title: SGTA-Dependent Regulation of Hsc70 Promotes Cytosol Entry of Simian Virus 40 from the Endoplasmic Reticulum.
abstract: Membrane penetration by nonenveloped viruses remains enigmatic. In the case of the nonenveloped polyomavirus simian virus 40 (SV40), the virus penetrates the endoplasmic reticulum (ER) membrane to reach the cytosol and then traffics to the nucleus to cause infection. We previously demonstrated that the cytosolic Hsc70-SGTA-Hsp105 complex is tethered to the ER membrane, where Hsp105 and SGTA facilitate the extraction of SV40 from the ER and transport of the virus into the cytosol. We now find that Hsc70 also ejects SV40 from the ER into the cytosol in a step regulated by SGTA. Although SGTA's N-terminal domain, which mediates homodimerization and recruits cellular adaptors, is dispensable during ER-to-cytosol transport of SV40, this domain appears to exert an unexpected post-ER membrane translocation function during SV40 entry. Our study thus establishes a critical function of Hsc70 within the Hsc70-SGTA-Hsp105 complex in promoting SV40 ER-to-cytosol membrane penetration and unveils a role of SGTA in controlling this step.IMPORTANCEHow a nonenveloped virus transports across a biological membrane to cause infection remains mysterious. One enigmatic step is whether host cytosolic components are co-opted to transport the viral particle into the cytosol. During ER-to-cytosol membrane transport of the nonenveloped polyomavirus SV40, a decisive infection step, a cytosolic complex composed of Hsc70-SGTA-Hsp105 was previously shown to associate with the ER membrane. SGTA and Hsp105 have been shown to extract SV40 from the ER and transport the virus into the cytosol. We demonstrate here a critical role of Hsc70 in SV40 ER-to-cytosol penetration and reveal how SGTA controls Hsc70 to impact this process.
authors.affiliation: Department of Cell and Developmental Biology, University of Michigan Medical School, Ann Arbor, Michigan, USA.|Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, Michigan, USA.
authors.forename: Allison
authors.initials: A
authors.lastname: Dupzyk
authors.affiliation: Department of Cell and Developmental Biology, University of Michigan Medical School, Ann Arbor, Michigan, USA.
authors.forename: Jeffrey M
authors.initials: JM
authors.lastname: Williams
authors.affiliation: Department of Cell and Developmental Biology, University of Michigan Medical School, Ann Arbor, Michigan, USA.
authors.forename: Parikshit
authors.initials: P
authors.lastname: Bagchi
authors.affiliation: Department of Cell and Developmental Biology, University of Michigan Medical School, Ann Arbor, Michigan, USA.
authors.forename: Takamasa
authors.initials: T
authors.lastname: Inoue
authors.affiliation: Department of Cell and Developmental Biology, University of Michigan Medical School, Ann Arbor, Michigan, USA btsai@umich.edu.
authors.forename: Billy
authors.initials: B
authors.lastname: Tsai
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000502:physiology; D019556:COS Cells; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D002522:Chlorocebus aethiops; D003600:Cytosol / Q000378:metabolism / Q000821:virology*; D004721:Endoplasmic Reticulum / Q000502:physiology / Q000821:virology*; D005786:Gene Expression Regulation; D057809:HEK293 Cells; D050883:HSC70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D054884:Host-Pathogen Interactions / Q000235:genetics; D006801:Humans; D007425:Intracellular Membranes / Q000821:virology; D018832:Molecular Chaperones / Q000378:metabolism; D034741:RNA, Small Interfering; D013539:Simian virus 40 / Q000502:physiology*; D053586:Virus Internalization
chemical_list: D002352:Carrier Proteins; D050883:HSC70 Heat-Shock Proteins; C494371:HSPA8 protein, human; D018832:Molecular Chaperones; D034741:RNA, Small Interfering; C114575:SGTA protein, human
keywords: chaperones; endoplasmic reticulum; membrane transport; simian virus 40