Myosin heavy chain degradation during apoptosis in endothelial cells

The cytoskeleton undergoes dramatic changes during apoptosis and many cytos keletal proteins are known to be degraded during this process. The number o f proteases found to be involved in apoptosis is growing but the role of th e proteolysis they cause remains poorly understood. This report describes f or the first time that myosin heavy chain is cleaved in aortic endothelial cell apoptosis induced either by tumour necrosis factor-m or okadaic acid. The cleavage was specific since a well-defined major 97 kDa fragment of myo sin heavy chain was produced. The intermediate filament component vimentin was also cleaved into well-defined fragments (31, 28 and 23 kDa). Kinetic s tudies showed that proteolysis occurred concomitantly with the morphologica l changes associated with apoptosis, i.e. cellular condensation and fragmen tation in apoptotic bodies. These data suggest that the degradation of myos in and vimentin could be involved in the execution of the morphological alt erations observed during apoptotic cell death.