Life Sciences Research for Lifelong Health

Publications heidi-welch

Title / Authors / Details Open Access Download

Platelets in neutrophil recruitment to sites of inflammation.
Pitchford S, Pan D, Welch HC

This review describes the essential roles of platelets in neutrophil recruitment from the bloodstream into inflamed and infected tissues, with a focus on recent findings.

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Current opinion in hematology, , 1531-7048, , 2016

PMID: 27820736

Truncating PREX2 mutations activate its GEF activity and alter gene expression regulation in NRAS-mutant melanoma.
Lissanu Deribe Y, Shi Y, Rai K, Nezi L, Amin SB, Wu CC, Akdemir KC, Mahdavi M, Peng Q, Chang QE, Hornigold K, Arold ST, Welch HC, Garraway LA, Chin L

PREX2 (phosphatidylinositol-3,4,5-triphosphate-dependent Rac-exchange factor 2) is a PTEN (phosphatase and tensin homolog deleted on chromosome 10) binding protein that is significantly mutated in cutaneous melanoma and pancreatic ductal adenocarcinoma. Here, genetic and biochemical analyses were conducted to elucidate the nature and mechanistic basis of PREX2 mutation in melanoma development. By generating an inducible transgenic mouse model we showed an oncogenic role for a truncating PREX2 mutation (PREX2(E824)*) in vivo in the context of mutant NRAS. Using integrative cross-species gene expression analysis, we identified deregulated cell cycle and cytoskeleton organization as significantly perturbed biological pathways in PREX2 mutant tumors. Mechanistically, truncation of PREX2 activated its Rac1 guanine nucleotide exchange factor activity, abolished binding to PTEN and activated the PI3K (phosphatidyl inositol 3 kinase)/Akt signaling pathway. We further showed that PREX2 truncating mutations or PTEN deletion induces down-regulation of the tumor suppressor and cell cycle regulator CDKN1C (also known as p57(KIP2)). This down-regulation occurs, at least partially, through DNA hypomethylation of a differentially methylated region in chromosome 11 that is a known regulatory region for expression of the CDKN1C gene. Together, these findings identify PREX2 as a mediator of NRAS-mutant melanoma development that acts through the PI3K/PTEN/Akt pathway to regulate gene expression of a cell cycle regulator.

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Proceedings of the National Academy of Sciences of the United States of America, , 1091-6490, , 2016

PMID: 26884185

Open Access

Norbin Stimulates the Catalytic Activity and Plasma Membrane Localization of the Guanine-Nucleotide Exchange Factor P-Rex1.
Pan D, Barber MA, Hornigold K, Baker MJ, Toth JM, Oxley D, Welch HC

P-Rex1 is a guanine-nucleotide exchange factor (GEF) that activates the small G protein (GTPase) Rac1 to control Rac1-dependent cytoskeletal dynamics, and thus cell morphology. Three mechanisms of P-Rex1 regulation are currently known: (i) binding of the phosphoinositide second messenger PIP3, (ii) binding of the Gβγ subunits of heterotrimeric G proteins, and (iii) phosphorylation of various serine residues. Using recombinant P-Rex1 protein to search for new binding partners, we isolated the G-protein coupled receptor (GPCR)-adaptor protein Norbin (Neurochondrin, NCDN) from mouse brain fractions. Coimmunoprecipitation confirmed the interaction between overexpressed P-Rex1 and Norbin in COS-7 cells, as well as between endogenous P-Rex1 and Norbin in HEK-293 cells. Binding assays with purified recombinant proteins showed that their interaction is direct, and mutational analysis revealed that the PH domain of P-Rex1 is required. Rac-GEF activity assays with purified recombinant proteins showed that direct interaction with Norbin increases the basal, PIP3- and Gβγ-stimulated Rac-GEF activity of P-Rex1. Pak-CRIB pull-down assays demonstrated that Norbin promotes the P-Rex1 mediated activation of endogenous Rac1 upon stimulation of HEK-293 cells with lysophosphatidic acid. Finally, immunofluorescence microscopy and subcellular fractionation showed that coexpression of P-Rex1 and Norbin induces a robust translocation of both proteins from the cytosol to the plasma membrane, as well as promoting cell spreading, lamellipodia formation and membrane ruffling, cell morphologies generated by active Rac1. In summary, we have identified a novel mechanism of P-Rex1 regulation through the GPCR-adaptor protein Norbin, a direct P-Rex1 interacting protein that promotes the Rac-GEF activity and membrane localization of P-Rex1.

