依托咪酯对大鼠脑缺血再灌注损伤的保护作用及机制

目的 探讨依托咪酯对大鼠脑缺血再灌注损伤的神经保护作用及其机制.方法 将120只♂ SD大鼠随机均分为假手术组、模型组和依托咪酯高、低剂量组,ip给予各组大鼠相应药物后,采用线栓法制备大脑中动脉栓塞再灌注模型,评价依托咪酯对大鼠脑缺血再灌注的保护作用.参照Bederson评分标准评价大鼠的神经功能损伤,采用TTC染色法观察大鼠的脑梗死体积,采用免疫组化法分析大鼠海马CA1区NAIP、caspase-3及caspase-7蛋白的表达,采用HE染色法观察大鼠脑组织的病理变化.结果 与模型组比较,依托咪酯组大鼠的神经功能损伤和脑梗死容积明显减轻,大鼠海马CA1区NAIP蛋白的表达明显增强,caspase-3蛋白的表达明显减少;依托咪酯高、低剂量组间比较无明显差异;各组大鼠海马CA1区caspase-7蛋白的表达无显著差异.结论 依托咪酯对大鼠脑缺血再灌注造成的脑损伤具神经细胞保护作用,其机制可能与上调NAIP蛋白的表达、抑制caspase-3蛋白的活化有关.     

SP600125对大鼠脑缺血再灌注神经元的保护作用

目的探讨SP600125-JNK特异性抑制剂对大鼠脑缺血再灌注神经元损伤的保护性作用及其作用机制。方法雄性SD大鼠54只,体重230～250g,随机分成假手术组(SH组),缺血再灌注组(IR组)和JNK抑制剂SP600125组(SP组),每组根据再灌注时间分为30min、24h和72h3个亚组,每亚组6只动物。采用4-VO法建立SD大鼠脑缺血模型,三组于缺血前30min侧脑室注射DMSO,DMSO及JNK抑制剂SP600125(溶媒采用DMSO),容积均为10μl;脑缺血再灌注后30min、24h、72h免疫组织化学方法测定各时间点海马CA1区Bcl-2和Bax蛋白表达阳性细胞数量,TUNEL法检测CA1区凋亡细胞。结果缺血再灌注使海马CA1区Bcl-2和Bax阳性锥体细胞数目表达增加,再灌注24h阳性锥体细胞数目表达至高峰(P<0.01),再灌注24～72h可见阳性锥体细胞数目表达减少(P<0.05)。其中SP组Bcl-2阳性锥体细胞数目显著多于IR组(P<0.05),而Bax阳性锥体细胞数目显著小于IR组(P<0.05)。脑缺血再灌注后海马CA1区神经元存活数目SP组高于IR组(P<0.01),凋亡细胞数目低于IR组(P<0.01)。结论 SP600125对大鼠脑缺血再灌注神经元损伤具有保护作用。     

2-脱氧葡萄糖对脑缺血再灌注模型大鼠脑组织中葡萄糖调节蛋白78及天冬氨酸半胱氨酸蛋白酶-12的影响研究

目的:探讨2-脱氧葡萄糖(2-DG)对脑缺血再灌注(IR)模型大鼠脑组织中葡萄糖调节蛋白78(GRP78)及天冬氨酸半胱氨酸蛋白酶-12(caspase-12)的影响。方法:取大鼠随机分为假手术组、模型组和2-DG组(2-DG100mg·kg-1),每组60只,后2组建立局灶性脑IR模型,假手术组行手术但不插入线栓。建模前7d开始给药,每天1次,连续7d,考察建模后3、6、12、24、48h各组大鼠海马CA1区细胞凋亡情况(阳性细胞率)、GRP78和caspase-12蛋白及其mRNA的表达情况。结果:与假手术组比较,模型组和2-DG组阳性细胞率、GRP78和caspase-12蛋白及其mRNA表达均明显升高(P均<0.01);与模型组比较,2-DG组阳性细胞率、cas-pase-12蛋白及其mRNA表达明显降低,GRP78蛋白及其mRNA表达明显升高(P<0.05或P<0.01)。结论:2-DG可能通过上调GRP78和下调caspase-12的表达来预防脑IR损伤。     

