Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P43146 (tumour suppressor)
 5,935 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

HPV16 E6 interacts with and degrades tumour suppressor protein TSC2 leading to the phosphorylation of p70 S6 kinase. We studied the association of S6 kinase phosphorylation and HPV16 infection in cervical cancer and esophageal cancer. Immunohistochemistry was used to assess phosphorylated S6 kinase (Thr 389) and phosphorylated S6 (Ser235/236) in 140 cervical cancer and 161 esophageal cancer specimens. Immunohistochemical staining for pS6 kinase and pS6 was significantly more frequent in the HPV16-infected cervical cancer specimens than the HPV16-negative specimens. In contrast, the expression of S6 kinase was similar in both HPV16-positive and -negative samples. The phosphorylation of Akt, the key regulator of S6 kinase, was also detected. Our analysis showed that Akt phosphorylation was unaffected by HPV16 infection. These results together with our previous study suggest that HPV16 modifies S6 kinase activation via mechanism, which activates S6 kinase downstream of Akt function.
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PMID:Increased phosphorylation of p70 S6 kinase is associated with HPV16 infection in cervical cancer and esophageal cancer. 1762 39

The tumour suppressor LKB1 plays a critical role in cell proliferation, polarity and energy metabolism. LKB1 is a Ser/Thr protein kinase that is associated with STRAD and MO25 in vivo. Here, we describe the individual expression of the three components of the LKB1 complex using monocistronic vectors and their co-expression using tricistronic vectors that were constructed from monocistronic vectors using a fully modular cloning approach. The data show that among the three individually expressed components of the LKB1 complex, only MO25alpha can be expressed in soluble form, whereas the other two, LKB1 and STRADalpha are found almost exclusively in inclusion bodies. However, using the tricistronic vector system, functional LKB1-MO25alpha-STRADalpha complex was expressed and purified from soluble extracts by sequential immobilized-metal affinity and heparin chromatography, as shown by Western blotting using specific antibodies. In size exclusion chromatography, MO25alpha and STRADalpha exactly co-elute with LKB1 with an apparent molecular weight of the heterotrimeric complex of 160 kDa. The specific activity in the peak fraction of the size exclusion chromatography was 250 U/mg at approximately 25% purity. As shown by autoradiography, LKB1 and STRADalpha, both strongly autophosphorylate in vitro. Moreover, recombinant LKB1 complex activates AMPK by phosphorylation of the alpha-subunit at the Thr-172 site as shown (i) by Western blotting using phospho-specific antibodies after LKB1-dependent phosphorylation, (ii) by LKB1-dependent incorporation of radioactive phosphate into the alpha-subunit of kinase dead AMPK heterotrimer, and (iii) by activity determination of AMPK. Functional mammalian LKB1 complex is constitutively active, and when enriched from bacteria should prove to be a valuable tool for studying its molecular function and regulation.
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PMID:Co-expression of LKB1, MO25alpha and STRADalpha in bacteria yield the functional and active heterotrimeric complex. 1787 8

Microcystins (MCs) are hepatotoxic cyclic heptapeptides produced by freshwater cyanobacteria. They are inhibitors of serine/threonine protein phosphatases 1A and 2A and are involved in liver tumour promotion. Several recent studies indicated that MCs are genotoxic and may also act as tumour initiators. Based on our previous results showing that microcystin-LR (MCLR) induces DNA damage in HepG2 cells, we have now explored the effect of MCLR on the expression of selected genes known to be involved in the cell response to DNA damage and apoptosis. The HepG2 cells were exposed to non-cytotoxic concentrations (0.01, 0.1 and 1 microg/ml) of MCLR for various periods of time (2-16 h) and the mRNA expression was determined with the quantitative real-time polymerase chain reaction (QRT-PCR). We found a significantly elevated expression of tumour suppressor gene p53 and its downstream-regulated genes involved in DNA repair and cell cycle regulation (p21, gadd 45a, mdm2), as well as increased expression of the pro-apoptotic gene bax, but no alterations of the anti-apoptotic bcl-2. Up-regulation of the expression of mdm2, p21 and gadd45a provides strong support for our previous suggestion that MCLR is a genotoxic carcinogen. The increased ratio of expression of bax to that of bcl-2 induced by MCLR suggests that apoptosis in HepG2 cells proceeds via the mitochondrial pathway.
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PMID:Patterns of microcystin-LR induced alteration of the expression of genes involved in response to DNA damage and apoptosis. 1819 Nov 68

