UMLS:C0023418 - FACTA Search

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Query: UMLS:C0023418 (leukemia)
93,477 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Leukemia-associated Rho guanine nucleotide exchange factor (LARG) was originally identified as a fusion partner with mixed-lineage leukemia in a patient with acute myeloid leukemia. LARG possesses a tandem Dbl homology and pleckstrin homology domain structure and, consequently, may function as an activator of Rho GTPases. In this study, we demonstrate that LARG is a functional Dbl protein. Expression of LARG in cells caused activation of the serum response factor, a known downstream target of Rho-mediated signaling pathways. Transient overexpression of LARG did not activate the extracellular signal-regulated kinase or c-Jun NH(2)-terminal kinase mitogen-activated protein kinase cascade, suggesting LARG is not an activator of Ras, Rac, or Cdc42. We performed in vitro exchange assays where the isolated Dbl homology (DH) or DH/pleckstrin homology domains of LARG functioned as a strong activator of RhoA, but exhibited no activity toward Rac1 or Cdc42. We found that LARG could complex with RhoA, but not Rac or Cdc42, in vitro, and that expression of LARG caused an increase in the levels of the activated GTP-bound form of RhoA, but not Rac1 or Cdc42, in vivo. Thus, we conclude that LARG is a RhoA-specific guanine nucleotide exchange factor. Finally, like activated RhoA, we determined that LARG cooperated with activated Raf-1 to transform NIH3T3 cells. These data demonstrate that LARG is the first functional Dbl protein mutated in cancer and indicate LARG-mediated activation of RhoA may play a role in the development of human leukemias.
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PMID:Leukemia-associated Rho guanine nucleotide exchange factor, a Dbl family protein found mutated in leukemia, causes transformation by activation of RhoA. 1137 93

Leukemia-associated Rho guanine-nucleotide exchange factor (LARG) belongs to the subfamily of Dbl homology RhoGEF proteins (including p115 RhoGEF and PDZ-RhoGEF) that possess amino-terminal regulator of G protein signaling (RGS) boxes also found within GTPase-accelerating proteins (GAPs) for heterotrimeric G protein alpha subunits. p115 RhoGEF stimulates the intrinsic GTP hydrolysis activity of G alpha 12/13 subunits and acts as an effector for G13-coupled receptors by linking receptor activation to RhoA activation. The presence of RGS box and Dbl homology domains within LARG suggests this protein may also function as a GAP toward specific G alpha subunits and couple G alpha activation to RhoA-mediating signaling pathways. Unlike the RGS box of p115 RhoGEF, the RGS box of LARG interacts not only with G alpha 12 and G alpha 13 but also with G alpha q. In cellular coimmunoprecipitation studies, the LARG RGS box formed stable complexes with the transition state mimetic forms of G alpha q, G alpha 12, and G alpha 13. Expression of the LARG RGS box diminished the transforming activity of oncogenic G protein-coupled receptors (Mas, G2A, and m1-muscarinic cholinergic) coupled to G alpha q and G alpha 13. Activated G alpha q, as well as G alpha 12 and G alpha 13, cooperated with LARG and caused synergistic activation of RhoA, suggesting that all three G alpha subunits stimulate LARG-mediated activation of RhoA. Our findings suggest that the RhoA exchange factor LARG, unlike the related p115 RhoGEF and PDZ-RhoGEF proteins, can serve as an effector for Gq-coupled receptors, mediating their functional linkage to RhoA-dependent signaling pathways.
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PMID:Leukemia-associated Rho guanine nucleotide exchange factor promotes G alpha q-coupled activation of RhoA. 1202 19

Plexins represent a novel family of transmembrane receptors that transduce attractive and repulsive signals mediated by the axon-guiding molecules semaphorins. Emerging evidence implicates Rho GTPases in these biological events. However, Plexins lack any known catalytic activity in their conserved cytoplasmic tails, and how they transduce signals from semaphorins to Rho is still unknown. Here we show that Plexin B2 associates directly with two members of a recently identified family of Dbl homology/pleckstrin homology containing guanine nucleotide exchange factors for Rho, PDZ-RhoGEF, and Leukemia-associated Rho GEF (LARG). This physical interaction is mediated by their PDZ domains and a PDZ-binding motif found only in Plexins of the B family. In addition, we show that ligand-induced dimerization of Plexin B is sufficient to stimulate endogenous RhoA potently and to induce the reorganization of the cytoskeleton. Moreover, overexpression of the PDZ domain of PDZ-RhoGEF but not its regulator of G protein signaling domain prevents cell rounding and neurite retraction of differentiated PC12 cells induced by activation of endogenous Plexin B1 by semaphorin 4D. The association of Plexins with LARG and PDZ-RhoGEF thus provides a direct molecular mechanism by which semaphorins acting on Plexin B can control Rho, thereby regulating the actin-cytoskeleton during axonal guidance and cell migration.
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PMID:Plexin B regulates Rho through the guanine nucleotide exchange factors leukemia-associated Rho GEF (LARG) and PDZ-RhoGEF. 1218 58

