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Alix (ALG-2-interacting Protein X), a Protein Involved in Apoptosis, Binds to Endophilins and Induces Cytoplasmic Vacuolization

2002; Elsevier BV; Volume: 277; Issue: 32 Linguagem: Inglês

10.1074/jbc.m204019200

1083-351X

Christine Chatellard-Causse, Béatrice Blot, Nadine Cristina, Sakina Torch, Marc Missotten, Rémy Sadoul,

Cell death mechanisms and regulation

ALG-2-interacting proteinX (Alix), also known as AIP1, is a cytoplasmic protein ubiquitously expressed and concentrated in phagosomes and exosomes. Alix may regulate apoptosis since it bindsapoptosis-linked gene 2 (ALG-2), a Ca 2+ -binding protein necessary for cell death, and also overexpression of its C-terminal half (Alix-CT) blocks death induced by several stimuli. This part of Alix contains a long proline-rich domain containing several potential SH3-binding sites. Using Alix as bait in a yeast two-hybrid system to screen a mouse brain library, we have found that SH3p4, SH3p8, and SH3p13, collectively known as endophilins, bind to Alix. Co-immunoprecipitations and overlay experiments allowed us to demonstrate that endophilins bind to Alix-CT through an SH3/proline-rich domain interaction. We have narrowed the region of Alix interacting with endophilins down to 14 amino acids containing a P X RPPPP consensus sequence, also present in synaptojanin and germinal center kinase-like kinase, allowing their interaction to endophilins. We further show that overexpression of Alix-CT, which blocks cell death, leads to cytoplasmic vacuolization into tubulo-vesicular structures delineated by Alix-CT. This vacuolization phenomenon is greatly enhanced upon co-expression with endophilins and may be part of the protecting mechanism afforded by Alix-CT.