Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Ras-GRF2 (GRF2) is a widely expressed, calcium-activated regulator of the small-type GTPases Ras and Rac. It is a multidomain protein composed of several recognizable sequence motifs in the following order (NH(2) to COOH): pleckstrin homology (PH), coiled-coil, ilimaquinone (IQ), Dbl homology (DH), PH, REM (Ras exchanger motif), PEST/destruction box, Cdc25. The DH and Cdc25 domains possess guanine nucleotide exchange factor (GEF) activity and interact with Rac and Ras, respectively. The REM-Cdc25 region was found to be sufficient for maximal activation of Ras in vitro and in vivo caused Ras and extracellular signal-regulated kinase (ERK) activation independent of calcium signals, suggesting that, at least when expressed ectopically, it contains all of the determinants required to access and activate Ras signaling. Additional mutational analysis of GRF2 indicated that the carboxyl PH domain imparts a modest inhibitory effect on Ras GEF activity and probably normally participates in intermolecular interactions. A variant of GRF2 missing the Cdc25 domain did not activate Ras and functions as an inhibitor of wild-type GRF2, presumably by competing for interactions with molecules other than calmodulin, Ras, and ligands of the PH domain. The binding of calmodulin was found to require several amino-terminal domains of GRF2 in addition to the IQ sequence, and no correlation between calmodulin binding by GRF2 and its ability to directly activate Ras and indirectly stimulate the mitogen-activated protein (MAP) kinase ERK in response to calcium was found. The precise role of the GRF2-calmodulin association, therefore, remains to be determined. A GRF2 mutant missing the IQ sequence was competent for Ras activation but failed to couple this to stimulation of the ERK pathway. This demonstrates that Ras-GTP formation is not sufficient for MAP kinase signaling. We conclude that in addition to directly activating Ras, GRF2, and likely other GEFs, promote the assembly of a protein network able to couple the GTPase with particular effectors.
Mol Cell Biol 2000 Apr
PMID:Calmodulin-independent coordination of Ras and extracellular signal-regulated kinase activation by Ras-GRF2. 1073 75

RasGRP is a recently described guanine nucleotide exchange factor (GEF) that possesses a single C1 domain homologous to that of protein kinase C (PKC). The phorbol ester [(3)H]phorbol 12, 13-dibutyrate ([(3)H]PDBu) bound to this C1 domain (C1-RasGRP) with a dissociation constant of 0.58 +/- 0.08 nM, similar to that observed previously for PKC. Likewise, the potent PKC activator bryostatin 1, a compound currently in clinical trials, showed high affinity binding for C1-RasGRP. Structure activity analysis using several phorbol ester analogs showed both similarities and differences in ligand selectivity compared with PKC; the differences were comparable in magnitude to those between different PKC isoforms. Similarly, the potency of the PKC inhibitor calphostin C to inhibit [(3)H]PDBu binding to C1-RasGRP was similar to that observed for PKC. In contrast to the relative similarities in ligand recognition, the lipid cofactor requirements differed between RasGRP and PKC. The C1 domain plus the EF-hand motif of RasGRP (C1EF-RasGRP) was markedly less dependent on acidic phospholipids than was PKCalpha. The differences in lipid requirements were reflected in differential ligand selectivity under conditions of limiting lipid. Despite the presence of twin EF-hand like motifs, calcium did not affect the binding of [(3)H]PDBu to C1EF-RasGRP. We conclude that RasGRP is a high affinity receptor for phorbol esters and diacylglycerol. RasGRP thus provides a direct link between diacylglycerol generation or phorbol ester/bryostatin treatment and Ras activation.
Mol Pharmacol 2000 May
PMID:The guanine nucleotide exchange factor RasGRP is a high -affinity target for diacylglycerol and phorbol esters. 1077 65

