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Differential role of MEK5alpha and MEK5beta in BMK1/ERK5 activation

Scott J Cameron1, Jun-Ichi Abe, Sundeep Malik

  • 1Department of Pharmacology/Physiology, Center for Cardiovascular Research, Department of Anesthesiology, University of Rochester Medical Center, Rochester, New York 14642, USA.

The Journal of Biological Chemistry
|October 30, 2003
PubMed

Insights

Alternative splicing of MEK5 (MAP kinase kinase 5) generates alpha and beta variants that differentially regulate big mitogen-activated protein kinase 1 (BMK1/ERK5) activation and cell proliferation, with MEK5beta exhibiting dominant-negative effects.

Area of Science:

  • Cellular signaling pathways
  • Molecular biology
  • Cancer research

Background:

  • Big mitogen-activated protein kinase 1/extracellular-regulated kinase 5 (BMK1/ERK5) is a key regulator in cellular signaling.
  • Upstream MAP kinase kinases (MEKs) activate BMK1/ERK5 through phosphorylation.
  • MEK5 exists as two splice variants, MEK5alpha and MEK5beta, with unknown functional differences.

Purpose of the Study:

  • To investigate the functional differences between MEK5alpha and MEK5beta splice variants.
  • To elucidate the role of MEK5 splice variants in BMK1/ERK5 activation and cell proliferation.

Main Methods:

  • Site-directed mutagenesis to create phosphorylation site mutants of MEK5alpha and MEK5beta.
  • Co-immunoprecipitation assays to assess protein interactions.
  • Western blotting to detect protein activation and nuclear translocation.
  • Analysis of MEF2 transcriptional activity and DNA synthesis.

Main Results:

  • MEK5alpha, but not MEK5beta, activated BMK1/ERK5 kinase activity and nuclear translocation upon dual phosphorylation site mutation.
  • MEK5beta inhibited both epidermal growth factor-induced BMK1/ERK5 activation and MEK5alpha-induced MEF2 activity.
  • MEK5beta interfered with MEK5alpha binding to BMK1/ERK5, explaining its dominant-negative effect.
  • The ratio of MEK5alpha to MEK5beta was elevated in cancer cell lines, and MEK5beta overexpression inhibited DNA synthesis.

Conclusions:

  • Alternative splicing of MEK5 generates functionally distinct variants, MEK5alpha and MEK5beta.
  • MEK5beta acts as a dominant-negative regulator of BMK1/ERK5 activation.
  • Differential expression of MEK5 splice variants may contribute to aberrant BMK1/ERK5 signaling and proliferation in cancer.

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