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)

Overexpression of HER2 in estrogen receptor (ER)-positive human breast tumors has been associated with resistance to endocrine therapy. Here we investigated the effects of HER2 on expression of apoptotic pathways and modulation of tamoxifen-induced apoptosis in ER-positive MCF-7 breast cancer cells. We report that HER2 overexpression in MCF-7 cells is accompanied by up-regulation of antiapoptotic Bcl-2 and Bcl-XL proteins and suppression of tamoxifen-induced apoptosis. In addition, human tumor cell lines that are both ER positive and overexpress HER2 also express enhanced levels of Bcl-2 compared to cells that are either ER positive or overexpress HER2 alone. Our findings suggest that possible deregulation of antiapoptotic Bcl-2 and Bcl-XL may be associated with the enhanced survival of HER2-overexpressing and ER-positive breast cancer cells treated with antiestrogens.
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PMID:Overexpression of HER2 modulates bcl-2, bcl-XL, and tamoxifen-induced apoptosis in human MCF-7 breast cancer cells. 981 90

Immunotoxins composed of antibodies linked to plant or bacterial toxins are being evaluated in the treatment of cancer. It is known that the toxin moieties of immunotoxins, including Pseudomonasexotoxin A (PE), diphtheria toxin, and ricin, are capable of inducing apoptosis. Since the efficiency of induction of apoptosis and the apoptosis pathway may have direct effects on the therapeutic usefulness of immunotoxins, we have studied how B3(Fv)-PE38, a genetically engineered immunotoxin in which the Fv fragment of an antibody is fused to a mutated form of PE, induces apoptosis of the MCF-7 breast cancer cell line. We show for the first time that a PE-containing immunotoxin activates ICE/ced-3 proteases, now termed caspases, and causes characteristic cleavage of the "death substrate" poly(ADP)-ribose polymerase (PARP) to an 89 kDa fragment with a time course of cleavage comparable to that induced by TNFalpha. Also the fluorescent substrate, DEVD-AFC, is cleaved 2-4-fold more rapidly by lysates from B3(Fv)-PE38 treated MCF-7 cells than untreated control cells, suggesting that a CPP32-like caspase is involved in B3(Fv)-PE38-mediated apoptosis. B3(Fv)-PE38-induced PARP cleavage is inhibited by several protease inhibitors known to inhibit caspases (zVAD-fmk, zDEVD-fmk, zIETD-fmk) as well as by overexpression of Bcl-2 providing additional evidence for caspase involvement. zVAD-fmk, a broad spectrum inhibitor of most mammalian caspases, prevents the early morphological changes and loss of cell membrane integrity produced by B3(Fv)-PE38, but not its ability to inhibit protein synthesis, arrest cell growth, and subsequently kill cells. Despite inhibition of apoptosis, the immunotoxin is still capable of selective cell killing, which indicates that B3(Fv)-PE38 kills cells by two mechanisms: one requires caspase activation, and the other is due to the arrest of protein synthesis caused by inactivation of elongation factor 2. The fact that an immunotoxin can specifically kill tumor cells without the need of inducing apoptosis makes such agents especially valuable for the treatment of cancers that are protected against apoptosis, e.g., by overexpression of Bcl-2.
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PMID:Role of caspases in immunotoxin-induced apoptosis of cancer cells. 983 86

We recently showed that estrogen induces expression of the anti-apoptotic protein, Bcl-2 in MCF-7 human breast cancer cells. Since estrogen-dependent breast tumours can regress following estrogen withdrawal, we hypothesized that stable Bcl-2 expression would prevent estrogen-withdrawal induced regression of MCF-7 tumours. We therefore established tumours in ovariectomized female nude mice implanted with an estrogen-release pellet using untransfected MCF-7 cells or MCF-7 cells stably transfected with a Bcl-2 cDNA sense or antisense expression vector. All tumours grew at similar rates indicating that Bcl-2 levels have no effect on tumour formation. After removal of the estrogen pellet, Bcl-2 antisense tumours and untransfected MCF-7 tumours regressed means of 49% and 52%, respectively, after estrogen pellet removal whereas Bcl-2 sense tumours were significantly stabilized. Regressing tumours displayed characteristics of apoptotic cells. These results show that Bcl-2 can prevent hormone-dependent breast tumour regression and are consistent with the notion that decreased Bcl-2 levels following estrogen withdrawal renders hormone-dependent breast tumour cells sensitive to apoptotic regression.
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PMID:Estrogen withdrawal-induced human breast cancer tumour regression in nude mice is prevented by Bcl-2. 987 11

