DNA damaging drugs-induced down-regulation of Bcl-2 is essential for induction of apoptosis in high-risk HPV-positive HEp-2 and KB cells.
ABSTRACT DNA damaging chemotherapeutic agents like carboplatin (Carb) and 5-fluorouracil (5-FU), whose effects are mediated through diverse intracellular targets, induce apoptosis in various cancer cells including human papillomavirus (HPV) positive HEp-2 and KB cells. The present work reports the involvement of Bcl-2 in response to the exposure of HEp-2 and KB cells to Carb or 5-FU. We demonstrate that both these drugs are potent inducers of apoptosis. Apoptosis was preceded by decrease in Bcl-2 protein level accompanied by caspase-9 activation and poly(ADP-ribose) polymerase (PARP) cleavage without altering Bax expression. Further analysis revealed down-regulation of Bcl-2 mRNA as well as protein in drugs treated cells. Ectopic expression of Bcl-2 protected cells against drugs mediated DNA damage-induced apoptosis. Overall, data indicates that genotoxic stress leads to down-regulation of Bcl-2 in HEp-2 and KB cells, which plays a decisive role in the outcome of stress in these cells.
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ABSTRACT: The Bcl-2 family consists of about 20 homologues of important pro- and anti-apoptotic regulators of programmed cell death. The established mode of function of the individual members is to either preserve or disturb mitochondrial integrity, thereby inducing or preventing release of apoptogenic factors like Cytochrome c (Cyt c) from mitochondria. Recent findings also indicate further Bcl-2-controlled mitochondria-independent apoptosis pathways. Bcl-2 represents the founding member of the new and growing class of cell death inhibiting oncoproteins. In this review, we try to briefly summarize current models of Bcl-2 family function and to outline the work demonstrating the influence of deregulated Bcl-2 family member expression on tumorigenesis and cancer therapy. Since several Bcl-2 homologues, in addition to influencing apoptotic behaviour, also impinge on cell cycle progression, we discuss possible implications of this additional role for the expression of Bcl-2 family members in tumor cells.Biochimica et Biophysica Acta 04/2004; 1644(2-3):229-49. · 4.66 Impact Factor
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ABSTRACT: In the therapy of various kinds of tumors, methylating agents gener- ating O6-methylguanine (O6MeG) in DNA are used. We studied the mo- lecular mechanism of cell death induced by these agents by comparing isogenic cell lines proficient (MGMT1) and deficient (MGMT2) for the DNA repair protein alkyltransferase and exhibiting the tolerance pheno- type. Hypersensitivity to methylation-induced cell killing of MGMT2 cells is attributable to the potent induction of apoptosis. We show that apo- ptosis is a late event occurring >48 h after methylation. It was preceded by decrease in Bcl-2 protein level and accompanied by activation of caspase-9 and caspase-3. We also observed cytochrome c release and hypophosphorylation of Bad. Other members of the Bcl-2 family (Bag-1, Bak, Bax, and Bcl-xL) were not altered in expression. Transfection of MGMT2 cells with bcl-2 protected against methylation-induced apopto- sis, indicating that Bcl-2 plays a key role in the response. Induction of apoptosis in MGMT2 cells was not triggered by Fas and Fas ligand (CD95, Apo-1) because both proteins remained unaltered in expression and receptor-proximal caspase-8 was not activated after methylation. Also, inhibition of caspase-8 was ineffective in modifying the apoptotic response, whereas inhibition of caspase-3 and caspase-9 blocked apopto- sis. Tolerant cells that are unable to repair O6MeG and are impaired in mismatch repair were less sensitive regarding the induction of apoptosis and Bcl-2 decline, supporting the view that O6MeG-induced apoptosis requires mismatch repair. The ultimate O6MeG-derived lesions triggering the apoptotic pathway are likely to be DNA double-strand breaks, which were significantly formed in MGMT2 but not in MGMT1 and tolerant cells and which preceded apoptosis. Overall, the data indicate that O6MeG induces apoptosis via secondary lesions that trigger Bcl-2 decline, cyto- chrome c release, and caspase-9 and caspase-3 activation independently of Fas/Fas ligand and p53, for which the cells are mutated.
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ABSTRACT: Bcl-2 protein plays a critical role in inhibiting anticancer drug-induced apoptosis, which is mediated by a mitochondria-dependent pathway that controls the release of cytochrome c from mitochondria through anion channels. Constitutive overexpression of Bcl-2 or unchanged expression after treatment with anticancer drugs confers drug resistance not only to hematologic malignancies but also to solid tumors. The down-regulation of Bcl-2 protein by the antisense (AS) Bcl-2 (oblimesen sodium) may be a useful method for targeting the antiapoptotic protein and thereby increasing the chemotherapeutic effect of anticancer drugs. Several randomized, controlled, Phase III trials have compared standard chemotherapy with a combination of AS Bcl-2 and standard chemotherapy for the treatment of patients with chronic lymphocytic leukemia, multiple myeloma, malignant melanoma, and nonsmall cell lung carcinoma. Nonrandomized clinical trials and preclinical evaluations of AS Bcl-2 also are underway for patients with other malignancies. Here, the authors review the current clinical and preclinical evaluations of AS Bcl-2 and discuss its potential to act as a chemosensitizer and to enhance the therapeutic effect of cancer chemotherapy. Cancer 2004. © 2004 American Cancer Society.Cancer 11/2004; 101(11):2491 - 2502. · 5.20 Impact Factor