Connecting reticulophagy and neuronal NTRK2/TrkB signaling

Area of Science:

• Cellular Biology
• Neuroscience
• Molecular Biology

Background:

• Cell surface expression of NTRK2/TrkB is crucial for modulating cellular responses to BDNF.
• Reticulophagy, a selective form of autophagy, has emerged as a mechanism to control NTRK2 availability at the cell membrane.
• The ER-chaperone calnexin (CANX) plays a role in delivering NTRK2 for degradation.

Purpose of the Study:

• To investigate the role of CANX in regulating NTRK2 cell surface expression.
• To elucidate the mechanism by which CANX influences NTRK2 trafficking and degradation.
• To explore the broader function of reticulophagy in cellular processes beyond misfolded protein degradation.

Main Methods:

• Co-immunoprecipitation assays to study protein interactions.
• Confocal microscopy to visualize protein localization.
• Western blotting to assess protein levels.
• Pharmacological inhibition and genetic manipulation of CANX and RETREG1.

Main Results:

• CANX directly binds to NTRK2 and facilitates its delivery to the reticulophagy receptor RETREG1/Fam134b for lysosomal degradation.
• Phosphorylation of CANX disrupts the CANX-NTRK2 interaction, leading to the release of NTRK2.
• This release of NTRK2 from the CANX-RETREG1 complex promotes its transport to the cell surface.
• The study demonstrates a novel regulatory pathway for NTRK2 cell surface expression involving CANX and reticulophagy.

Conclusions:

• CANX acts as a critical regulator of NTRK2 cell surface expression through its interaction with the reticulophagy machinery.
• The phosphorylation status of CANX dictates the fate of NTRK2, controlling its degradation or cell surface transport.
• These findings expand the known functions of reticulophagy, highlighting its role in regulating the trafficking of specific cell surface receptors, not just misfolded proteins.