Chlamydia trachomatis infection inhibits both Bax and Bak activation induced by staurosporine

We have previously shown that Chlamydia trachomatis inhibits host cell apoptosis and blocks mitochondrial cytochrome c release. We now report that activation of both Bax and Bak, two proapoptotic members of the Bcl-2 family that regulate mitochondrial cytochrome c release, was inhibited in chlamydia-infected cells. This observation has provided new information on the mechanisms of chlamydial antiapoptotic activity.     

亚硒酸钠通过线粒体途径诱导人胃癌SGC-7901细胞凋亡的机制

目的通过检测亚硒酸钠诱导人胃癌SGC-7901细胞系凋亡过程中Bax/Bcl-2、线粒体膜电位和细胞色素C(Cyt C)表达的变化,探讨亚硒酸钠诱导胃癌细胞凋亡的作用机制。方法将人胃癌细胞系SGC-7901细胞加入不同浓度亚硒酸钠(2.5、5.0、10.0mol/L)的培养液中培养24h、48h,免疫细胞化学法和免疫印迹法(Western blotting)检测Bax/Bcl-2蛋白的表达;以罗丹明123(rhodamine123)为细胞染色剂,采用流式细胞技术检测细胞的线粒体膜电位的变化;Western blotting检测细胞质Cyt C和线粒体Cyt C蛋白含量的变化。结果免疫细胞化学法和Western blotting检测结果显示,亚硒酸钠能够能够提高Bax蛋白的表达(P0.05)、降低Bcl-2蛋白的表达(P0.05),且呈剂量依懒性;流式细胞术结果显示,亚硒酸钠能够降低细胞线粒体膜电位;提示:亚硒酸钠可以通过改变Bax、Bcl-2蛋白的含量,降低线粒体的膜电位来诱导细胞凋亡。Western blotting检测结果显示,亚硒酸钠能够提高细胞质Cyt C蛋白的表达(P0.05)并降低线粒体内Cyt C蛋白的表达(P0.05),促使线粒体内的Cyt C向细胞质内释放。结论亚硒酸钠通过上调Bax并下调Bcl-2蛋白表达,降低线粒体膜电位,促进Cyt C从线粒体释放到细胞质,通过线粒体途径诱导人胃癌SGC-7901细胞凋亡。     

Persistent Chlamydia trachomatis infection of HeLa cells mediates apoptosis resistance through a Chlamydia protease-like activity factor-independent mechanism and induces high mobility group box 1 release

Intracellular persistence of Chlamydia trachomatis has been implicated in the development of chronic infection that can result in pelvic inflammatory disease and tubal sterility. By inhibition of host cell apoptosis, chlamydiae have evolved a strategy to maintain the intracellular environment for replication and persistence. Both antiapoptotic host cell-derived factors and the chlamydial protease-like activity factor (CPAF) are involved in Chlamydia-mediated apoptosis resistance. Here, we show that in HeLa cells infected with gamma interferon (IFN-γ)-induced persistent C. trachomatis serovar D, the expression of CPAF is downregulated, and proapoptotic protease substrates are not cleaved. Persistent infection protected HeLa cells from apoptosis when they were exposed to staurosporine. Small-interfering RNA-mediated inhibition of myeloid cell leukemia 1 (Mcl-1) protein upregulation sensitized persistently infected cells for apoptosis. The inhibitor of apoptosis protein 2 (IAP-2) seems not to be relevant in this context because IAP-2 protein was not induced in response to IFN-γ treatment. Although apoptosis was inhibited, persistent infection caused cell membrane disintegration, as measured by the increased release of cytokeratin 18 from HeLa cells. Moreover, persistently infected cells released significantly increased amounts of high mobility group box 1 (HMGB1) protein which represents a proinflammatory damage-associated pattern molecule. The data of this study suggest that cells infected with persistent C. trachomatis are protected from apoptosis independently of CPAF but may promote chronic inflammation through HMGB1 release.     

