Actin polymerization and depolymerization during apoptosis in HL-60 cells

Abstract

Little is known about the biochemical "machinery" responsible for the morphological features of apoptosis, although the cytoskeleton is presumed to be involved. Using flow cytometry, polyacrylamide gel electrophoresis, and fluorescence microscopy, we show that apoptosis induced by ultraviolet (UV) irradiation or 80 micrograms/ml etoposide correlates with early transient polymerization and later depolymerization of filamentous (F)-actin and dramatic changes in visible microfilament organization. Depolymerization of F-actin began before the formation of apoptotic bodies and was ultimately composed of decreases in both the detergent-insoluble (40%) and detergent-soluble (50%) pools of F-actin. Dihydrocytochalasin B (H2CB), which blocked apoptotic body formation, depolymerized F-actin in the detergent-insoluble pool only. Visually, H2CB treatment disrupted microfilament organization, resulting in short, brightly stained microfilaments dispersed throughout the cytoplasm. In contrast, apoptotic cells contained a network of fine microfilaments with bright staining concentrated at the site of apoptotic body formation. Together, these results suggest that reorganization of the microfilament network is necessary for the formation of apoptotic bodies and that depolymerization of F-actin may also be a necessary component of the process of apoptosis.

The self-incompatibility response in Papaver rhoeas pollen causes early and striking alterations to organelles

“…21 In addition to the DNA fragmentation, changes to the actin cytoskeleton also implicate the possibility of PCD in the SI response, as the highly sustained actin depolymerization that accompanies SI 17 has been observed in several animal cells undergoing apoptosis. [18][19][20] Our electron microscopy data describing the morphological changes in pollen undergoing the SI response revealed none of the morphological hallmarks that typically characterize necrosis, such as loss of membrane integrity, cellular swelling or rupture. Even though we cannot rule out the possibility of secondary necrosis, our data are not inconsistent with the hypothesis that PCD may occur in SI challenged pollen tubes.…”

“…17 Intriguingly, long-term F-actin depolymerization has been identified as a feature of apoptosis. [18][19][20] Preliminary data suggesting that a programmed cell death (PCD) signalling cascade may be stimulated in the SI response was provided by evidence that DNA fragmentation, generally considered a hallmark in PCD, is stimulated in SI challenged pollen tubes. 21 This, together with similarities between the P. rhoeas SI system and the hypersensitive response (HR), which triggers a PCD cascade, has led to the idea that PCD may be triggered by the SI response.…”

Actin reorganization in CHO AA8 cells undergoing mitotic catastrophe and apoptosis induced by doxorubicin

“…It has been reported that actin might be both an apoptotic target and an early modulator of cell commitment to apoptosis (18). Moreover, reorganization of the actin network was proved to be required for plasma membrane blebbing (19,20). There is growing evidence that intact F-actin is required for autophagocytosis, presumably for enabling cells to transport vacuoles to lysosomes (21,22).…”

Apoptotic volume decrease as a geometric determinant for cell dismantling into apoptotic bodies

“…Different cytoskeleton-disrupting agents, such as cytochalasins B, D and E and latrunculin A, prevent this second round of volume loss, along with DNA degradation and formation of apoptotic bodies. 7,8 In this second stage, both cytochrome c release and caspases seem to be involved and required for AVD (reviewed in Remillard and Yuan 6 ). Yet, a channel-mediated K þ outward movement is activated by cytochrome c independently of initiator caspase-9 activation.…”