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)

In response to genotoxic stress, cell cycle progression can be arrested at certain checkpoints which serve to maintain genomic integrity. We have investigated the mechanism of ultraviolet B (UVB) irradiation-induced cell cycle arrest in normal human keratinocytes and in the HaCaT keratinocyte cell line which carries mutant p53 tumour suppressor protein. While only normal keratinocytes showed a delay in G1 following sublethal UVB irradiation both cell types exhibited prolonged G2 arrest attributable to rapid inhibition of cyclin B-associated cdc2 kinase activity. This inhibition coincided with increased tyrosine phosphorylation of cdc2 and was reversed by the cdc25C phosphatase in vitro. The data indicate that UVB-induced G2 arrest in mammalian cells is mediated by inhibitory tyrosine phosphorylation of cdc2 and acts as a defense mechanism against DNA damage irrespective of the cells' p53 status.
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PMID:Ultraviolet B irradiation-induced G2 cell cycle arrest in human keratinocytes by inhibitory phosphorylation of the cdc2 cell cycle kinase. 747 36

This report describes a simple and efficient system for construction of recombinant pseudorabies (Aujeszky's disease) virus (PrV) which is based on the use of a unique restriction site inserted into the viral genome. This system enables the recovery of genetically modified viruses without screening or selection for a specific phenotype, since practically all mature viral particles obtained carry the foreign sequences. To demonstrate, we introduced the tumour suppressor protein-53 (p53) gene into two different intergenic locations of PrV: the ribonucleotide reductase (rr) gene and the promoter of a putative latency gene (PLAT), located at the inverted repeat (IR) region of the viral genome. As a first step, we engineered a unique EcoRI recognition site into the rr gene or into both copies of PLAT with the help of marker transfer using the bacterial lacZ gene. Then, in both cases viral DNAs were cut with the restriction endonuclease EcoRI followed by treatment with calf intestinal phosphatase and used for cotransfection into porcine kidney cells with a plasmid containing the p53 gene flanked by viral DNAs homologous to the target region. As a result of this process, in most of the experiments, we obtained recombinant viruses without the background of parental viruses. Here we show that this method can be used for directional insertion of exogenous sequences into either the unique or the IR region of the PrV chromosome. In principle, this system should be applicable to the construction of recombinant derivatives of any viruses having infectious DNA.
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PMID:A restriction cleavage and transfection system for introducing foreign DNA sequences into the genome of a herpesvirus. 960 3

The tumour suppressor PTEN has been implicated in a large number of human tumours and is conserved from humans to worms. Characterization of PTEN protein showed that it is a phosphatase that acts on proteins and on 3-phosphorylated phosphoinositides, including phosphatidylinositol (3,4,5)-trisphosphate, and can therefore modulate signal-transduction pathways that involve lipid second messengers. Recent results indicate that at least part of its role is to regulate the activity of the serine/threonine kinase AKT/PKB, and thus influence cell survival signalling. This article discusses the function of PTEN and how this could be linked to its activity as a tumour suppressor.
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PMID:PTEN: a tumour suppressor that functions as a phospholipid phosphatase. 1020 85

The tumour suppressor protein, PTEN (phosphatase and tensin homolog deleted on chromosome 10), is a phosphatase that can dephosphorylate tyrosine-containing peptides, Shc, focal adhesion kinase and phosphoinositide substrates. In cellular assays, PTEN has been shown to antagonize the PI-3K-dependent activation of protein kinase B (PKB) and to inhibit cell spreading and motility. It is currently unclear, however, whether PTEN accomplishes these effects through its lipid- or protein-phosphatase activity, although strong evidence has demonstrated the importance of the latter for tumour suppression by PTEN. By using a PTEN G129E (Gly(129)-->Glu) mutant that has lost its lipid phosphatase activity, while retaining protein phosphatase activity, we demonstrated a requirement for the lipid phosphatase activity of PTEN in the regulation of PKB activity, cell viability and membrane ruffling. We also made a small C-terminal deletion of PTEN, removing a putative PDZ (PSD95, Dlg and ZO1)-binding motif, with no detectable effect on the phosphatase activity of the protein expressed in HEK293 cells (human embryonic kidney 293 cells) assayed in vitro. Surprisingly, expression of this mutant revealed differential requirements for the C-terminus in the different functional assays. Wild-type and C-terminally deleted PTEN appeared to be equally active in down-regulating PKB activity, but this mutant enzyme had no effect on platelet-derived growth factor (PDGF)-induced membrane ruffling and was only partially active in a cell viability assay. These results stress the importance of the lipid phosphatase activity of PTEN in the regulation of several signalling pathways. They also identify a mutation, similar to mutations that occur in some human tumours, which removes the effect of PTEN on membrane ruffling but not that on PKB.
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PMID:Analysis of the cellular functions of PTEN using catalytic domain and C-terminal mutations: differential effects of C-terminal deletion on signalling pathways downstream of phosphoinositide 3-kinase. 1069 13

