Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.7.11.26 (GSK)
6,788 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The Kaposi's sarcoma-associated herpesvirus (KSHV) latency-associated nuclear antigen (LANA) is expressed in all KSHV-associated tumors, including Kaposi's sarcoma (KS) and primary effusion lymphoma (PEL). We found that beta-catenin is overexpressed in both PEL cells and KS tissue. Introduction of anti-LANA small interfering RNA (siRNA) into PEL cells eliminated beta-catenin accumulation; LANA itself upregulated expression of beta-catenin in transfected cells. LANA stabilizes beta-catenin by binding to the negative regulator GSK-3beta, causing a cell cycle-dependent nuclear accumulation of GSK-3beta. The LANA C terminus contains sequences similar to the GSK-3beta-binding domain of Axin. Disruption of this region resulted in a mutant LANA that failed to re-localize GSK-3beta or stabilize beta-catenin. The importance of this pathway to KSHV-driven cell proliferation was highlighted by the observation that LANA, but not mutant LANA, stimulates entry into S phase. Redistribution of GSK-3beta can therefore be a source of beta-catenin dysregulation in human cancers.
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PMID:A novel viral mechanism for dysregulation of beta-catenin in Kaposi's sarcoma-associated herpesvirus latency. 1261 69

Human herpesvirus 8 (HHV-8), the etiologic agent of Kaposi's sarcoma (KS), encodes a chemokine receptor homologue, the viral G protein-coupled receptor (vGPCR), that has been implicated in KS pathogenesis. Expression of vGPCR constitutively activates several signaling pathways, including NF-kappa B, and induces the expression of proinflammatory and angiogenic factors, consistent with the inflammatory hyperproliferative nature of KS lesions. Here we show that vGPCR also constitutively activates the nuclear factor of activated T cells (NF-AT), another transcription factor important in regulation of the expression of inflammatory cytokines and related factors. NF-AT activation by vGPCR depended upon signaling through the phosphatidylinositol 3-kinase-Akt-glycogen synthetase kinase 3 (PI3-K/Akt/GSK-3) pathway and resulted in increased expression of NF-AT-dependent cell surface molecules (CD25, CD29, Fas ligand), proinflammatory cytokines (interleukin-2 [IL-2], IL-4), and proangiogenic factors (granulocyte-macrophage colony-stimulating factor GMCSF and TNF alpha). vGPCR expression also increased endothelial cell-T-cell adhesion. Although infection with HHV-8 is necessary to cause KS, coinfection with human immunodeficiency virus type 1 (HIV-1), in the absence of antiretroviral suppressive therapy, increases the risk of KS by many orders of magnitude. NF-AT and NF-kappa B activation by vGPCR was greatly increased by the HIV-1 Tat protein, although Tat alone had little effect on NF-AT. The enhancement of NF-AT by Tat appears to be mediated through collaborative stimulation of the PI3-K/Akt/GSK-3 pathway by vGPCR and Tat. Our data further support the idea that vGPCR contributes to the pathogenesis of KS by a paracrine mechanism and, in addition, provide the first evidence of collaboration between an HIV-1 protein and an HHV-8 protein.
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PMID:Human herpesvirus 8-encoded vGPCR activates nuclear factor of activated T cells and collaborates with human immunodeficiency virus type 1 Tat. 1271 69

