The octamer binding site in the HPV16 regulatory region produces opposite effects on gene expression in cervical and non-cervical cells

Transgenic HPV11-E2 protein modulates URR activity in vivo

In vitro experiments have shown that the E2 protein of human papillomaviruses (HPV) binds to the upstream regulatory region (URR) of the viral genome and modulates transcription. Additionally, it seems to be a necessary component for viral DNA replication together with E1. We have developed a transgenic mouse model containing the URR region of the low-risk virus HPV11 that regulates the expression of the lacZ reporter gene. Most interestingly, in these mice, the transgene was exclusively expressed in the bulge region of the hair follicle but not in any other tissues. Further experimental data indicate that in double transgenic mice that also express the HPV11-E2 protein under the control of the Ubiquitin C-promoter, the transcription of the reporter gene is modulated. When E2 is present, the expression of the reporter gene also occurs exclusively in the bulge region of the hair follicles as it does in the single transgenic mice, but the expression of the lacZ driven by the URR is increased and the statistical spread is greater. Even if the expression of the reporter gene occurs in the hair follicles of the dorsal skin of an animal uniform, E2 obviously has the capacity for both to induce and to repress the URR activity in vivo.

Mechanisms of virus immune evasion lead to development from chronic inflammation to cancer formation associated with human papillomavirus infection

Human papillomavirus (HPV) has developed strategies to escape eradication by innate and adaptive immunity. Immune response evasion has been considered an important aspect of HPV persistence, which is the main contributing factor leading to HPV-related cancers. HPV-induced cancers expressing viral oncogenes E6 and E7 are potentially recognized by the immune system. The major histocompatibility complex (MHC) class I molecules are patrolled by natural killer cells and CD8+ cytotoxic T lymphocytes, respectively. This system of recognition is a main target for the strategies of immune evasion deployed by viruses. The viral immune evasion proteins constitute useful tools to block defined stages of the MHC class I presentation pathway, and in this way HPV avoids the host immune response. The long latency period from initial infection to persistence signifies that HPV evolves mechanisms to escape the immune response. It has now been established that there are oncogenic mechanisms by which E7 binds to and degrades tumor suppressor Rb, while E6 binds to and inactivates tumor suppressor p53. Therefore, interaction of p53 and pRb proteins can give rise to an increased immortalization and genomic instability. Overexpression of NF-κB in cervical and penile cancers suggests that NF-κB activation is a key modulator in driving chronic inflammation to cancer. HPV oncogene-mediated suppression of NF-κB activity contributes to HPV escape from the immune system. This review focuses on the diverse mechanisms of the virus immune evasion with HPV that leads to chronic inflammation and cancer.

The HPV Cellular Transactivator Brn-3a Can Be Used to Predict Cervical Adenocarcinoma and Squamous Carcinoma Precancer Lesions in the Developed and Developing Worlds

The cellular transactivator Brn-3a has previously been shown to be expressed at elevated levels in the cervix of women with squamous cell carcinoma of the cervix (SCC) and to activate the expression of HPV E6 mRNA. In this study, we show that common and rare cervical precancer lesions, including those of adenocarcinoma (AC), which are usually difficult to diagnose using classical procedures, also expressed high levels of Brn-3a and can be diagnosed by measuring the levels of Brn-3a and E6 mRNAs.

The cellular transcription factor Brn-3a and the smoking-related substance nicotine interact to regulate the activity of the HPV URR in the cervix

The cellular transcription factor Brn-3a differentially regulates different human papilloma virus (HPV)-16 variants that are associated with different risks of progression to cervical carcinoma in infected humans. The upstream regulatory regions (URRs) of high- and intermediate-risk HPV-16 variants are activated by the cellular transcription factor Brn-3a, whereas the URR of a low-risk HPV-16 variant is not. In this study, we show in transfection assays that Brn-3a and the smoking-related substance nicotine produce stronger responsiveness of the URR of the low- and high-risk variants than with either factor alone, but not the intermediate-risk variant. We determined that this synergistic activity of Brn-3a/nicotine is due to two nucleotide differences in the URR, crucial for oncogenic E6/E7 transactivation. Mutant constructs in which the nucleotide residues were substituted alter Brn-3a/nicotine responsiveness. Importantly, women smokers with high levels of Brn-3a infected with low- or high-risk HPV-16 variants have augmented E6 levels, and were more frequently diagnosed with higher grades of cervical intraepithelial neoplasia (CIN) and cancer, as compared with non-smokers who were infected with similar variants and expressed similar levels of Brn-3a. Therefore, this study defines the specific interplay between the cellular transactivator Brn-3a, the environmental smoking-related substance nicotine and specific HPV variants in cervical carcinogenesis, and thus helps to explain why some women are susceptible to rapid CIN progression and cancer and others are not.

