viral oncogenes, E6 and E7, are expressed. E6 is best known for its ability to inactivate the tumor suppressor p53, which is thought to arise through ubiquitin-mediated degradation of p53 and involve a ternary complex between E6, p53 and the E3 ligase, E6AP. In mice transgenic for wild-type HPV16 E6, its expression leads to epithelial hyperplasia and an abrogation of normal cellular responses to DNA damage. Whereas only the latter phenotype is dependent upon E6's inactivation of p53, both are reduced in transgenic mice expressing an E6 mutant severely reduced in its binding to E6AP and other cellular proteins that bind E6 through a shared alpha-helix motif. Here, we investigated whether E6AP is required for the induction of the above phenotypes through the use of both E6AP-mutant and E6AP-null mice. E6, in the absence of E6AP retains an ability to induce epithelial hyperplasia, abrogate DNA damage responses and inhibit the induction of p53 protein following exposure to ionizing radiation. We conclude that E6 is able to induce both p53-dependent and p53-independent phenotypes through E6AP-independent pathways in the mouse.

The nfkb1 promoter is controlled by proteins of the Ets family.

The gene encoding NFKB1 is autoregulated, responding to NF-kappa B/Rel activation through NF-kappa B binding sites in its promoter, which also contains putative sites for Ets proteins. One of the Ets sites, which we refer to as EBS4, is located next to an NF-kappa B/Rel binding site, kB3, which is absolutely required for activity of the promoter in Jurkat T cells in response to activation by phorbol 12-myristate 13-acetate (PMA), PMA/ionomycin, or the Tax protein from human T cell leukemia virus type I. We show that EBS4 is, required for the full response of the nfkb1 promoter to PMA or PMA/ionomycin in Jurkat cells. EBS4 is bound by Ets-1, Elf-1, and other species. Overexpression of Ets-1 augments the response to PMA/ionomycin and this is reduced by mutation of EBS4. Elf-1 has less effect in conjunction with PMA/ionomycin, but by itself activates the promoter 12-fold. This activation is only partly affected by mutation of EBS4, and a mutant promoter that binds Ets-1, but not Elf-1, at the EBS4 site responds to PMA/ionomycin as efficiently as the wild-type. Ets proteins may be responsible for fine-tuning the activity of the nfkb1 gene in a cell-type-specific manner.

Peripheral tolerance to human papillomavirus E7 oncoprotein occurs by cross-tolerization, is largely Th-2-independent, and is broken by dendritic cell immunization.

The E7 oncoprotein of human papillomavirus 16 functions as a tumor-specific antigen in transformed epithelial cells of the uterine cervix to which immunotherapeutic strategies aimed at CTL induction may be directed. We previously have shown in mice transgenic for the E7 gene driven off an epithelial specific (keratin-14) promoter, that expression of E7 protein in peripheral epithelium is sufficient to tolerize E7-directed CTL precursors (pCTL; Doan et al, J. Virol., 73: 6166-1670, 1999). Here we show that E7 is presented to T cells for tolerization by cells of bone marrow origin ("cross-tolerization"). We demonstrate that tolerization of E7-directed pCTLs occurs within 2 weeks of exposure to E7 in epithelium. It is maintained in the near absence of CD4+ cells and in the absence of the thymus, and is independent of a coexisting E7-directed Th2-type antibody response. Tolerance was broken by immunization with E7 CTL epitope-pulsed dendritic cells. These findings have implications for immunotherapy of patients with human papillomavirus 16-associated cervical carcinoma, whose immune systems may have experienced long-term exposure to E7-expressing epithelial cells.

Immunological responses in human papillomavirus 16 E6/E7-transgenic mice to E7 protein correlate with the presence of skin disease.

The human papillomavirus (HPV) oncogenes, E6 and E7, are believed to contribute to the development of cervical cancers in women infected with certain HPV genotypes, most notably HPV-16 and HPV-18. Given their expression in tumor tissue, E6 and E7 have been implicated as potential tumor-specific antigens. We have examined an HPV-16 E6- and E7-transgenic mouse lineage for immune responses to these viral oncoproteins. Mice in this lineage express the HPV-16 E6 and E7 genes in their skin and eyes, and on aging, these mice frequently develop squamous cell carcinomas and lenticular tumors. Young transgenic mice, which had measurable E7 protein in the eye but not in the skin, were immunologically naive to E7 protein. They mounted an immune response to E7 on immunization comparable to that of nontransgenic controls, suggesting a lack of immune tolerance to this protein. Older line 19 mice, which are susceptible to skin disease associated with transcription of the E6 and E7 open reading frames, had measurable E7 protein in their skin. These older transgenic mice spontaneously developed antibody responses to endogenous E7 protein, particularly in association with skin disease. Also detected in older mice were delayed-type hypersensitivity responses to E7. These finding parallel the humoral immune response to E7 protein in patients with HPV-associated cervical cancer and suggest that line 19 mice may provide a model for studying the immunobiology of HPV-associated cancers.

