USP inhibitors (Ellipses)

Ubiquitin-specific proteases represent a family of enzymes that catalyze the cleavage of ubiquitin from specific substrate proteins to regulate their activity. USP48 is a rarely studied USP, which has recently been linked to inflammatory signaling via regulation of the transcription factor nuclear factor kappa B. Nonetheless, a crystal structure of USP48 has not yet been resolved and potent inhibitors are not known. We screened a set of 14 commercially available USP inhibitors for their activity against USP48 and identified the USP2 inhibitor "ML364" as a candidate for further optimization. Using a ligand-based approach, we derived and synthesized a series of ML364 analogs. The IC₅₀ concentrations of the new compounds to inhibit USP48 were determined in a deubiquitinylase activity assay by measuring the fluorescence intensity using tetra-ubiquitin rhodamine110 as substrate. A compound containing a carboxylic acid functionalization (17e) inhibited USP48 activity toward tetra-ubiquitin rhodamine110 with an IC₅₀ of 12.6 µM. Further structure-based refinements are required to improve the inhibition activity and specificity.

Alphaherpesvirus infection results in severe health consequences in a wide range of hosts. USPs are the largest subfamily of deubiquitinating enzymes that play critical roles in immunity and other cellular functions. To investigate the role of USPs in alphaherpesvirus replication, we assessed 13 USP inhibitors for PRV replication. Our data showed that all the tested compounds inhibited PRV replication, with the USP14 inhibitor b-AP15 exhibiting the most dramatic effect. Ablation of USP14 also influenced PRV replication, whereas replenishment of USP14 in USP14 null cells restored viral replication. Although inhibition of USP14 induced the K63-linked ubiquitination of PRV VP16 protein, its degradation was not dependent on the proteasome. USP14 directly bound to ubiquitin chains on VP16 through its UBL domain during the early stage of viral infection. Moreover, USP14 inactivation stimulated EIF2AK3/PERK- and ERN1/IRE1-mediated signaling pathways, which were responsible for VP16 degradation through SQSTM1/p62-mediated selective macroautophagy/autophagy. Ectopic expression of non-ubiquitinated VP16 fully rescued PRV replication. Challenge of mice with b-AP15 activated ER stress and autophagy and inhibited PRV infection in vivo. Our results suggested that USP14 was a potential therapeutic target to treat alphaherpesvirus-induced infectious diseases.Abbreviations ATF4: activating transcription factor 4; ATF6: activating transcription factor 6; ATG5: autophagy related 5; ATG12: autophagy related 12; CCK-8: cell counting kit-8; Co-IP: co-immunoprecipitation; CRISPR: clustered regulatory interspaced short palindromic repeat; Cas9: CRISPR associated system 9; DDIT3/CHOP: DNA-damage inducible transcript 3; DNAJB9/ERdj4: DnaJ heat shock protein family (Hsp40) member B9; DUBs: deubiquitinases; EIF2A/eIF2α: eukaryotic translation initiation factor 2A; EIF2AK3/PERK: eukaryotic translation initiation factor 2 alpha kinase 3; EP0: ubiquitin E3 ligase ICP0; ER: endoplasmic reticulum; ERN1/IRE1: endoplasmic reticulum (ER) to nucleus signaling 1; FOXO1: forkhead box O1; FRET: Förster resonance energy transfer; HSPA5/BiP: heat shock protein 5; HSV: herpes simplex virus; IE180: transcriptional regulator ICP4; MAP1LC3/LC3: microtube-associated protein 1 light chain 3; MOI: multiplicity of infection; MTOR: mechanistic target of rapamycin kinase; PPP1R15A/GADD34: protein phosphatase 1, regulatory subunit 15A; PRV: pseudorabies virus; PRV gB: PRV glycoprotein B; PRV gE: PRV glycoprotein E; qRT-PCR: quantitative real-time polymerase chain reaction; sgRNA: single guide RNA; siRNA: small interfering RNA; SQSTM1/p62: sequestosome 1; TCID₅₀: tissue culture infective dose; UB: ubiquitin; UBA: ubiquitin-associated domain; UBL: ubiquitin-like domain; UL9: DNA replication origin-binding helicase; UPR: unfolded protein response; USPs: ubiquitin-specific proteases; VHS: virion host shutoff; VP16: viral protein 16; XBP1: X-box binding protein 1; XBP1s: small XBP1; XBP1(t): XBP1-total.