Department of Biomedical Sciences, Microbiology Section, University of Sassari, Viale S. Pietro 43B, I-07100 Sassari, Italy 1
Department of Cellular and Developmental Biology, La Sapienza University, Rome, Italy2
Author for correspondence: Antonina Dolei.Fax +39 079 212345. e-mail doleivir{at}ssmain.uniss.it
![]() |
Abstract |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
![]() |
Introduction |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Reciprocal interactions may occur between the two viruses, as it does between HIV and other viruses (Critchlow et al., 1998 ; Levy, 1994
; Harrington et al., 1997
; Heng et al., 1994
), and between HPV and human herpesvirus-6 (Chen et al., 1994
) or adeno-associated parvovirus (Walz et al., 1997
). HPV may facilitate HIV transmission through disruption of mucosal integrity and/or altered local immunosurveillance, and HIV may alter HPV-controlling cellular pathways (Arany et al., 1997
). HIV is present in genital secretions (Mostad & Kreiss, 1996
; Iversen et al., 1998
), and HPV and HIV-1 colocalize in cervical intraepithelial neoplasias (Vernon et al., 1994
). HPV-bearing cells are exposed to viral and cellular factors released within the tissue both by resident HIV-infected cells and by HIV-infected infiltrating cells (Levy, 1994
; Dolei et al., 1994
, 1996
; Fauci, 1996
). HPV and HIV can also share the same host cell type (Heng et al., 1994
; Dolei et al., 1996
). HIV-1 infection has been found, both in vivo and in vitro,in epithelial cells from various solid tissues, including epidermal, colorectal, vaginal, mammary, laryngeal, adrenal, hepatic and renal tissues [Heng et al ., 1994
; Dolei et al., 1996
(review); Furuta et al., 1994
; Toniolo et al., 1995
]. In addition, permissiveness of embryonal carcinoma cells to HIV infection was induced by differentiation (Hirka et al., 1991
).
During the natural course of infection, HPV transcriptional activity within the epithelium is tightly linked to the keratinocyte differentiation stages. Early transcription occurs in basal and suprabasal cell layers, and early gene products are detected in all layers of the infected epithelium. Late transcription, the synthesis of L1 and L2 capsid proteins and the production of infectious virus are restricted to the terminally differentiated keratinocytes of the upper layers, close to the epithelial surface (Flores & Lambert, 1997 ; Frattini et al., 1997
; Meyers et al., 1997
). Late transcripts are also detected in lower layers, but they remain in the nucleus, due to a block in RNA processing (Stoler et al., 1992
). In fact, an AU-rich, cis -acting inhibitory sequence that is found in HPV late mRNAs binds to cellular proteins and is probably involved in the inhibition of HPV late gene expression in undifferentiated epithelial cells (Zhao et al., 1996
). In HeLa cells, as well as in other cervical carcinoma cells, only the transcription of early HPV genes was detected, at least in the poly(A)+ RNA fraction (Hummel et al., 1995
; Inagaki et al., 1988
; Schwarz et al., 1985
).
The aim of this study was to highlight the effect of HIV infection on HPV-18 gene expression in epithelial cells, and to explore the possibility of a direct stimulation of HPV by HIV superinfection. HPV- 18-positive HeLa-T4 cells were exogenously exposed to HIV-1, to the HIV transactivator Tat or to cytokines induced by HIV. The E1 and L1 genes were selected, as representative of HPV-18 expression. The former encodes a phosphoprotein that provides several DNA replication functions (Melendy et al., 1995 ), while the latter encodes the major component of the HPV capsid. The data indicate that there are increased levels of E1 and L1 HPV-18 transcripts, followed, only in HIV-infected epithelial cells, by a de novo synthesis of the HPV L1 protein.
![]() |
Methods |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
HIV-1.
The T-tropic isolate HIV-1P1 was used. Virus characteristics and stock production have been described (Dolei et al., 1998 ). Infection of HeLa-T4 cells was done as in Dolei et al. (1994)
. The m.o.i. was 0·10·5 syncytium-forming units (s.f.u.) per cell. At various time-intervals, cell culture supernatants and washed monolayers were collected and then frozen at -80 °C. Virus replication was evaluated as infectious virus, as described (Dolei et al., 1994
; Toniolo et al., 1995
).
