Novel role of cathepsin V in TLRs‐MyD88 mediated signaling revealed in HMGB1‐TLR4 inhibitor screening (835.9)

Abstract

Toll‐like receptors (TLRs) recognize pathogen‐derived molecular patterns (PAMP) and danger‐associated molecular patterns (DAMP), and induce NF‐κB‐dependent pro‐inflammatory cytokines release such as TNF‐α and IL‐6. High Mobility Group Box 1 (HMGB1) is a prototypical DAMP that drives inflammation in many sterile and infectious diseases signaling through TLR4. A cell‐based high‐throughput screening identified a FDA‐approved HIV protease inhibitor Saquinavir (SQV) as a potent inhibitor of HMGB1‐TLR4 mediated signaling. We have previously identified human cathepsin V (CTSV) as a mammalian target of SQV and confirmed CTSV involves in HMGB1‐TLR4 signaling using genetic knockdown and pharmacological inhibition. In this study, we expanded these previous evidence for TLR4 and tested the effects of SQV and SID266 (a known CTSV inhibitor) on TNF‐α production induced by TLR 1/2, 4 and 9, using the TLR ligands Pam3CSK4, LPS and ODN2006, respectively. Similar to HMGB1, SQV and SID266 diminish TNF‐α production in a concentration‐dependent manner. SQV also acts upstream in the TLR‐NF‐κB pathway by attenuating phosphorylation of IRAK4 and IKKα/β. The activities of SQV are shared by SID266. Hinted from the mechanistic properties of SQV and SID266, we found that CTSV physically interacts with MyD88 in PMA‐differentiated THP‐1 cells stimulated with HMGB1, LPS or Pam3CSK4, which could be blocked by SQV administration. Our study uncovers a previously unknown mechanism of cathepsin V in TLRs‐MyD88 mediated signaling and suggests a potential novel therapeutic target in related inflammatory diseases, and paves the way for re‐purposing a drug already safely in humans.Grant Funding Source: Department of Surgery, University of Pittsburgh