A Cytosolic Chaperone Complexes with Dynamic Membrane J-Proteins and Mobilizes a Nonenveloped Virus out of the Endoplasmic Reticulum

Walczak, Christopher P.; Ravindran, Madhu Sudhan; Inoue, Takamitsu; Tsai, Billy

doi:10.1371/journal.ppat.1004007

Cited by 72 publications

(177 citation statements)

References 58 publications

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“…Because the foci selectively harbor ER components known to promote ER-to-cytosol transport of SV40 (4,40), reorganization of this NEF into the foci further supports the idea of its role in facilitating viral ER membrane penetration. This reorganization of Grp170 into the foci might clarify how SV40, upon release from BiP, is able to fully interact with the ER lipid bilayer to initiate membrane penetration and how it avoids repeated cycles of reengaging BiP.…”

Section: Discussionmentioning

confidence: 61%

“…By concentrating this NEF into the foci, SV40 released from BiP is likely to bind to ER membrane components (which are also concentrated in the foci) that assist the virus in engaging the ER lipid bilayer. As these foci have been postulated to represent the actual site from where PyVs exit the ER to enter the cytosol (4,40), additional experiments are required to clarify how PyVs released from BiP are mechanistically coupled to its ER membrane penetration in a step presumably aided by a membrane component(s) that initiates retrotranslocation within the foci.…”

Section: Discussionmentioning

confidence: 99%

“…Our laboratory and another group previously reported that SV40 induces ER lumenal proteins (e.g., BiP) and membrane proteins (e.g., BAP31) essential for viral infection to reorganize into discrete puncta (called foci) in the ER membrane (4,40). To assess whether Grp170 moves into these foci upon SV40 infection, cells expressing FLAG-BiP or Grp170-FLAG were incubated with or without (mock treatment) SV40 for 16 h, fixed, and subjected to immunofluorescence staining.…”

Section: Release Of Bip From Sv40 Promotes Viral Membrane Binding In mentioning

confidence: 95%

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A Nucleotide Exchange Factor Promotes Endoplasmic Reticulum-to-Cytosol Membrane Penetration of the Nonenveloped Virus Simian Virus 40

Inoue

Tsai

2015

J Virol

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The nonenveloped simian polyomavirus (PyV) simian virus 40 (SV40) hijacks the endoplasmic reticulum (ER) quality control machinery to penetrate the ER membrane and reach the cytosol, a critical infection step. During entry, SV40 traffics to the ER, where host-induced conformational changes render the virus hydrophobic. The hydrophobic virus binds and integrates into the ER lipid bilayer to initiate membrane penetration. However, prior to membrane transport, the hydrophobic SV40 recruits the ER-resident Hsp70 BiP, which holds the virus in a transport-competent state until it is ready to cross the ER membrane. Here we probed how BiP disengages from SV40 to enable the virus to penetrate the ER membrane. We found that nucleotide exchange factor (NEF) Grp170 induces nucleotide exchange of BiP and releases SV40 from BiP. Importantly, this reaction promotes SV40 ER-to-cytosol transport and infection. The human BK PyV also relies on Grp170 for successful infection. Interestingly, SV40 mobilizes a pool of Grp170 into discrete puncta in the ER called foci. These foci, postulated to represent the ER membrane penetration site, harbor ER components, including BiP, known to facilitate viral ER-to-cytosol transport. Our results thus identify a nucleotide exchange activity essential for catalyzing the most proximal event before ER membrane penetration of PyVs. IMPORTANCEPyVs are known to cause debilitating human diseases. During entry, this virus family, including monkey SV40 and human BK PyV, hijacks ER protein quality control machinery to breach the ER membrane and access the cytosol, a decisive infection step. In this study, we pinpointed an ER-resident factor that executes a crucial role in promoting ER-to-cytosol membrane penetration of PyVs. Identifying a host factor that facilitates entry of the PyV family thus provides additional therapeutic targets to combat PyV-induced diseases. Pathogens hijack protein quality control pathways of host cells to successfully cause infection. One pathway co-opted by pathogens during entry is endoplasmic reticulum (ER)-associated degradation (ERAD) (1-3). While ERAD is a surveillance system normally dedicated to the removal of misfolded ER proteins to the cytosol for proteasomal destruction, pathogens can co-opt elements of this pathway to gain entry into the host cytosol by disguising themselves as misfolded ER proteins. A clearer picture of the nature of this pathogen-host interaction is slowly emerging.Entry of the nonenveloped polyomavirus (PyV) family, including the simian virus 40 (SV40) and the human BK PyVs, serves as a salient example of pathogens that co-opt the ERAD pathway during infection (4-6). Structurally, SV40 is composed of 360 copies of the VP1 major coat protein arranged as 72 pentamers, with each pentamer engaging either the VP2 or VP3 internal hydrophobic minor coat protein. The pentamers are assembled as a 45-nm-diameter icosahedral particle that in turn encapsulates its viral DNA genome (7,8). To infect cells, SV40 undergoes receptor-mediated endocytosis a...

