Beatson Institute for Cancer Research, Garscube Estate, Glasgow G61 1QH, UK1
INSERM U385, Faculty of Medicine, University of Nice, Nice, France2
Author for correspondence: Gary Sibbet. Fax +44 141 942 6521. e-mail g.sibbet{at}beatson.gla.ac.uk
![]() |
Abstract |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
![]() |
Introduction |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
The difficulty in propagating papillomavirus in vitrohas made the identification of the receptor for papillomavirus problematic; most studies of infection have been conducted with artificial virions or virus-like particles (VLPs) rather than with infectious virions (Kirnbauer et al., 1993 ; Schiller & Lowy, 1996
; Volpers et al., 1995
; Zhou et al., 1992
, 1993
). Whilst VLPs share many structural aspects with real virions, as judged by immunology studies and the presence of conformational epitopes (Christensen et al., 1994
, 1996
; Kirnbauer, 1996
; Kirnbauer et al., 1996
; Lowy & Schiller, 1998
; Rose et al., 1994
), care should be taken with such studies, as VLPs may not accurately reproduce all aspects of papillomavirus infection. It has been shown that correctly assembled and normally folded VLPs can lack conformational epitopes (Chen et al., 1998
), and conversely morphologically normal virions presenting conformational epitopes can be non-infectious (P. OBrien, personal communication).
Although most papillomaviruses are extremely tissue and species specific, it has been proposed that the papillomavirus receptor is widely expressed, as both virions and VLPs bind to a variety of cell lines (Muller et al., 1995 ; Qi et al., 1996
). Bovine papillomavirus type 1 (BPV-1) is not strictly epitheliotropic: it infects both epidermal keratinocytes and dermal fibroblasts in vivo giving rise to fibropapillomas (Campo, 1987
) and it infects and transforms murine fibroblast C127 cells in vitro. The infection in vitro can be blocked by competition with VLPs of the strictly epitheliotropic human papillomavirus type 16 (HPV-16), indicating that the two viruses share the same receptor (Roden et al., 1994
). Recently, however, using VLPs for HPV-6b, a candidate receptor has been proposed, the integrin
6 partnered by either
1 or
4 integrin (Evander et al., 1997
).
In the skin and mucosae, integrin 6 exclusively binds to integrin
4 to form an heterodimeric cell receptor critical for hemidesmosome formation and cell adhesion. Genetic mutations affecting expression of integrin
6
4 result in junctional epidermolysis bullosa with pyloric atresia (PA-JEB), a severe genodermatosis characterized by extensive epithelial disadhesion (Vidal et al., 1995
; Ruzzi et al., 1997
).
By using bovine epithelial cells and PA-JEB keratinocytes, we have investigated whether 6 integrin is the cellular receptor for the strictly epitheliotropic papillomavirus BPV-4. Our results suggest strongly that
6 integrin is not the obligatory receptor for BPV-4.
![]() |
Methods |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Monoclonal antibodies.
The following rat monoclonal antibodies were used for both in situ immunofluorescence and FACS analysis as primary antibodies: GoH3, anti-CD49f, specific for 6 integrin, and 439-9B, anti-CD104, specific for
4 integrin (PharMingen) (Kennel et al., 1989
; Sonnenberg et al., 1987
). The secondary antibody was FITC-conjugated anti-rat IgG (whole molecule) (Sigma).
In situ immunofluorescence.
Cells were plated at 1·2x103 per well and grown in 0·4 ml lots on 8-well glass chamber slides (Labtek). Cells were washed with PBS and then fixed with formaldehyde (3·7%) and permeabilized (0·5% Triton X-100) and the nuclei were counter-stained with 1 µg/ml propidium iodide. Primary antibodies were typically used at 10100-fold dilution and secondary FITC-labelled antibodies were used 75-fold diluted. Cells were well washed (PBS plus 0·025% Tween 80) prior to mounting with Vectashield (Vector Labs).
FACS analysis.
