USP inhibitors (Ellipses)

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.

Protein ubiquitination is an important mechanism for regulating the activity and levels of proteins under physiological conditions. Loss of regulation by protein ubiquitination leads to various diseases, such as cancer. Two types of enzymes, namely, E1/E2/E3 ligases and deubiquitinases, are responsible for controlling protein ubiquitination. The ubiquitin-specific peptidases (USPs) are the main members of the deubiquitinase family. Many studies have addressed the roles of USPs in various diseases. An increasing number of studies have indicated that USPs are critical for cancer progression, and some USPs have been used as targets to develop inhibitors for cancer prevention. Herein we collect and organize most of the recent studies on the roles of USPs in cancer progression and discuss the development of USP inhibitors for cancer therapy in the future.