Activation of NF-kappaB following detachment delays apoptosis in intestinal epithelial cells

We reported earlier that IL-1beta, an NF-kappaB-regulated cytokine, was made by intestinal epithelial cells during detachment-induced apoptosis (anoikis) and that IL-1 was antiapoptotic for detached cells. Since surviving anoikis is a prerequisite for cancer progression and metastases, we are further exploring the link between anoikis and cytokines. Here we determined that multiple genes are expressed following detachment including a number of NF-kappaB-regulated products and therefore aimed to determine whether NF-kappaB signalling plays any role in regulating apoptosis. Using Western blotting, we detected that IkappaBalpha becomes phosphorylated immediately following detachment and that levels of phospho-IkappaBalpha peaked within 20 min. Phosphorylation of IkappaBalpha was followed by Rel A (p65) nuclear translocation. Increased NF-kappaB activity following detachment was confirmed using the detection of NF-kappaB-promoted luciferase gene expression delivered by adenovirus infection. Infection of cells with adenovirus expressing a super-repressor IkappaBalpha protein and pharmacological inhibitors of NF-kappaB resulted in the failure to phosphorylate IkappaBalpha, a more rapid activation of caspases and earlier apoptosis. We also detected that IkappaB kinase alpha (IKKalpha) and not IKKbeta became phosphorylated following detachment. Since IKKalpha is activated by NF-kappaB-inducing kinase (NIK), we overexpressed native NIK using an adenovirus vector that resulted in enhanced phospho-IkappaBalpha and nuclear p65 in detached cells compared to control detached cells but did not result in a significantly greater number of cells surviving to 24 h. We conclude that detachment directly activates NF-kappaB, which, in addition to launching an inflammatory cytokine wave, contributes to a delay in apoptosis in intestinal epithelial cells.     

Blocking protein geranylgeranylation is essential for lovastatin-induced apoptosis of human acute myeloid leukemia cells.

Lovastatin is an inhibitor of the enzyme 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, the major regulatory enzyme of the mevalonate pathway. We have previously reported that lovastatin induces a significant apoptotic response in human acute myeloid leukemia (AML) cells. To identify the critical biochemical mechanism(s) essential for lovastatin-induced apoptosis, add-back experiments were conducted to determine which downstream product(s) of the mevalonate pathway could suppress this apoptotic response. Apoptosis induced by lovastatin was abrogated by mevalonate (MVA) and geranylgeranyl pyrophosphate (GGPP), and was partially inhibited by farnesyl pyrophosphate (FPP). Other products of the mevalonate pathway including cholesterol, squalene, lanosterol, desmosterol, dolichol, dolichol phosphate, ubiquinone, and isopentenyladenine did not affect lovastatin-induced apoptosis in AML cells. Our results suggest that inhibiting geranylgeranylation of target proteins is the predominant mechanism of lovastatin-induced apoptosis in AML cells. In support of this hypothesis, the geranylgeranyl transferase inhibitor (GGTI-298) mimicked the effect of lovastatin, whereas the farnesyl transferase inhibitor (FTI-277) was much less effective at triggering apoptosis in AML cells. Inhibition of geranylgeranylation was monitored and associated with the apoptotic response induced by lovastatin and GGTI-298 in the AML cells. We conclude that blockage of the mevalonate pathway, particularly inhibition of protein geranylgeranylation holds a critical role in the mechanism of lovastatin-induced apoptosis in AML cells.     