高血压大鼠局灶脑缺血再灌注后X线修复交叉互补组1蛋白表达及DNA片段化损伤

目的　观察肾性高血压大鼠局灶脑缺血再灌注后DNA修复蛋白X线修复交叉互补组 1(XRCC1)蛋白的表达及与DNA片段化损伤的关系。方法　采用双肾双夹法建立肾性高血压大鼠模型 ,在此基础上采用线栓法制作大脑中动脉闭塞模型 ,采用免疫组织化学方法观察假手术组和缺血再灌注后 3h、6h、12h、2 4hXRCC1蛋白表达 ,采用TUNEL方法检测DNA片段化损伤。结果　免疫组织化学染色显示 ,假手术组大脑皮质和海马区出现大量XRCC1表达的阳性细胞 ,再灌注 3h缺血区皮质和海马CA1区XRCC1表达阳性细胞减少 ,即缺血区皮质和海马CA1区XRCC1灰度值升高 ,并一直持续到缺血再灌注 2 4h。缺血再灌注后 3h、6h、12h和 2 4h与假手术组相比差异有显著意义 (P <0 0 5 )。TUNEL染色显示 ,假手术组大脑皮质和海马CA1区未见阳性细胞 ,再灌注 2 4h缺血区皮质和海马CA1区可见较多阳性细胞。结论　脑缺血再灌注后XRCC1蛋白免疫活性下降和DNA修复机制的失败与DNA的片段化损伤及凋亡的发生有关。     

脑缺血再灌注损伤大鼠海马神经元凋亡及c—fos蛋白表达研究

目的：观察脑缺血再灌注损伤大鼠海马神经元凋亡及c-fos蛋白的表达。方法：采用大脑中动脉阻断法制备大鼠脑缺血再灌注模型,取海马组织,用免疫组织化学方法检测海马神经元c-fos蛋白表达及TUNEL法观察细胞凋亡情况。结果：脑缺血再灌注损伤大鼠与对照组比较海马区c-fos蛋白阳性细胞表达增强（P〈0．05）,凋亡细胞表达增多（P〈0．05）。结论：脑缺血再灌注损伤大鼠海马区c-fos蛋白阳性细胞表达增强,凋亡细胞表达增多。     

原花青素对大鼠局灶性脑缺血再灌注损伤后海马线粒体CytC的释放和Caspase-9的影响研究

目的:研究原花青素对大鼠局灶性脑缺血再灌注所致线粒体损伤的保护作用机制。方法:48只Wistar大鼠随机分为假手术组,缺血再灌注模型组,原花青素高、低剂量(400、40mg.kg-1)组,各组灌胃给予相应试药后30d,采用线栓法阻塞大鼠大脑中动脉(MCA)制作脑缺血再灌注损伤模型,24h后处死取脑。利用免疫荧光方法测定各组小鼠细胞色素C(CytC)的表达,以逆转录聚合酶链反应(RT-PCR)技术检测半胱氨酸蛋白酶(caspase)-9mRNA的表达。结果:与模型组比较,原花青素组CytC阳性细胞明显增多,而caspase-9mRNA表达减弱(P<0.05)。结论:原花青素可以抑制海马CA1区神经元CytC的释放,并减弱cas-pase-9mRNA的表达,对脑缺血再灌注损伤产生保护作用。     