Addition of a single E2 binding site to the human papillomavirus (HPV) type 16 long control region enhances killing of HPV positive cells via HPV E2 protein-regulated herpes simplex virus type 1 thymidine kinase-mediated suicide gene therapy

Human papillomavirus type 16 (HPV16) is associated with the development of anogenital cancers and their precursor lesions, intraepithelial neoplasia. Treatment strategies against HPV-induced intraepithelial neoplasia are not HPV specific and mostly consist of physical removal or ablation of lesions. We had previously designed an HPV-specific approach to kill HPV-infected cells by the herpes simplex virus type 1 thymidine kinase (TK) gene driven by HPV E2 binding to E2-binding sites (E2BS) in the native HPV16 long control region. E2-induced TK expression renders the cells sensitive to the prodrug ganciclovir. To optimize this therapeutic approach, we modified the native long control region by adding variable numbers of E2BS adjacent to E2BS4, resulting in greatly increased cell death in HPV-positive cell lines with variable levels of E2 protein expression and no reduction in HPV specificity. Our results showed maximum increase in TK expression and cell killing when one additional E2BS was added adjacent to E2BS. As HPV-infected patients also exhibit variable E2 expression across lesions and within a lesion, this approach may potentiate the clinical utility of the herpes simplex virus type 1 TK/ganciclovir therapeutic approach.

The role of HPV type in Recurrent Respiratory Papillomatosis

OBJECTIVE

Human Papillomavirus (HPV) 6 and 11 are the aetiological agents responsible for Recurrent Respiratory Papillomatosis (RRP). There is general consensus that HPV11 results in more aggressive disease compared to HPV6.

METHOD

Pubmed was searched using the terms respiratory papillomatosis, HPV 6 and HPV11. Comparisons were made in the outcomes of HPV6 versus HPV11 positive RRP disease.

RESULTS

There are numerous sub-types or variants of both HPV6 and HPV11. These sub-types have different activities at least in-vitro. The numbers of different HPV types within RRP tissue may be more extensive than initially appeared. This depends specifically upon the HPV types tested for.

CONCLUSION

The clinical differences between HPV6 and HPV11 disease may not be accurately predictable as these viruses exist in numerous sub-types. Also, RRP tissue may contain more than one subtype or even be co-infected with other viruses that may influence outcome. In-vitro studies upon cell lines are a reasonable starting point for evaluation of these differences.

Biomarkers in cervical precancer management: the new frontiers

The major cause of cervical cancer and its pre-invasive lesions is persistent infections with oncogenic human papillomavirus (HPV). Viral replication and integration in the cervix depends on the ordered expression of viral gene products, which can lead to overexpression of multiple molecular proteins or biomarkers. These novel biomarkers allow the monitoring of essential molecular events in histological or cytological specimens and are likely to improve the detection of lesions that have a high risk of progression in both primary screening and triage settings. This review focuses on these molecular markers and their role in the diagnosis and management of cervical dysplasia and cancer.

A potent replicative delta-24 adenoviral vector driven by the promoter of human papillomavirus 16 that is highly selective for associated neoplasms

BACKGROUND

Several human epithelial neoplasms are associated with high-risk strains of human papillomavirus (HPV) such as cervical, anorectal, and other carcinomas. For some tumor types the current therapeutic tools are only palliative. Conditionally replicative adenoviruses (CRAds) are promising antineoplastic agents, which also can trigger confined antitumor effects.

METHODS

We constructed a series of CRAds driven by the upstream regulatory promoter region (URR) of an Asian-American variant of HPV-16, which contained different mutations at the E1A region (dl1015 and/or Delta24) and wild-type. All vectors were tested in vitro for viral replication and cytotoxicity. Viral DNA replication and E1A expression were also assessed by quantitative PCR. Finally, we confirmed the antitumoral efficacy of this vector in injected and non-injected xenotransplanted cervical tumors in a murine model for tumor regression and survival studies.

RESULTS

A vector denominated Ad-URR/E1ADelta24 displayed a potent cytopathic effect associated with high selectivity for HPV+ cell lines. We found that the oncolytic effect of this CRAd was comparable to Ad-wt or Ad-Delta24, but this efficacy was significantly attenuated in HPV- cell lines, an effect that was contributed by the URR promoter. Ad-URR/E1ADelta24 was very effective to control tumor growth, in both, injected and non-injected tumors generated with two different HPV+ cell lines.