Coxiella burnetii inhibits activation of host cell apoptosis through a mechanism that involves preventing cytochrome c release from mitochondria

Coxiella burnetii is an obligate intracellular pathogen and the etiological agent of the human disease Q fever. C. burnetii infects mammalian cells and then remodels the membrane-bound compartment in which it resides into a unique lysosome-derived organelle that supports bacterial multiplication. To gain insight into the mechanisms by which C. burnetii is able to multiply intracellularly, we examined the ability of host cells to respond to signals that normally induce apoptosis. Our data show that mammalian cells infected with C. burnetii are resistant to apoptosis induced by staurosporine and UV light. C. burnetii infection prevented caspase 3/7 activation and limited fragmentation of the host cell nucleus in response to agonists that induce apoptosis. Inhibition of bacterial protein synthesis reduced the antiapoptotic effect that C. burnetii exerted on infected host cells. Inhibition of apoptosis in C. burnetii-infected cells did not correlate with the degradation of proapoptotic BH3-only proteins involved in activation of the intrinsic cell death pathway; however, cytochrome c release from mitochondria was diminished in cells infected with C. burnetii upon induction of apoptosis. These data indicate that C. burnetii can interfere with the intrinsic cell death pathway during infection by producing proteins that either directly or indirectly prevent release of cytochrome c from mitochondria. It is likely that inhibition of apoptosis by C. burnetii represents an important virulence property that allows this obligate intracellular pathogen to maintain host cell viability despite inducing stress that would normally activate the intrinsic death pathway.     

Characterization of Apoptotic Activities During Chlamydia trachomatis Infection in Primary Cervical Epithelial Cells

Chlamydiae are obligate intracellular bacteria that infect human epithelial cells. It has been reported that Chlamydia trachomatis, induces apoptosis in epithelial cells, however, the molecular mechanisms responsible for host cell death especially in primary epithelial cells remained largely unknown as most of the studies are in cell line like HeLa. In this study we demonstrated that C. trachomatis induces apoptosis signaling pathway and apoptosis in primary cervical epithelial cells in a time and dose dependent manner. Live cervical epithelial cells were isolated from endocervical cells and induction was done with chlamydial EBs. Our results demonstrated that apoptosis in infected epithelial cells was associated with an increased activity of caspase 8; however, caspase 9 was activated to a lesser extent. Analysis of apoptosis pathway revealed that expression level of McL-1, Bcl-2, CASP8, and TRADD genes were found to be significantly upregulated (P?<?0.01), where as levels of Caspase 1, Caspase 10 and BRIC2 were found to be significantly downregulated (p?<?0.01). Our results showed that Chlamydia induces apoptosis and caspase activation in epithelial cells through caspase 8, with an increased expression of the McL-1, which confers a block at the mitochondrial level.     

Characterization of antiapoptotic activities of Chlamydia pneumoniae in human cells

Chlamydia pneumoniae is an obligate intracellular bacterium which frequently causes airway infection in humans and has been implicated in atherosclerosis. Here we show that infection with C. pneumoniae protects HeLa human epithelioid cells against apoptosis induced by external stimuli. In infected HeLa cells, apoptosis induced by staurosporine and CD95-death-receptor signaling was strongly reduced. Upon treatment with staurosporine, generation of effector caspase activity, processing of caspase-3 and caspase-9 and cytochrome c redistribution were all profoundly inhibited in cells infected with C. pneumoniae. Bacterial protein synthesis during early infection was required for this inhibition. Furthermore, cytochrome c-induced processing and activation of caspases were inhibited in cytosolic extracts from infected cells, suggesting that a C. pneumoniae-dependent antiapoptotic factor was generated in the cytosol upon infection. Infection with C. pneumoniae failed to induce significant NF-kappaB activation in HeLa cells, indicating that no NF-kappaB-dependent cellular factors were involved in the protection against apoptosis. These results show that C. pneumoniae is capable of interfering with the host cell's apoptotic apparatus at probably at least two steps in signal transduction and might explain the propensity of these bacteria to cause chronic infections in humans.     

