Protein tyrosine phosphatase-dependent proteolysis of focal adhesion complexes in endothelial cell apoptosis

Adenosine and/or homocysteine causes endothelial cell apoptosis, a mechanis m requiring protein tyrosine phosphatase (PTPase) activity. We investigated the role of focal adhesion contact disruption in adenosine-homocysteine en dothelial cell apoptosis. Analysis of focal adhesion kinase (FAK), paxillin , and vinculin demonstrated disruption of focal adhesion complexes after 4 h of treatment with adenosine-homocysteine followed by caspase-induced prot eolysis of FAK, paxillin, and p130(CAS). No significant changes were noted in tyrosine phosphorylation of FAK or paxillin. Pretreatment with the caspa se inhibitor Z-Val-Ala-Asp-fluoromethylketone prevented adenosine-homocyste ine-induced DNA fragmentation and FAK, paxillin, and p130(CAS) proteolysis. Asp-Glu-Val-Asp-ase activity was detectable in endothelial cells after 4 h of treatment with adenosine-homocysteine. The PTPase inhibitor sodium orth ovanadate did not prevent endothelial cell retraction or FAK, paxillin, or vinculin redistribution. Sodium orthovanadate did block adenosine-homocyste ine-induced FAK, paxillin, and p130(CAS) proteolysis and Asp-Glu-Val-Asp-as e activity. Thus disruption of focal adhesion contacts and caspase-induced degradation of focal adhesion contact proteins occurs in adenosine-homocyst eine endothelial cell apoptosis. Focal adhesion contact disruption induced by adenosine-homocysteine is independent of PTPase or caspase activation. T hese studies demonstrate that disruption of focal adhesion contacts is an e arly, but not an irrevocable, event in endothelial cell apoptosis.