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Molecular and Cellular Biology, June 2007, p. 4028-4036, Vol. 27, No. 11
0270-7306/07/$08.00+0     doi:10.1128/MCB.01959-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Conformational Modification of Serpins Transforms Leukocyte Elastase Inhibitor into an Endonuclease Involved in Apoptosis ^,

Laura Padron-Barthe, Chloé Leprêtre, Elisabeth Martin, Marie-France Counis, and Alicia Torriglia^*

INSERM, Unité 598, Physiopathologie des maladies oculaires, Innovations thérapeutiques, Paris F-75006, France

Received 18 October 2006/ Returned for modification 3 January 2007/ Accepted 16 March 2007

The best-characterized biochemical feature of apoptosis is degradation of genomic DNA into oligonucleosomes. The endonuclease responsible for DNA degradation in caspase-dependent apoptosis is caspase-activated DNase. In caspase-independent apoptosis, different endonucleases may be activated according to the cell line and the original insult. Among the known effectors of caspase-independent cell death, L-DNase II (LEI [leukocyte elastase inhibitor]-derived DNase II) has been previously characterized by our laboratory. We have thus shown that this endonuclease derives from the serpin superfamily member LEI by posttranslational modification (A. Torriglia, P. Perani, J. Y. Brossas, E. Chaudun, J. Treton, Y. Courtois, and M. F. Counis, Mol. Cell. Biol. 18:3612-3619, 1998). In this work, we assessed the molecular mechanism involved in the change in the enzymatic activity of this molecule from an antiprotease to an endonuclease. We report that the cleavage of LEI by elastase at its reactive center loop abolishes its antiprotease activity and leads to a conformational modification that exposes an endonuclease active site and a nuclear localization signal. This represents a novel molecular mechanism for a complete functional conversion induced by changing the conformation of a serpin. We also show that this molecular transformation affects cellular fate and that both endonuclease activity and nuclear translocation of L-DNase II are needed to induce cell death.

Published ahead of print on 2 April 2007.

Supplemental material for this article may be found at http://mcb.asm.org/.

These authors contributed equally to this work.