Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P10415 (Bcl-2)
 33,771 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Calcineurin is a calcium-dependent protein phosphatase that functions in T cell activation. We present evidence that calcineurin functions more generally in calcium-triggered apoptosis in mammalian cells deprived of growth factors. Specifically, expression of epitope-tagged calcineurin A induces rapid cell death upon calcium signaling in the absence of growth factors. We show that this apoptosis does not require new protein synthesis and therefore calcineurin must operate through existing substrates. Co-expression of the Bcl-2 protooncogene efficiently blocks calcineurin-induced cell death. Significantly, we demonstrate that a calcium-independent calcineurin mutant induces apoptosis in the absence of calcium, and that this apoptotic response is a direct consequence of calcineurin's phosphatase activity. These data suggest that calcineurin plays an important role in mediating the upstream events in calcium-activated cell death.
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PMID:Calcineurin functions in Ca(2+)-activated cell death in mammalian cells. 759 93

The antiapoptosis potential of Bcl-2 protein is well established, but the mechanism of Bcl-2 action is still poorly understood. Using the phosphatase inhibitor okadaic acid or the chemotherapeutic drug taxol, we found that Bcl-2 was phosphorylated in lymphoid cells. Phospho amino acid analysis revealed that Bcl-2 was phosphorylated on serine. Under similar conditions, okadaic acid or taxol treatment led to the induction of apoptosis in these cells. Thus, phosphorylation of Bcl-2 seems to inhibit its ability to interfere with apoptosis. In addition, phosphorylated Bcl-2 can no longer prevent lipid peroxidation as required to protect cells from apoptosis.
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PMID:Inactivation of Bcl-2 by phosphorylation. 775 34

GL331 is a semisynthetic topoisomerase II inhibitor derived from a plant toxin podophyllotoxin. In 72-h exposure assays, LD50 values of GL331 range from 0.5 to 2 microM, which are three- to ten-fold lower than those of its homologous compound etoposide (VP-16), depending on different cancer cell lines including nasopharyngeal, hepatocellular, gastric, cervical and colon cancer types. Apoptotic DNA ladders could be detected when cancer cells were treated with GL331 for 24 h even if the Bcl-2 and Bax protein levels were not altered during the period. Besides acting as topoisomerase II inhibitors, both GL331 and VP-16 decrease the cellular protein tyrosine kinase (PTK) activities in cancer cells. The activities of protein tyrosine phosphatase (PTP) are significantly increased after GL331 treatment but are not affected by VP-16. GL331-induced internucleosomal cleavage can be efficiently prevented by two inhibitors of PTP, sodium orthovanadate and zinc chloride, but not by okadaic acid, which inhibits serine/threonine phosphatase activity. These results indicate that GL331 may induce apoptotic cell death, and that activation of protein tyrosine phosphatases may be involved in this process.
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PMID:Protein tyrosine phosphatase activities are involved in apoptotic cancer cell death induced by GL331, a new homolog of etoposide. 901 84

It is not known how the protein Bcl-2 inhibits cell death induced by calcium signalling and growth-factor withdrawal. Here we report that Bcl-2 forms a tight complex with calcineurin, resulting in the targeting of calcineurin to Bcl-2 sites on cytoplasmic membranes, and show that this interaction is dependent on the BH4 domain of Bcl-2. Calcineurin bound to Bcl-2 is an active phosphatase but is unable to promote the nuclear translocation of NF-AT, a transcription-factor required for induction of interleukin-2 expression, suggesting a mechanism by which Bcl-2 suppresses NF-AT activity. We also show that Bax, a pro-apoptotic member of the Bcl-2 family, interferes with interactions between calcineurin and Bcl-2. We propose that the ability of Bcl-2 to block NF-AT signalling is due to the sequestering of active calcineurin to the same domain of Bcl-2 which associates with Rad-1 (ref. 5), and that calcineurin may act in Bcl-2-regulated functions.
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PMID:Suppression of signalling through transcription factor NF-AT by interactions between calcineurin and Bcl-2. 910 91