Cells were detached, washed on ice and resuspended at 4x106 cells/ml. Aliquots (50 µl) of cells were placed in round-bottomed 96-well plates on ice and treated with the relevant monoclonal antibodies. After excess primary and secondary antibodies had been washed off, cells were fixed overnight with formaldehyde (3·7%) and analysed by FACS the following day. The number of fluorescent cells was plotted against the level of fluorescence on a log scale. The background levels of fluorescence (secondary antibody alone) were subtracted before determining the levels of integrins on the cell surface. The net levels of fluorescence for each cell line were plotted in a bar chart.
BPV-4 virus binding.
The concentration of virions was determined by electron microscopy (Gaukroger et al., 1996 ). Cells were plated at 5x105 per 3 cm dish in 2 ml medium. BPV-4 virus was added at an estimated 100 virus particles per cell and allowed to bind for up to 2 h at 4 or 37 °C. After extensive washing in DMEM and PBS, cells with bound virus were drained and harvested in 250 µl ProtK mix (0·1 mg/ml proteinase K, 50 mM KCl, 0·5% NP40, 0·5% Tween). Cell protein was digested for over 2 h at 56 °C and then for 15 min at 95 °C to inactivate the proteinase K. Viral DNA was detected by PCR. To quantify virus binding, aliquots of cell lysate or cell culture medium supernatant were subjected to PCR in a volume of 50 µl with a 5 min 95 °C hot start and 30 rounds of amplification, annealing at 60 °C (Perkin Elmer Taq polymerase and reagents). Amplified products were separated on 1·2% agarose gels and stained with ethidium bromide. Bands were quantified by image capture by using the Bio-Rad GelDoc 1000 system followed by scanning with the Bio-Rad Molecular Analyst (version 1.5) software. These conditions enabled quantification of PCR products within a linear range of almost two orders of magnitude, as determined by serial dilution of template prior to PCR.
BPV-4 virus infection.
Cells were plated at 5x106 and allowed to grow to 107 cells per T175 flask, and infected with purified BPV-4 virions at an estimated number of virus particles per cell of 50100. Infected cells were extensively washed and harvested and RNA was extracted (RNAzol) at early time-points and up to 7 days after infection (Chomczynski & Sacchi, 1987 ). Residual DNA was removed by RNase-free DNase I digestion followed by purification on SNAP columns (Invitrogen). Viral RNA was detected by reverse transcription (RT) followed by two rounds of PCR, as described below.
PCR and primer pairs.
Primers for actin were derived from the sequence of bovine actin-1 cDNA: 5' ATCCAGGCTGTGCTGTCTCT 3' (nt 178197) and 3' ATCTCCTGCTCGAAGTCCAA 5' (nt 433452). Primers for bovine myc were derived by sequence comparison of mouse, cat and human c-myc sequences and correspond to bases 10201037 and 12881307 of the human sequence: 5' AAGCAGATCAGCAACAAC 3' and 3' TTGTGTTTCAACTGTTCTCG 5'. The BPV-4 outer primer pair was 5' TGAGGCAGTAGCTCTCAT (nt 313330) and 3' TATAACCCGTCAAGAGCCCC 5' (nt 39573976). The BPV-4 inner primer pair was 5' GCTGACCTTCCAGTCTTAAT 3' (nt 642661) and 3' TGAAGAGGAGATTGAAACTG 5' (nt 793812). These primers amplify a 170 bp fragment from RNA transcribed from the E7 ORF.
RTPCR.
The method was derived from the Perkin Elmer RNA PCR core kit. Typically, 12 µg RNA was reverse-transcribed after annealing to oligo(dT) for 10 min at room temperature by reverse transcription at 42 °C for 60 min followed by 5 min in boiling water to denature the RT activity. The composition of the RT reaction mixture was then adjusted to suit Taq polymerase and two rounds of PCR were performed: 5 µl of the first PCR was used as the template for the second PCR. Both BPV-4 outer and inner primer pairs went through 30 rounds of amplification, with a 95 °C hot start and annealing at 60 °C. Contamination with DNA was avoided by RNase-free DNase I digestion and purification by SNAP columns (Invitrogen). Control reactions lacking RT were always included.
