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Phosphorylation of myocardin by extracellular signal-regulated kinase

Sebastien Taurin1, Nathan Sandbo, Douglas M Yau

  • 1Department of Medicine, The University of Chicago, Chicago, Illinois 60637, USA.

The Journal of Biological Chemistry
|September 25, 2009
PubMed

Insights

Extracellular signal-regulated kinases (ERK1/2) directly phosphorylate myocardin, a key protein in smooth muscle (SM) gene expression. This phosphorylation impairs myocardin

Area of Science:

  • Molecular Biology
  • Cell Biology
  • Biochemistry

Background:

  • Smooth muscle (SM) cell contractile phenotype relies on serum response factor (SRF) and SM-specific genes.
  • Myocardin, a SRF coactivator, is crucial for SM gene transcription.
  • Growth factors activate ERK1/2, inhibiting SM gene transcription during SM cell proliferation.

Purpose of the Study:

  • To investigate the mechanism by which ERK1/2 regulates SM gene transcription.
  • To determine if ERK1/2 directly interacts with and modifies myocardin.
  • To elucidate the functional consequences of myocardin phosphorylation by ERK1/2.

Main Methods:

  • Site-directed mutagenesis of mouse myocardin (isoform B) at four identified phosphorylation sites.
  • Assays to evaluate myocardin's ability to activate SRF and stimulate SM gene expression (promoter, mRNA, protein).
  • Analysis of myocardin's interaction with cAMP response element-binding protein-binding protein (CBP).

Main Results:

  • ERK1/2 phosphorylates mouse myocardin at four specific sites within its transactivation domain.
  • Phosphomimetic mutation (4xD) of these sites significantly impairs SRF activation and SM gene expression.
  • Phosphorylation at these sites reduces myocardin's interaction with CBP, a transcriptional coactivator.

Conclusions:

  • ERK1/2 directly phosphorylates myocardin, representing a novel regulatory mechanism for SM gene transcription.
  • This phosphorylation modulates myocardin's transcriptional activity and interaction with coactivators.
  • Understanding this pathway offers insights into smooth muscle cell biology and potential therapeutic targets.

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