Minute Virus of Mice NS1 Interacts with the SMN Protein, and They Colocalize in Novel Nuclear Bodies Induced by Parvovirus Infection

Finally, we present evidence that NS-1 and NS-2 proteins are synthesized at apparently the same levels whether or not NS-3 is expressed.Densoviruses (DNVs) are autonomously replicating parvoviruses known to be highly pathogenic for two phyla of invertebrates: insects and crustacea (3, 13). Like their vertebrate counterparts, DNVs are small icosahedral nonenveloped viruses with a single-stranded linear DNA genome 4 to 6 kb in length (3,4,26). Based on the size, organization of coding sequences, and structure of extremities of their genome, DNVs are distributed in three genera within the subfamily Densovirinae (5). Members of the genus Densovirus, with the Junonia coenia DNV (JcDNV) as the prototype, have a 6-kb genome, a long (Ͼ500-nucleotide [nt]) inverted terminal repeat (ITR), and an ambisense organization. The four structural proteins VP1, VP2, VP3, and VP4 are nested in a single large open reading frame (ORF), ORF1, located in the 5Ј half of one strand, whereas in the 5Ј half of the complementary strand ORF2, ORF3, and ORF4 encode the three nonstructural (NS) proteins NS-1, NS-2, and NS-3, respectively (11). VP and NS genes are transcribed from the P9 and P93 promoters, respectively. The four overlapping capsid polypeptides are synthesized from an unspliced 2.5-kb mRNA by a "leaky-scanning" mechanism whereby ribosomes initiate translation at the first, second, third, or fourth/fifth in-frame AUG codon. Thus, the four VPs share the same C-terminal sequence and differ only in their N-terminal region. The frequency of translation initiation events at each AUG codon is very likely responsible for the different levels of expression of the four polypeptides, as reflected by the presence of VP1, VP2, VP3, and VP4 in an approximate 1:9:9:41 ratio in the virion (27). The three NS proteins are synthesized from two mRNAs, an unspliced 2.4-kb mRNA coding for NS-3 and a spliced 1.7-kb mRNA coding for NS-1 and NS-2 (unpublished data). Among other functions, these proteins are likely to be involved in viral DNA replication. Sequence analyses revealed that NS-1 proteins of DNVs share homologies with NS-1 proteins of vertebrate parvoviruses, including NTP-binding and helicase activity domains (1,3,11,26). Recent in vitro studies of JcDNV NS-1 biochemical properties have confirmed its involvement in viral DNA replication by showing that it binds to specific DNA sequences within the A-AЈ region of the terminal palindrome and, like its vertebrate counterparts, has multiple functions (including a strand-and site-specific nicking activity), and has an ATPdependent DNA helicase activity (10). In contrast, no clear function could be assigned so far to NS-2 and NS-3 proteins of DNVs. These proteins share no homology with NS proteins of vertebrate parvoviruses or with protein sequences from data banks. In the present study we attempted to elucidate the function of NS-3 in the life cycle of JcDNV by generating deletion mutants and analyzing their ability to undergo a replicative cycle. Our results demonstrate that NS-3 is absolutely

Section: Discussionmentioning

confidence: 99%

NS-3 Protein of the Junonia coenia Densovirus Is Essential for Viral DNA Replication in an Ld 652 Cell Line and Spodoptera littoralis Larvae

Abd-Alla¹,

Jousset²,

Li³

et al. 2004

“…Besides NS1 and parvovirus DNA, host cell replication proteins that facilitate viral genome amplification, like PCNA, RPA, and RFC, as well as DNA polymerase ␣ and ␦, accumulate in these bodies (238)(239)(240)(241). Interestingly, the parvovirus RCs are distinct from any prominent nuclear structure, such as PML-NBs, nucleoli, coiled bodies, and/or speckled domains (238).…”

Section: Nuclear Dna Virus Replication Centersmentioning

confidence: 99%

“…NS1 is a multifunctional phosphoprotein that acts as a transcriptional activator of viral promoters as well as initiator and helicase in parvoviral DNA replication (232)(233)(234)(235)(236)(237). Furthermore, NS1 colocalizes with replicating viral DNA in virus-induced nuclear foci (238,239).…”

