@article{d7fa2514da6641638a161e5fe4004551,
title = "Rab5 regulates motility of early endosomes on microtubules",
abstract = "The small GTPase Rab5 regulates membrane docking and fusion in the early endocytic pathway. Here we reveal a new role for Rab5 in the regulation of endosome interactions with the microtubule network. Using Rab5 fused to green fluorescent protein we show that Rab5-positive endosomes move on microtubules in vivo. In vitro, Rab5 stimulates both association of early endosomes with microtubules and early-endosome motility towards the minus ends of microtubules. Moreover, similarly to endosome membrane docking and fusion, Rab5-dependent endosome movement depends on the phosphatidylinositol-3-OH kinase hVPS34. Thus, Rab5 functionally links regulation of membrane transport, motility and intracellular distribution of early endosomes.",
author = "Erik Nielsen and Fedor Severin and Backer, {Jonathan M.} and Hyman, {Anthony A.} and Marino Zerial",
note = "Funding Information: we have nevertheless found that these processes are coordinated through PI(3)K. The observation that endosome motility requires the PI(3)K activity of hVPS34 is of particular interest given the recent advances in the understanding of the role of PtdIns(3)P in membrane trafficking. In vivo, inhibition of PI(3)K activity with wortmannin or with function-blocking antibodies to hVPS34 interferes with the accumulation of newly endocytosed proteins in structures at the centre of the cell30,37. The Rab5 effector protein EEA1 and several other endosomal proteins are recruited to endosomes through interactions with PtdIns(3)P38–40. We have recently demonstrated that Rab5 selectively interacts with the PI(3)Ks p110β and hVPS34 (ref. 29). We propose that the interaction of Rab5–GTP with hVPS34 results in a localized production of PtdIns(3)P which, together with the recruitment of Rab5 effectors, contributes to the formation of a {\textquoteleft}microdomain{\textquoteright} on the endosomal membrane. This model is supported by recent studies showing that EEA1 forms high-molecular-weight oligomers with the Rabaptin-5 complex and the ATPase NSF (N-ethylmaleimide-sensitive factor) upon recruitment to endosomal membranes41. In such microdomains Rab5 could directly interact with a microtubule motor, as Rab6 does with Rabkinesin-6, or interact with an accessory protein associated with the motor protein, or recruit a regulatory protein that would stimulate a kinesin motor. In addition, the observation that Rab5 stimulates the stable association of endosomes with microtubules suggests that this GTPase may not only regulate motor activity but also modulate the activity of microtubule-associated proteins. In this way the multiplicity of effectors recruited by Rab5– GTP13 would be coordinated to regulate endosomal docking, fusion and motility on microtubules. □ Funding Information: ACKNOWLEDGEMENTS We thank M. McNiven for MC44 antibodies, B.H. Toh for EEA1 antibodies, and E. Karsenti for tubulin antibodies and purified centrosomes. R. Lippe and M. Miaczynska provided Rab5–RabGDI complex, and H. McBride provided recombinant α-SNAP L294A. E.N. and F.S. are recipients of EMBO Long-term and Max Planck Fellowships, respectively. This work was supported by the Max Planck Gesellschaft, grants from the Human Frontier Science Program (G-432/96), EU TMR (ERB-CT96-0020), and Biomed (BMH4-97-2410) (to M.Z.). J.M.B. is supported by NIH grant GM559692. Correspondence and requests for materials should be addressed to M.Z. Supplementary information is available on Nature Cell Biology{\textquoteright}s World-Wide Web site at http:// cellbio.nature.com.",
year = "1999",
month = oct,
doi = "10.1038/14075",
language = "English (US)",
volume = "1",
pages = "376--382",
journal = "Nature Cell Biology",
issn = "1465-7392",
publisher = "Nature Publishing Group",
number = "6",
}