异丙酚对兔缺血/再灌注损伤心肌半胱天冬酶-12的影响

目的观察异丙酚对兔缺血/再灌注损伤心肌半胱天冬酶-12(caspase-12)的影响,从内质网角度探讨异丙酚对减少缺血/再灌注损伤心肌细胞凋亡的机制.方法健康雄性新西兰大白兔24只,体重2.1～2.3 kg.随机分为假手术组(Sham组)、缺血/再灌注组(I/R组)和异丙酚组(P组)(每组8只).术中胸膜破裂和死亡者不纳入实验,再按照随机原则在相同条件下予以补齐.实验结束后取左心室缺血/再灌注区心肌组织,免疫组织化学方法检测caspase-12、半胱天冬酶-3(caspase-3),用Motic 6.0图像分析系统进行处理,比较各观测指标平均光密度值(Average optical value AO值);用流式细胞检测技术(flow cytometry,FCM)及DNA原位末端缺口标记法(TUNEL法)检测缺血/再灌注区心肌细胞凋亡.结果 Sham组caspase-12、caspase-3低表达;FCM检测有少量凋亡早期细胞,TUNEL染色见少量阳性细胞;与Sham组比较,I/R组和P组caspase-12、caspase-3表达增加(P＜0.05),FCM检测和TUNEL染色见凋亡细胞数增加(P＜0.05);与I/R组比较,P组Caspase-12、Caspase-3表达下降(P＜0.05),FCM和TUNEL染色见凋亡心肌细胞数减少(P＜0.05).结论抑制caspase-12介导的caspase级联反应性凋亡途径的激活是异丙酚减少缺血/再灌注损伤心肌细胞凋亡的机制之一.     

血府逐瘀汤对大鼠脑缺血再灌注后神经细胞凋亡及半胱氨酸蛋白酶表达的影响

目的观察血府逐瘀汤对大鼠脑缺血再灌注损伤早期神经细胞凋亡、Bcl-2、Bax蛋白及半胱氨酸蛋白酶(caspase-3)表达的影响。方法将40例健康SD大鼠随机分为中药组和对照组各20只。中药组将药物血府逐瘀汤按人与大鼠体表面积折算动物等效药量,按生药25g·kg-1·d-1灌胃。对照组同期给予等量的葡萄糖生理盐水灌胃,连续灌胃3d后采用线栓法制作大鼠大脑中动脉局灶性缺血再灌注损伤动物模型。40只大鼠建模成功后测量各组神经功能缺损评分,而后腹腔麻醉断头杀死大鼠,取侧脑室层面额叶皮层组织制备石蜡切片,TUNEL法检测脑皮层凋亡神经细胞,用氯化三苯四氮唑染色及免疫组化染色测量脑组织caspase-3阳性细胞数及Bcl-2、Bax蛋白表达。结果建模成功后,中药组神经功能缺损评分为(1.84±0.49)分低于对照组的(3.14±0.61)分,差异有统计学意义(P<0.05)。2组模型大鼠大脑皮层内均检测到凋亡细胞,其中中药组大鼠皮层内凋亡细胞指数明显低于对照组,差异有统计学意义(P<0.05)。中药组Bcl-2蛋白阳性细胞指数明显高于对照组,Bax蛋白阳性细胞指数及脑组织中caspase-3阳性细胞数明显低于对照组,差异均有统计学意义(P<0.05)。结论血府逐瘀方能够降低脑缺血再灌注后大鼠神经功能缺损程度,其机制可能与抑制低缺血再灌注后脑组织中caspase-3及Bax蛋白的表达,上调Bcl-2蛋白表达有关。     

黄芩苷对脑缺血-再灌注损伤大鼠神经细胞凋亡及相关基因表达的影响

目的:研究黄芩苷对大鼠局灶性脑缺血-再灌注损伤后神经细胞凋亡以及半胱氨酸天冬氨酸蛋白酶(caspase)-3、热休克蛋白(HSP)70表达的影响。方法:96只Wistar大鼠随机分为假手术组、脑缺血再灌注模型组、黄芩苷组(50,100,200 mg·kg-1),以及尼莫地平(0．4 mg·kg-1)组。利用大鼠大脑中动脉内栓线阻断法制备局灶性脑缺血-再灌注损伤模型,通过HE染色、流式细胞术、免疫组化以及RT- PCR等方法,观察黄芩苷对大鼠局灶性脑缺血-再灌注损伤后脑组织病理形态学改变、神经细胞凋亡率以及caspase-3、HSP70表达的影响。结果:黄芩苷可明显改善脑缺血-再灌注损伤所致的大鼠脑组织病理形态学改变,降低神经细胞凋亡率,抑制促凋亡基因caspase-3的表达,促进抑凋亡基因HSP70的表达。结论:黄芩苷对大鼠局灶性脑缺血-再灌注损伤具有保护作用,其作用机制可能与黄芩苷抑制caspase-3表达,促进HSP70表达,从而发挥抗凋亡作用有关。     

