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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Expression of the adaptor protein v-Crk in PC12 cells results in sustained activation of NGF signaling pathways and augmented neuritogenesis. However, the inhibitory effect of the v-Crk SH2 domain mutant on neurite elongation does not correlate with impaired Trk A dependent signaling events or gene induction. In contrast, immunofluorescence studies and Triton X-100 extraction experiments indicate that v-Crk co-localizes with the cytoskeletal protein paxillin in the actin cytoskeleton whereas the v-Crk SH2 mutant causes aberrant aggregration of actin filaments at the growth cones. Interestingly, the neurotrophin receptor p75 in v-CrkPC12 cells also displays enhanced localization to the cytoskeleton and these cells exhibit an increased rate of NGF internalization. Together our data suggest that v-Crk might target the NGF-activated receptor signaling complex to the cytoskeleton, thereby potentiating neuritogenesis at the growth cone level. However, mutation in the v-Crk SH2 domain uncouples NGF signaling from the cytoskeletal interactions necessary for neurite elongation.
Mol Cell Neurosci 1996
PMID:Dissociation of NGF induced signal transduction from neurite elongation by expression of a mutant adaptor protein v-Crk in PC12 cells. 891 32

Expression of the adaptor protein v-Crk in PC12 cells results in sustained activation of NGF signaling pathways and augmented neuritogenesis. However, the inhibitory effect of the v-Crk SH2 domain mutant on neurite elongation does not correlate with impaired Trk A dependent signaling events or gene induction. In contrast, immunofluorescence studies and Triton X-100 extraction experiments indicate that v-Crk co-localizes with the cytoskeletal protein paxillin in the actin cytoskeleton whereas the v-Crk SH2 mutant causes aberrant aggregration of actin filaments at the growth cones. Interestingly, the neurotrophin receptor p75 in v-CrkPC12 cells also displays enhanced localization to the cytoskeleton and these cells exhibit an increased rate of NGF internalization. Together our data suggest that v-Crk might target the NGF-activated receptor signaling complex to the cytoskeleton, thereby potentiating neuritogenesis at the growth cone level. However, mutation in the v-Crk SH2 domain uncouples NGF signaling from the cytoskeletal interactions necessary for neurite elongation.
Mol Cell Neurosci 1996 Aug
PMID:Dissociation of NGF Induced Signal Transduction from Neurite Elongation by Expression of a Mutant Adaptor Protein v-Crk in PC12 Cells 895 30

In the current studies, we investigated the relationship between tyrosine phosphorylation and neurite formation. In SH-SY5Y neuroblastoma cells, the tyrosine kinase inhibitor methyl 2, 5-dihydroxycinnimate blocked neurite formation on laminin. This corresponded with inhibition of paxillin and focal adhesion kinase tyrosine phosphorylation as well as a disruption of actin filament organization and actin polymerization. This suggests that tyrosine phosphorylation helps direct changes in the actin cytoskeleton required for neurite formation.
Brain Res Mol Brain Res 1996 Dec 31
PMID:The tyrosine kinase inhibitor methyl 2,5-dihydroxycinnimate disrupts changes in the actin cytoskeleton required for neurite formation. 903 51

Alveolar epithelial type II cells are the progenitor cells for restoring the alveolar epithelial barrier after acute lung injury. During repair of lung injury, the alveolar epithelial type II cells reepithelialize denuded air spaces, a process that involves breaking and reforming cell adhesions. A novel technique of mechanical separation of cultured alveolar epithelial cells from in vitro matrix was used to examine the intracellular signals that result when alveolar epithelial cell adhesions are broken. The results show that the tyrosine phosphorylation levels of focal adhesion kinase, paxillin, and pp60(src) decreased immediately after mechanical separation of the cells. Levels returned to nearly normal by 24 h after mechanical separation. Paxillin and pp60(scr) coprecipitated with focal adhesion kinase regardless of their phosphorylation state. Interestingly, the tyrosine phosphorylation level of the mitogen-activated protein kinase, p42(erk2), increased 15 min after mechanical separation. Preincubation of cell monolayers with phenylarsine oxide, a protein tyrosine phosphatase inhibitor, blocked the decrease in tyrosine phosphorylation levels of focal adhesion kinase, paxillin and pp60(src). Phenylarsine oxide incubation also prevented readhesion of mechanically separated cells at 24 h, but genistein, a tyrosine kinase inhibitor, had no effect. We conclude that protein tyrosine phosphatases are activated immediately after cultured alveolar epithelial cells are mechanically separated from in vitro matrix, and their activation is required for alveolar epithelial cell readhesion.
Am J Respir Cell Mol Biol 1997 May
PMID:Protein tyrosine phosphatases mediate cell readhesion in alveolar epithelial cells mechanically separated from in vitro matrix. 916 Aug 44