Eukaryotic translation initiation factor 2B (eIF2B) is the guanine nucleotide exchange factor for protein synthesis initiation factor 2 (eIF2). Composed of five subunits, it converts eIF2 from a GDP-bound form to the active eIF2-GTP complex. This is a regulatory step of translation initiation. In vitro, eIF2B catalytic function can be provided by the largest (epsilon) subunit alone (eIF2Bepsilon). This activity is stimulated by complex formation with the other eIF2B subunits. We have analyzed the roles of different regions of eIF2Bepsilon in catalysis, in eIF2B complex formation, and in binding to eIF2 by characterizing mutations in the Saccharomyces cerevisiae gene encoding eIF2Bepsilon (GCD6) that impair the essential function of eIF2B. Our analysis of nonsense mutations indicates that the C terminus of eIF2Bepsilon (residues 518 to 712) is required for both catalytic activity and interaction with eIF2. In addition, missense mutations within this region impair the catalytic activity of eIF2Bepsilon without affecting its ability to bind eIF2. Internal, in-frame deletions within the N-terminal half of eIF2Bepsilon disrupt eIF2B complex formation without affecting the nucleotide exchange activity of eIF2Bepsilon alone. Finally, missense mutations identified within this region do not affect the catalytic activity of eIF2Bepsilon alone or its interactions with the other eIF2B subunits or with eIF2. Instead, these missense mutations act indirectly by impairing the enhancement of the rate of nucleotide exchange that results from complex formation between eIF2Bepsilon and the other eIF2B subunits. This suggests that the N-terminal region of eIF2Bepsilon is an activation domain that responds to eIF2B complex formation.
Mol Cell Biol 2000 Jun
PMID:Identification of domains and residues within the epsilon subunit of eukaryotic translation initiation factor 2B (eIF2Bepsilon) required for guanine nucleotide exchange reveals a novel activation function promoted by eIF2B complex formation. 1080 39

In addition to the well-characterized interaction with classical and novel protein kinase C (PKC) isozymes, the phorbol ester tumor promoters bind to other receptors lacking kinase activity. Among these novel phorbol ester receptors, two families of proteins may play a role in the regulation of cell growth and malignant transformation: chimaerins and ras guanyl-releasing protein (ras-GRP). These proteins possess a single copy of the C1 domain that is involved in binding of phorbol esters and the lipid second messenger diacylglycerol. Four isoforms of chimaerins (alpha1-, alpha2-, beta1-, and beta2-chimaerins) have been isolated to-date, all of them possessing GTPase-activating protein activity for Rac, a small GTP-binding protein that controls actin cytoskeleton organization, cell-cycle progression, adhesion, and migration. Ras-GRP is a guanine nucleotide exchange factor for ras and promotes malignant transformation in fibroblasts in a phorbol ester-dependent manner. The C1 domain in Ras-GRP may, therefore, have a dominant role in Ras-GRP activation and is essential for phorbol ester-dependent activation of downstream effectors of ras, i.e., the mitogen-activated protein kinase cascade. Thus, a novel concept emerges in which phorbol esters may exert cellular responses through pathways not involving phorbol ester-responsive PKC isozymes. The discovery of "nonPKC" phorbol ester receptors adds an additional level of complexity to the understanding of phorbol ester effects and the molecular mechanisms of carcinogenesis.
Mol Carcinog 2000 May
PMID:Eyes wide shut: protein kinase C isozymes are not the only receptors for the phorbol ester tumor promoters. 1082 Apr 83

Salmonella typhimurium translocates effector proteins into host cells via the SPI1 type III secretion system to induce responses such as membrane ruffling and internalization by non-phagocytic cells. Activation of the host cellular RhoGTPase Cdc42 is thought to be a key event during internalization. The translocated Salmonella protein SopE is an activator for Cdc42. Because SopE is absent from most S. typhimurium strains it remains unclear whether all S. typhimurium strains rely on activation of Cdc42 to invade host cells. We have identified SopE2, a translocated effector protein common to all S. typhimurium strains. SopE2 is a guanine nucleotide exchange factor for Cdc42 and shows 69% sequence similarity to SopE. Analysis of S. typhimurium mutants demonstrated that SopE2 plays a role in recruitment of the actin-nucleating Arp2/3 complex to the membrane ruffles and in efficient host cell invasion. Transfection experiments showed that SopE2 is sufficient to activate host cellular Cdc42, to recruit the actin-nucleating Arp2/3 complex and to induce actin cytoskeletal rearrangements and internalization. In conclusion, as a result of SopE2 all S. typhimurium strains tested have the capacity to activate Cdc42 signalling inside host cells which is important to ensure efficient entry.
Mol Microbiol 2000 Jun
PMID:Identification of SopE2 from Salmonella typhimurium, a conserved guanine nucleotide exchange factor for Cdc42 of the host cell. 1093 Dec 74