CONCLUSIONS

CRAd Ad-URR/E1ADelta24 is a highly selective vector for HPV+ cell lines and tumors that preserves the oncolytic efficacy of Ad-wt and Ad-Delta24. Our preclinical data suggest that this vector may be useful and safe for the treatment of tumors induced by HPV, like cervical cancers.

Human papillomaviruses: basic mechanisms of pathogenesis and oncogenicity

Human papillomaviruses (HPVs) are small double-stranded DNA viruses that infect the cutaneous and mucosal epithelium. Infection by specific HPV types has been linked to the development of cervical carcinoma. HPV infects epithelial cells that undergo terminal differentiation and so encode multiple mechanisms to override the normal regulation of differentiation to produce progeny virions. Two viral proteins, E6 and E7, alter cell cycle control and are the main arbitrators of HPV-induced oncogenesis. Recent data suggest that E6 and E7 also play a major role in the inhibition of the host cell innate immune response to HPV. The E1 and E2 proteins, in combination with various cellular factors, mediate viral replication. In addition, E2 has been implicated in both viral and cellular transcriptional control. Despite decades of research, the function of other viral proteins still remains unclear. While prophylactic vaccines to block genital HPV infection will soon be available, the widespread nature of HPV infection requires greater understanding of both the HPV life cycle as well as the mechanisms underlying HPV-induced carcinogenesis.

Detection of cervical abnormalities in a developing country using measurement of Brn-3a in cervical smears

OBJECTIVE

We have previously shown that Brn-3a is elevated in biopsies from women in the United Kingdom with high grade cervical neoplasia, and that it specifically trans-activates the HPV URR in vitro and in vivo. The aim of this study is to establish the relationship of Brn-3a, HPV E6 and pathological diagnosis in cervical smear from women in a developing country with a high prevalence of cervical disease. This is a follow-up of our previous work in which for the first time Brn-3a and E6 levels in cervical smears from women in United Kingdom were shown to correlate with the histological diagnosis of cervical neoplasia and were even better in predicting underlying pre-malignant disease than conventional procedures.

METHOD

Cervical smears from 295 women with cervical abnormalities attending gynecological clinics in Brazil were used to make RNA. The mRNA levels of Brn-3a and HPV E6 were measured and the data obtained were used to establish the relationship between Brn-3a and the histological diagnosis.

RESULTS

The cellular transcription factor Brn-3a was readily measured in cervical smears from the Brazilian population. Its presence was shown to be frequently associated with the expression of HPV E6. The measured level of Brn-3a parallels the severity of the cervical ailment and predicts the pathological categories.

CONCLUSIONS

The ability of Brn-3a to predict for cervical ailments is independent to the geographical characteristics of the population, and hence it could be used routinely as an adjunct to colposcopy and pathological diagnosis in developing and developed countries.

Cloning, genomic organization, expression, and effect on beta-casein promoter activity of a novel isoform of the mouse Oct-1 transcription factor

The ubiquitously expressed transcription factor Oct-1, a member of the POU domain factors, is involved in the regulation of expression of many tissue-specific and house-keeping genes. Multiple alternatively spliced isoforms of Oct-1 have been identified in human and mouse cells. The expression patterns of these isoforms and the analysis of their genomic organization and structure have suggested that the structural variation of Oct-1 isoforms may be important in conferring target and tissue specificity to its transcriptional activity. In this study, we have cloned and sequenced a new mouse Oct-1 isoform, named mOct-1Z. This novel isoform differs markedly at the C-terminus from the previously identified Oct-1 isoforms A, B, and C. It is generated by alternative splicing from the Oct-1 gene and its transcript exhibits a frameshift followed by an early stop codon, thus, its predicted protein has a distinct, much shorter C-terminal tail. However, this truncated isoform could still effectively bind to a consensus Oct-1 motif oligonucleotide and, like Oct-1B, activated the basal promoter activity of the mouse beta-casein gene. Oct-1Z is another ubiquitously expressed Oct-1 isoform, its transcript being detected in all mouse tissues examined, including the mammary gland, liver, lung, kidney, spleen, small intestine mucosa, uterus, and ovary.