![]() |
Results |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
|
PalK cells were plated and infected with purified BPV-4 virions at a high ratio of virus particles per cell. Infected cells were harvested and RNA was extracted at early time-points and up to 7 days after infection. RNA samples were digested with DNase I and purified. An RTPCR protocol was developed to detect viral transcripts. Oligo(dT) was used to generate cDNA from the RNA and two rounds of PCR with nested primers specific for the viral E7 sequences were used to amplify BPV-4 transcripts. To exclude the possibility of contamination by viral DNA in the PCR step, controls included no RT and, to exclude non-specific uptake of virus, denatured virions were used in parallel. Fig. 2(a) shows that a specific viral transcript could be detected within 2 h of infection and remained for up to 7 days. The PCR product was sequenced and was confirmed to be E7. The same preparations of cDNA were amplified by one round of PCR with actin primers or c-myc primers (Fig. 2c
), showing that PCR amplification of cellular RNA was simply dependent upon RT and was unaffected by the presence or absence of infectious or denatured virus.
|
The candidate receptor is not required for virus binding or infection of keratinocytes
We have shown that the candidate receptor, 6 integrin, is highly expressed in PalK cells and absent from PalF cells, but that BPV-4 binds equally to both cell types. As we cannot monitor BPV-4 transcription in PalF cells, in order to examine the role of
6 integrin in infection, we required cells in which BPV-4 DNA could be efficiently transcribed but which lacked the candidate receptor. We derived a keratinocyte cell line from a patient with a genetic lesion in the
6 integrin gene (BO-SV) (Gache et al., 1998
; Ruzzi et al., 1997
). The level of
6
4 integrin expression was determined in this cell line by in situ immunofluorescence and FACS analysis and compared with the cell line KH-SV (normal human keratinocytes immortalized with SV40 large T antigen) and primary keratinocytes.
Fig. 3(a) shows the immunofluorescence of KH-SV cells and BO-SV cells decorated by monoclonal antibodies GoH3 and CD49e, specific for
6 and
4 integrins, respectively (Sonnenberg et al., 1987
). Both antibodies were derived from rat and were visualized with FITC-labelled anti-rat secondary antibody. The GoH3-staining pattern of KH-SV cells was very similar to that of PalK cells, although it was less extensive. The punctate distribution of
4 was also similar. In contrast, BO-SV cells showed negligible
6 integrin immunofluorescence, while the punctate
4 staining was very weak. Levels of fluorescence were normalized between cell lines by counter-staining the cell nuclei with propidium iodide (Fig. 3a
). The overall distribution of integrins over the cell surface was also quantified by FACS analysis by using the primary and secondary antibodies described above, and the results confirmed the in situ immunofluorescence results. The BO-SV cell line displayed extremely low levels of
6 integrin, while
4 integrin was much reduced compared with normal KH-SV cells (Fig. 4
).
|
|
Furthermore, having validated the in vitro infection of PalK cells (Fig. 2), we infected the BO-SV cells with BPV-4 exactly as before. After RTPCR of KH-SV and BO-SV RNA, the same RT-dependent E7 amplicon of 170 bp was detected (Fig. 3c
). Despite the presence of a very weak band in the -RT lanes, which may represent a residual trace of viral DNA resistant to DNase I digestion, the experiment shows clearly that both cell lines had internalized and transcribed the viral genome, independently of the amount of
6 or
4 integrin displayed on the cell surface.
![]() |
Discussion |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
By using HPV-6 L1 VLPs, it has recently been suggested that 6 integrin is a candidate cell receptor for papillomavirus (Evander et al., 1997
). However, we found that the presence of the candidate receptor is not required for BPV-4 binding, as both primary keratinocytes (which express
6 integrin) and primary fibroblasts (which do not) bind virion equally well. Likewise, human keratinocytes that do not express
6 integrin (BO-SV) bind virus to the same extent as wild-type keratinocytes (KH-SV).
Virion binding to the cell surface is one of the first steps of infection, followed by internalization, uncoating and transport of the viral genome into the nucleus (or, less often, retention in the cytoplasm for some viruses), where transcription of the viral genes takes place.
