Tadahito Kanda

Human Papillomavirus Type 16 Minor Capsid Protein L2 N-Terminal Region Containing a Common Neutralization Epitope Binds to the Cell Surface and Enters the Cytoplasm

ABSTRACT The first step of papillomavirus infection is believed to be binding of major capsid protein L1 to the cell surface without involvement of minor capsid protein L2, but the viral infectivity can be neutralized either by anti-L1 or anti-L2 antibody. To understand the role of L2 in human papillomavirus (HPV) infection, we examined a segment of HPV type 16 (HPV16) L2, which contains a neutralization epitope common to HPV6, for its involvement in adsorption and penetration of the capsids. Preincubation of monkey COS-1 cells with a synthetic peptide having amino acids (aa) 108 to 120 of HPV16 L2 reduced the susceptibility of COS-1 cells to infection with HPV16 pseudovirions. Confocal microscopy showed that the green fluorescence protein (GFP) fused with the L2 peptide was found to bind to the surface of a HeLa cell, an HPV18-positive human cancer cell line, at 4°C and to enter the cytoplasm after subsequent incubation at 37°C. Flow cytometry showed that fused GFP did not bind to HeLa cells that had been treated with trypsin. Besides COS-1 and HeLa cells, some human and rodent cell lines were detected by flow cytometry to be susceptible to binding with fused GFP, showing a tendency of epithelial cells toward higher susceptibility. Substitutions at aa 108 to 111 inhibited fused GFP from binding to HeLa cells and reduced the infectivity in COS-1 cells of the in vitro-constructed pseudovirions. The results suggest that L2 plays an important role in enhancing HPV infection through interaction between the N-terminal region and a cellular surface protein, facilitating penetration of the virions and determining part of the tropism of HPVs.

Identification of Monomorphic and Divergent Haplotypes in the 2006-2007 Norovirus GII/4 Epidemic Population by Genomewide Tracing of Evolutionary History

ABSTRACT Our norovirus (NoV) surveillance group reported a >4-fold increase in NoV infection in Japan during the winter of 2006-2007 compared to the previous winter. Because the increase was not linked to changes in the surveillance system, we suspected the emergence of new NoV GII/4 epidemic variants. To obtain information on viral changes, we conducted full-length genomic analysis. Stool specimens from 55 acute gastroenteritis patients of various ages were collected at 11 sites in Japan between May 2006 and January 2007. Direct sequencing of long PCR products revealed 37 GII/4 genome sequences. Phylogenetic study of viral genome and partial sequences showed that the two new GII/4 variants in Europe, termed 2006a and 2006b, initially coexisted as minorities in early 2006 in Japan and that 2006b alone had dominated over the resident GII/4 variants during 2006. A combination of phylogenetic and entropy analyses revealed for the first time the unique amino acid substitutions in all eight proteins of the new epidemic strains. These data and computer-assisted structural study of the NoV capsid protein are compatible with a model of antigenic drift with tuning of the structure and functions of multiple proteins for the global outgrowth of new GII/4 variants. The availability of comprehensive information on genome sequences and unique protein changes of the recent global epidemic variants will allow studies of diagnostic assays, molecular epidemiology, molecular biology, and adaptive changes of NoV in nature.

Immortalization of primary rat cells by human papillomavirus type 16 subgenomic DNA fragments controlled by the SV40 promoter

We tested the human papillomavirus 16 (HPV 16) early genes for their ability to immortalize or transform primary rat brain cells, using the expression plasmids that contain the neomycin-resistance-inducing unit (pSV2neo) and the transcriptional unit for the HPV 16 subgenomic DNA fragments controlled by the SV40 early promoter. After transfection, drug-resistant colonies were maintained by refeeding and replating for characterization. The E7 gene alone was found to be capable of immortalizing and morphologically transforming primary rat cells, and the transformed cells showed anchorage-independent growth. Although its activity was lower than that of the E7 gene, the E6 gene also immortalized primary rat cells. The immortalized or transformed cells contained HPV 16-specific DNA and mRNA.

Nasal immunization of mice with peptide having a cross-neutralization epitope on minor capsid protein L2 of human papillomavirus type 16 elicit systemic and mucosal antibodies.