松龄血脉康对大鼠局灶性脑缺血-再灌注损伤和细胞凋亡的影响

目的探讨松龄血脉康对局灶性脑缺血-再灌注损伤和细胞凋亡的作用及机制。方法线栓法制作大鼠大脑中动脉阻塞(MCAO)模型。观察松龄血脉康对脑缺血-再灌注损伤大鼠行为学、海马CA1区凋亡细胞数、细胞超微结构的影响;运用免疫组织化学法检测海马凋亡相关基因Bcl-2、Bax蛋白免疫反应阳性细胞表达。结果松龄血脉康显著降低MCAO模型大鼠神经功能缺损评分,明显减少海马组织凋亡细胞数,促进海马神经元修复,松龄血脉康组海马Bcl-2的表达明显增加、Bax的表达降低。结论松龄血脉康可减少脑缺血-再灌注损伤后神经元的凋亡而发挥脑保护作用,机制可能与增强Bcl-2的表达及抑制Bax的表达有关。     

右美托咪定对感染性休克大鼠脾脏及胸腺caspase-3、caspase-8、caspase-9表达及淋巴细胞凋亡的影响

目的研究右美托咪定对内毒素诱导感染性休克大鼠细胞免疫的作用。方法选取12周龄雄性Walse大鼠18只,采用数字表法随机分为空白组(S组)、内毒素组(E组)和右美托咪定治疗组(D组),每组6只。S组静脉推注1.0 mL/kg 0.9%生理盐水后,持续泵入同浓度的生理盐水,E组、D组均采用静脉注射内毒素(LPS)建立感染性休克大鼠模型,D组在注射内毒素后持续微泵右美托咪定。持续监测心率(HR)、呼吸、有创动脉血压(ABP)及平均动脉压(MAP),用药后0.5、1、2、3、4、6 h检测血清中IL-4(白介素-4)、IL-10、IFN-γ(γ干扰素)和IL-2的浓度,6 h后处死大鼠,检测大鼠脾脏及胸腺caspase-3、caspase-8、caspase-9活性,测定淋巴细胞凋亡情况及Th1/Th2。结果①与S组相比,E组、D组大鼠血清的抗炎因子IL-4、IL-10和促炎因子IFN-γ、IL-2均显著提高,其差异均有统计学意义(P<0.05)。随着治疗时间延长,E组的IL-4、IL-10水平降低,IFN-γ、IL-2水平升高;D组IL-4、IL-10水平升高,IFN-γ、IL-2水平降低;两组比较差异有统计学意义(P<0.05)。②与E组相比,D组大鼠脾脏及胸腺caspase-3、caspase-8、caspase-9表达及淋巴细胞凋亡的阳性细胞数均显著减少,差异有统计学意义(P<0.05)。③D组大鼠脾脏及胸腺Th1/Th2比率均显著高于E组,差异有统计学意义(P<0.05)。结论右美托咪定对感染性休克大鼠具有减轻炎症反应和改善免疫功能的作用,有利于改善预后。     

Non-apoptotic functions of caspase-8

Caspases are a family of aspartate-specific cysteine proteases that have been well characterized for their function in apoptosis signaling. Caspase-8 is implicated as an initiator caspase in death receptor-induced signaling to apoptosis and has been studied most extensively for its role in CD95-induced cell death. CD95 stimulation induces the binding of caspase-8 to a death-inducing signaling complex, leading to its autocatalytic cleavage and the formation of a caspase-8 homodimer, which is subsequently released into the cytosol where it further mediates the apoptotic signaling cascade. Over the past few years, however, several non-apoptotic functions for caspase-8 have been described, indicating that this protease plays a much more diverse role than previously assumed. Here we review the role of caspase-8 in embryonic development, monocyte differentiation, T and B cell proliferation, and the activation of NF-κB.     

