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Journal of Virology May 2022This study developed a system consisting of two rounds of screening cellular proteins involved in the nuclear egress of herpes simplex virus 1 (HSV-1). Using this...
This study developed a system consisting of two rounds of screening cellular proteins involved in the nuclear egress of herpes simplex virus 1 (HSV-1). Using this system, we first screened cellular proteins that interacted with the HSV-1 nuclear egress complex (NEC) consisting of UL34 and UL31 in HSV-1-infected cells, which are critical for the nuclear egress of HSV-1, by tandem affinity purification coupled with mass spectrometry-based proteomics technology. Next, we performed CRISPR/Cas9-based screening of live HSV-1-infected reporter cells under fluorescence microscopy using single guide RNAs targeting the cellular proteins identified in the first proteomic screening to detect the mislocalization of the lamin-associated protein emerin, which is a phenotype for defects in HSV-1 nuclear egress. This study focused on a cellular orphan transporter SLC35E1, one of the cellular proteins identified by the screening system. Knockout of SLC35E1 reduced HSV-1 replication and induced membranous invaginations containing perinuclear enveloped virions (PEVs) adjacent to the nuclear membrane (NM), aberrant accumulation of PEVs in the perinuclear space between the inner and outer NMs and the invagination structures, and mislocalization of the NEC. These effects were similar to those of previously reported mutation(s) in HSV-1 proteins and depletion of cellular proteins that are important for HSV-1 de-envelopment, one of the steps required for HSV-1 nuclear egress. Our newly established screening system enabled us to identify a novel cellular protein required for efficient HSV-1 de-envelopment. The identification of cellular protein(s) that interact with viral effector proteins and function in important viral procedures is necessary for enhancing our understanding of the mechanics of various viral processes. In this study, we established a new system consisting of interactome screening for the herpes simplex virus 1 (HSV-1) nuclear egress complex (NEC), followed by loss-of-function screening to target the identified putative NEC-interacting cellular proteins to detect a defect in HSV-1 nuclear egress. This newly established system identified SLC35E1, an orphan transporter, as a novel cellular protein required for efficient HSV-1 de-envelopment, providing an insight into the mechanisms involved in this viral procedure.
Topics: Animals; CRISPR-Cas Systems; Chlorocebus aethiops; Gene Knockout Techniques; HEK293 Cells; HeLa Cells; Herpesvirus 1, Human; Humans; Membrane Transport Proteins; Nuclear Envelope; Nuclear Proteins; Proteomics; Vero Cells; Viral Proteins; Virus Release
PubMed: 35475666
DOI: 10.1128/jvi.00306-22 -
ELife Dec 2020The inner nuclear membrane is functionalized by diverse transmembrane proteins that associate with nuclear lamins and/or chromatin. When cells enter mitosis,...
The inner nuclear membrane is functionalized by diverse transmembrane proteins that associate with nuclear lamins and/or chromatin. When cells enter mitosis, membrane-chromatin contacts must be broken to allow for proper chromosome segregation; yet how this occurs remains ill-understood. Unexpectedly, we observed that an imbalance in the levels of the lamina-associated polypeptide 1 (LAP1), an activator of ER-resident Torsin AAA+-ATPases, causes a failure in membrane removal from mitotic chromatin, accompanied by chromosome segregation errors and changes in post-mitotic nuclear morphology. These defects are dependent on a hitherto unknown chromatin-binding region of LAP1 that we have delineated. LAP1-induced NE abnormalities are efficiently suppressed by expression of wild-type but not ATPase-deficient Torsins. Furthermore, a dominant-negative Torsin induces chromosome segregation defects in a LAP1-dependent manner. These results indicate that association of LAP1 with chromatin in the nucleus can be modulated by Torsins in the perinuclear space, shedding new light on the LAP1-Torsin interplay.
