Differentiation-linked human papillomavirus types 6 and 11 transcription in genital condylomata revealed by in situ hybridization with message-specific RNA probes

Demonstration of human papillomavirus (HPV) genomic amplification and viral-like particles from CaSki cell line in SCID mice

We demonstrate that from the CaSki cervical cancer cell line, integrated HPV-16 genome was amplified and viral-like particles were generated in an in vivo SCID mouse model. The in vivo tumor growth of several HPV-containing cell lines and 2 HPV-negative cell lines was examined in SCID mice. Tumor growth was noted with the HeLa, CaSki, ME-180, and MS751 cell lines within 2 months after subcutaneous injection. Squamous differentiation was appreciated in focal areas of tumors derived from CaSki and ME-180. In the CaSki tumors, DNA in situ hybridization revealed homogeneous staining of nuclei in some cells in the differentiated areas, suggesting HPV genomic amplification. In contrast, punctate or speckled patterns of hybridization were identified in the less differentiated areas, suggesting continued integration of the HPV genome. Immunocytochemical staining for HPV-16 L1 capsid protein showed it to be concentrated in cells from the differentiated areas, correlating with the results of hybridization. Electron microscopic studies revealed 50 nm uniform particles, consistent with HPV viral-like particles, in the nuclei of some cells in well-differentiated areas. Furthermore, Southern transfer and hybridization of the Hirt's extract from the CaSki tumors was positive for HPV-16 DNA, indicating non-integrated, low molecular weight HPV-16 DNA. Our results show HPV genomic amplification of integrated viral DNA and generation of HPV viral-like particles in CaSki cancer cells in SCID mice and that viral DNA amplification and the formation of viral-like particles are coupled to cellular differentiation. This experimental model provides a potential system for studying the molecular pathogenesis of HPV infections.

Enhanced transcriptional activation by E2 proteins from the oncogenic human papillomaviruses

A systematic comparison of transcriptional activation by papillomavirus E2 proteins revealed that the E2 proteins from high-risk human papillomaviruses (human papillomavirus type 16 [HPV-16] and HPV-18) are much more active than are the E2 proteins from low-risk HPVs (HPV-6b and HPV-11). Despite the tropism of HPVs for particular epithelial cell types, this difference in transcriptional activation was observed in a number of different epithelial and nonepithelial cells. The enhanced activities of the E2 proteins from high-risk HPVs did not result from higher steady-state levels of protein in vivo, and in vitro DNA-binding assays revealed similar binding properties for these two classes of E2 proteins. These results demonstrate that the E2 proteins from high-risk HPVs have an intrinsically enhanced potential to activate transcription from promoters with E2-responsive elements. We found that there are also substantial differences between the activation properties of the bovine papillomavirus type 1 E2 protein and those of either of the two classes of HPV E2 proteins, especially with regard to requirements for particular configurations of E2 binding sites in the target promoter. Our results indicate that there are at least three distinct functional classes of E2 proteins and that these classes of E2 proteins may perform different roles during the respective viral life cycles.

A brief synopsis of the role of human papillomaviruses in cervical carcinogenesis

The expansion of our knowledge in the realms of pathology, epidemiology, and molecular biology of human papillomaviruses (HPV) has defined them as the major and best understood class of true human tumor viruses. The interaction of the papillomavirus genome with its host cell produces the majority of cytologic abnormalities at which cervical cancer screening is directed. The epidemiologic pattern of HPV infection accounts for the established association of cervical neoplasia with sexual activity. The molecular interactions of the HPV genome with its host cell suggest a plausible mechanism for its carcinogenic action. This presentation will succinctly review current knowledge of HPV biology to facilitate an understanding of the clinical significance of this virus.

Response to interferon treatment decreases with epidermal dedifferentiation in condylomas

After interferon (IFN) treatment of patients with condyloma acuminatum, groups clinically proven to be responders or nonresponders were selected, and cellular parameters that might influence the clinical response were studied in pretreatment biopsies by reverse transcription polymerase chain reaction (RT-PCR). The nonresponders were found to express higher amounts of cellular proliferative markers, such as proliferating cell nuclear antigen (PCNA), cyclin A, and cdc 2 kinase, but lower levels of growth suppressor genes (TGF-beta 1, TGF-beta 2 and p53) before IFN treatment. The responders retained the epidermal keratinization, except for some signs of hyperproliferation (K6, K16 cytokeratins). In addition, the nonresponders showed a shift in the keratinization pattern to a mucosal or fetal type, as evidenced by high expression of the K18, K6, K16 and K13 cytokeratins but decreased K5, K14 and K10 levels before treatment. The expression of the human papillomavirus (HPV) genes is consistent with these differentiation patterns. The crucial conclusion to be drawn from this study is that those condylomas whose pretreatment phenotype most closely resembles that of normal epidermis respond to IFN treatment, whereas those more akin to nonkeratinizing epithelia fail to respond, i.e. the resistance of condylomas to IFN treatment is correlated with dedifferentiation.

C/EBPbeta is a negative regulator of human papillomavirus type 11 in keratinocytes

We have evaluated the impact of the CCAAT enhancer-binding protein (C/EBP) transcription factors on human papillomavirus type 11 (HPV11). C/EBPbeta is in nuclei of cultured foreskin keratinocytes and binds its consensus sequence in HPV11 DNA. We have used the novel approach of depleting the availability of C/EBPs in vivo using nuclease-resistant oligomers containing C/EBP DNA binding sites. In cultured foreskin keratinocytes containing replicating HPV11 DNA, levels of both HPV11 transcripts and HPV DNA increase after treatment with oligomers; containing the C/EBPbeta DNA binding motif. These results indicate that C/EBPbeta is a repressor for HPV11 in keratinocytes.

Keratinocyte gene transfer and gene therapy

Gene therapy has moved beyond the pre-clinical stage to the treatment of a variety of inherited and acquired diseases. For such therapy to be successful, genes must be efficiently delivered to target cells and gene products must be expressed for prolonged periods of time without toxic effects to the host. This may be achieved by means of an in vivo strategy where genes are transferred directly into a host cell, or by means of an ex vivo approach through which cells are removed, cultured, targeted for gene delivery, and grafted back to the host. Several obstacles continue to delay safe and effective clinical application of gene therapy in a variety of target cells. The limited survival of transplanted cells, transient expression of transferred genes, and difficulties in targeting stem cells are technical issues requiring further investigation. Epidermal and oral keratinocytes are potential vehicles for gene therapy. Several features of these tissues can be utilized to achieve delivery of therapeutic gene products for local or systemic delivery. These qualities include: (1) the presence of stem cells; (2) the cell-, strata-, and site-specific regulation of keratinocyte gene expression; (3) tissue accessibility; and (4) secretory capacity. Such features can be exploited by the use of gene therapy strategies to facilitate: (1) identification, enrichment, and targeting of stem cells to ensure the continued presence of the transferred gene; (2) high-level and persistent transgene expression using keratinocyte-specific promoters; (3) tissue access needed for culture and grafting for ex vivo therapy and direct in vivo gene transfer; (4) secretion of transgene product for local or systemic delivery; and (5) monitoring of genetically modified tissue and removal if treatment termination is required. Optimal gene therapy strategies are being tested in a variety of tissues to treat dominant and recessive genetic disorders as well as acquired diseases such as neoplasia and infectious disease. This experience provides a basis for the application of such clinical studies to a spectrum of diseases effecting epidermal and oral keratinocytes. Gene therapy is in an early stage yet holds great promise for its ultimate clinical application.