Camalexin induces apoptosis in T-leukemia Jurkat cells by increased concentration of reactive oxygen species and activation of caspase-8 and caspase-9

Camalexin, a major indole phytoalexin of Arabidopsis thaliana, accumulates in various cruciferous plants in response to environmental stress and reportedly displays antimicrobial activities against various plant pathogens. However, its cytotoxicity against eukaryotic cells and potential as a prospective drug for human diseases has been examined only in a limited context. Our data demonstrate the time- and concentration-dependent cytotoxicity of camalexin on human T-leukemia Jurkat cells in the micromolar range, and the lower potency of cytotoxic effects on human lymphoblasts and primary fibroblasts. Cytotoxicity of camalexin is enhanced by the glutathione-depleting agent buthionine sulfoximine and completely blocked by pan-caspase inhibitor Z-VAD-FMK. Treatment of Jurkat cells with camalexin resulted in activation of caspase-8, caspase-9, caspases-3/7, and apoptosis that was detected by the presence of a sub-G1 population of cells, externalization of phosphatidyl serine and decreased mitochondrial membrane potential. Staining with 2',7'-dichlorodihydrofluorescein diacetate and dihydroethidium bromide displayed increased concentration of reactive oxygen species (ROS) early in camalexin-treated Jurkat cells, prior to the onset of apoptosis, while staining with MitoSOX(?) dye identified mitochondria as a source of increased ROS. Our data suggest that this phytochemical, which has a wide range of predicted pharmacological activities, induces apoptosis in Jurkat leukemia cells through increased ROS followed by dissipation of mitochondrial membrane potential and execution of caspase-9- and caspase-8-initiated apoptosis. This is, to the best of our knowledge, the first report on antileukemic activity and mode of action of this unique indole phytoalexin.     

Differential protection with inhibitors of caspase-8 and caspase-3 in murine models of tumor necrosis factor and Fas receptor-mediated hepatocellular apoptosis

Excessive apoptosis has been implicated in a number of acute and chronic human diseases. The activation of caspases has been shown to be critical for the apoptotic process. The objective of this investigation was to evaluate the beneficial effects and mechanism of action of the caspase-8 inhibitor IETD-CHO and the caspase-3 inhibitor DEVD-CHO against tumor necrosis factor (TNF)-induced hepatocellular apoptosis in vivo and compare these results to effects of the same inhibitors against Fas-induced apoptosis. Treatment of C3Heb/FeJ mice with 700 mg/kg galactosamine/100 microg/kg endotoxin induced parenchymal apoptosis (indicated by caspase-3 activation and morphology) and severe liver injury (indicated by the increase in plasma alanine aminotransferase activities and histology) at 7 h. Treatment with IETD-CHO or DEVD-CHO (10 mg/kg at 3, 4.5, and 5.5 h) significantly attenuated caspase-3 activation and liver injury. Western analysis showed that DEVD-CHO had no effect while IETD-CHO substantially reduced procaspase-3 and procaspase-9 processing. On the other hand, caspase-3 activation and liver injury by the anti-Fas antibody Jo-2 was completely prevented by a single dose of DEVD-CHO and, as previously shown, by IETD-CHO at 90 min. Both inhibitors prevented procaspase-3 and procaspase-9 processing. Thus, there are fundamental differences in the efficacy of caspase inhibitors in these two models. We conclude that Fas may rely exclusively on caspase-8 activation and mitochondria to activate caspase-3, which can process more procaspase-8 and thus propagate the amplification of the apoptotic signal. TNF can activate a similar signaling pathway. However, alternative signaling mechanisms seem to exist, which can compensate if the main pathway is blocked.     