Blocking the Raf/MEK/ERK pathway sensitizes acute myelogenous leukemia cells to lovastatin-induced apoptosis

The statin family of drugs are well-established inhibitors of 3-hydroxy-3-methylglutaryl-CoA reductase and are used clinically in the control of hypercholesterolemia. Recent evidence, from ourselves and others, shows that statins can also trigger tumor-specific apoptosis by blocking protein geranylgeranylation. We and others have proposed that statins disrupt localization and function of geranylgeranylated proteins responsible for activating signal transduction pathways essential for the growth and/or survival of transformed cells. To explore this further, we have investigated whether the mitogen-activated protein kinase (MAPK) signaling cascades play a role in regulating statin-induced apoptosis. Cells derived from acute myelogenous leukemia (AML) are used as our model system. We show that p38 and c-Jun NH2-terminal kinase/stress-activated kinase MAPK pathways are not altered during lovastatin-induced apoptosis. By contrast, exposure of primary and established AML cells to statins results in significant disruption of basal extracellular signal-regulated kinase (ERK) 1/2 phosphorylation. Addition of geranylgeranyl PPi reverses statin-induced loss of ERK1/2 phosphorylation and apoptosis. By establishing and evaluating the inducible Raf-1:ER system in AML cells, we show that constitutive activation of the Raf/MAPK kinase (MEK)/ERK pathway significantly represses but does not completely block lovastatin-induced apoptosis. Our results strongly suggest statins trigger apoptosis by regulating several signaling pathways, including the Raf/MEK/ERK pathway. Indeed, down-regulation of the Raf/MEK/ERK pathway potentiates statin-induced apoptosis because exposure to the MEK1 inhibitor PD98059 sensitizes AML cells to low, physiologically achievable concentrations of lovastatin. Our study suggests that lovastatin, alone or in combination with a MEK1 inhibitor, may represent a new and immediately available therapeutic approach to combat tumors with activated ERK1/2, such as AML.     

甲氨喋呤对肠黏膜上皮细胞增殖和凋亡影响的研究

目的:探讨甲氨喋呤对肠黏膜上皮IEC-6细胞增殖和凋亡的影响。方法:采用CCK-8法检测细胞增殖效应,TUNEL的流式细胞术分析凋亡细胞,分光光度法检测细胞内Caspase-3活性程度。结果:1)实验组细胞生长抑制率明显高于对照组,且随MTX药物浓度的增加和作用时间的延长而增加。2)0.05、0.5和5μg/mL MTX作用24 h,细胞凋亡率增加。与对照组相比,差异有统计学意义,P<0.01。3)0.05、0.5和5μg/mL MTX作用24 h,Caspase-3活性增加,3组Caspase-3的活性分别是对照组的1.97、3.07和5.01倍。与对照组相比,各浓度药物组Caspase-3活性明显增强(P<0.05),且呈浓度依赖性。结论:甲氨喋呤对IEC-6细胞增殖有抑制作用,并通过诱导Caspase-3活化导致细胞凋亡。     

Radiosensitization of mouse intestinal epithelial cells with BudR

For the radiosensitization of the repair rich epithelial cells of small intestine, BudR (B.U.) was continuously infused into mice. Its uptake into the DNA, as shown by the substitution rate (S.R.) of thymine to B.U., was dose-dependent in low dose, but above the 4 mg/d/head it did not increased. The radiosensitization effect was assayed by the clonogenecity of the cells, and (1) the repair capacity (recovery factor, RF.) of the cells and (2) the isoeffect dose (I.D) were obtained. From these data, their enhancement ratios (E.R) were estimated. E.R. by R.F. increased remarkably both in low dose and in low S.R., but showed the plateau at about 10 level after 4 mg/d/h of dose or 10% of S.R. Whereas E.R. by I.D. increased linearly in dose or it did quadratically in S.R. From these results, it was discussed that radiosensitization by debromozation of B.U. was seen in low dose, and the direct cytocidal effect of B.U. became dominant with the dose-increase. Also the clinical application of B.U. was discussed in cell kinetical aspect of B.U. labelling as well as the progress of infusion techniques.     

Isoflavones inhibit intestinal epithelial cell proliferation and induce apoptosis in vitro.

