Mitochondrial Regulation of Cell Death: Mitochondria Are Essential for Procaspase 3-p21 Complex Formation To Resist Fas-Mediated Cell Death

Abstract

Death receptor Fas transduces cell death signaling upon stimulation by Fas ligand, and this death signaling is mediated by caspase. Recently, we reported that the cell cycle regulator p21 interacts with procaspase 3 to resist Fas-mediated cell death. In the present study, the molecular characterization and functional region of the procaspase 3-p21 complex was further investigated. We observed the p21 expression in the mitochondrial fraction of HepG2 cells and detected Fas-mediated cell death only in the presence of actinomycin D. However, mitochondrial-DNA-lacking HepG2 (MDLH) cells showed this effect even in the absence of actinomycin D. Both p21 and procaspase 3 were expressed in MDLH cells, but the procaspase 3-p21 complex formation was not observed. Interestingly, the resistance to Fas-mediated cell death in the MDLH cells without actinomycin D was recovered after microinjection of HepG2-derived mitochondria into the MDLH cells. We conclude that mitochondria are necessary for procaspase 3-p21 complex formation and propose that the mitochondrial role during cell death is not only death induction but also death suppression.

ACKNOWLEDGMENTS

We thank Yoshihide Tsujimoto, Osaka University Medical School, for human hepatoma HepG2 cells; Shigeomi Shimizu, Osaka University Medical School, for his valuable advice about the preparation of MDLH cells; Naomi Haga, University of Tokyo, for his comments about experiments with mitochondria; Hiroko Katoh, Leica Co., Ltd., for her technical support of confocal-fluorescence microscopy; and Masayuki Miura, Osaka University of Medical School, and Mitsuru Furusawa, Daiichi Pharmaceutical Co., Ltd., for their valuable discussions.

The preparation of the manuscript was supported by the Idest Inc., Edmond, Okla.