Design and synthesis of new nonpeptide caspase-3 inhibitors

Highly effective computer-aided (virtual) and real biological screening over quinoline derivatives is described, which has led to the discovery of a new structural class of caspase-3 inhibitors. This enzyme (belonging to the group of cysteine proteases) is a promising therapeutically-significant biological target that is involved in the development of various pathological states in the human organism. The virtual screening method is based upon evaluation of a target-specific profile of compounds by means of a special algorithm intended for the analysis of multiparametric data arrays (self-organizing Kohonen maps). Using this approach, it is possible to carry out directed selection of compounds for a targeted synthesis. The biological screening among synthesized compounds led to a series of new effective inhibitors of caspase-3, the most active of which possess effective inhibiting concentrations in the range of IC₅₀ = 4–30 nM. The nonpeptide nature of the new chemotype offers potentially favorable pharmacokinetic parameters, while its belonging to large libraries (obtained by means of parallel combinatorial synthesis in solution) facilitates the subsequent optimization of active compounds. __________ Translated from Khimiko-Farmatsevticheskii Zhurnal, Vol. 40, No. 3, pp. 10–14, March, 2006.     

Lovastatin-induced cardiac toxicity involves both oncotic and apoptotic cell death with the apoptotic component blunted by both caspase-2 and caspase-3 inhibitors

The objective of this study was to evaluate the cardiac toxicity of the HMG-CoA reductase inhibitors by testing the hypothesis that lovastatin induces apoptotic and/or oncotic cell death in the myocyte element of the heart and further that cell death is mediated through interruption of the mevalonate pathway and that apoptosis is induced through activation of caspase-2 and caspase-3. Cardiomyocytes were cultured from embryonic chick heart. Lovastatin-induced apoptosis in these cells was demonstrated by three independent techniques, namely (1) FACS analysis of low DNA content by propidium iodide (PI); (2) microscopic assessment for cellular changes of apoptosis; and (3) FACS analysis of cells stained with PI and fluorescein diacetate. Lovastatin produced a concentration-dependent increase in apoptotic cell death and 100 microM lovastatin showed over a 4-fold increase in apoptosis compared to control. Lovastatin also induced oncotic cell death, as there was a 2.5-fold increase in the amount of oncotic cell death compared to control. Lovastatin-induced apoptosis operated, in part, through the mevalonate pathway. The caspase-2 inhibitor z-VDVAD-fmk and the caspase-3 inhibitor Ac-DEVD-CHO reduced the extent of lovastatin-induced cardiac apoptosis. In contrast, lovastatin-induced oncosis was not only insensitive to these caspase-2 or -3 inhibitors but occurred through a mevalonate-independent mechanism of action. In summary, lovastatin-induced cardiotoxicity is complex and represents the sum of two distinct modes of cell death operating in part through the mevalonate pathway with the apoptotic component subject to modification by inhibitors of the initiator caspase, caspase-2, as well as the effector caspase, caspase-3.     

Effects of sodium fluoride treatment in vitro on cell proliferation,apoptosis and caspase-3 and caspase-9 mRNA expression by neonatal rat osteoblasts

Long-term excessive fluoride intake is linked to skeletal disease. Skeletal health is influenced by the balance between bone formation and resorption of which osteoblast function is critical. The objectives of this study were to determine the effect of fluoride treatment on osteoblast proliferation, apoptosis and caspase-3 and caspase-9 mRNA expression in vitro. Neonatal rat osteoblasts were cultured in the presence of varying concentrations (0.5–30 mg/l) of sodium fluoride and effects of treatments were determined. Treatment with sodium fluoride inhibited osteoblast proliferation in a dose-dependent fashion and effects were maximal after 120 h incubation. A significant increase in osteoblast apoptosis was observed (after 24 and 72-h treatment) in response to the lowest dose of sodium fluoride (0.5 mg/l) and osteoblast apoptosis was further increased in response to higher doses. Increased-osteoblast caspase-3 and caspase-9 mRNA was also observed in response to sodium fluoride treatment (5 mg/l) for 72 h. Results indicate that negative effects of excess fluoride on skeletal health may be mediated in part by inhibition of osteoblast survival.     