Squamous epithelial hyperplasia and carcinoma in mice transgenic for the human papillomavirus type 16 E7 oncogene

The human papillomavirus type 16 (HPV-16) genome is commonly present in human cervical carcinoma, in which a subset of the viral genes, E6 and E7, are expressed. The HPV-16 E6 and E7 gene products can associated with and inactivate the tumor suppressor proteins p53 and Rb (the retinoblastoma susceptibility gene product), and in tissue culture cells, these viral genes display oncogenic properties. These findings have led to the hypothesis that E6 and E7 contribute to cervical carcinogenesis. This hypothesis has recently been tested by using transgenic mice as an animal model. HPV-16 E6 and E7 together were found to induce cancers in multiple tissues in which they were expressed, including squamous cell carcinoma, the cancer type most commonly associated with HPV-16 in the human cervix. We have extended these studies to investigate the in vivo activities of HPV-16 E7 when expressed in squamous epithelia of transgenic mice. Grossly, E7 transgenic mice had multiple phenotypes, including wrinkled skin that was apparent prior to the appearance of hair on neonates, thickened ears, and loss of hair in adults. In lines of mice expressing higher levels of E7, we observed stunted growth and mortality at an early age, potentially caused by an incapacity to feed. Histological analysis demonstrated that E7 causes epidermal hyperplasia in multiple transgenic lineages with high penetrance. This epithelial hyperplasia was characterized by an expansion of the proliferating compartment and an expansion of the keratin 10-positive layer of cells and was associated with hyperkeratosis. Hyperplasia was found at multiple sites in the animals in addition to the skin, including the mouth palate, esophagus, forestomach, and exocervix. In multiple transgenic lineages, adult animals developed skin tumors late in life with low penetrance. These tumors arose from the squamous epithelia and from sebaceous glands and were characterized histologically to be highly differentiated, locally invasive, and aggressive in their growth properties. On the basis of these phenotypes, we conclude that HPV-16 E7 can alter epithelial cell growth parameters sufficiently to potentiate tumorigenesis in mice.

A possible role for human papillomaviruses in head and neck cancer

Human papillomaviruses (HPVs) cause benign tumors in the respiratory tract. Mounting evidence suggests that they also play a role in the etiology of a subset of head and neck cancers. Carcinomas in patients with a history of recurrent respiratory papillomatosis clearly are caused by persisting HPV interacting with one of more carcinogenic agents. Verrucous carcinomas of the oral cavity, tonsillar and tongue carcinomas are strongly linked with HPVs, based on molecular epidemiologic data. Tonsillar cancer have been shown to express HPV RNA, presumed necessary to induce and maintain a carcinoma, supporting a viral etiology. This paper reviews the molecular and cellular basis for considering HPVs as causative agents of cancer, and reviews the literature that considers the possible role of HPVs in head and neck cancer.

The functions of human papillomavirus type 11 E1, E2, and E2C proteins in cell-free DNA replication

We examined the functions of human papillomavirus type 11 (HPV-11) E1 and E2 proteins purified from Sf9 cells infected with recombinant baculoviruses in cell-free HPV-11 origin (ori) replication. The E1 protein binds specifically to a wild type but not to a mutated sequence in the ori spanning nucleotide position 1. It also has a relatively strong affinity for nonspecific DNA. A neutralizing antiserum directed against the amino-terminal one-third of the E1 protein totally abolishes initiation and elongation, suggesting that it functions as an initiator and a helicase at the replication fork. An antiserum against the carboxyl-terminal portion of E1 protein abolished replication only when added prior to initiation. Thus this portion of E1 is hidden in the replication complexes. The HPV-11 E2 protein appears not to be essential for elongation, but it must be present in the preinitiation complex for the E1 protein to recruit host DNA replication machinery to the ori. E2 antiserum added after preincubation in the absence of the cell extracts totally abolished replication. An identical conclusion is also reached for the bovine papillomavirus type 1 E2 protein. Finally, the HPV-11 E2C protein lacking the transacting domain of the full-length E2 protein partially inhibits E2-dependent ori replication.

Differential regulation of human papillomavirus type 6 and 11 early promoters in cultured cells derived from laryngeal papillomas

Cells cultured from laryngeal papillomas contain episomal human papillomavirus type 6 or type 11 (HPV-6/11) DNA. We developed a sensitive RNase protection assay to simultaneously measure expression from the HPV E6, E7, and E1 promoters (P1, P2 and P3, respectively) in this manipulable culture system and found that P1, P2 and P3 transcript abundances could be independently modulated by culture medium composition and culture substrate. In undifferentiated cells grown in a low-calcium, serum-free medium, P1 transcripts commonly predominated over those from P2, P3 transcripts were often undetectable, and high concentrations of retinoic acid were able to selectively decrease P2 transcript abundance. When cultures were allowed to stratify and differentiate by growth on a collagen gel at he air-liquid interface, total HPV RNA increased up to sixfold because of selective increases in abundances of P1 and P3 transcripts. High-calcium submerged cultures also showed easily detectable P3 transcripts, and isolated suprabasal cells contained almost exclusively these transcripts. Growth arrest alone was not sufficient to induce P3 transcripts. Thus, in contrast to the HPV-6/11 E6 and E7 promoters, the E1 promoter was utilized primarily in a differentiation-specific manner. We also show that increased HPV gene dosage will not necessary bring about increased HPV transcript abundance, suggesting that other viral and cellular factors are responsible for regulation of total transcript levels as well as specific promoter usage.

Differentiation-dependent up-regulation of the human papillomavirus E7 gene reactivates cellular DNA replication in suprabasal differentiated keratinocytes

mRNA transcription, DNA amplification, and progeny production of human papillomaviruses (HPVs) are closely linked to squamous epithelial differentiation in patient papillomas. Because suprabasal, differentiated keratinocytes have exited the cell cycle for days or weeks and because viral DNA synthesis requires the host DNA replication machinery, HPVs must have a mechanism to reactivate the essential host genes. In this study, we show via acute recombinant retrovirus infection that an intact E7 gene of either high-risk or of low-risk HPV genotypes, under the control of its respective native enhancer-promoter, induced proliferating cell nuclear antigen (PCNAs) expression in the suprabasal cells of epithelial raft cultures of primary human foreskin keratinocytes (PHK). The cellular differentiation program was unaltered by the viral oncoprotein; it was essential for high HPV promoter activity. Furthermore, extensive host chromosomal DNA replication took place in differentiated cells of HPV-18 E7-expressing raft cultures and of patient laryngeal papillomas caused by HPV-6. These results indicate that the main function of the E7 protein is to reactivate host DNA replication machinery to support viral replication in differentiated, noncycling cells.