We examined the cellular and signaling mechanism of angiotensin II (Ang II) type 2 (AT2) receptor-induced apoptosis in PC12W (rat pheochromocytoma cell line) cells that express abundant AT2 receptor but not Ang II type 1 receptor. In these cells, nerve growth factor (NGF) inhibited the internucleosomal DNA fragmentation induced by serum depletion, whereas Ang II antagonized this NGF cell survival action and induced apoptosis. We studied the mechanism of NGF and AT2 receptor interaction on apoptosis by examining their effects on the survival factor Bcl-2. AT2 receptor activation did affect intracellular Bcl-2 protein levels. Bcl-2 phosphorylation was stimulated by NGF, whereas AT2 receptor activation blocked this NGF effect. Pretreatment with antisense oligonucleotide of mitogen-activated protein (MAP) kinase phosphatase-1 enhanced the effects of NGF on MAP kinase activation and Bcl-2 phosphorylation but attenuated the inhibitory effects of AT2 receptor on MAP kinase, Bcl-2 phosphorylation, and apoptosis. Taken together, these results suggest that MAP kinase plays a critical role in inhibiting apoptosis by phosphorylating Bcl-2. The AT2 receptor inhibits MAP kinase activation, resulting in the inactivation of Bcl-2 and the induction of apoptosis.
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PMID:Angiotensin type 2 receptor dephosphorylates Bcl-2 by activating mitogen-activated protein kinase phosphatase-1 and induces apoptosis. 922 85

We have studied the phosphorylation of the Bcl-2 family of proteins by different mitogen-activated protein (MAP) kinases. Purified Bcl-2 was found to be phosphorylated by the c-Jun N-terminal kinase/stress-activated protein kinase (JNK/SAPK) p54-SAPKbeta, and this is specific insofar as the extracellular signal-regulated kinase 1 (ERK1) and p38/RK/CSBP (p38) catalyzed only weak modification. Bcl-2 undergoes similar phosphorylation in COS-7 when coexpressed together with p54-SAPKbeta and the constitutive Rac1 mutant G12V. This is seen by both 32PO4 labeling and the appearance of five discrete Bcl-2 bands with reduced gel mobility. As anticipated, both intracellular p54-SAPKbeta activation and Bcl-2 phosphorylation are blocked by co-transfection with the MAP kinase specific phosphatase MKP3/PYST1. MAP kinase specificity is also seen in COS-7 cells as Bcl-2 undergoes only weak phosphorylation when co-expressed with enzymatically activated ERK1 or p38. Four critical residues undergoing phosphorylation in COS-7 cells were identified by expression of the quadruple Bcl-2 point mutant T56A,S70A,T74A, S87A. Sequencing phosphopeptides derived from tryptic digests of Bcl-2 indicates that purified GST-p54-SAPKbeta phosphorylates identical sites in vitro. This is the first report of Bcl-2 phosphorylation by the JNK/SAPK class of MAP kinases and could indicate a key modification allowing control of Bcl-2 function by cell surface receptors, Rho family GTPases, and/or cellular stresses.
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PMID:Bcl-2 undergoes phosphorylation by c-Jun N-terminal kinase/stress-activated protein kinases in the presence of the constitutively active GTP-binding protein Rac1. 931 39

