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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 p53 is a phosphoprotein and has growth and transformation suppression functions. Phosphorylation of wild-type p53 is known to modulate its function. To investigate the role of phosphorylation in modulating the functions of mutant p53, we constructed a series of phosphorylation site mutants based on mutant p53 Ala143 (p53-143) and p53 His175 (p53-175). When transfected into p53-negative Saos-2 cells, parental mutant p53-143 and p53-175 abolished both growth suppression and induction of apoptosis. However, DNA-activated protein kinase (DNA-PK) or cyclin-dependent kinase (cdks) phosphorylation site double mutants partially restored the growth suppression and induction of apoptosis and recovered the p53-specific DNA binding activity. We also observed a difference in sensitivity to calpain from parental mutants p53-175 and p53-175/15 or p53-175/315. These results suggest that the lack of phosphorylation at either the DNA-PK or cdks site in p53 mutants partially restores the wild-type functions by altering their conformation.
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PMID:Inhibition of mutant p53 phosphorylation at serine 15 or serine 315 partially restores the function of wild-type p53. 1042 75

Mutations that affect the oligomerization domain (OD) of the p53 tumor suppressor may be of particular interest because of the remarkable contradiction between the conservation of the OD and its relative functional resistance to amino acid substitutions, and because of recent hints that cellular protein factors may interact with the OD. Both point to the possibility that this domain fulfills tasks beyond oligomerization. We report that the tumor-associated mutants 330H, 334V, and 337C are defective for homo-oligomerization by three criteria. Accordingly, 330H and 337C failed to bind to a p53 recognition motif in gel-shift assays and to stimulate reporter genes efficiently in transient transfections. 334V retained some activity in both assays despite being oligomerization-defective. The ability of the mutants to induce apoptosis correlated with their performance in the DNA binding and transactivation assays. However, mutants 330H and 337C were able to provoke cell death when overexpressed, which in combination with their failure to transactivate genes suggests competence for the induction of transactivation-independent apoptosis at high protein levels. Although 334V and 337C failed to homo-oligomerize, they were able to hetero-oligomerize with a p53 with wild-type OD, and 334V was able to interfere with transactivation by wt p53. All mutants showed a reduced reactivity with antibody PAb421 and a distinct calpain cleavage pattern indicative of conformational alterations. In conclusion, tumor-associated OD mutants of p53 can be functionally competent to different degrees despite of being oligomerization defective.
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PMID:Function, oligomerization, and conformation of tumor-associated p53 proteins with mutated C-terminus. 1065 77

Damage to DNA produces cell cycle arrest, apoptosis, or both. The response in cells with p53 tumor suppressor function involves transcriptional changes, but whether that holds for cells lacking active p53, as in most tumors, is not known. Better characterization of the DNA damage response in tumors lacking p53 function is relevant to cytotoxic therapy. We have explored whether gamma-irradiated p53-null mouse T lymphoma cells undergo marked changes in transcription. Their arrest in G2/M prior to apoptosis required transcription. Transcripts whose abundance altered on irradiation were sought by subtractive hybridization, and 1010 candidate clones from two oppositely enriched cDNA populations were sequenced. Hybridization revealed small (<3-fold) increases or decreases in the transcripts of more than 15 genes, including some implicated in cell cycle control (e.g., BTG, Bap1) or apoptosis (e.g., STAT1, calpain), but no marked changes like those associated with other forms of T-cell death. Moreover, the expression of some critical apoptosis regulators, such as Bcl-2 family members, did not change. Hence, the G2/M arrest and apoptosis in the irradiated p53-null lymphoma appears to involve modest expression changes for many genes, but post-transcriptional alterations may be more critical.
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PMID:Gamma-radiation-induced growth arrest and apoptosis in p53-null lymphoma cells is accompanied by modest transcriptional changes in many genes. 1066 89

beta-Lapachone (beta-lap) effectively killed MCF-7 and T47D cell lines via apoptosis in a cell-cycle-independent manner. However, the mechanism by which this compound activated downstream proteolytic execution processes were studied. At low concentrations, beta-lap activated the caspase-mediated pathway, similar to the topoisomerase I poison, topotecan; apoptotic reactions caused by both agents at these doses were inhibited by zVAD-fmk. However at higher doses of beta-lap, a novel non-caspase-mediated "atypical" cleavage of PARP (i.e., an approximately 60-kDa cleavage fragment) was observed. Atypical PARP cleavage directly correlated with apoptosis in MCF-7 cells and was inhibited by the global cysteine protease inhibitors iodoacetamide and N-ethylmaleimide. This cleavage was insensitive to inhibitors of caspases, granzyme B, cathepsins B and L, trypsin, and chymotrypsin-like proteases. The protease responsible appears to be calcium-dependent and the concomitant cleavage of PARP and p53 was consistent with a beta-lap-mediated activation of calpain. beta-Lap exposure also stimulated the cleavage of lamin B, a putative caspase 6 substrate. Reexpression of procaspase-3 into caspase-3-null MCF-7 cells did not affect this atypical PARP proteolytic pathway. These findings demonstrate that beta-lap kills cells through the cell-cycle-independent activation of a noncaspase proteolytic pathway.
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PMID:Activation of a cysteine protease in MCF-7 and T47D breast cancer cells during beta-lapachone-mediated apoptosis. 1069 31