Differential promoter activity in benign and malignant human cells of skin origin

In order to develop systems to express mammalian proteins in human skin-derived cells, we tested 6 different viral and 1 eukaryotic promoter (pCMV, pRSV, pSV, pMMTV, pPoly E, pPoly L, pHMT) for their ability to drive the expression of the chloramphenicol acetyltransferase (CAT) enzyme in different human skin-derived cells. DNA was transfected in human keratinocytes derived from normal foreskin and cervix, in the HPV-negative cervical cancer line HT-3 and in malignant melanoma cell lines (SK-Mel 23, SK-Mel 37) using a liposome-based technique or calcium precipitation. Transfection efficacy was controlled by cotransfection of a beta-galactosidase gene construct. The enzymatic activity of the CAT-gene expression was determined by incubation of the cell extract prepared from the transfected cells with 14 C-labeled chloramphenicol. The CMV-promoter was highly active in all skin- or mucosal-derived cells. In contrast to the strong CMV-promoter, the RSV-, SV-, and HMT-promoter were less active and varied in dependence of the cell type. The pattern of the promoter activity differed between benign and transformed genital keratinocytes. Only the SV-promoter showed a comparable strong basal activity, which was restricted to the SK-Mel 37 cells. In conclusion, the promoter activity has to be tested for each cell type depending on the aims of the gene expression.

Human papillomavirus type 31b late gene expression is regulated through protein kinase C-mediated changes in RNA processing

Expression of the human papillomavirus (HPV) capsid genes, L1 and L2, as well as amplification of viral DNA and virion assembly occur in the terminally differentiated layers of infected stratified squamous epithelium in vivo. These processes can be duplicated in the laboratory through the use of organotypic or raft cultures. When CIN612 cells, which contain episomal copies of the high-risk HPV type 31b, are allowed to differentiate in raft cultures, the expression of transcripts encoding the early genes E1--E4 and E5 is induced. These transcripts are initiated at the differentiation-dependent P742 promoter located in the middle of the E7 open reading frame. Exposure of raft cultures to activators of protein kinase C, such as phorbol esters, results in the further induction of late gene expression as well as virion assembly. In this study, we have investigated the mechanism by which activators of protein kinase C induce late gene expression. The major L1 transcript was found to be encoded by a bicistronic E1--E4, L1 RNA which initiated at the differentiation-dependent promoter P742. Additional low-level expression of L1-containing RNAs was also observed from the early-region promoter, P97. The major L2 transcripts were found to be encoded by E1--E4, E5, L2, L1 RNAs which were also initiated in the early region, probably at the differentiation-specific promoter P742. While early and late RNAs were found to be expressed from the same promoter, they differed in utilization of splicing and polyadenylation sites. Raft cultures treated with activators of protein kinase C induced expression of late genes, but no change in the abundance of early RNAs initiated at the P742 promoter was observed. Thus, the increase in late gene expression was likely due to changes in RNA processing or stabilization rather than an increase in the rate of transcription from P742. Regulation of HPV late gene expression therefore occurs at two levels: differentiation-dependent induction of the P742 promoter, which can be mimicked in vitro by growth in raft cultures, and posttranscriptional changes that can be induced by activation of protein kinase C. These posttranscriptional changes may occur through inactivation or down-regulation of splicing factors which inhibit use of the late region polyadenylation site, resulting in increased stability of late region transcripts.

Epidemiology of cervical intraepithelial neoplasia: the role of human papillomavirus

The evidence implicating specific HPV types in the aetiology of cervical cancer is now strong enough to establish a causative role. HPV infection of the cervix affects the developing immature metaplastic cells of the transformation zone. Cervical neoplasia can be viewed as the interaction of high risk papillomavirus and immature metaplastic epithelium. Once maturity is reached, there is minimal risk of subsequent development of cervical squamous neoplasia. Exposure to HPV is an extremely common event, especially in young sexually active women. Yet, despite frequent HPV exposure at that phase of life in which the cervical transformation zone is at its most vulnerable, established expressed disease is relatively uncommon. Most studies in which the natural history of CIN is not altered by cervical biopsy reveal a progression rate from low to high grade CIN of less than one third. Where viral type is taken into account, however, the progression rate from normal but high risk HPV-infected cervical epithelium to CIN 2 or 3 is higher. Despite this, most cervical abnormalities will not transform into invasive cancer, even if left untreated. The variance between the high rate of HPV infection, the intermediate rate of CIN and the relatively low rate of cervical cancer establishes a stepwise gradient of disease of increasing severity with decreasing prevalence. In an immunocompetent host, HPV infection alone does not appear to be sufficient to induce the step from high grade CIN to invasion. Epidemiological studies indicating that HPV infection with oncogenic viral types is far more common than cervical neoplasia suggest the necessity of cofactors in cervical carcinogenesis. The long time-lag between initial infection and eventual malignant conversion suggests that random events may be necessary for such conversion, and the spontaneous regression of many primary lesions suggests that most patients are not exposed to these random events. Potential cofactors include cigarette smoking, hormonal effects of oral contraceptives and pregnancy, dietary deficiencies, immunosuppression and chronic inflammation. In those women who develop cervical cancer, malignant progression is rarely rapid, more commonly taking many years or decades. Malignant progression has been documented in patients who presented initially with only low grade HPV-induced atypia. On the other hand, progression may be a misnomer, as 'apparent' progression may really represent adjacent 'de novo' development of higher grade CIN. Although most cervical cancers contain high risk HPV types, up to 15% of such cancers test negative for HPV, raising the possibility that a few, usually more aggressive, cervical cancers may arise from from a non-viral source.(ABSTRACT TRUNCATED AT 400 WORDS)

Characterization of human papillomavirus type 16 activity in separate biopsies from a carcinoma of the cervix uteri

Human papillomavirus (HPV) 16-specific nucleic acid sequences were analysed in separate biopsies taken from a patient with a poorly differentiated squamous cell carcinoma of the uterine cervix. Biopsies were obtained from histopathologically normal epithelium adjacent to the carcinomatous epithelium, the primary carcinoma and a metastatic lymph node. Signals characterizing viral DNA and oncogene transcription were obviously differentiation dependent as shown by in situ hybridization of viral nucleic acids and immunofluorescence of epithelial differentiation specific proteins. In histologically normal parts of the epithelium viral DNA was amplified at the transition from basal to maturing cells, whereas E6/E7 genes were actively transcribed mainly in maturing epithelial cells following the basal cell layer. Some of the cells in the primary carcinoma and in the metastatic lymph node expressed involucrin at increased levels. Signals for viral DNA and HPV 16-specific E6/E7 transcripts decreased in intensity during differentiation in an inverse relationship to the observed involucrin increase in those cells. The absence of Ki67 in cells expressing large amounts of involucrin as revealed by immunostaining, support the inverse correlation between differentiation of cancer cells, HPV 16 replication and E6/E7 transcription. The changes in cytokine expression may indicate an HPV 16 associated disruption of normal cytokine expression pattern in the carcinoma.

