A serine protease, HtrA2, is released from the mitochondria and interacts with XIAP, inducing cell death.

X chromosome-linked inhibitor of apoptosis (XIAP) is an endogenous inhibitor of caspase-3, -7, and -9. Smac/DIABLO, an inhibitor of XIAP, is released from mitochondria upon receiving apoptotic stimuli and binds to the BIR2 and BIR3 domains of XIAP, thereby inhibiting its caspase-inhibitory activity. Here we report that a serine protease called HtrA2/Omi is released from mitochondria and inhibits the function of XIAP by direct binding in a similar way to Smac. Moreover, when overexpressed extramitochondrially, HtrA2 induces atypical cell death, which is neither accompanied by a significant increase in caspase activity nor inhibited by caspase inhibitors, including XIAP. A catalytically inactive mutant of HtrA2, however, does not induce cell death. In short, HtrA2 is a Smac-like inhibitor of IAP activity with a serine protease-dependent cell death-inducing activity.

[1]  M. Ehrmann,et al.  A Temperature-Dependent Switch from Chaperone to Protease in a Widely Conserved Heat Shock Protein , 1999, Cell.

[2]  Emad S. Alnemri,et al.  A conserved XIAP-interaction motif in caspase-9 and Smac/DIABLO regulates caspase activity and apoptosis , 2001, Nature.

[3]  D. Bredesen,et al.  An alternative, nonapoptotic form of programmed cell death. , 2000, Proceedings of the National Academy of Sciences of the United States of America.

[4]  C. Fusco,et al.  Characterization of a Novel Human Serine Protease That Has Extensive Homology to Bacterial Heat Shock Endoprotease HtrA and Is Regulated by Kidney Ischemia* , 2000, The Journal of Biological Chemistry.

[5]  H. Kawasaki,et al.  Production and separation of peptides from proteins stained with Coomassie brilliant blue R-250 after separation by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. , 1990, Analytical biochemistry.

[6]  J C Reed,et al.  Mitochondria and apoptosis. , 1998, Science.

[7]  E. Karran,et al.  Expression, purification, and functional analysis of the human serine protease HtrA2. , 2000, Protein expression and purification.

[8]  Xiaodong Wang,et al.  Structural and biochemical basis of apoptotic activation by Smac/DIABLO , 2000, Nature.

[9]  J C Reed,et al.  IAP family proteins--suppressors of apoptosis. , 1999, Genes & development.

[10]  Stephen W. Fesik,et al.  NMR Structure and Mutagenesis of the Third Bir Domain of the Inhibitor of Apoptosis Protein XIAP* , 2000, The Journal of Biological Chemistry.

[11]  J C Reed,et al.  IAP-family protein survivin inhibits caspase activity and apoptosis induced by Fas (CD95), Bax, caspases, and anticancer drugs. , 1998, Cancer research.

[12]  M. Tanabe,et al.  Studies on a new proteolytic enzyme from A chromobacter lyticus M497-1. I. Purification and some enzymatic properties. , 1981, Biochimica et biophysica acta.

[13]  J C Reed,et al.  Cleavage of human inhibitor of apoptosis protein XIAP results in fragments with distinct specificities for caspases , 1999, The EMBO journal.

[14]  C. Thompson,et al.  A conserved family of cellular genes related to the baculovirus iap gene and encoding apoptosis inhibitors. , 1996, The EMBO journal.

[15]  J C Reed,et al.  A Single BIR Domain of XIAP Sufficient for Inhibiting Caspases* , 1998, The Journal of Biological Chemistry.

[16]  Y. Lazebnik,et al.  Caspases: enemies within. , 1998, Science.

[17]  J C Reed,et al.  IAPs block apoptotic events induced by caspase‐8 and cytochrome c by direct inhibition of distinct caspases , 1998, The EMBO journal.

[18]  C. Thompson,et al.  Apoptosis in the pathogenesis and treatment of disease , 1995, Science.

[19]  C. Southan,et al.  Characterization of human HtrA2, a novel serine protease involved in the mammalian cellular stress response. , 2000, European journal of biochemistry.

[20]  R. Takahashi,et al.  Ubiquitin-protein ligase activity of X-linked inhibitor of apoptosis protein promotes proteasomal degradation of caspase-3 and enhances its anti-apoptotic effect in Fas-induced cell death , 2001, Proceedings of the National Academy of Sciences of the United States of America.

[21]  C. Georgopoulos,et al.  Sequence analysis and regulation of the htrA gene of Escherichia coli: a sigma 32-independent mechanism of heat-inducible transcription. , 1988, Nucleic acids research.

[22]  John Calvin Reed,et al.  X-linked Inhibitor of Apoptosis Protein (XIAP) Inhibits Caspase-3 and -7 in Distinct Modes* , 2001, The Journal of Biological Chemistry.

[23]  Guy S. Salvesen,et al.  X-linked IAP is a direct inhibitor of cell-death proteases , 1997, Nature.

[24]  R. Korneluk,et al.  XIAP, the guardian angel , 2001, Nature Reviews Molecular Cell Biology.

[25]  L K Miller,et al.  An exegesis of IAPs: salvation and surprises from BIR motifs. , 1999, Trends in cell biology.

[26]  H. Söling,et al.  The protein disulphide-isomerase family: unravelling a string of folds. , 1999, The Biochemical journal.

[27]  K. Tanaka,et al.  Protease Do is essential for survival of Escherichia coli at high temperatures: its identity with the htrA gene product. , 1991, Biochemical and biophysical research communications.

[28]  Xiaodong Wang,et al.  Smac, a Mitochondrial Protein that Promotes Cytochrome c–Dependent Caspase Activation by Eliminating IAP Inhibition , 2000, Cell.

[29]  G. Cohen,et al.  The Inhibitor of Apoptosis Protein-Binding Domain of Smac Is Not Essential for Its Proapoptotic Activity , 2001, The Journal of cell biology.

[30]  John Calvin Reed,et al.  The c‐IAP‐1 and c‐IAP‐2 proteins are direct inhibitors of specific caspases , 1997, The EMBO journal.

[31]  Yoshiyuki Kuchino,et al.  Caspase-independent programmed cell death with necrotic morphology , 1999, Cell Death and Differentiation.

[32]  C. Georgopoulos,et al.  The HtrA (DegP) protein, essential for Escherichia coli survival at high temperatures, is an endopeptidase , 1990, Journal of bacteriology.

[33]  Guido Kroemer,et al.  Mitochondrial control of cell death , 2000, Nature Medicine.

[34]  Robert L Moritz,et al.  Identification of DIABLO, a Mammalian Protein that Promotes Apoptosis by Binding to and Antagonizing IAP Proteins , 2000, Cell.

[35]  J. Abrams.  An emerging blueprint for apoptosis in Drosophila. , 1999, Trends in cell biology.

[36]  M. Raff,et al.  Programmed Cell Death in Animal Development , 1997, Cell.

[37]  D. Luk,et al.  Human HtrA, an Evolutionarily Conserved Serine Protease Identified as a Differentially Expressed Gene Product in Osteoarthritic Cartilage* , 1998, The Journal of Biological Chemistry.