Caspase proteolysis of the integrin β4 subunit disrupts hemidesmosome assembly, promotes apoptosis, and inhibits cell migration

Caspases are a conserved family of cell death proteases that cleave intracellular substrates at Asp residues to modify their function and promote apoptosis. In this report we identify the integrin β4 subunit as a novel caspase substrate using an expression cloning strategy. Together with its α6 partner, α6β4 integrin anchors epithelial cells to the basement membrane at specialized adhesive structures known as hemidesmosomes and plays a critical role in diverse epithelial cell functions including cell survival and migration. We show that integrin β4 is cleaved by caspase-3 and -7 at a conserved Asp residue (Asp¹¹⁰⁹) in vitro and in epithelial cells undergoing apoptosis, resulting in the removal of most of its cytoplasmic tail. Caspase cleavage of integrin β4 produces two products, 1) a carboxyl-terminal product that is unstable and rapidly degraded by the proteasome and 2) an amino-terminal cleavage product (amino acids 1-1109) that is unable to assemble into mature hemidesmosomes. We also demonstrate that caspase cleavage of integrin β4 sensitizes epithelial cells to apoptosis and inhibits cell migration. Taken together, we have identified a previously unrecognized proteolytic truncation of integrin β4 generated by caspases that disrupts key structural and functional properties of epithelial cells and promotes apoptosis.