The latency-associated nuclear antigen (LANA) of Kaposi's sarcoma-associated herpesvirus (KSHV) is expressed in all KSHV-associated malignancies. LANA is essential for replication and maintenance of the viral episomes during latent infection. However, LANA also has a transcriptional regulatory role and can affect gene expression both positively and negatively. A previously performed yeast two-hybrid screen identified glycogen synthase kinase 3 (GSK-3) as a LANA-interacting protein. Interaction with both GSK-3alpha and GSK-3beta was confirmed in transfected cells with coprecipitation assays. GSK-3beta also interacted with the herpesvirus saimiri homolog ORF73. GSK-3beta is an intermediate in the Wnt signaling pathway and a negative regulator of beta-catenin. In transfected cells, LANA was shown to overcome GSK-3beta-mediated degradation of beta-catenin. Examination of primary effusion lymphoma (PEL) cells found increased levels of beta-catenin relative to KSHV-negative B cells, and this translated into increased activity of a beta-catenin-responsive reporter containing Tcf/Lef binding sites. In tetradecanoyl phorbol acetate-treated PEL cells, loss of LANA expression correlated temporally with loss of detectable beta-catenin. LANA was found to alter the intracellular distribution of GSK-3beta so that nuclear GSK-3beta was more readily detectable in the presence of LANA. Mapping experiments with coimmunoprecipitation assays revealed that both N-terminal and C-terminal LANA sequences were required for efficient GSK-3beta interaction. LANA mutants that were defective for GSK-3beta interaction were unable to mediate GSK-3beta relocalization or activate a beta-catenin-responsive Tcf-luciferase reporter. This study identified manipulation of GSK-3beta activity as a mechanism by which LANA may modify transcriptional activity and contribute to the phenotype of primary effusion lymphoma.
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PMID:The latency-associated nuclear antigen of Kaposi's sarcoma-associated herpesvirus manipulates the activity of glycogen synthase kinase-3beta. 1282 41

The Kaposi's sarcoma-associated herpesvirus, KSHV, is associated with cancers that have increased incidence in patients who are also HIV positive or who have undergone organ transplantation. It has recently been observed that beta-catenin is overexpressed in two KSHV-associated cancers, Kaposi's sarcoma and primary effusion lymphoma. Investigation of the underlying defect in beta-catenin regulation revealed that the KSHV-encoded LANA protein stabilizes beta-catenin by binding to the negative regulator GSK-3, causing a cell-cycle-dependent nuclear accumulation of GSK-3. Thus, redistribution of GSK-3 has been identified as yet another mechanism through which beta-catenin can be dysregulated and contribute to human cancer.
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PMID:Manipulation of glycogen-synthase kinase-3 activity in KSHV-associated cancers. 1499 Nov 50

The Kaposi's sarcoma-associated herpesvirus (KSHV)-encoded latency-associated nuclear antigen (LANA) protein stabilizes beta-catenin by the novel mechanism of binding to the negative regulator, glycogen synthase kinase 3 (GSK-3), and depleting cytoplasmic GSK-3 levels. The two domains of LANA required for interaction with GSK-3 were further characterized. Evidence for similarity between the C-terminal LANA interaction domain and the axin GSK-3 interaction domain was obtained using GSK-3 and LANA mutants. GSK-3(F291L), which does not interact with axin, also failed to bind to LANA, and a mutation in the axin homology domain of LANA, L1132P, destroyed binding to GSK-3. The N-terminal LANA interaction domain was found to mediate interaction by acting as a substrate for GSK-3. GSK-3(R96A), a priming pocket mutant, did not bind to LANA, suggesting that LANA was a primed GSK-3 substrate. Phosphorylation of endogenous LANA precipitated from primary effusion lymphoma cells was inhibited by the GSK-3 inhibitor LiCl. GST-LANA(1-340) was phosphorylated by GSK-3, and mitogen-activated protein kinase (MAPK) and casein kinase I functioned as priming kinases in vitro. Mutation of consensus GSK-3 sites revealed that sites between LANA amino acids 219 and 268 were important for GSK-3 phosphorylation. Immunoprecipitation assays revealed that loss of GSK-3 phosphorylation of this N-terminal domain correlated with loss of GSK-3 interaction. Although LANA-associated GSK-3 actively phosphorylated LANA, GSK-3 coprecipitated with LANA was unable to phosphorylate an exogenous peptide substrate. LANA sequestration of GSK-3 may explain the ability of KSHV-infected cells to tolerate increased levels of nuclear GSK-3.
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PMID:Regulation of the interaction between glycogen synthase kinase 3 and the Kaposi's sarcoma-associated herpesvirus latency-associated nuclear antigen. 1605 35