Approaches to gene transfer in keratinocytes

The introduction and expression of exogenous genetic material in cultured cells has provided a powerful tool for studying gene function and regulation. Immortalized cell lines have been useful for establishing gene transfer methodologies that are generally inefficient. For investigators of epidermal and mucosal biology, wishing to make use of the tissue architecture produced by primary keratinocytes in vitro, the limited life span of these cells presents a host of unique problems. Primary cells require the use of gene transfer methods that are highly efficient and will not significantly alter the cell's normal differentiation pathway. The purpose of this review is to evaluate gene transfer technology as it applies to keratinocytes.

Papilloma formation by cottontail rabbit papillomavirus requires E1 and E2 regulatory genes in addition to E6 and E7 transforming genes

The present study used the cottontail rabbit papillomavirus DNA-rabbit system to evaluate whether the regulatory genes E1 and E2 and the transforming gene E6 are required for papilloma formation. Frameshift mutations were generated in the individual genes in the context of a full-length cottontail rabbit papillomavirus genome, and the mutant DNAs were intradermally inoculated into domestic rabbits. None of the mutants induced papillomas. Marker rescue experiments confirmed that the defects were due to mutations that we deliberately introduced. Marker rescue also confirmed our previous report that the upstream region of E7 around position 9 was critical for papilloma induction. These results demonstrate that the E1 and E2 regulatory genes as well as the E6 and E7 transforming genes are each required for papilloma formation. Each gene may provide molecular targets for therapeutic intervention.

Changes in RNA expression pattern during the malignant progression of cottontail rabbit papillomavirus-induced tumors in rabbits

Cottontail rabbit papillomavirus induces strictly epithelial tumors in both cottontail and domestic rabbits. A high proportion of the initial benign papillomas progress within 8 to 14 months to invasive carcinomas. With the help of mRNA-specific riboprobes for E6, E7, E1, E2, L1 and L2, we investigated by in situ hybridization the RNA expression pattern of cottontail rabbit papillomavirus in tissue sections of biopsies from different stages of tumor development. Common features of all lesions were high levels of E6 and E7 mRNAs and low levels of E1 and E2 mRNAs. In agreement with earlier reports, there was no evidence for a major mRNA class equivalent to the prominent E1-E4 RNA of human papillomavirus types 6/11 and 16. In cottontail rabbit papillomas, high levels of E6 and E7 mRNAs were present in the upper differentiated epithelial layers. These layers also contained most of the E1 and E2 mRNAs and the viral DNA. In contrast, papillomas of domestic rabbits revealed the opposite differentiation-dependent expression pattern for the E6 and E7 mRNAs; there were strong signals in the basal layers, and these declined with increased differentiation. Transcripts encoding the L1 mRNA were detected only in a few isolated cells of the granular layer. There was no difference between the amounts of E6, E7, E1, and E2 mRNAs present in highly dysplastic tissue and those present in adjacent normal papillomatous epithelium within a progressing papilloma. However, late transcripts and viral DNA detectable only in the upper layers of the papilloma were present throughout the thickness of the dysplastic tissue, indicating a newly acquired permissiveness of the dysplastic cells for viral DNA replication and late transcription. Carcinomas in general had the same expression patterns for E6, E7, and E1 but were dissimilar in the levels of expression of E2 and late transcripts.

Induction of proliferating cell nuclear antigen in differentiated keratinocytes of human papillomavirus-infected lesions

The expression of proliferating cell nuclear antigen (PCNA) was studied in human papillomavirus (HPV)-infected, benign and malignant lesions of the genital tract and larynx using immunocytochemical staining of formalin-fixed clinical specimens. We observed the induction of PCNA in squamous carcinomas and adenocarcinomas, as has been demonstrated with other malignancies. In addition, the differentiated keratinocytes of the upper spinous cells and granulocytes in condylomata acuminata and low-grade intraepithelial neoplasias showed a consistent induction of PCNA compared with the normal squamous epithelium, in which only some of the parabasal and basal cells were positive. This reactivation of PCNA synthesis correlated with the presence of high copy numbers of HPV DNA and was independent of the oncogenic risk potential of the infecting HPV genotype. We postulate that HPV gene products induce the expression of PCNA and other components of the host DNA replication machinery in differentiated cells of squamous lesions to facilitate vegetative viral replication.

Effects of E5a and E7 genes of human papillomavirus type 11 on immortalized human epidermal keratinocytes and NIH 3T3 cells

The E5a gene of HPV-11 expressed in NIH 3T3 cells led to tumorigenesis in nude mice; whereas when expressed in keratinocytes, E5a induced anchorage independent growth, but was nontumorigenic in nude mice. The E7 gene of HPV-11 expressed NIH 3T3 cells led to tumors in nude mice and morphological transformation, but not anchorage independent growth. Keratinocytes expressing the E7 gene induced colony formation in soft agarose, but not tumorigenesis in nude mice. Comparison of transforming activities of HPV-11 E5a and E7 genes of HPV-11 showed that the efficiency of cell transformation by E7 was weaker than that of E5a.

The predominant mRNA class in HPV16-infected genital neoplasias does not encode the E6 or the E7 protein

Human papillomavirus (HPV) type 16 is strongly implicated in the development of progressive neoplasias of the uterine cervix. Its oncogenic potential is decisively determined by the activity of the early gene products E6 and E7. To look for changes in the expression of these genes during tumour progression we cloned subgenomic fragments of HPV16 into RNA expression vectors, which allowed the generation of 35S-labelled riboprobes specific for distinct mRNA classes. Four constructs were made to differentiate between transcripts starting upstream of the E6 ORF or the E1 ORF, and one probe was specific for unspliced E6/E7 region transcripts. Five other constructs were used to identify transcripts covering the E1, E2, E4, L1 and L2 regions. With the help of these constructs, we analyzed by in situ hybridization 2 low-grade intraepithelial neoplasias of the vulva, 1 high-grade neoplasia of the cervix as well as 4 vulvar and 3 cervical carcinomas. Transcripts from the E1, E2, E4, L1 and L2 region that were consistently detected in the differentiated layers of benign lesions were variably expressed in precancers and carcinomas. None of the investigated cases revealed detectable amounts of unspliced E6/E7 transcripts with a coding potential for a full-length E6 protein. In benign lesions, the E7 transcripts were confined to isolated nuclei of differentiated cells, whereas high-grade lesions and invasive cancers showed elevated levels of equally distributed E7-specific signals in the cytoplasm of all tumour cells. The most abundant transcripts observed in intraepithelial neoplasias and in invasive cancers appear to initiate within ORF E7 and therefore have no coding potential for full-length E6 and E7 proteins. Our data show that the actual level of E7-specific transcripts in cancers is lower than anticipated from earlier studies using an ORF E6/E7-specific probe that hybridizes with the 5'-ends of the abundant mRNA class.

