Flavopiridol down-regulates antiapoptotic proteins and sensitizes human breast cancer cells to epothilone B-induced apoptosis

The molecular mechanisms underlying the cell cycle growth-inhibitory and apoptotic effects of flavopiridol (FP) were determined in human breast cancer cells. Treatment with FP caused accumulation in the G(1) phase of the cell cycle and induced apoptosis of SKBR-3 and MB-468 cells. This was associated with down-regulation of the levels of cyclins D1 and B1, as well as with inhibition of cyclin-dependent kinase (cdk) 1, cdk2, and cdk4. FP-induced apoptosis was accompanied by a conformational change and mitochondrial localization of Bax. This resulted in the accumulations of cytochrome c, Smac, and Omi/HtrA2 in the cytosol and induced the poly(ADP-ribose) polymerase cleavage activity of caspase-3. Treatment with FP also attenuated the mRNA and protein levels of XIAP, cIAP-2, Mcl-1, Bcl-x(L), and survivin. In MB-468 cells with overexpression of Bcl-2 (468/Bcl-2), FP-induced Bax conformational change and apoptosis were inhibited, whereas the FP-mediated decline in the levels of IAP proteins, Mcl-11 and Bcl-x(L) remained unaltered. The effects of cotreatment with FP and the nontaxane tubulin-polymerizing agent epothilone (Epo) B were also determined in MB-468 cells. Sequential treatment with Epo B followed by FP induced significantly more apoptosis of MB-468 cells than treatment with the reverse sequence of FP followed by Epo B or treatment with either agent alone (P < 0.05). Treatment with Epo B followed by FP induced more Bax conformational change and was associated with a greater decline in the levels of XIAP, cIAP-2, Mcl-1, and Bcl-x(L). However, MB-468/Bcl-2 cells remained relatively resistant to Epo B followed by FP. Taken together, these findings suggest that the superior sequence-dependent anti-breast cancer activity of Epo B followed by FP may be due to FP-induced Bax conformational change and down-regulation of the antiapoptotic IAP, Bcl-x(L), and Mcl-1 proteins, but this treatment may not overcome the resistance to apoptosis of breast cancer cells conferred by overexpression of Bcl-2.     

Smac induces cytochrome c release and apoptosis independently from Bax/Bcl-x(L) in a strictly caspase-3-dependent manner in human carcinoma cells

The mitochondrial apoptosis pathway mediates cell death through the release of various pro-apoptotic factors including cytochrome c and Smac, the second mitochondrial activator of caspases, into the cytosol. Smac was shown previously to inhibit IAP proteins and to facilitate initiation of the caspase cascade upon cytochrome c release. To investigate Smac function during apoptosis and to explore Smac as an experimental cancer therapeutic, we constructed an expression system based on a single adenoviral vector containing Smac under control of the Tet-off system supplied in cis. Conditional expression of Smac induced apoptosis in human HCT116 and DU145 carcinoma cells regardless of the loss of Bax or overexpression of Bcl-x(L). Nevertheless, apoptosis induced by Smac was associated with cytochrome c release and breakdown of the mitochondrial membrane potential. This indicates that Smac acts independently of Bax and Bcl-x(L) during initiation of apoptosis and triggers a positive feedback loop that results in Bax/Bcl-x(L)-independent activation of mitochondria. In caspase-proficient cells, Smac-induced apoptosis could be inhibited partially by cell-permeable LEHD (caspase-9 inhibitor) and DEVD (caspase-3 inhibitor) peptides. Furthermore, loss of caspase-3 expression in MCF-7 cells carrying a caspase-3 null mutation completely abrogated the sensitivity for Smac-induced apoptotic or nonapoptotic, necrosis-like cell death, while re-expression of caspase-3 conferred sensitivity. Altogether, caspase-3 but not caspase-9 activation was necessary for execution of Smac-induced cell death. Notably, Smac did not induce caspase-9 processing in the absence of caspase-3. Thus, caspase-9 processing occurs secondary to caspase-3 activation during Smac-induced apoptosis. Altogether, Smac is capable of circumventing defects in mitochondrial apoptosis signaling such as loss of Bax or overexpression of Bcl-x(L) that are frequently observed in tumor cells resistant to anticancer therapy. Consequently, Smac appears to be a promising therapeutic target in anticancer treatment.     