The effects of the non-tumor-promoting protein kinase C (PKC) activator bryostatin 1 and the PKC inhibitors staurosporine and UCN-01 were examined with respect to modulation of 1-[beta-D-arabinofuranosyl]cytosine (ara-C)-induced apoptosis in human myeloid leukemia cells (HL-60) overexpressing the antiapoptotic protein Bcl-2. HL-60/Bcl-2 cells displayed a 5-fold increase in Bcl-2 protein compared with empty-vector counter-parts (HL-60/pCEP4) but comparable levels of Bax, Mcl-1, and Bcl-xL. After exposure to an equimolar concentration of ara-C (10 microM for 6 hr), HL-60/Bcl-2 cells were significantly less susceptible to apoptosis, DNA fragmentation, and loss of clonogenicity than HL-60/pCEP4 cells. The protective effect of increased Bcl-2 expression was manifested by a failure of ara-C to induce activation/cleavage of the Yama protease (CPP32; caspase-3) and degradation of one of its substrates, poly(ADP-ribose)polymerase to an 85-kDa cleavage product. When HL-60/Bcl-2 cells were preincubated with bryostatin 1 (10 nM; 24 hr) or coincubated with either staurosporine (50 nM; 6 hr) or UCN-01 (300 nM; 6 hr) after a 1-hr preincubation, exposures that exerted minimal effects alone, ara-C-induced apoptosis and DNA fragmentation were restored to levels equivalent to, or greater than, those observed in empty-vector controls. These events were accompanied by restoration of the ability of ara-C to induce CPP32 cleavage and activation, poly(ADP-ribose) polymerase degradation, and inhibition of colony formation. Western analysis of Bcl-2 protein obtained from overexpressing cells treated with bryostatin 1, staurosporine, or UCN-01 revealed the appearance of a slowly migrating species and a general broadening of the protein band, effects that were insensitive to the protein synthesis inhibitor cycloheximide. Alterations in Bcl-2 protein mobility on sodium dodecyl sulfate-polyacrylamide gel electrophoresis were reversed by treatment of lysates with alkaline phosphatase or protein phosphatase 2A; actions of the latter were blocked by the specific phosphatase inhibitor okadaic acid. In vivo labeling studies of Bcl-2 protein demonstrated increased incorporation of [32PO4]orthophosphate in drug-treated cells. Last, phosphorylated Bcl-2 failed to display decreased binding to the proapoptotic protein Bax. Collectively, these findings indicate that bryostatin 1, which down-regulates PKC, and staurosporine and UCN-01, which directly inhibit the enzyme, circumvent resistance of Bcl-2-overexpressing leukemic cells to ara-C-induced apoptosis and activation of the protease cascade. They also raise the possibility that modulation of Bcl-2 phosphorylation status contributes to this effect.
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PMID:Agents that down-regulate or inhibit protein kinase C circumvent resistance to 1-beta-D-arabinofuranosylcytosine-induced apoptosis in human leukemia cells that overexpress Bcl-2. 939 80

Treatment of U-937 promonocytic cells with the DNA topoisomerase II inhibitor etoposide rapidly caused death by apoptosis, as determined by changes in chromatin structure, production of DNA breaks, nucleosome-sized DNA degradation, decrease in mitochondrial membrane potential and phosphatidyl serine translocation in the plasma membrane, and at the same time induced intracellular acidification. Both the execution of the apoptotic process and the intracellular acidification were reduced by the addition of forskolin plus theophylline or other cAMP increasing agents. These agents also attenuated the induction of apoptosis by camptothecin, heat-shock, cadmium chloride and X-radiation. Although etoposide slightly increased the production of reactive oxygen intermediates, this increase was not prevented by forskolin plus theophylline, and the addition of antioxidant agents failed to inhibit apoptosis. Etoposide caused a great increase in NF-(kappa)B binding activity, which was not prevented by forskolin plus theophylline, while AP-1 binding was little affected by the topoisomerase inhibitor. The treatments did not significantly alter the levels of Bcl-2 and Bax. By contrast, the expression of c-myc, which was very high in untreated U-937 cells and only partially inhibited by etoposide, was rapidly and almost totally abolished by the cAMP increasing agents. Finally, it was observed that etoposide caused a transient dephosphorylation of retinoblastoma (Rb), which was associated with cleavage of poly(ADP-ribose) polymerase (PARP). Both Rb dephosphorylation and PARP cleavage were inhibited by forskolin plus theophylline. The inhibition of Rb (type I) phosphatase and ICE/CED-3-like protease activities, and the abrogation of c-myc expression, are mechanisms which could explain the anti-apoptotic action of cAMP increasing agents in myeloid cells.
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PMID:cAMP increasing agents attenuate the generation of apoptosis by etoposide in promonocytic leukemia cells. 945 37