Multidrug-resistant cancer cells display elevated levels of glucosylceramide (Lavie, Y., Cao, H. T., Volner, A., Lucci, A., Han, T. Y., Geffen, V., Giuliano, A. E., and Cabot, M. C. (1997) J. Biol. Chem. 272, 1682-1687). In this study, we have introduced glucosylceramide synthase (GCS) into wild type MCF-7 breast cancer cells using a retroviral tetracycline-on expression system, and we developed a cell line, MCF-7/GCS. MCF-7/GCS cells expressed an 11-fold higher level of GCS activity compared with the parental cell line. Interestingly, the transfected cells demonstrated strong resistance to adriamycin and to ceramide, whereas both agents were highly cytotoxic to MCF-7 cells. The EC50 values of adriamycin and ceramide were 11-fold (p < 0.0005) and 5-fold (p < 0.005) higher, respectively, in MCF-7/GCS cells compared with MCF-7 cells. Ceramide resistance displayed by MCF-7/GCS cells closely paralleled the activity of expressed GCS with a correlation coefficient of 0.99. In turn, cellular resistance and GCS activity were dependent upon the concentration of the expression mediator doxycycline. Adriamycin resistance in MCF-7/GCS cells was related to the hyperglycosylation of ceramide and was not related to shifts in the levels of either P-glycoprotein or Bcl-2. This work demonstrates that overexpression of GCS, which catalyzes ceramide glycosylation, induces resistance to adriamycin and ceramide in MCF-7 breast cancer cells.
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PMID:Expression of glucosylceramide synthase, converting ceramide to glucosylceramide, confers adriamycin resistance in human breast cancer cells. 987 62

MCF-7 cells growing in culture were used to study the mechanism of the antiproliferative activity of the antiprogestin mifepristone, as compared with the antiestrogen 4-hydroxytamoxifen or the combination of both. These steroid antagonists induced a significant time- and dose-dependent cell growth inhibition (cytotoxicity). This inhibition of cell survival was associated with a significant increase in DNA fragmentation (apoptosis), downregulation of bcl2, and induction of TGFbeta1 protein. Abrogation of the mifepristone- and/or 4-hydroxytamoxifen-induced cytotoxicity by TGFbeta1 neutralizing antibody confirms the correlation between induction of active TGFbeta1 and subsequent cell death. The effect of a combination of mifepristone and 4-hydroxytamoxifen on cell growth inhibition, on the increase in DNA fragmentation, bcl2 downregulation, and induction of TGFbeta1 protein was additive and significantly different (P < 0.05) from the effect of monotherapy. A translocation of protein kinase C (PKC) activity from the soluble to the particulate and/or nuclear fraction appeared to be also additive in cells treated with a combination of both 4-hydroxytamoxifen and mifepristone. These results suggest that the mechanism of the additive antiproliferative activity of mifepristone and tamoxifen could be explained at least in part by an additive induction of apoptosis in both estrogen and progesterone receptor positive MCF-7 breast cancer cells. A bcl2 downregulation, the PKC transduction pathway, and TGFbeta1 expression seem to be involved in this additive mechanism of action. Our data further suggest that a combination of an antiprogestin with tamoxifen may be more effective than tamoxifen monotherapy in the management of human breast cancer.
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PMID:Additive effect of mifepristone and tamoxifen on apoptotic pathways in MCF-7 human breast cancer cells. 987 77

