Alix (ALG-2-interacting protein X), a protein involved in apoptosis, binds to endophilins and induces cytoplasmic vacuolization

J Biol Chem. 2002 Aug 9;277(32):29108-15. doi: 10.1074/jbc.M204019200. Epub 2002 May 28.


ALG-2-interacting protein X (Alix), also known as AIP1, is a cytoplasmic protein ubiquitously expressed and concentrated in phagosomes and exosomes. Alix may regulate apoptosis since it binds apoptosis-linked gene 2 (ALG-2), a Ca2+-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 PXRPPPP 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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptor Proteins, Signal Transducing*
  • Amino Acid Sequence
  • Amino Acids / chemistry
  • Animals
  • Apoptosis*
  • Binding Sites
  • Brain / metabolism
  • Calcium-Binding Proteins / metabolism*
  • Carrier Proteins / metabolism*
  • Cell Cycle Proteins
  • Cell Death
  • Cell Line
  • Cytoplasm / metabolism*
  • DNA, Complementary / metabolism
  • Electrophoresis, Gel, Two-Dimensional
  • Endosomal Sorting Complexes Required for Transport
  • Gene Deletion
  • Humans
  • Mice
  • Microscopy, Fluorescence
  • Molecular Sequence Data
  • Mutation
  • Phenotype
  • Precipitin Tests
  • Protein Binding
  • Protein Structure, Tertiary
  • Recombinant Proteins / metabolism
  • Transfection
  • Two-Hybrid System Techniques
  • src Homology Domains


  • Adaptor Proteins, Signal Transducing
  • Amino Acids
  • Calcium-Binding Proteins
  • Carrier Proteins
  • Cell Cycle Proteins
  • DNA, Complementary
  • Endosomal Sorting Complexes Required for Transport
  • PDCD6IP protein, human
  • Pdcd6ip protein, mouse
  • Recombinant Proteins
  • SH3GL2 protein, human
  • Sh3gl2 protein, mouse