Section: Nuclear Dna Virus Replication Centersmentioning

confidence: 99%

DNA Virus Replication Compartments

Schmid

Speiseder

Dobner

et al. 2014

158

142

bViruses employ a variety of strategies to usurp and control cellular activities through the orchestrated recruitment of macromolecules to specific cytoplasmic or nuclear compartments. Formation of such specialized virus-induced cellular microenvironments, which have been termed viroplasms, virus factories, or virus replication centers, complexes, or compartments, depends on molecular interactions between viral and cellular factors that participate in viral genome expression and replication and are in some cases associated with sites of virion assembly. These virus-induced compartments function not only to recruit and concentrate factors required for essential steps of the viral replication cycle but also to control the cellular mechanisms of antiviral defense. In this review, we summarize characteristic features of viral replication compartments from different virus families and discuss similarities in the viral and cellular activities that are associated with their assembly and the functions they facilitate for viral replication.

“…CREB and the Ets family of transcription factors (19,50) may also participate in the regulation of viral promoter. SGT (13) and SMN (72) are partners of NS1. Members of the 14-3-3 protein family (5) and the nuclear export receptor Crm1 (3) interact with NS2.…”

mentioning

confidence: 99%

Expression Profiling of Human Hepatoma Cells Reveals Global Repression of Genes Involved in Cell Proliferation, Growth, and Apoptosis upon Infection with Parvovirus H-1

Werner

Hergenhahn

et al. 2005

Autonomous parvoviruses are small, nonenveloped, linear single-strand DNA viruses. Their 5-kb-long genome consists of two overlapping transcription units. An early promoter, P4, directs the expression of nonstructural proteins NS1 and NS2, and a late promoter, P38, controls the expression of capsid proteins VP1 and VP2 (12). Owing to their low genetic complexity, parvoviruses are tightly dependent on cellular factors that are expressed as a function of proliferation and differentiation in order to complete their life cycle (53, 60). Parvoviruses are incapable of inducing quiescent cells to enter S phase (66), and infection remains cryptic until host cells start a round of genomic DNA replication on their own. Once the appropriate cellular conditions are met, the virus starts its replication at the G 1 /S transition and a lytic or even productive infection can ensue (12,22), during which the infected cells get blocked in S/G 2 phase and eventually die (48, 53). The tight dependence of parvovirus replication on S-phase-associated factors accounts, in part, for the tissue specificity, oncotropism, and oncolytic activity of parvoviruses (55). In particular, MVMp and the closely related H-1 virus were found to replicate and exert cytopathic effects in a variety of transformed or tumorderived cells while sparing their normal counterparts in vitro. In vivo, these viruses may prevent tumors from appearing or cause the repression of established tumors, making them candidates for vectors in cancer therapy (9).The molecular mechanisms underlying parvovirus-host cell interactions were the objects of a number of recent studies. On the viral side, the nonstructural proteins NS1 and NS2 are key regulators of the virus life cycle. NS1 is a multifunctional protein that is endowed with a transcriptional function targeted to parvoviral but also heterologous promoters (18,31,54,67), and with enzymatic (ATPase, helicase [69], and site-specific nickase [44]) and site-specific DNA binding properties (10). NS1 thus plays critical roles during parvovirus replication and gene expression, starting from the earlier stages of the viral life cycle. NS2 has more elusive functions and appears to be particularly important in certain cells for capsid assembly and release of progeny viruses (11,16). The viral effector of cytotoxicity has been assigned mainly to the nonstructural protein NS1 (6, 31), though other viral products may also be involved (4, 32). Completion of the viral life cycle requires the assistance of various cellular molecules; some of these have been identified, including transcription factors, cofactors, and other nuclear proteins. CyclinA (2), parvovirus initiation factor (PIF) (8), and two members of the protein kinase C (PKC/) family play distinct roles in virus replication (28,45). The transcription factors E2F (15) and SP1 (27), the transcription coactivator CBP (47), and the basal transcriptional factors TBP and TFIIA(␣/␤) (36) help NS1 to trans-regulate target promoters * Corresponding author. Mailing address: Applied Tu...