Genetic and biochemical analysis of cis regulatory elements within the keratinocyte enhancer region of the human papillomavirus type 31 upstream regulatory region during different stages of the viral life cycle

Using linker scanning mutational analysis, we recently identified potential cis regulatory elements contained within the 5' upstream regulatory region (URR) domain and auxiliary enhancer (AE) region of the human papillomavirus type 31 (HPV31) URR involved in the regulation of E6/E7 promoter activity at different stages of the viral life cycle. For the present study, we extended the linker scanning mutational analysis to identify potential cis elements located in the keratinocyte enhancer (KE) region (nucleotides 7511 to 7762) of the HPV31 URR and to characterize cellular factors that bind to these elements under conditions representing different stages of the viral life cycle. The linker scanning mutational analysis identified viral cis elements located in the KE region that regulate transcription in the presence and absence of any viral gene products or viral DNA replication and determine the role of host tissue differentiation on viral transcriptional regulation. Using electrophoretic mobility shift assays, we illustrated defined reorganization in the composition of cellular transcription factors binding to the same cis regulatory elements at different stages of the HPV differentiation-dependent life cycle. Our studies provide an extensive map of functional elements in the KE region of the HPV31 URR, identify cis regulatory elements that exhibit significant transcription regulatory potential, and illustrate changes in specific protein-DNA interactions at different stages of the viral life cycle. The variable recruitment of transcription factors to the same cis element under different cellular conditions may represent a mechanism underlying the tight link between keratinocyte differentiation and E6/E7 expression.

Measurement of Brn-3a levels in Pap smears provides a novel diagnostic marker for the detection of cervical neoplasia

OBJECTIVES

We have previously demonstrated that Brn-3a cellular transcription factor activates transcription of the human papillomavirus (HPV) E6 and E7 oncogenes in human cervical cancer cells and that Brn-3a levels are dramatically elevated in biopsies from women with high-grade cervical neoplasia. The aim of this study was to establish the relationship between Brn-3a levels in Pap smears and the histological diagnoses. We also analysed whether Brn-3a levels can be used in combination with Pap smear to predict the presence of cervical intraepithelial lesion.

METHODS

Two hundred thirty-eight women who were referred with abnormal Pap smear underwent a diagnostic colposcopy, repeat in-study Pap smear, colposcopically directed biopsy, and assessment of Brn-3a and HPV-16 E6 m-RNA levels. Data were analysed to assess the association between Brn-3a levels and the histological diagnosis.

RESULTS

Brn-3a was readily measured in smears and showed a statistically significant correlation with the grade of cervical abnormality. Positive Brn-3a is associated with increased relative risk of higher-grade lesion. Moreover, measurement of Brn-3a levels in smears can be used to detect a significant proportion of cervical lesions that were missed by Pap smear.

CONCLUSION

Measurement of Brn-3a levels in routinely taken Pap smears is a feasible technique that correlates with the severity of the epithelial abnormality and is a useful adjunct to cytology. Brn-3a appears to have great promise since it detects activation of oncogenic HPVs rather than simply detecting their presence, as is currently being done.

Involvement of Oct-1 in transcriptional regulation of beta-casein gene expression in mouse mammary gland

Mouse beta-casein gene promoter contains a region termed block C which is crucial for its gene transcription induced by lactogenic hormones. Nuclear extracts from mouse mammary glands contain at least two binding complexes (DS1 and DS2) which specifically bind to double-stranded block C region DNA. The binding sequence of these complexes was identified to be 5'-AAATTAGCATGT-3' which contains a sequence element related to the consensus octamer motif's complement ATTTGCAT. In the present study, we demonstrate that this sequence element indeed is the binding site for octamer-binding transcription factors (Octs) and Octs represent the double-stranded DNA binding proteins specifically binding to the block C region. Formation of the specific double-stranded binding complexes can be completely blocked by Oct binding motif oligonucleotides and anti-rOct-1 antiserum. We also show that Oct-1B represents at least partial, if not all, double-stranded binding protein, DS1, in mammary nuclear extract. Oct-1B may function as a transcriptional activator on casein gene promoter. The Oct binding activity to beta-casein gene promoter in the mammary gland is affected under influence of hormones both in vitro and in vivo. The DS1 binding activity can be induced by the combination of lactogenic hormones insulin, hydrocortisone and prolactin in organ culture of virgin mouse mammary gland. The binding activity in vivo can be induced by injection of progesterone or its combination with estradiol in virgin mice.

A novel silencer element in the bovine papillomavirus type 4 promoter represses the transcriptional response to papillomavirus E2 protein

