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

The GTPase activity of p21ras is stimulated by GTPase-activating proteins (GAPs) such as p120GAP and the product of the neurofibromatosis 1 gene, which may negatively regulate p21 function. GAPs are also proposed effectors of ras. We have sought activating substitutions in c-H-ras in the region encoding the effector domain, on the rationale that such mutations would dissociate effector function from negative regulation by GAP. One such activating mutation, Pro-34-->Arg, encodes protein that is substantially bound to GTP in vivo. In vitro, this protein is not stimulated by GAPs, and its binding to p120GAP is grossly impaired. The results support the idea that the p21 structural requirements for effector function and GAP interaction are quite different and suggest that some molecule(s) other than p120GAP serves as the ras effector. In contrast to the results obtained with p120GAP, the Pro-34-->Arg p21 species is effectively coupled to the raf-1 product, as judged from electrophoretic mobility shifts of the Raf-1 phosphoprotein.
Mol Cell Biol 1993 Dec
PMID:Effector domain mutations dissociate p21ras effector function and GTPase-activating protein interaction. 824 52

Recombinant expression of a chimeric EGFR/ErbB-3 receptor in NIH 3T3 fibroblasts allowed us to investigate cytoplasmic events associated with ErbB-3 signal transduction upon ligand activation. An EGFR/ErbB-3 chimera was expressed on the surface of NIH 3T3 transfectants as two classes of receptors possessing epidermal growth factor (EGF) binding affinities comparable to those of the wild-type EGF receptor (EGFR). EGF induced autophosphorylation in vivo of the chimeric receptor and DNA synthesis of EGFR/ErbB-3 transfectants with a dose response similar to that of EGFR transfectants. However, the ErbB-3 and EGFR cytoplasmic domains exhibited striking differences in their interactions with several known tyrosine kinase substrates. We demonstrated strong association of phosphatidylinositol 3-kinase activity with the chimeric receptor upon ligand activation comparable in efficiency with that of the platelet-derived growth factor receptor, while the EGFR exhibited a 10- to 20-fold-lower efficiency in phosphatidylinositol 3-kinase recruitment. By contrast, both phospholipase C gamma and GTPase-activating protein failed to associate with or be phosphorylated by the ErbB-3 cytoplasmic domain under conditions in which they coupled with the EGFR. In addition, though certain signal transmitters, including Shc and GRB2, were recruited by both kinases, EGFR and ErbB-3 elicited tyrosine phosphorylation of distinct sets of intracellular substrates. Thus, our findings show that ligand activation of the ErbB-3 kinase triggers a cytoplasmic signaling pathway that hitherto is unique within this receptor subfamily.
Mol Cell Biol 1994 Jan
PMID:Efficient coupling with phosphatidylinositol 3-kinase, but not phospholipase C gamma or GTPase-activating protein, distinguishes ErbB-3 signaling from that of other ErbB/EGFR family members. 826 17

Lysine 1423 of neurofibromin (neurofibromatosis type I gene product [NF1]) plays a crucial role in the function of NF1. Mutations of this lysine were detected in samples from a neurofibromatosis patient as well as from cancer patients. To further understand the significance of this residue, we have mutated it to all possible amino acids. Functional assays using yeast ira complementation have revealed that lysine is the only amino acid that produced functional NF1. Quantitative analyses of different mutant proteins have suggested that their GTPase-activating protein (GAP) activity is drastically reduced as a result of a decrease in their Ras affinity. Such a requirement for a specific residue is not observed in the case of other conserved residues within the GAP-related domain. We also report that another residue, phenylalanine 1434, plays an important role in NF1 function. This was first indicated by the finding that defective NF1s due to an alteration of lysine 1423 to other amino acids can be rescued by a second site intragenic mutation at residue 1434. The mutation partially restored GAP activity in the lysine mutant. When the mutation phenylalanine 1434 to serine was introduced into a wild-type NF1 protein, the resulting protein acquired the ability to suppress activated phenotypes of RAS2Val-19 cells. This suppression, however, does not involve Ras interaction, since the phenylalanine mutant does not stimulate the intrinsic GTPase activity of RAS2Val-19 protein and does not have an increased affinity for Ras proteins.
Mol Cell Biol 1994 Jan
PMID:Functional significance of lysine 1423 of neurofibromin and characterization of a second site suppressor which rescues mutations at this residue and suppresses RAS2Val-19-activated phenotypes. 826 48