Resistance of cancers to immunologic cytotoxicity and adoptive immunotherapy via X-linked inhibitor of apoptosis protein expression and coexisting defects in mitochondrial death signaling

The ability of cancers to evade immune surveillance and resist immunotherapy raises a fundamental question of how tumor cells survive in the presence of a competent immune system. Studies to address this question have primarily focused on mechanisms by which tumor cells avoid recognition by or induce tolerance in the immune system. However, little is known about whether cancer cells also acquire an intrinsic ability to resist killing by immune effectors. We find that cancer cells enhance their ability to withstand an attack by cytotoxic immune effector cells via acquisition of specific genetic alterations that interfere with the shared mitochondrial death signaling pathway entrained by granzyme B, IFN-gamma, and Apo2 ligand/tumor necrosis factor-related apoptosis inducing ligand (Apo2L/TRAIL), three key mediators of immunologic cell-mediated cytotoxicity. We show that the coexistence of specific mitochondrial signaling defects (either deletion of Bax, overexpression of Bcl-x(L), or deletion of Smac) with expression of X-linked inhibitor of apoptosis protein decreases the sensitivity of cancer cells to IFN-gamma/Apo2L/TRAIL- or granzyme B-induced apoptosis, lymphocyte-mediated cytotoxicity in vitro, and adoptive cellular immunotherapy in vivo. Conversely, negating X-linked inhibitor of apoptosis protein expression or function in tumor cells with defective mitochondrial signaling enables direct activation of caspase-3/-7 by granzyme B or Apo2L/TRAIL, and restores their susceptibility to immunologic cytotoxicity. These findings identify an important mechanism by which cancers evade elimination by immune effector cells and suggest that cancer immunotherapy might be improved by concurrent strategies to alleviate or circumvent the intrinsic mitochondrial death signaling defects that help cancer cells resist immunologic cytotoxicity.     

Flavokawain B,a kava chalcone,induces apoptosis via up‐regulation of death‐receptor 5 and Bim expression in androgen receptor negative,hormonal refractory prostate cancer cell lines and reduces tumor growth

Limited success has been achieved in extending the survival of patients with metastatic and hormone‐refractory prostate cancer (HRPC). There is a strong need for novel agents in the treatment and prevention of HRPC. We have shown that flavokawain B (FKB), a kava chalcone, is about 4‐ to 12‐fold more effective in reducing the cell viabilities of androgen receptor (AR)‐negative, HRPC cell lines DU145 and PC‐3 than AR‐positive, hormone‐sensitive prostate cancer cell lines LAPC4 and LNCaP, with minimal effect on normal prostatic epithelial and stromal cells. FKB induces apoptosis with an associated increased expression of proapoptotic proteins: death receptor‐5, Bim and Puma and a decreased expression of inhibitors of apoptosis protein: XIAP and survivin. Among them, Bim expression was significantly induced by FKB as early as 4 hr of the treatment. Knockdown of Bim expression by short‐hairpin RNAs attenuates the inhibitory effect on anchorage‐dependent and ‐independent growth and caspase cleavages induced by FKB. These findings suggest that the effect of FKB, at least in part, requires Bim expression. In addition, FKB synergizes with TRAIL for markedly enhanced induction of apoptosis. Furthermore, FKB treatment of mice bearing DU145 xenograft tumors results in tumor growth inhibition and increases Bim expression in tumor tissues. Together, these results suggest robust mechanisms for FKB induction of apoptosis preferentially for HRPC and the potential usefulness of FKB for prevention and treatment of HRPC in an adjuvant setting.     

