Induction of apoptosis and changes in nuclear G-actin are mediated by different pathways: the effect of inhibitors of protein and RNA synthesis in isolated rat hepatocytes.
Stressor-induced changes in the cytoskeleton, of which actin is a major component, may lead to apoptosis. The role of drug-induced changes in nuclear G-actin and apoptosis was studied in freshly isolated hepatocytes. Several protein synthesis inhibitors, cycloheximide, puromycin, and emetine, induced 10 to 15% apoptosis in hepatocytes after 4 h, as was determined by changes in nuclear morphology and flow cytometric analysis of Annexin V-positive cells. Apoptosis induced by protein synthesis inhibition could be prevented by the caspase inhibitors Z-Val-Ala-DL-Asp fluormethylketone (zVAD-fmk) and Ac-Asp-Glu-Val-Asp-aldehyde (DEVD-cho). Several (chemical) stressors cause a rapid increase in nuclear G-actin staining in hepatocytes or cell lines (Meijerman et al., Biochem. Biophys. Res. Commun. 240, 697-700, 1997). The protein synthesis inhibitors also increased G-actin staining in nuclei after 2 h; this could not be inhibited by zVAD-fmk or DEVD-cho. Changes in the cytosolic F-actin pattern did not occur until nuclear G-actin staining had already increased. The mRNA synthesis inhibitor actinomycin D, also increased nuclear G-actin staining, but did not induce apoptosis within the studied time frame. The results suggest that the induction of apoptosis and the increased nuclear staining of G-actin by protein synthesis inhibition are differently controlled.
Meijerman
I
I
Leiden-Amsterdam Center for Drug Research, Sylvius Laboratories, P.O. Box 9503, 2300 RA, Leiden, The Netherlands.
Blom
W M
WM
de Bont
H J
HJ
Mulder
G J
GJ
Nagelkerke
J F
JF
D000199:Actins / Q000032:analysis*; D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D020169:Caspases / Q000502:physiology; D002467:Cell Nucleus / Q000187:drug effects* / Q000378:metabolism; D002470:Cell Survival / Q000187:drug effects; D003513:Cycloheximide / Q000494:pharmacology; D003609:Dactinomycin / Q000494:pharmacology; D004640:Emetine / Q000494:pharmacology; D008099:Liver / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D008297:Male; D009336:Necrosis; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology*; D011691:Puromycin / Q000494:pharmacology; D012313:RNA / Q000096:biosynthesis*; D051381:Rats; D017208:Rats, Wistar
D000199:Actins; D011500:Protein Synthesis Inhibitors; D003609:Dactinomycin; D011691:Puromycin; D012313:RNA; D003513:Cycloheximide; D020169:Caspases; D004640:Emetine