HtrA2 promotes cell death through its serine protease activity and its ability to antagonize inhibitor of apoptosis proteins.
Inhibitor of apoptosis (IAP) proteins inhibit caspases, a function counteracted by IAP antagonists, insect Grim, HID, and Reaper and mammalian DIABLO/Smac. We now demonstrate that HtrA2, a mammalian homologue of the Escherichia coli heat shock-inducible protein HtrA, can bind to MIHA/XIAP, MIHB, and baculoviral OpIAP but not survivin. Although produced as a 50-kDa protein, HtrA2 is processed to yield an active serine protease with an N terminus similar to that of Grim, Reaper, HID, and DIABLO/Smac that mediates its interaction with XIAP. HtrA2 is largely membrane-associated in healthy cells, with a significant proportion observed within the mitochondria, but in response to UV irradiation, HtrA2 shifts into the cytosol, where it can interact with IAPs. HtrA2 can, like DIABLO/Smac, prevent XIAP inhibition of active caspase 3 in vitro and is able to counteract XIAP protection of mammalian NT2 cells against UV-induced cell death. The proapoptotic activity of HtrA2 in vivo involves both IAP binding and serine protease activity. Mutations of either the N-terminal alanine of mature HtrA2 essential for IAP interaction or the catalytic serine residue reduces the ability of HtrA2 to promote cell death, whereas a complete loss in proapoptotic activity is observed when both sites are mutated.
Verhagen
Anne M
AM
Walter and Eliza Hall Institute of Medical Research, Post Office Royal Melbourne Hospital, Victoria 3050, Australia. verhagen@wehi.edu.au
Silke
John
J
Ekert
Paul G
PG
Pakusch
Miha
M
Kaufmann
Hitto
H
Connolly
Lisa M
LM
Day
Catherine L
CL
Tikoo
Anjali
A
Burke
Richard
R
Wrobel
Carolyn
C
Moritz
Robert L
RL
Simpson
Richard J
RJ
Vaux
David L
DL
D000595:Amino Acid Sequence; D017209:Apoptosis; D001665:Binding Sites; D053148:Caspase 3; D061945:Caspase Inhibitors; D002868:Chromosomal Proteins, Non-Histone / Q000378:metabolism; D003600:Cytosol / Q000201:enzymology; D000074923:High-Temperature Requirement A Serine Peptidase 2; D006801:Humans; D051034:Inhibitor of Apoptosis Proteins; D008869:Microtubule-Associated Proteins; D008928:Mitochondria / Q000201:enzymology; D024101:Mitochondrial Proteins; D008969:Molecular Sequence Data; D009363:Neoplasm Proteins; D011506:Proteins / Q000037:antagonists & inhibitors* / Q000737:chemistry; D012697:Serine Endopeptidases / Q000737:chemistry / Q000502:physiology* / Q000528:radiation effects; D000077022:Survivin; D014466:Ultraviolet Rays; D051636:X-Linked Inhibitor of Apoptosis Protein
C107489:BIRC5 protein, human; D061945:Caspase Inhibitors; D002868:Chromosomal Proteins, Non-Histone; D051034:Inhibitor of Apoptosis Proteins; D008869:Microtubule-Associated Proteins; D024101:Mitochondrial Proteins; D009363:Neoplasm Proteins; D011506:Proteins; D000077022:Survivin; D051636:X-Linked Inhibitor of Apoptosis Protein; C496866:XIAP protein, human; D012697:Serine Endopeptidases; C000615914:HTRA2 protein, human; D000074923:High-Temperature Requirement A Serine Peptidase 2; C505407:CASP3 protein, human; D053148:Caspase 3