As binding of virions to the receptor is not necessarily followed by internalization, and a secondary receptor may be needed for this step (Broder & Dimitrov, 1996 ; Montgomery et al., 1996
; Whitbeck et al., 1997
; Wu et al., 1996
), it is possible that
6 integrin could act as a secondary receptor and mediate papillomavirus internalization rather than binding. We therefore used transcription of the viral E7 gene as a measure of efficient virus internalization. We developed an RTPCR assay for E7 transcripts in PalK cells; this assay proved to be very informative. The E7 amplicon was detected in PalK cells 2 h after infection and for up to 7 days, showing that infection had taken place and established itself. The amplicon was also detected when infection took place in the presence of pre-immune serum, but was not detected in the presence of competing VLPs or of virus-neutralizing anti-L1 antisera (Kirnbauer et al., 1996
). However, the E7 transcript was still detected in the presence of anti-L2 antisera. This is in total agreement with our results obtained in vivo showing that anti-L1 antibodies block infection whereas anti-L2 antibodies prevent disease but not infection (Gaukroger et al., 1996
). Although we did not detect spliced mRNA within the time-frame of these experiments (Smith et al., 1993
; White et al., 1998
), the competition with VLPs and the neutralization of virus by the immune sera show that our RTPCR assay is robust enough to reflect genuine infection in its early stages. As infection in vitro is abortive and does not proceed, it is likely that only pre-mRNA is made and that mature spliced forms are not produced.
We next applied the assay to keratinocytes defective in 6 integrin expression (Gache et al., 1998
; Ruzzi et al., 1997
) and, consistent with the virion-binding studies, we detected the E7 amplicon independently of the presence of
6 integrin on the cell surface. This shows that bovine and human keratinocytes are infected equally well by BPV-4, that they share the same receptor and that this receptor is not
6 integrin. We therefore conclude that
6 integrin is not an obligatory receptor for BPV-4.
This conclusion does not imply that 6 integrin is not a papillomavirus receptor, and does not preclude the possibility that
6 integrin could be closely associated with another cell surface molecule that acts as a receptor. The recent finding that the expression of
6 integrin confers papillomavirus binding to receptor-negative DG75 cells (McMillan et al., 1999
) may be explained by
6 integrin inducing or stabilizing a receptor such as
-dystroglycan, which is closely associated with integrins, binds laminin and can be localized along the basement membrane (Cao et al., 1998
; Henry & Campbell, 1998
).
Our investigation into the binding and infection of cells by a bovine papillomavirus does not preclude the possibility that BPV-4 and HPV-6 use different receptors. Whilst this would seem unlikely, given that BPV-1 and HPV-16 VLPs can compete for binding to the same cell (Roden et al., 1994 ), more than one receptor may well exist. Such diverse receptors could be used by the virus in different situations both in vivo and under experimental conditions. After all, BPV-1 infection forms fibropapillomas in cattle and thus infects both dermal keratinocytes, which express
6 integrin, the candidate receptor, and fibroblasts, which do not. The nature of the cell receptor used by BPV-4 to infect keratinocytes remains to be elucidated.
![]() |
Acknowledgments |
---|
![]() |
Footnotes |
---|
![]() |
References |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Aplin, J. D., Dawson, S. & Seif, M. W.(1996). Abnormal expression of integrin alpha 6 beta 4 in cervical intraepithelial neoplasia.British Journal of Cancer74, 240-245.[Medline]
Beutner, K. R. & Tyring, S.(1997). Human papillomavirus and human disease.American Journal of Medicine102, 9-15.[Medline]
Broder, C. C. & Dimitrov, D. S.(1996). HIV and the 7-transmembrane domain receptors.Pathobiology64, 171-179.[Medline]
Campo, M. S.(1987). Papillomas and cancer in cattle.Cancer Surveys6, 39-54.[Medline]
Campo, M. S.(1997). Bovine papillomavirus and cancer.Veterinary Journal154, 175-188.[Medline]
Cao, W., Henry, M. D., Borrow, P., Yamada, H., Elder, J. H., Ravkov, E. V., Nichol, S. T., Compans, R. W., Campbell, K. P. & Oldstone, M. B.(1998). Identification of alpha-dystroglycan as a receptor for lymphocytic choriomeningitis virus and Lassa fever virus.Science282, 2079-2081.