Semaphorins are axon guidance molecules that signal through the plexin family of receptors. Semaphorins also play a role in other processes such as immune regulation and tumorigenesis. However, the molecular signaling mechanisms downstream of plexin receptors have not been elucidated. Semaphorin 4D is the ligand for the plexin-B1 receptor and stimulation of the plexin-B1 receptor activates the small GTPase RhoA. Using the intracellular domain of plexin-B1 as an affinity ligand, two Rho-specific guanine nucleotide exchange factors, leukemia-associated Rho GEF (LARG; GEF, guanine nucleotide exchange factors) and PSD-95/Dlg/ZO-1 homology (PDZ)-RhoGEF, were isolated from mouse brain as plexin-B1-specific interacting proteins. LARG and PDZ-RhoGEF contain several functional domains, including a PDZ domain. Biochemical characterizations showed that the PDZ domain of LARG is directly involved in the interaction with the carboxy-terminal sequence of plexin-B1. Mutation of either the PDZ domain in LARG or the PDZ binding site in plexin-B1 eliminates the interaction. The interaction between plexin-B1 and LARG is specific for the PDZ domain of LARG and LARG does not interact with plexin-A1. A LARG-interaction defective mutant of the plexin-B1 receptor was created and was unable to stimulate RhoA activation. The data in this report suggest that LARG plays a critical role in plexin-B1 signaling to stimulate Rho activation and cytoskeletal reorganization.
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PMID:The semaphorin receptor plexin-B1 signals through a direct interaction with the Rho-specific nucleotide exchange factor, LARG. 1219 28

Three mammalian Rho guanine nucleotide exchange factors (RhoGEFs), leukemia-associated RhoGEF (LARG), p115RhoGEF, and PDZ-RhoGEF, contain regulator of G-protein signaling (RGS) domains within their amino-terminal regions. These RhoGEFs link signals from heterotrimeric G12/13 protein-coupled receptors to Rho GTPase activation, leading to various cellular responses, such as actin reorganization and gene expression. The activity of these RhoGEFs is regulated by Galpha12/13 through their RGS domains. Because RhoGEFs stimulate guanine nucleotide exchange by Rho GTPases, RhoGEF activation can be measured by monitoring GTP binding to or GDP dissociation from Rho GTPases. This article describes methods used to perform reconstitution assays to measure the activity of RhoGEFs regulated by Galpha12/13.
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PMID:Regulation of RGS-RhoGEFs by Galpha12 and Galpha13 proteins. 1548 84

The Rho-kinase pathway mediates Ca2+ sensitization in the penile circulation, which maintains the penis in the flaccid state. We aimed to investigate the functional effect of a novel Rho-kinase inhibitor, H-1152 [(S)-(+)-2-methyl-1-[(4-methyl-5-isoquinolinyl)sulfonyl]homopiperazine], both in vitro and in vivo as well as to demonstrate the expression of Rho guanine nucleotide exchange factors (RhoGEFs) in the rat corpus cavernosum (CC), by using a semiquantitative reverse transcription-polymerase chain reaction assay to measure their mRNA expression. Cumulative addition of H-1152 (0.001-3 microM) or Y-27632 [0.01-30 microM; (R)-(+)-trans-N-(4-pyridyl)-4-(1-aminoethyl)-cyclohexanecarboxamide] caused sustained relaxations of precontracted CC strips, which were not affected by inhibition of the nitric oxide signaling pathway. Addition of H-1152 (0.1 microM), Y-27632 (1 microM), or sodium nitroprusside (SNP; 0.1 microM) caused rightward shifts in the curves to phenylephrine (PE), but it had little effect on the contractions mediated by electrical field stimulation (EFS). It is noteworthy that when H-1152 or Y-27632 was combined with SNP, a marked synergistic inhibition was noted both on PE- and EFS-induced contractions. Intraperitoneal administration of H-1152 (100 nmol/kg) had a discrete effect on mean arterial pressure and significantly enhanced erectile responses evoked by stimulation of the cavernous nerve. The mRNA expression for PDZ-RhoGEF, p115RhoGEF, and leukemia-associated RhoGEF in cavernosal segments was visualized by electrophoresis on agarose gel. The results indicate that H-1152 is a powerful Rho-kinase inhibitor, giving rise to its therapeutic potential in the treatment of erectile dysfunction. The regulator of G-protein signaling-containing RhoGEFs may represent key components of the molecular mechanisms associated with the abnormal function of the cavernosal smooth muscle.
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PMID:Proerectile effects of the Rho-kinase inhibitor (S)-(+)-2-methyl-1-[(4-methyl-5-isoquinolinyl)sulfonyl]homopiperazine (H-1152) in the rat penis. 1597 17

