Actin depolymerization and polymerization are required during apoptosis inendothelial cells

In order to understand the role of actin microfilaments in the apoptotic pr ocess, we followed their evolution during tumor necrosis factor-alpha (TNF) -induced apoptosis in bovine aortic endothelial (BAE) cells. Using Western blotting analysis and immunofluorescence microscopy, we observed that the a ctin microfilaments network was disrupted in apoptotic cells. Depolymerizat ion of F-actin was concomitant with internucleosomal DNA degradation and wi th the morphological changes associated with apoptotic cell death. However, using the actin microfilament disrupting agent, cytochalasin, we present e vidence that the formation of blebs leading to apoptotic cell fragmentation requires neopolymerization of actin. Indeed, in the presence of cyochalasi n, induction of apoptosis (internucleosomal DNA degradation) in BAE cells b y TNF and cycloheximide was not associated with these classical morphologic al markers of apoptosis. Moreover, when added to BAE cells showing incipien t apoptotic fragmentation, cytochalasin E reversed this process. We also ob served an accumulation of actin at the basis of the apoptotic bodies in for mation in these cells. Together, these results suggest that the actin netwo rk of flattened cells is disrupted concomitantly to the morphological modif ications associated to the apoptotic cell death, and that the cytochalasin- sensitive reorganisation of actin is required to the formation of apoptotic blebs. J. Cell. Physiol. 184:239-245, 2000. (C) 2000 Wiley-Liss, Inc.