Chandrachud, L. M., Grindlay, G. J., McGarvie, G. M., ONeil, B. W., Wagner, E. R., Jarrett, W. F. & Campo, M. S.(1995). Vaccination of cattle with the N-terminus of L2 is necessary and sufficient for preventing infection by bovine papillomavirus-4.Virology211, 204-208.[Medline]
Chen, Y., Ghim, S.-j., Jenson, A. B. & Schlegel, R.(1998). Mutant canine oral papillomavirus L1 capsid proteins which form virus-like particles but lack native conformational epitopes.Journal of General Virology79, 2137-2146.[Abstract]
Chomczynski, P. & Sacchi, N.(1987). Single-step method of RNA isolation by acid guanidinium thiocyanatephenolchloroform extraction.Analytical Biochemistry162, 156-159.[Medline]
Christensen, N. D., Höpfl, R., DiAngelo, S. L., Cladel, N. M., Patrick, S. D., Welsh, P. A., Budgeon, L. R., Reed, C. A. & Kreider, J. W.(1994). Assembled baculovirus-expressed human papillomavirus type 11 L1 capsid protein virus-like particles are recognized by neutralizing monoclonal antibodies and induce high titres of neutralizing antibodies.Journal of General Virology75, 2271-2276.[Abstract]
Christensen, N. D., Reed, C. A., Cladel, N. M., Han, R. & Kreider, J. W.(1996). Immunization with viruslike particles induces long-term protection of rabbits against challenge with cottontail rabbit papillomavirus.Journal of Virology70, 960-965.[Abstract]
Coulson, B. S., Londrigan, S. L. & Lee, D. J.(1997). Rotavirus contains integrin ligand sequences and a disintegrin-like domain that are implicated in virus entry into cells.Proceedings of the National Academy of Sciences, USA94, 5389-5394.
de Villiers, E. M.(1998). Human papillomavirus infections in skin cancers.Biomedicine & Pharmacotherapy52, 26-33.[Medline]
Evander, M., Frazer, I. H., Payne, E., Qi, Y. M., Hengst, K. & McMillan, N. A.(1997). Identification of the alpha6 integrin as a candidate receptor for papillomaviruses.Journal of Virology71, 2449-2456.[Abstract]
Gache, Y., Romero-Graillet, C., Spadafora, A., Lepinard, C., Descamps, P., Bardon, C. B., Ortonne, J. P. & Meneguzzi, G.(1998). A novel homozygous mutation affecting integrin 6 in a case of junctional epidermolysis bullosa with pyloric atresia detected in utero by ultrasound examination.Journal of Investigative Dermatology 111, 914-916.
Gaukroger, J. M., Chandrachud, L. M., ONeil, B. W., Grindlay, G. J., Knowles, G. & Campo, M. S.(1996). Vaccination of cattle with bovine papillomavirus type 4 L2 elicits the production of virus-neutralizing antibodies.Journal of General Virology77, 1577-1583.[Abstract]
Henry, M. D. & Campbell, K. P.(1998). A role for dystroglycan in basement membrane assembly.Cell95, 859-870.[Medline]
Huttunen, P., Heino, J. & Hyypia, T.(1997). Echovirus 1 replication, not only virus binding to its receptor, VLA-2, is required for the induction of cellular immediate-early genes.Journal of Virology71, 4176-4180.[Abstract]
Kennel, S. J., Foote, L. J., Falcioni, R., Sonnenberg, A., Stringer, C. D., Crouse, C. & Hemler, M. E.(1989). Analysis of the tumor-associated antigen TSP-180. Identity with alpha 6-beta 4 in the integrin superfamily.Journal of Biological Chemistry264, 15515-15521.
