Nucleoporin TPR promotes tRNA nuclear export and protein synthesis in lung cancer cells

The robust proliferation of cancer cells requires vastly elevated levels of protein synthesis, which relies on a steady supply of aminoacylated tRNAs. Delivery of tRNAs to the cytoplasm is a highly regulated process, but the machinery for tRNA nuclear export is not fully elucidated. In this study, using a live cell imaging strategy that visualizes nascent transcripts from a specific tRNA gene in yeast, we identified the nuclear basket proteins Mlp1 and Mlp2, two homologs of the human TPR protein, as regulators of tRNA export. TPR expression is significantly increased in lung cancer tissues and correlated with poor prognosis. Consistently, knockdown of TPR inhibits tRNA nuclear export, protein synthesis and cell growth in lung cancer cell lines. We further show that NXF1, a well-known mRNA nuclear export factor, associates with tRNAs and mediates their transport through nuclear pores. Collectively, our findings uncover a conserved mechanism that regulates nuclear export of tRNAs, which is a limiting step in protein synthesis in eukaryotes.

Interaction of Nuclear Export Protein with G Protein Pathway Suppressor 2 (GPS2) Facilitates Influenza A Virus Replication by Weakening the Inhibition of GPS2 to RNA Synthesis and Ribonucleoprotein Assembly

ABSTRACT The nuclear export protein (NEP) serves multiple functions in the life cycle of influenza A virus (IAV). Identifying novel host proteins that interact with NEP and understanding their functions in IAV replication are of great interest. In this study, we screened and confirmed the direct interaction of G protein pathway suppressor 2 (GPS2) with NEP through a yeast two-hybrid screening assay and glutathione S-transferase pulldown and coimmunoprecipitation assays. Knockdown or knockout of GPS2 enhanced IAV titers, whereas overexpression of GPS2 impaired IAV replication, demonstrating that GPS2 acted as a negative host factor in IAV replication. Meanwhile, GPS2 inhibited viral RNA synthesis by reducing the assembly of IAV polymerase. Interestingly, IAV NEP interacted with GPS2 and mediated its nuclear export, thereby activating the degradation of GPS2. Thus, NEP-GPS2 interaction weakened the inhibition of GPS2 to viral polymerase activity and benefited virus replication. Overall, this study identified the novel NEP-binding host partner GPS2 as a critical host factor to participate in IAV replication. These findings provided novel insights into the interactions between IAV and host cells, revealing a new function for GPS2 during IAV replication. IMPORTANCE NEP is proposed to play multiple biologically important roles in the life cycle of IAV, which largely relies on host factors by interaction. Our study demonstrated that GPS2 could reduce the interaction between polymerase basic 1 (PB1) and PB2 and interfere with viral ribonucleoprotein (vRNP) assembly. Thus, GPS2 inhibited the RNA synthesis of IAV and negatively regulated its replication. Importantly, IAV NEP interacted with GPS2 and mediated the nuclear export of GPS2, thereby activating the degradation of GPS2. Thus, NEP-GPS2 interaction weakened the inhibition of GPS2 to viral polymerase activity and benefited virus replication.

INFLUENZA D VIRUSES - PATHOGENS FORMING A NEW GENUS IN THE ORTHOMYXOVIRIDAE FAMILY

Influenza pathogens belong to the Orthomyxoviridae family and are divided into genera: Influenzavirus A, B, C, D, as well as Quaranjavirus, Thogotovirus, and Isavirus. For the first time, the influenza D virus was isolated from swine nasal swabs in 2011 in the United States, and its widespread distribution among cattle in France, China, Italy, Ireland, Japan, and several African countries, as well as its ability to infect ferrets, guinea pigs, is further shown. Antibodies to influenza D virus are found in the blood serum of horses, sheep, goats, and in people who have been in contact with cattle. The RNA genome of the influenza D virus is represented by seven fragments responsible for the synthesis of nine proteins. The longest three segments encode for polymerases PB2, PB1, and P3; the fourth and fifth segments encode for hemagglutinin-esterase fusion protein – HEF and nucleoprotein – NP, respectively. The sixth fragment is involved in the synthesis of membrane polypeptides DM1 and DM2, which, in accordance, lines the viral membrane from the inside and performs the function of proton channels. The seventh segment encodes the non-structural protein NS1 and the nuclear export protein NEP; NS1 helps to neutralize cellular interferon and NEP mediates the nuclear export of ribonucleoprotein. Three phylogenetic lines of the influenza virus D are described – D/OK, D/660, and D/Japan, which must be taken into account when preparing vaccines. It is concluded that from its epidemiological, pathological and biological characteristics, the potential ability to cause disease in humans and be transmitted from person to person, new, more in-depth studies are required using ecological-virological and molecular genetic methods.