The long control regions (LCRs) of mucosal epitheliotropic papillomaviruses have similar organizations: a promoter region, an enhancer region, and a highly conserved distribution of E2 DNA binding sites (C. Desaintes and C. Demeret, Semin. Cancer Biol. 7:339--347, 1996). The enhancer of these viruses is epithelial cell specific, as it fails to activate transcription from heterologous promoters in nonepithelial cell types (B. Gloss, H. U. Bernard, K. Seedorf, and G. Klock, EMBO J. 6:3735--3743, 1987). Using the bovine papillomavirus type 4 (BPV-4) LCR and a bovine primary cell system, we have shown previously that a level of epithelial specificity resides in a papillomavirus promoter region. The BPV-4 promoter shows an enhanced response to transcriptional activators in epithelial cells compared with that of fibroblasts (K. W. Vance, M. S. Campo, and I. M. Morgan, J. Biol. Chem. 274:27839--27844, 1999). A chimeric lcr/tk promoter suggests that the upstream BPV-4 promoter region determines the cell-type-selective response of this promoter in fibroblasts and keratinocytes. Promoter deletion analysis identified two novel repressor elements that are, at least in part, responsible for mediating the differential response of this promoter to upstream activators in fibroblasts and keratinocytes. One of these elements, promoter repressor element 2 (PRE-2), is conserved in position and sequence in the related mucosal epitheliotropic papillomaviruses, BPV-3 and BPV-6. PRE-2 functions in cis to repress the basal activity of the simian virus 40 promoter and binds a specific protein complex. We identify the exact nucleotides necessary for binding and correlate loss of binding with loss of transcriptional repression. We also incorporate these mutations into the BPV-4 promoter and demonstrate an enhanced response of the mutated promoter to E2 in fibroblasts. The DNA binding protein in the detected complex is shown to have a molecular mass of approximately 50 kDa. The PRE-2 binding protein represents a novel transcriptional repressor and regulator of papillomavirus transcription.

The Brn-3a Transcription Factor Plays a Critical Role in Regulating Human Papilloma Virus Gene Expression and Determining the Growth Characteristics of Cervical Cancer Cells

The Brn-3a POU family transcription factor has previously been shown to activate the human papilloma virus type 16 (HPV-16) promoter driving the expression of the E6- and E7-transforming proteins. Moreover, Brn-3a is overexpressed approximately 300-fold in cervical biopsies from women with cervical intra-epithelial neoplasia type 3 (CIN3) compared with normal cervical material. To test the role of Brn-3a in cervical neoplasia we have manipulated its expression in cervical carcinoma-derived cell lines with or without endogenous HPV genes. In HPV-expressing cells, reduction in Brn-3a expression specifically reduces HPV gene expression, growth rate, saturation density and anchorage-independent growth, whereas these effects are not observed when Brn-3a expression is reduced in cervical cells lacking HPV genomes. Together with our previous observations, these findings indicate a critical role for Brn-3a in regulating HPV gene expression and thereby in controlling the growth/transformation of cervical cells.

The human papillomavirus type 11 upstream regulatory region triggers hair-follicle-specific gene expression in transgenic mice

We have generated transgenic mice carrying the URR of the human papillomavirus type 11 ligated in front of the Escherichia coli beta-galactosidase coding region sequence. Using X-Gal staining to demonstrate beta-galactosidase production, we observed a hair-specific transcription of the reporter gene. This transcription was limited to the epithelial cells of the hair bulge region. The transgene was developmentally regulated, as no LacZ staining was demonstrated during embryogenesis and specific staining was first observed after birth. Surprisingly, dexamethasone and ultraviolet B, but not phorbol myristate acetate or progesterone treatment of the animals resulted in an increase in number and intensity of hair follicles expressing the reporter gene.

Regulation of DNA virus transcription by cellular POU family transcription factors

In the same way as other viral functions, the transcription of viral genes is frequently controlled by cellular regulatory proteins either acting alone or together with virally encoded factors. In this review, I discuss three examples of such regulation in different types of DNA viruses by different members of the POU family of transcription factors, all of which involve viruses which play a role in the aetiology of specific human diseases. These are the glial cell-specific transcription of JC virus which is controlled by the glial cell specific POU factor Tst-1; the regulation of human papillomavirus gene expression in the cervix by positively and negatively acting POU factors and the manner in which the balance between lytic or latent infection with HSV is controlled by positively and negatively acting POU factors which differ in their ability to interact with the virally encoded transactivator VP16. As well as being of interest in themselves, these processes may offer a therapeutic target for controlling the diseases caused by these very different viruses.

The HPV-activating cellular transcription factor Brn-3a is overexpressed in CIN3 cervical lesions

The cervical cellular transcription factors Brn-3a and Brn-3b have antagonistic effects on transcription of the human papilloma virus types 16 and 18 E6 and E7 oncogenes, with Brn-3a activating expression and Brn-3b repressing it. We therefore measured expression of Brn-3a and Brn-3b mRNAs in biopsies from 16 women with no detectable cervical abnormality, and in 14 women with cervical intraepithelial neoplasia grade 3 (CIN3) lesions. Although the mean level of Brn-3b expression was similar in both groups, the mean level of Brn-3a expression was over 300-fold higher in the CIN3 samples when compared with normals. Elevated expression of Brn-3a was also detected in 16 histologically normal regions of the cervix adjacent to the CIN3 lesions, indicating that elevation of Brn-3a levels is not confined to the lesion in women with CIN3, and is thus not a consequence of the oncogenic process. The elevated levels of Brn-3a in the CIN3 patient samples, together with the activating effect of Brn-3a on HPV-16 and -18 oncogene expression, suggest that induction of this factor is involved in activating HPV-16 and -18 oncogene expression in the cervix, and hence in the production of cervical cancers induced by HPV.