Cytokine detection.
Culture fluids received 0·5% Triton X-100 to inactivate infectious HIV. To detect IL-1, IL-1ß, IL-6 and TNF-
, an ELISA assay (Medgenix Diagnostics, Fleurus, Belgium) was carried out, according to the manufacturer's instructions.
Cytokine and Tat treatment.
Human recombinant IL-1, IL-1ß, IL-6 and TNF-
(Boehringer Mannheim), and HIV-1 Tat (E. coli -derived HxB2 Tat; Intracell, London, UK) were added to cultures 24 h after seeding, at the following concentrations: 20 U/ml (IL-1
, IL-1ß); 101000 U/ml (IL-6); 20 pg/ml (TNF-
); 0·1100 ng/ml (Tat) (and maintained throughout the experiments).
RNA extraction.
Total cellular RNA was obtained as described (Chomczynski & Sacchi, 1987 ). To demonstrate that RNA extracts were free of contaminating DNA, aliquots of each RNA sample were treated with RNase prior to hybridization: this treatment abolished the positive signals obtained in untreated samples hybridized to specific probes. RNA concentrations in the preparations were determined as absorbance at 260 nm.
Preparation of E1-, L1- and ß-actin- specific probes.
A pGEM-2 plasmid containing the whole HPV-18 genome inserted in the EcoRI site and human cellular DNA (containing the ß-actin gene) were used to prepare the radiolabelled probes. The E1-, L1- and ß-actin-specific probes were prepared by PCR utilizing primers and procedures as described (Bernard et al., 1994 ; Contorni & Leoncini, 1993
). PCR reactions for each set of primers were performed separately in a total volume of 100 µl, containing 1 ng of HPV-18 recombinant plasmid DNA (or 1 µg of cellular DNA, as for ß-actin amplification) and 50 µCi [
-32P]dATP. The amplified products (probes) were gel-filtered through a QIAquick column to remove unincorporated nucleotides.
Dot-blot hybridization.
Aliquots of cellular RNA (1 µg) were mixed with 3 vols of 10x SSC, 6·16 M formaldehyde and denatured by heating at 65 °C for 5 min. Each RNA sample was spotted onto three nitrocellulose membranes (Hybond-C extra; Amersham), to be hybridized to the E1, L1 and ß-actin probes, essentially as in Sambrook et al. (1989) . The hybridization was carried out overnight at 42 °C and then excess free probe was washed off (stringent conditions: two washes with 0·1% SDS, 2x SSC at room temperature and a final wash with 0·1% SDS, 0·2x SSC at 56 °C). The membranes were air-dried at room temperature and specific hybridization was evaluated as radioactivity bound to the membranes (quantified by scanning the spots with an Instant Imager Electronic Autoradiography apparatus (Packard). Background radioactivity was subtracted from the crude spot values and data obtained with the E1 and L1 probes were then normalized with respect to those obtained with the same samples hybridized with the ß-actin probe, and therefore expressed as a percentage of the ß-actin counts. The latter gene was chosen as housekeeping gene since its expression has been shown to remain unchanged in cells infected with HIV or exposed to Tat (Fan et al., 1997
; Ito et al., 1998
). Since the E1, L1 and ß-actin probes were prepared separately, they differed in specific radioactivity: thus the data obtained for E1 and L1 expression cannot be quantitatively compared each other. The statistical analysis was based on the non-parametric paired Wilcoxon's test.
Northern blot hybridization.
Sixty µg of total RNA extracted from HeLa-T4 cells 2 days after HIV infection and from parallel control cultures was electrophoresed through 1% agarose gels in 1x MOPS and 16·5% formaldehyde (37%, v/v), transferred to nitrocellulose membranes as described (Sambrook et al., 1989 ), hybridized with the complete genomic HPV-18 DNA probe, and scored as described above for dot-blot hybridization. The HPV-18 genomic DNA was purified from a pGEM- 2 vector, after EcoRI digestion, by agarose gel electrophoresis and was labelled by nick-translation as described (Schwarz et al., 1985
).