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The Journal of biological chemistry, , 1083-351X, , 2016

PMID: 26792863

Open Access

Small GTPases and their guanine-nucleotide exchange factors and GTPase-activating proteins in neutrophil recruitment.
Baker MJ, Pan D, Welch HC

The review describes the roles of Rho- and Rap-guanosine triphosphatases (GTPases) and of their activators, guanine-nucleotide exchange factors (GEFs), and inhibitors, GTPase activating proteins (GAPs), in neutrophil recruitment from the blood stream into inflamed tissues, with a focus on recently identified roles in neutrophils, endothelial cells, and platelets.

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Current opinion in hematology, 23, 1531-7048, 44-54, 2016

PMID: 26619317

The dynamics of Rho GTPase signaling and implications for targeting cancer and the tumor microenvironment.
Pajic M, Herrmann D, Vennin C, Conway JR, Chin VT, Johnsson AE, Welch HC, Timpson P

Numerous large scale genomics studies have demonstrated that cancer is a molecularly heterogeneous disease, characterized by acquired changes in the structure and DNA sequence of tumor genomes. More recently, the role of the equally complex tumor microenvironment in driving the aggressiveness of this disease is increasingly being realized. Tumor cells are surrounded by activated stroma, creating a dynamic environment that promotes cancer development, metastasis and chemoresistance. The Rho family of small GTPases plays an essential role in the regulation of cell shape, cytokinesis, cell adhesion, and cell motility. Importantly, these processes need to be considered in the context of a complex 3-dimensional (3D) environment, with reciprocal feedback and cross-talk taking place between the tumor cells and host environment. Here we discuss the role of molecular networks involving Rho GTPases in cancer, and the therapeutic implications of inhibiting Rho signaling in both cancer cells and the emerging concept of targeting the surrounding stroma.

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Small GTPases, , 2154-1256, 1-11, 2015

PMID: 26103062

Open Access

Regulation and Function of P-Rex Family Rac-GEFs.
Welch HC

The P-Rex family are Dbl-type guanine-nucleotide exchange factors for Rac family small G proteins. They are distinguished from other Rac-GEFs through their synergistic mode of activation by the lipid second messenger phosphatidyl inositol (3,4,5) trisphosphate and the Gβγ subunits of heterotrimeric G proteins, thus acting as coincidence detectors for phosphoinositide 3-kinase and G protein coupled receptor signalling. Work in genetically-modified mice has shown that P-Rex1 has physiological importance in the inflammatory response and the migration of melanoblasts during development, whereas P-Rex2 controls the dendrite morphology of cerebellar Purkinje neurons as well as glucose homeostasis in liver and adipose tissue. Deregulation of P-Rex1 and P-Rex2 expression occurs in many types of cancer, and P-Rex2 is frequently mutated in melanoma. Both GEFs promote tumour growth or metastasis. This review critically evaluates the P-Rex literature and tools available and highlights exciting recent developments and open questions.

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Small GTPases, , 2154-1256, 0, 2015

PMID: 25961466

Open Access

P-Rex and Vav Rac-GEFs in platelets control leukocyte recruitment to sites of inflammation.
Pan D, Amison RT, Riffo-Vasquez Y, Spina D, Cleary SJ, Wakelam MJ, Page CP, Pitchford SC, Welch HC

