Identification of a Novel Cellular TPR-Containing Protein, SGT, That Interacts with the Nonstructural Protein NS1 of Parvovirus H-1

Abstract

The nonstructural protein NS1 of autonomous parvoviruses is essential for viral DNA amplification and gene expression and is also the major cytopathic effector of these viruses. NS1 acts as nickase, helicase, and ATPase and upregulates P38-driven transcription of the capsid genes. We report here the identification of a novel cellular protein that interacts with NS1 from parvovirus H-1 and which we termed SGT, for small glutamine-rich tetratricopeptide repeat (TPR)-containing protein. The cDNA encoding full-length SGT was isolated through a two-hybrid screen with, as bait, the truncated NS1dlC69 polypeptide, which lacks the C-terminal transactivation domain of NS1. Full-length NS1 and SGT interacted in the two-hybrid system and in an in vitro interaction assay. Northern blot analysis revealed one major transcript of about 2 kb that was present in all rat tissues investigated. Rat sgt cDNA coded for 314 amino acids, and the protein migrated in sodium dodecyl sulfate-polyacrylamide gel electrophoresis with an apparent molecular mass of 34 kDa. SGT could be detected in both the nucleus and the cytoplasm of rat cells, as determined by indirect immunofluorescence analysis and Western blotting of fractionated cellular extracts with an affinity-purified antiserum raised against recombinant SGT (AC1.1). In H-1 virus-infected rat and human cells, compared to mock-infected controls, differences in the migration of SGT polypeptides were revealed after Western blot analysis of total cellular extracts. Moreover, the transient expression of NS proteins was sufficient to induce SGT modification. These results show that cellular SGT, which we have identified as an NS1-interacting protein, is modified by parvovirus infection as well as NS expression.

Severe acute respiratory syndrome coronavirus protein 7a interacts with hSGT

“…3, middle panel), flag-hSGT was distributed to both the nucleus and cytoplasm of transfected cells (left panel) and untransfected cells did not stain (not shown) with the antibodies. The cellular distribution of SGT is consistent with a report by Cziepluch and coworkers [24] who found that untagged rat SGT is detectable in cytoplasm and nucleus of FREJ4 cells. Thus, 7a-HA was found to partially co-localize with flag-hSGT in Vero E6 cells (right panel).…”

“…The TPR-containing protein, hSGT, was first identified and described as a cellular binding partner for the non-structural (NS) protein of autonomous parvovirus H-1. Interestingly, both H1-virus infection and transient expression of the NS protein result in modification (most likely phosphorylation) of hSGT [24]. A subsequent study showed that hSGT interacts with HIV-I Vpu and Gag proteins, with Callahan and co-workers postulating that hSGT plays a role in HIV-1 virus assembly or release [25].…”

The roles of cytosolic quality control proteins, SGTA and the BAG6 complex, in disease

“…The TPR domain is responsible for SGTA binding to Hsp70 and Hsp90, along with other varying receptors and proteins (Philp et al, 2013;Roberts et al, 2015). Due to this, the TPR domain has been linked with SGTA's role in diseases such as HIV (Dutta & Tan, 2008) and the parvovirus (Cziepluch et al, 1998).…”

“…Early in the literature, SGTA was discovered in complex with the parvovirus H-1, specifically NS1, a non-structural protein of H-1 that is essential for DNA replication (Cziepluch et al, 1998). Another example of SGTA in complex with a virus involves Vpu, a viral core protein precursor from HIV-1 (Dutta & Tan, 2008).…”

Understanding the accessory viral proteins unique to the severe acute respiratory syndrome (SARS) coronavirus

“…TPR motif-containing proteins have been shown to be involved in many cellular processes including cell cycle control, transcription and splicing events, protein transport and protein folding (Blatch and Lassle, 1999). The SGT protein was first identified as a binding partner for the non-structural protein, NS1, of autonomous parvovirus H-1 (Cziepluch et al, 1998), and could also interact with HIV-1 (human immunodeficiency virus type 1) Vpu and Gag proteins (Callahan et al, 1998). The biological significance of the interaction between 7a and SGT needs to be elucidated.…”