DEK promotes HPV-positive and -negative head and neck cancer cell proliferation.

Head and neck squamous cell carcinoma (HNSCC) is the sixth most common malignancy worldwide, and patient outcomes using current treatments remain poor. Tumor development is etiologically associated with tobacco or alcohol use and/or human papillomavirus (HPV) infection. HPV-positive HNSCCs, which frequently harbor wild-type p53, carry a more favorable prognosis and are a biologically distinct subgroup when compared with their HPV-negative counterparts. HPV E7 induces expression of the human DEK gene, both in vitro and in vivo. In keratinocytes, DEK overexpression is sufficient for causing oncogenic phenotypes in the absence of E7. Conversely, DEK loss results in cell death in HPV-positive cervical cancer cells at least in part through p53 activation, and Dek knockout mice are relatively resistant to the development of chemically induced skin papillomas. Despite the established oncogenic role of DEK in HPV-associated cervical cancer cell lines and keratinocytes, a functional role of DEK has not yet been explored in HNSCC. Using an established transgenic mouse model of HPV16 E7-induced HNSCC, we demonstrate that Dek is required for optimal proliferation of E7-transgenic epidermal cells and for the growth of HNSCC tumors. Importantly, these studies also demonstrate that DEK protein is universally upregulated in both HPV-positive and -negative human HNSCC tumors relative to adjacent normal tissue. Furthermore, DEK knockdown inhibited the proliferation of HPV-positive and -negative HNSCC cells, establishing a functional role for DEK in human disease. Mechanistic studies reveal that attenuated HNSCC cell growth in response to DEK loss was associated with reduced expression of the oncogenic p53 family member, ΔNp63. Exogenous ΔNp63 expression rescued the proliferative defect in the absence of DEK, thereby establishing a functional DEK-ΔNp63 oncogenic pathway that promotes HNSCC. Taken together, our data demonstrate that DEK stimulates HNSCC cellular growth and identify ΔNp63 as a novel DEK effector.

Secondary structure at the bacteriophage G4 origin of complementary-strand DNA synthesis: in vivo requirements.

The bacteriophage G4 origin of complementary strand DNA synthesis, G4 ori, contains several regions of potential secondary structure. In this study, we ask whether DNA secondary structure is important for G4 ori function in vivo. Point mutations were generated within a region of potential secondary structure so as to disrupt intrastrand base pairing. These mutations led to a strong temperature-dependent reduction in ori function in vivo. A double point mutation which introduces the same base substitutions without destabilizing intrastrand base pairing did not cause a temperature-dependent disruption in ori function. The double mutant did display a slight temperature-independent reduction in ori function compared to the wild-type G4 ori. Based on these findings, we conclude that DNA secondary structure, as well as recognition of specific sequences, is required for G4 ori activity in vivo.

Multiple genetic loci modify risk for retinoblastoma in transgenic mice.

PURPOSE: Forty percent of cases of retinoblastoma, a childhood malignancy of the retina, are linked to the inheritance of a mutant allele of the retinoblastoma susceptibility gene Rb1. Tumor penetrance varies among carriers in different family pedigrees, indicating that other genetic factors may modify risk for occurrence of retinoblastoma. This study was undertaken to determine whether multiple genetic loci modify the risk for retinoblastoma in mice. METHODS: A line of alphaAcry-HPV16E6/E7 transgenic mice expressing the human papillomavirus type 16 E6 and E7 oncogenes (HPV-16 E6 and E7) ectopically in the retina was characterized. E6 and E7 proteins bind to and inactivate the cellular tumor suppressor proteins p53 and Rb, respectively. RESULTS: Retinoblastomas developed rarely when the alphaAcry-HPV16E6/E7 transgene was maintained on the FVB background, but tumors arose with high frequency on C57BL/6 X FVB and C3H x FVB F1 hybrid backgrounds. The incidence of retinoblastoma in the LHbeta-TAG transgenic mice, which express simian virus 40 large tumor antigen (SV40 T-ag), was also influenced by the FVB and C57BL/6 backgrounds. Resistance of the alphaAcry-HPV16E6/E7 FVB mice to retinoblastoma mapped in part to the retinal degeneration (rd) locus. However, multiple genetic experiments indicate that resistance to retinoblastoma depends on additional loci in FVB mice. CONCLUSIONS: Multiple cellular genes can modify risk for retinoblastoma in mice.