Differentiation-specific expression from the bovine papillomavirus type 1 P2443 and late promoters

The papillomavirus life cycle is tightly linked with keratinocyte differentiation in squamous epithelia. Vegetative viral DNA replication begins in the spinous layer, while synthesis of capsid proteins and virus maturation is restricted to the most differentiated or granular layer of the epithelium. In this study, in situ hybridization of bovine fibropapillomas was used to demonstrate that the activity of two promoters of bovine papillomavirus type 1 (BPV-1) is regulated in a differentiation-specific manner. In situ hybridization with a late promoter (PL)-specific oligonucleotide probe suggested that PL is dramatically upregulated in the granular layer of the fibropapilloma. Northern (RNA) blot analysis of RNA from BPV-1-infected fibropapillomas indicated that the three major BPV-1 late-region mRNAs were transcribed from PL. These RNAs include the previously described L1 (major capsid) mRNA as well as two larger mRNAs. The two larger mRNAs were characterized and shown to contain the L2 (minor capsid protein) open reading frame as well as the L1 open reading frame. In contrast to PL, the P2443 promoter was maximally active in basal keratinocytes and the fibroma. The major mRNA transcribed from P2443 is the putative E5 oncoprotein mRNA which is spliced between nucleotides 2505 and 3225. No signal was detected above the basal layer with use of a probe specific for this mRNA. The E5 oncoprotein has previously been localized by immunoperoxidase staining to the granular cell layer as well as the basal cell layer of the fibropapilloma (S. Burnett, N. Jareborg, and D. DiMaio, Proc. Natl. Acad. Sci. USA 89:5665-5669, 1992). These data suggest that E5 proteins in the basal cell and granular cell layers are not translated from the same mRNA.

Identification and characterization of novel promoters in the genome of human papillomavirus type 18

Most studies on the regulation of gene expression in human papillomaviruses (HPV) have focused on the promoter for the early genes E6 and E7. This promoter is located at the junction between the long control region and the E6 open reading frame. RNA mapping studies have suggested that additional promoters may exist in other parts of the genome. In this study, we used a combination of transcription in vitro and an analysis of RNA produced in vivo in transfected cells to identify three novel promoters in the genome of human papillomavirus type 18. These promoters are located in front of the E2 gene (P2598), within the E2 coding sequences (P3036), and at the end of the L2 open reading frame (P5600). They were active in HeLa cells, as shown by a chloramphenicol acetyltransferase assay. The activity of the P3036 promoter was stimulated by the bovine papillomavirus type 1 E2 protein.

Pathogenesis of genital HPV infection

Clinical, subclinical, and latent human papillomavirus (HPV) infections are distinguished from HPV-associated neoplasia. Besides HPV additional cofactors are necessary to transform HPV infected tissue to intraepithelial or invasive neoplasia. Risk factors for the presence of HPV are high number of sexual partners, early cohabitarche, young age at first delivery, suppression and alteration of immune status, young age and hormonal influences. While the fact of a high number of sexual partners exclusively increases the risk of HPV infection, it is not known whether the other factors lead to either an increased risk for HPV infection and/or to HPV-associated neoplasia. Subclinical and latent genital HPV infections are highly prevalent. The prevalence rate depends on the sensitivity of the HPV detection system used, on age and sexual activity of the population screened, and on the number of subsequent examinations performed for each subject. Sexual transmission is the main pathway for genital HPV's, however, vertical, peripartal, and oral transmission are also possible. Seroreactivity against genital HPV may be due to an active infection or the result of contact with HPV earlier in life. Antibodies against the HPV 16 E7 protein indicate an increased risk for cervical cancer. Compared with humoral response cellular immune response is probably more important for regression of genital HPV infection: impaired cellular response is characterized by depletion of T helper/inducer cells and/or Langerhans cells and impaired function of natural killer cells and/or the infected keratinocyte. In condylomata replication and transcription of viral nucleic acids and antigen production coincide with cellular differentiation. However, the interaction between HPV and the keratinocyte on a molecular level in subclinical and latent disease is not well understood. Regression or persistence of subclinical and latent genital HPV infections as observed in longitudinal investigations show a constant come-and-go of HPV presence. Subclinical or latent cervical infections with high-risk HPV types (such as HPV 16 and 18) have an increased risk for the development of HPV-associated neoplasia.

Regulation of the human papillomavirus type 11 E6 promoter by viral and host transcription factors in primary human keratinocytes

Human papillomavirus (HPV) type 11 is strictly trophic for epithelial cells and induces benign condylomata of the external genitalia and also causes laryngeal papillomas. Primary keratinocytes are the appropriate hosts for studies of HPV gene regulation, but they are not frequently used, owing to difficulties in culturing and low transfection efficiencies. By modifying a Polybrene transfection procedure, we achieved consistently high transfection efficiencies in primary human foreskin keratinocytes and characterized the HPV type 11 enhancer in the context of the homologous E6 promoter. Contrary to previous studies with immortalized human cervical carcinoma C-33A cells, constitutive enhancer element II in the upstream regulatory region conferred no enhancer activity and did not abrogate repression by the homologous E2 protein. Rather, repression was strong, ranging from 5.6- to 20-fold for the various enhancer deletion mutations. By deletion analysis, a strong enhancer that included three nuclear factor 1 sites and one nuclear factor 1-associated factor-binding site was localized to a 45-bp region within constitutive enhancer element I, and it showed some degree of tissue specificity.

Differentiation-induced and constitutive transcription of human papillomavirus type 31b in cell lines containing viral episomes

The expression of viral genes during the productive life cycle of human papillomaviruses (HPV) is tightly coupled to the differentiation program of epithelial cells. We have examined transcription of HPV as a function of differentiation in an in vitro organotypic raft culture system which allows for epithelial stratification at the air-liquid interface. When CIN612 cells, which contain episomal copies of HPV type 31b (HPV31b), were allowed to stratify in raft cultures, they differentiated in a manner which was histologically similar to that seen in a cervical intraepithelial neoplasia I biopsy lesion. In monolayer cultures of CIN612 cells, two major polycistronic HPV31b transcripts of 1.7 kb which encode (i) E6, E7, E1-E4, and E5 and (ii) E6*, E7, E1-E4, and E5 were identified. These RNAs initiated at a promoter, P97, in the upstream regulatory region of the virus. Following differentiation in raft cultures, the relative abundance of RNAs initiated at P97 was unchanged. In contrast, the expression of a 1.3-kb RNA encoding an E1-E4 fusion protein and E5 was found to increase substantially following differentiation. This transcript was initiated at a novel promoter within the E7 gene (P742). These studies have therefore identified a constitutive viral promoter which is active throughout stratified epithelium as well as a novel promoter which is induced upon epithelial cell differentiation.

Differential expression of HPV types 6 and 11 in condylomas and cervical preneoplastic lesions

Tumor biopsies from exophytic and flat condylomas at different locations on the genital epithelium (10 cases) and in cervical intraepithelial neoplasia (CIN) grades 1-2 (6 cases) were analysed for HPV types 6 and 11 DNA and RNA. The presence of mRNA species which could encode the E6, E7, E1M, E2, E2C, E4, E5 and L1 proteins was determined using the RNA polymerase chain reaction (PCR) technique with primers that flank previously mapped or predicted splice sites. The state of the viral DNA in the tumor biopsies was established by Southern blot analysis. We could detect the various mRNA species in biopsies from condylomas associated with both HPV types. The size of the RNA PCR products were in agreement with the previously mapped splice sites of mRNAs recovered from an experimental condyloma induced by HPV11. The major viral transcript encoding the E1i--E4 protein was detected in all the tumor biopsies. From the rare transcripts the rate of detection of mRNA species encoding the E1M, E2C proteins was the highest. In 2 of 6 CIN biopsies analysed only the major viral transcript was detected. The overall results of this study suggest that early gene products of HPV types 6 and 11 may be important in the induction of cellular proliferation and condylamatous differentiation but these possibly may not be required for the development of the HPV-associated cervical neoplasia.