Cell attachment to fibronectin stimulates the integrin-dependent interaction of p85-associated phosphatidylinositol (PI) 3-kinase with integrin-dependent focal adhesion kinase (FAK) as well as activation of the Ras/mitogen-activated protein (MAP) kinase pathway. However, it is not known if this PI 3-kinase-FAK interaction increases the synthesis of the 3-phosphorylated phosphoinositides (3-PPIs) or what role, if any, is played by activated PI 3-kinase in integrin signaling. We demonstrate here the integrin-dependent accumulation of the PI 3-kinase products, PI 3,4-bisphosphate [PI(3,4)P2] and PI(3,4,5)P3, as well as activation of AKT kinase, a serine/threonine kinase that can be stimulated by binding of PI(3,4)P2. The PI 3-kinase inhibitors wortmannin and LY294002 significantly decreased the integrin-induced accumulation of the 3-PPIs and activation of AKT kinase, without having significant effects on the levels of PI(4,5)P2 or tyrosine phosphorylation of paxillin. These inhibitors also reduced cell adhesion/spreading onto fibronectin but had no effect on attachment to polylysine. Interestingly, integrin-mediated Erk-2, Mek-1, and Raf-1 activation, but not Ras-GTP loading, was inhibited at least 80% by wortmannin and LY294002. In support of the pharmacologic results, fibronectin activation of Erk-2 and AKT kinases was completely inhibited by overexpression of a dominant interfering p85 subunit of PI 3-kinase. We conclude that integrin-mediated adhesion to fibronectin results in the accumulation of the PI 3-kinase products PI(3,4)P2 and PI(3,4,5)P3 as well as the PI 3-kinase-dependent activation of the kinases Raf-1, Mek-1, Erk-2, and AKT and that PI 3-kinase may function upstream of Raf-1 but downstream of Ras in integrin activation of Erk-2 MAP and AKT kinases.
Mol Cell Biol 1997 Aug
PMID:Phosphatidylinositol 3-kinase is required for integrin-stimulated AKT and Raf-1/mitogen-activated protein kinase pathway activation. 923 99

pp125FAK is a tyrosine kinase that appears to regulate the assembly of focal adhesions and thereby promotes cell spreading on the extracellular matrix. In some cells, the C terminus of pp125FAK is expressed as a separate protein, pp41/43FRNK. We have previously shown that overexpression of pp41/43FRNK inhibits tyrosine phosphorylation of pp125FAK and paxillin and, in addition, delays cell spreading and focal adhesion assembly. Thus, pp41/43FRNK functions as a negative inhibitor of adhesion signaling and provides a tool to dissect the mechanism by which pp125FAK promotes cell spreading. We report here that the inhibitory effects of pp41/43FRNK expression can be rescued by the co-overexpression of wild-type pp125FAK and partially rescued by catalytically inactive variants of pp125FAK. However, coexpression of an autophosphorylation site mutant of pp125FAK, which fails to bind the SH2 domain of pp60c-Src, or a mutant that fails to bind paxillin did not promote cell spreading. In contrast, expression of pp41/43FRNK and pp60c-Src reconstituted cell spreading and tyrosine phosphorylation of paxillin but did so without inducing tyrosine phosphorylation of pp125FAK. These data provide additional support for a model whereby pp125FAK acts as a "switchable adaptor" that recruits pp60c-Src to phosphorylate paxillin, promoting cell spreading. In addition, these data point to tyrosine phosphorylation of paxillin as being a critical step in focal adhesion assembly.
Mol Cell Biol 1997 Dec
PMID:Inhibition of cell spreading by expression of the C-terminal domain of focal adhesion kinase (FAK) is rescued by coexpression of Src or catalytically inactive FAK: a role for paxillin tyrosine phosphorylation. 937 22

It has been suggested that basic fibroblast growth factor (bFGF) affects hematopoietic cells directly and that it may also act indirectly by modulating stromal cell functions. We tested the response of phenotypically and functionally distinct stromal cell clones to this cytokine. We studied cell phenotype, the composition and organization of cytoskeleton and extracellular matrix, the ability to repopulate 'wounded areas', the expression of cytokine genes, and the capacity of the stroma to support long-term hematopoiesis in vitro. Although the impact of bFGF on cell growth was small, it induced a prominent morphological change in three stromal cell types that we tested. We analyzed the molecular basis for this change: bFGF modified the protein expression of alpha-smooth muscle actin (alpha-SMA), tropomyosin, alpha-tubulin, fibronectin and paxillin in a distinct manner characteristic of each of the stromal cell types. Immunofluorescence analysis of these proteins revealed profound changes in the cytoskeleton and extracellular matrix (ECM) networks accompanied by increased ability of the 14F1.1 stromal cells to scatter in in vitro 'wounded' areas. Furthermore, although only limited changes were monitored in the expression of cytokine genes, the ability of the stromal cells to support hematopoiesis was markedly modified. Thus bFGF profoundly changes the cellular organization of stromal cells, their adhesion and their motility properties. These changes are associated with modified capacity to support hematopoiesis in culture.
Cytokines Mol Ther 1996 Mar
PMID:Control of stroma-dependent hematopoiesis by basic fibroblast growth factor: stromal phenotypic plasticity and modified myelopoietic functions. 938 87