A common cross-neutralization epitope for human papillomavirus types 6 and 16 (HPV 6 and 16) is present in the region of amino acids (aa) 108-120 of HPV-16 minor capsid protein, L2. We nasally immunized Balb/c mice with a synthetic peptide with the 13 aa HPV 16 L2 sequence, and examined the antibodies elicited. ELISA showed that the immunization induced predominantly IgG and IgA antibodies cross-binding to L1/L2-capsids of HPVs 6, 16, and 18 in sera and in vaginal secretions, respectively. The serum containing the IgG antibody and the vaginal wash containing the IgA antibody neutralized HPV 16 pseudovirions and HPV 11 authentic virions, as shown by surrogate infectivity assays. From their cross-binding activity for HPV 16 and 18, the peptide-induced antibodies can probably cross-neutralize most of the genital HPVs. The peptide-induced neutralizing activity in vaginal wash was comparable to that induced by nasally immunization with HPV 16 L1-capsids. Unlike Balb/c, C57BL/10, which has different MHC class II, did not respond to the peptide immunization, but aa substitutions in the peptide to fulfill the requirement for the C57BL/10 agretope rendered the modified peptides immunogenic. The results provide a basis for development of a peptide vaccine against broad-spectrum of genital HPVs for humans.

Safety and immunogenicity of a peptide containing the cross-neutralization epitope of HPV16 L2 administered nasally in healthy volunteers

Amino acid (aa) 108-120 of L2 protein of human papillomavirus (HPV) type 16 contains a cross-neutralization epitope against genital HPV. We designed a placebo-controlled trial in healthy adults to evaluate the safety and immunogenicity of a synthetic peptide consisting of the aa 108-120 of HPV16 L2 (L2-108/120) region. A total of 13 volunteers were given nasal inoculations with 0.1 (n=5) or 0.5mg (n=5) doses of the peptides or placebo (n=3) without adjuvant at weeks 0, 4, and 12. Sera were collected before inoculation and at 6, 16 and 36 weeks. The inoculation caused no serious local and systemic complications. The inoculation generated anti-L2 antibodies binding to both HPV16 and 52 L1/L2-capsids in four of the five recipients in the 0.5mg group. Sera of the four recipients showed neutralizing activities against HPV16 and 52. Serological responses to the peptides were not found in the 0.1mg group and the placebo group recipients. This study suggests the L2-108/120 peptide is tolerable in humans and has the potential as a broad-spectrum prophylactic vaccine against genital HPV.

Divergent Evolution of Norovirus GII/4 by Genome Recombination from May 2006 to February 2009 in Japan

ABSTRACT Norovirus GII/4 is a leading cause of acute viral gastroenteritis in humans. We examined here how the GII/4 virus evolves to generate and sustain new epidemics in humans, using 199 near-full-length GII/4 genome sequences and 11 genome segment clones from human stool specimens collected at 19 sites in Japan between May 2006 and February 2009. Phylogenetic studies demonstrated outbreaks of 7 monophyletic GII/4 subtypes, among which a single subtype, termed 2006b, had continually predominated. Phylogenetic-tree, bootscanning-plot, and informative-site analyses revealed that 4 of the 7 GII/4 subtypes were mosaics of recently prevalent GII/4 subtypes and 1 was made up of the GII/4 and GII/12 genotypes. Notably, single putative recombination breakpoints with the highest statistical significance were constantly located around the border of open reading frame 1 (ORF1) and ORF2 (P ≤ 0.000001), suggesting outgrowth of specific recombinant viruses in the outbreaks. The GII/4 subtypes had many unique amino acids at the time of their outbreaks, especially in the N-term, 3A-like, and capsid proteins. Unique amino acids in the capsids were preferentially positioned on the outer surface loops of the protruding P2 domain and more abundant in the dominant subtypes. These findings suggest that intersubtype genome recombination at the ORF1/2 boundary region is a common mechanism that realizes independent and concurrent changes on the virion surface and in viral replication proteins for the persistence of norovirus GII/4 in human populations.

