Minute virus of canines (MVC) is a member of the genus

N 6-methyladenosine (m6A) constitutes one of the most abundant internal RNA modifications and is critical for RNA metabolism and function. It has been previously reported that viral RNA contains internal m6A modifications; however, only recently the function of m6A modification in viral RNAs has been elucidated during infections of HIV, hepatitis C virus and Zika virus. In the present study, we found that enterovirus 71 (EV71) RNA undergoes m6A modification during viral infection, which alters the expression and localization of the methyltransferase and demethylase of m6A, and its binding proteins. Moreover, knockdown of m6A methyltransferase resulted in decreased EV71 replication, whereas knockdown of the demethylase had the opposite effect. Further study showed that the m6A binding proteins also participate in the regulation of viral replication. In particular, two m6A modification sites were identified in the viral genome, of which mutations resulted in decreased virus replication, suggesting that m6A modification plays an important role in EV71 replication. Notably, we found that METTL3 interacted with viral RNA-dependent RNA polymerase 3D and induced enhanced sumoylation and ubiquitination of the 3D polymerase that boosted viral replication. Taken together, our findings demonstrated that the host m6A modification complex interacts with viral proteins to modulate EV71 replication.

Human parvovirus B19 (B19V) is a member of the genus Erythrovirus in the family Parvoviridae. In vitro, autonomous B19V replication is limited to human erythroid progenitor cells and in a small number of erythropoietin-dependent human megakaryoblastoid and erythroid leukemic cell lines. Here we report that the failure of B19V DNA replication in nonpermissive 293 cells can be overcome by adenovirus infection. More specifically, the replication of B19V DNA in the 293 cells and the production of infectious progeny virus were made possible by the presence of the adenovirus E2a, E4orf6, and VA RNA genes that emerged during the transfection of the pHelper plasmid. Using this replication system, we identified the terminal resolution site and the nonstructural protein 1 (NS1) binding site on the right terminal palindrome of the viral genome, which is composed of a minimal origin of replication spanning 67 nucleotides. Plasmids or DNA fragments containing an NS1 expression cassette and this minimal origin were able to replicate in both pHelper-transfected 293 cells and B19V-semipermissive UT7/Epo-S1 cells. Our results have important implications for our understanding of native B19V infection.

Parvovirus B19 (B19V) infection is highly restricted to human erythroid progenitor cells. Although previous studies have led to the theory that the basis of this tropism is receptor expression, this has been questioned by more recent observation. In the study reported here, we have investigated the basis of this tropism, and a potential role of erythropoietin (Epo) that EpoR signaling is absolutely required for B19V replication in ex vivo-expanded erythroid progenitor cells after initial virus entry and at least partly accounts for the remarkable tropism of B19V infection for human erythroid progenitors.Parvovirus B19 (B19V) is pathogenic to humans. It replicates autonomously and belongs to the genus Erythrovirus in the family Parvoviridae (14). Clinical manifestations of B19V infection vary among different health conditions. The most common manifestation is erythema infectiosum. However, B19V infection often results in bone marrow failure under the following conditions (9, 10, 62). In patients with increased destruction of erythrocytes and a high turnover of erythrocytes (e.g., sickle cell disease patients), acute B19V infection can cause transient aplastic crisis. In immunocompromised patients, persistent B19V infection may develop manifestations as pure red-cell aplasia, a chronic anemia. Moreover, B19V fetal infection can cause severe anemia in the fetus, resulting in nonimmune hydrops fetalis and fetal death (1,2,16,47,57).Erythropoiesis is the process whereby a fraction of primitive multipotent hematopoietic stem cells (CD34 ϩ ) commit to the erythroid lineage, forming burst-forming units-erythroid (BFU-E; earlier erythroid progenitor) cells, CFU-erythroid (CFU-E; later erythroid progenitor) cells, normoblasts, erythroblasts, reticulocytes, and ultimately, mature erythrocytes. B19V infection shows a remarkable tropism for BFU-E and CFU-E progenitors in human bone marrow and fetal livers. Notably, both cell types express the cell surface marker CD36 (30,39,50,60). The clinical manifestations of B19V infection seen in both aplastic crisis and pure red-cell aplasia are direct outcomes of cell death of the erythroid progenitors that are targets of B19V replication, and this cell death is due to direct cytotoxicity of the virus infection (9, 13). Progressive host cell apoptosis has been observed during B19V infection of erythroid progenitor cells (29,49,60), and this is likely induced during infection of the abundantly expressed 11-kDa nonstructural protein of the virus (12). Apoptosis of erythroid progenitor cells is also characteristic of B19V-induced hydrops fetalis (60).Polyadenylation at the proximal site [(pA)p], which is located in the center of the B19V genome, precludes the inclusion of the capsid-encoding open reading frame (ORF) in transcripts under some conditions (38,61). We have recently shown that replication of the B19V genome enhances readthrough of the (pA)p and, thereafter, the polyadenylation of B19V transcripts at the distal site. Therefore, replication of the B19V genome facilitates the p...