Western blotting.
Parallel cultures of HeLa-T4 cells were washed, lysed in 0·5% Triton X-100 and assayed for protein content by the bicinchoninic acid assay (Sigma). Fifteen µg of protein from each sample was resuspended in loading buffer (50 mM TrisHCl, pH 6·8, 2% SDS, 35 mM ß-mercaptoethanol, 10% glycerol and 0·1% bromophenol blue), loaded onto 10% SDSpolyacrylamide gels, and electrophoresed for 60 min at 60 mA, as described (Sambrook et al., 1989 ). Samples were then transferred onto nitrocellulose membranes (Hybond-C extra, Amersham) with a semi-dry blotter apparatus (KEM EN TECH) for 2 h at 4·7 V and 180 mA. Membranes were challenged with a polyclonal rabbit antiserum kindly provided by S. Campo, Beatson Institute, Glasgow, UK. This serum was raised against a recombinant L1ß-galactosidase hybrid protein, of Mr 140000, containing the L1a (L1a-55926150) and L1b (L1b- 61506878) subunits of HPV-16, and recognizes the carboxy- terminal moiety of HPV-16 and HPV-18 L1 protein, where the two viruses share high homology (Bernard et al., 1994
). Controls included Rainbow coloured protein MW markers (range 14300220000; Amersham), lysates from unrelated cell lines, either untreated or HIV-infected (negative control), and the recombinant L1ß-galactosidase hybrid protein (positive control). The blots were rinsed in 150 mM NaCl, 50 mM TrisHCl, pH 7·5, 5% foetal calf serum and reacted with alkaline phosphatase-conjugated secondary antibody against rabbit IgG (Boehringer Mannheim). Visualization was achieved by addition of the substrate X-phosphate/NBT/BCIP. Specific bands present on the membranes were quantified by scoring in an image analyser, by the use of Image Master Software, version 1.10 (Pharmacia Biotech).
![]() |
Results |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
|
|
|
Cells were therefore treated with graded amounts of recombinant HIV Tat. As shown in Fig. 3(A, B) exogenous Tat exerts a transcriptional effect on the HPV-18 E1 and L1 genes, and this action is dose dependent. This finding demonstrates a direct action of HIV on HPV-18 activation. The effect is seen as early as 24 h after treatment, while differences with controls are less pronounced after more prolonged incubations (data not shown).
|
HIV-induced translation of L1 major capsid protein
Lysates from parallel cultures of HeLa-T4 cells were challenged in Western blot assays with an HPV-specific antiserum recognizing the L1 major capsid protein. Fig. 4 shows the data obtained after HIV infection (A, C) and after a 3 day treatment with Tat or the inflammatory cytokines IL-6 and TNF-
(B, D). The blots themselves (A, B) and the quantification of specific bands, obtained by scoring with an image analyser (C, D), are shown. HeLa-T4 cells alone did not produce any detectable L1 protein. However, after HIV infection (arrows in A), a band recognized by the HPV L1-specific antiserum appeared and accumulated with time. Western blotting of lysates from cells treated with Tat, IL-6 or TNF-
did not show any L1 band (B). The specificity of the serum employed was demonstrated by its recognition of a recombinant L1ß-galactosidase hybrid protein (Fig. 4B
), thereby excluding any possible cross-reactivity with a cellular or viral protein of similar size, e.g. HIV p55gag. Lysates from untreated and HIV-infected C8166 cells were challenged in Western blot with the HPV-specific serum, and did not show any staining.
|
![]() |
Discussion |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
We observed basal transcription of both E1 and L1 in untreated HeLa- T4 cells. The latter finding is notable, since late gene expression is normally restricted to terminally differentiated keratinocytes (Flores & Lambert, 1997 ; Frattini et al., 1997
; Meyers et al., 1997
). One must recall, however, that we analysed total cellular RNA, thus including nuclear transcripts. When HeLa-T4 cells are infected by HIV-1, HPV-18 transcripts accumulate to levels 2- to 7-fold greater than in control cultures. HIV infection, however, does not change qualitatively the pattern of HPV-18 transcription (Schwarz et al., 1985
), as indicated by Northern blot hybridization, but transcripts are more abundant in HIV-infected cultures (Fig. 2
). The accumulation of HPV-18 RNAs could be due either to an increased transcription rate or to reduced degradation of E1 and L1 transcripts in HIV-infected cells. It is unlikely that a direct activation of specific cellular flanking genes could be responsible for HPV-18 activation, since HPV-18, as well as HPV-16, is integrated into several chromosomes (Popescu et al., 1987
; Jeon et al., 1995
).
