Mice lacking WRB reveal differential biogenesis requirements of tail-anchored proteins in vivo

Area of Science:

• Cell Biology
• Molecular Biology
• Protein Trafficking

Background:

• Tail-anchored (TA) proteins are essential membrane proteins inserted post-translationally.
• The TRC40 pathway, involving WRB and CAML, mediates TA protein targeting to the endoplasmic reticulum.
• In vivo relevance of the TRC40 pathway remains largely uncharacterized.

Purpose of the Study:

• To investigate the in vivo function of the TRC40 pathway.
• To determine if in vitro identified TA protein dependencies predict in vivo behavior upon receptor depletion.
• To elucidate the mechanism behind syntaxin 5's sensitivity to TRC40 pathway disruption.

Main Methods:

• Generation of tissue-specific WRB knockout mouse models.
• Analysis of TA protein fate following TRC40 pathway disruption in vivo.
• Comparative screening of yeast and mammalian TA proteins.
• Investigation of syntaxin 5 targeting and degradation pathways.

Main Results:

• In vitro TA protein dependencies on the TRC40 pathway do not consistently predict in vivo outcomes.
• Syntaxin 5 (Stx5) exhibits extreme sensitivity to TRC40 pathway disruption, a sensitivity conserved across species.
• The aggregation propensity of Stx5's cytoplasmic domain contributes to its sensitivity.
• Stx5 is identified as an autophagy target with inefficient alternative membrane targeting.

Conclusions:

• The TRC40 pathway's role in vivo is complex and not fully predictable from in vitro data.
• Syntaxin 5's unique sensitivity highlights specific vulnerabilities within TA protein targeting.
• Inefficient alternative targeting pathways and autophagy contribute to Stx5 homeostasis.
• These findings reveal a critical link between the TRC40 pathway and cellular proteostasis maintenance.