Positive regulation of apoptosis by HCA66, a new Apaf-1 interacting protein, and its putative role in the physiopathology of NF1 microdeletion syndrome patients.
As a component of the apoptosome, a caspase-activating complex, Apaf-1 plays a central role in the mitochondrial caspase activation pathway of apoptosis. We report here the identification of a novel Apaf-1 interacting protein, hepatocellular carcinoma antigen 66 (HCA66) that is able to modulate selectively Apaf-1-dependent apoptosis through its direct association with the CED4 domain of Apaf-1. Expression of HCA66 was able to potentiate Apaf-1, but not receptor-mediated apoptosis, by increasing downstream caspase activity following cytochrome c release from the mitochondria. Conversely, cells depleted of HCA66 were severely impaired for apoptosome-dependent apoptosis. Interestingly, expression of the Apaf-1-interacting domain of HCA66 had the opposite effect of the full-length protein, interfering with the Apaf-1 apoptotic pathway. Using a cell-free system, we showed that reduction of HCA66 expression was associated with a diminished amount of caspase-9 in the apoptosome, resulting in a lower ability of the apoptosome to activate caspase-3. HCA66 maps to chromosome 17q11.2 and is among the genes heterozygously deleted in neurofibromatosis type 1 (NF1) microdeletion syndrome patients. These patients often have a distinct phenotype compared to other NF1 patients, including a more severe tumour burden. Our results suggest that reduced expression of HCA66, owing to haploinsufficiency of HCA66 gene, could render NF1 microdeleted patients-derived cells less susceptible to apoptosis.
Piddubnyak
V
V
INSERM, Equipe Avenir, U697, Hôpital Saint-Louis, Paris, France.
Rigou
P
P
Michel
L
L
Rain
J-C
JC
Geneste
O
O
Wolkenstein
P
P
Vidaud
D
D
Hickman
J A
JA
Mauviel
A
A
Poyet
J-L
JL
D000595:Amino Acid Sequence; D000818:Animals; D000951:Antigens, Neoplasm / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D017209:Apoptosis / Q000502:physiology*; D053477:Apoptotic Protease-Activating Factor 1 / Q000235:genetics / Q000378:metabolism; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D053148:Caspase 3 / Q000235:genetics / Q000378:metabolism; D053453:Caspase 9 / Q000235:genetics / Q000378:metabolism; D002460:Cell Line; D002478:Cells, Cultured; D002850:Chromatography, Gel; D017353:Gene Deletion; D006367:HeLa Cells; D006801:Humans; D015151:Immunoblotting; D047468:Immunoprecipitation; D051379:Mice; D008969:Molecular Sequence Data; D009456:Neurofibromatosis 1 / Q000235:genetics / Q000473:pathology / Q000503:physiopathology*; D025542:Neurofibromin 1 / Q000235:genetics*; D034741:RNA, Small Interfering / Q000235:genetics; D016601:RNA-Binding Proteins; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D013577:Syndrome; D014162:Transfection
C506592:APAF1 protein, human; D000951:Antigens, Neoplasm; D053477:Apoptotic Protease-Activating Factor 1; D002352:Carrier Proteins; D025542:Neurofibromin 1; D034741:RNA, Small Interfering; D016601:RNA-Binding Proteins; C524211:UTP6 protein, human; D053148:Caspase 3; D053453:Caspase 9