The neurofibromatosis type 1 (NF1) gene was recently identified by positional cloning and found to encode a protein with structural and functional homology to mammalian and yeast GTPase-activating proteins (GAPs). Using antibodies directed against the NF1 gene product, a protein of approximately 250 kDa was identified and termed neurofibromin. Double-indirect immunofluorescent labeling with anti-neurofibromin and anti-tubulin antibodies demonstrates that neurofibromin associates with cytoplasmic microtubules. Immunoblotting of microtubule-enriched cytoplasmic fractions, using antibodies generated against neurofibromin, shows that neurofibromin copurifies with microtubules. When portions of neurofibromin are expressed in Sf9 insect cells they associate with polymerized microtubules; furthermore, the critical residues for this interaction reside within the GAP-related domain of neurofibromin. The unexpected association of neurofibromin with microtubules suggests that neurofibromin is involved in microtubule-mediated intracellular signal transduction pathways.
Somat Cell Mol Genet 1993 May
PMID:Neurofibromatosis type 1 gene product (neurofibromin) associates with microtubules. 833 34

n-Chimerin (alpha 1-chimerin) is a brain GTPase-activating protein (GAP) for the ras-related p21rac. We now report the occurrence of another form of chimerin, termed alpha 2-chimerin. This is the product of an alternately spliced transcript of the human n-chimerin gene encoding an N-terminal SH2 (src homology 2) domain in addition to the phorbol ester receptor and GAP domains. alpha 1- and alpha 2-chimerin mRNAs were expressed differently. In the rat brain, only alpha 1-chimerin mRNA was expressed in cerebellar Purkinje cells, although both alpha 1- and alpha 2-chimerin mRNAs occurred in neurons in the cerebral cortex, hippocampus, and thalamus. Only alpha 2-chimerin RNA was expressed in rat testes, in early pachytene spermatocytes. A 45-kDa SH2-containing chimerin corresponding to the alpha 2 form was purified from rat brain. As with Escherichia coli 45-kDa recombinant alpha 2-chimerin, purified brain alpha 2-chimerin exhibited racGAP activity which was stimulated by phosphatidylserine. The recombinant SH2 domain bound several 32P-labelled phosphoproteins of PC12 cells, whose phosphorylation increased in response to trophic factors, including nerve growth factor. To examine the relationships of alpha 1- and alpha 2-chimerin transcripts, human genomic DNA clones were characterized. In alpha 2-chimerin mRNA, a 3' splice acceptor site within exon 1 of alpha 1-chimerin mRNA was used, replacing its 5' untranslated region and N-terminal coding sequence. The single human n-chimerin gene was mapped to chromosome 2q31-q32.1, colocalizing with the CRE-BP1 transcription factor gene (2q32). It contained several splice junctions conserved with the sequence-related protein kinase C and bcr genes. alpha 2-Chimerin is only the second SH2-containing GAP and the first example of an SH2 domain generated by alternate splicing.
Mol Cell Biol 1993 Aug
PMID:Alpha 2-chimerin, an SH2-containing GTPase-activating protein for the ras-related protein p21rac derived by alternate splicing of the human n-chimerin gene, is selectively expressed in brain regions and testes. 833 31

