Removal of proteasomes from the nucleus and their accumulation in apoptotic blebs during programmed cell death.

Apoptosis can be initiated in immortalized cAMP-stimulated rat ovarian granulosa cells by induction of wild-type p53 activity. Immunocytochemical studies using confocal microscopy reveal that in apoptotic, unlike in normal growing cells, the proteasomes are removed from the nucleus and accumulate within the apoptotic blebs at the periphery of the cell. In parallel, a striking reorganization of the actin cytoskeleton is observed which forms a spherical network separating the apoptotic blebs from the cytoplasmic organelles, such as mitochondria and lipid droplets which remain in the perinuclear region. The reorganization of the actin cytoskeleton as well as disappearance of proteasomes from the nucleus suggest possible function of proteasomes in apoptotic regulation.