There have been many reports that high soya-based diets reduce the risk of certain types of cancer. This effect may be due to the presence of high levels of isoflavones derived from the soya bean, particularly genistein which has been shown to be a protein tyrosine kinase (PTK) inhibitor and have both oestrogenic and anti-oestrogenic properties. We have examined the effect of genistein and a number of novel synthetic analogues on both normal (IEC6, IEC18) and transformed (SW620, HT29) intestinal epithelial cell lines. Responses were compared to those elicited by oestradiol, the anti-oestrogen tamoxifen, and the tyrosine kinase inhibitor tyrphostin. Genistein and tamoxifen were potent inhibitors of cell proliferation. Of seven novel isoflavones tested, none were more potent inhibitors than genistein, and all displayed similar relative activities across the different cell lines. In addition to inhibiting cell proliferation, cell death via apoptosis was observed when the cells were exposed to the isoflavones and all but one exhibited PTK inhibitory activity. These data suggest that by reducing proliferation and inducing apoptosis, possibly due in part to PTK inhibition, isoflavones may have a role in protecting normal intestinal epithelium from tumour development (reducing the risk) and may reduce colonic tumour growth.     

Mechanism of ASC-mediated apoptosis: bid-dependent apoptosis in type II cells

Apoptosis-associated speck-like protein containing a CARD (ASC) is an adaptor molecule that mediates apoptotic and inflammatory signals, and implicated in tumor suppression. However, the mechanism of ASC-mediated apoptosis has not been well elucidated. Here, we investigated the molecular mechanisms of ASC-mediated apoptosis in several cell lines using a caspase recruitment domain 12-Nod2 chimeric protein that transduces the signal from muramyl dipeptide into ASC-mediated apoptosis. Experiments using dominant-negative mutants, small-interfering RNAs and peptide inhibitors for caspases indicated that caspase-8 was generally required for ASC-mediated apoptosis, whereas a requirement for caspase-9 depended on the cell type. In addition, caspase-like apoptosis-regulatory protein (CLARP)/Fas-like inhibitor protein, a natural caspase-8 inhibitor, suppressed ASC-mediated apoptosis, and Clarp-/- mouse embryonic fibroblasts were highly sensitive to ASC-mediated apoptosis. Bax-deficient HCT116 cells were resistant to ASC-mediated apoptosis as reported previously, although we failed to observe colocalization of ASC and Bax in cells. Like Fas-ligand-induced apoptosis, the ASC-mediated apoptosis was inhibited by Bcl-2 and/or Bcl-XL in type-II but not type-I cell lines. Bid was cleaved upon ASC activation, and suppression of endogenous Bid expression using small-interfering RNAs in type-II cells reduced the ASC-mediated apoptosis. These results indicate that ASC, like death receptors, mediates two types of apoptosis depending on the cell type, in a manner involving caspase-8.     

多西他赛诱导HL60细胞凋亡的实验研究

目的:探讨多西他赛诱导HL60细胞凋亡的作用机制。方法:应用形态学方法、流式细胞术、DNA凝胶电泳和Annexin V标记等方法检测细胞凋亡的发生,应用RT-PCR检测凋亡相关基因Fas、bcl-2和c-myc表达的变化。结果:多西他赛对HL60细胞的生长有明显的抑制作用。多西他赛使细胞分裂阻滞于G2M期,并诱导肿瘤细胞发生凋亡:具有典型的凋亡形态,细胞固缩,核染色质呈周边凝聚,形成凋亡小体,胞膜完整;DNA凝胶电泳呈凋亡特有的ladder带;FCM检测出现Sub-G1峰,0·1μmol/L多西他赛作用72h的apo%最高为33·46%;凋亡相关基因Fas转录水平比用药前增强,bcl-2和c-myc无明显变化;结论:多西他赛可诱导HL60细胞凋亡,可能主要与促进Fas基因表达有关。     

多西他赛诱导HL60细胞凋亡的实验研究

目的：探讨多西他赛诱导HL60细胞凋亡的作用机制。方法：应用形态学方法、流式细胞术、DNA凝胶电泳和Annexin V标记等方法检测细胞凋亡的发生，应用RT-PCR检测凋亡相关基因Fas、bcl-2和c-myc表达的变化。结果：多西他赛对HL60细胞的生长有明显的抑制作用。多西他赛使细胞分裂阻滞于G2M期，并诱导肿瘤细胞发生凋亡：具有典型的凋亡形态，细胞固缩，核染色质呈周边凝聚，形成凋亡小体，胞膜完整；DNA凝胶电泳呈凋亡特有的ladder带；FCM检测出现Sub-G1峰，0．1μmol／L多西他赛作用72h的apo％最高为33．46％；凋亡相关基因Fas转录水平比用药前增强，bcl-2和c-myc无明显变化；结论：多西他赛可诱导HL60细胞凋亡，可能主要与促进Fas基因表达有关。     

