BackgroundMerkel cell polyomavirus (MCPyV) has been detected in approximately 75% of patients with the rare skin cancer Merkel cell carcinoma. We investigated the prevalence of antibodies against MCPyV in the general population and the association between these antibodies and Merkel cell carcinoma.MethodsMultiplex antibody-binding assays were used to assess levels of antibodies against polyomaviruses in plasma. MCPyV VP1 antibody levels were determined in plasma from 41 patients with Merkel cell carcinoma and 76 matched control subjects. MCPyV DNA was detected in tumor tissue specimens by quantitative polymerase chain reaction. Seroprevalence of polyomavirus-specific antibodies was determined in 451 control subjects. MCPyV strain–specific antibody recognition was investigated by replacing coding sequences from MCPyV strain 350 with those from MCPyV strain w162.ResultsWe found that 36 (88%) of 41 patients with Merkel cell carcinoma carried antibodies against VP1 from MCPyV w162 compared with 40 (53%) of the 76 control subjects (odds ratio adjusted for age and sex = 6.6, 95% confidence interval [CI] = 2.3 to 18.8). MCPyV DNA was detectable in 24 (77%) of the 31 Merkel cell carcinoma tumors available, with 22 (92%) of these 24 patients also carrying antibodies against MCPyV. Among 451 control subjects from the general population, prevalence of antibodies against human polyomaviruses was 92% (95% CI = 89% to 94%) for BK virus, 45% (95% CI = 40% to 50%) for JC virus, 98% (95% CI = 96% to 99%) for WU polyomavirus, 90% (95% CI = 87% to 93%) for KI polyomavirus, and 59% (95% CI = 55% to 64%) for MCPyV. Few case patients had reactivity against MCPyV strain 350; however, indistinguishable reactivities were found with VP1 from strain 350 carrying a double mutation (residues 288 and 316) and VP1 from strain w162.ConclusionInfection with MCPyV is common in the general population. MCPyV, but not other human polyomaviruses, appears to be associated with Merkel cell carcinoma.

The E6 oncoprotein from high-risk genus alpha human papillomaviruses (α-HPVs), such as HPV 16, has been well characterized with respect to the host-cell proteins it interacts with and corresponding signaling pathways that are disrupted due to these interactions. Less is known regarding the interacting partners of E6 from the genus beta papillomaviruses (β-HPVs); however, it is generally thought that β-HPV E6 proteins do not interact with many of the proteins known to bind to α-HPV E6. Here we identify p300 as a protein that interacts directly with E6 from both α- and β-HPV types. Importantly, this association appears much stronger with β-HPV types 5 and 8-E6 than with α-HPV type 16-E6 or β-HPV type 38-E6. We demonstrate that the enhanced association between 5/8-E6 and p300 leads to p300 degradation in a proteasomal-dependent but E6AP-independent manner. Rather, 5/8-E6 inhibit the association of AKT with p300, an event necessary to ensure p300 stability within the cell. Finally, we demonstrate that the decreased p300 protein levels concomitantly affect downstream signaling events, such as the expression of differentiation markers K1, K10 and Involucrin. Together, these results demonstrate a unique way in which β-HPV E6 proteins are able to affect host-cell signaling in a manner distinct from that of the α-HPVs.

These data indicate that some individuals have BKV and/or JCV antibodies that cross-react with SV40, but they do not provide support for SV40 being a prevalent human pathogen.

To characterize epitopes on human papillomavirus (HPV) virus-like particles (VLPs), a panel of mutated HPV-16 VLPs was created. Each mutated VLP had residues substituted from HPV-31 or HPV-52 L1 sequences to the HPV-16 L1 backbone. Mutations were created on the HPV-31 and ؊52 L1 proteins to determine if HPV-16 type-specific recognition could be transferred. Correct folding of the mutated proteins was verified by resistance to trypsin digestion and by binding to one or more conformation-dependent monoclonal antibodies. Several of the antibodies tested were found to bind to regions already identified as being important for HPV VLP recognition (loops DE, EF, FG, and HI). Sequences at both ends of the long FG loop (amino acids 260 to 290) were required for both H16.V5 and H16.E70 reactivity. A new antibody-binding site was discovered on the C-terminal arm of L1 between positions 427 and 445. Recognition of these residues by the H16.U4 antibody suggests that this region is surface exposed and supports a recently proposed molecular model of HPV VLPs.The human papillomavirus (HPV) virion is composed of major (L1) and minor (L2) capsid proteins. The L1 protein self-assembles into virus-like particles (VLPs) that appear identical to infectious virus both by electron microscopy and immunologically (8, 9, 11). The L2 protein is important for assembly of infectious virus (20) but does not contain the conformation-dependent and type-specific epitopes most frequently recognized by anti-HPV sera (2, 9).The VLP is a T ϭ 7 icosahedron composed of 72 pentamers of L1, termed capsomers. Sixty of the capsomers subunits are at hexavalent positions, interacting with six neighboring capsomers with the remaining 12 capsomers at pentavalent positions (1). The only HPV L1 crystal structure solved to date is of T1 particles (3), in which all capsomers are at pentavalent positions. In the T1 particle, capsomers interact through a portion of the C-terminal tail. This flexible arm extends away from the capsomer of origin, interacts with similar regions from neighboring capsomers and returns to the capsomer from which it came. The remainder of this C-terminal region extends around the circumference of the capsomer, participating in the core ␤-sheet structure, forming a short helix (h5) and finally reinserting into the core of the pentamer from which it came. Missing from this model is an intercapsomer disulfide bond, shown by others to help stabilize the VLP structure (12, 21).A revised model for HPV VLPs was proposed by Modis et al. (18). In this model, the C-terminal extension adopts a conformation similar to its conformation in the T1 structure, but instead of returning to the capsomer of origin, the arm is displaced onto, and ultimately invades, a neighboring capsomer. The C-terminal arm is anchored by the previously described disulfide bond between the cysteine from this region (amino acids 428) and cysteine 175 of a neighboring capsomer. The new model was termed the "invading arm" model because of its similarity to the simian virus 40 a...