The small GTPase Rac is required for neutrophil recruitment during inflammation, but its GEF activators seem dispensable for this process, which led us to investigate the possibility of cooperation between Rac-GEF families. Thioglycollate-induced neutrophil recruitment into the peritoneum was more severely impaired in P-Rex1(-/-) Vav1(-/-) (P1V1) or P-Rex1(-/-) Vav3(-/-) (P1V3) mice than in P-Rex null or Vav null mice, suggesting cooperation between P-Rex and Vav Rac-GEFs in this process. Neutrophil transmigration and airway infiltration were all but lost in P1V1 and P1V3 mice during LPS-induced pulmonary inflammation, with altered ICAM1-dependent slow neutrophil rolling and strongly reduced L- and E-selectin dependent adhesion in airway postcapillary venules. Analysis of adhesion molecule expression, neutrophil adhesion, spreading and migration suggested these defects to be only partially neutrophil-intrinsic and not obviously involving vascular endothelial cells. Instead, P1V1 and P1V3 platelets recapitulated the impairment of LPS-induced intravascular neutrophil adhesion and recruitment, revealing P-Rex and Vav expression in platelets to be crucial. Similarly, during ovalbumin-induced allergic inflammation, pulmonary recruitment of P1V1 and P1V3 eosinophils, monocytes and lymphocytes was compromised in a platelet-dependent manner, and airway inflammation essentially abolished, resulting in improved airway responsiveness. Therefore, platelet P-Rex and Vav family Rac-GEFs play important proinflammatory roles in leukocyte recruitment.

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Blood, , 1528-0020, , 2014

PMID: 25538043

Open Access

A rac1-independent role for p-rex1 in melanoblasts.
Lindsay CR, Li A, Faller W, Ozanne B, Welch H, Machesky LM, Sansom OJ

The Journal of investigative dermatology, 135, 1523-1747, 314-8, 2015

PMID: 25075639

Open Access

P-Rex1 directly activates RhoG to regulate GPCR-driven Rac signalling and actin polarity in neutrophils.
G Damoulakis, L Gambardella, KL Rossman, CD Lawson, KE Anderson, Y Fukui, HC Welch, CJ Der, LR Stephens, PT Hawkins

G-protein-coupled receptors (GPCRs) regulate the organisation of the actin cytoskeleton by activating the Rac subfamily of small GTPases. The guanine-nucleotide-exchange factor (GEF) P-Rex1 is engaged downstream of GPCRs and phosphoinositide 3-kinase (PI3K) in many cell types, and promotes tumorigenic signalling and metastasis in breast cancer and melanoma, respectively. Although P-Rex1-dependent functions have been attributed to its GEF activity towards Rac1, we show that P-Rex1 also acts as a GEF for the Rac-related GTPase RhoG, both in vitro and in GPCR-stimulated primary mouse neutrophils. Furthermore, loss of either P-Rex1 or RhoG caused equivalent reductions in GPCR-driven Rac activation and Rac-dependent NADPH oxidase activity, suggesting they both function upstream of Rac in this system. Loss of RhoG also impaired GPCR-driven recruitment of the Rac GEF DOCK2, and F-actin, to the leading edge of migrating neutrophils. Taken together, our results reveal a new signalling hierarchy in which P-Rex1, acting as a GEF for RhoG, regulates Rac-dependent functions indirectly through RhoG-dependent recruitment of DOCK2. These findings thus have broad implications for our understanding of GPCR signalling to Rho GTPases and the actin cytoskeleton.

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Journal of cell science, 127, Pt 11, 2589-600, 2014

PMID: 24659802
DOI: 10.1242/jcs.153049

Open Access

The Rac-FRET mouse reveals tight spatiotemporal control of Rac activity in primary cells and tissues.
AK Johnsson, Y Dai, M Nobis, MJ Baker, EJ McGhee, S Walker, JP Schwarz, S Kadir, JP Morton, KB Myant, DJ Huels, A Segonds-Pichon, OJ Sansom, KI Anderson, P Timpson, HC Welch

The small G protein family Rac has numerous regulators that integrate extracellular signals into tight spatiotemporal maps of its activity to promote specific cell morphologies and responses. Here, we have generated a mouse strain, Rac-FRET, which ubiquitously expresses the Raichu-Rac biosensor. It enables FRET imaging and quantification of Rac activity in live tissues and primary cells without affecting cell properties and responses. We assessed Rac activity in chemotaxing Rac-FRET neutrophils and found enrichment in leading-edge protrusions and unexpected longitudinal shifts and oscillations during protruding and stalling phases of migration. We monitored Rac activity in normal or disease states of intestinal, liver, mammary, pancreatic, and skin tissue, in response to stimulation or inhibition and upon genetic manipulation of upstream regulators, revealing unexpected insights into Rac signaling during disease development. The Rac-FRET strain is a resource that promises to fundamentally advance our understanding of Rac-dependent responses in primary cells and native environments.

