Alterations of the actin polymerization status as an apoptotic morphological effector in HL‐60 cells

Abstract

The alterations of the cytoskeletal actin network have been implicated as a morphological effector in apoptosis. However, studies directly linking actin change to the morphological events in apoptosis are lacking. This study quantitatively examined the effect of actin alteration on the camptothecin (CPT)-induced apoptotic process in HL-60 cells. Actin alteration was induced by two distinctive types of agent: the polymerization-stimulating agent, Jasplakinolide (Jas), and the polymerization-blocking agent, cytochalasin B (CB). The actin polymerization status was measured by two complementary methods: the cell pellet-based DNase I inhibition method, and the individual cell-based quantitative fluorescence image analysis (QFIA) assay. Actin polymerization induced by Jas caused apoptosis directly. By contrast, CB, an actin polymerization-blocking agent, partially inhibited CPT-induced apoptosis. A similar inhibition of the CPT-induced apoptosis response was observed with a more specific actin depolymerization agent, cytochalasin E. The alterations of the actin polymerization status occurred in three sequential steps during the apoptotic process: first polymerization, followed by depolymerization, and finally degradation. However, compared with CPT-induced apoptosis, Jas-induced apoptosis was characterized by pronounced actin polymerization that corresponded morphologically with prominent membrane blebbing, but less apoptotic body formation. Furthermore, DNase I activity, which is normally inhibited by G-actin, was specifically detected in Jas-treated cells. These results show that the regulation of actin polymerization is an important apoptotic morphological effector, whereas the alterations of the actin polymerization status by chemicals have profound effects not only on altering the morphology of apoptotic cells, but on apoptosis induction in HL-60 cells as well.

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.…”

Rho GTPase signalling pathways in the morphological changes associated with apoptosis

“…18,20 Signalling downstream of Rho GTPases may contribute to both phases of actin reorganisation. During apoptosis, caspase-mediated cleavage of the Rho effector kinases PRK1 (also known as PKN) 54 and PRK2 55 as well as the Rac/Cdc42 effector kinase PAK2 (also known as g-PAK) 56,57 releases constitutively active kinase fragments.…”

“…However, numerous lines of evidence have demonstrated that the first phase of cell contraction and membrane blebbing (Figure 1) is a dynamic process associated with, and dependent upon, the presence of filamentous actin, 11 ± 23 increased myosin light chain (MLC) phosphorylation 15,16,19,22,24 and myosin ATPase activity. 15,16 After the initial phase of contraction and blebbing, a second phase of actin filament disassembly occurs via depolymerisation 18,20 and possibly through caspasemediated cleavage of actin monomers. 25 ± 27 First phase: contraction and blebbing active form of RhoA was shown to be sufficient for cell contraction and membrane blebbing.…”

Tetraspanin KAI1/CD82 inhibits cell migration-related cellular events via reorganizing actin network

“…Here, Ifound that CD82 can also inhibit migration through impairing actin cytoskeleton reorganization. Interestingly, disruption of cytoskeleton can trigger and accompany apoptosis (Rao et al, 1999). So far, whether CD82 inhibit cancer cell metastasis and trigger apoptosis through common pathway or different pathway remain unclear.…”