Control of lysosome function by the GTPase-activating protein TBC1D9B and its binding partner TMEM55B

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Lysosomes are vital organelles involved in degradation and signaling, with dysfunction linked to human diseases.
• Lysosome positioning and dynamics are regulated by the small GTPase ARL8.
• The regulatory mechanisms of ARL8 activity are not fully understood.

Purpose of the Study:

• To identify novel regulators of lysosome function and dynamics.
• To elucidate the mechanism by which ARL8 activity is controlled.
• To investigate the role of TBC1D9B in lysosome regulation.

Main Methods:

• Biochemical assays to determine protein interactions and GTPase activity.
• CRISPR-Cas9 gene editing to create knockout cell lines for TBC1D9B and TMEM55B.
• Microscopy to assess lysosome morphology and distribution.
• Analysis of autophagic flux and cellular responses to nutrient deprivation.

Main Results:

• TBC1D9B was identified as a negative regulator of ARL8B, binding to ARL8B-GTP and stimulating its GTPase activity.
• TBC1D9B associates with the lysosomal membrane protein TMEM55B.
• Loss of TBC1D9B or TMEM55B leads to lysosome dispersion, impaired autophagic flux, and defective nutrient adaptation.
• The observed phenotypes in TBC1D9B knockout cells were dependent on ARL8.

Conclusions:

• TBC1D9B acts as a critical negative regulator of ARL8B activity, controlling lysosome positioning and function.
• The TBC1D9B-TMEM55B complex plays a key role in maintaining lysosome homeostasis and cellular adaptive responses.
• This study reveals a novel regulatory axis for lysosome function with implications for human diseases.