Faculty Opinions recommendation of AMPylation of Rho GTPases by Vibrio VopS disrupts effector binding and downstream signaling.

Rho proteins of plants (ROPs) form a specific clade of Rho GTPases, which are involved in either plant immunity or susceptibility to diseases. They are intensively studied in grass host plants, in which ROPs are signaling hubs downstream of both cell surface immune receptor kinases and intracellular nucleotide-binding leucine-rich repeat receptors, which activate major branches of plant immune signaling. Additionally, invasive fungal pathogens may co-opt the function of ROPs for manipulation of the cytoskeleton, cell invasion and host cell developmental reprogramming, which promote pathogenic colonization. Strikingly, mammalian bacterial pathogens also initiate both effector-triggered susceptibility for cell invasion and effector-triggered immunity via Rho GTPases. In this review, we summarize central concepts of Rho signaling in disease and immunity of plants and briefly compare them to important findings in the mammalian research field. We focus on Rho activation, downstream signaling and cellular reorganization under control of Rho proteins involved in disease progression and pathogen resistance.

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Targeting and activation of Rac1 are mediated by the exchange factor β-Pix

The Journal of Cell Biology ◽

10.1083/jcb.200509096 ◽

2006 ◽

Vol 172 (5) ◽

pp. 759-769 ◽

Cited By ~ 174

Author(s):

Jean Paul ten Klooster ◽

Zahara M. Jaffer ◽

Jonathan Chernoff ◽

Peter L. Hordijk

Keyword(s):

Rho Gtpases ◽

Molecular Mechanisms ◽

Rho Gtpase ◽

Focal Adhesions ◽

Exchange Factor ◽

Downstream Signaling ◽

Intracellular Targeting ◽

Dynamics And Control ◽

P21 Activated Kinase ◽

Gtpase Activation

Rho guanosine triphosphatases (GTPases) are critical regulators of cytoskeletal dynamics and control complex functions such as cell adhesion, spreading, migration, and cell division. It is generally accepted that localized GTPase activation is required for the proper initiation of downstream signaling events, although the molecular mechanisms that control targeting of Rho GTPases are unknown. In this study, we show that the Rho GTPase Rac1, via a proline stretch in its COOH terminus, binds directly to the SH3 domain of the Cdc42/Rac activator β-Pix (p21-activated kinase [Pak]–interacting exchange factor). The interaction with β-Pix is nucleotide independent and is necessary and sufficient for Rac1 recruitment to membrane ruffles and to focal adhesions. In addition, the Rac1–β-Pix interaction is required for Rac1 activation by β-Pix as well as for Rac1-mediated spreading. Finally, using cells deficient for the β-Pix–binding kinase Pak1, we show that Pak1 regulates the Rac1–β-Pix interaction and controls cell spreading and adhesion-induced Rac1 activation. These data provide a model for the intracellular targeting and localized activation of Rac1 through its exchange factor β-Pix.

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Title: In vivo phosphatidylserine variations steer Rho GTPase signaling in a cell-context dependent manner

10.1101/471573 ◽

2018 ◽

Author(s):

Matthieu Pierre Platre ◽

Vincent Bayle ◽

Laia Armengot ◽

Joseph Bareille ◽

Maria Mar Marques-Bueno ◽

...

Keyword(s):

Single Molecule ◽

Rho Gtpases ◽

Rho Gtpase ◽

Plant Root ◽

Super Resolution ◽

Small Gtpase ◽

Auxin Signaling ◽

Dependent Manner ◽

Downstream Signaling

AbstractRho GTPases are master regulators of cell signaling, but how they are regulated depending on the cellular context is unclear. Here, we show that the phospholipid phosphatidylserine acts as a developmentally-controlled lipid rheostat that tunes Rho GTPase signaling in Arabidopsis. Live super-resolution single molecule imaging revealed that RHO-OF-PLANT6 (ROP6) is stabilized by phosphatidylserine into plasma membrane (PM) nanodomains, which is required for auxin signaling. Furthermore, we uncovered that the PM phosphatidylserine content varies during plant root development and that the level of phosphatidylserine modulates the quantity of ROP6 nanoclusters induced by auxin and hence downstream signaling, including regulation of endocytosis and gravitropism. Our work reveals that variations in phosphatidylserine levels are a physiological process that may be leveraged to regulate small GTPase signaling during development.One Sentence SummaryPhosphatidylserine acts as a developmentally-controlled lipid rheostat that regulates cellular auxin sensitivity and plant development.

