Noncanonical Functions of ATG5 and Membrane Atg8ylation in Regulating Retromer Assembly and Cargo Sorting

Keskeiset käsitteet

ATG5 and the membrane atg8ylation machinery play a critical role in regulating the function of the retromer complex, which is responsible for sorting and trafficking of key cellular cargoes such as the glucose transporter GLUT1.

Tiivistelmä

The content explores the noncanonical functions of ATG5 and the membrane atg8ylation process, which go beyond their roles in the canonical autophagy pathway. The key findings are:

ATG5 associates with the core components of the retromer complex (VPS26, VPS29, VPS35) and this interaction is enhanced upon lysosomal damage.

Knockout of ATG5 or other components of the membrane atg8ylation machinery (ATG3, ATG7, ATG16L1) disrupts the sorting and trafficking of the retromer cargo GLUT1, causing its mislocalization to lysosomes. This effect is independent of the canonical autophagy pathway.

The proper localization of the small GTPase Rab7, which is known to interact with the retromer, is also dependent on the membrane atg8ylation apparatus but not on the canonical autophagy machinery.

Induction of the membrane atg8ylation process CASM (LC3-associated single membrane atg8ylation) also affects GLUT1 sorting, suggesting a direct link between membrane atg8ylation and retromer function.

Maintenance of endolysosomal homeostasis and integrity, which is regulated by membrane atg8ylation-dependent processes like lipid transfer by ATG2 and ESCRT-mediated lysosomal repair, is crucial for proper retromer-dependent cargo sorting.

In summary, the content demonstrates that ATG5 and the membrane atg8ylation machinery play a critical, autophagy-independent role in regulating the function of the retromer complex and endosomal cargo trafficking.

Tilastot

"ATG5 associates with the retromer complex."
"Knockout of ATG5 or other components of the membrane atg8ylation machinery (ATG3, ATG7, ATG16L1) disrupts the sorting and trafficking of the retromer cargo GLUT1, causing its mislocalization to lysosomes."
"Proper localization of the small GTPase Rab7, which is known to interact with the retromer, is dependent on the membrane atg8ylation apparatus but not on the canonical autophagy machinery."
"Induction of the membrane atg8ylation process CASM (LC3-associated single membrane atg8ylation) affects GLUT1 sorting."
"Maintenance of endolysosomal homeostasis and integrity, which is regulated by membrane atg8ylation-dependent processes like lipid transfer by ATG2 and ESCRT-mediated lysosomal repair, is crucial for proper retromer-dependent cargo sorting."

Lainaukset

"ATG5 associates with the retromer complex and this interaction is enhanced upon lysosomal damage."
"Knockout of ATG5 or other components of the membrane atg8ylation machinery disrupts the sorting and trafficking of the retromer cargo GLUT1, causing its mislocalization to lysosomes."
"Proper localization of the small GTPase Rab7, which is known to interact with the retromer, is dependent on the membrane atg8ylation apparatus but not on the canonical autophagy machinery."

Tärkeimmät oivallukset

Noncanonical roles of ATG5 and membrane atg8ylation in retromer assembly and function

by Paddar,M. A.... klo www.biorxiv.org 07-12-2024

https://www.biorxiv.org/content/10.1101/2024.07.10.602886v1

Syvällisempiä Kysymyksiä

How might the insights into the role of membrane atg8ylation in retromer function be leveraged to develop new therapeutic strategies for diseases associated with endosomal trafficking defects?

The findings regarding the role of membrane atg8ylation in retromer function present significant opportunities for therapeutic development, particularly for diseases characterized by endosomal trafficking defects, such as neurodegenerative disorders, diabetes, and certain cancers. By understanding how ATG5 and the membrane atg8ylation machinery influence retromer-dependent sorting of cargo like GLUT1, researchers can target these pathways to restore proper trafficking and cellular homeostasis.

Targeting Membrane Atg8ylation: Therapeutics could be designed to enhance or mimic the effects of membrane atg8ylation, potentially improving the sorting and trafficking of key proteins that are mislocalized in various diseases. For instance, small molecules that activate the atg8ylation machinery could be developed to promote the proper localization of GLUT1 in insulin-responsive tissues, thereby improving glucose uptake in diabetic patients.

