TMEM9 activates Rab9-dependent alternative autophagy through interaction with Beclin1

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Transmembrane protein 9 (TMEM9) is known to regulate lysosomal acidification via interaction with the v-type ATPase complex.
• The specific role of TMEM9 within the lysosome-dependent autophagy pathway remains largely uncharacterized.

Purpose of the Study:

• To elucidate the function of TMEM9 in the autophagy machinery.
• To investigate the interaction of TMEM9 with key autophagy regulators, specifically Beclin1.
• To determine the mechanism by which TMEM9 influences autophagy, particularly alternative autophagy pathways.

Main Methods:

• Investigated the interaction between the cytosolic domain of TMEM9 and Beclin1 using biochemical assays.
• Utilized colocalization studies to examine the localization of TMEM9 with Rab9 and LC3 in late endosomes and lysosomes.
• Assessed the role of TMEM9 glycosylation in its lysosomal localization, Beclin1 interaction, and autophagy activation.

Main Results:

• TMEM9 directly interacts with Beclin1 through its Bcl-2-binding domain, leading to the dissociation of the autophagy inhibitor Bcl-2.
• TMEM9 colocalizes with Rab9 on late endosomes and lysosomes, but not with LC3, indicating involvement in LC3-independent autophagy.
• Glycosylation of TMEM9 is crucial for its lysosomal targeting, Beclin1 interaction, and subsequent activation of Rab9-dependent alternative autophagy.

Conclusions:

• TMEM9 acts as a crucial regulator of Rab9-dependent alternative autophagy.
• TMEM9 facilitates autophagy by recruiting and activating the Beclin1 complex at Rab9-dependent autophagosomes.
• These findings reveal a novel mechanism linking lysosomal function and autophagy regulation through TMEM9.