Control of human papillomavirus type 11 origin of replication by the E2 family of transcription regulatory proteins

Replication of human papillomavirus type 11 (HPV-11) DNA requires the full-length viral E1 and E2 proteins (C.-M. Chiang, M. Ustav, A. Stenlund, T. F. Ho, T. R. Broker, and L. T. Chow, Proc. Natl. Acad. Sci. USA 89:5799-5803, 1992). Using transient transfection of subgenomic HPV DNA into hamster CHO and human 293 cells, we have localized an origin of replication (ori) to an 80-bp segment in the upstream regulatory region spanning nucleotide 1. It overlaps the E6 promoter region and contains a short A + T-rich segment and a sequence which is homologous to the binding site of the bovine papillomavirus type 1 (BPV-1) E1 protein in the BPV-1 ori. However, unlike the BPV-1 ori, for which half an E2-responsive sequence (E2-RS) or binding site suffices, an intact binding site is essential for the HPV-11 ori. Replication was more efficient when additional E2-RSs were present. The intact HPV-11 genome also replicated in both cell lines when supplied with E1 and E2 proteins. Expression vectors of transcription repressor proteins that lack the N-terminal domain essential for E2 transcriptional trans activation did not support replication in collaboration with the E1 expression vector. Rather, cotransfection with the repressor expression vectors inhibited ori replication by the E1 and E2 proteins. These results demonstrate the importance of the N-terminal domain of the E2 protein in DNA replication and indicate that the family of E2 proteins positively and negatively regulates both viral DNA replication and E6 promoter transcription.

Transcription of the E6 and E7 genes of human papillomavirus type 6 in anogenital condylomata is restricted to undifferentiated cell layers of the epithelium

The E6 and E7 genes of human genital papillomaviruses (HPVs) appear to transform cells by different mechanisms. They seem to act synergistically but are not equally important when tested under diverse experimental conditions. We were therefore tempted to investigate the E6- and E7-specific transcription pattern in HPV6-infected condylomas separately, by in situ hybridization. Recent studies have identified three promoters within the E6-E7 region of HPV6 and HPV11 by applying S1, exonuclease VII, and cDNA analyses. On the basis of these data, we cloned subgenomic fragments of HPV6 into plasmid pBS to obtain riboprobes that differentiated between transcripts starting upstream of the E6 and E7 open reading frames, respectively. These different species of mRNAs were analyzed in serial thin sections of eight HPV6-positive anogenital condylomas. The E6 probe (nucleotides 7862 to 241) led to weak signals within the basal layer. In three cases, rather strong signals were confined to a few basal cells. The E7 probe (nucleotides 242 to 534) gave rise to a more pronounced labeling of all cells within the two to three lowest epidermal layers. In situ hybridization with a riboprobe for human c-fos revealed an expression pattern similar to that observed with the E7 probe. In contrast to the preferential expression of the transforming E6 and E7 genes in the lower epithelium, the major transcriptional activity of the virus was detected in the middle and upper third by probes colinear with the 3' moiety of the early region.

Detection of antibodies to the E4 or E7 proteins of human papillomaviruses (HPV) in human sera by western blot analysis: type-specific reaction of anti-HPV 16 antibodies

To determine the cross-reactivity between early (E) proteins of different human papillomavirus (HPV) types, 346 serum samples were tested with E4 and E7 of HPV 16. Two hundred and sixteen of them were also tested with HPV 1 E4, 21 with HPV 11 E4 and E7, and 109 with HPV 18 E4 and E7. Viral fusion proteins were expressed in Escherichia coli and used as antigens in Western blot experiments. The sera were obtained from patients with HPV-associated genital lesions or cervical cancer, from renal transplant recipients and from patients hospitalized for reasons unrelated to HPV infections (the controls). In contrast to findings relating to HPV 16 E4 specific antibodies, the prevalence of anti-HPV 1 E4 antibodies was not greater in renal transplant recipients than in the controls. In each age group of the control population more sera reacted with HPV 1 E4 than with HPV 16 E4. Sera of patients with HPV-associated cervical diseases and cervical cancer reacted less frequently with HPV 11 E4 or E7 and HPV 18 E4 or E7, respectively, than with the corresponding HPV 16 proteins. Thirty of 117 HPV 16 E4 or E7 positive sera showed reactivity to the corresponding protein of either HPV 1, 11 or 18. As demonstrated by cross-absorption experiments performed with 26 of the double-reacting sera, 24 contained two populations of antibodies reacting with proteins of different HPV types whereas only two contained cross-reacting antibodies. We concluded that in the majority of sera antibodies to the HPV 16 E4 and E7 proteins are type-specific.

Human papillomavirus type 16 (HPV 16) gene expression and DNA replication in cervical neoplasia: analysis by in situ hybridization

We have analyzed human papillomavirus (HPV) type 16 RNA expression in premalignant cervical lesions of different severity and in squamous cervical cancers by RNA-RNA in situ hybridization in order to find differences in the topographic distribution of viral RNA, which might correlate with the severity of disease. In the basal layer of low-grade squamous intraepithelial lesions (SIL) only weak transcription of viral early genes was observed. Signal intensity increased strongly in the more differentiated cells accompanied by high levels of HPV DNA replication. This pattern of viral gene expression, together with the onset of viral late transcription in the upper differentiated layer of the epithelium, most likely reflects the productive phase of viral infection. In contrast, in high-grade SIL viral transcription was comparatively strong in basal cells and evenly distributed throughout the undifferentiated epithelium. This difference of viral transcription in the basal layer of the respective lesions points to an altered regulation of viral gene expression which may be causally linked to the progression of precursor lesions. Evidence for disrupted expression of 3' early genes (E2, E4, and E5), analogous to the situation in HPV-DNA containing cervical carcinoma-derived cell lines, was not found in any of the HPV-16-positive premalignant lesions nor in the majority of cancers. The similarity of the viral transcription pattern of high-grade SIL and cancers suggests that additional host gene alterations are necessary for malignant progression.

