Figure 5. Succinate impairs the intracellular trafficking of influenza virus.

• A
  Schematic representation of the IAV replication cycle. After endocytosis, the viral ribonucleoprotein (vRNP) complexes are transported into the nucleus. Viral RNAs (vRNAs) serve as templates for the synthesis of messenger RNAs (mRNAs) and complementary RNAs (cRNAs) are used for the replication of vRNAs. mRNAs are exported in the cytoplasm for translation. Some proteins are transported back to the nucleus to form new vRNPs with neosynthesized vRNAs. Newly synthesized vRNPs are exported in the cytoplasm via the CRM1 protein. HA, NA, M2 proteins and the vRNPs are transported to the plasma membrane for assembly and budding of the progeny virions.
• B–F
  Human bronchial epithelial BEAS‐2B cells were infected with A/Scotland/20/74 (H3N2) virus (IAV) at MOI = 1. After 4 h, cells were treated or not with succinate (Suc; 4 mg/ml) up to 20 h. The effect of succinate on IAV transcription (B) and protein expression (C) were assessed by RT‐qPCR to quantify the M1 viral mRNA and Western blotting to detect viral proteins (β‐actin was used as a loading control), respectively. (D–F) Human alveolar epithelial A549 cells were infected with the recombinant influenza A/WSN/33 virus expressing a fusion NS1‐eGFP protein at MOI = 0.5 for 4 h, then treated with 4 mg/ml of succinate. A549 cells were monitored for 24 h using a BioStation IM‐Q device. (D) Single‐cell dynamics of the nuclear/cytoplasmic fluorescence ratio. (E) Single‐cell dynamics of cell death as assessed by morphological analysis. (F) Quantification of the nuclear/cytoplasmic fluorescence ratio measured at 13 h postsuccinate treatment. Data are represented as the mean ± SEM of 3 biological replicates (B, C) or 3 independent experiments with 3 technical replicates each (D–F). Statistical analysis was performed using the Mann–Whitney test (B–E) or t‐test (F), (*P < 0.05 and ***P < 0.001).