Regulation of the serine proteinase inhibitor (SERPIN) gene alpha 1-antitrypsin: a paradigm for other SERPINs

alpha 1-antitrypsin (AAT) is the archetypal member of the serine proteinase inhibitor (SERPIN) gene family. AAT is an acute-phase reactant and the plasma concentration increases three- to four-fold during the inflammatory response. In hepatocytes this increase is mediated primarily by the cytokine interleukin-6 (IL-6) via the transcription factor NF-IL6. The AAT gene contains at least two enhancer elements, one at the 5' end of the gene and the other at the 3' end. Functional studies performed in mammalian hepatoma cells (Hep G2) using constructs containing these AAT enhancer regions linked to a reporter gene have demonstrated that the 5' enhancer is dominant under basal conditions and that, following stimulation with IL-6, both enhancers are essential and the 3' enhancer plays a major role. We have identified a mutation associated with lung disease which occurs in the 3' AAT enhancer; the mutation occurs at a binding site for the ubiquitous transcription factor Oct-1. The functional significance of this mutation is a deficient IL-6 response. Using the AAT gene as a model, we describe the interactions which occur between transcription factors within the 3' enhancer and also those which take place between the 5' and 3' enhancers. These studies shed light on the molecular mechanism of the acute-phase response which could possibly be extended to other members of the SERPIN gene family.

Correlation of MIB-1 antigen expression with transcription factors Skn-1, Oct-1, AP-2, and HPV type in cervical intraepithelial neoplasia

Recently, interest in transcription factor coding genes has emerged in many human diseases. Transcription factors, responding both to extracellular and to intracellular signals, exercise an important regulatory control over the proliferation and differentiation of cells. During the development of CIN (cervical intraepithelial neoplasia) lesions, normal regulation of the cell cycle seems to be disturbed. Transcription factors have been shown in vitro to be intimately involved in the expression of HPV (human papillomavirus) early genes, which affect the development of cervical precancer lesions. To test the relevance of in vitro findings in clinical samples, the expression of transcription factors Skn-1, Oct-1, and AP-2 was analysed in 31 normal cervical epithelial samples and in 55 CIN lesions. The results were correlated with the HPV status and cell proliferation activity of the squamous epithelium as measured by MIB-1 antibody. MIB-1 staining is an applicable marker of CIN, correlating strongly with the CIN grade (P < 0.001). The presence of HPV DNA did not accelerate the cell proliferation rate or change significantly the immunoreactivity of Skn-1, Oct-1, or AP-2 antibodies. The staining patterns of these transcription factors were significantly influenced only by the CIN grade. Transcription factors generally showed weaker expression in the dysplastic samples, although the nuclear staining of AP-2 increased markedly (P = 0.046) in the superficial layer of the CIN III samples. These findings suggest that changes in the expression of transcription factors may be important in studying the proliferative activity of CIN lesions.

Transcription activities of human papillomavirus type 11 E6 promoter-proximal elements in raft and submerged cultures of foreskin keratinocytes

Human papillomaviruses (HPVs) replicate only in differentiated squamous epithelia in warts and in epithelial raft cultures grown at the medium-air interface. Virus-encoded and host transcription factors are thought to be responsible for repressing the viral enhancer and promoter located within the upstream regulatory region (URR) in the undifferentiated basal and parabasal cells while up-regulating their activities in the differentiated spinous cells. Using recombinant retroviruses, we acutely transduced neonatal foreskin keratinocytes (PHKs) with a lacZ reporter gene driven by the wild-type URR of the low-risk HPV type 11 or by a URR with individual mutations in seven promoter-proximal elements, some of which have not been characterized previously. Beta-galactosidase activities were detected in the submerged, proliferating PHKs and also in the differentiated spinous cells, but not in the steady-state proliferating basal cells, of stratified raft cultures. In particular, mutation of an Oct1, an Sp1, or a previously unknown promoter-proximal AP1 site severely reduced the reporter activity, whereas mutation of either of two NF1 sites flanking the Oct1 site had no effect. These results demonstrate changes in cellular transcription factor profiles under different culture conditions and begin to characterize the naturally differentiation-dependent activation of the URR. They provide one molecular explanation for the patterns of HPV expression in warts and help validate epithelial raft cultures as an important experimental system for genetic dissection of HPV regulatory elements.