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Section: Discussionmentioning

confidence: 61%

Section: Discussionmentioning

confidence: 99%

Section: Release Of Bip From Sv40 Promotes Viral Membrane Binding In mentioning

confidence: 95%

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A Nucleotide Exchange Factor Promotes Endoplasmic Reticulum-to-Cytosol Membrane Penetration of the Nonenveloped Virus Simian Virus 40

Inoue

Tsai

2015

J Virol

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“…The J domains of B12 and B14 are localized on the cytosolic face of the ER membrane to engage cytosolic Hsc70 (29,30). B12 and B14 also physically interact as a multiprotein complex (31). In the context of SV40 entry, we recently reported that B12 and B14 reorganize into discrete puncta, called foci, in the ER membrane, a phenomenon originally reported with BAP31 (23,31).…”

mentioning

confidence: 80%

“…B12 and B14 also physically interact as a multiprotein complex (31). In the context of SV40 entry, we recently reported that B12 and B14 reorganize into discrete puncta, called foci, in the ER membrane, a phenomenon originally reported with BAP31 (23,31). Importantly, focus formation is largely selective for those cellular components required in facilitating SV40's ER-to-cytosol transport.…”

mentioning

confidence: 93%

The Endoplasmic Reticulum Membrane J Protein C18 Executes a Distinct Role in Promoting Simian Virus 40 Membrane Penetration