Activation of multiple molecular mechanisms for apoptosis in human malignant glioblastoma T98G and U87MG cells treated with sulforaphane

Glioblastoma is the most malignant and prevalent brain tumor that still remains incurable. Recent studies reported anti-cancer effect of the broccoli-derived compound sulforaphane. We explored the mechanisms of sulforaphane-mediated apoptosis in human glioblastoma T98G and U87MG cells. Wright staining and ApopTag assay confirmed apoptosis in glioblastoma cells treated with sulforaphane. Increase in intracellular free Ca2+ was detected by fura-2 assay, suggesting activation of Ca2+-dependent pathways for apoptosis. Western blotting was used to detect changes in expression of Bax and Bcl-2 proteins resulting in increased Bax:Bcl-2 ratio that indicated a commitment of glioblastoma cells to apoptosis. Upregulation of calpain, a Ca2+-dependent cysteine protease, activated caspase-12 that in turn caused activation of caspase-9. With the increased Bax:Bcl-2 ratio, cytochrome c was released from mitochondria to cytosol for sequential activation of caspase-9 and caspase-3. Increased calpain and caspase-3 activities generated 145 kD spectrin breakdown product and 120 kD spectrin breakdown product, respectively. Activation of caspase-3 also cleaved the inhibitor-of-caspase-activated-DNase. Accumulation of apoptosis-inducing-factor in cytosol suggested caspase-independent pathway of apoptosis as well. Two of the inhibitor-of-apoptosis proteins were downregulated because of an increase in 'second mitochondrial activator of caspases/Direct inhibitor-of-apoptosis protein binding protein with low pI.' Decrease in nuclear factor kappa B and increase in inhibitor of nuclear factor kappa B alpha expression favored the process of apoptosis. Collectively, our results indicated activation of multiple molecular mechanisms for apoptosis in glioblastoma cells following treatment with sulforaphane.     

盐霉素抑制耐格列卫的人慢性粒细胞白血病细胞株K562/Glv增殖并诱导其凋亡

目的: 探讨盐霉素对耐格列卫的人慢性粒细胞白血病细胞株K562/Glv抑制增殖和诱导凋亡的作用及其机制。方法: 采用CCK-8的方法检测盐霉素对K562/Glv细胞生长的抑制作用;流式细胞术检测细胞凋亡、活性氧、细胞内Ca²⁺浓度([Ca²⁺]_i)和线粒体膜电位(ΔΨ_m);比色法检测caspase-3、-8和-9活性;Western blotting 分析细胞色素C、Bcl-2、Bax、β-catenin和磷酸化低密度脂蛋白受体相关蛋白6(p-LRP6)蛋白水平。结果: 盐霉素对K562/Glv细胞生长具有剂量依赖性抑制作用,0.2 μmol/L时细胞增殖抑制率为(36.70±2.31)%,细胞凋亡率为(19.66±2.43)%;0.2 μmol/L盐霉素作用于K562/Glv细胞,ΔΨ_m显著下降,24 h时下降至对照组的(19.8±2.4)%,细胞内活性氧和[Ca²⁺]_i在短期显著升高。Caspase-3、-8和-9活性均显著增加,与对照组比较,差异有统计学意义(P<0.01)。Bcl-2 的表达下调,Bax 的表达明显增加,Bcl-2/Bax 比值显著降低。同时,盐霉素也减少K562/Glv细胞内β-catenin和p-LRP6蛋白水平。结论: 盐霉素不仅通过Bcl-2/Bax途径和线粒体凋亡途径诱导耐格列卫人慢性粒细胞白血病细胞K562/Glv的凋亡,而且通过抑制Wnt信号途径抑制K562/Glv细胞增殖。     

Epithelial Cells Infected with Chlamydophila pneumoniae (Chlamydia pneumoniae) Are Resistant to Apoptosis