Kirnbauer, R.(1996). Papillomavirus-like particles for serology and vaccine development.Intervirology39, 54-61.[Medline]
Kirnbauer, R., Taub, J., Greenstone, H., Roden, R., Durst, M., Gissmann, L., Lowy, D. R. & Schiller, J. T.(1993). Efficient self-assembly of human papillomavirus type 16 L1 and L1-L2 into virus-like particles.Journal of Virology67, 6929-6936.[Abstract]
Kirnbauer, R., Chandrachud, L. M., ONeil, B. W., Wagner, E. R., Grindlay, G. J., Armstrong, A., McGarvie, G. M., Schiller, J. T., Lowy, D. R. & Campo, M. S.(1996). Virus-like particles of bovine papillomavirus type 4 in prophylactic and therapeutic immunization.Virology219, 37-44.[Medline]
Lowy, D. R. & Schiller, J. T. (1998). Papillomaviruses and cervical cancer: pathogenesis and vaccine development. Journal of the National Cancer Institute Monographs, 2730.
McMillan, N. A., Payne, E., Frazer, I. H. & Evander, M.(1999). Expression of the alpha6 integrin confers papillomavirus binding upon receptor-negative B-cells.Virology261, 271-279.[Medline]
Miquel, C., Gagnoux-Palacios, L., Durand-Clement, M., Marinkovich, P., Ortonne, J. P. & Meneguzzi, G.(1996). Establishment and characterization of cell line LSV5 that retains the altered adhesive properties of human junctional epidermolysis bullosa keratinocytes.Experimental Cell Research224, 279-290.[Medline]
Montgomery, R. I., Warner, M. S., Lum, B. J. & Spear, P. G.(1996). Herpes simplex virus-1 entry into cells mediated by a novel member of the TNF/NGF receptor family.Cell87, 427-436.[Medline]
Morgan, I. M., Grindlay, G. J. & Campo, M. S.(1999). The bovine papillomavirus type 4 long control region contains an epithelial specific enhancer.Journal of General Virology80, 23-27.[Abstract]
Muller, M., Gissmann, L., Cristiano, R. J., Sun, X. Y., Frazer, I. H., Jenson, A. B., Alonso, A., Zentgraf, H. & Zhou, J.(1995). Papillomavirus capsid binding and uptake by cells from different tissues and species.Journal of Virology69, 948-954.[Abstract]
OBrien, P. M., Aitken, R., ONeil, B. W. & Campo, M. S.(1999). Generation of native bovine mAbs by phage display.Proceedings of the National Academy of Sciences, USA96, 640-645.
Ohrui, T., Yamaya, M., Sekizawa, K., Terajima, M., Yamada, N., Suzuki, T., Okinaga, S., Hoshi, H., Suzuki, H. & Sasaki, H. (1996). [Rhinovirus infection and expression of adhesion molecules in human tracheal epithelium]. Nihon Kyobu Shikkan Gakkai Zasshi(Japanese Journal of Thoracic Diseases) 34, 121125 (in Japanese).
Qi, Y. M., Peng, S. W., Hengst, K., Evander, M., Park, D. S., Zhou, J. & Frazer, I. H.(1996). Epithelial cells display separate receptors for papillomavirus VLPs and for soluble L1 capsid protein.Virology216, 35-45.[Medline]
Roden, R. B., Kirnbauer, R., Jenson, A. B., Lowy, D. R. & Schiller, J. T.(1994). Interaction of papillomaviruses with the cell surface.Journal of Virology68, 7260-7266.[Abstract]
Rose, R. C., Reichman, R. C. & Bonnez, W.(1994). Human papillomavirus (HPV) type 11 recombinant virus-like particles induce the formation of neutralizing antibodies and detect HPV-specific antibodies in human sera.Journal of General Virology75, 2075-2079.[Abstract]
Ruzzi, L., Gagnoux-Palacios, L., Pinola, M., Belli, S., Meneguzzi, G., DAlessio, M. & Zambruno, G.(1997). A homozygous mutation in the integrin alpha6 gene in junctional epidermolysis bullosa with pyloric atresia.Journal of Clinical Investigation99, 2826-2831.