The effect of intracerebroventricular infusions of CRF, sauvagine, ACTH (1-24) and ACTH (4-10) on blood pressure in sheep.

This study reviews the effects of intracerebroventricular (i.c.v.) infusion of corticotrophin releasing factor (CRF) and adrenocorticotrophic hormone (ACTH) (1-24) on blood pressure in conscious sheep. The effects of sauvagine, a peptide with 50% homology with CRF and ACTH (4-10) and other analogues of ACTH were studied. Intracerebroventricular infusion of CRF for 24 h at 10 and 100 micrograms/h increased blood pressure and heart rate. Sodium (Na) excretion also increased. Sauvagine at 10 micrograms/h also increased blood pressure. Both peptides raised body temperature and produced 'arousal' behaviour. ACTH (1-24) at 0.8 microgram/h for 48 h raised blood pressure and body temperature but had no significant effect on Na excretion or behavior. ACTH (4-10) and other related analogs (alpha-MSH, alpha gamma 1-MSH) at up to 10 micrograms/h for 48 h had no effects. These studies show that neuropeptides involved in the physiological response to 'stress' may have central effects on blood pressure.

High incidence of female reproductive tract cancers in FA-deficient HPV16-transgenic mice correlates with E7's induction of DNA damage response, an activity mediated by E7's inactivation of pocket proteins.

Fanconi anemia (FA) is a rare genetic disorder caused by defects in a DNA damage repair system, the FA pathway. FA patients frequently develop squamous cell carcinoma (SCC) at sites that are associated with human papillomavirus (HPV)-driven cancer including the female reproductive tract. To assess experimentally whether FA deficiency increases susceptibility to HPV-associated cervical/vaginal cancer, we monitored cancer incidence in the female lower reproductive tract of FA-deficient mice expressing HPV16 oncogenes, E6 and/or E7. FA deficiency specifically increased the incidence of cancers in mice expressing E7; but this effect was not observed in mice just expressing E6. We also observed that E7, but not E6, induced DNA damage as scored by induction of γ-H2AX and 53BP1 (p53 binding protein 1) nuclear foci, and this induction was heightened in FA-deficient tissue. Finally, we discovered that this induction of DNA damage responses was recapitulated in mice deficient in expression of 'pocket' proteins, pRb, p107 and p130, which are established targets of E7. Our findings support the hypothesis that E7 induces cancer by causing DNA damage at least in part through the inactivation of pocket proteins. This hypothesis explains why a deficiency in DNA damage repair would increase susceptibility to E7-driven cancer.

Differential gene expression between skin and cervix induced by the E7 oncoprotein in a transgenic mouse model.

HPV16 E7 oncoprotein expression in K14E7 transgenic mice induces cervical cancer after 6 months of treatment with the co-carcinogen 17ß-estradiol. In untreated mice, E7 also induces skin tumors late in life albeit at low penetrance. These findings indicate that E7 alters cellular functions in cervix and skin so as to predispose these organs to tumorigenesis. Using microarrays, we determined the global genes expression profile in cervical and skin tissue of young adult K14E7 transgenic mice without estrogen treatment. In these tissues, the E7 oncoprotein altered the transcriptional pattern of genes involved in several biological processes including signal transduction, transport, metabolic process, cell adhesion, apoptosis, cell differentiation, immune response and inflammatory response. Among the E7-dysregulated genes were ones not previously known to be involved in cervical neoplasia including DMBT1, GLI1 and 17ßHSD2 in cervix, as well as MMP2, 12, 14, 19 and 27 in skin.

The immortalizing and transforming ability of two common human papillomavirus 16 E6 variants with different prevalences in cervical cancer.

