Generation and Characterization of Smac/DIABLO-Deficient Mice

Abstract

The mitochondrial proapoptotic protein Smac/DIABLO has recently been shown to potentiate apoptosis by counteracting the antiapoptotic function of the inhibitor of apoptosis proteins (IAPs). In response to apoptotic stimuli, Smac is released into the cytosol and promotes caspase activation by binding to IAPs, thereby blocking their function. These observations have suggested that Smac is a new regulator of apoptosis. To better understand the physiological function of Smac in normal cells, we generated Smac-deficient (Smac^−/− ) mice by using homologous recombination in embryonic stem (ES) cells. Smac^−/− mice were viable, grew, and matured normally and did not show any histological abnormalities. Although the cleavage in vitro of procaspase-3 was inhibited in lysates of Smac^−/− cells, all types of cultured Smac^−/− cells tested responded normally to all apoptotic stimuli applied. There were also no detectable differences in Fas-mediated apoptosis in the liver in vivo. Our data strongly suggest the existence of a redundant molecule or molecules capable of compensating for a loss of Smac function.

We thank Takeshi Yagi and Tetsuo Noda for the DT-A plasmid, and Emad S. Alnemri for the anti-Omi/HtrA2 antibody. We are grateful to numerous members of the Mak laboratory for helpful comments and discussion and to Mary Saunders for scientific editing.

This work was supported by National Cancer Institute of Canada. H.O. was partially supported by Japanese Foundation for Clinical Pharmacology. J.J. is supported by a DOD Breast Cancer Research Program postdoctoral fellowship. S.W.L. is supported by the Rita Allen Foundation and grant CA13106 from the NIH.