The obligate intracellular pathogen Chlamydophila pneumoniae (Chlamydia pneumoniae) initiates infections in humans via the mucosal epithelia of the respiratory tract. Here, we report that epithelial cells infected with C. pneumoniae are resistant to apoptosis induced by treatment with drugs or by death receptor ligation. The induction of protection from apoptosis depended on the infection conditions since only cells containing large inclusions were protected. The underlying mechanism of infection-induced apoptosis resistance probably involves mitochondria, the major integrators of apoptotic signaling. In the infected cells, mitochondria did not respond to apoptotic stimuli by the release of apoptogenic factors required for the activation of caspases. Consequently, active caspase-3 was absent in infected cells. Our data suggest a direct modulation of apoptotic pathways in epithelial cells by C. pneumoniae.     

Broad degradation of proapoptotic proteins with the conserved Bcl-2 homology domain 3 during infection with Chlamydia trachomatis

Chlamydiae are obligate intracellular bacteria that can inhibit apoptosis of their host cell. As shown recently, this inhibition is in part explained by the proteolytic degradation of the proapoptotic Bcl-2 family members (BH3-only proteins) Bim, Puma, and Bad upon chlamydial infection. In this study, we further explore this antiapoptotic mechanism. In cells infected with a Chlamydia trachomatis L2 strain, Bim, Puma, and Bad were degraded with similar kinetics, and the degradation of all three was blocked by inhibition of the proteasome. Furthermore, the BH3-only proteins Bmf, Noxa, and tBid were also targeted by chlamydial infection. The constitutively expressed Bmf disappeared during infection. When Noxa was experimentally induced, the levels were also reduced by infection with C. trachomatis. In death-receptor-induced apoptosis, cleaved and activated tBid was degraded, and this destruction was also prevented by inhibition of the proteasome. These results show that chlamydial infection leads to a broad degradation of BH3-only proteins. This loss of proapoptotic factors can explain the almost general protection of infected cells against apoptotic stimuli.     

Negative correlation between the ratio of Bax to Bcl-2 and the size of tumor treated by culture supernatants from Kupffer cells

Kupffer cells play an important role in keeping liver from occurrence of tumors. Apoptosis is thought to be a major mechanism responsible for the anti-tumor function of Kupffer cells. Previous studies have mainly concentrated on the direct contact and interaction between Kupffer cells and tumor cells. The present experiment is to investigate the apoptotic pathway in tumor induced by culture supernatant from activated Kupffer cells. The levels of Bax, Bcl-2 and iNOS were analyzed in an in vivo mouse tumor model, which was treated with culture supernatant from activated Kupffer cells. The results showed that the expression of Bax significantly increased while the expression of Bcl-2 decreased when tumor cells were treated with culture supernatants from activated Kupffer cells. The alteration of Bax and Bcl-2 levels resulted in an increase in the ratio of Bax to Bcl-2, which had negative correlation with the size of tumor and positive correlation with the expression of iNOS. The expression of TNFα and the occurrence of apoptosis were also increased in tumor treated with culture supernatants from activated Kupffer cells, compared with those which received no treatment. In conclusion, culture supernatants from activated Kupffer cells were able to change the balance between Bax and Bcl-2 in favor of the former. The ratio of Bax to Bcl-2 is a useful index to evaluate tumor apoptosis induced by Kupffer cells. Our experiment also suggests that alteration of the ratio of Bax to Bcl-2 may result from increased levels of iNOS and TNFα. This revised version was published online in July 2006 with corrections to the Cover Date.     