The importance of the HIV Tat and Rev regulatory proteins is well known, both in vivo and in vitro; HIV expression is under the control of two modulatory mechanisms, the Tat/TAR (Tat activation response) and Rev/RRE (Rev-responsive elements) pathways; these are linked to the endogenous cytokine network, and to possible interactions with other co-infecting agents [reviewed in Levy (1994) and Fauci (1996)
; see also Felber et al., 1990
]. Tat is a potent transactivator of transcription of both viral and cellular genes, through interactions with the TAR RNA elements and cellular proteins (Kao et al., 1987
; Levy, 1994
; Yang et al., 1997
). In vivo, biologically active Tat can be released by HIV-infected cells into circulating body fluids (Ensoli et al., 1994
), and both in vivo and in vitro may be captured by several uninfected cell types, through binding to integrin receptors, and transactivate cellular promoters as well as homologous and heterologous viral promoters (Levy, 1994
; Harrington et al., 1997
). Rev acts post-transcriptionally on viral and cellular mRNAs containing Rev-responsive sequences, both to prevent nuclear degradation of pre-mRNAs and to shuttle them from the nucleus to the cytoplasm (Levy, 1994
; Malim & Cullen, 1993
). In addition, HIV infection promotes the release of several cytokines, especially IL-6 and TNF-
(Table 1
), as shown for various cell systems, (Levy, 1994
; Dolei et al., 1994
1996
; Fauci, 1996
); these cytokines have been shown to stimulate HIV replication in circulating (Fauci, 1996
) and adherent cells (Dolei et al., 1994
, 1996
).
In patients infected by both HIV and HPV, HPV-bearing epithelial cells are exposed not only to HIV virions, but also to soluble viral and cellular factors released within the tissue both by resident HIV- infected cells or by HIV-infected infiltrating cells, especially Tat and pro-inflammatory cytokines (Levy, 1994 ; Fauci, 1996
). We therefore exposed HeLa-T4 cells to Tat or to HIV-inducible cytokines in our experimental system. Exposure to Tat resulted in dose-dependent increased transcription/accumulation of E1 and L1 genes, thus indicating that naturally integrated HPV genes are sensitive to Tat transactivation. Other workers have reported (results obtained by transfection of constructs) increased E2-dependent HPV-16 transcription (Vernon et al., 1993
), and HPV long control region transactivation and HPV-18 E7 expression (Tornesello et al., 1993
); in contrast, Gius & Laimins (1989)
did not find Tat effects studying an HPV-18 promoter-containing plasmid. On the other hand proinflammatory cytokines, whose production intended to contribute to the eradication of virus infection, can promote HIV gene expression and interrupt latency by rescuing defective HIV provirus and increasing Tat production (Levy, 1994
; Fauci, 1996
; Barillari et al., 1992
), virus release and binding to uninfected cells (Dolei et al., 1994
, 1996
). There are only two reports on cytokine regulation of HPV early gene expression: (i) a downregulation by IL-1 and by TNF-
(with no effect of IL-6) of HPV-16 early genes (by transfection of the HPV-16 noncoding region in HPV-18- positive HeLa cells; Kyo et al., 1994
); (ii) HPV-16 E6 and E7 downregulation by IL-1
and TNF-
in cervical carcinoma cells (Woodworth et al., 1995
). Of the cytokines produced by naturally infected HeLa-T4 cells after HIV infection (IL- 1
, IL-1ß, IL-6 and TNF-
), in our experimental conditions, no downregulation of E1 and L1 RNAs by IL-1
, IL- 1ß and TNF-
was observed, while IL-6 stimulated in a dose-dependent manner the transcription/accumulation of both genes (Fig. 3C
, D
), as it does also for HIV genes (Levy, 1996
; Dolei et al., 1994
, 1996
). Effects of IL-6 were detectable as early as after 24 h (E1) and 48 h (L1, increasing with time.
