Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P04637 (p53)
 77,613 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The tumor suppressor protein ARF inhibits MDM2 to activate and stabilize p53. Recent studies provided evidence for p53-independent tumor suppression functions of ARF. For example, it has been shown that ARF induces proteolysis of certain E2F species, including E2F1. In addition, ARF relocalizes E2F1 from the nucleoplasm to nucleolus and inhibits E2F1-activated transcription. Because DP1 is a functional partner of the E2F family of factors, we investigated whether DP1 is also regulated by ARF. Here we show that DP1 associates with ARF. Coexpression of ARF relocalizes DP1 from the cytoplasm to the nucleolus, suggesting that DP1 is also a target of the ARF regulatory pathways. Surprisingly, however, the E2F1/DP1 complex is refractory to ARF regulation. Coexpression of E2F1 and DP1 blocks ARF-induced relocalization of either subunit to the nucleolus. The E2F1/DP1 complex localizes in the nucleoplasm, whereas ARF is detected in the nucleolus, suggesting that ARF does not interact with the E2F1/DP1 complex. Moreover, we show that E2F1 is more stable in the presence of ARF when coexpressed with DP1. These results suggest that ARF differentially regulates the free and heterodimeric forms of E2F1 and DP1. DP1 is a constitutively expressed protein, whereas E2F1 is mainly expressed at the G(1)/S boundary of the cell cycle. Therefore, the E2F1/DP1 complex is abundant only between late G(1) and early S phase. Our results on the differential regulation E2F1, DP1, and the E2F1/DP1 complex suggest the possibility that ARF regulates the function of these cell cycle factors by altering the dynamics of their heterodimerization during progression from G(1) to S phase.
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PMID:Differential regulation of E2F1, DP1, and the E2F1/DP1 complex by ARF. 1244 60

Release of E2F1/DP1 heterodimers from repression mediated by the retinoblastoma tumor suppressor (pRB) triggers cell cycle entry into S phase, suggesting that E2F1 and DP1 proteins must act in unison, either to facilitate or to suppress cell-cycle progression. In stark contrast to the milder phenotypes that result from inactivation of E2Fs, we report that loss of Dp1 leads to death in utero because of the failure of extra-embryonic development. Loss of Dp1 compromises the trophectoderm-derived tissues - specifically, the expansion of the ectoplacental cone and chorion, and endoreduplication in trophoblast giant cells. Inactivation of p53 is unable to rescue the Dp1-deficient embryonic lethality. Thus, DP1 is absolutely required for extra-embryonic development and consequently embryonic survival, consistent with E2F/DP1 normally acting to promote growth in vivo.
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PMID:Dp1 is required for extra-embryonic development. 1258 46

DP1 and DP2 function as binding partners for E2F transcription factors. The association of DP with E2F directly enhances both the DNA binding affinity and the transactivation function of the heterodimer. Target genes include those involved in DNA synthesis, cell cycle and apoptosis. E2F/DP activity is carefully regulated since the heterodimer plays a central role in so many vital cellular functions. Indeed, the association of additional proteins, the phosphorylation state, the subcellular localization and the level of expression all contribute to modulating heterodimer activity and are all influenced by DP proteins. Active E2F1/DP1 promotes apoptosis in both a p53-dependent and independent manner. E2F1/DP1 induces the expression of ARF, which in turn blocks MDM2-mediated ubiquination of p53. E2F1/DP1, however, can mediate p53-dependent apoptosis in the absence of ARF through the upregulation of the p53 kinase ATM and by E2F1directly binding to p53, which enhances p53 transcriptional activity. E2F1/DP1 also promotes p53-independent apoptosis by inducing the expression of p73 in addition to upregulating central components of the apoptotic pathway such as casapases, Apaf1 and the pro-apoptotic Bcl2-family members. Lastly, E2F1 inhibits the NFkappaB survival signal. Although the DP proteins may not possess a biological function on their own, they are indispensable for regulating E2F activity and thus play a central role in important cellular functions such as apoptosis.
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PMID:The role of the transcription factor DP in apoptosis. 1297 77

Based on knockout mouse studies, Mdm2 and MdmX have been identified as critical regulators of the p53 tumor suppressor protein, at least during early development. While many of the functions attributed to Mdm2 and MdmX involve p53 and overexpression of each gene appears to have oncogenic activities, a number of studies have suggested that each protein also possesses p53-independent functions. While examining the effect of Mdm2 overexpression on E2F1 transactivation we uncovered a novel MdmX function, the ability to inhibit E2F1 transactivation in a p53 and Mdm2 independent manner. Using a series of MdmX deletion mutants the central region of MdmX, amino acids 128-444 appears to possess the repressive domain. While an in vivo association of MdmX with either E2F1 or DP1 was not observed, a slight reduction in DP1 and an increased cytoplasmic localization of E2F1 were seen in cells overexpressing MdmX. These results suggest that elevated MdmX expression may repress E2F1-regulated genes like p14ARF and thus represent another regulatory mechanism in the Rb-p53 signaling pathway.
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PMID:MdmX represses E2F1 transactivation. 1473 77