The ras genes from yeast and mammalian cells were fused to plant expression promoters, and introduced into plant cells via Agrobacterium, to study their effect on cell growth and development. All introduced ras genes had a strong inhibitory effect on callus and shoot regeneration from plant tissues. This is consistent with earlier findings that heterologous ras genes were highly lethal to protoplasts following direct DNA uptake. These effects could not be reversed by increasing exogenous or endogenous cytokinin levels. These effects were also independent of the v-Ha-ras mutations in functionally important regions of Ras proteins such as effector-binding and membrane-binding sites. Similarly, co-transformation with the genes encoding the Ras-negative regulators, GTPase-activating protein and neurofibromin did not affect the ras inhibitory effect, indicating that the mechanism of ras inhibition of plant cells is not related to normal ras cellular functions. This conclusion was supported by further studies in which ras gene expression was modified using various promoters and antisense constructs. The introduced ras sequences remained fully inhibitory regardless of which promoters (inducible or tissue-specific) or which orientations (sense or antisense) were tested. This strongly suggests that the ras DNA sequence itself, rather than the Ras protein or ras mRNA, is directly involved in the inhibitory effect. The mechanism underlying this novel phenomenon remains unknown. Introduced ras genes may inhibit plant cell growth by inducing co-suppression of unknown endogenous ras or ras-related genes, thereby leading to the arrest of cell growth.
Plant Mol Biol 1993 Aug
PMID:Investigation of the mechanism underlying the inhibitory effect of heterologous ras genes in plant cells. 835 27

A series of pieces of evidence have shown that Ras protein acts as a transducer of the platelet-derived growth factor (PDGF) receptor-mediated signaling pathway: (i) formation of Ras.GTP is detected immediately on PDGF stimulation, and (ii) a dominant inhibitory mutant Ras, as well as a neutralizing anti-Ras antibody, can interfere with PDGF-induced responses. On the other hand, several signal transducing molecules including phosphatidylinositol 3-kinase (PI3-K), GTPase-activating protein (GAP), and phospholipase C gamma (PLC gamma) bind directly to the PDGF receptor and become tyrosine phosphorylated. Recently, it was shown that specific phosphorylated tyrosines of the PDGF receptor are responsible for interaction between the receptor and each signaling molecule. However, the roles of these signaling molecules have not been elucidated, and it remains unclear which molecules are implicated in the Ras pathway. In this study, we measured Ras activation in cell lines expressing mutant PDGF receptors that are deficient in coupling with specific molecules. In fibroblast CHO cells, a mutant receptor (Y708F/Y719F [PI3-K-binding sites]) was unable to stimulate Ras, whereas another mutant (Y739F [the GAP-binding site]) could do so, suggesting an indispensable role of PI3-K or a protein that binds to the same sites as PI3-K for PDGF-stimulated Ras activation. By contrast, both of the above mutants were capable of stimulating Ras protein in a pro-B-cell line, BaF3. Furthermore, a mutant receptor (Y977F/Y989F [PLC gamma-binding sites]) could fully activate Ras, and the direct activation of protein kinase C and calcium mobilization had almost no effect on the GDP/GTP state of Ras in this cell line. These results suggest that, in the pro-B-cell transfectants, each of the above pathways (PI3-K, GAP, and PLC gamma) can be eliminated without a loss of Ras activation. It remains unclear whether another unknown essential pathway which regulates Ras protein exists within BaF3 cells. Therefore, it is likely that several different PDGF receptor-mediated signaling pathways function upstream of Ras, and the extent of the contribution of each pathway for the regulation of Ras may differ among different cell types.
Mol Cell Biol 1993 Jun
PMID:Platelet-derived growth factor receptor mediates activation of ras through different signaling pathways in different cell types. 838 43