Persistent infection with high-risk human papillomaviruses (HPVs), especially type 16 has been undeniably linked to cervical cancer. The Asian-American (AA) variant of HPV16 is more common in the Americas than the prototype in cervical cancer. The different prevalence is based on three amino acid changes within the E6 protein denoted Q14H/H78Y/L83V. To investigate the mechanism(s) behind this observation, both E6 proteins, in the presence of E7, were evaluated for their ability to extend the life span of and transform primary human foreskin keratinocytes (PHFKs). Long-term cell culture studies resulted in death at passage 9 of vector-transduced PHFKs (negative control), but survival of both E6 PHFKs to passage 65 (and beyond). Compared with E6/E7 PHFKs, AA/E7 PHFKs were significantly faster dividing, developed larger cells in monolayer cultures, showed double the epithelial thickness and expressed cytokeratin 10 when grown as organotypic raft cultures. Telomerase activation and p53 inactivation, two hallmarks of immortalization, were not significantly different between the two populations. Both were resistant to anoikis at later passages, but only AA/E7 PHFKs acquired the capacity for in vitro transformation. Proteomic analysis revealed markedly different protein patterns between E6/E7 and AA/E7, particularly with respect to key cellular metabolic enzymes. Our results provide new insights into the reasons underlying the greater prevalence of the AA variant in cervical cancer as evidenced by characteristics associated with higher oncogenic potential.

Bovine papillomavirus type 1 E1 replication-defective mutants are altered in their transcriptional regulation.

Bovine papillomavirus type 1 (BPV-1) is capable of replicating as a stable, high-copy-number plasmid in transformed rodent cells. The BPV-1 E1 open reading frame (ORF) encodes multiple functions involved in viral DNA replication. Mutations which disrupt the translational integrity of the E1 ORF disable the viral genome from replicating as a stable plasmid and result in the integration of the viral genome into the host chromosome generally at a low copy number. Despite the low copy number of the integrated genomes, BPV-1 E1 mutants transform rodent cells to anchorage independence very efficiently, at levels equal to or greater than that of wild-type (wt) BPV-1. Studies were performed to provide insight into why these low-copy-number, replication-defective mutants are capable of expressing an equal or greater transformation potential than wt BPV-1. Analysis of viral RNA revealed higher rates of transcription per viral genome in cells harboring E1 mutated BPV-1 DNA than in cells containing wt BPV-1 DNA. Furthermore, the levels of viral RNA mapping the P89 promoter were found to be 15- to 35-fold higher in cells transformed by E1 mutated DNAs compared with wt BPV-1 transformants. This promoter controls expression of the BPV-1 E6 transforming gene and is regulated by the viral E2 gene products. The studies presented in this report determined that the E1 mutants were perturbed in their E2 transcriptional regulation, suggesting a possible explanation for the observed P89 induction. Mutations throughout the E1 ORF, in either of the two regions previously identified as encoding distinct replication functions, were altered in viral transcription.

Use of transcriptional repressors to stabilize plasmid copy number of transcriptional fusion vectors.

Strong promoters cloned into transcriptional fusion vectors can adversely affect plasmid copy number. In this study, we investigated the use of transcriptional repressors, lacI and tetR, to stabilize the copy number of plasmids containing the lacUV5 and tetA promoters, respectively. Repression of these promoters was found to prevent plasmid copy number variation. Transcriptional strength of these promoters, when cloned into transcriptional fusion vectors, was determined by measuring the rate of synthesis after derepression with inducer. By using this approach, promoter strength can be accurately measured in vivo, without the need to compensate for copy number variation.

The 23-kilodalton E1 phosphoprotein of bovine papillomavirus type 1 is nonessential for stable plasmid replication in murine C127 cells.

The 23-kDa protein encoded by the 5' segment of the E1 open reading frame of bovine papillomavirus type 1 (BPV1) was previously ascribed a negative regulatory function for the replication of viral plasmid DNA. However, results from recent functional and biochemical studies do not readily support this genetic assignment. Therefore, we have reassessed the role of this protein in papillomavirus DNA replication by using a mutant of BPV1 which is unable to express this E1 protein. This mutant viral DNA was found to replicate extrachromosomally with stability and copy number per cell similar to those of wild-type plasmid DNA. Thus, the absence of expression of the 23-kDa E1 protein did not lead to deregulated viral plasmid replication. We conclude that the 23-kDa E1 protein is nonessential for stable plasmid replication.