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Cell reports, 6, 6, 1153-64, 2014

PMID: 24630994
DOI: 10.1016/j.celrep.2014.02.024

Open Access

P-Rex1 cooperates with PDGFRβ to drive cellular migration in 3D microenvironments.
AD Campbell, S Lawn, LC McGarry, HC Welch, BW Ozanne, JC Norman

Expression of the Rac-guanine nucleotide exchange factor (RacGEF), P-Rex1 is a key determinant of progression to metastasis in a number of human cancers. In accordance with this proposed role in cancer cell invasion and metastasis, we find that ectopic expression of P-Rex1 in an immortalised human fibroblast cell line is sufficient to drive multiple migratory and invasive phenotypes. The invasive phenotype is greatly enhanced by the presence of a gradient of serum or platelet-derived growth factor, and is dependent upon the expression of functional PDGF receptor β. Consistently, the invasiveness of WM852 melanoma cells, which endogenously express P-Rex1 and PDGFRβ, is opposed by siRNA of either of these proteins. Furthermore, the current model of P-Rex1 activation is advanced through demonstration of P-Rex1 and PDGFRβ as components of the same macromolecular complex. These data suggest that P-Rex1 has an influence on physiological migratory processes, such as invasion of cancer cells, both through effects upon classical Rac1-driven motility and a novel association with RTK signalling complexes.

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PloS one, 8, 1, e53982, 2013

PMID: 23382862
DOI: 10.1371/journal.pone.0053982

Open Access

Integrin activation by P-Rex1 is required for selectin-mediated slow leukocyte rolling and intravascular crawling.
JM Herter, J Rossaint, H Block, H Welch, A Zarbock

Integrin activation is essential for the function of leukocytes. Impaired integrin activation on leukocytes is the hallmark of the leukocyte adhesion deficiency syndrome in humans, characterized by impaired leukocyte recruitment and recurrent infections. In inflammation, leukocytes collect different signals during the contact with the microvasculature, which activate signaling pathways leading to integrin activation and leukocyte recruitment. We report the role of P-Rex1, a Rac-specific guanine nucleotide exchanging factor, in integrin activation and leukocyte recruitment. We find that P-Rex1 is required for inducing selectin-mediated lymphocyte function-associated antigen-1 (LFA-1) extension that corresponds to intermediate affinity and induces slow leukocyte rolling, whereas P-Rex1 is not involved in the induction of the high-affinity conformation of LFA-1 obligatory for leukocyte arrest. Furthermore, we demonstrate that P-Rex1 is involved in Mac-1-dependent intravascular crawling. In vivo, both LFA-1-dependent slow rolling and Mac-1-dependent crawling are defective in P-Rex1(-/-) leukocytes, whereas chemokine-induced arrest and postadhesion strengthening remain intact in P-Rex1-deficient leukocytes. Rac1 is involved in E-selectin-mediated slow rolling and crawling. In vivo, in an ischemia-reperfusion-induced model of acute kidney injury, abolished selectin-mediated integrin activation contributed to decreased neutrophil recruitment and reduced kidney damage in P-Rex1-deficient mice. We conclude that P-Rex1 serves distinct functions in LFA-1 and Mac-1 activation.

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Blood, 121, 12, 2301-10, 2013

PMID: 23343834
DOI: 10.1182/blood-2012-09-457085

Open Access

The guanine-nucleotide-exchange factor P-Rex1 is activated by protein phosphatase 1α.
MA Barber, A Hendrickx, M Beullens, H Ceulemans, D Oxley, S Thelen, M Thelen, M Bollen, HC Welch

