Expression of the cytoplasmic domain of β1 integrin induces apoptosis in adult rat ventricular myocytes (ARVM) via the involvement of caspase-8 and mitochondrial death pathway

Stimulation of β-adrenergic receptor (β-AR) induces cardiac myocyte apoptosis. Integrins, a family of cell-surface receptors, play an important role in the regulation of cardiac myocyte apoptosis and ventricular remodeling. Cleavage of extracellular domain of β1 integrin, also called integrin shedding, is observed during cardiac hypertrophy and progression to early heart failure. Here we show that stimulation of β-AR induces β1 integrin fragmentation in mouse heart. To examine the role of intracellular domain of β1 integrin in cardiac myocyte apoptosis, a chimeric receptor consisting of the cytoplasmic tail domain of β_1A integrin and the extracellular/transmembrane domain of the interleukin-2 receptor (TAC-β1) was expressed in adult rat ventricular myocytes (ARVM) using adenoviruses. TAC-β1 increased the percentage of apoptotic ARVM as measured by TUNEL-staining assay. TAC-β1-induced apoptosis was found to be associated with increased cytosolic cytochrome c and decreased mitochondrial membrane potential. TAC-β1 increased caspase-8 activity. Z-IETD-FMK, a specific caspase-8 inhibitor, significantly inhibited TAC-β1-induced apoptosis. TAC-β1 expression also increased cleavage of Bid, a pro-apoptotic Bcl-2 family protein. These data suggest that shedding of β1 integrin may be a mechanism of induction of apoptosis during β-AR-stimulated cardiac remodeling.