Extracellular signal-regulated kinase-1 and -2 (ERK1/2) are activated by dual threonine and tyrosine phosphorylation of a TEY motif. The highly related kinase ERK5 is also activated by phosphorylation at a TEY motif. Inactivation of ERK1/2 is achieved by distinct members of the dual-specificity protein phosphatase (DUSP) family, which are responsible for the specific, regulated de-phosphorylation of the TEY motif. These include both nuclear (DUSP5) and cytoplasmic (DUSP6) enzymes. DUSP6, a candidate tumour suppressor gene, is thought to be highly specific for inactivation of ERK1/2 but several reports have suggested that it may also inactivate ERK5. Here we have compared the ability of DUSP6 to regulate the ERK1/2 and ERK5 protein kinases. We find that DUSP6 binds to ERK1/2 in both yeast and human cells but fails to bind to ERK5. Recombinant ERK2 can induce catalytic activation of DUSP6 whereas ERK5 cannot. Ectopic expression of DUSP6 can de-phosphorylate a co-expressed ERK2 construct but does not de-phosphorylate ERK5. Finally, expression of DUSP6 blocks the MEK1-driven activation of GAL4-ELK1, an ERK1/2-regulated transcription factor, but fails to block the MEK5-driven activation of GAL4-MEF2D, an ERK5-regulated transcription factor. These results demonstrate that even upon over-expression DUSP6 fails to inactivate ERK5, confirming that it is indeed an ERK1/2-specific DUSP.
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PMID:DUSP6/MKP-3 inactivates ERK1/2 but fails to bind and inactivate ERK5. 1828 Jan 12

The GTP-binding protein Rap1 regulates integrin-mediated and other cell adhesion processes. Unlike most other Ras-related proteins, it contains a threonine in switch II instead of a glutamine (Gln61 in Ras), a residue crucial for the GTPase reaction of most G proteins. Furthermore, unlike most other GTPase-activating proteins (GAPs) for small G proteins, which supply a catalytically important Arg-finger, no arginine residue of RapGAP makes a significant contribution to the GTPase reaction of Rap1. For a detailed understanding of the reaction mechanism, we have solved the structure of Rap1 in complex with Rap1GAP. It shows that the Thr61 of Rap is away from the active site and that an invariant asparagine of RapGAPs, the Asn-thumb, takes over the role of the cis-glutamine of Ras, Rho or Ran. The structure and biochemical data allow to further explain the mechanism and to define the important role of a conserved tyrosine. The structure and biochemical data furthermore show that the RapGAP homologous region of the tumour suppressor Tuberin is sufficient for catalysis on Rheb.
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PMID:The Rap-RapGAP complex: GTP hydrolysis without catalytic glutamine and arginine residues. 1830 92

Renal carcinogenesis is promoted by overexpression of the activated serine/ threonine kinase Akt (p-Akt) and supposedly a concomitant reduction in phosphatase and tensin homologue deleted on chromosome 10 tumour suppressor gene (PTEN), which normally inhibits the activation of Akt. Because promising anti-cancer therapies increasingly focus on pathways involving p-Akt and PTEN, the present study evaluated the expression of p-Akt in renal cell carcinomas and compared it with prognosis. P-Akt and PTEN expression were analysed in a tissue microarray (TMA) from renal cell carcinoma (n = 386) and adjacent uninvolved renal tissue (n = 32) specimens. Increased p-Akt was found more often in the nucleus than in the cytoplasm, and PTEN was concomitantly reduced in about 50% of cases. Neither tumour grade nor stage influenced p-Akt expression, whereas the clear cell and papillary subtypes showed increased p-Akt more often than did the chromophobe or sarcomatoid types. Increased cytoplasmic and nuclear p-Akt levels were independent prognostic factors for diminishing patient survival. The present study found significantly increased nuclear but also cytoplasmic p-Akt expression in renal cell carcinoma subtypes. Increased nuclear and cytoplasmic p-Akt was an independent prognostic factor for diminishing patient survival. The considerable number of high-grade and high-stage RCC showing increased p-Akt and reduced PTEN would justify further evaluation of therapeutic concepts based on inhibitors of the PI3K/p-Akt/mTOR pathway.
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PMID:Increased activated Akt expression in renal cell carcinomas and prognosis. 1877 62

The PTEN tumour suppressor is a lipid and protein phosphatase that inhibits phosphoinositide 3-kinase (PI3K)-dependent signalling by dephosphorylating phosphatidylinositol 3,4,5-trisphosphate (PtdInsP(3)). Here, we discuss the concept of PTEN as an 'interfacial enzyme', which exists in a high activity state when bound transiently at membrane surfaces containing its substrate and other acidic lipids, such as PtdIns(4,5)P(2) and phosphatidylserine (PtdSer). This mechanism ensures that PTEN functions in a spatially restricted manner, and may explain its involvement in forming the gradients of PtdInsP(3), which are necessary for generating and/or sustaining cell polarity during motility, in developing neurons and in epithelial tissues. Coordinating PTEN activity with alternative mechanisms of PtdInsP(3) metabolism, by the tightly regulated SHIP 5-phoshatases, synthesizing the independent second messenger PtdIns(3,4)P(2), may also be important for cellular polarization in some cell types. Superimposed on this interfacial mechanism are additional post-translational regulatory processes, which generally act to reduce PTEN activity. Oxidation of the active site cysteine residue by reactive oxygen species and phosphorylation of serine/threonine residues at sites in the C-terminus of the protein inhibit PTEN. These phosphorylation sites also appear to play a role in regulating both stability and localization of PTEN, as does ubiquitination of PTEN. Because genetic studies in mice show that the level of expression of PTEN in an organism profoundly influences tumour susceptibility, factors that regulate PTEN, localization, activity and turnover should be important in understanding its biological functions as a tumour suppressor.
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PMID:Understanding PTEN regulation: PIP2, polarity and protein stability. 1879 81