The transcription factor c-Jun is critically involved in the regulation of proliferation and differentiation as well as cellular transformation induced by oncogenic Ras. The signal transduction pathways that couple Ras activation to c-Jun phosphorylation are still partially elusive. Here we show that an activated version of the Ras effector Rlf, a guanine nucleotide exchange factor (GEF) of the small GTPase Ral, can induce the phosphorylation of serines 63 and 73 of c-Jun. In addition, we show that growth factor-induced, Ras-mediated phosphorylation of c-Jun is abolished by inhibitory mutants of the RalGEF-Ral pathway. These results suggest that the RalGEF-Ral pathway plays a major role in Ras-dependent c-Jun phosphorylation. Ral-dependent regulation of c-Jun phosphorylation includes JNK, a still elusive JNKK, and possibly Src.
Mol Cell Biol 2000 Nov
PMID:Ras-dependent regulation of c-Jun phosphorylation is mediated by the Ral guanine nucleotide exchange factor-Ral pathway. 1104 44

In yeast, the Ypt1 GTPase is required for ER-to-cis-Golgi and cis-to-medial-Golgi protein transport, while Ypt31/32 are a functional pair of GTPases essential for exit from the trans-Golgi. We have previously identified a Ypt1 guanine nucleotide exchange factor (GEF) activity and characterized it as a large membrane-associated protein complex that localizes to the Golgi and can be extracted from the membrane by salt, but not by detergent. TRAPP is a large protein complex that is required for ER-to-Golgi transport and that has properties similar to those of Ypt1 GEF. Here we show that TRAPP has Ypt1 GEF activity. GST-tagged Bet3p or Bet5p, two of the TRAPP subunits, were expressed in yeast cells and were precipitated by glutathione-agarose (GA) beads. The resulting precipitates can stimulate both GDP release and GTP uptake by Ypt1p. The majority of the Ypt1 GEF activity associated with the GST-Bet3p precipitate has an apparent molecular weight of > 670 kDa, indicating that the GEF activity resides in the TRAPP complex. Surprisingly, TRAPP can also stimulate nucleotide exchange on the Ypt31/32 GTPases, but not on Sec4p, a Ypt-family GTPase required for the last step of the exocytic pathway. Like the previously characterized Ypt1 GEF, the TRAPP Ypt1-GEF activity can be inhibited by the nucleotide-free Ypt1-D124N mutant protein. This mutant protein also inhibits the Ypt32 GEF activity of TRAPP. Coprecipitation and overexpression studies suggest that TRAPP can act as a GEF for Ypt1 and Ypt31/32 in vivo. These data suggest the exciting possibility that a GEF complex common to Ypt1 and Ypt31/32 might coordinate the function of these GTPases in entry into and exit from the Golgi.
Mol Biol Cell 2000 Dec
PMID:The TRAPP complex is a nucleotide exchanger for Ypt1 and Ypt31/32. 1110 33

Wsc1 and Mid2 are highly O-glycosylated cell surface proteins that reside in the plasma membrane of Saccharomyces cerevisiae. They have been proposed to function as mechanosensors of cell wall stress induced by wall remodeling during vegetative growth and pheromone-induced morphogenesis. These proteins are required for activation of the cell wall integrity signaling pathway that consists of the small G-protein Rho1, protein kinase C (Pkc1), and a mitogen-activated protein kinase cascade. We show here by two-hybrid experiments that the C-terminal cytoplasmic domains of Wsc1 and Mid2 interact with Rom2, a guanine nucleotide exchange factor (GEF) for Rho1. At least with regard to Wsc1, this interaction is mediated by the Rom2 N-terminal domain. This domain is distinct from the Rho1-interacting domain, suggesting that the GEF can interact simultaneously with a sensor and with Rho1. We also demonstrate that extracts from wsc1 and mid2 mutants are deficient in the ability to catalyze GTP loading of Rho1 in vitro, providing evidence that the function of the sensor-Rom2 interaction is to stimulate nucleotide exchange toward this G-protein. In a related line of investigation, we identified the PMT2 gene in a genetic screen for mutations that confer an additive cell lysis defect with a wsc1 null allele. Pmt2 is a member of a six-protein family in yeast that catalyzes the first step in O mannosylation of target proteins. We demonstrate that Mid2 is not mannosylated in a pmt2 mutant and that this modification is important for signaling by Mid2.
Mol Cell Biol 2001 Jan
PMID:Wsc1 and Mid2 are cell surface sensors for cell wall integrity signaling that act through Rom2, a guanine nucleotide exchange factor for Rho1. 1111 1

