Rab7 and Arl8 GTPases are Necessary for Lysosome Tubulation in Macrophages

Authors

  • Amra Mrakovic,

    1. Molecular Science Program and the Department of Chemistry and Biology, Ryerson University, Toronto, ON, Canada
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    • These authors contributed equally.

  • Jason G. Kay,

    1. Program in Cell Biology, Hospital for Sick Children, Toronto, ON, Canada
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    • These authors contributed equally.

  • Wendy Furuya,

    1. Program in Cell Biology, Hospital for Sick Children, Toronto, ON, Canada
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  • John H. Brumell,

    1. Program in Cell Biology, Hospital for Sick Children, Toronto, ON, Canada
    2. Department of Molecular Genetics, University of Toronto, Toronto, ON, Canada
    3. Institute of Medical Science, University of Toronto, Toronto, ON, Canada
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  • Roberto J. Botelho

    Corresponding author
    • Molecular Science Program and the Department of Chemistry and Biology, Ryerson University, Toronto, ON, Canada
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Corresponding author: Roberto J. Botelho, rbotelho@ryerson.ca

Abstract

Lysosomes provide a niche for molecular digestion and are a convergence point for endocytic trafficking, phagosome maturation and autophagy. Typically, lysosomes are small, globular organelles that appear punctate under the fluorescence microscope. However, activating agents like phorbol esters transform macrophage lysosomes into tubular lysosomes (TLs), which have been implicated in retention of pinocytic uptake and phagosome maturation. Moreover, dendritic cells exposed to lipopolysaccharides (LPSs) convert their punctate class II major histocompatibility complex compartment, a lysosome-related organelle, into a tubular network that is thought to be involved in antigen presentation. Other than a requirement for microtubules and kinesin, little is known about the molecular mechanisms that drive lysosome tubulation. Here, we show that macrophage cell lines readily form TLs after LPS exposure, with a requirement for the Rab7 GTPase and its effectors RILP (Rab7-interacting lysosomal protein) and FYCO1 (coiled-coil domain-containing protein 1), which respectively modulate the dynein and kinesin microtubule motor proteins. We also show that Arl8B, a recently identified lysosomal GTPase, and its effector SKIP, are also important for TL biogenesis. Finally, we reveal that TLs are significantly more motile than punctate lysosomes within the same LPS-treated cells. Therefore, we identify the first molecular regulators of lysosome tubulation and we show that TLs represent a more dynamic lysosome population.

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