Cleavage of focal adhesion kinase by caspases during apoptosis.

Jun-Lin Guan,Sergiu Troie,Glenn D. Rosen,Kim Orth,Jimothy A. Fahrni,Long-Ping Wen

doi:10.1074/jbc.272.41.26056

Abstract

Apoptotic cells undergo characteristic morphological changes that include detachment of cell attachment from the substratum and loss of cell-cell interactions. Attachment of cells to the extracellular matrix and to other cells is mediated by integrins. The interactions of integrins with the extracellular matrix activates focal adhesion kinase (FAK) and suppresses apoptosis in diverse cell types. Members of the tumor necrosis family such as Fas and Apo-2L, also known as tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), induce apoptosis in both suspension and adherent cells through the activation of caspases. These caspases, when activated, cleave substrates that are important for the maintenance of nuclear and membrane integrity. In this study, we show that FAK is sequentially cleaved into two different fragments early in Apo-2L-induced apoptosis. We also demonstrate that FAK cleavage is mediated by caspases and that FAK shows unique sensitivity to different caspases. Our results suggest that disruption of FAK may contribute to the morphological changes observed in apoptotic suspension and adherent cells.

Highlights

Apoptotic cells undergo characteristic morphological changes that include detachment of cell attachment from the substratum and loss of cell-cell interactions
The precise function of focal adhesion kinase (FAK) is not known, but it may regulate the assembly of focal adhesions in spreading or migrating cells or it may participate in a signal transduction pathway to inform the nucleus that a cell is bound to the extracellular matrix (ECM), which may suppress apoptosis
The latter hypothesis is supported by recent studies which report the following: 1) FAK suppresses anoikis in epithelial cells; 2) inhibition of FAK in fibroblasts results in apoptosis; 3) attenuation of FAK induces apoptosis in tumor cells; and 4) FAK is cleaved early in myc-induced apoptosis of chick embryo fibroblasts and FAK cleavage, and apoptosis is inhibited by plating the cells on fibronectin or collagen (7, 26 –28)

Summary

Cleavage of Focal Adhesion Kinase by Caspases during Apoptosis*

Members of the tumor necrosis family such as Fas and Apo-2L, known as tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), induce apoptosis in both suspension and adherent cells through the activation of caspases. Richardson and Parsons [25] observed that overexpression of FRNK inhibits tyrosine phosphorylation of FAK, suggesting that FRNK may act as a competitive inhibitor of FAK The latter hypothesis is supported by recent studies which report the following: 1) FAK suppresses anoikis in epithelial cells; 2) inhibition of FAK in fibroblasts results in apoptosis; 3) attenuation of FAK induces apoptosis in tumor cells; and 4) FAK is cleaved early in myc-induced apoptosis of chick embryo fibroblasts and FAK cleavage, and apoptosis is inhibited by plating the cells on fibronectin or collagen (7, 26 –28). Our data suggest that cleavage of FAK by Apo-2L or Fas may cause some of the morphological changes in apoptotic cells

EXPERIMENTAL PROCEDURES

RESULTS AND DISCUSSION

Cleavage of Focal Adhesion Kinase during Apoptosis