Structure, DNaseI hypersensitivity and expression of integrated papilloma virus in the genome of HeLa cells

Detection of EBV, HBV, HCV, HIV-1, HTLV-I and -II, and SMRV in human and other primate cell lines

The high prevalence of contaminated cell cultures suggests that viral contaminations might be distributed among cultures. We investigated more than 460 primate cell lines for Epstein-Barr (EBV), hepatitis B (HBV), hepatitis C (HCV), human immunodeficiency virus type 1 (HIV-1), human T-cell leukemia/lymphoma virus I and II (HTLV-I/-II), and squirrel monkey retrovirus (SMRV) infections for risk assessment. None of the cell lines were infected with HCV, HIV-1, or HTLV-I/-II. However, one cell line displayed reverse transcriptase activity. Thirty-nine cell lines harbored EBV DNA sequences. Studies on the lytic phase of EBV revealed that five cell lines produce EBV particles and six further cell lines produced EBV upon stimulation. One cell line contained an integrated HBV genome fragment but showed no virus production. Six cell lines were SMRV-infected. Newly established cell lines should be tested for EBV infections to detect B-lymphoblastoid cell lines (B-LCL). B-LCLs established with EBV from cell line B95-8 should be tested for SMRV infections.

Adenovirus E1B55K region is required to enhance cyclin E expression for efficient viral DNA replication

Adenoviruses (Ads) with E1B55K mutations can selectively replicate in and destroy cancer cells. However, the mechanism of Ad-selective replication in tumor cells is not well characterized. We have shown previously that expression of several cell cycle-regulating genes is markedly affected by the Ad E1b gene in WI-38 human lung fibroblast cells (X. Rao, et al., Virology 350:418-428, 2006). In the current study, we show that the Ad E1B55K region is required to enhance cyclin E expression and that the failure to induce cyclin E overexpression due to E1B55K mutations prevents viral DNA from undergoing efficient replication in WI-38 cells, especially when the cells are arrested in the G(0) phase of the cell cycle by serum starvation. In contrast, cyclin E induction is less dependent on the function encoded in the E1B55K region in A549 and other cancer cells that are permissive for replication of E1B55K-mutated viruses, whether the cells are in the S phase or G(0) phase. The small interfering RNA that specifically inhibits cyclin E expression partially decreased viral replication. Our study provides evidence suggesting that E1B55K may be involved in cell cycle regulation that is important for efficient viral DNA replication and that cyclin E overexpression in cancer cells may be associated with the oncolytic replication of E1B55K-mutated viruses.

Genomic instability of the host cell induced by the human papillomavirus replication machinery

Development of invasive cervical cancer upon infection by 'high-risk' human papillomavirus (HPV) in humans is a stepwise process in which some of the initially episomal 'high-risk' type of HPVs (HR-HPVs) integrate randomly into the host cell genome. We show that HPV replication proteins E1 and E2 are capable of inducing overamplification of the genomic locus where HPV origin has been integrated. Clonal analysis of the cells in which the replication from integrated HPV origin was induced showed excision, rearrangement and de novo integration of the HPV containing and flanking cellular sequences. These data suggest that papillomavirus replication machinery is capable of inducing genomic changes of the host cell that may facilitate the formation of the HPV-dependent cancer cell.

Heparin (GAG-hed) inhibits LCR activity of human papillomavirus type 18 by decreasing AP1 binding

BACKGROUND

High risk HPVs are causative agents of anogenital cancers. Viral E6 and E7 genes are continuously expressed and are largely responsible for the oncogenic activity of these viruses. Transcription of the E6 and E7 genes is controlled by the viral Long Control Region (LCR), plus several cellular transcription factors including AP1 and the viral protein E2. Within the LCR, the binding and activity of the transcription factor AP1 represents a key regulatory event in maintaining E6/E7 gene expression and uncontrolled cell proliferation. Glycosaminoglycans (GAGs), such as heparin, can inhibit tumour growth; they have also shown antiviral effects and inhibition of AP1 transcriptional activity. The purpose of this study was to test the heparinoid GAG-hed, as a possible antiviral and antitumoral agent in an HPV18 positive HeLa cell line.

