Overview of host-directed antiviral targets for future research and drug development

Figure 1. The biogenesis of miRNA. RNAP II transcripts (pri-miRNAs) undergo processing into miRNAs by the microprocessor and RISC, and meanwhile are transported out of the nucleus via nuclear export machinery. miRNAs associate with AGO2 to form the minimal RISC, guiding it to target mRNAs primarily by recognizing the 3′UTRs of mRNAs. The level of complementarity between miRNAs and their target mRNAs determines the fate of the mRNAs: direct degradation (high complementarity) or translational repression (lower complementarity). (Created in BioRender. Gu, X. (2025) https://BioRender.com/z08y439).

Figure 2. The antiviral mechanism of miR-124, miR-24, and miR-744. The p38 MAPK pathway receives upstream signal transduction, including signals from GPCR, DNA damage, oxidative stress, UV radiation, inflammatory cytokines, FasL, and TGF-β, and regulates downstream effectors, activating transcription and leading to cytokine production, apoptosis, and other cellular responses. miR-124, miR-24, and miR-744 have been identified as targeting the p38 MAPK signaling pathway, specifically focusing on the MK2 kinase. (Created in BioRender. Gu, X. (2025) https://BioRender.com/z08y439).

Figure 3. The mechanism of miR-342-5p regulating sterol metabolism. miR-342-5p targets the mevalonate-sterol biosynthesis pathway through a multi-hit mechanism, suppressing the pathway at various functional levels: transcriptionally viaSREBF2, post-transcriptionally via miR-33, and enzymatically viaIDI1 and SC4MOL. This leads to a reduction in intermediate sterol pathway metabolites and total cholesterol levels. (Created in BioRender. Gu, X. (2025) https://BioRender.com/z08y439).

Figure 4. The proviral mechanisms of miRNAs. The IL-6 family/IL-6R, IFN I/IFN receptors, TLRs, and CXCL12/CXCR pathways mediate diverse antiviral immune responses. In contrast, miRNAs such as miR-124, miR-1225-3p, miR-548, miR-23a, miR-135a, and miR-125a disrupt these antiviral responses at various levels. (Created in BioRender. Gu, X. (2025) https://BioRender.com/z08y439).

Figure 5. The IRF-mediated antiviral response and their regulation by viruses. IRF3 and IRF7 are activated by upstream signal transduction triggered by stimuli like DNA, RNA, and LPS from intracellular or extracellular sources, leading to the activation of the interferon response. Given their critical functions in antiviral responses, various viruses have developed specific proteins that target IRF3 and IRF7. (Created in BioRender. Gu, X. (2025) https://BioRender.com/z08y439).

Figure 6. The domain arrangement of ZAP and schematic of each domain's function. The comparison of PARP consensus residues is sourced from a recent report102. The full-length structure of ZAP is revealed through the AlphaFold-predicted model, while the complex structures of the N-terminal domain with RNA, the central domain with ADP-ribose, and the alignment of the PARP-like domain with PARP15 are elucidated by PDB entries 6UEJ, 7TJQ, 2X5Y (and 3BLJ for PARP15), respectively. (Created in BioRender. Gu, X. (2025) https://BioRender.com/z08y439).

Figure 7. The proviral effects of Hsp70 impact multiple stages of the viral infection cycle, such as entry, replication, assembly, and release, and involve various viruses, with their interacting proteins specified in the brackets. (Created in BioRender. Gu, X. (2025) https://BioRender.com/z08y439).

Figure 8. The vital role of the AMPK signaling pathway in cellular progress. This pathway integrates various signaling factors to govern diverse and essential cellular processes, encompassing cytoskeletal signaling, acute metabolic regulation, transcriptional control of metabolism, as well as protein metabolism and autophagy. (Created in BioRender. Gu, X. (2025) https://BioRender.com/z08y439).

Figure 9. The binding modes between ACE2 and the RBDs from the S proteins of SARS-CoV, NL63-CoV, and SARS-CoV-2. The upper left panel illustrates the binding mode between ACE2 and the S RBD from SARS-CoV or NL63-CoV, with VBMs distinguished by different colors. The upper right section displays the location of residues in ACE2's VBMs, color-coded to match the left side, and highlights contacting residues within a labeled dotted box (mirrored in the lower right diagram). The lower left section depicts the interaction between ACE2 and the S RBD from SARS-CoV or SARS-CoV-2, featuring RBMs in red, contacting residues represented as sticks, and equivalent residues marked in red. The letter ‘C’ signifies the shared contacting residues between SARS-CoV and SARS-CoV-2 during their ACE2 interaction. (Created in BioRender. Gu, X. (2025) https://BioRender.com/z08y439).

Figure 10. The domain arrangement of ACE2 and the S glycoprotein from SARS-CoV and SARS-CoV-2. Domains are depicted as purple boxes, while the transmembrane (TM) and intracellular (IC) regions are shown as dark and light yellow boxes, respectively. Interacting domains are illustrated as red boxes, with corresponding interacting proteins labeled above. The recognition sites of the two proteases, furin and TMPRSS2, are denoted by blue and orange arrow symbols, respectively. (Created in BioRender. Gu, X. (2025) https://BioRender.com/z08y439).

Figure 11. Host-directed targets in the purine and pyrimidine biosynthesis pathways. Panels (A) and (B) display the catalytic activities of four proteases (DHFR, CAD, DHODH, UMPS), with specific activities of multifunctional proteases indicated below the arrows. Panels (C–F) showcase complex structures of these proteases with their substrates, products, or inhibitors. Specifically, the structure of DHFR is detailed by PDB 4M6K with NADP+ and folic acid. The full-length CAD structure is depicted by the AlphaFold-predicted model, colored by domain, with specific domains detailed using PDB models. Notably, the GLNase domain and CPSase domain are yet to be resolved. The ATCase domain is illustrated by PDB 5G1P (CP denotes the substrate carbamoyl phosphate), while the DHOase domain is depicted by PDB 4C6I (CA-asp and DHO represent the substrate carbamoyl aspartate and the product dihydroorotic acid, respectively). The structure of DHODH is elaborated by PDB 6M2B, featuring the product orotic acid, the cofactor flavin mononucleotide (FMN), and the inhibitor S416. Lastly, the structure of UMPS is detailed by PDB 7AM9 with its substrate OMP and by PDB 7ASQ with the product UMP. (Created in…

Figure 12. The scheme of ubiquitin–proteasome system. Ubiquitination relies on three pivotal enzymes: ubiquitin-activating enzymes (E1), ubiquitin-conjugating enzymes (E2), and ubiquitin ligases (E3). Ubiquitin (Ub) can attach to targeted proteins via internal lysines (K6, K11, K27, K29, K33, K48, K63) or the amino-terminal methionine, resulting in a spectrum of ubiquitination modifications. This process can be counteracted by ubiquitin hydrolases/deubiquitinating enzymes (DUBs). These modifications may trigger the degradation of modified targets by the proteasome or facilitate diverse cellular processes. (Created in BioRender. Gu, X. (2025) https://BioRender.com/z08y439).