Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P05412 (c-Jun)
 11,453 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The oncogenic protein Vav harbours a complex array of structural motifs, including leucine-rich, Dbl-homology, pleckstrin-homology, zinc-finger, SH2 and SH3 domains. Upon stimulation by antigens or mitogens, Vav becomes phosphorylated on key tyrosine residues and associates with other signalling proteins, including the mitogen receptors Zap-70 (ref. 6), Vap-1 (ref. 5) and Slp-76 (ref. 7). Disruption of the vav locus by homologous recombination causes severe defects in signalling by primary antigen receptors, leading to abnormal lymphocyte proliferation and lymphopenia. Despite the importance of Vav cell signalling, the function of this protein remains unknown. Here we show that tyrosine-phosphorylated Vav, but not the non-phosphorylated protein, catalyses GDP/GTP exchange on Rac-1, a protein implicated in cell proliferation and cytoskeletal organization, causing this GTPase to switch from its inactive to its active state. Transfection experiments also show that phosphorylation of Vav on tyrosine residues leads to nucleotide exchange on Rac-1 in vivo and stimulates c-Jun kinase, a downstream element in the signalling pathway involving this GTPase. Our results have identified a function for Vav and define a mechanism in which engaged membrane receptors activate its signalling pathway.
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PMID:Phosphotyrosine-dependent activation of Rac-1 GDP/GTP exchange by the vav proto-oncogene product. 899 Jan 21

Mitogen-activated protein kinases (MAPKs) are components of sequential kinase cascades that are activated in response to a variety of extracellular signals. Members of the MAPK family include the extracellular response kinases (ERKs or p42/44(MAPK)), the c-Jun amino-terminal kinases (JNKs), and the p38/Hog 1 protein kinases. MAPKs are phosphorylated and activated by MAPK kinases (MKKs or MEKs), which in turn are phosphorylated and activated by MKK/MEK kinases (Raf and MKKK/MEKKs). We have isolated two cDNAs encoding splice variants of a novel MEK kinase, MEKK4. The MEKK4 mRNA is widely expressed in mouse tissues and encodes for a protein of approximately 180 kDa. The MEKK4 carboxyl-terminal catalytic domain is approximately 55% homologous to the catalytic domains of MEKKs 1, 2, and 3. The amino-terminal region of MEKK4 has little sequence homology to the previously cloned MEKK proteins. MEKK4 specifically activates the JNK pathway but not ERKs or p38, distinguishing it from MEKKs 1, 2 and 3, which are capable of activating the ERK pathway. MEKK4 is localized in a perinuclear, vesicular compartment similar to the Golgi. MEKK4 binds to Cdc42 and Rac; kinase-inactive mutants of MEKK4 block Cdc42/Rac stimulation of the JNK pathway. MEKK4 has a putative pleckstrin homology domain and a proline-rich motif, suggesting specific regulatory functions different from those of the previously characterized MEKKs.
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PMID:Cloning of a novel mitogen-activated protein kinase kinase kinase, MEKK4, that selectively regulates the c-Jun amino terminal kinase pathway. 907 50

Rho-like GTPases, including Cdc42, Rac, and Rho, regulate signaling pathways that control actin cytoskeletal structures and transcriptional activation. The Tiam1 gene encodes an activator of Rac1, and similarly to constitutively activated (V12)Rac1, overexpression of Tiam1 in fibroblasts induces the formation of membrane ruffles. Tiam1 contains a Dbl homology (DH) domain and adjacent pleckstrin homology (PH) domain, hallmarks for activators of Rho-like GTPases. Unique for Tiam1 are an additional PH domain and a Discs-large homology region in the NH2-terminal part of the protein. Here we show that both in fibroblasts and COS cells, membrane localization of Tiam1 is required for the induction of membrane ruffling. A detailed mutational analysis, in combination with confocal laser scanning microscopy and immunoelectron microscopy, demonstrates that the NH2-terminal PH domain of Tiam1, but not the DH-adjacent PH domain, is essential for membrane association. This NH2-terminal PH domain of Tiam1 can be functionally replaced by the myristoylated membrane localization domain of c-Src, indicating that the primary function of this PH domain is to localize the protein at the membrane. After serum starvation, both membrane association of Tiam1 and ruffling can be induced by serum, suggesting that receptor stimulation induces membrane translocation of Tiam1. Similar to V12Rac1, Tiam1 stimulates the activity of the c-Jun NH2-terminal kinase (JNK). This Rac-dependent stimulation of JNK also requires membrane association of Tiam1. We conclude that the regulated membrane localization of Tiam1 through its NH2-terminal PH domain determines the activation of distinct Rac-mediated signaling pathways.
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PMID:Regulated membrane localization of Tiam1, mediated by the NH2-terminal pleckstrin homology domain, is required for Rac-dependent membrane ruffling and C-Jun NH2-terminal kinase activation. 912 50

The Ras-GRF1 exchange factor molecule contains in addition to the catalytic domain two pleckstrin homology (PH1 and PH2), one IQ and one Dbl homology (DH) domains. In this study we investigated the role of such additional domains. We found that a Ras-GRF1 mutant lacking PH1 and IQ domains is sufficient to activate c-fos promoter in response to lysophosphatidic acid (LPA). The same mutant did not increase external stimuli-regulated kinase (ERK) activity, suggesting an additional mechanism for the induction of gene transcription. Isolated DH-PH2 module activates c-Jun NH(2)-terminal kinase and the c-fos promoter in response to LPA, providing the basis for an ERK-independent mechanism. These results provide evidence that Ras-GRF1 acts as a bifunctional molecule on both ERK-dependent and independent pathways.
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PMID:CDC25(Mm)/Ras-GRF1 regulates both Ras and Rac signaling pathways. 1054 64