METHODS

Using in vivo and in vitro approaches we tested GAG-hed effects on HeLa tumour cell growth, cell proliferation and on the expression of HPV18 E6/E7 oncogenes. GAG-hed effects on AP1 binding to HPV18-LCR-DNA were tested by EMSA.

RESULTS

We were able to record the antitumoral effect of GAG-hed in vivo by using as a model tumours induced by injection of HeLa cells into athymic female mice. The antiviral effect of GAG-hed resulted in the inhibition of LCR activity and, consequently, the inhibition of E6 and E7 transcription. A specific diminishing of cell proliferation rates was observed in HeLa but not in HPV-free colorectal adenocarcinoma cells. Treated HeLa cells did not undergo apoptosis but the percentage of cells in G2/M phase of the cell cycle was increased. We also detected that GAG-hed prevents the binding of the transcription factor AP1 to the LCR.

CONCLUSION

Direct interaction of GAG-hed with the components of the AP1 complex and subsequent interference with its ability to correctly bind specific sites within the viral LCR may contribute to the inhibition of E6/E7 transcription and cell proliferation. Our data suggest that GAG-hed could have antitumoral and antiviral activity mainly by inhibiting AP1 binding to the HPV18-LCR.

Progression from productive infection to integration and oncogenic transformation in human papillomavirus type 59-immortalized foreskin keratinocytes

Studies of changes in the virus and host cell upon progression from human papillomavirus (HPV) episomal infection to integration are critical to understanding HPV-related malignant transformation. However, there exist only a few in vitro models of both productive HPV infection and neoplastic progression on the same host background. We recently described a unique foreskin keratinocyte cell line (ERIN 59) that contains HPV 59 (a close relative of HPV 18). Early passages of ERIN 59 cells (passages 9-13) contained approximately 50 copies of episomes/cell, were feeder cell-dependent, and could be induced to differentiate and produce infectious virus in a simple culture system. We now report that late passage cells (passages greater than 50) were morphologically different from early passage cells, were feeder cell independent, and did not differentiate or produce virus. These late passage cells contained HPV in an integrated form. An integration-derived oncogene transcript was expressed in late passage cells. The E2 open reading frame was interrupted in this transcript at nucleotide 3351. Despite a lower viral genome copy number in late passage ERIN 59 cells, expression of E6/E7 oncogene transcripts was similar to early passage cells. We conclude that ERIN 59 cells are a valuable cell line representing a model of progression from HPV 59 episomal infection and virus production to HPV 59 integration and associated oncogenic transformation on the same host background.

Identification of a novel promoter in the E2 open reading frame of the human papillomavirus type 18 genome

Northern blot and RT-PCR analyses indicated that the human papillomavirus E4 open reading frame is expressed in HeLa cells. Because integration at the E1 or E2 open reading frame would place the viral upstream regulatory region downstream of the viral late genes, the expression of E4 in HeLa cells is most likely regulated by host cellular promoter(s) or unidentified viral promoter(s) in the E2 region. Primer extension analysis and transient transfection experiments with luciferase reporter constructs under the transcriptional control of various subgenomic fragments of HPV-18 were carried out to identify and characterize functional promoters within the E2 region. The in vivo activity of a novel promoter located within the 5'-end region of the E2 open reading frame of human papillomavirus type 18 is demonstrated.

Delineation of mRNA export pathways by the use of cell-permeable peptides

The transport of messenger RNAs (mRNAs) from the nucleus to the cytoplasm involves adapter proteins that bind the mRNA as well as receptor proteins that interact with the nuclear pore complex. We demonstrate the utility of cell-permeable peptides designed to interfere with interactions between potential adapter and receptor proteins to define the pathways accessed by particular mRNAs. We show that HuR, a protein implicated in the stabilization of short-lived mRNAs containing AU-rich elements (AREs), serves as an adapter for c-fos mRNA export through two pathways. One involves the HuR shuttling domain, HNS, which exhibits a heat shock-sensitive interaction with transportin 2 (Trn2); the other involves two protein ligands of HuR-pp32 and APRIL-which contain leucine-rich nuclear export signals (NES) recognized by the export receptor CRM1. Heterokaryon and in situ hybridization experiments reveal that the peptides selectively block the nucleocytoplasmic shuttling of their respective adapter proteins without perturbing the overall cellular distribution of polyadenylated mRNAs.