An interesting finding of the present work is the detection of L1 protein in HIV-infected HeLa-T4 cells. This was believed to be synthesized only in terminally differentiated keratinocytes of the upper layers (Frattini et al., 1997 ), due to a block in late RNA processing (Stoler et al., 1992
; Zhao et al., 1996
). Unexpectedly, HIV infection of HeLa-T4 cells bypassed this inhibition, as indicated by the accumulation of HPV- 18 L1 protein with time during HIV replication (Fig. 4
), and this confirms that HIV can disrupt the tight regulation of HPV transcription and translation. In keeping with our results, obtained with a more natural system, are the data from Tan et al. (1995)
and Tan & Schwartz (1995)
who, by cell cotransfection with constructs containing HIV and HPV genes, showed that Rev expression by epithelial cells counteracts the effect of the AU-rich negative element in HPV late mRNAs. This helps to explain why in our hands cell exposure to Tat activates only HPV transcription, while HIV infection (with endogenous production of Rev) is required for L1 protein translation. From these results of ourselves and others, it may be concluded that the mechanism of HPV induction by HIV could be as follows. HIV activation of HPV transcription occurs directly through Tat and indirectly through IL-6 induction, followed by late HPV translation, due to Rev shuttling of mRNA and counteraction of the AU- rich negative element in the HPV late 3' untranslated region. Moreover, published data show that in vivo HIV infects herpes simplex virus-1-infected epidermal keratinocytes, with reciprocal enhancement of replication (Heng et al., 1994
). This might be a more general phenomenon, raising the possibility that HPV infection could render keratinocytes more susceptible to HIV, therefore entering a vicious circle of synergistic expression of the two viruses. In this respect, the finding of early regression of HPV lesions in HIV-infected women responding to anti-retroviral therapy (Heard et al., 1998
) is relevant.
![]() |
Acknowledgments |
---|
![]() |
References |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Barillari, G. , Buonaguro, L. , Fiorelli, V. , Hoffman, J. , Michaels, F. , Gallo, R. C. & Ensoli, B. (1992). Effects of cytokines from activated immune cells on vascular cell growth and HIV-1 gene expression. Journal of Immunology 149, 3727-3734 .
Bernard, H. U. , Chan, S. Y. , Manos, M. M. , Hong, C. K. , Villa, L. L. , Delius, H. , Peyton, L. , Bauer, H. M. & Wheeler, C. M. (1994). Identification and assessment of known and novel human papillomaviruses by polymerase chain reaction amplification, restriction fragment length polymorphism, nucleotide sequence and phylogenetic algorithms.Journal of Infectious Diseases 170, 1077-1085 .[Medline]
Chen, M. , Popescu, N. , Woodworth, C. , Bernerman, Z. , Corbellino, M. , Lusso, P. , Ablashi, D. V. & DiPaolo, J. A. (1994). Human herpesvirus 6 infects cervical epithelial cells and transactivates human papillomavirus gene expression.Journal of Virology 68, 1173-1178 .[Abstract]
Chomczynski, P. & Sacchi, N. (1987). Single-step method of RNA isolation by acid guanidinium thiocyanatephenolchloroform extraction.Analytical Biochemistry 162, 156-159.[Medline]
Contorni, M. & Leoncini, P. (1993). Typing of human papillomavirus DNAs by restriction endonuclease mapping of the PCR products. Journal of Virological Methods 41, 29-36.[Medline]
Critchlow, C. W. , Hawes, S. E. , Kuypers, J. M. , Goldbaum, G. M. , Holmes, K. K. , Surawicz, C. M. & Kiviat, N. B. (1998). Effect of HIV infection on the natural history of anal human papillomavirus infection.AIDS 12, 1177-1184 .[Medline]
Dolei, A. , Serra, C. , Arca, M. V. , Tilocca, F. , Pietravalle, M. , Alemanno, L. , Toniolo, A. & Ameglio, F. (1994). Mutual interactions of HIV-1 and cytokines in adherent cells during acute infection.Archives of Virology 134, 157-168.[Medline]
Dolei, A. , Serra, C. , Biolchini, A. , Serra, C. , Curreli, S. , Gomes, E. & Dianzani, F. (1996). HIV-permissive cells from solid tissues: cytokine induction and effects.Perspectives in Drugs Discovery and Design 5, 90-101.
