Nuclear localization and apoptotic regulation of an amino-terminal domain focal adhesion kinase fragment in endothelial cells

This study investigated the subcellular compartmentalization of focal adhes ion kinase (FAK) fragments and their regulation during apoptosis of human u mbilical vein endothelial cells. A 50 kDa NH2-terminal FAK fragment and a 1 20 kDa FAB variant were constitutively expressed and specifically found in the nuclear fraction of cells, while a 55 kDa COOH-terminal FAK fragment wa s only in the cytosolic fraction, FAK cleavage fragments generated during a poptosis remained in the cytosol, while p120FAK and p50 NH2-terminal FAK re mained in the nuclear compartment, The caspase inhibitor, ZVAD-fmk, prevent ed the apoptosis-induced proteolysis of p125 and p120FAK, generation of the 80 kDa cleavage product, and increased expression of p50N-FAK. Western blo t with phospho-specific FAB: showed that nuclear p125(FAK) was phosphorylat ed at a significant level at Y861, while FAB phosphorylated at Y397 and Y40 7 was largely in the cytosol. These results indicate that FAK NH2- and COOH -terminal domain fragments are segregated between nuclear and cytosolic com partments in endothelial cells and suggest novel functions for the FAK NH2- terminal domain. (C) 2000 Academic Press.