Inhibition of caspase-3 activity and activation by protein glutathionylation

Protein glutathionylation is a post-translational modification that may account for a broad mechanism of redox signaling. The caspase family of cysteine proteases represents a potential target for regulation by glutathionylation. To examine this, caspase proteins, derived from HL-60 cells after activation with actinomycin D, were incubated with GSSG. Total protein glutathionylation was enhanced and caspase-3 activity was inhibited in a dose- and time-dependent manner by GSSG. Caspase inhibition was reversible by thiol-specific reducing reagents. Proteolytic activation of caspases was also affected, as the activation of procaspase-3 and procaspase-9 in HL-60 cell extracts induced by cytochrome c and dATP was inhibited by pre-incubation with GSSG. When biotin-labeled GSSG was incubated with recombinant caspase-3, biotin label was found associated with both p12 and p17 subunits of active caspase-3 by non-reducing SDS-PAGE. Caspase-3 glutathionylation was confirmed by matrix assisted laser desorption ionization (MALDI) mass spectrometric analysis of GSSG-treated recombinant caspase-3. Specific sites of glutathionylation were identified as Cys¹³⁵ of the p17 protein (the active site) and Cys⁴⁵ of the p12 protein. These results indicate that glutathionylation of caspase can occur at physiologically relevant concentrations of GSSG and results in the inhibition of caspase activation and activity.     

Environmental chemical-induced bone marrow B cell apoptosis: death receptor-independent activation of a caspase-3 to caspase-8 pathway

Programmed cell death is a critical process in B lymphocyte development. Premature apoptosis in developing B cells could affect the repertoire and number of mature B cells produced. Of particular concern is the ability of environmentally ubiquitous polycyclic aromatic hydrocarbons (PAH) to induce B cell apoptosis within the bone marrow microenvironment in a clonally nonspecific way. Here, models of bone marrow B cell development were used to assess the role of the "extrinsic" apoptosis pathway in PAH-induced apoptosis and to compare PAH-induced apoptosis with that induced during clonal deletion. As demonstrated previously with a nontransformed pro-/pre-B cell line, primary pro-B cells cultured on bone marrow stromal cells underwent apoptosis after exposure to a prototypic PAH, 7,12-dimethylbenz[a]anthracene (DMBA). Apoptosis was preceded by cleavage of caspase-3 (4-6 h) and caspase-8 (6-8 h) and their respective substrates, alpha-fodrin and Bid. Inhibition of caspase-3 blocked caspase-8 activation and apoptosis. Furthermore, a pan-caspase inhibitor blocked apoptosis and activation of both caspases-3 and -8. Cells from mice defective in tumor necrosis factor (TNF)-alpha, TNF-beta, lymphotoxin-beta, or TNFR1, TNFR2, Fas, or death receptor 6 were as susceptible to apoptosis signaling as wild-type cells. These results suggest a complex death receptor-independent B cell apoptosis pathway in which caspase-8 is activated downstream of caspase-3.     

c-FLIP knockdown induces ligand-independent DR5-, FADD-, caspase-8-, and caspase-9-dependent apoptosis in breast cancer cells

Cellular-FLICE inhibitory protein (c-FLIP) is an inhibitor of apoptosis downstream of the death receptors Fas, DR4, and DR5, and is expressed as long (c-FLIP(L)) and short (c-FLIP(S)) splice forms. We found that the knockdown of c-FLIP using small interfering RNA (siRNA) triggered ligand-independent caspase-8- and -9-dependent spontaneous apoptosis and decreased the proliferation of MCF-7 breast cancer cells. Further analysis revealed that an apoptotic inhibitory complex (AIC) comprised of DR5, FADD, caspase-8, and c-FLIP(L) exists in MCF-7 cells, and the absence of c-FLIP(L) from this complex induces DR5- and FADD-mediated caspase-8 activation in the death inducing signaling complex (DISC). c-FLIP(S) was not detected in the AIC, and using splice form-specific siRNAs we showed that c-FLIP(L) but not c-FLIP(S) is required to prevent spontaneous death signaling in MCF-7 cells. These results clearly show that c-FLIP(L) prevents ligand-independent death signaling and provides direct support for studying c-FLIP as a relevant therapeutic target for breast cancers.