Germline PTEN mutations cause Cowden syndrome (CS) and Bannayan-Riley-Ruvalcaba syndrome (BRR), two hamartoma-tumour syndromes, and somatic PTEN alterations have been shown to participate, to a greater or lesser extent, in a wide variety of sporadic neoplasia. PTEN is a tumour suppressor and dual-specificity phosphatase which affects apoptosis via its lipid phosphatase activity in the phosphoinositol-3-kinase and AKT pathway as well as inhibiting cell spreading via the focal adhesion kinase pathway. CS and BRR share some features, such as hamartomas and lipomatosis. To determine whether other syndromes characterized by overgrowth and lipomas are part of the PTEN syndrome spectrum, we ascertained six individuals with overgrowth and lipomas but who did not meet the diagnostic criteria for CS or BRR. Five had Proteus syndrome and one, a Proteus-like syndrome. When germline DNA and DNA from at least one involved tissue per case were examined for PTEN mutations, only the Proteus-like patient was found to harbour a germline R335X mutation. Interestingly, a lipomatous mass, an epidermoid naevus and arteriovenous malformation tissue, all of which were sampled from physically distinct sites, were all found to carry a second hit R130X mutation on the allele opposite the germline R335X. Both mutations have been described in CS and BRR. We postulate that the second hit, R130X, occurred early in embryonic development and may even represent germline mosaicism. Thus, PTEN may be involved in Proteus-like syndrome with its implications for cancer development in the future.
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PMID:Germline and germline mosaic PTEN mutations associated with a Proteus-like syndrome of hemihypertrophy, lower limb asymmetry, arteriovenous malformations and lipomatosis. 1074 83

The prostate cancer cell lines PC3 and LNCaP have been shown to lack expression of the tumour suppressor gene MMAC1/PTEN, in contrast to the immortalized non-tumorigenic epithelial lines PNT1a and PNT2. We have measured the effects of reintroduction of wild type (wt) and mutant MMAC1 genes on to these genetic backgrounds, using gene constructs expressing either wt MMAC1 or various mutants deficient in the dual specificity phosphatase domain of the protein. Over-expression of wild type PTEN protein induced cell shrinkage and rounding, but did not result in increased levels of classical apoptosis. Permanently transfected lines containing the MMAC1 gene could only be obtained from the PNT cells, as PTEN expression resulted in rapid loss of both tumour lines. In contrast, mutation of the phosphatase domain resulted in partial attenuation of the phenotypic effects of MMAC1 after transient transfection, and also allowed the derivation of permanent tumour cell lines containing the mutated MMAC1 gene. The results suggest that re-expression of wt PTEN is incompatible with survival of human prostate cancer cells in vitro, and that the full biological activity of this common tumour suppressor requires functions additional to the established protein and lipid phosphatase activities in epithelial systems.
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PMID:Phenotypic effects of overexpression of the MMAC1 gene in prostate epithelial cells. 1099 60

Phosphorylation of protein kinase C (PKC) provides an amplitude control that operates in conjunction with allosteric effectors. Under many conditions, PKC isotypes appear to be highly phosphorylated; however, the cellular inputs that maintain these phosphorylations are not characterized. In the present work, it is shown that there is a differential phosphorylation of PKCdelta in adherent versus suspension cultures of transfected HEK-293 cells. It is established that integrin activation is sufficient to trigger PKCdelta phosphorylation and that this signals through phosphoinositide 3-kinase (PI3-kinase) to stimulate the phosphorylation of two sites, T505 and S662. The loss of signal input to PKCdelta in suspension culture is dependent on the tumour suppressor gene PTEN, which encodes a bi-functional phosphotyrosine/phosphoinositide 3-phosphate phosphatase. In the PTEN(-/-) UM-UC-3 bladder carcinoma cell line grown in suspension, transfected PKCdelta no longer accumulates in a dephospho-form on serum removal. By contrast, in a UM-UC-3-derivative cell line stably expressing PTEN, PKCdelta does become dephosphorylated under these conditions. Employing the PTEN Gly(129)-->Glu mutant, which is selectively defective in lipid phosphatase activity, it was established that it is the lipid phosphatase activity that controls PKCdelta phosphorylation. The evidence indicates that PKCdelta phosphorylation and its latent activity are maintained in serum-deprived adherent cultures through integrin-matrix interactions. This control acts through a pathway involving a lipid product of PI3-kinase in a manner that can be suppressed by PTEN.
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PMID:Beta1-integrin and PTEN control the phosphorylation of protein kinase C. 1108 36