Malignant cell proliferation and accumulation depends on the balance between the rates of cell production and cell death. Recent evidence indicates that apoptosis is important in the development of cancer. Apoptosis is strictly controlled by various regulators, which can take part in the apoptotic process, proliferation and differentiation alike. Apoptosis was induced in myeloid cell line ML-2 by camptothecin, an inhibitor of topoisomerase I. After 18 hours of induction by camptothecin 50% of cells were apoptotic. The apoptotic effect of CAM was reversible in the cells studied. The induction of apoptosis influenced the expression of apoptosis and cell cycle regulators as detected by cDNA arrays, RT-PCR or Western blotting. According to cDNA arrays e.g. bax, bfl1, bak, pRb2, c-jun, jun-B were upregulated, and cdk4, cyclin B1, wee1, CRAF1, DP1 were downregulated. A number of other regulators like p21 and cdc25A, as well as some other genes linked with apoptosis, as p53 and the bcl-2 family, were up- or down-regulated as determined by real-time PCR. Changes in gene expression were found not only in the group of regulators of apoptosis and the cell cycle, but also among regulators of differentiation.
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PMID:Gene expression during camptothecin-induced apoptosis in human myeloid leukemia cell line ML-2. 1525 69

The tumor suppressor ARF inhibits cell growth in response to oncogenic stress in a p53-dependent manner. Also, there is an increasing appreciation of ARF's ability to inhibit cell growth via multiple p53-independent mechanisms, including its ability to regulate the E2F pathway. We have investigated the interaction between the tumor suppressor ARF and DP1, the DNA binding partner of the E2F family of factors (E2Fs). We show that ARF directly binds to DP1. Interestingly, binding of ARF to DP1 results in an inhibition of the interaction between DP1 and E2F1. Moreover, ARF regulates the association of DP1 with its target gene, as evidenced by a chromatin immunoprecipitation assay with the dhfr promoter. By analyzing a series of ARF mutants, we demonstrate a strong correlation between ARF's ability to regulate DP1 and its ability to cause cell cycle arrest. S-phase inhibition by ARF is preceded by an inhibition of the E2F-activated genes. Moreover, we provide evidence that ARF inhibits the E2F-activated genes independently of p53 and Mdm2. Also, the interaction between ARF and DP1 is enhanced during oncogenic stress and "culture shock." Taken together, our results show that DP1 is a critical direct target of ARF.
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PMID:ARF directly binds DP1: interaction with DP1 coincides with the G1 arrest function of ARF. 1613 94

We have recently shown that the expression levels of both cannabinoid receptors CB(1) and CB(2) are higher in human prostate cancer cells than in normal prostate epithelial cells, and treatment of LNCaP cells with WIN-55,212-2 (a mixed CB(1)/CB(2) agonist) resulted in inhibition of cell growth and induction of apoptosis (Sarfaraz, S., Afaq, F., Adhami, V. M., and Mukhtar, H. (2005) Cancer Res. 65, 1635-1641). This study was conducted to understand the mechanistic basis of these effects. Treatment of LNCaP cells with WIN-55,212-2 (1-10 microm; 24 h) resulted in: (i) an arrest of the cells in the G(0)/G(1) phase of the cell cycle; (ii) an induction of p53 and p27/KIP1; (iii) down-regulation of cyclins D1, D2, E; (iii) decrease in the expression of cdk-2, -4, and -6; (iv) decrease in protein expression of pRb; (v) down-regulation of E2F (1-4); and (vi) decrease in the protein expression of DP1 and DP2. Similar effects were also observed when androgen-independent PC3 cells were treated with WIN-55,212-2 (5-30 microm). We further observed sustained up-regulation of ERK1/2 and inhibition of PI3k/Akt pathways in WIN-55,212-2-treated cells. Inhibition of ERK1/2 abrogated WIN-55,212-2-indued cell death suggesting that sustained activation of ERK1/2 leads to cell cycle dysregulation and arrest of cells in G(0)/G(1) phase subsequently leading to an induction of apoptosis. Further, WIN-55,212-2 treatment of cells resulted in a dose-dependent increase in Bax/Bcl-2 ratio in such a way that favors apoptosis. The induction of apoptosis proceeded through down-regulation of caspases 3, 6, 7, and 9 and cleavage of poly (ADP-ribose) polymerases. Based on these data we suggest that cannabinoid receptor agonists should be considered as novel agents for the management of prostate cancer.
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PMID:Cannabinoid receptor agonist-induced apoptosis of human prostate cancer cells LNCaP proceeds through sustained activation of ERK1/2 leading to G1 cell cycle arrest. 1706 43