Human scribble, a novel tumor suppressor identified as a target of high‐risk HPV E6 for ubiquitin‐mediated degradation, interacts with adenomatous polyposis coli

Recently, we have identified human scribble (hScrib), human homolog of the Drosophila tumor suppressor Scribble, as a substrate of human papillomavirus E6 oncoproteins for ubiquitin‐mediated degradation dependent on ubiquitin‐protein ligase E6AP. Human Scribble, classified as a LAP protein containing leucine‐rich repeats and PDZ domains, interacts with E6 through its PDZ domains and C‐terminal PDZ domain‐binding motif of E6 protein. Interaction between human Discs Large (hDlg), which is a substrate of E6 for the ubiquitin‐mediated degradation, and adenomatous polyposis coli (APC) has been shown. Here, we investigated whether hScrib and APC interact with each other in vitro and in vivo. Interaction between hScrib and APC is mediated by the PDZ domains 1 and 4 of hScrib and C‐terminal PDZ domain‐binding motif of APC. Human Scribble co‐localized with APC at the synaptic sites of hippocampal neuron and at the tip of membrane protrusion in the epithelial cell line. Interference of the interaction between hScrib and APC caused disruption of adherens junction. Knockdown of hScrib expression by RNAi disrupts localization of APC at the adherens junction. These data suggest that hScrib may participate in the hDlg‐APC complex through its PDZ domains and regulate cell cycle and neural function by associating with APC.

Modification of human papillomavirus-like particle vaccine by insertion of the cross-reactive L2-epitopes.

Infection with human papillomavirus 16 (HPV16), which is one of the 15 types of HPV causally associated with cervical cancer and accounts for 50% of the cases, can be prevented in a type‐specific manner by an HPV16 virus‐like particle (VLP) vaccine comprised of particles of the L1 protein alone. We attempted to modify the VLP vaccine by inserting the HPV16 L2‐peptides including cross‐neutralization epitopes into the L1 polypeptide. The chimeric L1 had, between L1 amino acids (aa) 430 and 433, the L2 sequence of aa 18–38, 56–75, or 96–115 (with the replacements of S at aa 101 and T at aa 112 with L and S, respectively). The three chimeric L1s were each expressed from the recombinant baculovirus in insect Sf9 cells, and the resultant VLPs were characterized. The chimeric VLPs were shown to present the L2‐peptides on their surface. By immunizing rabbits with the VLPs, it was shown that they retained capability to induce the antibody neutralizing HPV16 and acquired capability to elicit antibodies cross‐neutralizing the infectious HPV18, 31, 52, and 58 pseudovirions. Although the cross‐neutralizing titers were lower than the type‐specific neutralizing titer, the results suggest that the chimeric VLPs have potential to serve as a vaccine candidate for a broad spectrum of high‐risk HPVs. J. Med. Virol. 80:841–846, 2008.

Enhanced oncogenicity of human papillomavirus type 16 (HPV16) variants in Japanese population

To investigate whether HPV16 E6 variants carry an elevated risk for cervical cancer in Japanese population, we investigated the E6 sequence variation in 40 cervical intraepithelial neoplasias (CINs) I-III and 43 invasive cervical cancers (ICCs), all positive for HPV16. HPV16 E6 variants were frequently found in ICCs than in CINs (88 vs. 65%, P=0.01). The E6 D25E, a rare variant in Western countries, was most frequently observed in ICC (44%). CIN I/II lesions with HPV16 variants were less likely to regress than those with HPV16 prototype (P=0.048). The finding that HPV16 E6 variants represent a significant risk factor is common between Western and Japanese women despite the different distribution of each variant.

Human papillomavirus type 16 E6 proteins with glycine substitution for cysteine in the metal-binding motif

The human papillomavirus type 16 (HPV 16) E6 is a 151 amino acid protein containing four metal-binding motifs, Cys-X-X-Cys. We constructed and characterized three mutants with Gly substitutions for Cys within the motif; for Cys-66, for Cys-136, and for both, respectively. Zinc binding to bacterially expressed E6 was markedly reduced by the substitution for Cys-66, but DNA binding was unaffected by any of these mutations. Immunofluorescence staining showed that, whereas the E6 expressed in monkey COS-1 cells appeared mostly nuclear, the Cys-66 mutant appeared cytoplasmic. Subcellular fractionation followed by immunoprecipitation showed that the E6 in COS-1 cells was located in the membrane, nuclear, and nuclear-wash fractions, but not in the soluble cytoplasmic fraction, and that the nuclear Cys-66 protein was markedly reduced. The mutant proteins in COS-1 cells appeared to be less stable than the wild type, because the immunofluorescent cells were fewer and because the E6 bands in autoradiograms were less dense. The substitution mutants lost their capacity to enhance HPV 16 E7 transformation of rat 3Y1 cells. The data indicate that Cys-66 plays a crucial role for zinc binding and nuclear localization of E6 and that both Cys-66 and Cys-136 are required for a stable or functional structure of E6.