Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The polycomb protein Bmi-1 represses the INK4a locus, which encodes the tumor suppressors p16 and p14(ARF). Here we report that Bmi-1 is downregulated when WI-38 human fibroblasts undergo replicative senescence, but not quiescence, and extends replicative life span when overexpressed. Life span extension by Bmi-1 required the pRb, but not p53, tumor suppressor protein. Deletion analysis showed that the RING finger and helix-turn-helix domains of Bmi-1 were required for life span extension and suppression of p16. Furthermore, a RING finger deletion mutant exhibited dominant negative activity, inducing p16 and premature senescence. Interestingly, presenescent cultures of some, but not all, human fibroblasts contained growth-arrested cells expressing high levels of p16 and apparently arrested by a p53- and telomere-independent mechanism. Bmi-1 selectively extended the life span of these cultures. Low O(2) concentrations had no effect on p16 levels or life span extension by Bmi-1 but reduced expression of the p53 target, p21. We propose that some human fibroblast strains are more sensitive to stress-induced senescence and have both p16-dependent and p53/telomere-dependent pathways of senescence. Our data suggest that Bmi-1 extends the replicative life span of human fibroblasts by suppressing the p16-dependent senescence pathway.
Mol Cell Biol 2003 Jan
PMID:Control of the replicative life span of human fibroblasts by p16 and the polycomb protein Bmi-1. 1248 90

We have stably expressed in HeLa cells a chimeric protein made of the green fluorescent protein (GFP) fused to the transmembrane and cytoplasmic domains of the mannose 6-phosphate/insulin like growth factor II receptor in order to study its dynamics in living cells. At steady state, the bulk of this chimeric protein (GFP-CI-MPR) localizes to the trans-Golgi network (TGN), but significant amounts are also detected in peripheral, tubulo-vesicular structures and early endosomes as well as at the plasma membrane. Time-lapse videomicroscopy shows that the GFP-CI-MPR is ubiquitously detected in tubular elements that detach from the TGN and move toward the cell periphery, sometimes breaking into smaller tubular fragments. The formation of the TGN-derived tubules is temperature dependent, requires the presence of intact microtubule and actin networks, and is regulated by the ARF-1 GTPase. The TGN-derived tubules fuse with peripheral, tubulo-vesicular structures also containing the GFP-CI-MPR. These structures are highly dynamic, fusing with each other as well as with early endosomes. Time-lapse videomicroscopy performed on HeLa cells coexpressing the CFP-CI-MPR and the AP-1 complex whose gamma-subunit was fused to YFP shows that AP-1 is present not only on the TGN and peripheral CFP-CI-MPR containing structures but also on TGN-derived tubules containing the CFP-CI-MPR. The data support the notion that tubular elements can mediate MPR transport from the TGN to a peripheral, tubulo-vesicular network dynamically connected with the endocytic pathway and that the AP-1 coat may facilitate MPR sorting in the TGN and endosomes.
Mol Biol Cell 2003 Jan
PMID:Visualization of TGN to endosome trafficking through fluorescently labeled MPR and AP-1 in living cells. 1252 33

The astrocytomas represent the most common primary tumors of the brain. Despite efforts to improve the treatment of astrocytomas, these tumors and in particular the high-grade astrocytoma termed glioblastoma multiforme still carry a poor prognosis. In recent years, there has been an intensive effort to gain an understanding of the cellular and molecular mechanisms that contribute to the pathogenesis of astrocytomas as a first step toward the development of better treatments for these devastating tumors. Here, we will review our current understanding of the signaling pathways that underlie glial transformation. Studies of astrocytomas have led to the identification of two major groups of signaling proteins whose abnormalities contribute to gliomagenesis: the cell cycle pathways and the growth factor-regulated signaling pathways. Among the cell cycle proteins, the p16-cdk4-pRb and ARF-MDM2-p53 cell cycle arrest pathways play a prominent role in glial transformation. In addition, deregulation of polypeptide growth factors acting via receptor tyrosine kinases (RTKs) and of intracellular signals, including the lipid phosphatase PTEN, that regulate cellular responses to RTKs plays a critical role in gliomagenesis. In addition to the identification of the signaling proteins targeted in glial transformation, the cell-of-origin of astrocytomas has been investigated. Genetic modeling of astrocytomas in mice suggests that neuroepithelial precursor cells represent preferred cellular substrates of gliomas or that either astrocytes or precursor cells constitute potential cells-of-origin of astrocytomas. During normal brain development, neuroepithelial precursor cells, including neural stem cells, differentiate into astrocytes. As the mechanisms that control gliogenesis during normal brain development become better understood, it will be important to determine if deregulation of these mechanisms might contribute to the pathogenesis of astrocytomas. The elucidation of the molecular underpinnings of astrocytomas holds the promise of improved treatment options for patients with these devastating brain tumors.
Curr Mol Med 2003 Feb
PMID:Signaling pathways regulating gliomagenesis. 1255 76