Endocrine treatments for human breast cancer have been based largely upon the removal of estrogenic stimuli. The regression of tumors after estrogen deprivation has generally been characterized as being due to reduced proliferation but more recently has been recognized to also involve increased apoptosis. The aim of our experiments was to define the associated changes in certain proliferation- and cell death-related biological parameters after hormone withdrawal from estrogen-dependent MCF-7 xenografts in athymic nude mice using immunohistochemical techniques. The baseline estrogen receptor (ER) level of this MCF-7 xenograft was relatively low (average H score 23) but it was strongly Bcl-2-, PgR- and pS2-positive, indicating the functional integrity of estrogen signaling. Changes in proliferation (Ki-67), apoptosis, ER, progesterone receptor (PgR), cyclin D1, p27kip1, Bcl-2 and Bax expression were assessed during the 2 weeks after estrogen deprivation. ER levels rose markedly after estrogen ablation, whereas PgR levels fell to about 10% of baseline and pS2 levels halved. The proportion of Ki-67-positive cells was unchanged after 24 hr but by day 14 had reduced by about 80%. The normal levels of cyclin D1 also reduced after estrogen withdrawal in contrast to the rapid increase in levels of cyclin-dependent kinase inhibitor p27kip1. This latter increase appeared to occur in advance of the changes in Ki-67. The proportion of apoptotic cells increased from a mean 1.5% at baseline to 2.9% after 3 days and 4.7% after 14 days. There were reductions in both Bcl-2 and Bax staining but these appeared to be greater for Bcl-2, effectively decreasing the Bcl-2/Bax ratio. Our results provide a framework for the use of these parameters as intermediate markers in comparisons of hormonal agents for human breast cancer treatment.
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PMID:Time-related effects of estrogen withdrawal on proliferation- and cell death-related events in MCF-7 xenografts. 1018 36

The mechanism of Taxol-induced apoptosis was investigated in MCF-7 human breast carcinoma cells. Taxol-induced apoptosis was associated with phosphorylation of both c-Raf-1 and Bcl-2 and activation of ERK and JNK MAP kinases. The serine protease inhibitor N-tosyl-L-phenylalanine chloromethyl ketone (TPCK) effectively blocked apoptosis, but N-p-tosyl-L-lysine chloromethyl ketone (TLCK), another serine protease inhibitor, was without effect. TPCK treatment also prevented phosphorylation of c-Raf-1 and Bcl-2 in response to Taxol treatment. The serine protease inhibitor did not alter JNK activity, but it enhanced Taxol-induced activation of ERK1/2. Treatment of cells with the inhibitor of MEK activation, PD98059, prevented Taxol-induced ERK activation both in the presence and absence of TPCK, but did not influence survival of either Taxol- or Taxol plus TPCK-treated cells. In addition, PD98059 had no effect on c-Raf-1 or Bcl-2 phosphorylation. Thus, while the Taxol-induced phosphorylations of c-Raf-1 and Bcl-2 proteins appear to be coupled, these events can be disassociated from ERK1/2 activation. In summary, these findings suggest that phosphorylation of c-Raf-1 and Bcl-2, but not ERK1/2, are important signaling events in Taxol-induced apoptosis of MCF-7 breast cancer cells and that a TPCK inhibitable protease(s) is required for these processes.
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PMID:Serine protease inhibitor TPCK prevents Taxol-induced cell death and blocks c-Raf-1 and Bcl-2 phosphorylation in human breast carcinoma cells. 1037 21

Derivatives of camptothecins, topoisomerase I inhibitors and 7-hydroxystaurosporine (UCN-01), a protein kinase C (PKC) inhibitor and cell cycle checkpoint abrogator, are promising anticancer drugs. We characterized the apoptotic response to camptothecin and UCN-01 for the 8 human breast carcinoma cell lines (MCF-7, MCF-7/ADR, T47D, HS578T, BT549, MDA-N, MDA MB231, MDA435) from the National Cancer Institute (NCI) Anticancer Drug Screen. MCF-7 and T47D cells exhibited marked resistance to apoptosis, whereas MCF-7/ADR (NCI/ADR-RES) and HS578T cells exhibited the most pronounced apoptotic response. Apoptotic response was not correlated with growth inhibition measured by sulforhodamine B (SRB) assay, indicating that apoptosis is not the only mechanism of drug-induced cell death. Measurements of topoisomerase I levels and cleavage complexes and of PKC isoforms demonstrated that primary target inhibition was not correlated with apoptotic response. Several key apoptotic pathways were evaluated. Only MCF-7 cells had wild-type p53, indicating that p53 is not required for drug-induced apoptosis. MCF-7 cells also showed the highest MDM-2 expression (along with T47D cells, which were also resistant to apoptosis). Bcl-2, Mcl-1 and caspases 2 and 3 protein levels varied widely, whereas Bax expression was comparable among cell lines. Interestingly, Bcl-2, Mcl-1 and Bcl-X(L) cumulative expressions were inversely correlated with apoptotic response. Our results provide a comparative molecular characterization for the breast cancer cell lines of the NCI Anticancer Drug Screen and demonstrate the diversity of cellular responses to drugs (apoptosis vs. cell cycle arrest) and the importance of multifactorial analyses for modulating/predicting the apoptotic response to chemotherapy.
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PMID:Apoptotic response to camptothecin and 7-hydroxystaurosporine (UCN-01) in the 8 human breast cancer cell lines of the NCI Anticancer Drug Screen: multifactorial relationships with topoisomerase I, protein kinase C, Bcl-2, p53, MDM-2 and caspase pathways. 1039 57