Proteomic analysis of intestinal epithelial cells expressing stabilized beta-catenin

Aberrant accumulation of beta-catenin protein because of mutation of either the beta-catenin or adenomatous polyposis coli gene plays an essential role in the development of colorectal carcinoma. We established previously a stable clone of the rat small intestinal epithelial cell line IEC6, which is capable of inducing stabilized beta-catenin protein lacking NH(2)-terminal glycogen synthase kinase-3beta phosphorylation site under a strict control of the tetracycline-regulatory system. This clone, IEC6-TetOFF-beta-catenin DeltaN89, shows in vitro polypoid growth on the removal of doxycycline and seems to be an appropriate model for analyzing the molecular mechanisms of early intestinal carcinogenesis. Of >2000 protein spots displayed by newly developed two-dimensional difference gel electrophoresis, 22 were found to be up- or down-regulated on the induction of stabilized beta-catenin. The majority of these proteins fell into two categories: (a) redox-status regulatory proteins and (b) cytoskeleton-associated proteins. Representatively, a key redox-status regulatory protein, manganese superoxide dismutase, up-regulated in IEC6 cells expressing stabilized beta-catenin protein, was overexpressed in adenoma and adenocarcinoma cells of familial adenomatous polyposis patients in parallel with the accumulation of beta-catenin. These results suggest that aberrant accumulation of beta-catenin might contribute to colorectal carcinogenesis by affecting redox status in the mitochondria of intestinal epithelial cells.     

Protective effect of aged garlic extract (AGE) on the apoptosis of intestinal epithelial cells caused by methotrexate

Purpose  Methotrexate (MTX) causes intestinal damage, resulting in diarrhea. The side effects often disturb the cancer chemotherapy. We previously reported that AGE protected the small intestine of rats from the MTX-induced damage. In the present paper, the mechanism of the protection of AGE against the MTX-induced damage of small intestine was investigated, using IEC-6 cells originating from rat jejunum crypt. Methods  The viability and apoptosis of IEC-6 cells were examined in the presence of MTX and/or AGE. Results  The viability of IEC-6 cells exposed to MTX was decreased by the increase of MTX concentration. The MTX-induced loss of viable IEC-6 cells was almost completely prevented by the presence of more than 0.1% AGE. In IEC-6 cells exposed to MTX, the cromatin condensation, DNA fragmentation, caspase-3 activation and cytochrome c release were observed. These were preserved to the control levels by the presence of AGE. MTX markedly decreased intracellular GSH in IEC-6 cells, but the presence of AGE in IEC-6 cells with MTX preserved intracellular GSH to the control level. IEC-6 cells in G2/M stage markedly decreased 72 h after the MTX treatment, which was preserved to the control level by the presence of AGE. These results indicated that AGE protected IEC-6 cells from the MTX-induced damage. Conclusions  The MTX-induced apoptosis of IEC-6 cells was shown to be depressed by AGE. AGE may be useful for the cancer chemotherapy with MTX, since AGE reduces the MTX-induced intestinal damage.     

Downregulation of topoisomerase I in differentiating human intestinal epithelial cells.

