Arl8b Directs LAMP1 Trafficking to Lysosomes and Maintains Cellular Function
Research Summary: This study uncovers that Arl8b recruits Rab11a GAP TBC1D9B to inactivate Rab11a-dependent recycling of LAMP1 to the cell surface, thereby ensuring its delivery to functional lysosomes.
Researcher Spotlight
Co-first author’s: Priya Chouhan and Yogita Phogat
Priya Chouhan (CSIR-IMTECH) and Yogita Phogat (IISER Mohali) are Senior Research Fellows pursuing their PhD research under the guidance of Amit Tuli (Senior Principal Scientist, CSIR-IMTECH) and Mahak Sharma (Professor, IISER Mohali), respectively. Their research focuses on understanding how Arl8b regulates lysosomal trafficking pathways.
Linkedin www.linkedin.com/in/priya-chauhan-5b1667141
Twitter @PriyaChauhan97 | @YPhogat68284
Instagram @priyachauhan961 | @yogitaphogat941
Labs:
Dr. Amit Tuli, CSIR-Institute of Microbial Technology (CSIR-IMTECH); Chandigarh | Twitter
Prof. Mahak Sharma, Indian Institute of Science Education and Research (IISER), Mohali | Twitter
What was the core problem you aimed to solve with this research?
Small GTPases are ‘molecular switches’ that establish and maintain the compartment identity. Coordinated switching of small GTPases drive directional flow of membrane and cargo enabling compartment maturation and identity transitions. Arf-like GTPase Arl8b, is a well known major regulator of lysosome positioning and fusion; however, its contribution to lysosome biogenesis has remained largely unexplored. We unexpectedly observed that depletion of Arl8b increased LAMP1 levels at the cell surface, suggesting a defect in its delivery to lysosomes, raising a possibility that Arl8b might play an unrecognized role in lysosomal cargo trafficking. This intriguing finding prompted us to investigate how newly synthesized LAMP1 is sorted and delivered to lysosomes, and how Arl8b prevents the misrouting of LAMP1 to the plasma membrane. Understanding the mechanism could provide important insights into the cargo sorting pathways that ensure biogenesis of functional lysosomes.
How did you go about solving this problem?
In this study, we have majorly used Retention Using Selective Hook (RUSH) assay to track the journey of newly synthesized LAMP1 from the Golgi to lysosomes in real time using live-cell imaging and confocal microscopy. We found that depletion of Arl8b delays LAMP1 delivery to the active lysosome and promotes its recycling to the plasma membrane. To uncover the underlying mechanism, we identified TBC1D9B, a Rab11a GTPase-activating protein (GAP), as a novel interacting partner of Arl8b. Using a combination of biochemical and imaging approaches, we deciphered Arl8b recruits TBC1D9B to recycling endosomes, where it suppresses Rab11a-dependent recycling of LAMP1. This ensures the efficient delivery of LAMP1 to the functional lysosomes.
“Our study shows that small GTPase Arl8b mediates inactivation of the Rab11-dependent endocytic recycling pathway for trafficking of lysosomal glycoprotein, LAMP1 to its correct functional location, preventing its recycling to the cell surface.” – Dr. Amit Tuli & Prof. Mahak Sharma
How would you explain your research outcomes (Key findings) to the non-scientific community?
A cell functions much like a postal delivery network, where every package needs to be delivered to the correct address. In the same way, LAMP1, an important lysosomal cargo, needs to be delivered to the lysosomes to support their proper function. We discovered that Arl8b acts as a sorting supervisor, ensuring that LAMP1 is not sent to the wrong destination. Arl8b recruits another protein, TBC1D9B, which switches off a recycling pathway driven by Rab11a. By preventing LAMP1 from being recycled back to the cell surface, Arl8b ensures its efficient delivery to lysosomes. When this process is disrupted, delivery of LAMP1 to lysosomes is delayed, leading to impaired lysosome function.
What are the potential implications of your findings for the field and society?
Our study uncovers a role of Arl8b in lysosome biogenesis other than its function in lysosome positioning and fusion. We decipher that Arl8b recruits Rab11a GAP TBC1D9B to recycling endosomes, where it inactivates Rab11a-mediated recycling to ensure the efficient delivery of newly synthesized LAMP1 to active lysosomes. Arl8b deletion leads to misrouting of LAMP1 to the plasma membrane resulting in defective lysosomal function. This reveals an important trafficking checkpoint to maintain lysosome degradative function. These findings have broader implications in human diseases linked to lysosomal defects, including neurodegenerative disorders, cancer, and lysosome storage disorders. Furthermore, our finding opens new avenues for investigating the trafficking of other lysosomal proteins and whether their dysregulation contributes to disease progression. Overall, our study advances our understanding of mechanisms regulating the LAMP1 trafficking to maintain lysosomal function.
What was the exciting moment during your research?
Research is often like solving a jigsaw puzzle, where unexpected observation gradually comes together to reveal the bigger picture. One of the most exciting moments of our research came from the RUSH assay, which revealed that newly synthesized LAMP1 accumulated in the peripheral recycling compartment instead of reaching lysosomes upon Arl8b depletion. This finding provided a clear explanation for increased surface localization of LAMP1 on the cell surface. Another exciting breakthrough was identifying TBC1D9B (Rab11a GAP) as the interacting partner of Arl8b. This revelation helped us connect the remaining pieces of the puzzle and uncover the mechanism by which Arl8b regulates LAMP1 trafficking to lysosomes and prevent its misrouting.
Paper reference: Priya Chouhan#, Yogita Phogat#, Kshitiz Walia, Saikat Debnath, Sandeep Choubey, Medha Gupta, Amit Tuli*, and Mahak Sharma*. Arl8b inactivates the Rab11a recycling pathway to promote LAMP1 sorting and lysosome biogenesis. Journal of Cell Biology (2026). https://doi.org/10.1083/jcb.202509040