Calpain is a calcium-dependent cysteine protease that is implicated in calcium-dependent cell death, and calpain inhibitors are generally considered as inhibitors of apoptosis. To the contrary, in the present study, we found that calpain inhibitor II (CPI-2) triggers rapid apoptosis in acute lymphoblastic leukemia (ALL) and non-Hodgkin's lymphoma (NHL) cells. All target cell lines were killed by CPI-2, including: ALL-1, a multidrug-resistant BCR-ABL fusion transcript-positive t(9;22) pro-B ALL cell line; RS4;11, a highly radiation-resistant MLL-AF4 fusion transcript-positive t(4;11) pre-pre B ALL cell line; RAMOS, a highly radiation-resistant and p53-deficient Burkitt's lymphoma cell line; DAUDI, a Burkitt's leukemia/lymphoma cell line; NALM-6, a pre-B ALL cell line; and JURKAT and MOLT-3, two T-lineage ALL/NHL cell lines. CPI-2-induced apoptosis in LYN-deficient and BTK-deficient subclones of the DT-40 lymphoma B cell line as effectively as it did in wild-type DT-40 cells. Thus, CPI-2-induced apoptosis is not dependent on the protein tyrosine kinases LYN or BTK. Notably, caspase inhibitor I effectively inhibited CPI-2-induced apoptosis, suggesting that the inhibition of a CPI-2-susceptible protease results in caspase activation, leading to apoptosis in ALL/NHL cells. Unlike the high calpain-expressing ALL/NHL cell lines, myeloid leukemia cell lines HL-60/AML, K562/CML, and U937/AMML, or solid tumor cell lines BT-20/breast cancer, PC-3/prostate cancer, U373/glioblastoma, and HeLa/epitheloid cancer, were not susceptible to the cytotoxicity of CPI-2. Taken together, our results identify calpain as a new molecular target for the treatment of ALL and NHL. CPI-2 and its analogues represent a promising new class of antileukemia/lymphoma agents that deserves further development.
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PMID:Calpain inhibitor II induces caspase-dependent apoptosis in human acute lymphoblastic leukemia and non-Hodgkin's lymphoma cells as well as some solid tumor cells. 1087 99

Inhibitors of proteases are currently emerging as a potential anti-cancer modality. Nonselective protease inhibitors are cytotoxic to leukemia and cancer cell lines and we found that this cytotoxicity is correlated with their potency as inhibitors of the proteasome but not as inhibitors of calpain and cathepsin. Highly selective inhibitors of the proteasome were more cytotoxic and fast-acting than less selective inhibitors (PS341>>ALLN>>ALLM). Induction of wt p53 correlated with inhibition of the proteasome and antiproliferative effect in MCF7, a breast cancer cell line, which was resistant to apoptosis caused by proteasome inhibitors. In contrast, inhibitors of the proteasome induced apoptosis in four leukemia cell lines lacking wt p53. The order of sensitivity of leukemia cells was: Jurkat>HL60> or =U937>>K562. The highly selective proteasome inhibitor PS-341 induced cell death with an IC50 as low as 5 nM in apoptosis-prone leukemia cells. Cell death was preceded by p21WAF1/CIP1 accumulation, an alternative marker of proteasome inhibition, and by cleavage of PARP and Rb proteins and nuclear fragmentation. Inhibition of caspases abrogated PARP cleavage and nuclear fragmentation and delayed, but did not completely prevent cell death caused by PS-341. Reintroduction of wt p53 into p53-null PC3 prostate carcinoma cells did not increase their sensitivity to proteasome inhibitors. Likewise, comparison of parental and p21-deficient cells demonstrated that p21WAF1/CIP1 was dispensable for proteasome inhibitor-induced cytotoxicity. We conclude that accumulation of wt p53 and induction of apoptosis are independent markers of proteasome inhibition.
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PMID:Protease inhibitor-induced apoptosis: accumulation of wt p53, p21WAF1/CIP1, and induction of apoptosis are independent markers of proteasome inhibition. 1091 53