Flavopiridol is a synthetic flavone, which inhibits growth in vitro and in vivo of several solid malignancies such as renal, prostate, and colon cancers. It is a potent cyclin-dependent kinase inhibitor presently in clinical trials. In this study, we examined the effect of flavopiridol on a panel of glioma cell lines having different genetic profiles: five of six have codeletion of p16(INK4a) and p14(ARF); three of six have p53 mutations; and one of six shows overexpression of mouse double minute-2 (MDM2) protein. Independent of retinoblastoma and p53 tumor suppressor pathway alterations, flavopiridol induced apoptosis in all cell lines but through a caspase-independent mechanism. No cleavage products for caspase 3 or its substrate poly(ADP-ribose) polymerase or caspase 8 were detected. The pan-caspase inhibitor Z-VAD-fmk did not inhibit flavopiridol-induced apoptosis. Mitochondrial damage measured by cytochrome c release and transmission electron microscopy was not observed in drug-treated glioma cells. In contrast, flavopiridol treatment induced translocation of apoptosis-inducing factor from the mitochondria to the nucleus. The proteins cyclin D(1) and MDM2 involved in the regulation of retinoblastoma and p53 activity, respectively, were down-regulated early after flavopiridol treatment. Given that MDM2 protein can confer oncogenic properties under certain circumstances, loss of MDM2 expression in tumor cells could promote increased chemosensitivity. After drug treatment, a low Bcl-2/Bax ratio was observed, a condition that may favor apoptosis. Taken together, the data indicate that flavopiridol has activity against glioma cell lines in vitro and should be considered for clinical development in the treatment of glioblastoma multiforme.
Mol Cancer Ther 2003 Feb
PMID:Flavopiridol induces apoptosis in glioma cell lines independent of retinoblastoma and p53 tumor suppressor pathway alterations by a caspase-independent pathway. 1258 31

We have used GST pulldowns from A431 cell cytosol to identify three new binding partners for the gamma-adaptin appendage: Snx9, ARF GAP1, and a novel ENTH domain-containing protein, epsinR. EpsinR is a highly conserved protein that colocalizes with AP-1 and is enriched in purified clathrin-coated vesicles. However, it does not require AP-1 to get onto membranes and remains membrane-associated in AP-1-deficient cells. Moreover, although epsinR binds AP-1 via its COOH-terminal domain, its NH(2)-terminal ENTH domain can be independently recruited onto membranes, both in vivo and in vitro. Brefeldin A causes epsinR to redistribute into the cytosol, and recruitment of the ENTH domain requires GTPgammaS, indicating that membrane association is ARF dependent. In protein-lipid overlay assays, the epsinR ENTH domain binds to PtdIns(4)P, suggesting a possible mechanism for ARF-dependent recruitment onto TGN membranes. When epsinR is depleted from cells by RNAi, cathepsin D is still correctly processed intracellularly to the mature form. This indicates that although epsinR is likely to be an important component of the AP-1 network, it is not necessary for the sorting of lysosomal enzymes.
Mol Biol Cell 2003 Feb
PMID:EpsinR: an ENTH domain-containing protein that interacts with AP-1. 1258 59

CP-31398, a styrylquinazoline, emerged from a high throughput screen for therapeutic agents that restore a wild-type-associated epitope (monoclonal antibody 1620) on the DNA-binding domain of the p53 protein. We found that CP-31398 can not only restore p53 function in mutant p53-expressing cells but also significantly increase the protein level and promote the activity of wild-type p53 in multiple human cell lines, including ATM-null cells. Cells treated with CP-31398 undergo either cell cycle arrest or apoptosis. Further investigation showed that CP-31398 blocks the ubiquitination and degradation of p53 but not in human papillomavirus E6-expressing cells. Of note, CP-31398 does not block the physical association between p53 and MDM2 in vivo. Moreover, unlike the DNA-damaging agent adriamycin, which induces strong phosphorylation of p53 on serines 15 and 20, CP-31398 exposure leads to no measurable phosphorylation on these sites. We found that CP-31398 could also stabilize exogenous p53 in p53 mutant, wild-type, and p53-null human cells, even in MDM2-null p53(-/-) mouse embryonic fibroblasts. Our results suggest a model wherein CP-31398-mediated stabilization of p53 may result from reduced ubiquitination, leading to high levels of transcriptionally active p53. Further understanding of this mechanism may lead to novel strategies for p53 stabilization and tumor suppression in cancers, even those with absent ARF or high MDM2 expression.
Mol Cell Biol 2003 Mar
PMID:Stabilization of p53 by CP-31398 inhibits ubiquitination without altering phosphorylation at serine 15 or 20 or MDM2 binding. 1261 87