Survivin expression is regulated by coexpression of human epidermal growth factor receptor 2 and epidermal growth factor receptor via phosphatidylinositol 3-kinase/AKT signaling pathway in breast cancer cells

Survivin, a member of the inhibitor of apoptosis protein family, is widely expressed in a variety of human cancer tissues. Survivin inhibits activation of caspases, and its overexpression can lead to resistance to apoptotic stimuli. In this study, survivin protein expression was assessed by immunohistochemical staining of 195 invasive breast cancer specimens. Overall, 79.5% of the tumors were positive for survivin. The expression of epidermal growth factor receptor (EGFR) family, human epidermal growth factor receptor 2 (HER2) and EGFR, was also examined in 53 cases, and consequently, it was indicated that survivin positivity might be correlated with the coexpression of HER2 and EGFR. To clarify the regulatory mechanism of survivin expression in breast cancer cells, the effect of HER2 and/or EGFR expression on the survivin levels was examined. It was revealed that the survivin protein level was up-regulated by the coexpression of HER2 and EGFR, leading to the increased resistance against etoposide-induced apoptosis in breast cancer cells. Conversely, survivin levels and apoptosis resistance were decreased when cells were treated with HER2-specific inhibitor, Herceptin. Although Herceptin could down-regulate both phosphatidylinositol 3-kinase (PI3K)/AKT signal and mitogen-activated protein/extracellular signal-related kinase (ERK) kinase 1 (MEK1)/ERK signal in HER2-positive breast cancer cells, PI3K-specific inhibitor but not MEK1-specific inhibitor could decrease the survivin levels. The present study clarified the regulatory mechanism of HER2 in the expression of survivin protein in breast cancer cells.     

Sevoflurane inhibits proliferation, induces apoptosis, and blocks cell cycle progression of lung carcinoma cells

Purpose: Sevoflurane, an inhalational anesthetic, is used extensively during lung cancer surgery. However, the effect of sevoflurane on growth of lung carcinoma cells remains unclear. The purpose of this study is to investigate effects on proliferation, apoptosis, and cell cycling in the A549 human lung adenocarcinoma cell line. Methods: A549 cells were treated with 1.7%, 3.4%, and 5.1 % sevoflurane for 2, 4, and 6 hours. Cell proliferation was evaluated by the MTT assay and colony formation assay. Apoptosis and cell cycle was analyzed by flow cytometry. Expression of X-linked inhibitor of apoptosis protein (XIAP), survivin, Bcl-2, Bax, caspase-3, cyclin A, cyclin B1, and cdc2 was measured by Western blotting. Results: Sgnificant inhibition of cell proliferation and induction of apoptosis were found in A549 cells after sevoflurane treatment. Simultaneously, expression of XIAP and survivin was surpressed, while that of caspase-3 increased significantly, but Bcl-2 and Bax were not altered. Sevoflurane caused cell cycle arrest at the G2/M phase. At the same time, data revealed that cyclin A, cyclin B1, and cdc2 expression was down-regulated after sevoflurane treatment. Conclusion: This study demonstrated that sevoflurane inhibited proliferation, and induced apoptosis in human lung adenocarcinoma A549 cells, associated with down-regulated expression of XIAP and suvivin, and activating caspase-3.     

丹参酮ⅡA对人肺癌细胞株A549/CDDP细胞增殖和凋亡的影响

目的研究丹参酮ⅡA（TanⅡA）对人耐药非小细胞肺癌细胞株（A549/CDDP）增殖与凋亡的影响。方法体外培养A549/CDDP,以不同剂量组TanⅡA干预A549/CDDP,在48、72、96小时后用四氮唑盐（MTT）法检测活细胞OD值;采用Heochst33258荧光染色观察TanⅡA干预后细胞凋亡的形态学变化;半定量RT-PCR检测用药后A549/CDDP survivin和Bax基因表达;流式细胞术检测TanⅡA干预后细胞周期分布。结果在0.6-5.0 mg/L浓度范围内,TanⅡA对A549/CDDP均有增殖抑制作用,并呈剂量依赖趋势,在96小时各组增殖抑制率达高峰;5.0mg/L 72小时组,形态学观察细胞凋亡明显;2.5、5.0 mg/L 72小时组,survivin DNA条带强度较对照组减弱,BaxDNA条带强度较对照组明显增强;流式细胞术检测显示TanⅡA明显抑制A549/CDDP进入增殖周期,与对照组比较差异均有统计学意义（P〈0.05）。结论 TanⅡA可诱导凋亡抑制A549/CDDP增殖并影响细胞周期,其分子机制可能与survivin下调,Bax上调有关。     