While ischemic damage to myofibrillar proteins is thought to be responsible in part for depressed cardiac function, the relation between myofilament protein breakdown and chronic hypoxia has not been defined. We previously characterized a chemical hypoxia model of neonatal cardiomyocytes mediated by 1 mM azide that exhibits features of calpain activation (Mol Cell Biochem 178:141-149, 1998). We here show that both hypoxia and azide-mediated metabolic inhibition induced heme oxygenase-1 expression, and caused cell death associated with lipid peroxidation. While blocking calcium influx or inhibiting calpain activity efficiently attenuated hypoxia-induced cell injury, it failed to prevent cell injury caused by adenoviral overexpression of the tumor suppressor protein p53. Inhibitors of caspases, on the other hand, suppressed cell injury caused by p53 overexpression. Hypoxia caused selective cleavage of troponin I (TnI), which could be suppressed by either nifedipine or calpeptin. Other myofilament proteins such as troponin T, myosin heavy chain, and actin appeared to remain largely intact. p53-mediated cell injury exhibited proteolysis of the caspase protein substrate lamin B without appreciable breakdown of TnI. We suggest that calpain-induced TnI breakdown may constitute a unique biochemical marker associated with chronically hypoxic cardiomyocytes.
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PMID:Calpain-mediated proteolytic cleavage of troponin I induced by hypoxia or metabolic inhibition in cultured neonatal cardiomyocytes. 1119 89

It has been suggested that BRCA2, the protein product of the breast cancer susceptibility gene BRCA2, is involved in DNA damage repair. It is therefore likely that BRCA2 plays a role in a signaling pathway induced by DNA-damaging agents. To test this possibility, we examined the alteration of the BRCA2 protein level in human cell lines after UV irradiation. We found that UV irradiation down-regulated BRCA2 in a dose-dependent manner in all cell lines tested. The down-regulation of BRCA2 occurred soon (within 4 h) after UV treatment. Surprisingly, down-regulation of BRCA2 by UV does not require functional p53, which has been suggested to be required for the down-regulation of BRCA1 and BRCA2 mRNAs by DNA-damaging agents. Moreover, the proteosome- and calpain-mediated protein degradation pathways do not have an important role in the UV-induced BRCA2 depletion. However, blocking protein synthesis temporally inhibited the depletion of BRCA2 and BRCA1 in some cell lines. Ectopic expression of BRCA2 in cells increased resistance of cells to high-dose UV irradiation. These results demonstrate that BRCA2 is involved in a DNA-damaging signaling pathway induced by UV radiation and that expression of BRCA2 can protect cells from UV-mediated cell death.
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PMID:Ultraviolet irradiation induces BRCA2 protein depletion through a p53-independent and protein synthesis-dependent pathway. 1130 54

Gas2 is a caspase-3 substrate that plays a role in regulating microfilament and cell shape changes during apoptosis. Here we provide evidence that overexpression of Gas2 efficiently increases cell susceptibility to apoptosis following UV irradiation, etoposide and methyl methanesulfonate treatments, and that these effects are dependent on increased p53 stability and transcription activity. To investigate possible pathways linking Gas2 to p53, a yeast two-hybrid screen swas performed, indicating m-calpain as a strong Gas2- interacting protein. Moreover, we demonstrate that Gas2 physically interacts with m-calpain in vivo and that recombinant Gas2 inhibits calpain-dependent processing of p53. Importantly, the Gas2 dominant-negative form (Gas2171-314) that binds calpain but is unable to inhibit its activity abrogates Gas2's ability to stabilize p53, to enhance p53 transcriptional activity and to induce p53-dependent apoptosis. Finally, we show that Gas2 is able to regulate the levels of p53 independently of Mdm2 status, suggesting that, like calpastatin, it may enhance p53 stability by inhibiting calpain activity.
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PMID:The death substrate Gas2 binds m-calpain and increases susceptibility to p53-dependent apoptosis. 1138 5

The tumor suppressor protein p53 is a phosphoprotein which shows growth and transformation suppression functions. Mutational loss of p53 function is the most frequently detected genetic event in human cancers. We examined whether 9-hydroxyellipticine (9HE), a cytotoxic agent, affected the tertiary structure of mutant p53 and DNA binding characteristics. Although several types of p53 mutants were resistant to degradation by calpain, the p53 mutants treated with 9HE were markedly sensitive to calpain as well as wild-type p53. Furthermore, mutant p53 proteins isolated from 9HE-treated cells regained the ability to bind a wild-type-specific p53 DNA consensus sequence. Wild-type p53 proteins prepared from both untreated and 9HE-treated cells bound the p53 consensus sequence and were degradaded by calpain equally well. These results suggest that 9HE affects the tertiary structure of mutated p53, which results in the restoration of DNA binding characteristics.
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PMID:9-Hydroxyellipticine alters the conformation and DNA binding characteristics of mutated p53 protein. 1172 37


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