RHO FAMILY SMALL GTPASES IN SHEAR STRESS SIGNALING

Blood vessels and blood cells are under continuous fluid shear. Studies on vascular endothelium and smooth muscle cells have shown the importance of this mechanical stress in cell signal transduction, gene expression, vascular remodeling, and cell survival. However, in circulating leukocytes, shear-induced signal transduction has not been investigated. Here we examine in vivo and in vitro the control of pseudopods in leukocytes under the influence of fluid shear stress and the role of the Rho family small GTPases. We used a combination of HL-60 cells differentiated into neutrophils (1.4% dimethyl sulfoxide for 5 days) and fresh leukocytes from Rac knockout mice. The cells responded to shear stress (5 dyn/cm2) with retraction of pseudopods and reduction of their projected cell area. The Rac1 and Rac2 activities were decreased by fluid shear in a time- and magnitude-dependent manner, whereas the Cdc42 activity remained unchanged (up to 5 dyn/cm2). The Rho activity was transiently increased and recovered to static levels after 10 min of shear exposure (5 dyn/cm2). Inhibition of either Rac1 or Rac2 slightly but significantly diminished the fluid shear response. Transfection with Rac1-positive mutant enhanced the pseudopod formation during shear. Leukocytes from Rac1-null and Rac2-null mice had an ability to form pseudopods in response to platelet-activating factor but did not respond to fluid shear in vitro. Leukocytes in wild-type mice retracted pseudopods after physiological shear exposure, whereas cells in Rac1-null mice showed no retraction during equal shear. On leukocytes from Rac2-null mice, however, fluid shear exerted a biphasic effect. Leukocytes with extended pseudopods slightly decreased in length, whereas initially round cells increased in length after shear application. The disruption of Rac activity made leukocytes nonresponsive to fluid shear, induced cell adhesion and microvascular stasis, and decreased microvascular density. These results suggest that deactivation of Rac activity by fluid shear plays an important role in stable circulation of leukocytes.

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Regulators and Effectors of Small GTPases: Rho Family

10.1016/s0076-6879(06)x1068-6 ◽

2006 ◽

Keyword(s):

Small Gtpases ◽

Rho Family

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Faculty Opinions recommendation of Matrix-specific suppression of integrin activation in shear stress signaling.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.1052844.504771 ◽

2006 ◽

Author(s):

Mina J Bissell

Keyword(s):

Shear Stress ◽

Stress Signaling ◽

Integrin Activation ◽

Specific Suppression

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PseudoGTPase domains in p190RhoGAP proteins: a mini-review

Biochemical Society Transactions ◽

10.1042/bst20180481 ◽

2018 ◽

Vol 46 (6) ◽

pp. 1713-1720 ◽

Cited By ~ 6

Author(s):

Amy L. Stiegler ◽

Titus J. Boggon

Keyword(s):

Family Members ◽

Small Gtpases ◽

Small Gtpase ◽

Signaling Proteins ◽

New Family ◽

Gtpase Activating Proteins ◽

Rho Family ◽

Biochemical Analyses ◽

Catalytic Cleft

Pseudoenzymes generally lack detectable catalytic activity despite adopting the overall protein fold of their catalytically competent counterparts, indeed ‘pseudo’ family members seem to be incorporated in all enzyme classes. The small GTPase enzymes are important signaling proteins, and recent studies have identified many new family members with noncanonical residues within the catalytic cleft, termed pseudoGTPases. To illustrate recent discoveries in the field, we use the p190RhoGAP proteins as an example. p190RhoGAP proteins (ARHGAP5 and ARHGAP35) are the most abundant GTPase activating proteins for the Rho family of small GTPases. These are key regulators of Rho signaling in processes such as cell migration, adhesion and cytokinesis. Structural biology has complemented and guided biochemical analyses for these proteins and has allowed discovery of two cryptic pseudoGTPase domains, and the re-classification of a third, previously identified, GTPase-fold domain as a pseudoGTPase. The three domains within p190RhoGAP proteins illustrate the diversity of this rapidly expanding pseudoGTPase group.

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Identification and characterization of a new isoform of small GTPase RhoE

Communications Biology ◽

10.1038/s42003-020-01295-4 ◽

2020 ◽

Vol 3 (1) ◽

Author(s):

Yuan Dai ◽

Weijia Luo ◽

Xiaojing Yue ◽

Wencai Ma ◽

Jing Wang ◽

...

