Abstract
Influenza remains one of the most prevalent viral infections worldwide, once again surpassing COVID-19 in infection rates, and continues to place a substantial burden on global public health. Highly pathogenic avian influenza (HPAI) virus strains, often arising from different influenza A virus (IAV) strains through genetic shift or drift, pose particular concern. Therefore, it is important to investigate the host–IAV interactions to identify the determinants of IAV pathogenesis, particularly for severe flu.
Histone deacetylase 1 (HDAC1), a class I deacetylase with established roles in gene expression and innate immunity, and tripartite motif-containing protein 21 (TRIM21), an E3 ubiquitin ligase and interferon-stimulated gene, both change expression following IAV infection and show increased association. However, the functional implications of this interaction remain unclear.
Here, we characterized HDAC1–TRIM21 association during IAV infection using a human lung epithelial cell model (A549). We hypothesized that this interaction could be pro-viral, by TRIM21 targeting HDAC1 for ubiquitination and degradation, or antiviral, with HDAC1 employing TRIM21 as an effector protein within its complex. Protein levels were examined via quantitative western blot following small interfering RNA (siRNA)-mediated knockdown of HDAC1 or TRIM21.
We observed a significant increase in TRIM21 protein levels post-infection, while HDAC1 levels showed no conclusive change. HDAC1 knockdown insignificantly seemed to reduce TRIM21 protein levels under basal conditions; however, infection again insignificantly restored TRIM21 expression to levels seemingly comparable to or higher than controls, suggesting infection-dependent stabilization or induction. Conversely, HDAC1 expression in TRIM21-depleted cells remained stable under basal and infected conditions but may suggest an elevation in TRIM21 knock down-infected cells, implying that TRIM21 may reduce HDAC1 levels post-infection in a pro-viral capacity. Plaque assays suggested a trend toward reduced viral titre in TRIM21 and HDAC1 knockdown cells, though differences were not statistically significant.
These findings indicate that TRIM21 could function as a pro-viral factor, as its depletion seemed to correlate with reduced viral effectiveness and restored HDAC1 abundance. In contrast, HDAC1 appears to exert limited regulation over TRIM21 protein levels. Together, these results suggest that TRIM21 may act on an alternative target within the HDAC1 complex, influencing infection outcomes. Further work should confirm this with more replicates and look to identify the specific ubiquitination targets and to define how this interplay impacts IAV pathogenesis. These data also point to HDAC1–TRIM21 dynamics as a potential source of infection biomarkers or surveillance markers of disease severity.