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Functional interdependence of NHE1 and merlin in human melanoma cells

Biochemistry and Cell Biology ◽

10.1139/bcb-2014-0041 ◽

2014 ◽

Vol 92 (6) ◽

pp. 530-540 ◽

Cited By ~ 4

Author(s):

Fabian Frontzek ◽

Svenja Nitzlaff ◽

Malte Horstmann ◽

Albrecht Schwab ◽

Christian Stock

Keyword(s):

Tumor Suppressor ◽

Rho Gtpases ◽

Melanoma Cells ◽

Human Melanoma ◽

Tumor Suppressor Function ◽

Functional Link ◽

Downstream Signaling ◽

Nhe1 Activity ◽

Cytosolic Acidification ◽

Expression And Activity

Upregulation of the Na+/H+ exchanger isoform 1 (NHE1) has been correlated with tumor malignancy. In contrast, moesin-radixin-ezrin–like protein (merlin) is a tumor suppressor that protects from cancerogenesis. Merlin is highly related to the members of the ezrin, radixin, and moesin (ERM) protein family that are directly attached to and functionally linked with NHE1. In addition, merlin inhibits the MAPK cascade and the Rho-GTPases known to activate NHE1 activity. The present study investigates whether NHE1 expression and activity affect merlin or, conversely, whether merlin has an impact on NHE1 in human melanoma (MV3) cells. Indeed, features of merlin-deficient MV3 cells point to a functional link: merlin-deficient cells showed a decreased NHE1 expression and, paradoxically, an increase in NHE1 activity as measured upon cytosolic acidification (NH4Cl prepulse method). Loss of merlin also led to an elevated cell motility that could be further increased by NHE1 overexpression, whereas NHE1 overexpression alone had no effect on migration. In contrast, neither NHE1 expression nor its activity had an impact on merlin expression. These results suggest a novel tumor suppressor function of merlin in melanoma cells: the inhibition of the proto-oncogenic NHE1 activity, possibly including its downstream signaling pathways.

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The Multi-Level Mechanism of Action of a Pan-Ras Inhibitor Explains its Antiproliferative Activity on Cetuximab-Resistant Cancer Cells

Frontiers in Molecular Biosciences ◽

10.3389/fmolb.2021.625979 ◽

2021 ◽

Vol 8 ◽

Author(s):

Renata Tisi ◽

Michela Spinelli ◽

Alessandro Palmioli ◽

Cristina Airoldi ◽

Paolo Cazzaniga ◽

...

Keyword(s):

Experimental Data ◽

Mathematical Model ◽

Cancer Cells ◽

Water Soluble ◽

Downstream Signaling ◽

Ras Activation ◽

Multi Level ◽

Activation Cycle ◽

Effector Binding ◽

Ras Inhibitors

Ras oncoproteins play a crucial role in the onset, maintenance, and progression of the most common and deadly human cancers. Despite extensive research efforts, only a few mutant-specific Ras inhibitors have been reported. We show that cmp4–previously identified as a water-soluble Ras inhibitor– targets multiple steps in the activation and downstream signaling of different Ras mutants and isoforms. Binding of this pan-Ras inhibitor to an extended Switch II pocket on HRas and KRas proteins induces a conformational change that down-regulates intrinsic and GEF-mediated nucleotide dissociation and exchange and effector binding. A mathematical model of the Ras activation cycle predicts that the inhibitor severely reduces the proliferation of different Ras-driven cancer cells, effectively cooperating with Cetuximab to reduce proliferation even of Cetuximab-resistant cancer cell lines. Experimental data confirm the model prediction, indicating that the pan-Ras inhibitor is an appropriate candidate for medicinal chemistry efforts tailored at improving its currently unsatisfactory affinity.