The Sec7 domain guanine nucleotide exchange factors (GEFs) for the GTPase ARF are highly conserved regulators of membrane dynamics and protein trafficking. The interactions of large ARF GEFs with cellular membranes for localization and/or activation are likely to participate in regulated recruitment of ARF and effectors. However, these interactions remain largely unknown. Here we characterize Gmh1p, the first Golgi transmembrane-domain partner of any of the high-molecular-weight ARF-GEFs. Gmh1p is an evolutionarily conserved protein. We demonstrate molecular interaction between the yeast Gmh1p and the large ARF-GEFs Gea1p and Gea2p. This interaction involves a domain of Gea1p and Gea2p that is conserved in the eukaryotic orthologues of the Gea proteins. A single mutation in a conserved amino acid residue of this domain is sufficient to abrogate the interaction, whereas the overexpression of Gmh1p can compensate in vivo defects caused by mutations in this domain. We show that Gmh1p is an integral membrane protein that localizes to the early Golgi in yeast and in human HeLa cells and cycles through the ER. Hence, we propose that Gmh1p acts as a positive Golgi-membrane partner for Gea function. These results are of general interest given the evolutionary conservation of both ARF-GEFs and the Gmh proteins.
Mol Biol Cell 2003 Jun
PMID:A novel Golgi membrane protein is a partner of the ARF exchange factors Gea1p and Gea2p. 1280 35

We have previously demonstrated that the CrkII and CrkL adapter proteins are required for the spreading of epithelial colonies and the breakdown of adherens junctions in response to hepatocyte growth factor. When overexpressed, CrkII and CrkL promote lamellipodia formation, cell spreading, and the loss of epithelial adherens junctions in the absence of hepatocyte growth factor. The exact mechanism by which Crk proteins elicit these changes is unclear. We show that the overexpression of CrkII or CrkL, but not Src homology 2 or amino-terminal Src homology 3 domain mutant Crk proteins, promotes the relocalization of Paxillin to focal contacts throughout the cell and within lamellipodia in a Rac-dependent manner. In stable cell lines overexpressing CrkII, enhanced lamellipodia formation and cell spreading correlate with an increased association of CrkII with Paxillin, GIT2 (an ARF-GAP) and beta-PIX (a Rac1 exchange factor). Mutants of Paxillin that fail to associate with Crk or GIT2, or do not target to focal adhesions inhibit Crk-dependent cell spreading and lamellipodia formation. We conclude from these studies that the association of Crk with Paxillin is important for the spreading of epithelial colonies, by influencing the recruitment of Paxillin to focal complexes and promoting the enhanced assembly of Paxillin/GIT2/beta-PIX complexes.
Mol Biol Cell 2003 Jul
PMID:Crk associates with a multimolecular Paxillin/GIT2/beta-PIX complex and promotes Rac-dependent relocalization of Paxillin to focal contacts. 1285 67

The p53 tumor suppressor is regulated by MDM2-mediated ubiquitination and degradation. Mitogenic signals activate p53 by induction of ARF expression, which inhibits p53 ubiquitination by MDM2. Recent studies showed that the MDM2 homolog MDMX is also an important regulator of p53. We present evidence that MDM2 promotes MDMX ubiquitination and degradation by the proteasomes. This effect is stimulated by ARF and correlates with the ability of ARF to bind MDM2. Promotion of MDM2-mediated MDMX ubiquitination requires the N-terminal domain of ARF, which normally inhibits MDM2 ubiquitination of p53. An intact RING domain of MDM2 is also required, both to interact with MDMX and to provide E3 ligase function. Increase of MDM2 and ARF levels by DNA damage, recombinant ARF adenovirus infection, or inducible MDM2 expression leads to proteasome-mediated down-regulation of MDMX levels. Therefore, MDMX and MDM2 are coordinately regulated by stress signals. The ARF tumor suppressor differentially regulates the ability of MDM2 to promote p53 and MDMX ubiquitination and activates p53 by targeting both members of the MDM2 family.
Mol Cell Biol 2003 Aug
PMID:MDM2 promotes ubiquitination and degradation of MDMX. 1286 Sep 99

One mechanism by which a cell affords protection from the transforming effects of oncogenes is via the action of the tumor suppressor, ARF, which activates p53 by inactivating Mdm2. Many oncogenes have also been shown to activate the transcription factor NF-kappa B, which can contribute toward the malignant phenotype in many ways, including an ability to antagonize p53. Here we find that ARF inhibits NF-kappa B function and its antiapoptotic activity independent of Mdm2 and p53. ARF represses the transcriptional activation domain of the NF-kappa B family member RelA by inducing its association with the histone deacetylase, HDAC1. Further, we show that the response of NF-kappa B to the oncogene Bcr-Abl is determined by the ARF status of the cell. These results reveal an important function of ARF that can regulate the NF-kappa B response to oncogene activation.
Mol Cell 2003 Jul
PMID:p53- and Mdm2-independent repression of NF-kappa B transactivation by the ARF tumor suppressor. 1288 89


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