Production of human papillomavirus and modulation of the infectious program in epithelial raft cultures. OFF

Human papillomaviruses trophic for anogenital epithelia cause benign warts, and certain genotypes are closely associated with cervical neoplasia. By using our modifications of the epithelial raft culture system, we were able to recapitulate and modulate the infectious program of a papillomavirus in vitro for the first time. Small pieces of a condyloma containing human papillomavirus type 11 were explanted onto a dermal equivalent consisting of a collagen matrix with fibroblasts and were cultured at the medium-air interface. The infected stem cells proliferated rapidly across the matrix, stratified, and differentiated, as judged by histology. The results correlated with the state of epithelial differentiation, which, in turn, was dependent on the type of fibroblast in the matrix. Under conditions where the epithelial outgrowth underwent terminal differentiation, the entire productive program took place, leading to virion assembly. In contrast, using an alternative condition where the outgrowth failed to achieve terminal differentiation, only the E-region RNAs from the E1 promoter accumulated to any appreciable extent. The proliferating cell nuclear antigen was induced in the differentiated suprabasal cells in the productive cyst growth, which also exhibited high copy viral DNA and abundant E6-E7 RNAs. Comparable cells in the nonproductive cyst outgrowth were negative for all three. These results suggest that the E6 and E7 proteins may play a role in establishing a cellular environment conducive to vegetative viral replication. The culture conditions described should be useful for genetic analysis of this family of important human pathogens and for testing potential pharmacological agents.

Heterogeneity in state and expression of viral DNA in polyoma virus-induced tumors of the mouse

We have examined the state and expression of polyoma viral DNA in representative epithelial and mesenchymal tumors, using a combination of biochemical and in situ methods. Results showed wide variations among tumor types and also in different regions within individual tumors, with respect to copy number of viral DNA, presence or absence of deletions, and expression of early and late viral proteins. Epithelial tumors showed the greatest heterogeneity. High copy free viral DNA, frequently with deletions, was found in all such tumors. A portion of free viral DNA was recoverable as transcriptionally active minichromosomes. Three distinct subpopulations of cells were distinguished by in situ analyses. Type 1 cells showed high copy free viral DNA and expressed the major viral capsid protein VP1; these cells appeared to be at various stages of productive (lytic) viral infection. Some productively infected cells were able to undergo mitosis; in a portion of these cells, VP1 was found in close association with the mitotic spindle. Type 2 cells contained high copy free DNA but did not express VP1; by some unknown mechanism, these cells manifest a post-replication block to late gene expression and lytic infection. Type 3 cells contained only low copy, presumably integrated, viral DNA and expressed no VP1; they thus resemble cells transformed in vitro by the virus. Epithelial tumors contained variable mixtures of these subpopulations, while mesenchymal tumors were composed of Type 3 cells only. Differences in virus-cell interactions are discussed in terms of their possible implications in tumor development.

Effective vaccination against papilloma development by immunization with L1 or L2 structural protein of cottontail rabbit papillomavirus

Immunization of rabbits with either L1, the major structural protein, or L2, a minor structural protein of cottontail rabbit papillomavirus (CRPV), protected against challenge with the virus. Neutralizing antibodies were elicited by both the L1 and L2 trpE fusion proteins. Neutralization with anti-L1 serum, however, was more efficient than with anti-L2 serum. In contrast, when tested on Western blots the immune response to L2 was stronger than to L1. Rabbits were also protected against CRPV infection by immunization with L1 expressing recombinant vaccinia virus. Sera from two of three rabbits immunized with recombinant vaccinia virus were negative on Western blots but all three were positive in ELISA's with nondenatured fusion protein or in immunoprecipitations. The results suggest that both the viral structural proteins, L1 and L2, merit consideration in the development of a vaccine against papillomavirus.

Human papillomavirus type 16 and 18 gene expression in cervical neoplasias

Human papillomavirus (HPV) types 16 and 18 are strongly implicated in the generation of progressive cervical neoplasms. The viruses produce complex families of overlapping messenger RNAs that are linked to differentiation, making it necessary to analyze gene expression in the context of morphology. We have developed HPV type 16 and type 18 subgenomic clones from which 3H-labeled riboprobes specific to individual mRNA families can be generated in vitro. Using these probes for in situ hybridization, we examined serial sections of archival biopsy specimens of the spectrum of genital lesions. In low-grade squamous lesions, all viral open reading frames were expressed, and the most abundant transcription spanned the E4 and E5 open reading frames at the 3' end of the E region. L region transcription coding for the capsid proteins was restricted to terminally differentiated keratinocytes. As the grade of neoplasia increased, cellular differentiation and overall viral transcription decreased and, with few exceptions, the L2 and L1 transcripts ceased to exist. The E6-E7 transforming region was invariably derepressed. Interestingly, the patterns of HPV-16 gene expression suggested the coexistence of episomal and integrated viral DNAs. In contrast, in HPV-18 lesions, all the viral template DNA appeared to have integrated. Integration was deduced to have occurred near the boundary of the E1 and E2 open reading frames. Viral transcription patterns were similar in carcinomas in situ and in invasive carcinomas, regardless of the histologic cell types or the associated virus types, consistent with the notion that additional host gene alterations were necessary for progression. On the basis of viral gene expression in vivo and the E6 promoter regulation previously characterized in vitro, we discuss a molecular mechanism for HPV-associated carcinogenesis.

Replication and persistence of HPV DNA in cultured cells derived from laryngeal papillomas

We have investigated the replication and persistence of human papillomavirus (HPV) type 6 and 11 DNA in cultured cells derived from laryngeal papillomas, with paradoxical findings. Measured by bromodeoxyuridine incorporation into heavy/light DNA separated on a cesium chloride gradient, viral DNA replicates in both primary and secondary cells. The ratio of the fraction of replicated viral to replicated cellular DNA was equal to or greater than 1 in all but one case and was closer to 2 in primary cells. Despite this efficient replication, HPV DNA is rapidly lost from the cells with passage. We propose that infected cells, or those with a high HPV copy number, show a selective decrease in plating efficiency compared to uninfected cells or those with a low copy number, which explains the loss of HPV DNA with repeated passage.

Molecular cloning, analysis, and chromosomal localization of a mouse genomic sequence related to the human papillomavirus type 18 E5 region

The E5 open reading frame (ORF) from bovine papillomavirus type 1 (BPV 1) as well as the E5 ORFs from human papillomaviruses (HPV) type 6 and type 16 have been reported to transform immortalized rodent cells. In an analysis of murine and human tumors for the presence of putative papillomavirus-related sequences, we cloned amplified cellular sequences from the mouse cell line Eb that cross-hybridized with the E5 ORF of HPV 18. A 2.1-kb fragment termed HC1 was sequenced. In normal murine cells, it was present as a single-copy genomic sequence located on chromosome 8. A region of 213 nucleotides corresponded to the E5 gene (HC1 E5), based on the best alignments and on the presence of direct and inverted repeats bearing a central sequence motif. These structural elements are also present in the HPV 18 E5 ORF. HC1 E5 contained an ORF that was transcribed bidirectionally. The transcription in the E5 direction was enhanced in RNA obtained from organs and tumors from carcinogen-treated animals and C127 cells. The polypeptide deduced from the sequence was related to E5 proteins from genital papillomaviruses, to the putative product of the Q300 mouse gene, and to several viral and human growth factors. The data suggest that there may be several cellular counterparts to the viral E5 proteins.

Sexually transmitted diseases: viruses and ectoparasites. Committee on Sexually Transmitted Diseases of the American Academy of Dermatology

This review highlights recent developments in the epidemiology, pathogenesis, diagnosis, and treatment of nonbacterial sexually transmitted infections. Genital herpes simplex, anogenital human papillomavirus disease, molluscum contagiosum, pediculosis pubis, and scabies are discussed.

