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MST2 kinase regulates osteoblast differentiation by phosphorylating and inhibiting Runx2 in C2C12 cells

Gun Woo Won1, Minji Sung1, YoungJoo Lee2

  • 1Department of Biochemistry, College of Medicine, Chungbuk National University, Cheongju, Chungbuk, 28644, South Korea.

Biochemical and Biophysical Research Communications
|March 27, 2019
PubMed

Insights

The mammalian Ste20-like kinase (MST) pathway regulates osteoblast differentiation by interacting with Runx2. This pathway inhibits Runx2 activity and reduces key osteoblast marker gene expression.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Developmental Biology

Background:

  • The mammalian Ste20-like kinase (MST) pathway, also known as the Hippo pathway, is crucial for regulating cell proliferation, apoptosis, and organ size.
  • Runx2 is a critical transcription factor essential for osteoblast differentiation, the process of bone formation.

Purpose of the Study:

  • To investigate the potential role of the MST pathway in modulating Runx2 activity and osteoblast differentiation.
  • To elucidate the molecular mechanisms underlying MST pathway regulation of Runx2.

Main Methods:

  • Interaction studies using co-immunoprecipitation to identify binding partners of Runx2.
  • Luciferase reporter assays to assess the transcriptional activity of Runx2.
  • Quantitative real-time PCR and enzyme activity assays to measure osteoblast differentiation markers.
  • Mass spectrometry to identify phosphorylation sites on Runx2.
  • Site-directed mutagenesis to confirm the functional significance of phosphorylation sites.

Main Results:

  • Runx2 was found to interact with MST2 and SAV1.
  • Co-expression of MST2 and SAV1 inhibited Runx2 transcriptional activity, while their down-regulation enhanced it.
  • MST2 and SAV1 significantly reduced the expression of osteoblast differentiation markers (alkaline phosphatase, osteocalcin) and impaired Runx2-induced osteoblast differentiation.
  • Two novel phosphorylation sites (Ser-339 and Ser-370) on mouse Runx2 were identified.
  • Mutation of these phosphorylation sites abolished the inhibitory effects of MST2 and SAV1 on Runx2 activity and osteoblast differentiation.

Conclusions:

  • The MST kinase pathway directly regulates osteoblast differentiation.
  • This regulation occurs through the modulation of Runx2 activity via phosphorylation at specific serine residues.
  • The findings provide novel insights into the molecular mechanisms controlling bone formation and the role of the Hippo pathway in this process.
Keywords:
HippoMSTOsteoblast differentiationPhosphorylationRunx2SAV1

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