RUFY3 links Arl8b and JIP4-Dynein complex to regulate lysosome size and positioning

Area of Science:

• Cell Biology
• Molecular Biology
• Organelle Dynamics

Background:

• Lysosome positioning relies on bidirectional movement along microtubule tracks.
• Arl8b (a small GTP-binding protein) is known to promote anterograde lysosome transport via kinesin-1.

Purpose of the Study:

• To identify Arl8b effectors involved in lysosome retrograde transport.
• To elucidate the role of RUFY3 in lysosome positioning and cellular function.

Main Methods:

• Co-immunoprecipitation to identify protein interactions.
• Knockdown studies using siRNA to assess protein function.
• Confocal microscopy to analyze lysosome distribution and colocalization.
• Analysis of autophagic flux and lysosome size.

Main Results:

• RUFY3 interacts with the JIP4-dynein-dynactin complex, mediating Arl8b's association with retrograde motors.
• RUFY3 depletion disrupts the positioning of Arl8b-positive endosomes and reduces their colocalization with Rab7.
• RUFY3 regulates nutrient-dependent lysosome distribution but does not affect autophagic degradation.
• RUFY3 depletion leads to significantly smaller lysosomes, a phenotype rescued by PIKFYVE inhibition.

Conclusions:

• RUFY3 is a key regulator of lysosome retrograde transport and positioning.
• The perinuclear lysosome arrangement controlled by RUFY3 influences both lysosome positioning and size.
• These findings reveal a novel mechanism for lysosome size regulation linked to organelle positioning.