Biology subjects

Tsai, B.

Publications and source records attributed to Tsai, B..

8 recordsLinked to original sources

bioRxiv2026

SV40 exploits the Nesprin-2-SUN1-KPNA4 axis for stepwise targeting and entry into the host nucleus to promote infection

Many DNA viruses including polyomaviruses (PyVs) enter the host nucleus to cause infection, although how this is accomplished is unclear. To infect cells, the prototype PyV SV40 targets to the Nesprin-2 outer nuclear membrane protein and enters the nucleus via the nuclear pore complex (NPC). Host factors that function with Nesprin-2 to target SV40 to the nuclear membrane and drive NPC-dependent nuclear entry are unknown. Here we demonstrate that the SUN1 inner nuclear membrane protein acts coordinately with its binding-partner Nesprin-2 to target cytosol-localized SV40 to the nuclear membrane. Strikingly, despite localizing to the perinuclear space, the SUN domain of SUN1 plays a crucial role in Nesprin-2-dependent recruitment of cytosolic SV40. After targeting, SV40 binds to the NPC-associated importin receptor KPNA4, which translocates the virus into the nucleus. Our results reveal how a DNA virus exploits the Nesprin-2-SUN1-KPNA4 axis for stepwise targeting and entry into the nucleus to cause infection. Author summaryNuclear entry is required for most DNA viruses to cause infection, although the molecular mechanism of this step remains enigmatic. The DNA virus SV40 targets to the nuclear membrane by exploiting the Nesprin-2 outer nuclear membrane protein. In this study, we report that the SUN1 inner nuclear membrane protein functions with Nesprin-2 to target SV40 to the nuclear membrane, followed by nuclear entry of the virus via the action of the KNPA4 importin receptor.

microbiology↗

bioRxiv2025

In situ cryo-ET redefines HPV disassembly and transport paradigms

Human papillomavirus (HPV) causes 4.5% of all human cancers, although a complete cellular basis of infection remains unclear. The mechanisms of virus disassembly and transport are particularly enigmatic. Here, we use in situ cryo-electron tomography (cryo-ET) to provide direct visualization of high-risk HPV16 during its infection cycle. We demonstrate that, when HPV reaches the lysosome, it remains intact and infection competent, contrary to the prevailing view of viral inactivation within lysosomes. We challenge the current model of HPV trafficking, which predicts progressive disassembly of the L1 capsid during retrograde transport, by showing that HPV remains intact when it reaches the Golgi en route to the nucleus for infection. Finally, we provide snapshots of the HPV containing transport vesicles budding from the Golgi lumen in a COPI coat-dependent fashion and show that HPV is connected to the overlying membrane by proteinaceous structural bridges, possibly formed by the L2 capsid, to guide virus trafficking. Our results redefine the dominant models of HPV entry, revealing the virus capsids resilience to disassembly during retrograde trafficking, a coat-dependent budding mechanism for transport, and demonstrate that the lysosome serves as a reservoir for infectious HPV.

cell biology↗

bioRxiv2025

Golgi-associated nuclear import receptor importin-7 targets HPV from the Golgi to the nucleus to promote infection

During human papillomavirus (HPV) entry, the virus exploits COPI-dependent retrograde transport to cross the trans-Golgi network and Golgi stacks before reaching the nucleus to cause infection. How HPV enters the nucleus after exiting the Golgi is unclear, although mitotic nuclear envelop breakdown (NEB) appears important. Here we show that importin-7 (IPO7), a nuclear pore import receptor, associates with the Golgi and promotes HPV infection. Upon IPO7 knockdown, HPV infection is inhibited and the virus accumulates in the Golgi but does not enter the nucleus, demonstrating that IPO7 promotes Golgi-to-nucleus transport of HPV. We further reveal that the C-terminus of HPV capsid protein L2, which is thought to contain overlapping nuclear localization and cell-penetrating peptide sequences, binds directly to IPO7 in a step that requires COPI-dependent virus trafficking. Together these data identify a role of an importin in HPV infection, raising the possibility that the canonical nuclear pore import machinery plays an unanticipated role in NEB-dependent nuclear entry. TeaserHPV, a cancer-causing human pathogen, exploits the Golgi-associated nuclear import receptor IPO7 for Golgi-to-nucleus trafficking to promote infection.