The effects of interferon on the expression of human papillomavirus oncogenes

The effects of interferon (IFN)-alpha, IFN-beta and IFN-gamma on human papillomavirus (HPV) oncogene expression were studied in various cervical carcinoma cell lines containing integrated copies of either HPV type 16 or HPV type 18. The levels of E6 and E7 transcripts were examined 6 h and 30 h after treatment with IFN. In HeLa cells, all three classes of IFNs effected a decrease in the level of HPV-18 E6 and E7 transcripts. On the other hand, none of the IFNs altered the level of these transcripts in C-4II cells. Only IFN-gamma decreased the level of HPV-16 E6 and E7 transcripts in CaSki and HPK1A cells, while IFN-gamma actually increased the level of these transcripts in SiHa cells. This differential IFN regulation of HPV expression in various cervical cancer cell lines may account for the contradictory clinical results observed after treatment of cervical cancer with IFN.

The integration of HPV-18 DNA in cervical carcinoma

AIMS

Little information is available on the patterns of integration into the host chromosomal DNA of cervical carcinomas of human papillomavirus type 18 (HPV-18) DNA, which is associated with up to 20% of these carcinomas. Because integration of the viral genome may be extremely important in the pathogenesis of cervical carcinoma, the aim of this study was to investigate which regions of HPV-18 DNA are integrated into the cellular DNA of cervical carcinomas.

METHODS

Southern analysis using four subgenomic probes covering the entire HPV-18 genome was used to map viral DNA integrated within cellular DNA. The polymerase chain reaction (PCR) was used to confirm the presence of specific regions of the viral genome.

RESULTS

In all 11 carcinomas there was a single major HPV-18 DNA integrant, retaining approximately 4000 bp of HPV-18 DNA, indicating that approximately half of the virus genome had been lost upon integration. Southern analysis suggested strongly that the viral breakpoint was within the E1/E2 gene boundary, with concomitant loss of part or all of the E2 ORF (open reading frame), all of the E4, E5, and L2 ORFs and part of the L1 ORF. These data were supported by the PCR results, which confirmed that the region of integrated HPV-18 DNA from nucleotides 6558 to 162 was present in all the carcinoma samples studied. Assuming that no genomic rearrangements, deletions, or insertions had occurred, 4131 bp of integrated HPV-18 DNA could be accounted for in eight cervical carcinoma samples. The results of Southern analysis also suggested that integration of HPV-18 DNA may have occurred at a specific host chromosomal site.

CONCLUSIONS

Broadly, the viral sequences retained upon HPV-18 integration resemble those found when HPV-16 is integrated. However, it appears that the HPV-18 E2 region is more consistently deleted.

Deletion in human chromosome region 12q13-15 by integration of human papillomavirus DNA in a cervical carcinoma cell line

In human cervical carcinomas papillomavirus DNA is frequently integrated in the cell genome. We have cloned the integration site of human papillomavirus-18 DNA in human chromosome region 12q13-15 present in the SW756 cervical carcinoma cell line. Viral DNA is broken from nucleotides 2643 to 3418 in the E1 and E2 open reading frames, resulting in a deletion of 775 bases of viral DNA. Cloning and sequence analysis of the rearranged and germline alleles shows that there is no homology between the target cellular and viral DNA, suggesting it is a nonhomologous recombination. The target cellular region is called papillomavirus associated locus 2 (PAL2). The 5'- and 3'-flanking probes derived from the hybrid viral-cellular clone detect completely different germline restriction fragments in DNA from cells with normal chromosome 12. There is no overlap between the restriction maps of the target germline clones obtained with 5'- and 3'-flanking probes. Probes from these germline clones beyond the breakpoint position do not detect any DNA rearrangement in SW756 cells DNA. These data prove that there is a deletion of cellular DNA as consequence of the integration, with an estimated minimum size of 14 kilobases. Both cellular flanking probes are outside the amplicon of this chromosome region identified in the OSA and RMS13 sarcoma cell lines, comprising SAS-CHOP-CDK4-MDM2 genes and where translocation breakpoints are located in liposarcomas. The integration at 12q13-15 might have been selected by its contribution to the tumor phenotype.

