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)

E2F integrates and coordinates cell cycle progression with the transcription apparatus through its cyclical interactions with important regulators of cellular proliferation, such as pRb, cyclins, and cdk's. Physiological E2F is a heterodimeric transcription factor composed of an E2F and a DP family member, and while E2F proteins can stimulate proliferation, certain members of the family are known to be endowed with growth-inhibitory and tumor suppressor-like activity. We have investigated the product of the human mdm2 oncogene, hDM2, and report on its ability to regulate E2F-dependent apoptosis in a fashion that is independent of p53. hDM2 can prevent p53(-/-) cells from entering E2F-dependent apoptosis, an outcome that is dependent upon the presence of the DP subunit. Cells rescued from apoptosis possess lower levels of E2F subunits, although the rescued cells show an increase in DNA synthesis and possess enhanced viability that reflects cooperation between E2F-DP and hMD2. Furthermore, the regulation of E2F activity correlates with an hDM2-dependent effect on the intracellular distribution of DP-1, since hDM2 causes the nuclear accumulation of DP-1. The control of E2F by hDM2 therefore has certain parallels with the targeted degradation by MDM2 of p53. However, the domains in hDM2 required for the regulation of E2F activity can be distinguished from those necessary for p53 degradation, suggesting that control of E2F and p53 by hDM2 may be mechanistically distinct. These experiments define a new level of interplay between E2F and hDM2 whereby hDM2 has a profound impact on the physiological consequences of E2F activation. They suggest that the oncogenic properties of hDM2 may in part be mediated by an antiapoptotic activity that converts E2F from a negative to a positive regulator of cell cycle progression and thereby retains E2F at a level that contributes to a continual state of growth stimulation.
Mol Cell Biol 2000 Mar
PMID:Apoptotic and growth-promoting activity of E2F modulated by MDM2. 1068 65

Tumor suppressor protein p53 is a positive regulator of MDM2 gene expression and the mdm2 protein can bind to p53, preventing the transactivation of p53 responsive genes, thus mimicking TP53 mutation. The authors looked for alterations that could affect, directly and indirectly, p53 function in 13 patients with extrahepatic cholangiocarcinoma. Molecular analysis by single strand conformation polymorphism and DNA sequencing revealed that TP53 gene mutations occurred in only 2 of 13 cholangiocarcinomas. High levels of mdm2 protein were found, by immunohistochemical staining, in 61% of the cholangiocarcinomas and in almost all specimens (70%) displaying stabilized p53 protein in the absence and in the presence of TP53 mutations. The finding of co-overexpressed mdm2 and p53 proteins in cholangiocarcinomas indicates that they can upregulate the expression of mdm2 protein to a level sufficient for binding and accumulating p53 in a presumably inactive complexed form. The presence of TP53 mutations or upregulation of MDM2 gene expression in 9 of the 13 cholangiocarcinomas strongly supports that the impairment of the p53 pathway is an important and specific step in cholangiocarcinoma pathogenesis. At variance with other authors, no alteration of p16ink4/CDKN2 gene was observed in all 13 cholangiocarcinomas.
Diagn Mol Pathol 2000 Mar
PMID:TP53 mutations and mdm2 protein overexpression in cholangiocarcinomas. 1071 12

The p53 tumor suppressor is activated by many diverse stress signals through mechanisms that result in stabilization and accumulation of the p53 protein. p53 is normally degraded through the proteasome following interaction with MDM2, which both functions as a ubiquitin ligase for p53 and shuttles to the cytoplasm, where p53 degradation occurs. Stabilization of p53 in response to stress is associated with inhibition of MDM2-mediated degradation, which has been associated with phosphorylation of p53 in response to DNA damage or activation of ARF. In this study we show distinct responses, as measured by phosphorylation, transcriptional activity, and subcellular localization, of p53 stabilized by different activating signals. Although normal cells and wild-type p53-expressing tumor cells showed similar responses to actinomycin D and camptothecin treatment, the transcriptional activity of stabilized p53 induced by deferoxamine mesylate, which mimics hypoxia, in normal cells was lost in all three tumor cell lines tested. Our results show that multiple pathways exist to stabilize p53 in response to different forms of stress, and they may involve down-regulation of MDM2 expression or regulation of the subcellular localization of p53 or MDM2. Loss of any one of these pathways may predispose cells to malignant transformation, although reactivation of p53 might be achieved through alternative pathways that remain functional in these tumor cells.
Mol Cell Biol 2000 May
PMID:Stress signals utilize multiple pathways to stabilize p53. 1075 6