Keyword(s):

Rho Gtpase ◽

Small Gtpases ◽

Small Gtpase ◽

Biological Functions ◽

Coding Region ◽

Alternative Translation ◽

Rho Family ◽

Binding Capability ◽

Identification And Characterization

Abstract The Rho family of GTPases consists of 20 members including RhoE. Here, we discover the existence of a short isoform of RhoE designated as RhoEα, the first Rho GTPase isoform generated from alternative translation. Translation of this new isoform is initiated from an alternative start site downstream of and in-frame with the coding region of the canonical RhoE. RhoEα exhibits a similar subcellular distribution while its protein stability is higher than RhoE. RhoEα contains binding capability to RhoE effectors ROCK1, p190RhoGAP and Syx. The distinct transcriptomes of cells with the expression of RhoE and RhoEα, respectively, are demonstrated. The data propose distinctive and overlapping biological functions of RhoEα compared to RhoE. In conclusion, this study reveals a new Rho GTPase isoform generated from alternative translation. The discovery provides a new scope of understanding the versatile functions of small GTPases and underlines the complexity and diverse roles of small GTPases.

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SmgGDS: An Emerging Master Regulator of Prenylation and Trafficking by Small GTPases in the Ras and Rho Families

Frontiers in Molecular Biosciences ◽

10.3389/fmolb.2021.685135 ◽

2021 ◽

Vol 8 ◽

Author(s):

Anthony C. Brandt ◽

Olivia J. Koehn ◽

Carol L. Williams

Keyword(s):

Splice Variants ◽

Therapeutic Strategies ◽

Small Gtpases ◽

Peptide Inhibitors ◽

Signaling Cascades ◽

Therapeutic Targeting ◽

Growing Body ◽

History Of ◽

Rho Family ◽

Mutant Forms

Newly synthesized small GTPases in the Ras and Rho families are prenylated by cytosolic prenyltransferases and then escorted by chaperones to membranes, the nucleus, and other sites where the GTPases participate in a variety of signaling cascades. Understanding how prenylation and trafficking are regulated will help define new therapeutic strategies for cancer and other disorders involving abnormal signaling by these small GTPases. A growing body of evidence indicates that splice variants of SmgGDS (gene name RAP1GDS1) are major regulators of the prenylation, post-prenylation processing, and trafficking of Ras and Rho family members. SmgGDS-607 binds pre-prenylated small GTPases, while SmgGDS-558 binds prenylated small GTPases. This review discusses the history of SmgGDS research and explains our current understanding of how SmgGDS splice variants regulate the prenylation and trafficking of small GTPases. We discuss recent evidence that mutant forms of RabL3 and Rab22a control the release of small GTPases from SmgGDS, and review the inhibitory actions of DiRas1, which competitively blocks the binding of other small GTPases to SmgGDS. We conclude with a discussion of current strategies for therapeutic targeting of SmgGDS in cancer involving splice-switching oligonucleotides and peptide inhibitors.

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Co-ordinated Ras and Rac activity shapes macropinocytic cups and enables phagocytosis of geometrically diverse bacteria

10.1101/763748 ◽

2019 ◽

Author(s):

Catherine M. Buckley ◽

Henderikus Pots ◽

Aurelie Gueho ◽

Ben A. Phillips ◽

Bernd Gilsbach ◽

...

Keyword(s):

Dictyostelium Discoideum ◽

Small Gtpases ◽

Small Gtpase ◽

Extracellular Material ◽

Multidomain Protein ◽

Complex Shapes ◽

Rho Family ◽

Phagocytic Cups ◽

Interior Domain ◽

Professional Phagocyte

AbstractEngulfment of extracellular material by phagocytosis or macropinocytosis depends on the ability of cells to generate specialised cup shaped protrusions. To effectively capture and internalise their targets, these cups are organised into a ring or ruffle of actin-driven protrusion encircling a non-protrusive interior domain. These functional domains depend on the combined activities of multiple Ras and Rho family small GTPases, but how their activities are integrated and differentially regulated over space and time is unknown. Here, we show that the amoeba Dictyostelium discoideum coordinates Ras and Rac activity using the multidomain protein RGBARG (RCC1, RhoGEF, BAR and RasGAP-containing protein). We find RGBARG uses a tripartite mechanism of Ras, Rac and phospholipid interactions to localise at the protruding edge and interface with the interior of both macropinocytic and phagocytic cups. There, RGBARG shapes the protrusion by driving Rac activation at the rim whilst suppressing expansion of the active Ras interior domain. Consequently, cells lacking RGBARG form enlarged, flat interior domains unable to generate large macropinosomes. During phagocytosis, we find that disruption of RGBARG causes a geometry-specific defect in engulfing rod-shaped bacteria and ellipsoidal beads. This demonstrates the importance of co-ordinating small GTPase activities during engulfment of more complex shapes and thus the full physiological range of microbes, and how this is achieved in a model professional phagocyte.

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