HPV-16 viral transcripts in vulvar neoplasia: preliminary studies

Specific human papillomavirus (HPV) types are strongly associated with intraepithelial neoplasia and invasive cancer of the cervix. In contrast, the role of HPVs in the pathogenesis of invasive carcinoma of the vulva is poorly understood. We have employed in situ hybridization for the detection of subgenomic transcripts in four vulvar specimens to elucidate the role of HPV type 16 in the development and progression of vulvar cancer. These analyses revealed that the transcripts of the E6-E7 region were more abundant than those of the L1-L2 region in vulvar neoplastic tissues. The transcripts from early and late region of HPV-16 continued to increase with the differentiation of the epithelial cells in both the warty and the basaloid types of vulvar precancerous lesions. This pattern persisted in invasive warty carcinoma but not in basaloid invasive carcinoma; the transcripts in basaloid carcinoma were distributed in an even and discrete pattern. In contrast to earlier studies, L1-L2-region transcripts, as well as viral capsid protein, were detected in focal areas of well-differentiated cells of invasive warty carcinoma. These findings suggest that expression of HPV-16 is regulated by the degree of cellular differentiation.

Pathobiology of papillomavirus-related cervical diseases: prospects for immunodiagnosis

In recent years, the relationship between human papillomaviruses (HPV) and genital neoplasia has been explored intensively, and a molecular basis for the role of HPV in the genesis of these diseases has been convincingly demonstrated. These findings have provided justification for efforts to apply this molecular information to the early detection and possible prevention of HPV-related neoplasia. The technology of detecting viral nucleic acids in genital fluids brought with it initial hopes that it would serve to identify women at risk for having or developing precancers or cancers of the cervix. Subsequent studies, however, have demonstrated limitations of the technology for predicting future disease. Recently, molecular immunology has complemented these prior efforts, with the intent to identify serological indices of exposure to HPV and perhaps delineate individuals at risk. The molecular basis for this approach, its limitations, and future prospects for immunodiagnosis are the subject of this review.

Detection of human papillomavirus DNA by in situ DNA hybridization and polymerase chain reaction in premalignant and malignant oral lesions

The sensitivity of detection of human papillomavirus (HPV) DNA in premalignant and malignant oral lesions by in situ hybridization (ISH) and polymerase chain reaction (PCR) were compared. With both methods HPV DNA was found in 4 of 24 cases of epithelial dysplasia, 4 of 14 cases of verrucous hyperplasia, and 1 of 10 cases of squamous cell carcinoma. The 10 cases of smokeless tobacco keratoses and 3 cases of verrucous carcinoma that we examined were all negative for HPV DNA. The PCR for the E6 open reading frame of HPV-16 correctly identified all cases that were positive by ISH. Only a single case that was positive by PCR was negative by ISH for HPV DNA. However, the PCR demonstrated the presence of HPV-16 infection in one case, which had hybridized most intensely with the probe for types 31/33/35 in the ISH. This discrepancy probably is due to the high degree of cross-hybridization in the ISH assay. PCR appears to be an effective technique for identifying HPV-16 DNA sequences in biopsy material from premalignant and malignant oral lesions.

Characterization of in vivo expression of the human papillomavirus type 16 E4 protein in cervical biopsy tissues

The role of human papillomavirus (HPV) proteins in the pathogenesis of cervical intra-epithelial neoplasia (CIN) and invasive cervical cancer is poorly understood. To characterize E4 protein expression in 49 paraffin-embedded cervical biopsies representing different histopathologic grades of disease, antibodies were elicited to a synthetic peptide corresponding to amino acids 20-34 of a protein predicted to be encoded by the HPV 16 E4 open reading frame. The E4 protein was detected throughout the spectrum of CIN, from CIN1 to CIN3. Expression was localized to the cell nucleus, primarily in the superficial layers of the squamous cervical epithelium. Ultrastructural studies showed that the E4 protein was organized into compact, intranuclear arrays 25-35 nm in diameter. E4 protein expression was also demonstrated in some histologically normal tissues containing HPV 16 DNA, but not in any of five cervical cancers containing HPV 16 DNA. These results suggest that E4 protein expression may precede development of light microscopic tissue abnormalities, that it may continue through the spectrum of CIN, and that expression of this protein may be reduced or terminated in invasive cancer. The function of this protein remains unknown, but its nuclear localization may be consistent with a role in viral maturation.

An E1M--E2C fusion protein encoded by human papillomavirus type 11 is asequence-specific transcription repressor

We have isolated a putative, spliced E5 cDNA of human papillomavirus type 11 (HPV-11) by polymerase chain reaction amplification of cDNAs from an experimental condyloma. Using retrovirus-mediated gene transfer, we isolated two novel HPV-11 cDNAs, one of which had a splice linking nucleotides 1272 and 3377. This transcript also existed in experimental condylomata and in cervical carcinoma cells transfected with cloned genomic HPV-11 DNAs. The 5' end of the transcript in transfected cells originated upstream of the initiation codon of the E1 open reading frame (ORF). It could conceptually encode a fusion protein consisting of the amino-terminal 23% of the E1 ORF and the carboxy-terminal 40% of the E2 ORF. This E1M--E2C fusion protein contained both the DNA replication modulator domain E1M, as defined in the bovine papillomavirus system, and the DNA binding domain of the E2 protein, which regulates viral transcriptional activities. Indirect immunofluorescence with polyclonal antibodies raised against the bacterially expressed TrpE-HPV-11 E2 protein demonstrated nuclear localization of the E1M--E2C protein in cells transiently transfected with an expression plasmid. Immunoprecipitation revealed a specific protein with an apparent molecular weight of 42,000 in transfected cells. The chloramphenicol acetyltransferase assay established that the putative E1M--E2C protein was a potent transcriptional repressor of both E2-dependent and E2-independent HPV-11 enhancer/promoter activities. Northern (RNA) blot hybridization indicated the repression was on the transcriptional level. Mutational analysis suggested that the E1M--E2C protein is an E2-binding site-specific repressor. The fusion protein also repressed bovine papillomavirus type 1 (BPV-1) E2 protein-dependent BPV-1 enhancer activity. When constitutively expressed in mouse C127 cells, the E1M--E2C protein inhibited BPV-1 transformation and episomal DNA replication, consistent with a role in the modulation of replication.

A negative regulatory element in the human papillomavirus type 16 genome acts at the level of late mRNA stability

A negative regulatory element present in the human papillomavirus type 16 genome has been characterized. Deletion analysis has localized the 5' end of the element to the late region of the genome at the extreme 3' end of the coding region of the L1 open reading frame, around the L1 stop codon, with the element extending into the L1 3' untranslated region. For the cell lines used, the element's function was independent of cell type, tissue, or species of origin, unlike papillomavirus infection, which is very dependent on such factors. By using an mRNA decay assay, we have determined that polyadenylated RNA containing the element is much less stable than polyadenylated RNA lacking the element. This indicates that the element acts as an mRNA instability element. The significance of A-rich, GU-rich, and AUG-rich sequences for the functioning of this human papillomavirus type 16 instability element is discussed.