P-Rex1 is a GEF (guanine-nucleotide-exchange factor) for the small G-protein Rac that is activated by PIP3 (phosphatidylinositol 3,4,5-trisphosphate) and Gβγ subunits and inhibited by PKA (protein kinase A). In the present study we show that PP1α (protein phosphatase 1α) binds P-Rex1 through an RVxF-type docking motif. PP1α activates P-Rex1 directly in vitro, both independently of and additively to PIP3 and Gβγ. PP1α also substantially activates P-Rex1 in vivo, both in basal and PDGF (platelet-derived growth factor)- or LPA (lysophosphatidic acid)-stimulated cells. The phosphatase activity of PP1α is required for P-Rex1 activation. PP1β, a close homologue of PP1α, is also able to activate P-Rex1, but less effectively. PP1α stimulates P-Rex1-mediated Rac-dependent changes in endothelial cell morphology. MS analysis of wild-type P-Rex1 and a PP1α-binding-deficient mutant revealed that endogenous PP1α dephosphorylates P-Rex1 on at least three residues, Ser834, Ser1001 and Ser1165. Site-directed mutagenesis of Ser1165 to alanine caused activation of P-Rex1 to a similar degree as did PP1α, confirming Ser1165 as a dephosphorylation site important in regulating P-Rex1 Rac-GEF activity. In summary, we have identified a novel mechanism for direct activation of P-Rex1 through PP1α-dependent dephosphorylation.

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The Biochemical journal, 443, 1, 173-83, 2012

PMID: 22242915
DOI: 10.1042/BJ20112078

Open Access

P-Rex1 is required for efficient melanoblast migration and melanoma metastasis.
CR Lindsay, S Lawn, AD Campbell, WJ Faller, F Rambow, RL Mort, P Timpson, A Li, P Cammareri, RA Ridgway, JP Morton, B Doyle, S Hegarty, M Rafferty, IG Murphy, EW McDermott, K Sheahan, K Pedone, AJ Finn, PA Groben, NE Thomas, H Hao, C Carson, JC Norman, LM Machesky, WM Gallagher, IJ Jackson, L Van Kempen, F Beermann, C Der, L Larue, HC Welch, BW Ozanne, OJ Sansom

Metastases are the major cause of death from melanoma, a skin cancer that has the fastest rising incidence of any malignancy in the Western world. Molecular pathways that drive melanoblast migration in development are believed to underpin the movement and ultimately the metastasis of melanoma. Here we show that mice lacking P-Rex1, a Rac-specific Rho GTPase guanine nucleotide exchange factor, have a melanoblast migration defect during development evidenced by a white belly. Moreover, these P-Rex1(-/-) mice are resistant to metastasis when crossed to a murine model of melanoma. Mechanistically, this is associated with P-Rex1 driving invasion in a Rac-dependent manner. P-Rex1 is elevated in the majority of human melanoma cell lines and tumour tissue. We conclude that P-Rex1 has an important role in melanoblast migration and cancer progression to metastasis in mice and humans.

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Nature communications, 2, , 555, 2011

PMID: 22109529
DOI: 10.1038/ncomms1560

Open Access

Characterization of the Rac guanine nucleotide exchange factor P-Rex1 in platelets.
JE Aslan, AM Spencer, CP Loren, J Pang, HC Welch, DL Greenberg, OJ McCarty

Blood platelets undergo a carefully regulated change in shape to serve as the primary mediators of hemostasis and thrombosis. These processes manifest through platelet spreading and aggregation and are dependent on platelet actin cytoskeletal changes orchestrated by the Rho GTPase family member Rac1. To elucidate how Rac1 is regulated in platelets, we captured Rac1-interacting proteins from platelets and identified Rac1-associated proteins by mass spectrometry.

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Journal of molecular signaling, 6, , 11, 2011

PMID: 21884615
DOI: 10.1186/1750-2187-6-11

Open Access

Ca2+-dependent monomer and dimer formation switches CAPRI Protein between Ras GTPase-activating protein (GAP) and RapGAP activities.
Y Dai, SA Walker, E de Vet, S Cook, HC Welch, PJ Lockyer

CAPRI is a member of the GAP1 family of GTPase-activating proteins (GAPs) for small G proteins. It is known to function as an amplitude sensor for intracellular Ca(2+) levels stimulated by extracellular signals and has a catalytic domain with dual RasGAP and RapGAP activities. Here, we have investigated the mechanism that switches CAPRI between its two GAP activities. We demonstrate that CAPRI forms homodimers in vitro and in vivo in a Ca(2+)-dependent manner. The site required for dimerization was pinpointed by deletion and point mutations to a helix motif that forms a hydrophobic face in the extreme C-terminal tail of the CAPRI protein. Deletion of this helix motif abolished dimer formation but did not affect translocation of CAPRI to the plasma membrane upon cell stimulation with histamine. We found that dimeric and monomeric CAPRI coexist in cells and that the ratio of dimeric to monomeric CAPRI increases upon cell stimulation with histamine. Free Ca(2+) at physiologically relevant concentrations was both necessary and sufficient for dimer formation. Importantly, the monomeric and dimeric forms of CAPRI exhibited differential GAP activities in vivo; the wild-type form of CAPRI had stronger RapGAP activity than RasGAP activity, whereas a monomeric CAPRI mutant showed stronger RasGAP than RapGAP activity. These results demonstrate that CAPRI switches between its dual GAP roles by forming monomers or homodimers through a process regulated by Ca(2+). We propose that Ca(2+)-dependent dimerization of CAPRI may serve to coordinate Ras and Rap1 signaling pathways.