Dolei, A. , Biolchini, A. , Serra, C. , Curreli, S. , Gomes, E. & Dianzani, F. (1998). Increased replication of T-cell- tropic HIV strains and CXC-chemokine receptor-4 induction in T cells treated with macrophage inflammatory protein (MIP)-1, MIP- 1ß and RANTES ß-chemokines.AIDS 12, 183-190.[Medline]
Ensoli, B. , Gendelman, R. , Markham, P. , Fiorelli, V. , Colombini, S. , Raffeld, M. M. , Cafaro, A. , Chang, H. K. , Brady, J. N. & Gallo, R. C. (1994). Synergy between basic fibroblast growth factor and HIV-1 Tat protein in induction of Kaposi's sarcoma.Nature 371, 674-680.[Medline]
Fan, J. , Li, P. , Kok, T. W. & Burrell, C. J. (1997). AZT blocks down- regulation of IL-2 and IFN-gamma gene expression in HIV acutely infected cells.Archives of Virology 142, 1035-1043 .[Medline]
Fauci, A. S. (1996). Host factors and the pathogenesis of HIV-induced disease.Nature 384, 529-534.[Medline]
Felber, B. K. , Drysdale, C. M. & Pavlakis, G. N. (1990). Feedback regulation of human immunodeficiency virus type 1 expression by the Rev protein. Journal of Virology 64, 3734-3741 .[Medline]
Flores, E. R. & Lambert, P. F. (1997). Evidence for a switch in the mode of human papillomavirus type 16 DNA replication during the virus life cycle.Journal of Virology 10, 7167-7179 .
Frattini, M. G. , Lim, H. B. , Doorbar, J. & Laimins, L. A. (1997). Induction of human papillomavirus type 18 late gene expression and genomic amplification in organotypic cultures from transfected DNA templates. Journal of Virology 71, 7068-7072 .[Abstract]
Furuta, Y. , Eriksson, K. , Svennerholm, B. , Fredman, P. , Horal, P. , Jeansson, S. , Vahlne, A. , Holmgren, J. & Czerkinsky, C. (1994). Infection of vaginal and colonic epithelial cells by the human immunodeficiency virus type 1 is neutralized by antibodies raised against conserved epitopes in the envelope glycoprotein gp120.Proceedings of the National Academy of Sciences, USA 91, 12559-12563 .
Gius, D. & Laimins, L. A. (1989). Activation of human papillomavirus type 18 gene expression by herpes simplex virus type 1 viral transactivators and phorbol ester.Journal of Virology 63, 555-563.[Medline]
Goulsston, C. , McFarland, W. & Katzenstein, D. (1998). Human immunodeficiency virus type 1 RNA shedding in the female genital tract.Journal of Infectious Diseases 177, 1100-1103 .[Medline]
Harrington, W. , Sieczkowski, L. , Sosa, C. , Chan-a-Sue, S. , Cai, J. P. , Cabral, L. & Wood, C. (1997). Activation of HHV-8 by HIV-1 Tat. Lancet 349, 774-775.[Medline]
Heard, I. , Schmitz, V. , Costagliola, D. , Orth, G. & Kazatchine, M. D. (1998). Early regression of cervical lesions in HIV-seropositive women receiving highly active antiretroviral therapy.AIDS 12, 1459-1464 .[Medline]
Heng, M. C. Y. , Heng, S. Y. & Allen, S. G. (1994). Co-infection and synergy of human immunodeficiency virus-1 and herpes simplex virus-1. Lancet 343, 255-258.[Medline]
Hirka, G. , Prakash, K. , Kawashima, H. , Plotkin, S. A. , Andrews, P. W. & Gonczol, E. (1991). Differentiation of human embryonal carcinoma cells induces human immunodeficiency virus permissiveness which is stimulated by human cytomegalovirus coinfection. Journal of Virology 65, 2732-2735 .[Medline]
