The primary research interests of my lab focus on studying the molecular mechanisms regulating the trafficking towards late endosomes and lysosomes. Lysosomes are membrane-bound organelles present in eukaryotes which receive and degrade macromolecules from the endocytic, autophagic and phagocytic membrane trafficking pathways. Besides the normal degradative function, lysosomes are involved in mediating various physiological processes, including cholesterol homeostasis, plasma membrane repair, antigen presentation and microbial killing.
Recent studies have identified the role of small GTP-binding protein Arl8, a member of Arl (Arf-like) family of small GTPases in regulating lysosomal trafficking and phagosome-lysosome fusion. Arl8 is the first small GTP-binding protein shown to be localized primarily on lysosomal membranes. Upon GTP-binding, small GTPases like Arl8 recruit downstream tethering factors to intracellular membranes which permit vesicle docking and fusion with the target membranes. One such tethering complex recruited by Arl8 on lysosomal membranes is the HOPS (HOmotypic fusion and vacuole Protein Sorting)complex. We are characterizing the functions of different human HOPS complex subunits and the role of Arl8-HOPS interaction in regulating cargo trafficking towards lysosomes. To answer these questions we are using state-of-the-art techniques including confocal microscopy (both qualitative and quantitative imaging), flow cytometry-based assays, protein-protein interaction techniques including immunoprecipitations, GST-protein pulldown assays, purified protein-protein and protein-lipid interactions and yeast two-hybrid analysis.
Given that many diseases result from defects in the lysosomal trafficking pathway and the normal functioning of the lysosome is critical for immunity against wide variety of pathogens, our research will answer a key question of how lysosomal trafficking and function is regulated by Arl8 and its effectors.
- Rituraj Marwaha#, Subhash B. Arya#, Divya Jagga, Harmeet Kaur, Amit Tuli* and Mahak Sharma*. The Rab7 effector PLEKHM1 binds Arl8b to promote cargo traffic to lysosomes. Journal of Cell Biology 2017 Apr 3;216(4):1051-1070.doi: 10.1083/jcb.201607085. #equal contribution; *corresponding author.
- Divya Khatter, Aastha Sindhwani, and Mahak Sharma*. Arf-like GTPase Arl8: Moving from the periphery to the center of lysosomal biology [review article]. *Corresponding author. Cellular Logistics 2015 Sep 21; 5(3):e1086501.
- Divya Khatter, Vivek B. Raina, Devashish Dwivedi, Aastha, Sindhwani, Surbhi Bahl, and Mahak Sharma*. The small GTPase Arl8b regulates assembly of the mammalian HOPS complex to lysosomes. *Corresponding author. Journal of Cell Science, 128(9):1746-1761 (2015).This research article was selected as the “top most read” article for the month of May 2015 by the Journal of Cell Science.
- Amit Tuli, Jerome Thiery, Ashley M. James, Xavier Michelet, Mahak Sharma, Salil Garg, Keri B. Sanborn, Jordan S. Orange, Judy Lieberman, and Michael B. Brenner. Arf-like GTPase Arl8b regulates lytic granule polarization and natural killer cell–mediated cytotoxicity. Molecular Biology of the Cell, 24(23):3721-3735 (2013). This research article was featured on the cover of the Molecular Biology of the Cell journal December issue.
- Salil Garg*, Mahak Sharma*, Cindy Ung, Amit Tuli, Duarte C. Barral, David L. Hava, Natacha Veerapen, Gurdyal S. Besra, Nir Hacohen and Michael B. Brenner. Lysosomal trafficking, antigen presentation, and microbial killing are controlled by the Arf-like GTPase Arl8b. *Equal contribution. Immunity, 35(2):182-193 (2011). This research article was highlighted in the Cell Press published monthly podcasts (September 1, 2011).
- Saumya Pant, Mahak Sharma, Kruti Patel, Steve Caplan, Chavela Carr and Barth Grant. AMPH-1/Amyphysin/Bin1 functions with RME-1/Ehd1 in endocytic recycling. Nature Cell Biology, 11(12):1399-1410 (2009).
- Mahak Sharma, Sai Srinivas Panapakkam Giridharan, Juliati Rahajeng, Naava Naslavsky and Steve Caplan. MICAL-L1 links EHD1 to tubular recycling endosomes and regulates receptor recycling. Molecular Biology of the Cell, 20(24):5181-5194 (2009).