Phosphorylation of Bcl-2 protein is a post-translational modification of unclear functional consequences. We studied the correlation between Bcl-2 phosphorylation, mitotic arrest, and apoptosis induced by the anti-tubulin agent paclitaxel. Continuous exposure of human cervical carcinoma HeLa cells to 50 ng/ml paclitaxel resulted in mitotic arrest with a symmetrical bell-shaped curve over time. The number of mitotic cells was highest at 24 h (82%), then declined as arrested cells progressed into apoptosis, and barely no mitotic cells were present at 48-60 h. The time curves of paclitaxel-induced cyclin B1 accumulation and stimulation of Cdc2/cyclin B1 kinase activity were identical and superimposable to that of M phase arrest. In contrast, apoptosis was first detected at 12 h and steadily increased thereafter until the termination of the experiments at 48-60 h, when about 80-96% of cells were apoptotic. Bcl-2 phosphorylation was closely associated in time with M phase arrest, accumulation of cyclin B1, and activation of Cdc2/cyclin B1 kinase, but not with apoptosis. At 24 h, when about 82% of the cells were in mitosis, almost all Bcl-2 protein was phosphorylated, whereas at 48 h, when 70-90% of the cells were apoptotic, all Bcl-2 protein was unphosphorylated. Similar results were obtained with SKOV3 cells, indicating that the association of paclitaxel-induced M phase arrest and Bcl-2 phosphorylation is not restricted to HeLa cells. We used short exposure to nocodazole and double thymidine to synchronize HeLa cells and investigate the association of Bcl-2 phosphorylation with mitosis. These studies demonstrated that Bcl-2 phosphorylation occurs in tight association with the number of mitotic cells in experimental conditions that do not lead to apoptosis. However, a continuous exposure to nocodazole resulted in a pattern of Bcl-2 phosphorylation, M phase arrest, and apoptosis similar to that observed with paclitaxel. The phosphatase inhibitor okadaic acid was found to inhibit the dephosphorylation of phosphorylated Bcl-2 and to delay the progression of nocodazole M phase-arrested cells into interphase. In contrast, the serine/threonine kinase inhibitor staurosporine, but not the tyrosine kinase inhibitor genistein, led to rapid dephosphorylation of phosphorylated Bcl-2 and accelerated the progression of nocodazole M phase-arrested cells into interphase. Immune complex kinase assays in cell-free systems demonstrated that Bcl-2 protein can be a substrate of Cdc2/cyclin B1 kinase isolated from paclitaxel-treated cells arrested in M phase. Taken together, these studies suggest that Bcl-2 phosphorylation is tightly associated with mitotic arrest and fail to demonstrate that it is a determinant of progression into apoptosis after mitotic arrest induced by anti-tubulin agents.
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PMID:Phosphorylation of Bcl-2 is a marker of M phase events and not a determinant of apoptosis. 966 78

The murine TS1alphabeta T cell line expresses the anti-apoptotic protein Bcl-2 upon IL-2 stimulation, whereas IL-4-mediated growth of this cell line proceeds in the absence of Bcl-2 expression. In addition, IL-4 stimulation inhibits Bcl-2 expression and modulates its mRNA level. IL-2-induced DNA binding activity for these transcription factors is sensitive to phosphatidylinositol 3 kinase inhibitor wortmannin and to Rho inhibitor Clostridium difficile toxin B, which inhibit IL-2-induced Bcl-2 expression. NF-AT transcription factor appears to be the most important in the control Bcl-2 expression, since inhibition of the calcium-calmodulin-dependent phosphatase calcineurin, which regulates NF-AT activity, downregulates Bcl-2 expression in IL-2-stimulated cells. Constitutive expression of this phosphatase also upregulates Bcl-2 expression in IL-4-stimulated cells. In addition, a dominant negative NF-AT expression vector downregulates Bcl-2 expression in IL-2-stimulated cells. These results suggest that IL-2 induction of Bcl-2 expression may be directly or indirectly mediated by NF-AT.
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PMID:The Bcl-2 gene is differentially regulated by IL-2 and IL-4: role of the transcription factor NF-AT. 977 66


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