title: The neuronal apoptosis inhibitory protein is a direct inhibitor of caspases 3 and 7.
abstract: The neuronal apoptosis inhibitory protein (NAIP) was identified as a candidate gene for the inherited neurodegenerative disorder spinal muscular atrophy. NAIP is the founding member of a human protein family that is characterized by highly conserved N-terminal motifs called baculovirus inhibitor of apoptosis repeats (BIR). Five members of the human family of inhibitor of apoptosis proteins including NAIP have been shown to be antiapoptotic in various systems. To date, a mechanism for the antiapoptotic effect of NAIP has not been elucidated. To investigate NAIP function, we found cytoprotection of NAIP-expressing primary cortical neurons treated to undergo caspase-3-dependent apoptosis. The additional treatment of these neurons with the pancaspase inhibitor boc-aspartyl(OMe)-fluoromethylketone did not result in increased survival. Similar cytoprotective effects were obtained using HeLa cells transiently transfected with a NAIP N-terminal construct and treated to undergo a caspase-3-dependent cell death. To examine whether NAIP inhibits caspases directly, recombinant N-terminal NAIP protein containing BIR domains was overexpressed, purified, and tested for caspase inhibition potential. Our results demonstrate that inhibition of caspases is selective and restricted to the effector group of caspases, with K(i) values as low as approximately 14 nm for caspase-3 and approximately 45 nm for caspase-7. Additional investigations with NAIP fragments containing either one or two NAIP BIRs revealed that the second BIR and to a lesser extent the third BIR alone are sufficient to mediate full caspase inhibition.
authors.affiliation: Solange Gauthier Karsh Laboratory, Children's Hospital of Eastern Ontario Research Institute, Ottawa, Ontario, Canada.
authors.forename: Johannes K X
authors.initials: JK
authors.lastname: Maier
authors.forename: Zahia
authors.initials: Z
authors.lastname: Lahoua
authors.forename: Nathalie H
authors.initials: NH
authors.lastname: Gendron
authors.forename: Raouf
authors.initials: R
authors.lastname: Fetni
authors.forename: Anne
authors.initials: A
authors.lastname: Johnston
authors.forename: Jamshid
authors.initials: J
authors.lastname: Davoodi
authors.forename: Dita
authors.initials: D
authors.lastname: Rasper
authors.forename: Sophie
authors.initials: S
authors.lastname: Roy
authors.forename: Ruth S
authors.initials: RS
authors.lastname: Slack
authors.forename: Donald W
authors.initials: DW
authors.lastname: Nicholson
authors.forename: Alex E
authors.initials: AE
authors.lastname: MacKenzie
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D053148:Caspase 3; D053179:Caspase 7; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism*; D002478:Cells, Cultured; D019610:Cytoprotection / Q000187:drug effects / Q000502:physiology; D004791:Enzyme Inhibitors / Q000378:metabolism / Q000494:pharmacology; D005434:Flow Cytometry; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D016297:Mutagenesis, Site-Directed; D009419:Nerve Tissue Proteins / Q000378:metabolism* / Q000494:pharmacology; D051616:Neuronal Apoptosis-Inhibitory Protein; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D017434:Protein Structure, Tertiary / Q000502:physiology; D011994:Recombinant Proteins / Q000378:metabolism / Q000494:pharmacology; D013329:Structure-Activity Relationship; D014162:Transfection
chemical_list: D061945:Caspase Inhibitors; D004791:Enzyme Inhibitors; C496800:NAIP protein, human; C496801:Naip1 protein, mouse; D009419:Nerve Tissue Proteins; D051616:Neuronal Apoptosis-Inhibitory Protein; D011994:Recombinant Proteins; C505407:CASP3 protein, human; C505520:CASP7 protein, human; C505409:Casp3 protein, mouse; C505524:Casp7 protein, mouse; D053148:Caspase 3; D053179:Caspase 7; D020169:Caspases