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

Rho family GTPases Rac and Cdc42 are pivotal regulators of apoptosis in multiple cell types. However, little is known about the mechanism by which these GTPases are regulated in response to apoptotic stimuli. Here, we demonstrate that TIAM1, a Rac-specific guanine nucleotide exchange factor, is cleaved by caspases during apoptosis. TIAM1 cleavage occurs in multiple cell lines in response to diverse apoptotic stimuli such as ceramide, Fas, and serum deprivation. Processing occurs at residue 993 of TIAM1 and removes the NH(2)-terminal of TIAM's two pleckstrin homology domains, leaving a stable fragment containing the Dbl homology and COOH-terminal pleckstrin homology domains. This leads to functional inactivation of TIAM1, as determined by failure of the cleavage product to stimulate GTP loading of Rac in vivo. Furthermore, this product is defective in signaling to two independent Rac effectors, c-Jun NH(2)-terminal kinase and serum response factor. Finally, we demonstrate that in cells treated with ceramide, cleavage of TIAM1 coincided with the inactivation of endogenous Rac. These results reveal a novel mechanism for regulating guanine nucleotide exchange factor activity and GTPase-mediated signaling pathways.
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PMID:Caspase-mediated cleavage of the TIAM1 guanine nucleotide exchange factor during apoptosis. 1175 55

The oncogenic transcription factor c-Jun plays an important role in cell proliferation, transformation and differentiation. All identified c-Jun-interacting proteins are localized to the nucleus or cytoplasm and function in their intact forms. Here we show that the pleckstrin homology domain-containing protein CKIP-1 (casein kinase 2-interacting protein-1) functions as a plasma membrane-bound AP-1 regulator. During apoptosis, CKIP-1 is cleaved by caspase-3 and translocated to the cytoplasm and then to the nucleus. C-terminal fragments of cleaved CKIP-1 strongly repress AP-1 activity. Importantly, CKIP-1 overexpression promotes apoptosis by forming a positive feedback loop between CKIP-1 and caspase-3. RNA interference of CKIP-1 or overexpression of c-Jun attenuates the sensitivity to apoptosis, indicating a novel role of CKIP-1 in apoptosis. CKIP-1 is the first case of a c-Jun-interacting protein that regulates AP-1 activity via caspase-3-dependent cleavage and translocation.
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PMID:Role for the pleckstrin homology domain-containing protein CKIP-1 in AP-1 regulation and apoptosis. 1570 51

FGD1 encodes a guanine nucleotide exchange factor for Cdc42. Mutations in the FGD1 gene are responsible for an X-linked disorder known as Aarskog-Scott syndrome (AAS). While most mutations were found in the catalytic region, which consists of Dbl homology (DH) domain and adjacent pleckstrin homology (PH) domain, a missense mutation in the proline-rich domain is also found in a patient with typical clinical features as AAS. In this mutant FGD1, the serine residue at 205 is replaced with isoleucine. We recently demonstrated that FGD1 translocated to the membrane in response to extracellular stimuli such as epidermal growth factor (EGF) whereas FGD1 with S(205)/I substitution did not. Here we show that the proline-rich domain is critical for FGD1-induced directionally persistent cell migration. When inducibly expressed in HeLa Tet-Off cells, FGD1 stimulates directional migration whereas FGD1 with S(205)/I substitution does not affect it. We further demonstrate that FGD1 augments EGF-stimulated c-Jun NH(2)-terminal kinase (JNK) activation. In the presence of JNK inhibitor SP600125, motility of FGD1-expressing cells is significantly impaired, indicating a critical role of JNK in cell migration. However, FGD3, an FGD1 homologue lacking the proline-rich domain, and FGD1 with S(205)/I substitution augment EGF-stimulated JNK activation similarly to FGD1, suggesting that the proline-rich domain is not involved in the regulation of JNK. Finally, we show that FGD1, but not FGD1 with S(205)/I substitution, is phosphorylated in response to EGF, suggesting that the phosphorylation of S(205) may trigger the FGD1 translocation to the leading edge membrane and enable cells to undergo directional migration.
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PMID:Role of FGD1, a Cdc42 guanine nucleotide exchange factor, in epidermal growth factor-stimulated c-Jun NH2-terminal kinase activation and cell migration. 2121 17

Osteosarcoma (OS) is the most common bone tumor in pediatric patients. Metastasis is a major cause of mortality and morbidity. The rarity of this disease coupled with the challenges of drug development for metastatic cancers have slowed the delivery of improvements in long-term outcomes for these patients. In this study, we collected 18 OS cell lines, confirmed their expression of bone markers and complex karyotypes, and characterized their in vivo tumorgenicity and metastatic potential. Since prior reports included conflicting descriptions of the metastatic and in vivo phenotypes of these models, there was a need for a comparative assessment of metastatic phenotypes using identical procedures in the hands of a single investigative group. We expect that this single characterization will accelerate the study of this metastatic cancer. Using these models we evaluated the expression of six previously reported metastasis-related OS genes. Ezrin was the only gene consistently differentially expressed in all the pairs of high/low metastatic OS cells. We then used a subtractive gene expression approach of the high and low human metastatic cells to identify novel genes that may be involved in OS metastasis. PHLDA1 (pleckstrin homology-like domain, family A) was identified as one of the genes more highly expressed in the high metastatic compared to low metastatic cells. Knocking down PHLDA1 with siRNA or shRNA resulted in down regulation of the activities of MAPKs (ERK1/2), c-Jun N-terminal kinases (JNK), and p38 mitogen-activated protein kinases (MAPKs). Reducing the expression of PHLDA1 also delayed OS metastasis progression in mouse xenograft models.
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PMID:Characterization of the metastatic phenotype of a panel of established osteosarcoma cells. 2632 Jan 82