2-Methoxyestradiol induces mitochondria dependent apoptotic signaling in pancreatic cancer cells

The antiproliferative action of 2-methoxyestradiol (2-ME), an endogenous estrogen metabolite is specific for cancer cells and is mediated by the induction of programmed cell death or apoptosis. But the identity of the downstream effectors of apoptotic signaling induced by 2-ME is not known. In the present study, we explored the effect of 2-ME on apoptosis in a panel of human pancreatic cancer cell lines. We have identified two categories of pancreatic cancer cell lines, which are either sensitive to 2-ME such as MIA PaCa-2, CFPAC-1, PANC-1, or non-sensitive to 2-ME such as Hs 766T. The results presented here indicated that the cell lines responsive to 2-ME could undergo apoptosis either by G2-M arrest (PANC-1) with Bcl-x(L) phosphorylation or by the accumulation of tetraploid cells in G1-S region (MIA PaCa-2) without Bcl-2/ Bcl-x(L) phosphorylation. Furthermore, 2-ME induced apoptosis in pancreatic cancer cells is mitochondria dependent as evident by the release of cytochrome c into the cytosol. 2-ME exposed cells exhibit Bid cleavage that is accompanied by the translocation of Bax into the mitochondria. Also 2-ME could induce phosphorylation of Bcl-x(L) in G2-M arrested cells, thus indicating the involvement of various anti- and pro-apoptotic regulators in the signaling cascade. The dissection of differential response of pancreatic cancer cell lines holds promise for future therapeutic intervention.     

Garlic constituent diallyl trisulfide suppresses x-linked inhibitor of apoptosis protein in prostate cancer cells in culture and in vivo

We have shown previously that garlic constituent diallyl trisulfide (DATS) inhibits growth of cultured and xenografted human prostate cancer cells in association with apoptosis induction, but the mechanism of cell death is not fully understood. The present study systematically investigates the role of inhibitor of apoptosis (IAP) family proteins in the regulation of DATS-induced apoptosis using cultured PC-3 and LNCaP human prostate cancer cells and dorsolateral prostate from control and DATS-treated transgenic adenocarcinoma of mouse prostate (TRAMP) mice. Level of X-linked inhibitor of apoptosis (XIAP) protein was decreased on 8-hour treatment with 20 and 40 μmol/L DATS, but this effect was partially attenuated at the 16-hour time point. DATS-mediated decline in XIAP protein level was partially reversible in the presence of proteasomal inhibitor MG132. In contrast, DATS-treated PC-3 and LNCaP cells exhibited marked induction of survivin and cellular inhibitor of apoptosis protein 1 (cIAP1) proteins. Induction of survivin protein expression resulting from DATS exposure was associated with an increase in its mRNA level. Dorsolateral prostates from DATS-treated TRAMP mice exhibited statistically significant downregulation of XIAP and induction of survivin protein compared with those of control mice. Ectopic expression of XIAP conferred partial but significant protection against DATS-induced apoptosis. On the other hand, DATS-induced apoptosis was only marginally affected by RNA interference of survivin or cIAP1. In conclusion, the present study indicates that the DATS-induced apoptosis in prostate cancer cells is mediated in part by suppression of XIAP protein expression, and that XIAP represents a viable biomarker of DATS response for future clinical investigations.     

