Partial Cleavage of RasGAP by Caspases Is Required for Cell Survival in Mild Stress Conditions

Abstract

Tight control of apoptosis is required for proper development and maintenance of homeostasis in multicellular organisms. Cells can protect themselves from potentially lethal stimuli by expressing antiapoptotic factors, such as inhibitors of apoptosis, FLICE (caspase 8)-inhibitory proteins, and members of the Bcl2 family. Here, we describe a mechanism that allows cells to survive once executioner caspases have been activated. This mechanism relies on the partial cleavage of RasGAP by caspase 3 into an amino-terminal fragment called fragment N. Generation of this fragment leads to the activation of the antiapoptotic Akt kinase, preventing further amplification of caspase activity. Partial cleavage of RasGAP is required for cell survival under stress conditions because cells expressing an uncleavable RasGAP mutant cannot activate Akt, cannot prevent amplification of caspase 3 activity, and eventually undergo apoptosis. Executioner caspases therefore control the extent of their own activation by a feedback regulatory mechanism initiated by the partial cleavage of RasGAP that is crucial for cell survival under adverse conditions.

SUPPLEMENTAL MATERIAL

We thank Dorinne Savoy, Paola Rivera, and Christelle Bonvin for technical assistance. The cell lines derived from wild-type and RasGAP knockout mice (clones 12.78, 12.37, and 12.64) were a generous gift from Anthony Pawson and Peter van der Geer. We thank Andreas Strasser, Lorraine O'Reilly, Richard Flavell, and Saquib Lakhani for providing caspase-deficient cells and Jürg Tschopp for providing the caspase 8-deficient Jurkat cells. We thank Pascal Schneider for the gift of soluble FasL. We thank Peter Vollenweider, Graham Knott, Pascal Schneider, Peter Clarke, Fabio Martinon, and Jürg Tschopp for suggestions and comments.

This work is supported by the Swiss National Science Foundation (grant no. 3100-066797/1), the Oncosuisse Foundation (grant no. OCS 1110-2-2001), and the Botnar Foundation (Lausanne, Switzerland).