PTEN, a tumour suppressor gene located at chromosome 10q23 and commonly mutated or deleted in a variety of tumours, encodes a dual-specific/phosphatidylinositol-3,4,5-triphosphate (PIP3) phosphatase. We report the generation of an anti-PTEN monoclonal antibody (MAb) that recognises an epitope at the C-terminus of PTEN, and describe the heterogeneous lack of expression of the PTEN protein in human tumour tissues, as demonstrated by immunohistochemical methods. Our anti-PTEN MAb provides a useful tool for the study of PTEN protein expression in tumour samples, in the search for tumour prognostic molecular markers.
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PMID:Heterogeneous lack of expression of the tumour suppressor PTEN protein in human neoplastic tissues. 1116 38

The tumour suppressor gene PTEN/MMAC1/TEP1 encodes a dual-specificity phosphatase that recognizes phosphatidylinositol-3,4,5-triphosphate and protein substrates. We have shown previously that over-expression of PTEN in a tetracycline-controlled inducible system blocks cell cycle progression and induces apoptosis in MCF-7 breast cancer cells. Here, we demonstrate that over-expression of wild-type PTEN leads to the suppression of cell growth through the blockade of cell cycle progression, an increase in the abundance of p27, a decrease in the protein levels of cyclin D1 and the inhibition of Akt phosphorylation. In contrast, expression of the phosphatase-dead mutant, C124S, promotes cell growth and has the opposite effect on the abundance of p27, cyclin D1 levels and the phosphorylation of Akt. The G129E mutant, which does not have lipid phosphatase activity but retains protein phosphatase activity, behaves like C124S except that the former causes decreases in cyclin D1 levels similar to wild-type PTEN. Therefore, PTEN exerts its growth suppression through lipid phosphatase-dependent and independent activities and most likely, via the coordinate effect of both protein phosphatase and lipid phosphatase activities. Addition of either estrogen or insulin abrogates PTEN-mediated up-regulation of p27 and partially blocks PTEN-mediated growth suppression, whereas the combination of estrogen and insulin eliminates the alterations of p27 and cyclin D1 and completely blocks PTEN-mediated growth suppression. Our findings demonstrate that PTEN blocks cell cycle progression differentially through down-regulating the positive cell cycle regulator, cyclin D1, by its protein phosphatase activity, and up-regulating the negative cell cycle regulator, p27, by its lipid phosphatase activity.
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PMID:PTEN coordinates G(1) arrest by down-regulating cyclin D1 via its protein phosphatase activity and up-regulating p27 via its lipid phosphatase activity in a breast cancer model. 1123 Jan 79

When exposed to ionizing radiation (IR), eukaryotic cells activate checkpoint pathways to delay the progression of the cell cycle. Defects in the IR-induced S-phase checkpoint cause 'radioresistant DNA synthesis', a phenomenon that has been identified in cancer-prone patients suffering from ataxia-telangiectasia, a disease caused by mutations in the ATM gene. The Cdc25A phosphatase activates the cyclin-dependent kinase 2 (Cdk2) needed for DNA synthesis, but becomes degraded in response to DNA damage or stalled replication. Here we report a functional link between ATM, the checkpoint signalling kinase Chk2/Cds1 (Chk2) and Cdc25A, and implicate this mechanism in controlling the S-phase checkpoint. We show that IR-induced destruction of Cdc25A requires both ATM and the Chk2-mediated phosphorylation of Cdc25A on serine 123. An IR-induced loss of Cdc25A protein prevents dephosphorylation of Cdk2 and leads to a transient blockade of DNA replication. We also show that tumour-associated Chk2 alleles cannot bind or phosphorylate Cdc25A, and that cells expressing these Chk2 alleles, elevated Cdc25A or a Cdk2 mutant unable to undergo inhibitory phosphorylation (Cdk2AF) fail to inhibit DNA synthesis when irradiated. These results support Chk2 as a candidate tumour suppressor, and identify the ATM-Chk2-Cdc25A-Cdk2 pathway as a genomic integrity checkpoint that prevents radioresistant DNA synthesis.
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PMID:The ATM-Chk2-Cdc25A checkpoint pathway guards against radioresistant DNA synthesis. 1129 30


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