Hummel, M. , Lim, H. B. & Laimins, L. A. (1995). Human papillomavirus type 31b late gene expression is regulated through protein kinase C- mediated changes in RNA processing.Journal of Virology 69, 3381-3388 .[Abstract]
Inagaki, Y. , Tsunokawa, Y. , Takebe, N. , Nawa, H. , Nakanishi, S. , Terada, M. & Sugimura, T. (1988). Nucleotide sequences of cDNAs for human papillomavirus type 18 transcripts in HeLa cells. Journal of Virology 62, 1640-1646 .[Medline]
Ito, M. , Ishida, T. , He, L. , Tanabe, F. , Rongge, Y. , Miyakawa, Y. & Terunuma, H. (1998). HIV type 1 Tat protein inhibits interleukin 12 production by human peripheral blood mononuclear cells. AIDS Research and Human Retroviruses 14, 845-849.[Medline]
Iversen, A. K. N. , Larsen, A. R. , Jensen, T. , Fugger, L. , Balslev, U. , Wahl, S. , Gerstoft, J. , Mullins, J. L. & Skinhoj, J. (1998). Distinct determinants of human immunodeficiency virus type 1 RNA and DNA loads in vaginal and cervical secretions.Journal of Infectious Diseases 177, 1214-1220 .[Medline]
Jeon, S. , Allen-Hoffmann, B. L. & Lambert, P. F. (1995). Integration of human papillomavirus type 16 into the human genome correlates with a selective growth advantage of cells.Journal of Virology 69, 2989-2997 .[Abstract]
Kao, S. Y. , Calman, A. F. , Luciw, P. A. & Peterlin, B. M. (1987). Antitermination of transcription within the long terminal repeat of HIV-1 by tat gene product.Nature 330, 489-493.[Medline]
Kyo, S. , Inoue, M. , Hayasaka, N. , Inoue, T. , Yutsudo, M. , Tanizawa, O. & Hakura, A. (1994). Regulation of early gene expression of human papillomavirus type 16 by inflammatory cytokines. Virology 200, 130-139.[Medline]
Levy, J. A. (1994). HIV and the Pathogenesis of AIDS. Washington, DC: American Society for Microbiology.
Malim, M. H. & Cullen, B. R. (1993). Rev and the fate of pre-mRNA in the nucleus: implications for the regulation of RNA processing in eukaryotes.Molecular and Cellular Biology 13, 6180-6189 .[Abstract]
Melendy, T. , Sedman, J. & Stenlund, A. (1995). Cellular factors required for papillomavirus DNA replication.Journal of Virology 69, 7857-7867 .[Abstract]
Meyers, C. , Mayer, T. J. & Ozbun, M. A. (1997). Synthesis of infectious human papillomavirus type 18 in differentiating epithelium transfected with viral DNA.Journal of Virology 71, 7381-7386 .[Abstract]
Mostad, S. B. & Kreiss, J. K. (1996). Shedding of HIV-1 in the genital tract.AIDS 10, 1305-1315 .[Medline]
Palefsky, J. M. (1997). Cutaneous and genital HPV-associated lesions in HIV-infected patients. Clinical Dermatology 15, 439-447.[Medline]
Popescu, N. C. , DiPaolo, J. A. & Amsbaugh, S. C. (1987). Integration sites of human papillomavirus 18 DNA sequences on HeLa cell chromosomes. Cytogenetics and Cell Genetics 44, 58-62.[Medline]
Sambrook, J., Fritsch, E. F. & Maniatis, T. (1989). Molecular Cloning: A Laboratory Manual, 2nd edn. Cold Spring Harbor, NY: Cold Spring Harbor Laboratory.