Although MDM2, p21/WAF1, and p53 are considered as regulating each other based on in vitro studies, the relation in human lung cancer is not fully understood. The expressions of these proteins were examined immunohistochemically in 112 resected non-small cell lung cancer specimens and the correlation between them were analyzed. MDM2 was expressed in 45% of all lung cancers. In advanced stage, MDM2-positive cases were observed more frequently than in early stage, showing significant difference. No significant difference was observed in the prognosis of the patients regardless of the expression of any protein. Although no correlation was observed between MDM2 expression and p53 expression, or between p21/WAF1 expression and p53 expression, MDM2 expression was strongly related with p21/WAF1 expression. Therefore, MDM2 expression may relate to the progress of the stage of lung cancer, and MDM2 expression and p21/WAF1 expression may be associated not through the p53-related pathway.
Int J Mol Med 2000 Jun
PMID:MDM2 expression is associated with progress of disease and WAF1 expression in resected lung cancer. 1081 14

Control of proliferation and differentiation by the retinoblastoma tumor suppressor protein (pRB) and related family members depends upon their interactions with key cellular substrates. Efforts to identify such cellular targets led to the isolation of a novel protein, EID-1 (for E1A-like inhibitor of differentiation 1). Here, we show that EID-1 is a potent inhibitor of differentiation and link this activity to its ability to inhibit p300 (and the highly related molecule, CREB-binding protein, or CBP) histone acetylation activity. EID-1 is rapidly degraded by the proteasome as cells exit the cell cycle. Ubiquitination of EID-1 requires an intact C-terminal region that is also necessary for stable binding to p300 and pRB, two proteins that bind to the ubiquitin ligase MDM2. A pRB variant that can bind to EID1, but not MDM2, stabilizes EID-1 in cells. Thus, EID-1 may act at a nodal point that couples cell cycle exit to the transcriptional activation of genes required for differentiation.
Mol Cell Biol 2000 Dec
PMID:Cells degrade a novel inhibitor of differentiation with E1A-like properties upon exiting the cell cycle. 1107 89

To investigate the effect of mutations in the p53 C-terminal domain on MDM2-mediated degradation, we introduced single and multiple point mutations into a human p53 cDNA at four putative acetylation sites (amino acid residues 372, 373, 381, and 382). Substitution of all four lysine residues by alanines (the A4 mutant) and single lysine-to-alanine substitutions were functional in sequence-specific DNA binding and transactivation; however, the A4 mutant protein was resistant to MDM2-mediated degradation, whereas the single lysine substitutions were not. Although the A4 mutant protein and the single lysine substitutions both bound MDM2 reasonably well, the single lysine substitutions underwent normal MDM2-dependent ubiquitination, whereas the A4 protein was inefficiently ubiquitinated. In addition, the A4 mutant protein was found in the cytoplasm as well as in the nucleus of a subpopulation of cells, unlike wild-type p53, which is mostly nuclear. The partially cytoplasmic distribution of A4 mutant protein was not due to a defect in nuclear import because inhibition of nuclear export by leptomycin B resulted in nuclear accumulation of the protein. Taken together, the data suggest that mutations in the putative acetylation sites of the p53 C-terminal domain interfere with ubiquitination, thereby regulating p53 degradation.
Mol Cell Biol 2000 Dec
PMID:Multiple lysine mutations in the C-terminal domain of p53 interfere with MDM2-dependent protein degradation and ubiquitination. 1109 89

The p53 gene in neuroblastoma tumors (NB) is rarely mutated but the protein accumulates in the cytoplasm. Because p53 can mediate the cytotoxic effects of chemotherapeutic agents, it is important to determine whether accumulation of p53 in the cytoplasm impairs p53 function. Data presented here indicate that hyperactive nuclear export of p53 suppresses etoposide-induced apoptosis but does not prevent growth arrest. We compared p53 function in a pair of NB subclones. Our data show etoposide induces complete trans-location of p53 to the nucleus and activation of apoptosis in the neuroblastic NB cell line SH-SY5Y (N-type), which expresses low levels of MDM2. However, in Schwann cell-like SH-EP1 cells (S-type), which have up to 10-fold higher levels of MDM2, p53 accumulates in the cytoplasm and the cells are extremely resistant to etoposide-induced apoptosis. Notably, when MDM2 expression is inhibited in S-type cells, with a phosphorothioated antisense oligonucleotide (AS5), then p53 accumulates in the nucleus and the SH-EP1 cells undergo apoptosis. Surprisingly, induction of p21 and G1-arrest are not attenuated in S-type cells, despite the predominantly cytoplasmic location of p53. Whereas, G1-arrest is attenuated in the SH-SY5Y cells, which have high levels of nuclear p53. Taken together, these findings suggest attenuation of G1-arrest is related to the differentiation status of neuroblastomas and occurs downstream of p53 nuclear accumulation. These results demonstrate for the first time that hyperactive nuclear export of p53 attenuates chemotherapy-induced apoptosis in NB cells, and our findings suggest that inhibitors of MDM2 may enhance the therapeutic efficacy of etoposide by promoting apoptosis rather than trans-differentiation.
Mol Pharmacol 2001 Jan
PMID:MDM2 mediated nuclear exclusion of p53 attenuates etoposide-induced apoptosis in neuroblastoma cells. 1112 34