Recent studies demonstrated that proinflammatory migration inhibitory factor(MIF) blocks p53-dependent apoptosis and interferes with the tumor suppressor activity of p53. To explore the mechanism underlying this MIF-p53 relationship, we studied spontaneous tumorigenesis in genetically matched p53-/- and MIF-/-p53-/- mice. We show that the loss of MIF expression aggravates the tumor-prone phenotype of p53-/- mice and predisposes them to a broader tumor spectrum, including B-cell lymphomas and carcinomas. Impaired DNA damage response is at the root of tumor predisposition of MIF-/-p53-/- mice. We provide evidence that MIF plays a role in regulating the activity of Cul1-containing SCF ubiquitin ligases. The loss of MIF expression uncouples Chk1/Chk2-responsive DNA damage checkpoints from SCF-dependent degradation of key cell-cycle regulators such as Cdc25A, E2F1 and DP1, creating conditions for the genetic instability of cells. These MIF effects depend on its association with the Jab1/CSN5 subunit of the COP9/CSN signalosome. Given that CSN plays a central role in the assembly of SCF complexes in vivo, regulation of Jab1/CSN5 by MIF is required to sustain optimal composition and function of the SCF complex.
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PMID:Impaired DNA damage checkpoint response in MIF-deficient mice. 1729 Feb 23

Sp1 transcription factor regulates the expression of multiple genes, including the Sp1 gene itself. We analyzed the ability of different cell cycle regulatory proteins to interact with Sp1 and to affect Sp1 promoter activity. Using an antibody array, we observed that CDK4, SKP2, Rad51, BRCA2 and p21 could interact with Sp1 and we confirmed these interactions by co-immunoprecipitation. CDK4, SKP2, Rad51, BRCA2 and p21 also activated the Sp1 promoter. Among the known Sp1-interacting proteins, E2F-DP1, Cyclin D1, Stat3 and Rb activated the Sp1 promoter, whereas p53 and NF kappaB inhibited it. The proteins that regulated Sp1 gene expression were shown by positive chromatin immunoprecipitation to be bound to the Sp1 promoter. Moreover, SKP2, BRCA2, p21, E2F-DP1, Stat3, Rb, p53 and NF kappaB had similar effects on an artificial promoter containing only Sp1 binding sites. Transient transfections of CDK4, Rad51, E2F-DP1, p21 and Stat3 increased mRNA expression from the endogenous Sp1 gene in HeLa cells whereas overexpression of NF kappaB, and p53 decreased Sp1 mRNA levels. p21 expression from a stably integrated inducible promoter in HT1080 cells activated Sp1 expression at the promoter and mRNA levels, but at the same time it decreased Sp1 protein levels due to the activation of Sp1 degradation. The observed multiple effects of cell cycle regulators on Sp1 suggest that Sp1 may be a key mediator of cell cycle associated changes in gene expression.
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PMID:Regulation of Sp1 by cell cycle related proteins. 1876 60

The Mdm2 oncoprotein is an E3 ubiquitin ligase required to maintain the p53 protein at low levels in embryonic and adult tissues. It also contributes to tumor formation by antagonizing p53 tumor suppressor activity when amplified and/or overexpressed. p53-independent role for Mdm2 has been suggested by transfection studies. Among the growing list of putative Mdm2-regulated proteins are several proteins playing a key role in the control of cell proliferation such as pRb, E2F1/DP1, Numb, Smads, Lats2 or IGF-1R. Consistent with the ability of Mdm2 to promote ubiquitylation and proteasome destruction of IGFR-I independently of p53, we show herein that loss of Mdm2 leads to a significant increase in IGF1-R-beta protein levels both in cells lacking or expressing p53. Interestingly, IGF-1 protects cells from DNA-damage-induced apoptosis only in absence of Mdm2. These data therefore further highlight a physiological role for Mdm2 in the control of IGF1 signalling and provide genetic evidence for a p53-independent proapoptotic function of Mdm2.
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PMID:Mdm2 exerts pro-apoptotic activities by antagonizing insulin-like growth factor-I-mediated survival. 1880 3


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