BH3 mimetic ABT-737 potentiates TRAIL-mediated apoptotic signaling by unsequestering Bim and Bak in human pancreatic cancer cells

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has been shown to induce mitochondrial apoptotic signaling that can be negatively regulated by prosurvival Bcl-2 proteins. ABT-737 is a small-molecule BH3 mimetic that binds to and antagonizes Bcl-2/Bcl-x(L) but not Mcl-1. We show that ABT-737 can synergistically enhance TRAIL-mediated cytotoxicity in human pancreatic cancer cell lines. ABT-737 was shown to enhance TRAIL-induced apoptosis as shown by DNA fragmentation, activation of caspase-8 and Bid, and cleavage of caspase-3 and poly(ADP-ribose) polymerase. A Bax conformational change induced by TRAIL was enhanced by ABT-737. ABT-737 disrupted the interaction of Bak with Bcl-x(L) in both cell lines. Furthermore, ABT-737 untethered the proapoptotic BH3-only protein Bim from its sequestration by Bcl-x(L) or Bcl-2. Bim small hairpin RNA (shRNA) was shown to attenuate caspase-3 cleavage and to reduce the cytotoxic effects of TRAIL plus ABT-737 compared with shRNA control cells. Finally, Mcl-1 shRNA potentiated caspase-3 cleavage by ABT-737 and enhanced its cytotoxic effects. Taken together, ABT-737 augments TRAIL-induced cell killing by unsequestering Bim and Bak and enhancing a Bax conformational change induced by TRAIL. These findings suggest a novel strategy to enhance cross-talk between the extrinsic and intrinsic apoptotic pathways to improve therapeutic efficacy against pancreatic cancer.     

Lipoxygenase inhibitors induce death receptor 5/TRAIL-R2 expression and sensitize malignant tumor cells to TRAIL-induced apoptosis

Lipoxygenases induce malignant tumor progression and lipoxygenase inhibitors have been considered as promising anti-tumor agents. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is one of the most promising candidates for new cancer therapeutics. Combined treatment with nordihydroguaiaretic acid (NDGA), a lipoxygenase inhibitor, and TRAIL markedly induced apoptosis in Jurkat T-cell leukemia cells at suboptimal concentrations for each agent. The combined treatment efficiently activated caspase-3, -8 and -10, and Bid. The underling mechanism by which NDGA enhanced TRAIL-induced apoptosis was examined. NDGA did not change the expression levels of anti-apoptotic factors, Bcl-x(L), Bcl-2, cIAP-1, XIAP and survivin. The expression of death receptor-related genes was investigated and it was found that NDGA specifically up-regulated the expression of death receptor 5 (DR5) at mRNA and protein levels. Down-regulation of DR5 by small interfering RNA prevented the sensitizing effect of NDGA on TRAIL-induced apoptosis. Furthermore, NDGA sensitized prostate cancer and colorectal cancer cells to TRAIL-induced apoptosis. In contrast, NDGA neither enhanced TRAIL-induced apoptosis nor up-regulated DR5 expression in normal peripheral blood mononuclear cells. Another lipoxygenase inhibitor, AA861, also up-regulated DR5 and sensitized Jurkat and DU145 cells to TRAIL. These results indicate that lipoxygenase inhibitors augment the apoptotic efficiency of TRAIL through DR5 up-regulation in malignant tumor cells, and raise the possibility that the combination of lipoxygenase inhibitor and TRAIL is a promising strategy for malignant tumor treatment.     

Gene silence-induced downregulation of survivin inhibits bladder cancer cells

Urinary bladder cancer accounts for approximately 3% of all cancers in humans. Treatment for urinary bladder is not satisfactory. The present study aims to elucidate the effect of gene silencing of survivin on the inhibition of bladder cancer cells. In this study, we constructed survivin shRNA-carrying lentiviral vectors. Bladder cancer cell lines, T24 cells and BJ cells, were transduced with the constructed shRNA of survivin. The frequency of apoptotic bladder cancer cells was assessed by flow cytometry. The results showed that transfection with survivin shRNA significantly inhibited cell proliferation of both T24 and BJ cells. Most T24 and BJ cells accumulated at the G2/M stage; a portion of them was at sub-G1 stage. An increase in the fraction of bladder cancer cells undergoing apoptosis was noted. Among eight apoptosis-associated proteins, the amounts of BAX and BAD were significantly increased in the survivin-deficient bladder cancer cells. The findings suggest that survivin may be a therapeutic target of bladder cancer to selectively inhibit cell proliferation of bladder cancer cells.     

