IGF2BP1 Significantly Enhances Translation Efficiency of Duck Hepatitis A Virus Type 1 without Affecting Viral Replication.

As a disease characterized by severe liver necrosis and hemorrhage, duck viral hepatitis (DVH) is mainly caused by duck hepatitis A virus (DHAV). The positive-strand RNA genome of DHAV type 1 (DHAV-1) contains an internal ribosome entry site (IRES) element within the 5' untranslated region (UTR), structured sequence elements within the 3' UTR, and a poly(A) tail at the 3' terminus. In this study, we first examined that insulin-like growth factor-2 mRNA-binding protein-1 (IGF2BP1) specifically interacted with the DHAV-1 3' UTR by RNA pull-down assay. The interaction between IGF2BP1 and DHAV-1 3' UTR strongly enhanced IRES-mediated translation efficiency but failed to regulate DHAV-1 replication in a duck embryo epithelial (DEE) cell line. The viral propagation of DHAV-1 strongly enhanced IGF2BP1 expression level, and viral protein accumulation was identified as the key point to this increment. Collectively, our data demonstrated the positive role of IGF2BP1 in DHAV-1 viral proteins translation and provided data support for the replication mechanism of DHAV-1.

Identification of a functional nuclear localization signal in 3Dpol/3CD of duck hepatitis A virus 1.

The nuclear localization signals (NLS) were usually composed of basic residues (K and R) and played an important role in delivery of genomes and structural protein into nucleus. In this research, we identified that 3Dpol/3CD entered into nucleus during viral propagation of duck hepatitis A virus type 1 (DHAV-1). To investigate the reason that 3Dpol/3CD entered into nucleus, the amino acid sequence of 3CD was analyzed through NLS Mapper program. The basic region 17PRKTAYMRS25 was subsequently proved to be a functional NLS to guide 3Dpol/3CD into nucleus. 18R, 19K and 24R were found essential for maintaining the nuclear targeting activity, and exchange between 24R and 24K had no impact on cellular localization of 3Dpol. Since the entry of 3Dpol/3CD into nucleus was essential for shutoff of host cell transcription and maintaining the viral propagation of picornavirus numbers, our study provided new insights into the mechanism of DHAV-1 propagation.

SCFAs-Induced GLP-1 Secretion Links the Regulation of Gut Microbiome on Hepatic Lipogenesis in Chickens.

The impact of gut microbiota and its metabolites on fat metabolism have been widely reported in human and animals. However, the critical mediators and the signal transductions are not well demonstrated. As ovipara, chicken represents a specific case in lipid metabolism that liver is the main site of lipid synthesis. The aim of this study is to elucidate the linkage of gut microbiota and fat synthesis in broiler chickens. The broilers were subjected to dietary treatments of combined probiotics (Animal bifidobacterium: 4 × 108 cfu/kg; Lactobacillus plantarum: 2 × 108 cfu/kg; Enterococcus faecalis: 2 × 108 cfu/kg; Clostridium butyrate: 2 × 108 cfu/kg, PB) and guar gum (1 g/kg, GG), respectively. Results showed that dietary supplementation of PB and GG changed the cecal microbiota diversity, altered short chain fatty acids (SCFAs) contents, and suppressed lipogenesis. In intestinal epithelial cells (IECs), SCFAs (acetate, propionate, and butyrate) up-regulated the expression of glucagon-like peptide-1 (GLP-1) via mitogen-activated protein kinase (MAPK) pathways, mainly via the phospho - extracellular regulated protein kinase (ERK) and phospho-p38 mitogen activated protein kinase (p38 MAPK) pathways. GLP-1 suppressed lipid accumulation in primary hepatocytes with the involvement of (AMP)-activated protein kinase/Acetyl CoA carboxylase (AMPK/ACC) signaling. In conclusion, the result suggests that SCFAs-induced GLP-1 secretion via MAPK pathway, which links the regulation of gut microbiota on hepatic lipogenesis in chickens.

The Functional Role of the 3' Untranslated Region and Poly(A) Tail of Duck Hepatitis A Virus Type 1 in Viral Replication and Regulation of IRES-Mediated Translation.

The duck hepatitis A virus type 1 (DHAV-1) is a member of Picornaviridae family, the genome of the virus contains a 5' untranslated region (5' UTR), a large open reading frame that encodes a polyprotein precursor and a 3' UTR followed by a poly(A) tail. The translation initiation of virus proteins depends on the internal ribosome-entry site (IRES) element within the 5' UTR. So far, little information is known about the role of the 3' UTR and poly(A) tail during the virus proliferation. In this study, the function of the 3' UTR and poly(A) tail of DHAV-1 in viral replication and IRES-mediated translation was investigated. The results showed that both 3' UTR and poly(A) tail are important for maintaining viral genome RNA stability and viral genome replication. During DHAV-1 proliferation, at least 20 adenines were required for the optimal genome replication and the virus replication could be severely impaired when the poly (A) tail was curtailed to 10 adenines. In addition to facilitating viral genome replication, the presence of 3' UTR and poly(A) tail significantly enhance IRES-mediated translation efficiency. Furthermore, 3' UTR or poly(A) tail could function as an individual element to enhance the DHAV-1 IRES-mediated translation, during which process, the 3' UTR exerts a greater initiation efficiency than the poly(A)25 tail.