Pristimerin induces apoptosis by targeting the proteasome in prostate cancer cells

Pristimerin is a natural product derived from the Celastraceae and Hippocrateaceae families that were used as folk medicines for anti inflammation in ancient times. Although it has been shown that pristimerin induces apoptosis in breast cancer cells, the involved mechanism of action is unknown. The purpose of the current study is to investigate the primary target of pristimerin in human cancer cells, using prostate cancer cells as a working model. Nucleophilic susceptibility and in silico docking studies show that C6 of pristimerin is highly susceptible towards a nucleophilic attack by the hydroxyl group of N-terminal threonine of the proteasomal chymotrypsin subunit. Consistently, pristimerin potently inhibits the chymotrypsin-like activity of a purified rabbit 20S proteasome (IC50 2.2 micromol/L) and human prostate cancer 26S proteasome (IC50 3.0 micromol/L). The accumulation of ubiquitinated proteins and three proteasome target proteins, Bax, p27 and I kappa B-alpha, in androgen receptor (AR)-negative PC-3 prostate cancer cells supports the conclusion that proteasome inhibition by pristimerin is physiologically functional. This observed proteasome inhibition subsequently led to the induction of apoptotic cell death in a dose- and kinetic-dependent manner. Furthermore, in AR-positive, androgen-dependent LNCaP and AR-positive, androgen-independent C4-2B prostate cancer cells, proteasome inhibition by pristimerin results in suppression of AR protein prior to apoptosis. Our data demonstrate, for the first time, that the proteasome is a primary target of pristimerin in prostate cancer cells and inhibition of the proteasomal chymotrypsin-like activity by pristimerin is responsible for its cancer cell death-inducing property.     

Myostatin induces mitochondrial metabolic alteration and typical apoptosis in cancer cells

Myostatin, a member of the transforming growth factor-β superfamily, regulates the glucose metabolism of muscle cells, while dysregulated myostatin activity is associated with a number of metabolic disorders, including muscle cachexia, obesity and type II diabetes. We observed that myostatin induced significant mitochondrial metabolic alterations and prolonged exposure of myostatin induced mitochondria-dependent apoptosis in cancer cells addicted to glycolysis. To address the underlying mechanism, we found that the protein levels of Hexokinase II (HKII) and voltage-dependent anion channel 1 (VDAC1), two key regulators of glucose metabolisms as well as metabolic stress-induced apoptosis, were negatively correlated. In particular, VDAC1 was dramatically upregulated in cells that are sensitive to myostatin treatment whereas HKII was downregulated and dissociated from mitochondria. Myostatin promoted the translocation of Bax from cytosol to mitochondria, and knockdown of VDAC1 inhibited myostatin-induced Bax translocation and apoptosis. These apoptotic changes can be partially rescued by repletion of ATP, or by ectopic expression of HKII, suggesting that perturbation of mitochondrial metabolism is causally linked with subsequent apoptosis. Our findings reveal novel function of myostatin in regulating mitochondrial metabolism and apoptosis in cancer cells.     

Activation of mitochondrial lactate uptake by flavone induces apoptosis in human colon cancer cells

Lactate production from glucose even in the presence of oxygen is a characteristic of cancer cell metabolism and an important feature for tumor progression. Here, we describe that an increased uptake of lactate into mitochondria of HT-29 human colon cancer cells by treatment of cells with the flavonoid flavone is associated with an increased production of mitochondrial superoxide anions and apoptotic cell death. In search of the mitochondrial transporter that could promote enhanced lactate uptake and energetic flow through the electron transport chain, we used fluorescein as a model substrate. Flavone increased fluorescein uptake at pH 7.4 into mitochondria of HT-29 cells almost tenfold while lactate inhibited uptake significantly. Uptake of fluorescein in the absence or presence of flavone was strongly increased by lowering pH from 7.4 to 6.0 and almost abolished by the protonophore carbonyl cyanide m-chlorophenylhydrazone (CCCP). The lactate-sensitive part of fluorescein transport was completely blocked by p-chloromercuribenzenesulfonic acid (pCMBS), a specific inhibitor of the monocarboxylate transporter-1 (MCT-1) that by Western blotting and immunofluorescence was identified in mitochondria of HT-29 cells. Finally, lactate increased and pCMBS inhibited the flavone-induced generation of mitochondrial O2-* radicals and in turn blunted the apoptotic response. In conclusion, our studies provide evidence that flavone reverts the metabolic phenotype of transformed colonocytes towards a phenotype characteristic for normal cells. Transformed colonocytes, however, seem especially vulnerable to O2-*, produced in mitochondria as a consequence of these metabolic alterations, and respond with the induction of apoptosis.     