Se-methylselenocysteine induces apoptosis through caspase activation and Bax cleavage mediated by calpain in SKOV-3 ovarian cancer cells

Se-methylselenocysteine (Se-MSC) is a potent chemopreventive agent in many test systems and has been shown to inhibit tumor promotion and induce apoptosis, but its mechanism of action is still not well understood. The present study was designed to assess the mechanism of Se-MSC on the induction of apoptosis in SKOV-3 ovarian cancer cells. Se-MSC displayed strong inhibitory effects on cell proliferation and viability of SKOV-3 cells in dose and time dependent manners and induced apoptosis. Investigation of the mechanism of Se-MSC-induced apoptosis revealed that treatment with Se-MSC produced morphological features of apoptosis and DNA fragmentation. This was associated with caspase-3 activation and cleavage of poly(ADP-ribose) polymerase and phospholipase C-gamma1 proteins. However, SKOV-3 cells treated with Se-MSC did not demonstrate cytochrome c accumulation in the cytosol during apoptosis induction. Pretreatment of cells with the caspase inhibitors (z-VAD-fmk and DEVD-CHO) prevented Se-MSC-induced apoptosis. These results suggested that Se-MSC induces apoptosis through cytochrome c-independent caspase-3 activation in SKOV-3 cells. In late stage of apoptosis, p18kDa fragment of Bax was generated with the down-regulation of the expressions of survivin, X-linked inhibitor of apoptosis protein, and human inhibitor of apoptosis protein 1 following Se-MSC treatment, suggesting that the modulation of Bax and IAP (inhibitors of apoptosis) family proteins play some role in Se-MSC-mediated apoptosis. Pre-treatments of z-VAD-fmk and the calpain inhibitor, calpeptin inhibited Bax cleavage. These results suggested that Bax cleavage is mediated by calpain, and calpain activation may be a caspase-dependent one. Taken together, the chemopreventive effects of Se-MSC may be related in part to the caspase-3 activation, the down-regulation of IAP family proteins, and Bax cleavage mediated by caspase-dependent calpain activation.     

Survivin小分子干扰RNA对膀胱癌T24细胞生物学行为的影响

背景与目的:膀胱癌是泌尿系统最常见的恶性肿瘤,通常与体内某些基因突变导致细胞周期改变和抗凋亡机制有关。凋亡抑制蛋白家族(IAPs)的新成员Survivin,通过诱导细胞增殖和抑制细胞凋亡参与了人类多种肿瘤的发生,其中包括膀胱癌。本研究探讨转染靶向survivin的小分子干扰RNA(smallinterfering RNA,siRNA)对膀胱癌生物学行为的影响。方法:设计、合成一对survivin编码基因序列特异的siRNA,用脂质体包裹转染T24膀胱癌细胞,分成不同的浓度组(50～200nmol/L);鼠异位膀胱肿瘤模型中瘤内注射不同剂量的siRNA(5!g和50!g)。分别于体外和体内观察siRNA对膀胱癌生物学行为的影响。结果:survivin编码基因序列特异性siRNA能有效下调survivin基因表达水平,最大效应浓度为100nmol/L,此时survivin表达水平下调了75.91%,并显著的抑制了细胞增殖,抑制率达55.29%,与对照组相比差异有统计学意义(P<0.01)。同时,细胞凋亡率亦由2.8%增加至45.70%,与对照组相比差异有统计学意义(P<0.01)。裸鼠移植瘤内重复多次注射50!g survivin-siRNA能够明显抑制肿瘤生长,与对照相比差异有统计学意义(P<0.01)。结论:survivin-siRNA能显著下调膀胱癌细胞survivin基因表达水平,促进细胞凋亡,抑制肿瘤细胞增殖。