Disruption of alpha-actinin-integrin interactions at focal adhesions renders osteoblasts susceptible to apoptosis

Am J Physiol Cell Physiol. 2006 Nov;291(5):C909-21. doi: 10.1152/ajpcell.00113.2006. Epub 2006 Jun 28.

Abstract

Maintenance of bone structural integrity depends in part on the rate of apoptosis of bone-forming osteoblasts. Because substrate adhesion is an important regulator of apoptosis, we have investigated the role of focal adhesions in regulating bone cell apoptosis. To test this, we expressed a truncated form of alpha-actinin (ROD-GFP) that competitively displaces endogenous alpha-actinin from focal adhesions, thus disrupting focal adhesions. Immunofluorescence and morphometric analysis of vinculin and tyrosine phosphorylation revealed that ROD-GFP expression dramatically disrupted focal adhesion organization and reduced tyrosine phosphorylation at focal adhesions. In addition, Bcl-2 protein levels were reduced in ROD-GFP-expressing cells, but caspase 3 cleavage, poly(ADP-ribose) polymerase cleavage, histone H2A.X phosphorylation, and cytotoxicity were not increased due to ROD-GFP expression alone. Increases in both ERK and Akt phosphorylation were also observed in ROD-GFP-expressing cells, although inhibition of either ERK or Akt individually or together failed to induce apoptosis. However, we did find that ROD-GFP expression sensitized, whereas alpha-actinin-GFP expression protected, cells from TNF-alpha-induced apoptosis. Further investigation revealed that activation of TNF-alpha-induced survival signals, specifically Akt phosphorylation and NF-kappaB activation, was inhibited in ROD-GFP-expressing cells. The reduced expression of antiapoptotic Bcl-2 and inhibited survival signaling rendered ROD-GFP-expressing cells more susceptible to TNF-alpha-induced apoptosis. Thus we conclude that alpha-actinin plays a role in regulating cell survival through stabilization of focal adhesions and regulation of TNF-alpha-induced survival signaling.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Actinin / antagonists & inhibitors
  • Actinin / metabolism*
  • Actins / metabolism
  • Animals
  • Apoptosis / drug effects
  • Apoptosis / physiology*
  • Cell Survival / drug effects
  • Cell Survival / physiology
  • Enzyme Activation / drug effects
  • Extracellular Signal-Regulated MAP Kinases / metabolism
  • Focal Adhesions / drug effects
  • Focal Adhesions / metabolism*
  • Humans
  • Integrins / antagonists & inhibitors
  • Integrins / metabolism*
  • Mice
  • Mutant Proteins / metabolism*
  • NF-kappa B / metabolism
  • Osteoblasts / cytology*
  • Osteoblasts / drug effects
  • Phosphorylation / drug effects
  • Phosphotyrosine / metabolism
  • Protein Binding / drug effects
  • Proto-Oncogene Proteins c-akt / metabolism
  • Proto-Oncogene Proteins c-bcl-2 / metabolism
  • Rats
  • Receptors, Cell Surface / metabolism
  • Recombinant Fusion Proteins / metabolism
  • Stress Fibers / drug effects
  • Stress Fibers / metabolism
  • Tumor Necrosis Factor-alpha / pharmacology

Substances

  • Actins
  • Integrins
  • Mutant Proteins
  • NF-kappa B
  • Proto-Oncogene Proteins c-bcl-2
  • Receptors, Cell Surface
  • Recombinant Fusion Proteins
  • Tumor Necrosis Factor-alpha
  • Actinin
  • Phosphotyrosine
  • Proto-Oncogene Proteins c-akt
  • Extracellular Signal-Regulated MAP Kinases