To better understand the increased sensitivity of proliferating intestinal epithelial cells to topoisomerase I (topo I) poisons, we examined differentiation of a human intestinal cell line (Caco-2) in the presence of camptothecin (CPT) and its analogs irinotecan (CPT-11) and topotecan (TPT). The prodrug CPT-11 exerts its antitumor activity after transformation to SN-38. We show that cleavable complex formation in vivo (on genomic DNA) induced by CPT or SN-38 is 4- to 7-fold reduced in fully differentiated cells relative to undifferentiated cells. TPT-induced cleavable complexes, however, are reduced by 30-fold. In contrast, CPT-11-driven cleavable complexes did not change during cell differentiation. In general, cytotoxicity closely paralleled cleavable complex formation, as attested to by the four- to 6-fold decrease in cytotoxicity in fully differentiated cells treated with CPT and SN-38 compared with proliferating cells. Topo I activity and polypeptide levels decreased 4-fold over the course of differentiation. This reduction occurs as Caco-2 cells approach G(1) and simultaneously differentiate. In contrast, human diploid fibroblasts do not show a reduction in topo I when entering G(1); therefore, topo I downregulation is a differentiation-specific event in the Caco-2 cell line. Cleavable complex formation and cytotoxicity induced by CPT and SN-38 correlate with topo I level and activity in cells at different stages in their differentiation. Thus, high target levels correspond closely with drug sensitivity and since proliferating cells contain larger amounts of topo I, we conclude that epithelial crypt cells probably succumb to chemotherapy involving topo I poisons.     

MECHANISM OF TAXOL-INDUCED APOPTOSIS IN HUMAN BREAST CANCER CELLS

ＭＥＣＨＡＮＩＳＭＯＦＴＡＸＯＬＩＮＤＵＣＥＤＡＰＯＰＴＯＳＩＳＩＮＨＵＭＡＮＢＲＥＡＳＴＣＡＮＣＥＲＣＥＬＬＳＣｈｅｎＬｉｒｏｎｇ陈丽荣ＺｈｅｎｇＳｈｕ郑树ＭＣＷｉｌｉｎｇｈａｍＦａｎＷｅｉｍｉｎ范伟民ＣａｎｃｅｒＩｎｓｔｉｔｕｔｅ，Ｚｈ...     

紫杉醇诱发人乳癌细胞凋亡的机制研究

探讨紫杉醇诱发人乳腺癌细胞凋亡的发生机制。方法应用细胞形态观察、琼脂糖凝胶电泳、流式细胞仪、活细胞视频观察和蛋白印迹免疫法进行检测和观察。结果癌细胞在紫杉醇作用下,细胞分裂阻滞在分裂期的中期,并诱导细胞发生凋亡。凋亡细胞表现为细胞固缩,核染色质凝聚或者断裂。细胞ＤＮＡ裂解片段呈现典型的“阶梯状”排列的条带。凋亡抑制基因Ｂｃｌ－２在细胞凋亡过程中呈低表达并发生修饰反应,而凋亡诱导基因Ｂａｘ先呈高表达然后表达降低。结论紫杉醇诱发的人乳癌细胞的凋亡与细胞分裂期阻滞密切相关,Ｂｃｌ－２和Ｂａｘ在紫杉醇诱发的人乳癌细胞凋亡中可能起着重要的调控作用     

Internalisation of the Bowman-Birk protease inhibitor by intestinal epithelial cells

Protease inhibitors have been shown to be effective suppressors of carcinogenesis in vitro and in vivo. For example, the soybean-derived Bowman-Birk inhibitor (BBI) suppresses dimethylhydrazine-induced colon carcinogenesis in mice. Relatively little is known about the effects of protease inhibitors on intestinal epithelial cells. In the present study, we have investigated the interaction of the anticarcinogenic BBI with intestinal epithelial cells. At the concentrations examined, BBI was non-toxic and had no effect on the doubling time, saturation density or rate of DNA synthesis by these cells. This compound was taken up by these cells in a time dependent manner and was present in the cells for 12 h following a 2 h incubation with BBI. Subcellular fractionation experiments demonstrated that the bulk of the internalised inhibitor was present in the cytosol. Analysis of BBI from treated cells on a chymotrypsin affinity column revealed that active inhibitor was present in the cells. Our results indicate that the BBI is internalised by colonic epithelial cells which would allow BBI to inhibit critical intracellular proteases and thus suppress malignant transformation.