1. Rho-kinase (ROK) stimulation represents a key step in the maintenance of agonist-induced contraction, an effect counteracted by nitric oxide (NO) released from the endothelium. The aim of the present study was to characterize the involvement of ROK in smooth muscle contraction of the rat coeliac artery using functional and expression studies. 2. Rings of rat coeliac artery were mounted in 5 mL myographs containing warmed and oxygenated Krebs' solution. Rings were connected to isometric transducers and data were recorded in a PowerLab system (ADInstruments, Colorado Springs, CO, USA). After a 60 min equilibration period, preparations were precontracted with phenylephrine (1 micromol/L). Endothelial integrity was assessed by treating the vessels with acetylcholine (1 micromol/L). Expression of ROKalpha, ROKbeta and RhoA was analysed using western blot, whereas Rho guanine nucleotide exchange factors (RhoGEF) were measured at the mRNA level. 3. The addition of Y-27632 (0.01-30 micromol/L) caused sustained relaxation of rings contracted with phenylephrine (PE; 1 micromol/L), with intact or denuded endothelium (pEC50 = 6.38 +/- 0.03 and 5.65 +/- 0.02, respectively). NG-Nitro-L-arginine methyl ester (100 micromol/L) or 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (10 micromol/L), but not indomethacin (10 micromol/L), caused marked rightward shifts of the concentration-response curves to Y-27632. The contractile response to KCl (80 mmol/L) was significantly reduced by Y-27632, with a maximal inhibition of 57 +/- 6%. Nifedipine (0.1-100 nmol/L) fully blocked KCl-evoked contractions, but only marginally affected those in response to PE (27 +/- 2% maximal inhibition). At 1 micromol/L, Y-27632 also significantly enhanced relaxations to sodium nitroprusside (SNP; 0.0001-1 micromol/L). 4. At 1 micromol/L, SNP (but not 1 micromol/L Y-27632) significantly elevated the cGMP content above basal levels. Coincubation with SNP and Y-27632 increased cGMP levels, but the results were not significantly different from those in the presence of SNP alone. 5. Western blot analysis revealed the protein expression of RhoA, ROKalpha and ROKbeta. The PDZ-RhoGEF, p115RhoGEF and leukaemia-associated RhoGEF (LARG) mRNA expression in coeliac artery was visualized by electrophoresis on agarose gels. 6. The results clearly demonstrate a role for the RhoA/ROK signalling pathway in the regulation of rat coeliac artery smooth muscle contraction. The findings of the present study suggest that endogenous nitric oxide-induced relaxation is mediated, in part, by inhibition of RhoA/ROK signalling in this tissue.
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PMID:Expression and functional role of the RhoA/Rho-kinase pathway in rat coeliac artery. 1617 42

In vascular smooth muscle, stimulation of heterotrimeric G protein-coupled receptors (GPCRs) by various contractile agonists activates intracellular signaling molecules to result in an increase in cytosolic Ca2+ and the subsequent phosphorylation of myosin light chain (MLC) by Ca2+/calmodulin-dependent MLC kinase. In addition, a portion of agonist-induced contraction is partially mediated by the Ca2+-independent activation of the small G protein RhoA and a downstream target, Rho-kinase. The activation of RhoA is controlled by several regulatory proteins, including guanine nucleotide exchange factors (GEFs). GEFs activate RhoA by promoting the release of GDP and then facilitating the binding of GTP. There are three Rho-specific GEFs (RhoGEFs) in vascular smooth muscle that contain a binding domain [regulator of G protein signaling (RGS) domain] capable of linking GPCRs to RhoA activation: PDZ-RhoGEF, leukemia-associated RhoGEF (LARG), and p115RhoGEF. We hypothesized that RGS domain-containing RhoGEFs, especially LARG, participate in linking GPCR to RhoA activation in vascular smooth muscle. We observed that angiotensin II up-regulates LARG via the AT1 receptor, and this up-regulation is signaled via the phosphatidylinositol 3-kinase pathway. Furthermore, angiotensin II treatment caused a small, but significant, increase in the component of contractile responses sensitive to Rho-kinase antagonism. These observations support the hypothesis that RhoGEFs, particularly LARG, participate in linking GPCR to RhoA activation in vascular smooth muscle.
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PMID:Angiotensin II up-regulates the leukemia-associated Rho guanine nucleotide exchange factor (RhoGEF), a regulator of G protein signaling domain-containing RhoGEF, in vascular smooth muscle cells. 1635 63