Primary effusion lymphoma (PEL) is a rare subtype of non-Hodgkin's lymphoma, which is associated with infection by Kaposi's sarcoma herpesvirus (KSHV)/human herpesvirus-8. The c-Myc transcription factor plays an important role in cellular proliferation, differentiation and apoptosis. Lymphomas frequently have deregulated c-Myc expression owing to chromosomal translocations, amplifications or abnormal stabilization. However, no structural abnormalities were found in the c-myc oncogene in PEL. Given that c-Myc is often involved in lymphomagenesis, we hypothesized that it is deregulated in PEL. We report that PEL cells have abnormally stable c-Myc protein. The turnover of c-Myc protein is stringently regulated by post-transcriptional modifications, including phosphorylation of c-Myc threonine 58 (T58) by glycogen synthase kinase-3beta (GSK-3beta). Our data show that the impaired c-Myc degradation in PEL cells is associated with a significant underphosphorylation of c-Myc T58. The KSHV latency-associated nuclear antigen (LANA) is responsible for this deregulation. Overexpression of LANA in human embryonic kidney 293 or peripheral blood B cells leads to post-transcriptional deregulation of c-Myc protein. Conversely, when LANA is eliminated from PEL cells using RNA interference, GSK-3beta-mediated c-Myc T58 phosphorylation is restored. The presence of c-Myc and LANA in GSK-3beta-containing complexes in PEL cells further confirms the significance of these interactions in naturally KSHV-infected cells.
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PMID:Deregulation of c-Myc in primary effusion lymphoma by Kaposi's sarcoma herpesvirus latency-associated nuclear antigen. 1731 Sep 99

The Kaposi's sarcoma-associated herpesvirus latency-associated nuclear antigen (LANA) protein interacts with glycogen synthase kinase 3 (GSK-3) and relocalizes GSK-3 in a manner that leads to stabilization of beta-catenin and upregulation of beta-catenin-responsive cell genes. The LANA-GSK-3 interaction was further examined to determine whether there were additional downstream consequences. In the present study, the nuclear GSK-3 bound to LANA in transfected cells and in BCBL1 primary effusion lymphoma cells was found to be enriched for the inactive serine 9-phosphorylated form of GSK-3. The mechanism of inactivation of nuclear GSK-3 involved LANA recruitment of the extracellular signal-regulated kinases 1 and 2 (ERK1/2) and the ribosomal S6 kinase 1 (RSK1). ERK1/2 and RSK1 coprecipitated with LANA, and LANA was a substrate for ERK1 in vitro. A model is proposed for the overall inactivation of nuclear GSK-3 that incorporates the previously described GSK-3 phosphorylation of LANA itself. Functional inactivation of nuclear GSK-3 was demonstrated by the ability of LANA to limit phosphorylation of the known GSK-3 substrates C/EBPbeta and C/EBPalpha. The effect of LANA-mediated ablation of C/EBP phosphorylation on differentiation was modeled in the well-characterized 3T3L1 adipogenesis system. LANA-expressing 3T3L1 cells were impaired in their ability to undergo differentiation and adipogenesis. C/EBPbeta induction followed the same time course as that seen in vector-transduced cells, but there was delayed and reduced induction of C/EBPbeta transcriptional targets in LANA-expressing cells. We conclude that LANA inactivates nuclear GSK-3 and modifies the function of proteins that are GSK-3 substrates. In the case of C/EBPs, this translates into LANA-mediated inhibition of differentiation.
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PMID:Kaposi's sarcoma-associated herpesvirus LANA protein downregulates nuclear glycogen synthase kinase 3 activity and consequently blocks differentiation. 1731 69

