16807302

pubmed:Citation

5

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.

eng

IM

MEDLINE

0363-6143

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NLM

C909-21

pubmed-meshheading:16807302-Actinin, pubmed-meshheading:16807302-Actins, pubmed-meshheading:16807302-Animals, pubmed-meshheading:16807302-Apoptosis, pubmed-meshheading:16807302-Cell Survival, pubmed-meshheading:16807302-Enzyme Activation, pubmed-meshheading:16807302-Extracellular Signal-Regulated MAP Kinases, pubmed-meshheading:16807302-Focal Adhesions, pubmed-meshheading:16807302-Humans, pubmed-meshheading:16807302-Integrins, pubmed-meshheading:16807302-Mice, pubmed-meshheading:16807302-Mutant Proteins, pubmed-meshheading:16807302-NF-kappa B, pubmed-meshheading:16807302-Osteoblasts, pubmed-meshheading:16807302-Phosphorylation, pubmed-meshheading:16807302-Phosphotyrosine, pubmed-meshheading:16807302-Protein Binding, pubmed-meshheading:16807302-Proto-Oncogene Proteins c-akt, pubmed-meshheading:16807302-Proto-Oncogene Proteins c-bcl-2, pubmed-meshheading:16807302-Rats, pubmed-meshheading:16807302-Receptors, Cell Surface, pubmed-meshheading:16807302-Recombinant Fusion Proteins, pubmed-meshheading:16807302-Stress Fibers, pubmed-meshheading:16807302-Tumor Necrosis Factor-alpha

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

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