Chromosomal organization of viral integration sites in human papillomavirus-immortalized human keratinocyte cell lines

The target specificity of viral integration is essential to determining the biologic significance of this integration to various pathologic conditions, including cancer. In this study the chromosomal features of several human papillomavirus (HPV)-16 integration sites mapped by in situ hybridization in human keratinocyte lines were visualized directly by G-banding and differential labeling with bromodeoxyuridine of later replicating domains. G-negative chromosomal bands exhibiting late replication were selectively targeted by HPV-16, suggesting that the structural and functional relationship of the state of chromatin condensation and replication is critical in accessibility to virus integration.

Integration site of human papillomavirus type-18 DNA in chromosome band 8q22.1 of C4-I cervical carcinoma: DNase I hypersensitivity and methylation of cellular flanking sequences

The C4-I cell line derived from a non-keratinizing squamous cell carcinoma of the uterine cervix contains integrated human papillomavirus-18 DNA. Fluorescence in situ hybridization of C4-I cells demonstrated a single viral integration site at 8q22.1 on a derivative chromosome originating from an 8q;12q translocation. 8q22 is a site of chromosome fragility and is also recombinogenic in several human malignancies. DNase I hypersensitivity of the integration site was studied with a cellular flanking probe. A hypersensitive site was detected within 3 kb from viral DNA. The integration sites are undermethylated in C4-I and HeLa cells and fully methylated in tumor cell lines of other origin, such as lymphoid cells.

Detection of genital papillomavirus types by polymerase chain reaction using common primers

We describe the detection of eight genital human papillomavirus (HPV) types, including HPV16 and HPV18, by PCR amplification of a 323 base-pair region of the genome within the L1 open reading frame (ORF). The primer sequences are: TGYAAATATCCWGATTWTWT and GTATCWACMACAGTAACAAA. The method will detect purified HPV16 DNA down to a concentration of as little as a single molecule in 100 microliters. The method is also applicable to purified DNA and crude lysates from tumour biopsies. Typing of the PCR product can be achieved with specific oligonucleotide probes.

Sensitivity of in situ hybridization techniques using biotin- and 35S-labeled human papillomavirus (HPV) DNA probes

In order to evaluate the sensitivity of our modified in situ DNA hybridization technique using biotinylated probes, formalin fixed, paraffin embedded biopsies from 20 cervical lesions known to contain human papillomavirus (HPV) DNA were re-examined by the technique using both 35S-labeled- and biotinylated HPV DNA probes. The probe concentrations as well as the detection limits of biotin probing were screened by spotting known amounts of HPV 16 DNA on nylon filter, and allowed to hybridize with biotinylated HPV 16 DNA probe. By this method, 4 pg of HPV 16 DNA could be detected using a probe concentration of 0.2 micrograms/ml. HPV DNA could be demonstrated in all 20 biopsies with both hybridization techniques. However, signals in subrabasal cells were detected more frequently with biotin- than with 35S-labeled probes. Additional experiments were performed using three cervical cancer cell lines (with known copy numbers of HPV DNA), to assess the detection limits of HPV infections by the in situ hybridization techniques. The CaSki cells (500-600 HPV 16 copies/cell) were unequivocally positive with both labelling systems. HeLa cells (10-50 HPV 18 copies/cell) were positive with the biotin probing in 10/10 smears, as compared to 7/10 smears when 35S-labeled probes were used. Radioactive probing was inferior to biotinylated probing in detecting the signals in SiHa cells (1-2 HPV 16 copies/cell). This is because even weak background signals could mask true positive signals when 35S-labeled probes are used. In contrast, no background is generated with the biotinylated probes, detected with streptavidin-biotinylated alkaline phosphatase complex. In situ hybridization with biotinylated DNA probes is as sensitive as techniques using 35S-labeled probes for detecting HPV infections in routine cervical biopsies or smears.