The Kaposi's sarcoma-associated herpesvirus (KSHV) latency-associated nuclear antigen (LANA) protein is functionally pleiotropic. LANA contributes to KSHV-associated pathogenesis, in part, by increasing entry of cells into S phase through a process that is driven by LANA interaction with the serine-threonine kinase glycogen synthase kinase 3 (GSK-3) and stabilization of beta-catenin. We now show that LANA affects the activity of another protein involved in cell cycle regulation, c-Myc. Sequencing of c-Myc coding sequences revealed that c-Myc in KSHV-positive primary effusion lymphoma (PEL) cell lines is wild type in the N-terminal region that regulates c-Myc protein stability. Despite this, c-Myc in PEL cells is stabilized. In LANA-expressing cells, inactivation of nuclear GSK-3 reduced phosphorylation of c-Myc at Thr58 and contributed to c-Myc stabilization by decreasing c-Myc ubiquitination. Phosphorylation of c-Myc on Ser62 also affects c-Myc stability and function. We now show that LANA increases the level of phosphorylated extracellular signal-regulated kinase 1 (ERK1) and increases ERK phosphorylation of c-Myc on Ser62. LANA also interacted with c-Myc, and c-Myc amino acids 147 to 220 were required for this interaction. LANA (L1006P) retained the ability to bind to c-Myc and activate ERK1, indicating that these events did not require LANA interaction with GSK-3. Thus, LANA stabilizes c-Myc; prevents the phosphorylation of c-Myc at Thr58, an event that promotes Myc-induced apoptosis; and independently stimulates phosphorylation of c-Myc at Ser62, an event that transcriptionally activates c-Myc. LANA-mediated manipulation of c-Myc function is likely to contribute to KSHV-associated tumorigenesis through the induction of c-Myc regulated cellular genes, as well as by the stimulation of cell cycle progression.
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PMID:The Kaposi's sarcoma-associated herpesvirus LANA protein stabilizes and activates c-Myc. 1763 26

Kaposi's sarcoma (KS) herpesvirus (KSHV) is the etiological agent of several immunodeficiency-linked cancers, including KS. Our previous work showed that the proto-oncogene c-kit is upregulated in KSHV-infected endothelial cells (ECs), as well as in KS lesions. We show here that KSHV-dependent induction of both c-kit mRNA and protein requires the establishment of a latent infection and that this upregulation occurs in primary DMVECs as well as in immortalized DMVECs (eDMVECs). Interestingly, we find that while the lymphatic EC (LEC) subpopulation exhibits KSHV-induced c-Kit upregulation, the blood EC (BEC) subpopulation does not. Despite this upregulation of c-Kit, receptor activation and phosphorylation of downstream effectors such as MAP Kinase Erk 1/2 and GSK-3 still requires the addition of exogenous c-Kit ligand, stem cell factor (SCF). These data indicate that KSHV does not induce constitutive c-Kit signaling, but instead upregulates c-Kit receptor levels, thus allowing infected ECs to respond to endogenous and exogenous SCF. Nonetheless, inhibition of either c-Kit activation or its downstream effectors reverses the characteristic spindle phenotype of infected eDMVECs. Together, these results contribute to our overall understanding of the role that the c-kit proto-oncogene plays in KS pathogenesis.
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PMID:Characterization of c-Kit expression and activation in KSHV-infected endothelial cells. 1950 68

Kaposi's sarcoma-associated herpes virus (KSHV)-encoded latency-associated nuclear antigen (LANA) protein has been reported to interact with glycogen synthase kinase 3beta (GSK-3beta) and to negatively regulate its activity, leading to stimulation of GSK-3beta-dependent beta-catenin degradation. We show here that the I-mfa domain proteins, HIC (human I-mfa domain-containing protein) and I-mfa (inhibitor of MyoD family a), interacted in vivo with LANA through their C-terminal I-mfa domains. This interaction affected the intracellular localization of HIC, inhibited the LANA-dependent transactivation of a beta-catenin-regulated reporter construct, and decreased the level of the LANA.GSK-3beta complex. These data reveal for the first time that I-mfa domain proteins interact with LANA and negatively regulate LANA-mediated activation of Wnt signaling-dependent transcription by inhibiting the formation of the LANA.GSK-3beta complex.
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PMID:Human I-mfa domain proteins specifically interact with KSHV LANA and affect its regulation of Wnt signaling-dependent transcription. 2041 16


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