Analysis of type-restricted and cross-reactive epitopes on virus-like particles of human papillomavirus type 33 and in infected tissues using monoclonal antibodies to the major capsid protein

The human papillomavirus (HPV) capsid protein L2 is essential for viral entry. To gain a deeper understanding of the role of L2, we searched for novel cellular L2-interacting proteins. A yeast two-hybrid analysis uncovered the actin-depolymerizing factor gelsolin, the membrane glycoprotein dysadherin, the centrosomal protein 68 (Cep68), and the cytoskeletal adaptor protein obscurin-like 1 protein (OBSL1) as putative L2 binding molecules. Pseudovirus (PsV) infection assays identified OBSL1 as a host factor required for gene transduction by three oncogenic human papillomavirus types, HPV16, HPV18, and HPV31. In addition, we detected OBSL1 expression in cervical tissue sections and noted the involvement of OBSL1 during gene transduction of primary keratinocytes by HPV16 PsV. Complex formation of HPV16 L2 with OBSL1 was demonstrated in coimmunofluorescence and coimmunoprecipitation studies after overexpression of L2 or after PsV exposure. We observed a strong colocalization of OBSL1 with HPV16 PsV and tetraspanin CD151 at the plasma membrane, suggesting a role for OBSL1 in viral endocytosis. Indeed, viral entry assays exhibited a reduction of viral endocytosis in OBSL1-depleted cells. Our results suggest OBSL1 as a novel L2-interacting protein and endocytosis factor in HPV infection. IMPORTANCEHuman papillomaviruses infect mucosal and cutaneous epithelia, and the high-risk HPV types account for 5% of cancer cases worldwide. As recently discovered, HPV entry occurs by a clathrin-, caveolin-, and dynamin-independent endocytosis via tetraspanin-enriched microdomains. At present, the cellular proteins involved in the underlying mechanism of this type of endocytosis are under investigation. In this study, the cytoskeletal adaptor OBSL1 was discovered as a previously unrecognized interaction partner of the minor capsid protein L2 and was identified as a proviral host factor required for HPV16 endocytosis into target cells. The findings of this study advance the understanding of a so far less well-characterized endocytic pathway that is used by oncogenic HPV subtypes. Human papillomaviruses (HPVs) are small, nonenveloped DNA viruses that infect dividing basal keratinocytes of skin and mucosa via microlesions of the tissue. HPV is capable of inducing benign epithelial warts on the skin and mucosa, and infection with a high-risk HPV type may cause cervical and other anogenital and oropharyngeal cancers (1, 2). Cervical cancer is the third most common cancer in women worldwide and is associated with HPV infection, more precisely with high-risk HPV types such as HPV16, HPV18, and HPV31 (3). HPV is composed of a viral capsid with the major capsid protein L1, the minor capsid protein L2, and the viral genome. One icosahedral capsid contains 360 copies of L1, which can self-assemble to 72 pentamers, and up to 72 copies of the minor capsid protein L2, located inside the L1 shell (4-6). The capsid proteins L1 and L2 are key players in early events of infection, such as virus binding at the plasma membrane, cell entry, and t...

Section: Methodsmentioning

confidence: 99%

The Cytoskeletal Adaptor Obscurin-Like 1 Interacts with the Human Papillomavirus 16 (HPV16) Capsid Protein L2 and Is Required for HPV16 Endocytosis

Wüstenhagen

Hampe

Boukhallouk

et al. 2016

“…The Bromo-2=-deoxy-uridine (BrdU) Labeling and Detection Kit I was from Roche. The L1-7 and RG-1 monoclonal antibodies were kind gifts from M. Sapp (Louisiana State University, Shreveport, LA, USA) (36) and from R. Roden (Johns Hopkins University, Baltimore, MD, USA) (37), respectively. The CAMVIR-1 and LAMP1 (H4A3) antibodies were from Santa Cruz Biotechnology, the monoclonal kallikrein-8 (KLK8) rabbit antibody (EPR5752) (2) was from Abcam, the TGN46 antibody (AHP1586) was from Abd Serotec, and the tubulin antibody (DM1A) was from Sigma.…”

Section: Methodsmentioning

confidence: 99%

Kallikrein-8 Proteolytically Processes Human Papillomaviruses in the Extracellular Space To Facilitate Entry into Host Cells

