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)

p53 exerts its tumor suppressor activity through both transcription-dependent and transcription-independent processes. Although the transcription-dependent activity of p53 has been extensively studied, the mechanism for transcription-independent p53-mediated tumor suppression is less well known. Recently, it was reported that p53 can directly induce mitochondrial permeabilization and promote apoptosis. This occurs through complexation of the DNA-binding region of p53 with the anti-apoptotic proteins Bcl-x(L) and Bcl-2 (Mihara, M. et al. (2003) Mol. Cell 11, 577-590). Using nuclear magnetic resonance (NMR) spectroscopy we show that the interaction surface on p53 involves the same region that is used by the protein to contact DNA. The p53-binding site on Bcl-x(L) consists of the carboxy-terminus of the first alpha-helix, the loop between alpha3 and alpha4, and the loop between alpha5 and alpha6 of Bcl-x(L). Furthermore, the interaction of p53 with Bcl-x(L) is blocked by the binding of a 25-residue peptide derived from the BH3 region of the pro-apoptotic protein referred to as Bad.
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PMID:Defining the p53 DNA-binding domain/Bcl-x(L)-binding interface using NMR. 1496 Mar 27

The tumor suppressor p53 exerts its anti-neoplastic activity primarily through the induction of apoptosis. We found that cytosolic localization of endogenous wild-type or trans-activation-deficient p53 was necessary and sufficient for apoptosis. p53 directly activated the proapoptotic Bcl-2 protein Bax in the absence of other proteins to permeabilize mitochondria and engage the apoptotic program. p53 also released both proapoptotic multidomain proteins and BH3-only proteins [Proapoptotic Bcl-2 family proteins that share only the third Bcl-2 homology domain (BH3)] that were sequestered by Bcl-xL. The transcription-independent activation of Bax by p53 occurred with similar kinetics and concentrations to those produced by activated Bid. We propose that when p53 accumulates in the cytosol, it can function analogously to the BH3-only subset of proapoptotic Bcl-2 proteins to activate Bax and trigger apoptosis.
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PMID:Direct activation of Bax by p53 mediates mitochondrial membrane permeabilization and apoptosis. 1496 30

p53, a chief tumor suppressor in multicellular organisms, induces cell cycle arrest, DNA repair and apoptosis to promote genomic stability and tissue homeostasis. The function of p53 is normally ascribed to its regulation of numerous p53-responsive genes through direct interactions with both chromatin and regulators of transcription. Nonetheless, evidence exists that p53 has an extranuclear role in the cytoplasm to induce apoptosis. Recently, p53 has been shown to directly activate the pro-apoptotic Bcl-2 protein Bax allowing for mitochondrial membrane permeabilization and apoptosis. In parallel, p53 can release pro-apoptotic Bcl-2 proteins sequestered by Bcl-x(L). These data suggest that cytoplasmic p53 functions analogously to the BH3-only proteins, a subset of pro-apoptotic Bcl-2 proteins.
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PMID:Cytoplasmic p53: bax and forward. 1502 Aug 44