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TAMI-42. THE ROLE OF HFE AND IRON IN CELL ADHESION AND MIGRATION IN GLIOBLASTOMA

Neuro-Oncology ◽

10.1093/neuonc/noab196.825 ◽

2021 ◽

Vol 23 (Supplement_6) ◽

pp. vi207-vi207

Author(s):

Ganesh Shenoy ◽

Katie M Troike ◽

Madison Kuhn ◽

Becky Slagle Webb ◽

Amanda Snyder ◽

...

Keyword(s):

Basement Membrane ◽

Surgical Resection ◽

Rho Gtpases ◽

Iron Status ◽

Modern Medicine ◽

Downstream Signaling ◽

Migratory Capacity ◽

Cell Adhesion And Migration ◽

Iron Pool ◽

Mouse Glioma

Abstract Glioblastoma (GBM) remains one of the most difficult to treat malignancies facing modern medicine. The strong migratory and invasive capacity of GBM cells allows for diffuse invasion into neighboring healthy brain which presents a significant hurdle for complete surgical resection of these tumors. Unsurprisingly, even after receiving maximal surgical resection, radiation and chemotherapy, the majority of GBM patients end up with recurrent disease. Increased expression levels of the homeostatic iron regulator gene (HFE) in brain tumors such as GBM have been associated with poorer outcomes. In order to better understand how HFE expression impacts the adhesive and migratory capacity of GBM, we utilized syngeneic mouse glioma models (KR158, CT2A) that have been transfected to either over-express or under-express HFE. We observed that knocking down HFE in the KR158 model resulted in significantly decreased migratory capacity as well as decreased adhesion to fibronectin and artificial basement membrane. Likewise, overexpressing HFE in a CT2A model resulted in increased adhesion to fibronectin or artificial basement membrane. Since HFE is known to regulate iron uptake, we studied how modulating the iron status of GBM cells impacted their ability to migrate and adhere. We found that increasing the iron pool of these mouse glioma models by exposure to exogenous iron compounds decreased migratory capacity. To better understand mechanistically how HFE and iron status impacted migration and adhesion, we probed how expression of integrins and their downstream signaling molecules, the Rho GTPases were altered in response to iron. We found that exposure to iron decreased levels of the Rho GTPases Cdc42 and RhoA. Furthermore, cells that overexpressed HFE were found to have increased expression of integrin β1 and integrin α5 suggesting that HFE and iron may impact integrins and their downstream signaling pathways to alter migration of GBM cells.

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Distinct signaling by insulin and IGF-1 receptors and their extra- and intracellular domains

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.2019474118 ◽

2021 ◽

Vol 118 (17) ◽

pp. e2019474118

Author(s):

Hirofumi Nagao ◽

Weikang Cai ◽

Nicolai J. Wewer Albrechtsen ◽

Martin Steger ◽

Thiago M. Batista ◽

...

Keyword(s):

Cell Cycle ◽

Membrane Trafficking ◽

Rho Gtpases ◽

Cell Cycle Progression ◽

Biological Effects ◽

Mammalian Target Of Rapamycin ◽

Cycle Progression ◽

Downstream Signaling ◽

Molecular Signals ◽

Intracellular Domains

Insulin and insulin-like growth factor 1 (IGF-1) receptors share many downstream signaling pathways but have unique biological effects. To define the molecular signals contributing to these distinct activities, we performed global phosphoproteomics on cells expressing either insulin receptor (IR), IGF-1 receptor (IGF1R), or chimeric IR-IGF1R receptors. We show that IR preferentially stimulates phosphorylations associated with mammalian target of rapamycin complex 1 (mTORC1) and Akt pathways, whereas IGF1R preferentially stimulates phosphorylations on proteins associated with the Ras homolog family of guanosine triphosphate hydrolases (Rho GTPases), and cell cycle progression. There were also major differences in the phosphoproteome between cells expressing IR versus IGF1R in the unstimulated state, including phosphorylation of proteins involved in membrane trafficking, chromatin remodeling, and cell cycle. In cells expressing chimeric IR-IGF1R receptors, these differences in signaling could be mapped to contributions of both the extra- and intracellular domains of these receptors. Thus, despite their high homology, IR and IGF1R preferentially regulate distinct networks of phosphorylation in both the basal and stimulated states, allowing for the unique effects of these hormones on organismal function.

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