Cerqueira

Ventayol

Vogeley

et al. 2015

104

The entry of human papillomaviruses into host cells is a complex process. It involves conformational changes at the cell surface, receptor switching, internalization by a novel endocytic mechanism, uncoating in endosomes, trafficking of a subviral complex to the Golgi complex, and nuclear entry during mitosis. Here, we addressed how the stabilizing contacts in the capsid of human papillomavirus 16 (HPV16) may be reversed to allow uncoating of the viral genome. Using biochemical and cell-biological analyses, we determined that the major capsid protein L1 underwent proteolytic cleavage during entry. In addition to a dispensable cathepsin-mediated proteolysis that occurred likely after removal of capsomers from the subviral complex in endosomes, at least two further proteolytic cleavages of L1 were observed, one of which was independent of the low-pH environment of endosomes. This cleavage occurred extracellularly. Further analysis showed that the responsible protease was the secreted trypsin-like serine protease kallikrein-8 (KLK8) involved in epidermal homeostasis and wound healing. Required for infection, the cleavage was facilitated by prior interaction of viral particles with heparan sulfate proteoglycans. KLK8-mediated cleavage was crucial for further conformational changes exposing an important epitope of the minor capsid protein L2. Occurring independently of cyclophilins and of furin that mediate L2 exposure, KLK8-mediated cleavage of L1 likely facilitated access to L2, located in the capsid lumen, and potentially uncoating. Since HPV6 and HPV18 also required KLK8 for entry, we propose that the KLK8-dependent entry step is conserved. IMPORTANCEOur analysis of the proteolytic processing of incoming HPV16, an etiological agent of cervical cancer, demonstrated that the capsid is cleaved extracellularly by a serine protease active during wound healing and that this cleavage was crucial for infection. The cleavage of L1 is one of at least four structural alterations that prime the virus extracellularly for receptor switching, internalization, and possibly uncoating. This step was also important for HPV6 and HPV18, which may suggest that it is conserved among the papillomaviruses. This study advances the understanding of how HPV16 initially infects cells, strengthens the notion that wounding facilitates infection of epidermal tissue, and may help the development of antiviral measures. Human papillomaviruses (HPVs) comprise a large family of small, nonenveloped DNA viruses with transforming potential. HPVs selectively infect basal keratinocytes of stratified skin and mucosal epithelia and persist, mostly without clinical symptoms, in virtually every part of the human skin. The biological costs of HPV persistence range from benign papilloma and genital warts over preneoplastic lesions to anogenital or oropharyngeal cancers (1). In fact, infection by the so-called "high-risk" HPV causes about 5% of all human cancers (2). Of these, cervical cancers are the most prevalent. However, HPV-associated oropharyngea...

“…All cells were grown in Dulbecco modified Eagle medium (DMEM) supplemented with 10% fetal calf serum and antibiotics at 37°C. L1-and L2-specific mouse monoclonal antibodies (MAbs) and rabbit polyclonal antibodies were as described elsewhere (29,37,38). Daxxspecific antibody was purchased from Santa Cruz.…”

Section: Methodsmentioning

confidence: 99%

Nuclear Localization but Not PML Protein Is Required for Incorporation of the Papillomavirus Minor Capsid Protein L2 into Virus-Like Particles

Becker

Florin

Sapp

et al. 2004

Recent reports suggest that nuclear domain(s) 10 (ND10) is the site of papillomavirus morphogenesis. The viral genome replicates in or close to ND10. In addition, the minor capsid protein, L2, accumulates in these subnuclear structures and recruits the major capsid protein, L1. We have now used cell lines deficient for promyelocytic leukemia (PML) protein, the main structural component of ND10, to study the role of this nuclear protein for L2 incorporation into virus-like particles (VLPs). L2 expressed in PML protein knockout (PML ؊/؊ ) cells accumulated in nuclear dots, which resemble L2 aggregates forming at ND10 in PML protein-containing cells. These L2 assemblies also attracted L1 and the transcriptional repressor Daxx, suggesting that they are functional in the absence of PML protein. In addition, L2-containing VLPs assembled in PML ؊/؊ cells. In order to analyze whether incorporation of L2 into VLPs requires any specific subcellular localization, an L1 mutant defective for nuclear transport and L2 mutants deficient in nuclear translocation and/or ND10 localization were constructed. Using this approach, we identified two independent L2 domains interacting with L1. Mutant L2 proteins not accumulating in ND10 were incorporated into VLPs. Mutant L1 protein, which assembled into VLPs in the cytoplasm, did not incorporate L2 defective for nuclear translocation. The same mutant L2 protein, which passively diffuses into the nucleus, is incorporated into wild-type L1-VLPs in the nucleus. Our data demonstrate that the incorporation of L2 into VLPs requires nuclear but not ND10 localization.Human papillomaviruses (HPVs) comprise a large group of nonenveloped epitheliotropic viruses causing tumors of the skin and mucosa. They are composed of 360 copies of the major capsid protein, L1, organized in 72 capsomeres, probably 12 copies of the minor capsid protein, L2, and a closed circular, double-stranded DNA genome of approximately 8,000 bp (3, 35). The viral life cycle depends on terminally differentiating keratinocytes and includes infection of cells of the basal layer (stratum germinativum), vegetative DNA replication in nondividing cells of the stratum spinosum, and capsid protein synthesis and virion morphogenesis in fully differentiated cells of the stratum granulosum (reviewed in reference 21). Due to difficulties in generating HPVs in vitro and in mimicking the papillomavirus life cycle in cell culture, surrogate assays have been developed for the study of certain aspects of their life cycle, including the HPV infection process, viral DNA replication, and virion morphogenesis.Heterologous expression of capsid protein L1 in eukaryotic cells results in spontaneous assembly into virus-like particles (VLPs) that incorporate L2 protein when coexpressed (13,18,28,39). VLPs have been used to study cell binding and internalization of the papillomavirus capsid (24,40). If present during capsid protein synthesis, extrachromosomal plasmids are also encapsidated to yield pseudovirions, a useful tool for the study of the HPV ...