Downstream target genes of p53 are thought to mediate its tumor-suppressive activity, but it is unknown whether differential transactivation of these genes is regulated at the level of p53 binding to their promoters. To address this issue, p53 binding in vivo to consensus sites in the p21(Waf1), MDM2, and PIG3 promoters was investigated in cells exposed to adriamycin (ADR) or ionizing radiation as well as in an inducible p53 cell line. p53-DNA complexes were cross-linked in vivo by treating the cells with formaldehyde and processed by chromatin immunoprecipitation-PCR. This methodology allowed for the analysis of relevant p53-DNA complexes by preventing redistribution of cellular components upon collection of cell extracts. Increased p53 binding to the p21(Waf1), MDM2, and PIG3 promoters occurred within 2 h after p53 activation; however, significant increases in PIG3 transcription did not occur until 15 h after p53 binding. Gel shift analyses indicated that p53 had lower affinity for the consensus binding site in the PIG3 promoters compared to its consensus sites in the p21 and MDM2 genes, which suggests that additional factors may be required to stabilize the interaction of p53 with the PIG3 promoter. Further, acetylated p53 (Lys382) was found in chemically cross-linked complexes at all promoter sites examined after treatment of cells with ADR. In summary, the kinetics of p53 binding in vivo to target gene regulatory regions does not uniformly correlate with target gene mRNA expression for the p53 target genes examined. Our results suggest that target genes with low-affinity p53 binding sites may require additional events and will have delayed kinetics of induction compared to those with high-affinity binding sites.
Mol Cell Biol 2001 May
PMID:Kinetics of p53 binding to promoter sites in vivo. 1131 63

While the transactivation function of the tumor suppressor p53 is well understood, less is known about the transrepression functions of this protein. We have previously shown that p53 interacts with the corepressor protein mSin3a (hereafter designated Sin3) in vivo and that this interaction is critical for the ability of p53 to repress gene expression. In the present study, we demonstrate that expression of Sin3 results in posttranslational stabilization of both exogenous and endogenous p53, due to an inhibition of proteasome-mediated degradation of this protein. Stabilization of p53 by Sin3 requires the Sin3-binding domain, determined here to map to the proline-rich region of p53, from amino acids 61 to 75. The correlation between Sin3 binding and stabilization supports the hypothesis that this domain of p53 may normally be subject to a destabilizing influence. The finding that a synthetic mutant of p53 lacking the Sin3-binding domain has an increased half-life in cells, compared to wild-type p53, supports this premise. Interestingly, unlike retinoblastoma tumor suppressor protein, MDMX, and p14(ARF), Sin3 stabilizes p53 in an MDM2-independent manner. The ability of Sin3 to stabilize p53 is consistent with the model whereby these two proteins must exist on a promoter for extended periods, in order for repression to be an effective mechanism of gene regulation. This model is consistent with our data indicating that, unlike the p300-p53 complex, the p53-Sin3 complex is immunologically detectable for prolonged periods following exposure of cells to agents of DNA damage.
Mol Cell Biol 2001 Jun
PMID:The corepressor mSin3a interacts with the proline-rich domain of p53 and protects p53 from proteasome-mediated degradation. 1135 5

Transcription factor p53 can induce growth arrest and/or apoptosis in cells through activation or repression of downstream target genes. Recently, we reported that ZBP-89 cooperates with histone acetyltransferase coactivator p300 in the regulation of p21(waf1), a cyclin-dependent kinase inhibitor whose associated gene is a target gene of p53. Therefore, we examined whether ZBP-89 might also inhibit cell growth by activating p53. In the present study, we demonstrate that elevated levels of ZBP-89 induce growth arrest and apoptosis in human gastrointestinal cell lines. The ZBP-89 protein accumulated within 4 h, and the p53 protein accumulated within 16 h, of serum starvation without changes in p14ARF levels, demonstrating a physiological increase in the cellular levels of these two proteins. Overexpression of ZBP-89 stabilized the p53 protein and enhanced its transcriptional activity through direct protein-protein interactions. The DNA binding and C-terminal domains of p53 and the zinc finger domain of ZBP-89 mediated the interaction. A point mutation in the p53 DNA binding domain, R273H, greatly reduced ZBP-89-mediated stabilization but not their physical interaction. Furthermore, ZBP-89 formed a complex with p53 and MDM2 and therefore did not prevent the MDM2-p53 interaction. However, heterokaryon assays demonstrated that ZBP-89 retained p53 in the nucleus. Collectively, these data indicate that ZBP-89 regulates cell proliferation in part through its ability to directly bind the p53 protein and retard its nuclear export. Our findings further our understanding of how ZBP-89 modulates cell proliferation and reveals a novel mechanism by which the p53 protein is stabilized.
Mol Cell Biol 2001 Jul
PMID:ZBP-89 promotes growth arrest through stabilization of p53. 1141 44


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