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J Virol. 2017 May 26;91(12). pii: e00232-17. doi: 10.1128/JVI.00232-17. Print 2017 Jun 15.

SGTA-Dependent Regulation of Hsc70 Promotes Cytosol Entry of Simian Virus 40 from the Endoplasmic Reticulum.

Author information

1
Department of Cell and Developmental Biology, University of Michigan Medical School, Ann Arbor, Michigan, USA.
2
Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, Michigan, USA.
3
Department of Cell and Developmental Biology, University of Michigan Medical School, Ann Arbor, Michigan, USA btsai@umich.edu.

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.IMPORTANCE How 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.

KEYWORDS:

chaperones; endoplasmic reticulum; membrane transport; simian virus 40

PMID:
28356524
PMCID:
PMC5446632
DOI:
10.1128/JVI.00232-17
[Indexed for MEDLINE]
Free PMC Article

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