The octamer-binding proteins Oct-1 and Oct-2 repress the HIV long terminal repeat promoter and its transactivation by Tat

Although the HIV-1 long terminal repeat (LTR) contains four potential binding sites for the octamer-binding protein, Oct-1, which is known to interact with the HIV-1 Tat protein, the effect of the Oct-1 factor on HIV LTR-driven gene expression has not previously been reported. We show here that both Oct-1, and to a lesser extent the related Oct-2 protein, can repress both the basal activity of the HIV-1 LTR and its transactivation by Tat. These effects are still observed with an HIV LTR construct containing only a single octamer-binding site located between the TATA box and the transcriptional start site. The stronger inhibitory effect of Oct-1 on both these promoters is dependent upon its C-terminal region which cannot be effectively replaced by the equivalent region of Oct-2. These effects are discussed in terms of the regulation of HIV LTR activity in different cell types and in response to T-cell activation.

Regulation of human papillomavirus transcription by the differentiation-dependent epithelial factor Epoc-1/skn-1a

Human papillomavirus (HPV) early gene expression is closely linked to the differentiation status of infected epithelial cells. Typically, HPV type 16 (HPV16) or HPV18 E6 and E7 transcripts are only barely detectable within the undifferentiated basal cell layer, but their levels increase concomitantly with higher degrees of epithelial cell differentiation in suprabasal cells. A similar differentiation-dependent distribution of expression has been reported for the recently cloned epithelial cell specific transcription factor Epoc-1/skn-1a. We therefore examined whether Epoc-1/skn-1a may be directly involved in the activation of HPV E6/E7 transcription. Transient transfection studies showed that Epoc-1/skn-1a specifically stimulated the HPV16 and HPV18 E6/E7 promoters. Moreover, ectopically expressed Epoc-1/skn-1a was sufficient to stimulate HPV transcription also in nonepithelial cells. By deletion analyses, the Epoc-1/skn-1a-responsive element was mapped to the promoter-proximal portion of the HPV18 transcriptional control region. Footprint analyses and gel retardation assays demonstrated direct binding of Epoc-1/skn-1a to a hitherto uncharacterized site within this region. Mutation of the Epoc-1/skn-1a recognition site within the context of the complete HPV18 upstream regulatory region inhibited Epoc-1/skn-1a-mediated transactivation. These results show that Epoc-1/skn-1a can directly activate the E6/E7 promoter by binding to the viral transcriptional control region. Thus, Epoc-1/skn-1a may be involved in the differentiation-dependent regulation of HPV transcription.

The enhancer in the long control region of human papillomavirus type 16 is up-regulated by PEF-1 and down-regulated by Oct-1

The minimal enhancer in the long control region of human papillomavirus type 16 regulates cell type and constitutive expression from the promoter P97. This region contains at least four DNase I footprints (fp4e, fp5e, fp6e, and fp7e). We have shown that fp5e is crucial to enhancer function and have described an apparently novel factor (PEF-1) binding fp5e (S. Cuthill, G. J. Sibbet, and M. S. Campo, Mol. Carcinog. 8:9-104, 1993). Further analyses reveal that Oct-1 or an Oct-related factor binds fp5e at a site overlapping that of PEF-1. The binding of Oct-1 to fp5e has been demonstrated by electrophoretic mobility shift assays, by oligonucleotide competition studies, and by using an Oct-1-specific anti-POU serum. The location of the Oct-1 site has been confirmed by a panel of mutants across fp5e. Mutations that block PEF-1 binding to fp5e also block enhancer/promoter activity of the long control region, whereas mutations that block Oct-1 binding significantly increase enhancer/promoter activity. Thus, although both PEF-1 and Oct-1 interact with fp5e, they appear to regulate human papillomavirus expression in opposite ways.

The opposite and antagonistic effects of the closely related POU family transcription factors Brn-3a and Brn-3b on the activity of a target promoter are dependent on differences in the POU domain

The Brn-3a, Brn-3b, and Brn-3c POU family transcription factors are closely related to one another and are members of the group IV subfamily of POU factors. Here we show that despite this close relationship, the factors have different effects on the activity of a target promoter: Brn-3a and Brn-3c stimulate the promoter whereas Brn-3b represses it. Moreover, Brn-3b can antagonize the stimulatory effect of Brn-3a on promoter activity and can also inhibit promoter activation by the Oct-2.1 POU factor. The difference in the transactivation activities of Brn-3a and Brn-3b is dependent upon the C-terminal region containing the POU domain of the two proteins, since exchange of this domain between the two factors converts Brn-3a into a repressor and Brn-3b into an activator.