Increased Bcl-2 and reduced Bax expression in infected macrophages in slowly progressive primary murine Mycobacterium tuberculosis infection

Mycobacterium tuberculosis (MTB) persists in host macrophages (Mphis) because it has developed mechanisms to escape Mphi killing. In vitro studies have shown that MTB can induce and inhibit apoptosis by causing the expression of Bax and Bcl-2, respectively, suggesting that the infected cells' fate depends on pro- and antiapoptotic signals. In the present study, we investigated the role of Bcl-2 in MTB infection in situ. The aim was to study the pattern and distribution of Bcl-2 and Bax in cellular infiltrates of MTB-infected B6D2F1 hybrid mice and correlate the expression with the presence of MTB antigens (MAgs). Using formalin-fixed lung tissues (n = 45), our results showed a significant difference in the percentage of Mphis stained for Bcl-2 or MAgs and Bax (P < 0.0001). Bcl-2 expression was increased in a population of Mphis and corresponded in intensity, colocalization and percentage with that of MAgs on the same cells, while Bax expression was reduced. In lymphocyte aggregates, Bcl-2 and Bax did not show any differences. We conclude that overexpression of Bcl-2 in Mphis containing MTB may be associated with intracellular survival of the bacilli, thus demonstrating one way by which MTB can escape the host's cellular response and killing.     

Anticancer efficacy of 5F in NNK-induced lung cancer development of A/J mice and human lung cancer cells

The mechanism responsible for the apoptotic effect induced by ent-11α-hydroxy-15-oxo-kaur-16-en-19-oic-acid (5F) is not fully understood and its in vivo effect has not been tested. In this study, the effect and mechanism of 5F was investigated in cigarette smoking carcinogen 4-methylnitrosamino-1-3-pyridyl-butanone (NNK)-induced mouse lung tumor model and in cultured lung cancer cells NCI-H23 and CRL-2066. 5F were given to mice after they were treated with NNK for 18 weeks. The effect of 5F on the lung tumor formation was examined, and its side effect was monitored. Cell proliferation and apoptosis were determined through expression of PCNA, Bcl-2, Bax, and TUNEL assay in in vivo animal model. 5F significantly inhibited the NNK-induced lung tumors by inducing apoptosis and suppressing cell proliferation in vivo with minimal side effects. Cell culture experiments showed that 5F translocated Bax into the mitochondria, downregulated Bcl-2, activated caspase-9 and caspase-3, released cytochrome c into the cytosol, and translocated AIF from the mitochondria to the nucleus, which leading to G2-M cell cycle arrest and cell apoptosis. 5F also activated ERK1/2 and the inhibition of ERK1/2 suppressed 5F-mediated changes in apoptotic molecules. In addition to ERK1/2, 5F activated Akt. The inhibition of Akt further facilitated the apoptosis induced, suggesting that Akt activation was anti-apoptotic rather than pro-apoptotic. Collectively, 5F is effective against lung cancer in vivo with minimal side effects. It induces apoptosis in lung cancer through the mitochondrial-mediated pathway, in which the activation of ERK is critical.     

Early activation of the mitochondrial apoptotic pathway in Vesicular Stomatitis virus-infected cells

Vesicular Stomatitis Virus (VSV) has been shown to induce apoptosis in a caspase-dependent manner, but the precise apoptotic pathway remains unknown. We found that caspases 9 and 3, but not caspase 8, were activated during VSV-induced apoptosis in infected Vero cells. Since caspase 9 is related to the mitochondrial apoptotic pathway, we analyzed some mitochondrial events such as changes in the mitochondrial transmembrane potential (Deltapsim) and mitochondrial release of apoptogenic proteins such as cytochrome c and the apoptosis inducing factor (AIF). We found that VSV infection triggers the dissipation of the Deltapsim and the release of both cytochrome c and AIF from the mitochondrial intermembrane space very early in the VSV infection. These results indicate that the trigger of apoptosis in VSV-infected cells occurs through the early activation of the mitochondrial apoptotic pathway. On the other hand, intracellular levels of the anti-apoptotic proteins, such as Bcl-2 and Bcl-xL, and the pro-apoptotic protein Bax, were assessed during viral infection. These analyses showed that as viral infection proceeded, the cellular level of Bcl-xL decreased, while the levels of Bax and Bcl-2 remained unaffected. The significance of the Bcl-xL modulation is also discussed.     