The variable surface loops on human papillomavirus (HPV) virions required for type-specific neutralization by human sera remain poorly defined. To determine which loops are required for neutralization, a series of hybrid virus-like particles (VLPs) were used to adsorb neutralizing activity from HPV type 16 (HPV16)-reactive human sera before being tested in an HPV16 pseudovirion neutralization assay. The hybrid VLPs used were composed of L1 sequences of either HPV16 or HPV31, on which one or two regions were replaced with homologous sequences from the other type. The regions chosen for substitution were the five known loops that form surface epitopes recognized by monoclonal antibodies and two additional variable regions between residues 400 and 450. Pretreatment of human sera, previously found to react to HPV16 VLPs in enzyme-linked immunosorbent assays, with wild-type HPV16 VLPs and hybrid VLPs that retained the neutralizing epitopes reduced or eliminated the ability of sera to inhibit pseudovirus infection in vitro. Surprisingly, substitution of a single loop often ablated the ability of VLPs to adsorb neutralizing antibodies from human sera. However, for all sera tested, multiple surface loops were found to be important for neutralizing activity. Three regions, defined by loops DE, FG, and HI, were most frequently identified as being essential for binding by neutralizing antibodies. These observations are consistent with the existence of multiple neutralizing epitopes on the HPV virion surface.Human papillomaviruses (HPVs) are a family of doublestranded DNA viruses that infect epithelial cells in a tissuespecific fashion. Infection with certain "high-risk" types that infect the genital mucosa, such as types 16 (HPV16), 18, and 31, has been shown to be a necessary step in the progression to cervical cancer (1). In nations without effective cervical cancer screening programs, HPVs are the cause of considerable morbidity and mortality (25). In the United States, more than $6 billion is spent annually on evaluation and management of low-grade lesions caused by HPV infection (9). For these reasons, the newly developed vaccines that can prevent HPV infection and that hold promise for eradication of cervical cancer have been greeted with enthusiasm. Currently, vaccines for types 16 and 18 and for the "low-risk" types 6 and 11 (which cause genital warts) are in phase 3 clinical trials (11, 24).The vaccines that are now being evaluated are composed of the HPV major late protein (L1) for each type. This protein self-assembles into empty capsids, also referred to as virus-like particles (VLPs) (10, 13). Early indications are that VLP vaccines are safe and provide protection from persistent HPV infection in a type-specific fashion (11,24). Animal studies suggest that protection from papillomavirus infection is mediated by antibodies (2, 23).Type-specific antibodies recognize conformation-dependent epitopes involving the surface-exposed loops of L1 proteins that exhibit considerable amino acid sequence variation between t...

The IgG fraction of sera of healthy human subjects contains natural antibodies to cytoskeletal elements of the donors own red blood cell membranes. Autoantibodies to spectrin are characterized in more detail: their Fab portion binds to the antigen. Autoantibodies, affinity-purified on immobilized spectrin band 1, precipitate 0.4 microgram of spectrin dimer per 1 microgram of autoantibody. They bind to band 1 and cross-react with band 2 of spectrin as well as with breakdown products of spectrin on blots from separated membrane polypeptides. Autoantibodies purified on spectrin band 2 after absorption on band 1 do not cross-react with band 1. The evidence strongly suggests the existence of such autoantibodies in healthy human subjects. This finding indicates that autoantibody production to normally unexposed antigens is not suppressed in ontogeny. These anti-cytoskeleton autoantibodies may have a physiologic role in clearance of debris from lysed cells. Their existence may open a new understanding of elevated anti-spectrin autoantibody concentrations in diseases with different etiologies.