In this study we have examined the interaction of CD44 (a major hyaluronan (HA) receptor) with a RhoA-specific guanine nucleotide exchange factor (leukemia-associated RhoGEF (LARG)) in human head and neck squamous carcinoma cells (HNSCC-HSC-3 cell line). Immunoprecipitation and immunoblot analyses indicate that CD44 and the LARG protein are expressed in HSC-3 cells and that these two proteins are physically associated as a complex. HA-CD44 binding induces LARG-specific RhoA signaling and phospholipase C epsilon (PLC epsilon) activity. In particular, the activation of RhoA-PLC epsilon by HA stimulates inositol 1,4,5-triphosphate production, intracellular Ca2+ mobilization, and the up-regulation of Ca2+/calmodulin-dependent kinase II (CaMKII), leading to phosphorylation of the cytoskeletal protein, filamin. The phosphorylation of filamin reduces its interaction with filamentous actin, promoting tumor cell migration. The CD44-LARG complex also interacts with the EGF receptor (EGFR). Most importantly, the binding of HA to the CD44-LARG-EGFR complex activates the EGFR receptor kinase, which in turn promotes Ras-mediated stimulation of a downstream kinase cascade including the Raf-1 and ERK pathways leading to HNSCC cell growth. Using a recombinant fragment of LARG (the LARG-PDZ domain) and a binding assay, we have determined that the LARG-PDZ domain serves as a direct linker between CD44 and EGFR. Transfection of the HSC-3 cells with LARG-PDZcDNA significantly reduces LARG association with CD44 and EGFR. Overexpression of the LARG-PDZ domain also functions as a dominant-negative mutant (similar to the PLC/Ca2+-calmodulin-dependent kinase II (CaMKII) and EGFR/MAPK inhibitor effects) to block HA/CD44-mediated signaling events (e.g. EGFR kinase activation, Ras/RhoA co-activation, Raf-ERK signaling, PLC epsilon-mediated inositol 1,4,5-triphosphate production, intracellular Ca2+ mobilization, CaMKII activity, filamin phosphorylation, and filamin-actin binding) and to abrogate tumor cell growth/migration. Taken together, our findings suggest that CD44 interaction with LARG and EGFR plays a pivotal role in Rho/Ras co-activation, PLC epsilon-Ca2+ signaling, and Raf/ERK up-regulation required for CaMKII-mediated cytoskeleton function and in head and neck squamous cell carcinoma progression.
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PMID:Hyaluronan-CD44 interaction with leukemia-associated RhoGEF and epidermal growth factor receptor promotes Rho/Ras co-activation, phospholipase C epsilon-Ca2+ signaling, and cytoskeleton modification in head and neck squamous cell carcinoma cells. 1656 89

The neuropeptides bombesin and endothelin-1 stimulate prostate cancer (PC) cell migration and invasion (J Clin Invest, 2000; 106: 1399-1407). The intracellular signaling pathways that direct this cell movement are not well delineated. The monomeric GTPase RhoA is required for migration in several cell types including neutrophils, monocytes and fibroblasts. We demonstrate that bombesin-stimulated PC cell migration occurs via the heterotrimeric G-protein-coupled receptors (G-protein) G alpha 13 subunit leading to activation of RhoA, and Rho-associated coiled-coil forming protein kinase (ROCK). Using siRNA to suppress expression of the three known G-protein alpha-subunit-associated RhoA guanine nucleotide exchange factors (GEFs), we also show that two of these RhoA GEFs, PDZ-RhoGEF and leukemia-associated RhoGEF (LARG), link bombesin receptors to RhoA in a non-redundant manner in PC cells. We next show that focal adhesion kinase, which activates PDZ-RhoGEF and LARG, is required for bombesin-stimulated RhoA activation. Neutral endopeptidase (NEP) is expressed on normal prostate epithelium whereas loss of NEP expression contributes to PC progression. We also demonstrate that NEP inhibits neuropeptide activation of RhoA. Together, these results establish a contiguous signaling pathway from the bombesin receptor to ROCK in PC cells, and they implicate NEP as a major regulator of neuropeptide-stimulated RhoA in these cells. This work also identifies members of this signaling pathway as potential targets for rational pharmacologic manipulation of neuropeptide-stimulated migration of PC cells.
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PMID:Neuropeptide-stimulated cell migration in prostate cancer cells is mediated by RhoA kinase signaling and inhibited by neutral endopeptidase. 1665 49

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