Engagement of the B-cell antigen receptor complex induces immediate activation of receptor-associated Src family tyrosine kinases including p55blk, p59fyn, p53/56lyn, and perhaps p56lck, and this response is accompanied by tyrosine phosphorylation of distinct cellular substrates. These kinases act directly or indirectly to phosphorylate and/or activate effector proteins including p42 (microtubule-associated protein kinase) (MAPK), phospholipases C-gamma 1 (PLC gamma 1) and C-gamma 2 (PLC gamma 2), phosphatidylinositol 3-kinase (PI 3-K), and p21ras-GTPase-activating protein (GAP). Although coimmunoprecipitation results indicate that the Src family protein tyrosine kinases interact physically with some of these effector molecules, the molecular basis of this interaction has not been established. Here, we show that three distinct sites mediate the interaction of these kinases with effectors. The amino-terminal 27 residues of the unique domain of p56lyn mediate association with PLC gamma 2, MAPK, and GAP. Binding to PI 3-K is mediated through the Src homology 3 (SH3) domains of the Src family kinases. Relatively small proportions of cellular PI 3-K, PLC gamma 2, MAPK, and GAP, presumably those which are tyrosine phosphorylated, bind to the SH2 domains of these kinases. Comparative analysis of binding activities of Blk, Lyn, and Fyn shows that these kinases differ in their abilities to associate with MAPK and PI 3-K, suggesting that they may preferentially bind and subsequently phosphorylate distinct sets of downstream effector molecules in vivo. Fast protein liquid chromatography Mono Q column-fractionated MAPK maintains the ability to bind bacterially expressed Lyn, suggesting that the two kinases may interact directly.
Mol Cell Biol 1993 Sep
PMID:Mapping of sites on the Src family protein tyrosine kinases p55blk, p59fyn, and p56lyn which interact with the effector molecules phospholipase C-gamma 2, microtubule-associated protein kinase, GTPase-activating protein, and phosphatidylinositol 3-kinase. 839 16

Sequence analysis has shown significant homology between the catalytic regions of the mammalian ras GTPase-activating protein (GAP), yeast Ira1p and Ira2p (inhibitory regulators of the RAS-cyclic AMP pathway), and neurofibromin, the protein encoded by the NF1 gene. Yeast expression experiments have confirmed that a 381-amino-acid segment of neurofibromin, dubbed the GAP-related domain (GRD), can function as a GAP. Using the RNA polymerase chain reaction with primers flanking the NF1-GRD, we have identified evidence for alternative splicing in this region of the NF1 gene. In addition to the already published sequence (type I), an alternative RNA carrying a 63-nucleotide insertion (type II) is present in all tissues examined, although the relative amounts of types I and II vary. The insertion is conserved across species but is not present in GAP, IRA1, or IRA2. GenBank searches have failed to identify significant similarity between the inserted sequence and known DNA or protein sequences, although the basic amino acid composition of the insertion shares features with nuclear targeting sequences. Expression studies in yeasts show that despite the partial disruption of the neurofibromin-IRA-GAP homology by this insertion, both forms of the NF1-GRD can complement loss of IRA function. In vivo assays designed to compare the GAP activity of the two alternatively spliced forms of the NF1-GRD show that both can increase the conversion of GTP-bound ras to its GDP-bound form, although the insertion of the 21 amino acids weakens this effect. The strong conservation of this alternative splicing suggests that both type I and II isoforms mediate important biological functions of neurofibromin.
Mol Cell Biol 1993 Jan
PMID:A conserved alternative splice in the von Recklinghausen neurofibromatosis (NF1) gene produces two neurofibromin isoforms, both of which have GTPase-activating protein activity. 841 46

Treatment of intact Rat-1 fibroblasts with epidermal growth factor (EGF) leads to rapid activation of cellular ras-encoded proteins. By using the bacterial toxin streptolysin O to permeabilize these cells, it was shown that the low basal rate at which guanine nucleotides bind to, and dissociate from, ras-encoded protein in quiescent fibroblasts was greatly accelerated by EGF treatment. Nucleotide binding to other proteins was not affected. Stimulation of nucleotide exchange on ras-encoded protein required tyrosine kinase but not phospholipase activity. EGF had no effect on total GTPase-activating protein activity. Regulation of ras-encoded protein in Rat-1 fibroblasts is therefore mediated by stimulation, either directly or indirectly, of ras-encoded protein-specific guanine nucleotide exchange factors by the EGF receptor tyrosine kinase.
Mol Cell Biol 1993 Mar
PMID:Epidermal growth factor regulates the exchange rate of guanine nucleotides on p21ras in fibroblasts. 844 21


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>