The small GTPase RhoA plays a critical role in signaling pathways activated by serum-derived factors, such as lysophosphatidic acid (LPA), including the formation of stress fibers in fibroblasts and neurite retraction and rounding of soma in neuronal cells. Previously, we have shown that ectopic expression of v-Crk, an SH2/SH3 domain-containing adapter proteins, in PC12 cells potentiates nerve growth factor (NGF)-induced neurite outgrowth and promotes the survival of cells when NGF is withdrawn. In the present study we show that, when cultured in 15% serum or lysophosphatidic acid-containing medium, the majority of v-Crk-expressing PC12 cells (v-CrkPC12 cells) display a flattened phenotype with broad lamellipodia and are refractory to NGF-induced neurite outgrowth unless serum is withdrawn. v-Crk-mediated cell flattening is inhibited by treatment of cells with C3 toxin or by mutation in the Crk SH2 or SH3 domain. Transient cotransfection of 293T cells with expression plasmids for p160ROCK (Rho-associated coiled-coil-containing kinase) and v-Crk, but not SH2 or SH3 mutants of v-Crk, results in hyperactivation of p160ROCK. Moreover, the level of phosphatidylinositol-4,5-bisphosphate is increased in v-CrkPC12 cells compared to the levels in mutant v-Crk-expressing cells or wild-type cells, consistent with PI(4)P5 kinase being a downstream target for Rho. Expression of v-Crk in PC12 cells does not result in activation of Rac- or Cdc42-dependent kinases PAK and S6 kinase, demonstrating specificity for Rho. In contrast to native PC12 cells, in which focal adhesions and actin stress fibers are not observed, immunohistochemical analysis of v-CrkPC12 cells reveals focal adhesion complexes which are formed at the periphery of the cell and are connected to actin cables. The formation of focal adhesions correlates with a concomitant upregulation in the expression of focal adhesion proteins FAK, paxillin, alpha3-integrin, and a higher-molecular-weight form of beta1-integrin. Our results indicate that v-Crk activates the Rho-signaling pathway and serves as a scaffolding protein during the assembly of focal adhesions in PC12 cells.
Mol Cell Biol 1998 May
PMID:Activation of Rho-dependent cell spreading and focal adhesion biogenesis by the v-Crk adaptor protein. 956 23

We recently identified a cellular protein named E6BP or ERC-55 that binds cancer-related papillomavirus E6 proteins (Chen, J. J., Reid, C. E., Band, V., and Androphy, E. J. (1995) Science 269, 529-531). By construction of a series of deletion mutants, the region of E6BP that is necessary and sufficient for complex formation with human papillomavirus type 16 E6 has been mapped to a 25-amino acid domain. The corresponding peptide was synthesized and found by nuclear magnetic resonance spectroscopy to bind calcium and fold into a classical helix-loop-helix EF-hand conformation. Additional deletion mutagenesis showed that 13 amino acids that form the second alpha helix mediated E6 association. Alanine replacement mutagenesis indicated that amino acids of this helix were most important for E6 binding. Alignment of this alpha helical E6 binding peptide with the 18-amino acid E6 binding region of E6AP (Huibregtse, J. M., Scheffner, M., and Howley, P. M. (1993) Mol. Cell. Biol. 13, 4918-4927) and the first LD repeat of another E6-binding protein, paxillin (Tong, X., and Howley, P. M. (1997) J. Biol. Chem. 272, 33373-33376), revealed substantial similarities among these E6 binding domains. The extent of homology and the mutational data define the peptide as an E6 binding motif.
 ...
PMID:Identification of an alpha helical motif sufficient for association with papillomavirus E6. 959 89

We have previously shown that the LIM domains of paxillin operate as the focal adhesion (FA)-targeting motif of this protein. In the current study, we have identified the capacity of paxillin LIM2 and LIM3 to serve as binding sites for, and substrates of serine/threonine kinases. The activities of the LIM2- and LIM3-associated kinases were stimulated after adhesion of CHO.K1 cells to fibronectin; consequently, a role for LIM domain phosphorylation in regulating the subcellular localization of paxillin after adhesion to fibronectin was investigated. An avian paxillin-CHO.K1 model system was used to explore the role of paxillin phosphorylation in paxillin localization to FAs. We found that mutations of paxillin that mimicked LIM domain phosphorylation accelerated fibronectin-induced localization of paxillin to focal contacts. Further, blocking phosphorylation of the LIM domains reduced cell adhesion to fibronectin, whereas constitutive LIM domain phosphorylation significantly increased the capacity of cells to adhere to fibronectin. The potentiation of FA targeting and cell adhesion to fibronectin was specific to LIM domain phosphorylation as mutation of the amino-terminal tyrosine and serine residues of paxillin that are phosphorylated in response to fibronectin adhesion had no effect on the rate of FA localization or cell adhesion. This represents the first demonstration of the regulation of protein localization through LIM domain phosphorylation and suggests a novel mechanism of regulating LIM domain function. Additionally, these results provide the first evidence that paxillin contributes to "inside-out" integrin-mediated signal transduction.
Mol Biol Cell 1998 Jul
PMID:Serine and threonine phosphorylation of the paxillin LIM domains regulates paxillin focal adhesion localization and cell adhesion to fibronectin. 965 72


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