Kinase-Independent Small-Molecule Inhibition of JAK-STAT Signaling

J Am Chem Soc. 2015 Jun 24;137(24):7929-34. doi: 10.1021/jacs.5b04284. Epub 2015 Jun 15.


Phenotypic cell-based screening is a powerful approach to small-molecule discovery, but a major challenge of this strategy lies in determining the intracellular target and mechanism of action (MoA) for validated hits. Here, we show that the small-molecule BRD0476, a novel suppressor of pancreatic β-cell apoptosis, inhibits interferon-gamma (IFN-γ)-induced Janus kinase 2 (JAK2) and signal transducer and activation of transcription 1 (STAT1) signaling to promote β-cell survival. However, unlike common JAK-STAT pathway inhibitors, BRD0476 inhibits JAK-STAT signaling without suppressing the kinase activity of any JAK. Rather, we identified the deubiquitinase ubiquitin-specific peptidase 9X (USP9X) as an intracellular target, using a quantitative proteomic analysis in rat β cells. RNAi-mediated and CRISPR/Cas9 knockdown mimicked the effects of BRD0476, and reverse chemical genetics using a known inhibitor of USP9X blocked JAK-STAT signaling without suppressing JAK activity. Site-directed mutagenesis of a putative ubiquitination site on JAK2 mitigated BRD0476 activity, suggesting a competition between phosphorylation and ubiquitination to explain small-molecule MoA. These results demonstrate that phenotypic screening, followed by comprehensive MoA efforts, can provide novel mechanistic insights into ostensibly well-understood cell signaling pathways. Furthermore, these results uncover USP9X as a potential target for regulating JAK2 activity in cellular inflammation.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Apoptosis / drug effects
  • Cell Line
  • Cell Survival / drug effects
  • Humans
  • Insulin-Secreting Cells / cytology
  • Insulin-Secreting Cells / drug effects*
  • Insulin-Secreting Cells / immunology
  • Interferon-gamma / immunology*
  • Janus Kinase 2 / immunology*
  • Phosphorylation / drug effects
  • Protective Agents / chemistry*
  • Protective Agents / pharmacology*
  • Rats
  • STAT1 Transcription Factor / immunology*
  • Signal Transduction / drug effects
  • Ubiquitin Thiolesterase / immunology
  • Ubiquitination / drug effects


  • Protective Agents
  • STAT1 Transcription Factor
  • USP9X protein, human
  • Interferon-gamma
  • Janus Kinase 2
  • Ubiquitin Thiolesterase