Biology subjects

Schelhaas, M.

Publications and source records attributed to Schelhaas, M..

5 recordsLinked to original sources

bioRxiv2025

Tracking Replicating HPV Genomes in Proliferating Keratinocytes

Human papillomavirus (HPV) genomes replicate and partition as minichromosomes alongside host chromatin during persistent infection. However, it is difficult to monitor genome dynamics in living cells because the small and compact genome will not easily tolerate expression cassettes. Here, we use ANCHOR technology to detect HPV18 genomes in living cells. We incorporated the cis element from ANCHORTM technology into the late region of the HPV18 genome and expressed the ParB-GFP protein from an HPV18-dependent replicon. The replicon contains the HPV18 replication origin and viral transcriptional enhancer element and can replicate stably in keratinocytes when complemented by the HPV18 genome. This small replicon expresses the neomycin resistance gene in both bacteria and eukaryotic cells and has minimal prokaryotic elements that could induce innate immunity. This molecular tool enables us to indirectly monitor the presence of the virus by detecting these fluorescent proteins in live cells and allows for real-time tracking of replicating HPV18-ANCH3 genomes in proliferating keratinocytes to inform on models of HPV genome maintenance, tethering, and amplification. Here, we visualize partitioning of the viral DNA in dividing cells and show that HPV18-ANCH genomes are distributed somewhat equally to daughter cells by random attachment to host chromosomes. ImportanceIn persistent HPV infection, the viral genome is maintained at a constant copy number, replicates in synchrony with host DNA during S-phase, and is partitioned into daughter cells. The exact method by which HPVs partition to daughter cells is not well understood and the elucidation of such mechanisms may reveal relevant pharmacological targets to combat persistent HPV infection.

microbiology↗

bioRxiv2024

Site-specific sulfations regulate the physicochemical properties of papillomavirus-heparan sulfate interactions for entry

Certain human papillomaviruses (HPVs) are etiological agents for several anogenital and oropharyngeal cancers. During initial infection, HPV16, the most prevalent cancer-causing type, specifically interacts with heparan sulfates (HS), not only enabling initial cell attachment but also triggering a crucial conformational change in viral capsids termed structural activation. It is unknown, whether such HS-HPV16 interactions depend on HS sulfation patterns. Thus, we probed potential roles of HS sulfations using cell-based functional and physicochemical assays, including single molecule force spectroscopy. Our results demonstrate that N-sulfation of HS is crucial for virus binding and structural activation by providing high affinity sites, and that additional 6O-sulfation is required to mechanically stabilize the interaction, whereas 2O-sulfation and 3O-sulfation are mostly dispensable. Together, our findings identify the contribution of HS sulfation patterns to HPV16 binding and structural activation and reveal how distinct sulfation groups of HS synergize to facilitate HPV16 entry, which, in turn, likely influences the tropism of HPVs. TeaserDistinct heparan sulfations facilitate HPV16 binding and structural activation through their physico-chemical properties.

microbiology↗

bioRxiv2024

Glycan-induced structural activation softens the human papillomavirus capsid for entry through reduction of intercapsomere flexibility

High-risk human papillomaviruses (HPVs) cause various cancers. While type-specific prophylactic vaccines are available, additional anti-viral strategies are highly desirable. Initial HPV cell entry involves receptor-switching induced by structural capsid modifications. These modifications are initiated by interactions with cellular heparan sulphates (HS), however, their molecular nature and functional consequences remain elusive. Combining virological assays with hydrogen/deuterium exchange mass spectrometry, and atomic force microscopy, we investigated the effect of capsid-HS binding and structural activation. We show how HS-induced structural activation requires a minimal HS-chain length and simultaneous engagement of several binding sites by a single HS molecule. This engagement introduces a pincer-like force that stabilizes the capsid in a conformation with extended capsomer linkers. It results in capsid enlargement and softening, thereby facilitating L1 proteolytic cleavage and subsequent L2-externalization, as needed for cell entry. Our data will help further devising prophylactic strategies against HPV infections.

microbiology↗

bioRxiv2021

Endocytic vacuole formation by WASH-mediated endocytosis

Endocytosis is a fundamental cellular process facilitated by diverse mechanisms. Remarkably, several distinct clathrin-independent endocytic processes were identified and characterized following virus uptake into cells. For some, however, mechanistic execution and biological function remain largely unclear. This includes an endocytic process exploited by human papillomavirus type 16 (HPV16). Using HPV16, we examined how vesicles are formed by combining systematic cellular perturbations with electron and video microscopy. Cargo uptake occurred by uncoated, inward-budding pits. Mechanistically, vesicle scission was facilitated by actin polymerization controlled through the actin nucleation promoting factor WASH. While WASH typically functions in conjunction with the retromer complex on endosomes during retrograde trafficking, endocytic vesicle formation was largely independent of retromer itself and the heterodimeric membrane-bending SNX-BAR retromer adaptor, thereby uncovering a role of WASH in endocytosis in addition to its canonical role in intracellular membrane trafficking.

cell biology↗

bioRxiv2018

Infectious Entry of Merkel Cell Polyomavirus

Merkel Cell Polyomavirus (MCPyV) is a small, non-enveloped tumor virus associated with an aggressive form of skin cancer, the Merkel cell carcinoma (MCC). MCPyV infections are highly prevalent in the human population with MCPyV virions being continuously shed from human skin. However, the precise host cell tropism(s) of MCPyV remains unclear: MCPyV is able to replicate within a subset of dermal fibroblasts, but MCPyV DNA has also been detected in a variety of other tissues. However, MCPyV appears different from other polyomaviruses as it requires sulfated polysaccharides such as heparan sulfates and/or chondroitin sulfates for initial attachment. Like other polyomaviruses, MCPyV engages sialic acid as a (co-receptor). To explore the infectious entry process of MCPyV, we analyzed the cell biological determinants of MCPyV entry into A549 cells, a highly transducible lung carcinoma cell line, in comparison to well-studied simian virus 40 and a number of other viruses. Our results indicate that MCPyV enters cells via caveolar/lipid raft-mediated endocytosis but not macropinocytosis, clathrin-mediated endocytosis or glycosphingolipid-enriched carriers. The viruses internalized in small endocytic pits that led the virus to endosomes and from there to the endoplasmic reticulum (ER). Similar to other polyomaviruses, trafficking required microtubular transport, acidification of endosomes, and a functional redox environment. To our surprise, the virus was found to acquire a membrane envelope within endosomes, a phenomenon not reported for other viruses. Only minor amounts of viruses reached the ER, while the majority was retained in endosomal compartments suggesting that endosome-to-ER trafficking is a bottleneck during infectious entry.\n\nImportanceMCPyV is the first polyomavirus directly implicated in the development of an aggressive human cancer, the Merkel Cell Carcinoma (MCC). Although MCPyV is constantly shed from healthy skin, MCC incidence increases among aging and immunocompromised individuals. To date, the events connecting initial MCPyV infection and subsequent transformation still remain elusive. MCPyV differs from other known polyomaviruses concerning its cell tropism, entry receptor requirements, and infection kinetics. In this study, we examined the cellular requirements for endocytic entry as well as the subcellular localization of incoming virus particles. A thorough understanding of the determinants of the infectious entry pathway and the specific biological niche will benefit prevention of virus-derived cancers such as MCC.

microbiology↗