The opposite and antagonistic effects of the closely related POU family transcription factors Brn-3a and Brn-3b on the activity of a target promoter are dependent on differences in the POU domain

The Brn-3a, Brn-3b, and Brn-3c POU family transcription factors are closely related to one another and are members of the group IV subfamily of POU factors. Here we show that despite this close relationship, the factors have different effects on the activity of a target promoter: Brn-3a and Brn-3c stimulate the promoter whereas Brn-3b represses it. Moreover, Brn-3b can antagonize the stimulatory effect of Brn-3a on promoter activity and can also inhibit promoter activation by the Oct-2.1 POU factor. The difference in the transactivation activities of Brn-3a and Brn-3b is dependent upon the C-terminal region containing the POU domain of the two proteins, since exchange of this domain between the two factors converts Brn-3a into a repressor and Brn-3b into an activator.

Cellular control of human papillomavirus oncogene transcription

Specific types of human papillomaviruses (HPVs) are closely associated with the development of cervical cancer. The transforming ability of these high-risk HPV types depends on the expression of the viral E6 and E7 oncogenes. It is therefore of particular interest to elucidate the molecular mechanisms that result in the activation of E6/E7 expression during HPV-associated tumorigenesis. Recently, much progress has been made in characterizing the proteins involved in the regulation of HPV oncogene transcription. This review describes the functional significance of cellular factors involved in the transcriptional control of the E6/E7 promoter for the two most common HPV types associated with cervical cancer, HPV16 and HPV18. In addition, we discuss regulatory pathways that may contribute to the epithelial cells specificity of E6/E7 transcription. The definition of the factors that regulate HPV oncogene transcription could provide new insights into the molecular mechanisms activating viral oncogene expression during cervical carcinogenesis and forms an experimental basis for investigating the specific biochemical pathways that contribute to HPV-associated malignant cell transformation.

Transcriptional control of human papillomavirus (HPV) oncogene expression: composition of the HPV type 18 upstream regulatory region

The malignant transformation potential of high-risk human papillomaviruses (HPVs) is closely linked to the expression of the viral E6 and E7 genes. To elucidate the molecular mechanisms resulting in HPV oncogene expression, a systematic analysis of the cis-regulatory elements within the HPV type 18 (HPV18) upstream regulatory region (URR) which regulate the activity of the E6/E7 promoter was performed. As the functional behavior of a given cis-regulatory element can be strongly influenced by the overall composition of a transcriptional control region, individual elements were inactivated by site-directed mutagenesis in the physiological context of the complete HPV18 URR. Subsequently, the effects of these mutations on the activity of the E6/E7 promoter were assessed by transient transfection assays. We found that the transcriptional stimulation of the E6/E7 promoter largely depends on the integrity of cis-regulatory elements bound by AP1, SP1, and in certain epithelial cells, KRF-1. In contrast to previous reports by implying a key role for NF1 and Oct-1 recognition motifs in the stimulation of papillomavirus oncogene expression, the inactivation of these elements in the context of the HPV18 URR did not strongly affect the transcriptional activity of the E6/E7 promoter. Mutation of a promoter-proximal glucocorticoid response element completely abolished dexamethasone inducibility of the HPV18 E6/E7 promoter and resulted in an increase of its basal activity. Functional dissection of the HPV18 constitutive enhancer region indicates that its transcriptional activity is largely generated by functional synergism between a centrally located AP1 module and thus far undetected cis-active elements present in the 5' flank of the enhancer. Furthermore, comparative analyses using homologous and heterologous promoters show that the transcriptional activity of HPV18 enhancer elements is influenced by the nature of the test promoter in a cell-type-specific manner.

Transactivation of the human papilloma virus 16 octamer motif by the octamer binding protein Oct-2 requires both the N and C terminal activation domains

The upstream regulatory region (URR) of the human papillomaviruses HPV16 and 18 contains a sequence with a seven out of eight base match to the consensus binding site for octamer binding transcription factors. This motif acts as a target for repression by the Oct-1 transcription factor and therefore inhibits promoter activity in non-cervical cells expressing only Oct-1. In contrast the HPV octamer motif activates promoter activity in cervical cells. Here we show that cervical cells express the activating form of the Oct-2 transcription factor, Oct 2.1 and that this factor can transactivate promoter activity via the HPV16 octamer. This effect is dependent upon both the N and C-terminal activation domains of Oct-2. The expression of specific octamer binding proteins such as Oct-2 in cervical cells thus allows the HPV16 motif to produce opposite effects on gene expression in cervical and non-cervical cells suggesting that it may play a role in the cervical specificity of URR driven gene expression.