Mixed lineage kinase 3 inhibition induces T cell activation and cytotoxicity

Proc Natl Acad Sci U S A. 2020 Apr 7;117(14):7961-7970. doi: 10.1073/pnas.1921325117. Epub 2020 Mar 24.


Mixed lineage kinase 3 (MLK3), also known as MAP3K11, was initially identified in a megakaryocytic cell line and is an emerging therapeutic target in cancer, yet its role in immune cells is not known. Here, we report that loss or pharmacological inhibition of MLK3 promotes activation and cytotoxicity of T cells. MLK3 is abundantly expressed in T cells, and its loss alters serum chemokines, cytokines, and CD28 protein expression on T cells and its subsets. MLK3 loss or pharmacological inhibition induces activation of T cells in in vitro, ex vivo, and in vivo conditions, irrespective of T cell activating agents. Conversely, overexpression of MLK3 decreases T cell activation. Mechanistically, loss or inhibition of MLK3 down-regulates expression of a prolyl-isomerase, Ppia, which is directly phosphorylated by MLK3 to increase its isomerase activity. Moreover, MLK3 also phosphorylates nuclear factor of activated T cells 1 (NFATc1) and regulates its nuclear translocation via interaction with Ppia, and this regulates T cell effector function. In an immune-competent mouse model of breast cancer, MLK3 inhibitor increases Granzyme B-positive CD8+ T cells and decreases MLK3 and Ppia gene expression in tumor-infiltrating T cells. Likewise, the MLK3 inhibitor in pan T cells, isolated from breast cancer patients, also increases cytotoxic CD8+ T cells. These results collectively demonstrate that MLK3 plays an important role in T cell biology, and targeting MLK3 could serve as a potential therapeutic intervention via increasing T cell cytotoxicity in cancer.

Keywords: CD8+ T cell; MLK3; T cell activation; breast cancer; cytotoxic T cell.

Publication types

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

MeSH terms

  • Animals
  • Breast Neoplasms / blood
  • Breast Neoplasms / drug therapy
  • Breast Neoplasms / immunology*
  • Breast Neoplasms / pathology
  • Cell Line, Tumor / transplantation
  • Cyclophilin A / metabolism
  • Female
  • Humans
  • Lymphocyte Activation / drug effects
  • Lymphocytes, Tumor-Infiltrating / drug effects
  • Lymphocytes, Tumor-Infiltrating / immunology*
  • Lymphocytes, Tumor-Infiltrating / metabolism
  • MAP Kinase Kinase Kinases / antagonists & inhibitors
  • MAP Kinase Kinase Kinases / genetics
  • MAP Kinase Kinase Kinases / metabolism*
  • Mammary Neoplasms, Experimental / blood
  • Mammary Neoplasms, Experimental / immunology*
  • Mammary Neoplasms, Experimental / pathology
  • Mice
  • NFATC Transcription Factors / metabolism
  • Phosphorylation / drug effects
  • Phosphorylation / immunology
  • Primary Cell Culture
  • Protein Kinase Inhibitors / pharmacology
  • Protein Kinase Inhibitors / therapeutic use
  • Pyridines / pharmacology
  • Pyridines / therapeutic use
  • Pyrroles / pharmacology
  • Pyrroles / therapeutic use
  • T-Lymphocytes, Cytotoxic / drug effects
  • T-Lymphocytes, Cytotoxic / immunology*
  • T-Lymphocytes, Cytotoxic / metabolism
  • Tumor Escape / drug effects


  • NFATC Transcription Factors
  • Nfatc1 protein, mouse
  • Protein Kinase Inhibitors
  • Pyridines
  • Pyrroles
  • URMC-099
  • MAP Kinase Kinase Kinases
  • mitogen-activated protein kinase kinase kinase 11
  • Cyclophilin A