Topics: Adenosine Triphosphatases; Carrier Proteins; Cell Line, Tumor; Chromatin; Chromosome Segregation; Gene Knockout Techniques; HCT116 Cells; HSC70 Heat-Shock Proteins; HeLa Cells; Hep G2 Cells; Humans; Mitosis; Molecular Chaperones; Nuclear Envelope
PubMed: 33320087
DOI: 10.7554/eLife.63614 -
Cells Mar 2020Newly assembled herpesvirus nucleocapsids traverse the intact nuclear envelope by a vesicle-mediated nucleo-cytoplasmic transport for final virion maturation in the...
Newly assembled herpesvirus nucleocapsids traverse the intact nuclear envelope by a vesicle-mediated nucleo-cytoplasmic transport for final virion maturation in the cytoplasm. For this, they bud at the inner nuclear membrane resulting in primary enveloped particles in the perinuclear space (PNS) followed by fusion of the primary envelope with the outer nuclear membrane (ONM). While the conserved viral nuclear egress complex orchestrates the first steps, effectors of fusion of the primary virion envelope with the ONM are still mostly enigmatic but might include cellular proteins like SUN2 or ESCRT-III components. Here, we analyzed the influence of the only known AAA+ ATPases located in the endoplasmic reticulum and the PNS, the Torsins (Tor), on nuclear egress of the alphaherpesvirus pseudorabies virus. For this overexpression of wild type and mutant proteins as well as CRISPR/Cas9 genome editing was applied. Neither single overexpression nor gene knockout (KO) of TorA or TorB had a significant impact. However, TorA/B double KO cells showed decreased viral titers at early time points of infection and an accumulation of primary virions in the PNS pointing to a delay in capsid release during nuclear egress.
Topics: ATPases Associated with Diverse Cellular Activities; Active Transport, Cell Nucleus; Animals; Cell Nucleus; Cytoplasm; Herpesvirus 1, Suid; Molecular Chaperones; Nuclear Envelope; Rabbits; Viral Proteins; Virus Release
PubMed: 32192107
DOI: 10.3390/cells9030738 -
Journal of Virology Mar 2020Protein kinases homologous to the US3 gene product (pUS3) of herpes simplex virus (HSV) are conserved throughout the alphaherpesviruses but are absent from...
Protein kinases homologous to the US3 gene product (pUS3) of herpes simplex virus (HSV) are conserved throughout the alphaherpesviruses but are absent from betaherpesviruses and gammaherpesviruses. pUS3 homologs are multifunctional and are involved in many processes, including modification of the cytoskeleton, inhibition of apoptosis, and immune evasion. pUS3 also plays a role in efficient nuclear egress of alphaherpesvirus nucleocapsids. In the absence of pUS3, primary enveloped virions accumulate in the perinuclear space (PNS) in large invaginations of the inner nuclear membrane (INM), pointing to a modulatory function for pUS3 during deenvelopment. The HSV and pseudorabies virus (PrV) US3 genes are transcribed into two mRNAs encoding two pUS3 isoforms, which have different aminoterminal sequences and abundances. To test whether the two isoforms in PrV serve different functions, we constructed mutant viruses expressing exclusively either the larger minor or the smaller major isoform, a mutant virus with decreased expression of the smaller isoform, or a mutant with impaired kinase function. Respective virus mutants were investigated in several cell lines. Our results show that absence of the larger pUS3 isoform has no detectable effect on viral replication in cell culture, while full expression of the smaller isoform and intact kinase activity is required for efficient nuclear egress. Absence of pUS3 resulted in only minor titer reduction in most cell lines tested but disclosed a more severe defect in Madin-Darby bovine kidney cells. However, accumulations of primary virions in the PNS do not account for the observed titer reduction in PrV. A plethora of substrates and functions have been assigned to the alphaherpesviral pUS3 kinase, including a role in nuclear egress. In PrV, two different pUS3 isoforms are expressed, which differ in size, abundance, and intracellular localization. Their respective role in replication is unknown, however. Here, we show that efficient nuclear egress of PrV requires the smaller isoform and intact kinase activity, whereas absence of the larger isoform has no significant effect on viral replication. Thus, there is a clear distinction in function between the two US3 gene products of PrV.