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The Journal of biological chemistry, 286, 22, 19905-16, 2011

PMID: 21460216
DOI: 10.1074/jbc.M110.201301

Open Access

P-Rex1 and Vav1 cooperate in the regulation of formyl-methionyl-leucyl-phenylalanine-dependent neutrophil responses.
CD Lawson, S Donald, KE Anderson, DT Patton, HC Welch

G protein-coupled receptor (GPCR) activation elicits neutrophil responses such as chemotaxis and reactive oxygen species (ROS) formation, which depend on the small G protein Rac and are essential for host defense. P-Rex and Vav are two families of guanine-nucleotide exchange factors (GEFs) for Rac, which are activated through distinct mechanisms but can both control GPCR-dependent neutrophil responses. It is currently unknown whether they play specific roles or whether they can compensate for each other in controlling these responses. In this study, we have assessed the function of neutrophils from mice deficient in P-Rex and/or Vav family GEFs. We found that both the P-Rex and the Vav family are important for LPS priming of ROS formation, whereas particle-induced ROS responses and cell spreading are controlled by the Vav family alone. Surprisingly, fMLF-stimulated ROS formation, adhesion, and chemotaxis were synergistically controlled by P-Rex1 and Vav1. These responses were more severely impaired in neutrophils lacking both P-Rex1 and Vav1 than those lacking the entire P-Rex family, the entire Vav family, or both P-Rex1 and Vav3. P-Rex1/Vav1 (P1V1) double-deficient cells also showed the strongest reduction in fMLF-stimulated activation of Rac1 and Rac2. This reduction in Rac activity may be sufficient to cause the defects observed in fMLF-stimulated P1V1 neutrophil responses. Additionally, Mac-1 surface expression was reduced in P1V1 cells, which might contribute further to defects in responses involving integrins, such as GPCR-stimulated adhesion and chemotaxis. We conclude that P-Rex1 and Vav1 together are the major fMLFR-dependent Dbl family Rac-GEFs in neutrophils and cooperate in the control of fMLF-stimulated neutrophil responses.

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Journal of immunology (Baltimore, Md. : 1950), 186, 3, 1467-76, 2011

PMID: 21178006
DOI: 10.4049/jimmunol.1002738

Open Access

Control of cerebellar long-term potentiation by P-Rex-family guanine-nucleotide exchange factors and phosphoinositide 3-kinase.
C Jackson, HC Welch, TC Bellamy

Long-term potentiation (LTP) at the parallel fibre-Purkinje cell synapse in the cerebellum is a recently described and poorly characterized form of synaptic plasticity. The induction mechanism for LTP at this synapse is considered reciprocal to "classical" LTP at hippocampal CA1 pyramidal neurons: kinases promote increased trafficking of AMPA receptors into the postsynaptic density in the hippocampus, whereas phosphatases decrease internalization of AMPA receptors in the cerebellum. In the hippocampus, LTP occurs in overlapping phases, with the transition from early to late phases requiring the consolidation of initial induction processes by structural re-arrangements at the synapse. Many signalling pathways have been implicated in this process, including PI3 kinases and Rho GTPases.

