Beta-catenin levels influence rapid mechanical responses in osteoblasts

J Biol Chem. 2008 Oct 24;283(43):29196-205. doi: 10.1074/jbc.M801907200. Epub 2008 Aug 22.

Abstract

Mechanical loading of bone initiates an anabolic, anticatabolic pattern of response, yet the molecular events involved in mechanical signal transduction are not well understood. Wnt/beta-catenin signaling has been recognized in promoting bone anabolism, and application of strain has been shown to induce beta-catenin activation. In this work, we have used a preosteoblastic cell line to study the effects of dynamic mechanical strain on beta-catenin signaling. We found that mechanical strain caused a rapid, transient accumulation of active beta-catenin in the cytoplasm and its translocation to the nucleus. This was followed by up-regulation of the Wnt/beta-catenin target genes Wisp1 and Cox2, with peak responses at 4 and 1 h of strain, respectively. The increase of beta-catenin was temporally related to the activation of Akt and subsequent inactivation of GSK3beta, and caveolin-1 was not required for these molecular events. Application of Dkk-1, which disrupts canonical Wnt/LRP5 signaling, did not block strain-induced nuclear translocation of beta-catenin or up-regulation of Wisp1 and Cox2 expression. Conditions that increased basal beta-catenin levels, such as lithium chloride treatment or repression of caveolin-1 expression, were shown to enhance the effects of strain. In summary, mechanical strain activates Akt and inactivates GSK3beta to allow beta-catenin translocation, and Wnt signaling through LRP5 is not required for these strain-mediated responses. Thus, beta-catenin serves as both a modulator and effector of mechanical signals in bone cells.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Active Transport, Cell Nucleus
  • Animals
  • Bone and Bones / metabolism
  • CCN Intercellular Signaling Proteins
  • Caveolin 1 / metabolism
  • Cell Nucleus / metabolism
  • Cyclooxygenase 2 / metabolism
  • Cytoplasm / metabolism
  • Glycogen Synthase Kinase 3 / metabolism
  • Glycogen Synthase Kinase 3 beta
  • Mice
  • Models, Biological
  • Oncogene Proteins / metabolism
  • Osteoblasts / metabolism*
  • Phosphorylation
  • Proto-Oncogene Proteins
  • Signal Transduction
  • beta Catenin / biosynthesis*
  • beta Catenin / metabolism
  • beta Catenin / physiology

Substances

  • CCN Intercellular Signaling Proteins
  • CCN4 protein, mouse
  • Caveolin 1
  • Oncogene Proteins
  • Proto-Oncogene Proteins
  • beta Catenin
  • Ptgs2 protein, mouse
  • Cyclooxygenase 2
  • Glycogen Synthase Kinase 3 beta
  • Gsk3b protein, mouse
  • Glycogen Synthase Kinase 3