Nervous necrosis virus capsid protein exploits nucleolar phosphoprotein Nucleophosmin (B23) function for viral replication

Nucleophosmin 1a translocated from nucleus to cytoplasm and facilitate GCRV replication

To decipher the functional characterization of Nucleophosmin 1a (NPM1a) from grass carp (Ctenopharyngodon idellus) (CiNPM1a), its cDNA was cloned and bioinformatic analysis were conducted. The full-length cDNA sequence of CiNPM1a is 1732 bp, which encodes 307 amino acids. CiNPM1a contains conserved domains of Nucleoplasmin domain, NPM1-C terminal domain, as well as nuclear localization signals, nuclear export signal (NES) and acid patches. There are 52 and 20 consensus amino acids exist in the Nucleoplasmin domain and the NPM1-C terminal domain of all blasted species. In addition, the immune function of CiNPM1a were analyzed. The Ciirf7, Ciifn1 and Ciifn2 transcription was inhibited, whereas the vp2 and vp7 expressions were enhanced in CiNPM1a overexpressing cells after GCRV infection (P < 0.05). Moreover, the Ciirf7, Ciifn1 and Ciifn2 mRNA levels were significantly up-regulated, but the vp2 and vp7 expressions were significantly down-regulated in CiNPM1a knockdown cells after infection. This indicated that CiNPM1a played negative roles in the induction of Type I IFN reaction and thus the GCRV replication. Finally, the NES domain that affect the nucleous-cytoplasm shuttle and the replication of GCRV were investigated. The deletion of NES1 and NES(1 + 2+3) absolutely limited the transloacation of CiNPM1a△NES1 protein and CiNPM1a △NES(1 + 2+3) protein to cytoplasm after infection, and the deletion of NES2 resulted in partially limitation of protein shuttle. In general, Ciirf3, Ciirf7, Ciifn1 and Ciifn2 expressions were enhanced in the CiNPM1a△NES1, CiNPM1a△NES2 and CiNPM1a△NES3 overexpression groups, and the deletion of functional domains in CiNPM1a led to significantly reduction of the vp2 and vp7 replication. The results indicated that CiNPM1a may be a target molecular for GCRV infection curation, and a candidate molecular for resistance strain breeding of grass carp.

Nucleolar Phosphoprotein NPM1 Interacts With Porcine Circovirus Type 3 Cap Protein and Facilitates Viral Replication

Porcine circovirus type 3 (PCV3) is a recently discovered virus with potentially significant implications on the global swine industry. PCV3 replication involves the entry of the viral capsid (Cap) protein with nucleolar localization signals into the nucleus. Using liquid chromatography-mass spectrometry analysis, nucleolar phosphoprotein NPM1 was identified as one of the cellular proteins bound to PCV3 Cap. Co-immunoprecipitation demonstrated that PCV3 Cap interacts directly with NPM1, where the region binding with NPM1 is mapped to amino acid residues 1–38 of Cap. Upon co-transfection, the expression of Cap protein promoted the redistribution of NPM1, which translocated from the nucleus to the cytoplasm and colocalized with Cap in cultured PK15 cells. NPM1 expression was upregulated and translocated from the nucleus to the cytoplasm in PCV3-infected cells, upon siRNA-mediated depletion, or upon treatment with NPM1 inhibitor in PK15 cells with impaired PCV3 replication, as evidenced by decreased levels of viral DNA synthesis and protein expression. By contrast, the replication of PCV3 was enhanced in stably NPM1-expressing cells via a lentivirus-delivered system. Taken together, these findings indicate that NPM1 interacts with PCV3 Cap and plays a crucial role in PCV3 replication.

Characterization of GAB3 and its association with NNV resistance in the Asian seabass

Understanding the functions of genes related to disease resistance and identifying polymorphisms in these genes are essential in molecular breeding for disease resistance. Viral nervous necrosis (VNN) is one of the major diseases in the Asian seabass, Lates calcarifer. Our previous works on QTL mapping, GWAS and cell-line transcriptome analysis of the Asian seabass after NNV challenge revealed that the gene GAB3 might be a candidate gene for VNN resistance. In this study, we cloned and characterized GAB3, and identified SNPs in the gene of the Asian seabass. The cDNA of the gene was 2165 bp, containing an ORF of 1674 bp encoding 557 amino acids. The gene consisted of 10 exons and nine introns. It was ubiquitously expressed in normal fish. An analysis of the association between two SNPs in the second intron and NNV resistance in 1035 fish descended from 43 families revealed that the two SNPs were significantly associated with VNN resistance. After NNV infection, the expression of GAB3 was significantly increased in the brain, spleen, muscle and gut, and was suppressed in the liver. The GAB3 protein was localized in the nucleus. Overexpression of GAB3 with specific GAB3-pcDNA was positively correlated to increased viral RNA and titer in NNV-infected Asian seabass cells. Our study provides new evidence to support that GAB3 may be an important gene related to NNV resistance. In addition, the SNPs provide DNA markers for the selection of candidate genes resistance to NNV at the juvenile stage of Asian seabass.