Ubiquitin inhibitors act at many levels to enhance apoptosis signaling. For TNF-related apoptosis-inducing ligand (TRAIL)-mediated apoptosis signaling, there are at least five mechanisms by which apoptosis are regulated by the ubiquitin-proteasome pathway. First, proteasome inhibitors can decrease Fas-like inhibitor protein (FLIP) protein levels in tumors, resulting in increased apoptosis signaling due to increased caspase-8 activation. This appears to involve the ubiquitin ligase TNF receptor activation factor-2 (TRAF2) and acts indirectly by causing cell-cycle arrest at a stage where there is high degradation of the FLIP-TRAF2 complex. Second, the regulation of the proapoptotic Bcl-2 family member BAX occurs indirectly. Apoptosis signaling and caspase activation results in a confirmation change in the normally monomeric BAX, which exposes the BH3 domain of BAX, leading to dimerization and resistance to ubiquitin degradation. BAX then translocates into the mitochondria, resulting in the release of proapoptotic mitochondrial factors such as cytochrome c and second mitochondria-derived activator of caspase (SMAC). This results in the activation of caspase-9 and formation of the apoptosome and efficient apoptosis signaling. A third mechanism of the regulation of TRAIL signaling in the ubiquitin-proteasome pathway is mediated by the inhibitor of apoptosis proteins (IAP) E3 ligases. These IAPs can directly bind to caspases but also can act as ubiquitin ligases for caspases, resulting in the degradation of these caspases. IAP binding to caspases can be inhibited by SMAC, which exhibits a caspase-9 homology domain. The fourth mechanism for apoptosis activation by proteasome inhibitors is through the stabilization of the inhibitor of the kappaB (IkappaB)/NF-kappaB complex and prevention of nuclear translocation of the antiapoptosis transcription factor NF-kappaB. During TRAIL-DR4, DR5 signaling, this pathway is activated by interactions of activated Fas-associated death domain with activated receptor-interacting protein (RIP), which in turn activates NF-kappaB-inducing kinase and phosphorylates IkappaB. Therefore, the inhibition of IkappaB degradation blocks this RIP-mediated antiapoptosis signaling event. Last, p53 protein levels, and susceptibility to apoptosis, can be deregulated by the human homolog Hdm2 (Mdm2) E3 ligase. This process is inhibited by p53 phosphorylation and by sequestration of Mdm2 by ARF. Better mechanisms to inhibit the ubiquitin-proteasome pathway targeted at the ubiquitin-proteasome degradation process itself, or more specifically at the E3 ligases known to modulate and downregulate proapoptosis pathways will lead to the enhancement of TRAIL apoptosis signaling and better cancer therapeutic outcomes act through this pathway.
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PMID:Regulation of apoptosis proteins in cancer cells by ubiquitin. 1502 88

Heart remodeling is associated with the loss of cardiomyocytes and increase of fibrous tissue owing to abnormal mechanical load in a number of heart disease conditions. In present study, a well-described in vitro sustained stretch model was employed to study mechanical stretch-induced responses in both neonatal cardiomyocytes and cardiac fibroblasts. Cardiomyocytes, but not cardiac fibroblasts, underwent mitochondria-dependent apoptosis as evidenced by cytochrome c (cyto c) and Smac/DIABLO release from mitochondria into cytosol accompanied by mitochondrial membrane potential (Deltapsi(m)) reduction, indicative of mitochondrial permeability transition pore (PTP) opening. Cyclosporin A, an inhibitor of PTP, inhibited stretch-induced cyto c release, Deltapsi(m) reduction and apoptosis, suggesting an important role of mitochondrial PTP in stretch-induced apoptosis. The stretch also resulted in increased expression of the pro-apoptotic Bcl-2 family proteins, including Bax and Bad, in cardiomyocytes, but not in fibroblasts. Bax was accumulated in mitochondria following stretch. Cell permeable Bid-BH3 peptide could induce and facilitate stretch-induced apoptosis and Deltapsi(m) reduction in cardiomyocytes. These results suggest that Bcl-2 family proteins play an important role in coupling stretch signaling to mitochondrial death machinery, probably by targeting to PTP. Interestingly, the levels of p53 were increased at 12 h after stretch although we observed that Bax upregulation and apoptosis occurred as early as 1 h. Adenovirus delivered dominant negative p53 blocked Bax upregulation in cardiomyocytes but showed partial effect on preventing stretch-induced apoptosis, suggesting that p53 was only partially involved in mediating stretch-induced apoptosis. Furthermore, we showed that p21 was upregulated and cyclin B1 was downregulated only in cardiac fibroblasts, which may be associated with G2/M accumulation in response to mechanical stretch.
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PMID:Mechanical stretch induces mitochondria-dependent apoptosis in neonatal rat cardiomyocytes and G2/M accumulation in cardiac fibroblasts. 1504 Aug 86