The pre-mRNA processing strategy of the B19 virus is unique among parvoviruses. B19 virus-generated pre-mRNAs are transcribed from a single promoter and are extensively processed by alternative splicing and alternative polyadenylation to generate 12 transcripts. Blockage of the production of full-length B19 virus transcripts at the internal polyadenylation site [(pA)p] was previously reported to be a limiting step in B19 virus permissiveness. We show here that in the absence of genome replication, internal polyadenylation of B19 virus RNAs at (pA)p is favored in cells which are both permissive and nonpermissive for B19 viral replication. The human parvovirus B19 virus (B19V) is a member of the Erythrovirus genus in the subfamily Parvoviridae (8, 41). B19V causes a number of human diseases, such as fifth disease in children, arthropathy, particularly in women, transient aplastic crisis in individuals with a high red cell turnover rate, pure red cell aplasia in immunocompromised patients, and hydrops fetalis following infection of pregnant women (4).The B19V virion is approximately 20 nm in diameter and contains a single-stranded DNA genome of either plus or minus polarity. The left-hand portion of the genome contains the NS-encoding region, which is essential for virus replication, transcription transactivation, and cytotoxicity. The right-hand portion harbors the sequences for the two structural proteins, VP1 and VP2. At least 12 transcripts are generated by alternative splicing and alternative polyadenylation from a single pre-mRNA that is transcribed from the single promoter at map unit 6 (P6) (Fig. 1) (24, 46). B19V transcripts polyadenylated at the proximal polyadenylation site [(pA)p] accumulate as either spliced or unspliced mRNAs. As unspliced mRNAs, they encode the nonstructural NS1 protein, which is essential for virus replication. Spliced RNAs polyadenylated internally at (pA)p encode a 7.5-kDa protein whose function is unknown. All B19V transcripts detected so far that are polyadenylated at the distal polyadenylation site [(pA)d] excise the first intron (D1 to A1-1 or D1 to A1-2) (Fig. 1). Those that are not additionally spliced encode the capsid protein VP1. RNAs in which the second intron (D2 to A2-1) is additionally spliced encode the capsid protein VP2, while those additionally spliced between D2 and A2-2 encode the nonstructural 11-kDa protein that is essential for virus export from the nuclei (38, 48). Two internal polyadenylation sites, (pA)p1 and (pA)p2, have been identified. (pA)p1, which accounts for approximately 90% of the internal polyadenylation events, has a noncanonical cleavage and polyadenylation specificity factor binding motif (AUUAAA) located at nucleotide (nt) 2819. (pA)p2, which accounts for approximately 10% of the internal polyadenylation events, has a canonical signal of AAUAAA located at nt 3115 (46). B19V has been shown to undergo productive replication in erythroid progenitors of human hematopoietic stem cells (26,37). Different disease manifestations are due to the direct...

No abstract

Human parvovirus B19 (B19V) infection shows a strong erythroid tropism and drastically destroys erythroid progenitor cells, thus leading to most of the disease outcomes associated with B19V infection. In this study, we systematically examined the 3 B19V nonstructural proteins, 7.5kDa, 11kDa, and NS1, for their function in inducing apoptosis in transfection of primary ex vivo-expanded erythroid progenitor cells, in comparison with apoptosis induced during B19V infection. Our results show that 11kDa is a more significant inducer of apoptosis than NS1, whereas 7.5kDa does not induce apoptosis. Furthermore, we determined that caspase-10, an initiator caspase in death receptor signaling, is the most active caspase in apoptotic erythroid progenitors induced by 11kDa and NS1 as well as during B19V infection. More importantly, cytoplasm-localized 11kDa is expressed at least 100 times more than nucleuslocalized NS1 at the protein level in primary erythroid progenitor cells infected with B19V; and inhibition of 11kDa expression using antisense oligos targeting specifically to the 11kDa-encoding mRNAs reduces apoptosis significantly during B19V infection of erythroid progenitor cells. Taken together, these results demonstrate that the 11kDa protein contributes to erythroid progenitor cell death during B19V infection. (Blood.

Tilapia is one of the most important economic and fastest-growing species in aquaculture worldwide. In 2015, an epidemic associated with severe mortality occurred in adult tilapia in Hubei, China. The causative pathogen was identified as Tilapia parvovirus (TiPV) by virus isolation, electron microscopy, experimental challenge, In situ hybridization (ISH), indirect immunofluorescence (IFA), and viral gene sequencing. Electron microscopy revealed large numbers of parvovirus particles in the organs of diseased fish, including kidney, spleen, liver, heart, brain, gill, intestine, etc. The virions were spherical in shape, non-enveloped and approximately 30nm in diameter. The TiPV was isolated and propagated in tilapia brain cells (TiB) and induced a typical cytopathic effect (CPE) after 3 days post-infection (dpi). This virus was used to experimentally infect adult tilapia and clinical disease symptoms similar to those observed naturally were replicated. Additionally, the results of ISH and IFA showed positive signals in kidney and spleen tissues from TiPV-infected fish. To identify TiPV-specific sequences, the near complete genome of TiPV was obtained and determined to be 4269 bp in size. Phylogenetic analysis of the NS1 sequence revealed that TiPV is a novel parvovirus, forms a separate branch in proposed genus Chapparvovirus of Parvoviridae . Results presented here confirm that TiPV is a novel parvovirus pathogen that can cause massive mortality in adult tilapia. This provides a basis for the further studies to define the epidemiology, pathology, diagnosis, prevention and treatment of this emerging viral disease.