Schwarz, E. , Freese, U. K. , Gissman, L. , Mayer, W. , Roggenbuck, B. , Stremlau, A. & zur Hausen, H. (1985). Structure and transcription of human papillomavirus sequences in cervical carcinoma cells. Nature 314, 111-114.[Medline]
Six, C. , Heard, I. , Bergeron, I. , Orth, G. , Poveda, J. D. , Zagury, P. , Cesbron, P. , Crenn-Hébert, C. , Pradinaud, R. , Sobesky, M. , Marty, C. , Babut, M. L. , Malkin, J. E. , Odier, A. , Fridmann, S. , Aubert, J. P. , Brunet, J. B. & de Vincenzi, I. (1998). Comparative prevalence, incidence and short-term prognosis of cervical squamous intraepithelial lesions amongst HIV-positive and HIV-negative women.AIDS 12, 1047-1056 .[Medline]
Stoler, M. H. , Rhodes, C. R. , Whitebeck, A. , Wolinsky, S. M. , Chow, L. T. & Broker, T. R. (1992). Human papillomavirus type 16 and 18 gene expression in cervical neoplasias.Human Pathology 23, 117-128.[Medline]
Sun, X. W. , Kuhn, L. , Ellerbrock, T. V. , Chiasson, M. A. , Bush, T. J. & Wright, T. C. (1997). Human papillomavirus infection in women infected with the human immunodeficiency virus. New England Journal of Medicine 337, 1343-1349 .
Tan, W. & Schwartz, S. (1995). The rev protein of human immunodeficiency virus type 1 counteracts the effect of an AU-rich negative element in the human papillomavirus type 1 late 3' untranslated region.Journal of Virology 69, 2932-2945 .[Abstract]
Tan, W. , Felber, B. K. , Zolotukhin, A. S. , Pavlakis, G. N. & Schwartz, S. (1995). Efficient expression of the human papillomavirus type 16 L1 protein in epithelial cells by using Rev and the Rev-responsive element of human immunodeficiency virus or the cis- acting transactivation element of simian retrovirus type 1. Journal of Virology 69, 5607-5620 .[Abstract]
Toniolo, A. , Serra, C. , Conaldi, P. G. , Basolo, F. , Falcone, V. & Dolei, A. (1995). Productive HIV-1 infection of normal human mammary epithelial cells.AIDS 9, 859-866.[Medline]
Tornesello, M. L. , Buonaguro, F. M. , Giraldo, E. B. & Giraldo, G. (1993). Human immunodeficiency virus type 1 tat gene enhances human papillomavirus early gene expression. Intervirology 36, 57-64.[Medline]
Vernon, S. D. , Hart, C. E. , Reeves, W. C. & Icenogle, J. P. (1993). The HIV-1 tat protein enhances E2-dependent human papillomavirus 16 transcription. Virus Research 27, 133-145.[Medline]
Vernon, S. D. , Zaki, S. R. & Reeves, W. C. (1994). Localisation of HIV-1 to human papillomavirus associated cervical lesions.Lancet 344, 954-955.[Medline]
Walz, C. , Deprez, A. , Dupressoir, T. , Durst, M. , Rabreau, M. & Schlehofer, J. R. (1997). Interaction of human papillomavirus type 16 and adeno-associated virus type 2 co- infecting human cervical epithelium.Journal of General Virology 78, 1441-1452 .[Abstract]
Woodworth, C. D. , McMullin, E. , Iglesias, M. & Plowman, G. D. (1995). Interleukin and tumor necrosis factor
stimulate autocrine amphiregulin expression and proliferation of human papillomavirus-immortalized and carcinoma-derived cervical epithelial cells.Proceedings of the National Academy of Sciences, USA 92, 2840-2844 .[Abstract]
Yang, L. , Morris, G. F. , Lockyer, J. M. , Lu, M. , Wang, Z. & Morris, C. B. (1997). Distinct transcriptional pathways of TAR-dependent and TAR-independent human immunodeficiency type 1 transactivation by tat.Virology 235, 48-64.[Medline]
Zhao, C. , Tan, W. , Sokolowski, M. & Schwartz, S. (1996). Identification of nuclear and cytoplasmic proteins that interact specifically with an AU-rich, cis -acting inhibitory sequence in the 3' untranslated region of human papillomavirus type 1 late mRNAs.Journal of Virology 70, 3659-3667 .[Abstract]
Received 23 June 1999;
accepted 9 July 1999.