The transcriptional activity of the tumour suppressor, p53, requires direct binding between its transactivation domain (TAD, 1-57) and the transcriptional coactivator, p300. We systematically assessed the role of TAD phosphorylation on binding of the p300 domains CH3, Taz1, Kix and IBiD. Thr18 phosphorylation increased the affinity up to sevenfold for CH3 and Taz1, with smaller increases from phosphorylation of Ser20, Ser15, Ser37, Ser33, Ser46 and Thr55. Binding of Kix and IBiD was less sensitive to phosphorylation. Strikingly, hepta-phosphorylation of all Ser and Thr residues increased binding 40- and 80-fold with CH3 and Taz1, respectively, but not with Kix or IBiD. Substitution of all phospho-sites with aspartates partially mimicked the effects of hepta-phosphorylation. Mdm2, the main negative regulator of p53, competes with p300 for binding to TAD. Binding of Mdm2 to TAD was reduced significantly only on phosphorylation of Thr18 (sevenfold) or by hepta-phosphorylation (24-fold). The relative affinities of Mdm2 and p300 for p53 TAD can thus be changed by up to three orders of magnitude by phosphorylation. Accordingly, phosphorylation of Thr18 and hepta-phosphorylation dramatically shifts the balance towards favouring the binding of p300 with p53, and is thus likely to be an important factor in its regulation.
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PMID:Regulation by phosphorylation of the relative affinities of the N-terminal transactivation domains of p53 for p300 domains and Mdm2. 1936 23

In response to DNA damage, eukaryotic cells initiate a complex signalling pathway, termed the DNA damage response (DDR), which coordinates cell cycle arrest with DNA repair. Studies have shown that oncogene-induced senescence, which provides a barrier to tumour development, involves activation of the DDR. Using a genome-wide RNA interference (RNAi) screen, we have identified 17 factors required for oncogenic BRAF to induce senescence in primary fibroblasts and melanocytes. One of these factors is an F-box protein, FBXO31, a candidate tumour suppressor encoded in 16q24.3, a region in which there is loss of heterozygosity in breast, ovarian, hepatocellular and prostate cancers. Here we study the cellular role of FBXO31, identify its target substrate and determine the basis for its growth inhibitory activity. We show that ectopic expression of FBXO31 acts through a proteasome-directed pathway to mediate the degradation of cyclin D1, an important regulator of progression from G1 to S phase, resulting in arrest in G1. Cyclin D1 degradation results from a direct interaction with FBXO31 and is dependent on the F-box motif of FBXO31 and phosphorylation of cyclin D1 at Thr 286, which is known to be required for cyclin D1 proteolysis. The involvement of the DDR in oncogene-induced senescence prompted us to investigate the role of FBXO31 in DNA repair. We find that DNA damage induced by gamma-irradiation results in increased FBXO31 levels, which requires phosphorylation of FBXO31 by the DDR-initiating kinase ATM. RNAi-mediated knockdown of FBXO31 prevents cells from undergoing efficient arrest in G1 after gamma-irradiation and markedly increases sensitivity to DNA damage. Finally, we show that a variety of DNA damaging agents all result in a large increase in FBXO31 levels, indicating that induction of FBXO31 is a general response to genotoxic stress. Our results reveal FBXO31 as a regulator of the G1/S transition that is specifically required for DNA damage-induced growth arrest.
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PMID:F-box protein FBXO31 mediates cyclin D1 degradation to induce G1 arrest after DNA damage. 1941 62

Dual specificity phosphatases are characterised by their ability to dephosphorylate both phosphotyrosine and phosphoserine/threonine residues within the one substrate. The aim of this study was to characterise the phosphatase activity of the atypical dual specificity phosphatase, DUSP26 on MAP kinases, and to determine its expression, regulation and function in cancer cells. Overexpression and knockdown of DUSP26 in epithelial cells and in vitro phosphatase assays were used to demonstrate that, contrary to several published reports, DUSP26 does not act as a dual specificity phosphatase on ERK, JNK or p38 MAPKs. However, overexpression of DUSP26 in MCF10A epithelial cells suppressed colony formation and acinar growth in 3D culture, effects dependent on its phosphatase activity, while knockdown of DUSP26 in HOSE17.1 cells enhanced colony formation and cellular proliferation. DUSP26 mRNA expression was reduced in neuroblastoma, brain and ovarian cancer cell lines. Consistent with epigenetic silencing of DUSP26, expression was enhanced by treatment of cells with 5-aza-2-deoxycitidine and trichostatin A, and a CpG island upstream of the DUSP26 transcriptional start site was variably methylated in cancer cell lines. Together, these results help to clarify confusion in the literature relating to DUSP26 substrate specificity and support recent reports that substrates other than MAPKs are the primary substrates of this phosphatase. In addition, they indicate that DUSP26 may function as a tumour suppressor in particular cancers.
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PMID:DUSP26 negatively affects the proliferation of epithelial cells, an effect not mediated by dephosphorylation of MAPKs. 2034 85


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