Mediator Kinase Phosphorylation of STAT1 S727 Promotes Growth of Neoplasms With JAK-STAT Activation

Ioana I. Nitulescu, Sara C. Meyer, Qiang Jeremy Wen, John D. Crispino, Madeleine E. Lemieux, Ross L. Levine, Henry E. Pelish, Matthew D. Shair*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

27 Scopus citations


Constitutive JAK-STAT signaling drives the proliferation of most myeloproliferative neoplasms (MPN) and a subset of acute myeloid leukemia (AML), but persistence emerges with chronic exposure to JAK inhibitors. MPN and post-MPN AML are dependent on tyrosine phosphorylation of STATs, but the role of serine STAT1 phosphorylation remains unclear. We previously demonstrated that Mediator kinase inhibitor cortistatin A (CA) reduced proliferation of JAK2-mutant AML in vitro and in vivo and also suppressed CDK8-dependent phosphorylation of STAT1 at serine 727. Here we report that phosphorylation of STAT1 S727 promotes the proliferation of AML cells with JAK-STAT pathway activation. Inhibition of serine phosphorylation by CA promotes growth arrest and differentiation, inhibits colony formation in MPN patient samples and reduces allele burden in MPN mouse models. These results reveal that STAT1 pS727 regulates growth and differentiation in JAK-STAT activated neoplasms and suggest that Mediator kinase inhibition represents a therapeutic strategy to regulate JAK-STAT signaling.

Original languageEnglish (US)
Pages (from-to)112-125
Number of pages14
StatePublished - Dec 2017


  • CDK8
  • Cortistatin A
  • Kinase inhibitor
  • Leukemia
  • MPN
  • Ruxolitinib
  • STAT1
  • Super-enhancer

ASJC Scopus subject areas

  • Biochemistry, Genetics and Molecular Biology(all)


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