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Synaptopodin orchestrates actin organization and cell motility via regulation of RhoA signalling

Nature Cell Biology volume 8, pages 485–491 (2006)Cite this article

Abstract

The Rho family of small GTPases (RhoA, Rac1 and Cdc42) controls signal-transduction pathways that influence many aspects of cell behaviour, including cytoskeletal dynamics1,2,3. At the leading edge, Rac1 and Cdc42 promote cell motility through the formation of lamellipodia and filopodia, respectively. On the contrary, RhoA promotes the formation of contractile actin–myosin-containing stress fibres in the cell body and at the rear1,2,4. Here, we identify synaptopodin, an actin-associated protein, as a novel regulator of RhoA signalling and cell migration in kidney podocytes. We show that synaptopodin induces stress fibres by competitive blocking of Smurf1-mediated ubiquitination of RhoA, thereby preventing the targeting of RhoA for proteasomal degradation. Gene silencing of synaptopodin in kidney podocytes causes the loss of stress fibres and the formation of aberrant non-polarized filopodia and impairment of cell migration. Together, these data show that synaptopodin is essential for the integrity of the podocyte actin cytoskeleton and for the regulation of podocyte cell migration.

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Figure 1: Synaptopodin regulates the expression and function of RhoA.
Figure 2: Antagonistic regulation of stress fibre formation by synaptopodin and Smurf1.
Figure 3: Synaptopodin upregulates RhoA protein expression and activity by blocking the Smurf1-mediated degradation of RhoA.
Figure 4: Regulation of podocyte migration by synaptopodin.

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Acknowledgements

We thank S. Ratner and M. Donnelly for excellent technical assistance. We thank J. Wrana (University of Toronto, Toronto, Canada) for RhoAK6,7R cDNA, F. Gertler (MIT, Cambridge, MA) for anti-Mena antibodies, T. Takenawa (University of Tokyo, Tokyo, Japan) for GST–RhoAT19N cDNA, T. Imamura (The JFCR Cancer Institute, Tokyo, Japan) for Smurf1 (wild-type and C710A) cDNA, K. Tanaka (Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan) for ubiquitin cDNA and M. Pollak (Brigham and Women's Hospital and Harvard Medical School, Boston, MA) for α-actinin-4 antibody. It is a pleasure to acknowledge helpful discussions with H. Yamaguchi (Albert Einstein College of Medicine, Bronx, New York, NY). K. Asanuma was supported by the National Kidney Foundation and the Alumini Association of Juntendo University (Juntendo University, Tokyo, Japan), and K. Kim by the Kidney and Urology Foundation of America. This work was supported by National Institutes of Health grants (DA18886, DK57683), and the George M. O'Brien Kidney Center (DK064236) to P.M.

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  1. Katsuhiko Asanuma and Etsuko Yanagida-Asanuma: These authors contributed equally to this work.

Authors and Affiliations

  1. Department of Medicine, Mount Sinai School of Medicine, New York, 10029, NY, USA

    Katsuhiko Asanuma, Etsuko Yanagida-Asanuma, Christian Faul, Kwanghee Kim & Peter Mundel

  2. Department of Internal Medicine, Juntendo University School of Medicine, Tokyo, 113–8421, Japan

    Yasuhiko Tomino

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  1. Katsuhiko Asanuma
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Correspondence to Peter Mundel.

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Asanuma, K., Yanagida-Asanuma, E., Faul, C. et al. Synaptopodin orchestrates actin organization and cell motility via regulation of RhoA signalling. Nat Cell Biol 8, 485–491 (2006). https://doi.org/10.1038/ncb1400

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