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ALG-2 activates the MVB sorting function of ALIX through relieving its intramolecular interaction.
Sheng Sun1, Xi Zhou2, Joe Corvera3
1Department of Experimental Therapeutics, The University of Texas MD Anderson Cancer Center, Houston, TX, USA; The University of Texas Graduate School of Biomedical Sciences, Houston, TX, USA.
Cell Discovery
|July 28, 2016
Summary
Calcium-dependent ALG-2 binding to ALIX protein activates ALIX for epidermal growth factor receptor (EGFR) sorting into multivesicular bodies (MVBs). This specific activation is crucial for receptor sorting but not other cellular processes.
Area of Science:
- Cell biology
- Molecular mechanisms of protein-protein interactions
- Membrane trafficking
Background:
- The adaptor protein ALIX (Apoptosis-linked gene 2-interacting protein X) is essential for endosomal sorting complexes required for transport (ESCRT)-mediated sorting of activated epidermal growth factor receptor (EGFR).
- ALIX possesses an intrinsic intramolecular interaction that inhibits its ESCRT function.
- ALG-2 (Apoptosis-linked gene 2) is a calcium-binding protein that interacts with ALIX.
Purpose of the Study:
- To investigate the role of ALG-2 in regulating ALIX function during the multivesicular body (MVB) sorting of activated EGFR.
- To determine if ALG-2 binding to ALIX can overcome the inhibitory intramolecular interaction of ALIX.
Main Methods:
- Investigated the effect of calcium on ALG-2 and ALIX interaction.
- Assessed the impact of ALG-2 on ALIX association with membranes and CHMP4.
- Examined the role of ALG-2 in EGFR MVB sorting upon EGFR activation.
- Compared the effects of inhibiting ALG-2-mediated ALIX activation with inhibiting ALIX-CHMP4 interaction on EGFR sorting, cytokinetic abscission, and equine infectious anemia virus (EIAV) budding.
Main Results:
- Calcium-dependent binding of ALG-2 to ALIX completely relieves ALIX's intramolecular interaction.
- ALG-2 binding promotes CHMP4-dependent ALIX association with the membrane.
- EGFR activation leads to increased ALG-2 interaction with ALIX, enhancing ALIX membrane association.
- Inhibition of ALG-2-mediated ALIX activation effectively blocks EGFR MVB sorting, similar to inhibiting ALIX-CHMP4 interaction.
- Inhibition of ALG-2-mediated ALIX activation does not affect cytokinetic abscission or EIAV budding.
Conclusions:
- Calcium-dependent ALG-2 interaction with ALIX specifically generates functional ALIX required for MVB sorting of ubiquitinated membrane receptors like EGFR.
- ALG-2 acts as a specific regulator, activating ALIX for EGFR sorting without affecting other ALIX-dependent processes such as viral budding or cytokinesis.
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