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Constitutively active mutants of MAP kinase kinase (MEK1) induce growth factor-relaxation and oncogenicity when

A Brunet1, G Pagès, J Pouysségur

  • 1Centre de Biochimie-CNRS, Université de Nice, France.

Oncogene
|November 1, 1994
PubMed

Insights

Mitogen Activated Protein Kinase Kinase (MAPKK) activation is sufficient to trigger fibroblast proliferation. Constitutively active MAPKK mutants induced autonomous cell cycling and tumor formation, demonstrating sufficiency in growth factor signaling.

Area of Science:

  • Cellular Biology
  • Molecular Biology
  • Signal Transduction

Background:

  • Mitogen Activated Protein Kinase (MAPK) signaling pathways regulate cell surface to nucleus communication.
  • Previous studies established MAPK activation is necessary for fibroblast cell cycle progression from G0 to G1.
  • The sufficiency of MAPK activation in driving cell proliferation remained undetermined.

Purpose of the Study:

  • To determine if Mitogen Activated Protein Kinase Kinase (MAPKK) activation is sufficient to trigger cell proliferation.
  • To investigate the role of MAPKK-MAPK signaling in autonomous cell cycling.

Main Methods:

  • Generated constitutively active mutants of hamster MAPKK (S218D, S222D, S218D/S222D) by substituting phosphorylation sites with aspartic acid.
  • Expressed MAPKK mutants in Chinese hamster lung fibroblasts.
  • Assessed p42/p44 MAPK activation, early gene transcription (fos promoter), DNA synthesis reinitiation, and tumor formation in nude mice.

Main Results:

  • Mutants S218D and S218D/S222D exhibited 2- and 5-fold higher basal activity than serum-stimulated wild-type MAPKK, respectively.
  • These active MAPKK mutants induced p42 MAPK activation in growth factor-deprived cells.
  • S218D and S218D/S222D mutants promoted growth factor-independent early gene transcription, enhanced sensitivity to growth factors for DNA synthesis, autonomous cell cycling, and rapid tumor formation.

Conclusions:

  • Mitogen Activated Protein Kinase Kinase (MAPKK) and downstream Mitogen Activated Protein Kinase (MAPK) are sufficient to promote growth factor signals.
  • MAPKK-MAPK signaling is sufficient to drive autonomous cell cycling in fibroblasts.
  • This pathway's activation can lead to uncontrolled cell proliferation and tumor formation.

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