Inhibition of apoptosis by gamma interferon in cells and mice infected with Chlamydia muridarum (the mouse pneumonitis strain of Chlamydia trachomatis)

The effect of gamma interferon (IFN-gamma) on apoptosis due to infection by Chlamydia muridarum (the mouse pneumonitis strain of Chlamydia trachomatis) was studied in epithelial cells in culture and in the genital tracts of mice. IFN-gamma concentrations that induce the formation of aberrant, persistent chlamydiae inhibit apoptosis due to C. muridarum infection. In cells treated with an IFN-gamma concentration that leads to the development of a heterogenous population of normal and aberrant Chlamydia vacuoles, apoptosis was inhibited preferentially in cells that contained the aberrant vacuoles. The inhibitory effect of IFN-gamma appears to be due in part to expression of host cell indoleamine 2,3-dioxygenase activity, since inhibition of apoptosis could be partially reversed through coincubation with exogenous tryptophan. Apoptotic cells were observed in the genital tracts of wild-type mice infected with C. muridarum, and a significantly larger number of apoptotic cells was detected in infected IFN-gamma-deficient mice. These results suggest that IFN-gamma may contribute to pathogenesis of persistent Chlamydia infections in vivo by preventing apoptosis of infected cells.     

Functional expression of CD134 by neutrophils

CD134 (OX40) is a member of the tumor necrosis factor (TNF) receptor superfamily expressed on activated T cells. Here, we show that human peripheral blood neutrophils express CD134. Activation of CD134 by soluble CD134 ligand (OX40 ligand/gp34) resulted in delayed caspase-3 activation and consequently in delayed neutrophil apoptosis in vitro. Moreover, CD134 ligand, like G-CSF, maintained anti-apoptotic Mcl-1 levels and inhibited cleavage of the pro-apoptotic Bcl-2 family members Bid and Bax in these cells, suggesting that CD134-mediated signals block apoptosis pathways proximal to mitochondria activation. In conclusion, CD134 regulates neutrophil survival, suggesting that this molecule does not only contribute to adaptive but also to innate immune responses.     

Hypothesis links emergence of chloroquine-resistant malaria and other intracellular pathogens and suggests a new strategy for treatment of diseases caused by intracellular parasites

Chloroquine and related anti-malarial drugs appear to promote apoptosis in T-cells by suppressing NF-kappa-B, which enhances the expression of anti-apoptotic proteins (e.g., Bcl-2). Thus, chloroquine has found applications in autoimmune diseases where it apparently facilitates apoptosis of abnormally persistent T-cell clones. The mode of action of chloroquine in prevention of malaria is not known, but it may be to minimize replication of the parasite in the liver cells, which occurs before invasion of the erythrocytes, by facilitating premature apoptosis of the infected host cells. After introduction of chloroquine in the 1950s world-wide for prophylactic use, chloroquine-resistant malaria emerged. Here it is hypothesized that concurrent with emergence of chloroquine-resistant malaria (presumably with enhanced anti-apoptotic capabilities), other intracellular parasites have evolved to enhance their ability to prevent apoptosis in host cells. Two examples of viral diseases that have emerged from areas of high incidence of chloroquine-resistant malaria are AIDS from HIV and SARS from coronavirus. The hypothesis holds that prophylactic exposure to pro-apoptotic chloroquine drugs caused natural selection for strains of viruses and other parasites that have enhanced anti-apoptotic abilities. When transmitted to host organisms that are not under the influence of the pro-apoptotic drug, the new "anti-apoptotic" strains may cause unexpected diseases. In the case of SARS, the coronavirus appears to have accessed a new niche where it proves to be lethal to its host. In the case of AIDS, the HIV (which has had a long-term symbiotic relationship with primates) has run amuck because the infected cells are now substantially more tolerant to the toxins (i.e., resistant to apoptosis) that they secrete than the uninfected bystander cells, which are not unusually resistant to apoptosis. A corollary to the hypothesis is that if the level of resistance to apoptosis in the infected cells were no higher than the level of resistance in the bystander cells, then the infected cells would preferentially kill themselves through apoptosis. It appears that in the case of HIV, the increased resistance to apoptosis is provided by expression of Bcl-2 and suppression of p53. Hence, drugs that suppresses Bcl-2 or restore p53 function might be effective in restoring the parity of resistance to apoptosis between infected and uninfected cells. Currently, an antisense drug targeting Bcl-2 (G3139/Genasense(TM), Genta, Inc.) is in late-stage cancer trials and may be on the market for those indications in months. It would be interesting to try these drugs against various intracellular parasites including HIV. This approach to prevent or eliminate active infections might be particularly attractive against a range of parasites (virus, bacteria, protozoa, fungus) when safe and effective vaccines are not available.     