Lymphoid malignancies can escape from DNA-damaging anti-cancer drugs and gamma-radiation by blocking apoptosis-signaling pathways. How these regimens induce apoptosis is incompletely defined, especially in cells with nonfunctional p53. We report here that the BH3-only Bcl-2 family member Bid is required for mitochondrial permeabilization and apoptosis induction by etoposide and gamma-radiation in p53 mutant T leukemic cells. Bid is not transcriptionally up-regulated in response to these stimuli but is activated by cleavage on aspartate residues 60 and/or 75, which are the targets of caspase-8 and granzyme B. Bid activity is not inhibitable by c-Flip(L), CrmA, or dominant negative caspase-9 and therefore is independent of inducer caspase activation by death receptors or the mitochondria. Caspase-2, which has been implicated as inducer caspase in DNA damage pathways, appeared to be processed in response to etoposide and gamma-radiation but downstream of caspase-9. Knock down of caspase-2 by short interfering RNA further excluded its role in Bid activation by DNA damage. Caspase-2 was implicated in the death receptor pathway however, where it contributed to effector caspase processing downstream of inducer caspases. Granzyme B-specific serpins could not block DNA damage-induced apoptosis, excluding a role for granzyme B in the generation of active Bid. We conclude that Bid, cleaved by an undefined aspartate-specific protease, can be a key mediator of the apoptotic response to DNA-damaging anticancer regimens.
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PMID:Requirement for aspartate-cleaved bid in apoptosis signaling by DNA-damaging anti-cancer regimens. 1511 53

Loss of p53 function by inactivating mutations results in abrogation of NO*induced apoptosis in human lymphoblastoid cells. Here we report characterization of apoptotic signaling pathways activated by NO* in these cells by cDNA microarray expression and immunoblotting. A p53-mediated transcriptional response to NO* was observed in p53-wild-type TK6, but not in closely related p53-mutant WTK1, cells. Several previously characterized p53 target genes were up-regulated transcriptionally in TK6 cells, including phosphatase PPM1D (WIP1), oxidoreductase homolog PIG3, death receptor TNFRSF6 (Fas/CD95), and BH3-only proteins BBC3 (PUMA) and PMAIP1 (NOXA). NO* also modulated levels of several gene products in the mitochondria-dependent and death-receptor-mediated apoptotic pathways. Inhibitors of apoptosis proteins X-chromosome-linked inhibitor of apoptosis, cellular inhibitor of apoptosis protein-1, and survivin were significantly down-regulated in TK6 cells, but not in WTK1 cells. Smac release from mitochondria was induced in both cell types, but release of apoptosis-inducing factor and endonuclease G was detected only in TK6 cells. Fas/CD95 was increased, and levels of the antiapoptotic proteins Bcl-2 and Bcl-x/L were reduced in TK6 cells. Activation of procaspases 3, 8, 9, and 10, as well as Bid and poly(ADP-ribose) polymerase cleavage, were observed only in TK6 cells. NO* treatment did not alter levels of death receptors 4 and 5, Fas-associated death domain or proapoptotic Bax and Bak proteins in either cell line. Collectively, these data show that NO* exposure activated a complex network of responses leading to p53-dependent apoptosis via both mitochondrial and Fas receptor pathways, which were abrogated in the presence of mutant p53.
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PMID:Apoptotic signaling pathways induced by nitric oxide in human lymphoblastoid cells expressing wild-type or mutant p53. 1512 37