The dbl oncogene product (onco-Dbl) is the prototype member of a family of guanine nucleotide exchange factors (GEFs) for Rho GTPases. The Dbl homology (DH) domain of onco-Dbl is responsible for the GEF catalytic activity, and the DH domain, together with the immediately adjacent pleckstrin homology (PH) domain, constitutes the minimum module bearing transforming function. In the present study, we demonstrate that the onco-Dbl protein exists in oligomeric form in vitro and in cells. The oligomerization is mostly homophilic in nature and is mediated by the DH domain. Mutagenesis studies mapped the region involved in oligomerization to the conserved region 2 of the DH domain, which is located at the opposite side of the Rho GTPase interacting surface. Residue His556 of this region, in particular, is important for this activity, since the H556A mutant retained the GEF catalytic capability and the binding activity toward Cdc42 and RhoA in vitro but was deficient in oligomer formation. Consequently, the Rho GTPase activating potential of the H556A mutant was significantly reduced in cells. The focus-forming and anchorage-independent growth activities of onco-Dbl were completely abolished by the His556-to-Ala mutation, whereas the abilities to stimulate cell growth, activate Jun N-terminal kinase, and cause actin cytoskeletal changes were retained by the mutant. The ability of onco-Dbl to oligomerize allowed multiple Rho GTPases to be recruited to the same signaling complex, and such an ability is defective in the H556A mutant. Taken together, these results suggest that oligomerization of onco-Dbl through the DH domain is essential for cellular transformation by providing the means to generate a signaling complex that further augments and/or coordinates its Rho GTPase activating potential.
Mol Cell Biol 2001 Jan
PMID:Oligomerization of DH domain is essential for Dbl-induced transformation. 1113 31

FGD1, the gene responsible for the inherited disease faciogenital dysplasia, encodes a guanine nucleotide exchange factor (GEF) that specifically activates the p21 GTPase Cdc42. In order, FGD1 is composed of a proline-rich N-terminal region, adjacent GEF and pleckstrin homology (PH) domains, a FYVE-finger domain and a second C-terminal PH domain (PH2), structural motifs involved in signaling and subcellular localization. Fgd1, the mouse FGD1 ortholog, is expressed in regions of active bone formation within osteoblasts and in the osteoblast-like cell line MC3T3-E1, a finding consistent with its role in skeletal formation. Here, we use subcellular fractionation studies to show that endogenous Fgd1 protein is localized in the cytosolic and Golgi and plasma membrane fractions of mouse calvarial cells. Immunocytochemical studies performed with osteoblast-like MC3T3-E1 cells and other mammalian cell lines confirm the localization of Fgd1 and show that the proline-rich N-terminal region is necessary and sufficient for Fgd1 subcellular localization to the plasma membrane and Golgi complex. In contrast, the FYVE-finger and PH2 domains do not appear to direct the localization of Fgd1 or the activation of Cdc42. In addition, microinjection studies indicate that the N-terminal Fgd1 domain inhibits filopodia formation, suggesting that this region down-regulates GEF function. These results characterize the function of the Fgd1 domains for both protein localization and Cdc42 activation and indicate that the Fgd1 Cdc42GEF protein is involved in the regulation of Cdc42 activity at the subcortical actin cytoskeleton and Golgi complex.
Hum Mol Genet 2001 Mar 01
PMID:Fgd1, the Cdc42 guanine nucleotide exchange factor responsible for faciogenital dysplasia, is localized to the subcortical actin cytoskeleton and Golgi membrane. 1118 72


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