cell biology↗

bioRxiv2024

Rab6a enables BICD2/dynein-mediated trafficking of human papillomavirus from the trans-Golgi network during virus entry

Rab GTPases control intracellular vesicular transport, including retrograde trafficking of human papillomavirus (HPV) during cell entry, guiding the virus from the endosome to the trans-Golgi network (TGN), the Golgi apparatus, and eventually the nucleus. Rab proteins that act prior to the arrival of HPV to the TGN have been identified, but Rab proteins operating in later stages of entry remain elusive. Here, we report that knockdown of Rab6a impairs HPV entry by impeding intra-Golgi transport of the incoming virus, resulting in HPV accumulation in the TGN. Rab6a supports HPV trafficking by facilitating the association of HPV with dynein, a motor protein complex, and BICD2, a dynein adaptor. L2 can bind directly to GTP-Rab6a in vitro, and excess of either GTP-Rab6a or GDP-Rab6 inhibits HPV entry, suggesting that cycling between GDP- Rab6 and GTP-Rab6 is critical. Notably, Rab6a is crucial for HPV-BICD2 and HPV-dynein association in the TGN of infected cells, but the HPV-dynein association in the endosome does not require Rab6a. Our findings reveal an important feature of the molecular basis of intra-Golgi trafficking of HPV and identify potential targets for therapeutic approaches to inhibit HPV infection.

microbiology↗

bioRxiv2022

Structural and mechanistic insights into the DNA glycosylase AAG-mediated base excision in nucleosome

DNA glycosylase engaging with damaged base marks the initiation of base excision repair. Nucleosome-based packaging of eukaryotic genome obstructs DNA accessibility, and how DNA glycosylases locate the substrate site on nucleosomes is currently unclear. Here, we report cryo-electron microscopy structures of nucleosomes bearing a deoxyinosine (DI) in various geometric positions and structures of them in complex with DNA glycosylase AAG. The apo nucleosome structures show that the presence of a deoxyinosine alone perturbs nucleosomal DNA globally, leading to a general weakening of the interface between DNA and the histone core and a greater flexibility to the exit/entry of the nucleosomal DNA. AAG makes use of this nucleosomal plasticity and imposes further local deformation of the DNA through the formation of the stable enzyme-substrate complex. Mechanistically, local distortion augment, translation/rotational register shift and partial opening of the nucleosome are employed by AAG to cope with substrate sites in fully exposed, occluded and complete buried positions, respectively. Our findings reveal the molecular basis for the DI-induced modification on the structural dynamics of the nucleosome and elucidate how DNA glycosylase AAG accesses damaged sites on the nucleosome with different solution accessibility.

molecular biology↗

bioRxiv2021

Distinct states of proinsulin misfolding in MIDY

A precondition for efficient proinsulin export from the endoplasmic reticulum (ER) is that proinsulin meets ER quality control folding requirements, including formation of the Cys(B19)-Cys(A20) "interchain" disulfide bond, facilitating formation of the Cys(B7)-Cys(A7) bridge. The third proinsulin disulfide, Cys(A6)-Cys(A11), is not required for anterograde trafficking, i.e., a "lose-A6/A11" mutant [Cys(A6), Cys(A11) both converted to Ser] is well secreted. Nevertheless, an unpaired Cys(A11) can participate in disulfide mispairings, causing ER retention of proinsulin. Among the many missense mutations causing the syndrome of Mutant INS gene-induced Diabetes of Youth (MIDY), all seem to exhibit perturbed proinsulin disulfide bond formation. Here we have examined a series of seven MIDY mutants [including G(B8)V, Y(B26)C, L(A16)P, H(B5)D, V(B18)A, R(Cpep+2)C, E(A4)K], six of which are essentially completely blocked in export from the ER in pancreatic {beta}-cells. Three of these mutants, however, must disrupt the Cys(A6)-Cys(A11) pairing to expose a critical unpaired cysteine thiol perturbation of proinsulin folding and ER export, because when introduced into the proinsulin lose-A6/A11 background, these mutants exhibit native-like disulfide bonding and improved trafficking. This maneuver also ameliorates dominant-negative blockade of export of co-expressed wild-type proinsulin. A growing molecular understanding of proinsulin misfolding may permit allele-specific pharmacological targeting for some MIDY mutants.