Schiller, J. T. & Lowy, D. R.(1996). Papillomavirus-like particles and HPV vaccine development.Seminars in Cancer Biology7, 373-382.[Medline]
Shafren, D. R., Dorahy, D. J., Ingham, R. A., Burns, G. F. & Barry, R. D.(1997). Coxsackievirus A21 binds to decay-accelerating factor but requires intercellular adhesion molecule 1 for cell entry.Journal of Virology71, 4736-4743.[Abstract]
Sibbet, G. J., Cuthill, S. & Campo, M. S.(1995). The enhancer in the long control region of human papillomavirus type 16 is up-regulated by PEF-1 and down-regulated by Oct-1.Journal of Virology69, 4006-4011.[Abstract]
Smith, L. H., Foster, C., Hitchcock, M. E. & Isseroff, R.(1993). In vitro HPV-11 infection of human foreskin.Journal of Investigative Dermatology 101, 292-295.[Abstract]
Sonnenberg, A., Janssen, H., Hogervorst, F., Calafat, J. & Hilgers, J.(1987). A complex of platelet glycoproteins Ic and IIa identified by a rat monoclonal antibody.Journal of Biological Chemistry262, 10376-10383.
Suzuki, Y. (1997). [Host range of influenza viruses and their receptor binding specificities]. Nippon Rinsho (Japanese Journal of Clinical Medicine) 55, 26402647 (in Japanese).
Terpe, H. J., Stark, H., Ruiz, P. & Imhof, B. A.(1994). Alpha 6 integrin distribution in human embryonic and adult tissues.Histochemistry101, 41-49.[Medline]
Vidal, F., Aberdam, D., Miquel, C., Christiano, A. M., Pulkkinen, L., Uitto, J., Ortonne, J. P. & Meneguzzi, G.(1995). Integrin beta-4 mutation associated with junctional epidermolysis bullosa with pyloric atresia.Nature Genetics10, 229-234.[Medline]
Volpers, C., Unckell, F., Schirmacher, P., Streeck, R. E. & Sapp, M.(1995). Binding and internalization of human papillomavirus type 33 virus-like particles by eukaryotic cells.Journal of Virology69, 3258-3264.[Abstract]
Whitbeck, J. C., Peng, C., Lou, H., Xu, R., Willis, S. H., Ponce de Leon, M., Peng, T., Nicola, A. V., Montgomery, R. I., Warner, M. S., Soulika, A. M., Spruce, L. A., Moore, W. T., Lambris, J. D., Spear, P. G., Cohen, G. H. & Eisenberg, R. J.(1997). Glycoprotein D of herpes simplex virus (HSV) binds directly to HVEM, a member of the tumor necrosis factor receptor superfamily and a mediator of HSV entry.Journal of Virology71, 6083-6093.[Abstract]
White, W. I., Wilson, S. D., Bonnez, W., Rose, R. C., Koenig, S. & Suzich, J. A.(1998). In vitro infection and type-restricted antibody-mediated neutralization of authentic human papillomavirus type 16.Journal of Virology72, 959-964.
Wickham, T. J., Mathias, P., Cheresh, D. A. & Nemerow, G. R.(1993). Integrins alpha v beta 3 and alpha v beta 5 promote adenovirus internalization but not virus attachment.Cell73, 309-319.[Medline]
Wu, L., Gerard, N. P., Wyatt, R., Choe, H., Parolin, C., Ruffing, N., Borsetti, A., Cardoso, A. A., Desjardin, E., Newman, W., Gerard, C. & Sodroski, J.(1996). CD4-induced interaction of primary HIV-1 gp120 glycoproteins with the chemokine receptor CCR-5.Nature384, 179-183.[Medline]
Zhou, J., Sun, X. Y., Davies, H., Crawford, L., Park, D. & Frazer, I. H.(1992). Definition of linear antigenic regions of the HPV16 L1 capsid protein using synthetic virion-like particles.Virology189, 592-599.[Medline]
Zhou, J., Stenzel, D. J., Sun, X.-Y. & Frazer, I. H.(1993). Synthesis and assembly of infectious bovine papillomavirus particles in vitro.Journal of General Virology74, 763-768.[Abstract]
Zur Hausen, H. & Rosl, F.(1994). Pathogenesis of cancer of the cervix.Cold Spring Harbor Symposia on Quantitative Biology59, 623-628.[Medline]
Received 27 July 1999;
accepted 26 October 1999.