The roles of nuclear focal adhesion kinase (FAK) on Cancer: a focused review

FAK is a tyrosine kinase overexpressed in cancer cells and plays an important role in the progression of tumors to a malignant phenotype. Except for its typical role as a cytoplasmic kinase downstream of integrin and growth factor receptor signaling, related studies have shown new aspects of the roles of FAK in the nucleus. FAK can promote p53 degradation through ubiquitination, leading to cancer cell growth and proliferation. FAK can also regulate GATA4 and IL-33 expression, resulting in reduced inflammatory responses and immune escape. These findings establish a new model of FAK from the cytoplasm to the nucleus. Activated FAK binds to transcription factors and regulates gene expression. Inactive FAK synergizes with different E3 ligases to promote the turnover of transcription factors by enhancing ubiquitination. In the tumor microenvironment, nuclear FAK can regulate the formation of new blood vessels, affecting the tumor blood supply. This article reviews the roles of nuclear FAK in regulating gene expression. In addition, the use of FAK inhibitors to target nuclear FAK functions will also be emphasized.

C/D box snoRNAs in viral infections: RNA viruses use old dogs for new tricks

C/D box snoRNAs (SNORDs) are a highly expressed class of non-coding RNAs. Besides their well-established role in rRNA modification, C/D box snoRNAs form protein complexes devoid of fibrillarin and regulate pre-mRNA splicing and polyadenylation of numerous genes. There is an emerging body of evidence for functional interactions between RNA viruses and C/D box snoRNAs. The infectivity of some RNA viruses depends on enzymatically active fibrillarin, and many RNA viral proteins associate with nucleolin or nucleophosmin, suggesting that viruses benefit from their cytosolic accumulation. These interactions are likely reflected by morphological changes in the nucleolus, often leading to relocalization of nucleolar proteins and ncRNAs to the cytosol that are a characteristic feature of viral infections. Knock-down studies have also shown that RNA viruses need specific C/D box snoRNAs for optimal replication, suggesting that RNA viruses benefit from gene expression programs regulated by SNORDs, or that viruses have evolved “new” uses for these humble ncRNAs to advance their prospects during infection.

RGNNV-induced cell cycle arrest at G1/S phase enhanced viral replication via p53-dependent pathway in GS cells

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Infection of RGNNV redistributed NPM1, stabilized p53 and inhibited cell proliferation by inducing G1 arrest.

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Infection of RGNNV activated p53-dependent pathway, resulting in G1/S phase cell cycle arrest in host cells and directly impacting viral replication.

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NPM1 knockdown could abrogate RGNNV-induced cell proliferation inhibition and cell cycle arrest.

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Our results revealed that RGNNV infection could perturb the progression of cell cycle via the NPM1-p53 pathway and facilitate virus gene replication.

Nervous necrosis virus (NNV) is a ubiquitous pathogen in the aquaculture worldwide. Little is known about the relationship between NNV virus and host cells. Our studies showed that RGNNV infection could induce cell cycle arrest via activation of p53 signaling in cultured host cells. Infection of RGNNV redistributed NPM1, stabilized p53 and inhibited cell proliferation by inducing G1 arrest. RGNNV infection also led to phosphorylation and accumulation of p53 in a time-dependent manner. Furthermore, RGNNV infection upregulated cyclin-dependent kinase inhibitor 1 A (p21) and downregulated cyclin E and cyclin-dependent kinase 2 (CDK2). The expression of genes in the p53 pathway did not change significantly after p53 knockdown by pifithrin-α during RGNNV infection. However, NPM1 knockdown could abrogate RGNNV-induced cell proliferation inhibition, activation of p53 signaling and cell cycle arrest. In addition, RGNNV infection of the cells synchronized in various stages of cell cycle showed that viral genomic RNA and virus titer were higher in the cells released from G1 phase- or S phase-synchronized cells than that in the cells released from the G2 phase-synchronized or asynchronous cells after 18 h p.i. Therefore, our study reveals that RGNNV infection induces the p53-dependent pathway, resulting in a cell cycle arrest at G1 phase in host cells, which might provide a favorable condition for viral replication.

Nucleophosmin (NPM1)/B23 in the Proteome of Human Astrocytic Cells Restricts Chikungunya Virus Replication

Chikungunya virus (CHIKV), a positive-stranded RNA virus, can cause neurological complications by infecting the major parenchymal cells of the brain such as neurons and astrocytes. A proteomic analysis of CHIKV-infected human astrocytic cell line U-87 MG revealed tight functional associations among the modulated proteins. The predominant cellular pathways involved were of transcription-translation machinery, cytoskeletol reorganization, apoptosis, ubiquitination, and metabolism. In the proteome, we could also identify a few proteins that are reported to be involved in host-virus interactions. One such protein, Nucleophosmin (NPM1)/B23, a nucleolar protein, showed enhanced cytoplasmic aggregation in CHIKV-infected cells. NPM1 aggregation was predominantly localized in areas wherein CHIKV antigen could be detected. Furthermore, we observed that inhibition of this aggregation using a specific NPM1 oligomerization inhibitor, NSC348884, caused a significant dose-dependent enhancement in virus replication. There was a marked increase in the amount of intracellular viral RNA, and ∼10⁵-fold increase in progeny virions in infected cells. Our proteomic analysis provides a comprehensive spectrum of host proteins modulated in response to CHIKV infection in astrocytic cells. Our results also show that NPM1/B23, a multifunctional chaperone, plays a critical role in restricting CHIKV replication and is a possible target for antiviral strategies.