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PloS one, 5, 8, e11962, 2010

PMID: 20694145
DOI: 10.1371/journal.pone.0011962

Open Access

P-Rex2 regulates Purkinje cell dendrite morphology and motor coordination.
S Donald, T Humby, I Fyfe, A Segonds-Pichon, SA Walker, SR Andrews, WJ Coadwell, P Emson, LS Wilkinson, HC Welch

The small GTPase Rac controls cell morphology, gene expression, and reactive oxygen species formation. Manipulations of Rac activity levels in the cerebellum result in motor coordination defects, but activators of Rac in the cerebellum are unknown. P-Rex family guanine-nucleotide exchange factors activate Rac. We show here that, whereas P-Rex1 expression within the brain is widespread, P-Rex2 is specifically expressed in the Purkinje neurons of the cerebellum. We have generated P-Rex2(-/-) and P-Rex1(-/-)/P-Rex2(-/-) mice, analyzed their Purkinje cell morphology, and assessed their motor functions in behavior tests. The main dendrite is thinned in Purkinje cells of P-Rex2(-/-) pups and dendrite structure appears disordered in Purkinje cells of adult P-Rex2(-/-) and P-Rex1(-/-)/P-Rex2(-/-) mice. P-Rex2(-/-) mice show a mild motor coordination defect that progressively worsens with age and is more pronounced in females than in males. P-Rex1(-/-)/P-Rex2(-/-) mice are ataxic, with reduced basic motor activity and abnormal posture and gait, as well as impaired motor coordination even at a young age. We conclude that P-Rex1 and P-Rex2 are important regulators of Purkinje cell morphology and cerebellar function.

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Proceedings of the National Academy of Sciences of the United States of America, 105, 11, 4483-8, 2008

PMID: 18334636
DOI: 10.1073/pnas.0712324105

Open Access

Membrane translocation of P-Rex1 is mediated by G protein betagamma subunits and phosphoinositide 3-kinase.
MA Barber, S Donald, S Thelen, KE Anderson, M Thelen, HC Welch

P-Rex1 is a guanine-nucleotide exchange factor (GEF) for the small GTPase Rac that is directly activated by the betagamma subunits of heterotrimeric G proteins and by the lipid second messenger phosphatidylinositol (3,4,5)-trisphosphate (PIP(3)), which is generated by phosphoinositide 3-kinase (PI3K). Gbetagamma subunits and PIP(3) are membrane-bound, whereas the intracellular localization of P-Rex1 in basal cells is cytosolic. Activation of PI3K alone is not sufficient to promote significant membrane translocation of P-Rex1. Here we investigated the subcellular localization of P-Rex1 by fractionation of Sf9 cells co-expressing P-Rex1 with Gbetagamma and/or PI3K. In basal, serum-starved cells, P-Rex1 was mainly cytosolic, but 7% of the total was present in the 117,000 x g membrane fraction. Co-expression of P-Rex1 with either Gbetagamma or PI3K caused only an insignificant increase in P-Rex1 membrane localization, whereas Gbetagamma and PI3K together synergistically caused a robust increase in membrane-localized P-Rex1 to 23% of the total. PI3K-driven P-Rex1 membrane recruitment was wortmannin-sensitive. The use of P-Rex1 mutants showed that the isolated Dbl homology/pleckstrin homology domain tandem of P-Rex1 is sufficient for synergistic Gbetagamma- and PI3K-driven membrane localization; that the enzymatic GEF activity of P-Rex1 is not required for membrane translocation; and that the other domains of P-Rex1 (DEP, PDZ, and IP4P) contribute to keeping the enzyme localized in the cytosol of basal cells. In vitro Rac2-GEF activity assays showed that membrane-derived purified P-Rex1 has a higher basal activity than cytosol-derived P-Rex1, but both can be further activated by PIP(3) and Gbetagamma subunits.

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The Journal of biological chemistry, 282, 41, 29967-76, 2007

PMID: 17698854
DOI: 10.1074/jbc.M701877200

Open Access

Gbetagammas and the Ras binding domain of p110gamma are both important regulators of PI(3)Kgamma signalling in neutrophils.
S Suire, AM Condliffe, GJ Ferguson, CD Ellson, H Guillou, K Davidson, H Welch, J Coadwell, M Turner, ER Chilvers, PT Hawkins, L Stephens

