Abstract
Influenza A virus (IAV) has historically coexisted with humankind. Being an RNA virus with a segmented genome, IAV undergoes constant genetic drift and shift, causing global outbreaks. The lack of a universal vaccine against IAV poses a significant burden on healthcare systems, highlighting the need for further research to develop long-lasting antiviral strategies. Furthermore, the varied pathogenesis of IAV subtypes in different hosts and humans of different ethnicities highlights the need to understand the molecular basis of IAV pathogenesis. To facilitate replication, IAV manipulates the expression of several host proteins. One such proteins family is the histone deacetylases (HDACs). Recently, HDACs have emerged as anti-IAV factors, and in turn, IAV antagonises HDACs. The highly conserved sole member of class IV HDAC, HDAC11, also exhibits anti-IAV properties. HDAC11 exerts its anti-IAV function by regulating the IAV-induced expression of interferon-stimulated genes (ISGs), including ISG15, IFITM3, and viperin. In turn, IAV antagonises HDAC11 by downregulating its expression at the mRNA level.
This study aimed to investigate the mechanisms underlying the antagonism of HDAC11 and the effector molecules involved in its antiviral response during IAV (H1N1) infection. For the former, we analysed HDAC11 protein levels in human lung epithelial cells (A549) infected with IAV under different infection conditions. For the latter, we analysed the HDAC11 network using Sequential Window Acquisition of all Theoretical Mass Spectrometry (SWATH-MS) in HDAC11-depleted A549 cells. Our study demonstrated that IAV downregulates HDAC11 protein levels in a dose-dependent, time-dependent, and strain-independent manner. IAV utilises the host proteasomal machinery to exert its antagonistic effect on HDAC11 protein. In addition, we found that the IAV PA protein is involved in the antagonism of HDAC11 at both the mRNA and protein levels. Conversely, using high-throughput proteomic analysis, we identified that HDAC11 regulates the expression of several ISGs that are predominantly involved in the defence response to viruses. The shortlisted differentially expressed proteins (DEPs) were validated using western blotting. We found that during IAV infection, the expression of Mx1, TRIM21, and IFIT1 was positively regulated by HDAC11. We found that HDAC11 regulates Mx1 protein via both IFN-a and IFN-g signalling. Furthermore, upon HDAC11 overexpression, we observed significant upregulation of Mx1 at both the mRNA and protein levels in IAV infected and uninfected A549 cells. Interestingly, findings from IFN-a treatment indicate that HDAC11, apart from regulating several ISGs, could be an ISG. Overall, this study elucidates the effector molecules involved in the HDAC11 antiviral network and demonstrates that IAV employs proteasomal machinery to degrade the HDAC11 protein. Ultimately, this study contributes to our understanding of the HDAC11-IAV axis as a potential target for host-directed antiviral therapies and determines the basis of IAV pathogenesis in different populations.