Caspases are cysteine proteases that mediate apoptosis by proteolysis of specific substrates. Although many caspase substrates have been identified, for most substrates the physiologic caspase(s) required for cleavage is unknown. The Bcl-2 protein, which inhibits apoptosis, is cleaved at Asp-34 by caspases during apoptosis and by recombinant caspase-3 in vitro. In the present study, we show that endogenous caspase-3 is a physiologic caspase for Bcl-2. Apoptotic extracts from 293 cells cleave Bcl-2 but not Bax, even though Bax is cleaved to an 18-kDa fragment in SK-NSH cells treated with ionizing radiation. In contrast to Bcl-2, cleavage of Bax was only partially blocked by caspase inhibitors. Inhibitor profiles indicate that Bax may be cleaved by more than one type of noncaspase protease. Immunodepletion of caspase-3 from 293 extracts abolished cleavage of Bcl-2 and caspase-7, whereas immunodepletion of caspase-7 had no effect on Bcl-2 cleavage. Furthermore, MCF-7 cells, which lack caspase-3 expression, do not cleave Bcl-2 following staurosporine-induced cell death. However, transient transfection of caspase-3 into MCF-7 cells restores Bcl-2 cleavage after staurosporine treatment. These results demonstrate that in these models of apoptosis, specific cleavage of Bcl-2 requires activation of caspase-3. When the pro-apoptotic caspase cleavage fragment of Bcl-2 is transfected into baby hamster kidney cells, it localizes to mitochondria and causes the release of cytochrome c into the cytosol. Therefore, caspase-3-dependent cleavage of Bcl-2 appears to promote further caspase activation as part of a positive feedback loop for executing the cell.
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PMID:Caspase-3-dependent cleavage of Bcl-2 promotes release of cytochrome c. 1040 69

The promoting action of E2 in breast cancer cells has been, until now, mainly linked to its action on prolifieration. Because of the importance of an increase in apoptosis in breast cancer prevention, we have studied the possible effects of various antiestrogens, progestins and an androgen on its occurrence in three hormone-dependent breast cancer cell lines. The antiestrogens were, a triphenylethylene derivative, 4 hydroxytamoxifen (4OHTAM) and two steroidal antiestrogens, IC1182780 and RU58668. The progestins were Org2058, a pregnane derivative, tibolone (OrgOD14), a normethyltestosterone derivative and OrgOM38 (the delta4 isomer of OrgOD14) and the androgen dihydrotestosterone (DHT). Apoptosis was studied in MCF-7, ZR75-1 and T47-D cells using morphological approaches and flow cytometry. The antiestrogens, the progestins and DHT were proapoptotic but to different potencies according to the cell line studied. Indeed, the 'pure' steroidal antiestrogens were more efficient than 4OHTam in increasing apoptosis. We have also studied the level of expression of some of the proteins involved in the regulation of apoptosis. Bcl-2 and bcxL, two antiapoptotic members of the bcl-2 family proteins, were inhibited by the progestins and the antiestrogens. In contrast, the proapoptotic proteins, bax and bak seemed to be constitutively expressed. Thus, since the ratio of proapoptotic and antiapoptotic proteins determines apoptosis or cell survival, the hormone effects are operating by modulating the antiapoptotic regulators of the balance. These data demonstrate that antiestrogens, progestins, and androgens can promote apoptosis in breast cancer cells, an effect which could be of importance in the therapeutic prevention of breast cancer.
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PMID:Proapoptotic effects of antiestrogens, progestins and androgen in breast cancer cells. 1041 26


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