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© The Rockefeller University Press, 0021-9525/1998//1361 $5.00
The Journal of Cell Biology, Volume 143, Number 5, , 1998 1361-1373

Article

SAPK2/p38-dependent F-Actin Reorganization Regulates Early Membrane Blebbing during Stress-induced Apoptosis



Jacques Huot*, François Houle*, Simon Rousseau*, Réna G. Deschesnes*, Girish M. Shah{ddagger}, and Jacques Landry*

* Centre de recherche en cancérologie de l'Université Laval, L'Hôtel-Dieu de Québec, Québec, G1R 2J6, Canada; and {ddagger} Laboratoire de recherche sur le cancer de la peau CHUL, RC-9700, Sainte-Foy, Québec, Canada

In endothelial cells, H2O2 induces the rapid formation of focal adhesion complexes at the ventral face of the cells and a major reorganization of the actin cytoskeleton into dense transcytoplasmic stress fibers. This change in actin dynamics results from the activation of the mitogen-activated protein (MAP) kinase stress-activated protein kinase-2/p38 (SAPK2/p38), which, via MAP kinase-activated protein (MAPKAP) kinase-2/3, leads to the phosphorylation of the actin polymerization modulator heat shock protein of 27 kD (HSP27). Here we show that the concomitant activation of the extracellular signal-regulated kinase (ERK) MAP kinase pathway by H2O2 accomplishes an essential survival function during this process. When the activation of ERK was blocked with PD098059, the focal adhesion complexes formed under the plasma membrane, and the actin polymerization activity led to a rapid and intense membrane blebbing. The blebs were delimited by a thin F-actin ring and contained enhanced levels of HSP27. Later, the cells displayed hallmarks of apoptosis, such as DEVD protease activities and internucleosomal DNA fragmentation. Bleb formation but not apoptosis was blocked by extremely low concentrations of the actin polymerization inhibitor cytochalasin D or by the SAPK2 inhibitor SB203580, indicating that the two processes are not in the same linear cascade. The role of HSP27 in mediating membrane blebbing was assessed in fibroblastic cells. In control fibroblasts expressing a low level of endogenous HSP27 or in fibroblasts expressing a high level of a nonphosphorylatable HSP27, H2O2 did not induce F-actin accumulation, nor did it generate membrane blebbing activity in the presence or absence of PD098059. In contrast, in fibroblasts that expressed wild-type HSP27 to a level similar to that found in endothelial cells, H2O2 induced accumulation of F-actin and caused bleb formation when the ERK pathway was inhibited. Cis-platinum, which activated SAPK2 but induced little ERK activity, also induced membrane blebbing that was dependent on the expression of HSP27. In these cells, membrane blebbing was not followed by caspase activation or DNA fragmentation. We conclude that the HSP27-dependent actin polymerization–generating activity of SAPK2 associated with a misassembly of the focal adhesions is responsible for induction of membrane blebbing by stressing agents.

Key Words: SAPK2/p38 • HSP27 • F-actin • blebbing • apoptosis

Abbreviations used in this paper: EBSS, Earle's balanced salt solution; ECGS, endothelial cell growth supplement; FGF, fibroblast growth factor; ERK, extracellular signal-regulated kinase; GST, glutathione S-transferase; HSP27, heat shock protein of 27 kD; HUVEC, human umbilical vein endothelial cells; ICE, interleukin 1β–converting enzyme; IL, interleukin; JNK/SAPK1, jun NH2-terminal kinase/stress-activated protein kinase-1; MAP kinase, mitogen-activated protein kinase; MAPKAP K2, MAP kinase-activated protein kinase-2; PARP, poly-(ADP-ribose)-polymerase; SAPK2, stress-activated protein kinase-2/p38; TNF{alpha}, tumor necrosis factor {alpha}; VEGF, vascular endothelial growth factor.


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