Bagchi

Walczak

Tsai

2015

J Virol

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The nonenveloped simian virus 40 (SV40) hijacks the three endoplasmic reticulum (ER) membrane-bound J proteins B12, B14, and C18 to escape from the ER into the cytosol en route to successful infection. How C18 controls SV40 ER-to-cytosol membrane penetration is the least understood of these processes. We previously found that SV40 triggers B12 and B14 to reorganize into discrete puncta in the ER membrane called foci, structures postulated to represent the cytosol entry site (C. P. Walczak, M. S. Ravindran, T. Inoue, and B. Tsai, PLoS Pathog 10:e1004007, 2014). We now find that SV40 also recruits C18 to the virus-induced B12/B14 foci. Importantly, the C18 foci harbor membrane penetration-competent SV40, further implicating this structure as the membrane penetration site. Consistent with this, a mutant SV40 that cannot penetrate the ER membrane and promote infection fails to induce C18 foci. C18 also regulates the recruitment of B12/B14 into the foci. In contrast to B14, C18's cytosolic Hsc70-binding J domain, but not the lumenal domain, is essential for its targeting to the foci; this J domain likewise is necessary to support SV40 infection. Knockdown-rescue experiments reveal that C18 executes a role that is not redundant with those of B12/B14 during SV40 infection. Collectively, our data illuminate C18's contribution to SV40 ER membrane penetration, strengthening the idea that SV40-triggered foci are critical for cytosol entry. IMPORTANCEPolyomaviruses (PyVs) cause devastating human diseases, particularly in immunocompromised patients. As this virus family continues to be a significant human pathogen, clarifying the molecular basis of their cellular entry pathway remains a high priority. To infect cells, PyV traffics from the cell surface to the ER, where it penetrates the ER membrane to reach the cytosol. In the cytosol, the virus moves to the nucleus to cause infection. ER-to-cytosol membrane penetration is a critical yet mysterious infection step. In this study, we clarify the role of an ER membrane protein called C18 in mobilizing the simian PyV SV40, a PyV archetype, from the ER into the cytosol. Our findings also support the hypothesis that SV40 induces the formation of punctate structures in the ER membrane, called foci, that serve as the portal for cytosol entry of the virus. While polyomaviruses (PyVs) are known to establish asymptomatic persistent infections in the kidney, blood, skin, and brain of healthy individuals, they carry the potential to cause debilitating diseases, especially during immunosuppression. For example, infections caused by the human BK, JC, and Merkel cell PyVs can lead to PyV-associated nephropathy, progressive multifocal leukoencephalopathy, and Merkel cell carcinoma, respectively (1, 2). Simian virus 40 (SV40) traditionally has been used as a model for studying this virus family and has structural and genetic similarities to human PyVs. SV40 and all other PyVs are nonenveloped icosahedral particles, approximately 45 nm in diameter, and contain a double-stranded DNA gen...

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Alphaherpesvirus upregulates NDRG1 expression to facilitate the nuclear import of viral UL31 and UL34 proteins

Zhang

Ming

Zeng

et al. 2023

Journal of Medical Virology

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Proteins UL31 and UL34 encoded by alphaherpesvirus are critical for viral primary envelopment and nuclear egress. We report here that pseudorabies virus (PRV), a useful model for research on herpesvirus pathogenesis, uses N‐myc downstream regulated 1 (NDRG1) to assist the nuclear import of UL31 and UL34. PRV promoted NDRG1 expression through DNA damage‐induced P53 activation, which was beneficial to viral proliferation. PRV induced the nuclear translocation of NDRG1, and its deficiency resulted in the cytosolic retention of UL31 and UL34. Therefore, NDRG1 assisted the nuclear import of UL31 and UL34. Furthermore, in the absence of the nuclear localization signal (NLS), UL31 could still translocate to the nucleus, and NDRG1 lacked an NLS, thus suggesting the existence of other mediators for the nuclear import of UL31 and UL34. We demonstrated that heat shock cognate protein 70 (HSC70) was the key factor in this process. UL31 and UL34 interacted with the N‐terminal domain of NDRG1 and the C‐terminal domain of NDRG1 bound to HSC70. Replenishment of HSC70ΔNLS in HSC70‐knockdown cells, or interference in importin α expression, abolished the nuclear translocation of UL31, UL34, and NDRG1. These results indicated that NDRG1 employs HSC70 to facilitate viral proliferation in the nuclear import of PRV UL31 and UL34.

show abstract

A Cytosolic Chaperone Complexes with Dynamic Membrane J-Proteins and Mobilizes a Nonenveloped Virus out of the Endoplasmic Reticulum

Cited by 72 publications

References 58 publications

A Nucleotide Exchange Factor Promotes Endoplasmic Reticulum-to-Cytosol Membrane Penetration of the Nonenveloped Virus Simian Virus 40

A Nucleotide Exchange Factor Promotes Endoplasmic Reticulum-to-Cytosol Membrane Penetration of the Nonenveloped Virus Simian Virus 40

The Endoplasmic Reticulum Membrane J Protein C18 Executes a Distinct Role in Promoting Simian Virus 40 Membrane Penetration

Alphaherpesvirus upregulates NDRG1 expression to facilitate the nuclear import of viral UL31 and UL34 proteins

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