Topics: Active Transport, Cell Nucleus; Animals; Apoptosis; Cattle; Cell Nucleus; Chlorocebus aethiops; Cytoskeleton; Genome, Viral; Herpesvirus 1, Suid; Kidney; Mutation; Nuclear Envelope; Phenotype; Protein Isoforms; Protein Serine-Threonine Kinases; Rabbits; Vero Cells; Viral Proteins; Virus Assembly
PubMed: 31941788
DOI: 10.1128/JVI.02029-19 -
The Journal of Clinical Investigation Aug 2019Deciphering novel pathways regulating liver lipid content has profound implications for understanding the pathophysiology of nonalcoholic fatty liver disease and...
Deciphering novel pathways regulating liver lipid content has profound implications for understanding the pathophysiology of nonalcoholic fatty liver disease and nonalcoholic steatohepatitis. Recent evidence suggests that the nuclear envelope is a site of regulation of lipid metabolism but there is limited appreciation of the responsible mechanisms and molecular components within this organelle. We showed that conditional hepatocyte deletion of the inner nuclear membrane protein lamina-associated polypeptide 1 (LAP1) caused defective VLDL secretion and steatosis, including intranuclear lipid accumulation. LAP1 binds to and activates torsinA, an AAA+ ATPase that resides in the perinuclear space and continuous main ER. Deletion of torsinA from mouse hepatocytes caused even greater reductions in VLDL secretion and profound steatosis. Both of these mutant mouse lines developed hepatic steatosis and subsequent steatohepatitis on a regular chow diet in the absence of whole-body insulin resistance or obesity. Our results establish an essential role for the nuclear envelope-localized torsinA-LAP1 complex in hepatic VLDL secretion and suggest that the torsinA pathway participates in the pathophysiology of nonalcoholic fatty liver disease.
Topics: Animals; Carrier Proteins; Hepatocytes; Lipid Metabolism; Lipoproteins, VLDL; Membrane Proteins; Mice; Mice, Knockout; Molecular Chaperones; Non-alcoholic Fatty Liver Disease; Nuclear Envelope
PubMed: 31408437
DOI: 10.1172/JCI129769 -
Nucleic Acids Research Dec 2021G-quadruplexes (G4s) are secondary structures forming in G-rich nucleic acids. G4s are assumed to play critical roles in biology, nonetheless their detection in cells is...
G-quadruplexes (G4s) are secondary structures forming in G-rich nucleic acids. G4s are assumed to play critical roles in biology, nonetheless their detection in cells is still challenging. For tracking G4s, synthetic molecules (G4 ligands) can be used as reporters and have found wide application for this purpose through chemical functionalization with a fluorescent tag. However, this approach is limited by a low-labeling degree impeding precise visualization in specific subcellular regions. Herein, we present a new visualization strategy based on the immuno-recognition of 5-bromo-2'-deoxyuridine (5-BrdU) modified G4 ligands, functionalized prior- or post-G4-target binding by CuAAC. Remarkably, recognition of the tag by antibodies leads to the detection of the modified ligands exclusively when bound to a G4 target both in vitro, as shown by ELISA, and in cells, thereby providing a highly efficient G4-ligand Guided Immunofluorescence Staining (G4-GIS) approach. The obtained signal amplification revealed well-defined fluorescent foci located in the perinuclear space and RNase treatment revealed the preferential binding to G4-RNA. Furthermore, ligand treatment affected significantly BG4 foci formation in cells. Our work headed to the development of a new imaging approach combining the advantages of immunostaining and G4-recognition by G4 ligands leading to visualization of G4/ligands species in cells with unrivaled precision and sensitivity.
Topics: A549 Cells; Bromodeoxyuridine; Cell Line; Click Chemistry; Enzyme-Linked Immunosorbent Assay; Fluorescence Resonance Energy Transfer; Fluorescent Antibody Technique; G-Quadruplexes; Humans; Ligands
PubMed: 34875077
DOI: 10.1093/nar/gkab1166 -
Journal of Virology Jan 2022During the nuclear export of nascent nucleocapsids of herpesviruses, the nucleocapsids bud through the inner nuclear membrane (INM) by acquiring the INM as a primary...