bFGF对卵巢癌CAOV3细胞Bcl-2、Bcl-xl、Bax、Bad表达的影响

目的研究bFGF调控卵巢癌CAOV3凋亡的信号通路及对Bcl-2、Bcl-xl、Bax、Bad表达的影响。方法无血清饥饿诱导细胞凋亡。分为饥饿对照、bFGF、bFGF PD98059、bFGF Wortmannin组。流式细胞术、DNA Ladder检测细胞凋亡;Western印迹法检测ERK、PKB、Bad活性以及Bcl-2、Bax表达,RT- PCR检测Bcl-2、Bcl-xl mRNA变化。结果bFGF促进p-ERK、p-PKB、p-Bad、Bcl-2表达,抑制Bax表达及饥饿诱导的细胞凋亡。激酶抑制剂PD98059可抑制bFGF对ERK、Bcl-2、Bax的调节作用,Wortmannin可抑制bFGF对PKB、Bad、Bax的调控作用,二者均可阻断bFGF对凋亡的抑制作用。bFGF对Bcl-xl表达无影响。结论bFGF可能通过激活MEK/ERK、P13K/PKB信号途径通路调节Bcl-2、Bax、Bad表达,抑制饥饿诱导的卵巢癌CAOV3细胞凋亡。     

Lipopolysaccharide protects primary B lymphocytes from apoptosis by preventing mitochondrial dysfunction and bax translocation to mitochondria

Mature B lymphocytes undergo apoptosis when they are cultured in the absence of survival factors. Gram-negative bacterial lipopolysaccharide (LPS) prevents this spontaneous apoptosis. This study aimed to better define the signaling pathway(s) involved in the antiapoptotic activity of this endotoxin. We report here that, in addition to its effects on spontaneous apoptosis, LPS protects B cells from apoptosis induced by the broad-spectrum protein kinase inhibitor staurosporine. LPS increased cell viability and concomitantly maintained the mitochondrial transmembrane potential (DeltaPsim) and high glutathione levels. Moreover, LPS inhibited cytosolic cytochrome c release and decreased caspase-9 activation. Unlike staurosporine, LPS induced the retention of Bax, a proapoptotic protein of the Bcl-2 family, in the cytosol by preventing its translocation to mitochondria. These results suggest that Bax relocalization from the cytosol to the mitochondria is an important step of mature B-cell apoptosis and that the antiapoptotic activity of LPS occurs upstream of mitochondrial events.     

Degradation of the proapoptotic proteins Bik, Puma, and Bim with Bcl-2 domain 3 homology in Chlamydia trachomatis-infected cells

We have previously correlated Chlamydia trachomatis antiapoptotic activity with the blockade of mitochondrial cytochrome c release and the inhibition of Bax and Bak activation. We now report that C. trachomatis infection leads to degradation of Bik, Puma, and Bim, three upstream proapoptotic BH3-only proteins of the Bcl-2 family that can transmit death signals to mitochondria by inhibiting the Bcl-2 antiapoptotic proteins and/or activating the Bcl-2 proapoptotic members, such as Bax and Bak. This observation has provided new information on the chlamydial antiapoptosis mechanisms.