Modulating Retromer Activity: Since retromer is crucial for the recycling of membrane proteins, strategies that enhance retromer function could be beneficial. This could involve the use of pharmacological agents that stabilize retromer complexes or enhance their interaction with cargo proteins, thereby improving their sorting and preventing their degradation in lysosomes.

Gene Therapy Approaches: Gene editing techniques, such as CRISPR/Cas9, could be employed to correct mutations in genes encoding retromer components or atg8ylation machinery, restoring normal function in cells affected by genetic disorders that disrupt endosomal trafficking.

Combination Therapies: Given the interconnected nature of these pathways, combination therapies that target both membrane atg8ylation and retromer function may yield synergistic effects, enhancing the overall efficacy of treatment strategies for diseases linked to endosomal dysfunction.

What other cellular processes or pathways might be influenced by the noncanonical functions of ATG5 and the membrane atg8ylation machinery beyond the retromer system?

The noncanonical functions of ATG5 and the membrane atg8ylation machinery extend beyond the retromer system, influencing a variety of cellular processes and pathways:

Lysosomal Repair and Homeostasis: ATG5 and membrane atg8ylation play critical roles in lysosomal membrane repair mechanisms, particularly in response to damage. This includes the recruitment of ESCRT machinery and lipid transfer proteins like ATG2, which are essential for maintaining lysosomal integrity and function.

Endocytosis and Phagocytosis: The machinery involved in membrane atg8ylation is also implicated in processes such as LC3-associated phagocytosis (LAP) and LC3-associated endocytosis (LANDO), which are vital for the clearance of pathogens and cellular debris, thereby influencing immune responses and inflammation.

Cellular Stress Responses: The activation of membrane atg8ylation pathways can be a response to various forms of cellular stress, including nutrient deprivation, oxidative stress, and hypoxia. This suggests that ATG5 and its associated pathways may play a role in cellular adaptation to stress, influencing survival and apoptosis.

Regulation of Autophagy: While the study emphasizes the noncanonical roles of ATG5, it is important to note that these functions may still intersect with canonical autophagy pathways, particularly under conditions of nutrient stress or cellular damage, thereby influencing overall cellular metabolism and homeostasis.

Cellular Signaling Pathways: The interaction of ATG5 with various signaling molecules may also impact pathways related to cell growth, differentiation, and apoptosis, suggesting a broader regulatory role in cellular physiology.

Given the complex interplay between membrane atg8ylation, endolysosomal homeostasis, and retromer function, how might these interconnected systems be dynamically regulated in response to different cellular stresses or environmental cues?

The dynamic regulation of membrane atg8ylation, endolysosomal homeostasis, and retromer function in response to cellular stresses or environmental cues is likely a multifaceted process involving several mechanisms:

Feedback Mechanisms: Cellular stressors such as oxidative stress or nutrient deprivation can trigger feedback loops that enhance membrane atg8ylation and retromer activity. For instance, under nutrient-limiting conditions, the activation of autophagy may lead to increased membrane atg8ylation, which in turn could enhance retromer-mediated sorting of essential cargo proteins.

Post-Translational Modifications: The activity of ATG5 and other components of the atg8ylation machinery may be regulated by post-translational modifications such as phosphorylation, ubiquitination, or acetylation, which can be influenced by cellular signaling pathways activated during stress responses.

Altered Protein Interactions: Changes in the expression levels or activity of proteins involved in the retromer complex or atg8ylation machinery can modulate their interactions. For example, stress-induced changes in the levels of sorting nexins or retromer components could affect cargo sorting and trafficking.

Environmental Cues: External factors such as changes in nutrient availability, hypoxia, or pathogen presence can influence the activation of membrane atg8ylation pathways. Cells may adapt their trafficking and sorting mechanisms in response to these cues to maintain homeostasis and ensure survival.

Cellular Communication: Intercellular signaling, such as cytokine release during inflammation, can also impact the regulation of these pathways, leading to coordinated responses across cell populations to manage stress and maintain tissue homeostasis.

In summary, the interplay between membrane atg8ylation, endolysosomal homeostasis, and retromer function is a dynamic and responsive system that adapts to various cellular stresses and environmental changes, ensuring proper cellular function and survival.