Activation of MTK1/MEKK4 by GADD45 through induced N-C dissociation and dimerization-mediated trans autophosphorylation of the MTK1 kinase domain

Mol Cell Biol. 2007 Apr;27(7):2765-76. doi: 10.1128/MCB.01435-06. Epub 2007 Jan 22.


The mitogen-activated protein kinase (MAPK) module, composed of a MAPK, a MAPK kinase (MAPKK), and a MAPKK kinase (MAPKKK), is a cellular signaling device that is conserved throughout the eukaryotic world. In mammalian cells, various extracellular stresses activate two major subfamilies of MAPKs, namely, the Jun N-terminal kinases and the p38/stress-activated MAPK (SAPK). MTK1 (also called MEKK4) is a stress-responsive MAPKKK that is bound to and activated by the stress-inducible GADD45 family of proteins (GADD45alpha/beta/gamma). Here, we dissected the molecular mechanism of MTK1 activation by GADD45 proteins. The MTK1 N terminus bound to its C-terminal segment, thereby inhibiting the C-terminal kinase domain. This N-C interaction was disrupted by the binding of GADD45 to the MTK1 N-terminal GADD45-binding site. GADD45 binding also induced MTK1 dimerization via a dimerization domain containing a coiled-coil motif, which is essential for the trans autophosphorylation of MTK1 at Thr-1493 in the kinase activation loop. An MTK1 alanine substitution mutant at Thr-1493 has a severely reduced activity. Thus, we conclude that GADD45 binding induces MTK1 N-C dissociation, dimerization, and autophosphorylation at Thr-1493, leading to the activation of the kinase catalytic domain. Constitutively active MTK1 mutants induced the same events, but in the absence of GADD45.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • COS Cells
  • Chlorocebus aethiops
  • Dimerization
  • Enzyme Activation
  • Intracellular Signaling Peptides and Proteins / genetics
  • Intracellular Signaling Peptides and Proteins / metabolism*
  • MAP Kinase Kinase Kinase 4 / genetics
  • MAP Kinase Kinase Kinase 4 / metabolism*
  • Mutation
  • Phosphorylation
  • Protein Binding
  • Protein Structure, Tertiary
  • Signal Transduction
  • Tyrosine / metabolism


  • GADD45 protein
  • Intracellular Signaling Peptides and Proteins
  • Tyrosine
  • MAP Kinase Kinase Kinase 4