During the nuclear export of nascent nucleocapsids of herpesviruses, the nucleocapsids bud through the inner nuclear membrane (INM) by acquiring the INM as a primary envelope (primary envelopment). We recently reported that herpes simplex virus 1 (HSV-1) nuclear egress complex (NEC), which consists of UL34 and UL31, interacts with an endosomal sorting complex required for transport III (ESCRT-III) adaptor ALIX and recruits ESCRT-III machinery to the INM for efficient primary envelopment. In this study, we identified a cluster of six arginine residues in the disordered domain of UL34 as a minimal region required for the interaction with ALIX, as well as the recruitment of ALIX and an ESCRT-III protein CHMP4B to the INM in HSV-1-infected cells. Mutations in the arginine cluster exhibited phenotypes similar to those with ESCRT-III inhibition reported previously, including the mislocalization of NEC, induction of membranous invagination structures containing enveloped virions, aberrant accumulation of enveloped virions in the invaginations and perinuclear space, and reduction of viral replication. We also showed that the effect of the arginine cluster in UL34 on HSV-1 replication was dependent primarily on ALIX. These results indicated that the arginine cluster in the disordered domain of UL34 was required for the interaction with ALIX and the recruitment of ESCRT-III machinery to the INM to promote primary envelopment. Herpesvirus UL34 homologs contain conserved amino-terminal domains that mediate vesicle formation through interactions with UL31 homologs during primary envelopment. UL34 homologs also comprise other domains adjacent to their membrane-anchoring regions, which differ in length, are variable in herpesviruses, and do not form distinguished secondary structures. However, the role of these disordered domains in infected cells remains to be elucidated. In this study, we present data suggesting that the arginine cluster in the disordered domain of HSV-1 UL34 mediates the interaction with ALIX, thereby leading to the recruitment of ESCRT-III machinery to the INM for efficient primary envelopment. This is the first study to report the role of the disordered domain of a UL34 homolog in herpesvirus infections.
Topics: Arginine; Calcium-Binding Proteins; Cell Cycle Proteins; Endosomal Sorting Complexes Required for Transport; HeLa Cells; Herpesvirus 1, Human; Humans; Morphogenesis; Mutation; Nuclear Envelope; Nucleocapsid; Phosphorylation; Viral Proteins; Virion; Virus Release; Virus Replication
PubMed: 34730397
DOI: 10.1128/JVI.01704-21 -
Biology of the Cell Jun 2021Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection induces an alteration in the endomembrane system of the mammalian cells. In this study, we used...
BACKGROUND INFORMATION
Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection induces an alteration in the endomembrane system of the mammalian cells. In this study, we used transmission electron microscopy and electron tomography to investigate the main structural alterations in the cytoplasm of Vero cells infected with a SARS-CoV-2 isolate from São Paulo state (Brazil).
RESULTS
Different membranous structures derived from the zippered endoplasmic reticulum were observed along with virus assembly through membrane budding. Also, we demonstrated the occurrence of annulate lamellae in the cytoplasm of infected cells and the presence of virus particles in the perinuclear space.
CONCLUSIONS AND SIGNIFICANCE
This study contributes to a better understanding of the cell biology of SARS-CoV-2 and the mechanisms of the interaction of the virus with the host cell that promote morphological changes, recruitment of organelles and cell components, in a context of a virus-induced membrane remodelling.
Topics: Animals; COVID-19; Chlorocebus aethiops; Electron Microscope Tomography; Endoplasmic Reticulum; Humans; Intracellular Membranes; Microscopy, Electron, Transmission; Nuclear Envelope; SARS-CoV-2; Vero Cells; Virus Assembly; Virus Replication
PubMed: 33600624
DOI: 10.1111/boc.202000146 -
Molecular Biology of the Cell Mar 2024The multisubunit HOPS tethering complex is a well-established regulator of lysosome fusion with late endosomes and autophagosomes. However, the role of the HOPS complex...
