Article

The Rho Family GTPase Rif Induces Filopodia through mDia2

Mammalian Cell Biology Laboratory, Department of Biochemistry, School of Medical Sciences, University of Bristol, Bristol BS8 1TD, United Kingdom.
Current Biology (Impact Factor: 9.92). 02/2005; 15(2):129-33. DOI: 10.1016/j.cub.2005.01.011
Source: PubMed

ABSTRACT Eukaryotic cells produce a variety of specialized actin-rich surface protrusions. These include filopodia-thin, highly dynamic projections that help cells to sense their external environment. Filopodia consist of parallel filaments of actin, bundled by actin crosslinking proteins. The filaments are oriented with their rapidly growing "barbed" ends at the protruding tip and their slowly growing "pointed" ends at the base. Extension occurs by polymerization at the tip and is controlled by regulation of filament capping. The Rho GTPase Cdc42 is a key mediator of filopodia formation, which it regulates through binding CRIB domain-containing effectors. Cdc42 binds and activates the WASP proteins, which in turn activate the actin-nucleating complex Arp2/3. It also binds and activates IRSp53, which recruits the Ena/WASP family protein Mena to the filopodial tip and protects elongating actin filaments from capping. Previously, we identified another Rho family GTPase, Rif, as a potent stimulator of filopodial protrusion through a mechanism that does not require Cdc42. Here we characterize the differences between filopodia induced by these two small GTPases and show that the Rif effector in this pathway is the Diaphanous-related formin mDia2. Thus, Rif and Cdc42 represent two distinct routes to the induction of filopodia-producing structures with both shared and unique properties.

0 Followers
 · 
109 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: Cells employ protrusive leading edges to navigate and promote their migration in diverse physiological environments. Classical models of leading edge protrusion rely on a treadmilling dendritic actin network that undergoes continuous assembly nucleated by the Arp2/3 complex, forming ruffling lamellipodia. Recent work demonstrated, however, that in the absence of the Arp2/3 complex, fibroblast cells adopt a leading edge with filopodia-like protrusions (FLP) and maintain an ability to move, albeit with altered responses to different environmental signals. Here, we show that formin-family actin nucleators are required for the extension of FLPs but are insufficient to produce a continuous leading edge in fibroblasts lacking Arp2/3 complex. Myosin-II is concentrated in arc-like regions of the leading edge in-between FLPs, and its activity is required for coordinated advancement of these regions with formin-generated FLP. We propose that actomyosin contraction acting against membrane tension advances the web of arcs between FLPs. Predictions of this model are verified experimentally. The dependence of myosin-II in leading edge advancement helps explain the previously reported defect in directional movement in the Arpc3 null fibroblasts. We provide further evidence that this defect is cell-autonomous during chemotaxis. © 2015 by The American Society for Cell Biology.
    Molecular Biology of the Cell 01/2015; 26(5). DOI:10.1091/mbc.E14-07-1250 · 4.55 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: RhoF is a member of the Rho GTPase family that has been implicated in various cell functions including long filopodia formation, adhesion, and migration of cells. Although RhoF is expressed in lymphoid tissues, the roles of RhoF in B cell development remain largely unclear. On the other hand, other members of the Rho GTPase family, such as Cdc42, RhoA, and Rac, have been intensively studied and are known to be required for B cell development in the bone marrow and spleen. We hypothesized that RhoF is also involved in B cell development. To examine our hypothesis, we analyzed B cell development in RhoF knockout (KO) mice and found a significant reduction in marginal zone (MZ) B cells in the spleen, although T cell development in the thymus and spleen was not affected. Consistent with these results, the width of the MZ B cell region in the spleen was significantly reduced in the RhoF KO mice. However, the antigen-specific antibody titer of IgM and IgG3 after MZ B cell-specific antigen (T cell-independent antigen, type I) stimulation was not affected by RhoF deletion. Furthermore, we demonstrated that RhoF was dispensable for stromal cell-derived factor-1α- and B lymphocyte chemoattractant-induced B cell migration. These results suggest that RhoF promotes MZ B cell development in the spleen.
    Nagoya journal of medical science 08/2014; 76(3-4):293-305. · 0.80 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Rho GTPases are critical for platelet function. Although the roles of RhoA, Rac and Cdc42 are characterized, platelets express other Rho GTPases, whose activities are less well understood. This review summarizes our understanding of the roles of platelet Rho GTPases and focuses particularly on the functions of Rif and RhoG. In human platelets, Rif interacts with cytoskeleton regulators including formins mDia1 and mDia3, whereas RhoG binds SNARE-complex proteins and cytoskeletal regulators ELMO and DOCK1. Knockout mouse studies suggest that Rif plays no critical functions in platelets, likely due to functional overlap with other Rho GTPases. In contrast, RhoG is essential for normal granule secretion downstream of the collagen receptor GPVI. The central defect in RhoG-/- platelets is reduced dense granule secretion, which impedes integrin activation and aggregation and limits platelet recruitment to growing thrombi under shear, translating into reduced thrombus formation in vivo. Potential avenues for future work on Rho GTPases in platelets are also highlighted, including identification of the key regulator for platelet filopodia formation and investigation of the role of the many Rho GTPase regulators in platelet function in both health and disease.