The p53- and Bcl-2-negative leukemic K562 cell line showed resistant to DNA damage-induced Bax activation and apoptosis. The constitutive balanced ratio of Bax/Bcl-XL in K562 mitochondria allowed the formation of active Bax and cytochrome c release from mitochondria in the presence of a BH3-only protein, tBid, in a cell-free system. Bax transfection led to Bax undergoing a conformational change, translocation to mitochondria and homo-oligomerization but not apoptosis in the K562 cell line. After treatment with UV light, while Bcl-XL but not Bax translocated to mitochondria in K562, both Bax and Bcl-XL translocated to mitochondria in the Bax stable transfectant K/Bax cells. The increased ratio of Bax/Bcl-XL in K/Bax mitochondria led to an increased conformationally changed Bax, formation of the homo-multimer of Bax-Bax, and a reduced hetero-dimerization of Bax-Bcl-XL. Increased proportion of active Bax was accompanied with increased percentage of apoptosis. We therefore demonstrate that direct increase in the ratio of mitochondrial Bax/Bcl-XL can induce Bax activation in the p53- and Bcl-2-negative leukemic cells. Increased Bcl-XL translocation and failure in Bax translocation from cytosol to mitochondria play important roles in preventing Bax activation.
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PMID:Increase in the ratio of mitochondrial Bax/Bcl-XL induces Bax activation in human leukemic K562 cell line. 1525 70

Microtubule-damaging agents (MDA) are potent antineoplastic drugs that are widely used in clinical treatment for a variety of cancers. However, the precise mechanisms underlying MDA-induced cell death are largely unknown. Here, we report that both p53 and Bax are central participants in the MDA-mediated cell death machinery in HCT116 human colon cancer cells. MDA, including epothilone B analogue (BMS-247550) and vinblastine, induced apoptosis of Bax-positive HCT116 cells in a p53-dependent manner; p53 was required for MDA-induced Bax conformational change. In response to MDA treatment, the BH3-only proapoptotic protein PUMA was up-regulated in p53-positive but not in p53 knockout HCT116 cells. Moreover, PUMA knockout HCT116 cells were resistant to MDA-induced Bax conformational change and apoptosis. In addition, introducing p53 plasmid DNA into p53-deficient HCT116 cells restored PUMA expression and apoptotic response to MDA treatment. However, ectopic expression of the p53 point mutation L22Q/W23S, but not the proline-rich domain deletion mutants 83-393 and DeltaProAE, could also sensitize p53 knockout HCT116 cells to MDA-induced Bax activation and apoptosis, although all mutants failed to restore PUMA expression. Together, these findings suggest that p53 acts upstream of Bax to promote MDA-mediated cell death in a proline-rich domain-dependent manner through both transcription-dependent (by up-regulating PUMA expression) and -independent mechanisms in human colon cancer HCT116 cells.
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PMID:Regulation of Bax activation and apoptotic response to microtubule-damaging agents by p53 transcription-dependent and -independent pathways. 1526 86

Once melanoma metastasizes, no effective treatment modalities prolong survival in most patients. This notorious refractoriness to therapy challenges investigators to identify agents that overcome melanoma resistance to apoptosis. Whereas many survival pathways contribute to the death-defying phenotype in melanoma, a defect in apoptotic machinery previously highlighted inactivation of Apaf-1, an apoptosome component engaged after mitochondrial damage. During studies involving Notch signaling in melanoma, we observed a gamma-secretase tripeptide inhibitor (GSI; z-Leu-Leu-Nle-CHO), selected from a group of compounds originally used in Alzheimer's disease, induced apoptosis in nine of nine melanoma lines. GSI only induced G2-M growth arrest (but not killing) in five of five normal melanocyte cultures tested. Effective killing of melanoma cells by GSI involved new protein synthesis and a mitochondrial-based pathway mediated by up-regulation of BH3-only members (Bim and NOXA). p53 activation was not necessary for up-regulation of NOXA in melanoma cells. Blocking GSI-induced NOXA using an antisense (but not control) oligonucleotide significantly reduced the apoptotic response. GSI also killed melanoma cell lines with low Apaf-1 levels. We conclude that GSI is highly effective in killing melanoma cells while sparing normal melanocytes. Direct enhancement of BH3-only proteins executes an apoptotic program overcoming resistance of this lethal tumor. Identification of a p53-independent apoptotic pathway in melanoma cells, including cells with low Apaf-1, bypasses an impediment to current cytotoxic therapy and provides new targets for future therapeutic trials involving chemoresistant tumors.
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PMID:p53-independent NOXA induction overcomes apoptotic resistance of malignant melanomas. 1529 72


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