The multisubunit HOPS tethering complex is a well-established regulator of lysosome fusion with late endosomes and autophagosomes. However, the role of the HOPS complex in other stages of endo-lysosomal trafficking is not well understood. To address this, we made HeLa cells knocked out for the HOPS-specific subunits Vps39 or Vps41, or the HOPS-CORVET-core subunits Vps18 or Vps11. In all four knockout cells, we found that endocytosed cargos were trapped in enlarged endosomes that clustered in the perinuclear area. By correlative light-electron microscopy, these endosomes showed a complex ultrastructure and hybrid molecular composition, displaying markers for early (Rab5, PtdIns3P, EEA1) as well as late (Rab7, CD63, LAMP1) endosomes. These "HOPS bodies" were not acidified, contained enzymatically inactive cathepsins and accumulated endocytosed cargo and cation-independent mannose-6-phosphate receptor (CI-MPR). Consequently, CI-MPR was depleted from the TGN, and secretion of lysosomal enzymes to the extracellular space was enhanced. Strikingly, HOPS bodies also contained the autophagy proteins p62 and LC3, defining them as amphisomes. Together, these findings show that depletion of the lysosomal HOPS complex has a profound impact on the functional organization of the entire endosomal system and suggest the existence of a HOPS-independent mechanism for amphisome formation.
Topics: Humans; HeLa Cells; Endosomes; Endocytosis; Intracellular Membranes; Lysosomes
PubMed: 38198575
DOI: 10.1091/mbc.E23-08-0328 -
American Journal of Physiology. Renal... Feb 2023Vasopressin (VP)-regulated aquaporin-2 (AQP2) trafficking between cytoplasmic vesicles and the plasma membrane of kidney principal cells is essential for water...
Vasopressin (VP)-regulated aquaporin-2 (AQP2) trafficking between cytoplasmic vesicles and the plasma membrane of kidney principal cells is essential for water homeostasis. VP affects AQP2 phosphorylation at several serine residues in the COOH-terminus; among them, serine 256 (S256) appears to be a major regulator of AQP2 trafficking. Mutation of this serine to aspartic acid, which mimics phosphorylation, induces constitutive membrane expression of AQP2. However, the intracellular location(s) at which S256 phosphorylation occurs remains elusive. Here, we used strategies to block AQP2 trafficking at different cellular locations in LLC-PK1 cells and monitored VP-stimulated phosphorylation of S256 at these sites by immunofluorescence and Western blot analysis with phospho-specific antibodies. Using methyl-β-cyclodextrin, cold block or bafilomycin, and taxol, we blocked AQP2 at the plasma membrane, in the perinuclear -Golgi network, and in scattered cytoplasmic vesicles, respectively. Regardless of its cellular location, VP induced a significant increase in S256 phosphorylation, and this effect was not dependent on a functional microtubule cytoskeleton. To further investigate whether protein kinase A (PKA) was responsible for S256 phosphorylation in these cellular compartments, we created PKA-null cells and blocked AQP2 trafficking using the same procedures. We found that S256 phosphorylation was no longer increased compared with baseline, regardless of AQP2 localization. Taken together, our data indicate that AQP2 S256 phosphorylation can occur at the plasma membrane, in the -Golgi network, or in cytoplasmic vesicles and that this event is dependent on the expression of PKA in these cells. Phosphorylation of aquaporin-2 by PKA at serine 256 (S256) occurs in various subcellular locations during its recycling itinerary, suggesting that the protein complex necessary for AQP2 S256 phosphorylation is present in these different recycling stations. Furthermore, we showed, using PKA-null cells, that PKA activity is required for vasopressin-induced AQP2 phosphorylation. Our data reveal a complex spatial pattern of intracellular AQP2 phosphorylation at S256, shedding new light on the role of phosphorylation in AQP2 membrane accumulation.
Topics: Animals; Aquaporin 2; LLC-PK1 Cells; Phosphorylation; Serine; Swine; Vasopressins; Intracellular Space
PubMed: 36454701
DOI: 10.1152/ajprenal.00123.2022