Through their ability to regulate production of the key lipid messenger PtdIns(3,4,5)P(3), the class I phosphatidylinositol-3-OH kinases (PI(3)Ks) support many critical cell responses. They, in turn, can be regulated by cell-surface receptors through signals acting on either their adaptor subunits (for example, through phosphotyrosine or Gbetagammas) or their catalytic subunits (for example, through GTP-Ras). The relative significance of these controlling inputs is undefined in vivo. Here, we have studied the roles of Gbetagammas, the adaptor p101, Ras and the Ras binding domain (RBD) in the control of the class I PI(3)K, PI(3)Kgamma, in mouse neutrophils. Loss of p101 leads to major reductions in the accumulation of PtdIns(3,4,5)P(3), activation of protein kinase B (PKB) and in migration towards G-protein activating ligands in vitro, and to an aseptically inflamed peritoneum in vivo. Loss of sensitivity of PI(3)Kgamma to Ras unexpectedly caused similar reductions, but additionally caused a substantial loss in production of reactive oxygen species (ROS). We conclude that Gbetagammas, p101 and the Ras-RBD interaction all have important roles in the regulation of PI(3)Kgamma in vivo and that they can simultaneously, but differentially, control distinct PI(3)Kgamma effectors.

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Nature cell biology, 8, 11, 1303-9, 2006

PMID: 17041586
DOI: 10.1038/ncb1494

P-Rex1 regulates neutrophil function.
Welch HC, Condliffe AM, Milne LJ, Ferguson GJ, Hill K, Webb LM, Okkenhaug K, Coadwell WJ, Andrews SR, Thelen M, Jones GE, Hawkins PT, Stephens LR

Rac GTPases regulate cytoskeletal structure, gene expression, and reactive oxygen species (ROS) production. Rac2-deficient neutrophils cannot chemotax, produce ROS, or degranulate upon G protein-coupled receptor (GPCR) activation. Deficiency in PI3Kgamma, an upstream regulator of Rac, causes a similar phenotype. P-Rex1, a guanine-nucleotide exchange factor (GEF) for Rac, is believed to link GPCRs and PI3Kgamma to Rac-dependent neutrophil responses. We have investigated the functional importance of P-Rex1 by generating a P-Rex1(-/-) mouse. P-Rex1(-/-) mice are viable and healthy, with apparently normal leukocyte development, but with mild neutrophilia. In neutrophils from P-Rex1(-/-) mice, GPCR-dependent Rac2 activation is impaired, whereas Rac1 activation is less compromised. GPCR-dependent ROS formation is absent in lipopolysaccharide (LPS)-primed P-Rex1(-/-) neutrophils, but less affected in unprimed or TNFalpha-primed cells. Recruitment of P-Rex1(-/-) neutrophils to inflammatory sites is impaired. Surprisingly, chemotaxis of isolated neutrophils is only slightly reduced, with a mild defect in cell speed, but normal polarization and directionality. Secretion of azurophil granules is unaffected. In conclusion, P-Rex1 is an important regulator of neutrophil function by mediating a subset of Rac-dependent neutrophil responses. However, P-Rex1 is not an essential regulator of neutrophil chemotaxis and degranulation.

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Current biology : CB, 15, 0960-9822, 1867-73, 2005

PMID: 16243035

Open Access

P-Rex1, a PtdIns(3,4,5)P3- and Gbetagamma-regulated guanine-nucleotide exchange factor for Rac.
Welch HC, Coadwell WJ, Ellson CD, Ferguson GJ, Andrews SR, Erdjument-Bromage H, Tempst P, Hawkins PT, Stephens LR

Rac, a member of the Rho family of monomeric GTPases, is an integrator of intracellular signaling in a wide range of cellular processes. We have purified a PtdIns(3,4,5)P3-sensitive activator of Rac from neutrophil cytosol. It is an abundant, 185 kDa guanine-nucleotide exchange factor (GEF), which we cloned and named P-Rex1. The recombinant enzyme has Rac-GEF activity that is directly, substantially, and synergistically activated by PtdIns(3,4,5)P3 and Gbetagammas both in vitro and in vivo. P-Rex1 antisense oligonucleotides reduced endogenous P-Rex1 expression and C5a-stimulated reactive oxygen species formation in a neutrophil-like cell line. P-Rex1 appears to be a coincidence detector in PtdIns(3,4,5)P3 and Gbetagamma signaling pathways that is particularly adapted to function downstream of heterotrimeric G proteins in neutrophils.

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Cell, 108, 0092-8674, 809-21, 2002

PMID: 11955434

Open Access