Simian Virus 40 Depends on ER Protein Folding and Quality Control Factors for Entry into Host Cells

Abstract

Cell entry of Simian Virus 40 (SV40) involves caveolar/lipid raft-mediated endocytosis, vesicular transport to the endoplasmic reticulum (ER), translocation into the cytosol, and import into the nucleus. We analyzed the effects of ER-associated processes and factors on infection and on isolated viruses and found that SV40 makes use of the thiol-disulfide oxidoreductases, ERp57 and PDI, as well as the retrotranslocation proteins Derlin-1 and Sel1L. ERp57 isomerizes specific interchain disulfides connecting the major capsid protein, VP1, to a crosslinked network of neighbors, thus uncoupling about 12 of 72 VP1 pentamers. Cryo-electron tomography indicated that loss of interchain disulfides coupled with calcium depletion induces selective dissociation of the 12 vertex pentamers, a step likely to mimic uncoating of the virus in the cytosol. Thus, the virus utilizes the protein folding machinery for initial uncoating before exploiting the ER-associated degradation machinery presumably to escape from the ER lumen into the cytosol.

How Viruses Use the Endoplasmic Reticulum for Entry, Replication, and Assembly

“…ERresident redox-active protein disulfide isomerase (PDI) family members, including the canonical PDI, ERp57, and ERp72, can isomerize or reduce the virus disulfide bonds ( Fig. 2A, step 1a) Schelhaas et al 2007;Walczak and Tsai 2011;Nelson et al 2012). However, the precise combination of PDI proteins engaging a specific Py family member may differ because of subtle differences in the viral disulfide bond arrangements.…”

Replication and Assembly of Human Papillomaviruses

“…4A) (Chen et al, 2000). This is a rational assumption, since the C-terminal "invading arm" of SV40 is stabilized by an N-terminal disulfide bridge (Sapp et al, 1998;Jao et al, 1999;Schelhaas et al, 2007). However, analyses of recombinant VLPs suggest that a critical interpentameric disulfide bridge occurs between Cys428 and Cys175, and potentially Cys185 in HPV16, rather than between neighboring Cys428 residues (Sapp et al, 1998;Chen et al, 2000;Kondo et al, 2007).…”

“…Recent studies involving entry pathways (e.g., clathrin-vs. caveolar-mediated endocytosis) and entry kinetics (e.g., few vs. many hours) of HPV have suffered due to a lack of consistency (Bousarghin et al, 2003;Culp and Christensen, 2004;Hindmarsh and Laimins, 2007;Smith et al, 2007;Laniosz et al, 2008). This may be due to the use of multiple types of synthetic papillomavirus particles and cell lines, in addition to the use of native virions, and cross-talk between clathrin and caveolar pathways (Fligge et al, 2001;Bousarghin et al, 2003;Hindmarsh and Laimins, 2007;Schelhaas et al, 2007;Laniosz et al, 2008). Recent discoveries with polyomaviruses suggest that controversies over papillomavirus entry may be from the initial usage of clathrin-mediated endocytosis and later exploitation of caveolar endocytic machinery within the cell (Bousarghin et al, 2003;Querbes et al, 2006;Laniosz et al, 2008).…”

Too smart to fail—how viruses exploit the complexity of host cells during entry

“…It is, however, antagonized by anti-viral defense mechanisms, which decode structural features of viral particles and trigger an conditions provide additional cues and change interchain disulfides in the viral capsid [7].…”