Evidence for a switch in the mode of human papillomavirus type 16 DNA replication during the viral life cycle.

The study of human papillomavirus type 16 (HPV-16) replication has been impaired because of the lack of a cell culture system that stably maintains viral replication. Recently, cervical epithelial cell populations that stably maintain HPV-16 replicons at a copy number of approximately 1,000 per cell were derived from an HPV-16-infected patient (W12 cell clone 20863 [W12-E cells]). We used neutral/neutral and neutral/alkaline two-dimensional gel electrophoretic techniques to characterize HPV-16 DNA replication in these cells. When W12-E cells were maintained in an undifferentiated state mimicking the nonproductive stage of the life cycle, HPV-16 DNA was found to replicate primarily by theta structures in a bidirectional manner. The initiation site of HPV-16 DNA replication was mapped to approximately nucleotide 100, and the termination site was mapped to between nucleotides 3398 and 5990. To study the productive stage of HPV-16 DNA replication, W12-E cells were grown under culture conditions that promote differentiation of epithelial cell types. Under these conditions, where virus-like particles were detected, the mode of viral DNA replication changed from theta structure to what is apparently a rolling circle mode. Additionally, CIN 612-9E cells, which were derived from an HPV-31-infected patient and harbor HPV-31 extrachromosomally, exhibited the same switch in the mode of DNA replication upon induction of differentiation. These data argue that a fundamental switch in the mechanism of viral DNA replication occurs during the life cycle of the papillomavirus.

Role of papillomavirus oncogenes in human cervical cancer: transgenic animal studies.

Human papillomaviruses are believed to be etiologic agents for the majority of human cervical carcinoma, a common cancer that is a leading cause of death by cancer among women worldwide. In cervical carcinoma, a subset of papillomaviral genes, namely E6 and E7, are expressed. In vitro tissue culture studies indicate that HPV E6 and E7 are oncogenes, and that their oncogenicity is due in part to their capacity to inactivate cellular tumor suppressor genes. The behavior of E6 and E7 in vitro and the genetic evidence from analysis of human cancers suggest that the E6 and E7 genes play a significant role in the development of cervical cancer. This hypothesis is now being tested using animal models. In this review, we summarize our current knowledge of the oncogenicity of papillomavirus genes that has been generated through their study in transgenic mice.

Bovine papillomavirus type 1 E2 transcriptional regulators directly bind two cellular transcription factors, TFIID and TFIIB.

The bovine papillomavirus type 1 (BPV-1) E2 translational open reading frame encodes three proteins that regulate viral transcription and DNA replication: the E2 transcriptional activator (E2TA), the E2 transcriptional repressor (E2TR) and the E8/E2 transcriptional repressor (E8/E2TR). E2TA is a strong activator of papillomaviral promoters and is required for viral DNA replication. E2TR and E8/E2TR inhibit the activities of E2TA but also possess weak transactivational properties of their own. Two components of the cellular transcription apparatus, TFIID and TFIIB, have previously been shown to associate with other viral and cellular transcriptional activators. We present evidence here that E2TA, the full-length E2 open reading frame gene product, directly binds both of these transcription factors in vitro. Glutathione S-transferase E2TA (GST-E2TA) fusion protein bound in vitro-synthesized TATA-box-binding protein (TBP), a component of TFIID, and in vitro-synthesized TFIIB. Likewise, GST-E2TA bound TFIID and TFIIB present in a nuclear extract from the human cervical cancer-derived cell line, HeLa. The binding of GST-E2TA to TBP and TFIIB required no additional mammalian factors, as shown by direct binding of GST-E2TA to bacterially synthesized recombinant TBP and recombinant TFIIB. The domain of E2TA required for its interaction with both TBP and TFIIB was localized to the C terminus of E2TA, a region also present in E2TR and E8/E2TR. This domain lies within the region of E2TA previously shown to confer cooperative DNA binding by E2TA and TBP and overlaps with the region of E2TA required for DNA binding and dimerization. Our findings, taken in context with previous studies, lead us to conclude that (i) cooperative DNA binding by E2 proteins and TBP is likely mediated by the direct binding of E2 proteins to TBP, (ii) the weak transcriptional transactivation by E2TR and E8/E2TR may result as a consequence of direct TBP and TFIIB binding by these proteins, and (iii) TBP and/or TFIIB binding may be required but is not sufficient for E2TA's strong transactivational activity.