biochemistry↗

bioRxiv2020

Phase separation of Mer2 organizes the meiotic loop-axis structure of chromatin during meiosis I

Sexually reproducing organisms acquire genetic diversity through meiotic recombination during meiosis I, which is initiated via programmed DNA double-strand breaks (DSBs) induced by Spo11-containing machinery in each meiotic cell. The combination of programmed DSB sites in each meiotic cell must be diverse, which requires a certain degree of randomness in the distribution of DSBs. The formation of programmed DSBs requires a preestablished loop-axis structure of chromatin. Here, we demonstrate that the axial element protein Mer2 undergoes liquid-liquid phase separation in vitro and in vivo through its intrinsically disordered C-terminal domain. A DNA binding motif within its central domain is responsible for bringing DNA into Mer2 liquid droplets and Mer2-DNA complex could assemble into filamentous structures extending from the droplets. These results suggest that phase separation of Mer2 drives the formation of a droplet-loop structure of meiotic chromatin to facilitate and to diversify programmed DSB formation.

biophysics↗

bioRxiv2018

Prenatal Bisphenol A Exposure in Mice Induces Multi-tissue Multi-omics Disruptions Linking to Cardiometabolic Disorders

The health impacts of endocrine disrupting chemicals (EDCs) remain debated and their tissue and molecular targets are poorly understood. Here we leveraged systems biology approaches to assess the target tissues, molecular pathways, and gene regulatory networks associated with prenatal exposure to the model EDC Bisphenol A (BPA). Prenatal BPA exposure led to scores of transcriptomic and methylomic alterations in the adipose, hypothalamus, and liver tissues in mouse offspring, with cross-tissue perturbations in lipid metabolism as well as tissue-specific alterations in histone subunits, glucose metabolism and extracellular matrix. Network modeling prioritized main molecular targets of BPA, including Pparg, Hnf4a, Esr1, and Fasn. Lastly, integrative analyses identified the association of BPA molecular signatures with cardiometabolic phenotypes in mouse and human. Our multi-tissue, multi-omics investigation provides strong evidence that BPA perturbs diverse molecular networks in central and peripheral tissues, and offers insights into the molecular targets that link BPA to human cardiometabolic disorders.\n\nAuthor summaryThe inability to pinpoint the mechanistic underpinnings of environmentally-induced diseases likely stems from the pleiotropic effects of chemicals such as BPA on diverse tissues and molecular space (transcriptome, epigenome, etc.). This makes it challenging to fully dissect their health impact and merits a call for modern big data approaches to examine environmental factors. Our data-driven study is the first unbiased, multi-tissue multiomic systems biology investigation of the molecular circuitry and mechanisms underlying offspring response to prenatal BPA exposure. Importantly, the incorporation of network-based modeling allows us to capture novel players in the regulation of BPA activities in vivo, and the integration with human disease association datasets helps bridge the molecular pathways affected by BPA with diverse human diseases. In doing so, our study provides compelling molecular evidence that developmental BPA exposure significantly perturbs metabolic and endocrine systems in the offspring, and supports BPA as one of the environmental factors involved in the developmental origins of health and disease (DOHaD).

systems biology↗