Shikonin selectively induces apoptosis in human prostate cancer cells through the endoplasmic reticulum stress and mitochondrial apoptotic pathway

Background

Despite the recent progress in screening and therapy, a majority of prostate cancer cases eventually attain hormone refractory and chemo-resistant attributes. Conventional chemotherapeutic strategies are effective at very high doses for only palliative management of these prostate cancers. Therefore chemo-sensitization of prostate cancer cells could be a promising strategy for increasing efficacy of the conventional chemotherapeutic agents in prostate cancer patients. Recent studies have indicated that the chemo-preventive natural agents restore the pro-apoptotic protein expression and induce endoplasmic reticulum stress (ER stress) leading to the inhibition of cellular proliferation and activation of the mitochondrial apoptosis in prostate cancer cells. Therefore reprogramming ER stress-mitochondrial dependent apoptosis could be a potential approach for management of hormone refractory chemoresistant prostate cancers. We aimed to study the effects of the natural naphthoquinone Shikonin in human prostate cancer cells.

Results

The results indicated that Shikonin induces apoptosis in prostate cancer cells through the dual induction of the endoplasmic reticulum stress and mitochondrial dysfunction. Shikonin induced ROS generation and activated ER stress and calpain activity. Moreover, addition of antioxidants attenuated these effects. Shikonin also induced the mitochondrial apoptotic pathway mediated through the enhanced expression of the pro-apoptotic Bax and inhibition of Bcl-2, disruption of the mitochondrial membrane potential (MMP) followed by the activation of caspase-9, caspase-3, and PARP cleavage.

Conclusion

The results suggest that shikonin could be useful in the therapeutic management of hormone refractory prostate cancers due to its modulation of the pro-apoptotic ER stress and mitochondrial apoptotic pathways.

Electronic supplementary material

The online version of this article (doi:10.1186/s12929-015-0127-1) contains supplementary material, which is available to authorized users.     

Seleno-short-chain chitosan induces apoptosis in human breast cancer cells through mitochondrial apoptosis pathway in vitro

Seleno-short-chain chitosan (SSCC) was a synthesized chitosan derivative with the molecular weight of 4826.986 Da. The study is aimed to investigate cytotoxicity of SSCC on human breast cancer MCF-7 and BT-20 cells and explore apoptosis-related mechanism in vitro. The MTT (3- [4,5-Dimethylthiazol-2-yl]-2, 5-diphenylterazolium bromide) assay showed that SSCC exhibited significantly cytotoxic effects on MCF-7 and BT-20 cells in a dose- and time-dependent manner, and the effective inhibitory concentration was 100 μg/ml and 200 μg/ml, respectively. Apoptosis assay of these two kinds of cells was determined by Hoechst 33,342/PI and Annexin V-FITC/PI double staining. The cell cycle assay showed that SSCC triggered S and G2/M phase cell cycle arrest in MCF-7 cells and S phase cell cycle arrest in BT-20 cells in a time-dependent manner. Further studies demonstrated that SSCC led to the generation of reactive oxygen species (ROS) and the disruption of mitochondrial membrane potential (MMP) in these two kinds of cells. N- acetyl-L cysteine (NAC), as a radical scavenger, significantly inhibited the generation of ROS and decreased the apoptosis of MCF-7 and BT-20 cells. Moreover, the expression of mitochondrial apoptosis-related proteins was detected by western blot assay. SSCC up-regulated the expression of Bax, down-regulated the expression of Bcl-2, subsequently increased the release of cytochrome c from mitochondria to cytoplasm, and activated the cleavage of caspase-9 and ?3, which finally induced apoptosis in MCF-7 and BT-20 cells in vitro. Consequently, these data indicated that SSCC could induce apoptosis of MCF-7and BT-20 cells in vitro by mitochondrial pathway.     

Resveratrol induces mitochondrial respiration and apoptosis in SW620 colon cancer cells

BackgroundThe polyphenol resveratrol (RSV) is found in the skin of red grapes and has been reported to exhibit anticancer properties. The antitumor effects of RSV in the gastrointestinal tract have gained considerable interest due to the high exposure of this tissue to this dietary compound. One of the hallmarks of cancer cells is their particular metabolism mainly relying on glycolysis for ATP production rather than mitochondrial oxidative phosphorylation. Although RSV has been described to act as a calorie-restriction mimetic, modulating energy metabolism in normal tissues, little efforts have been done to study the effects of this polyphenol in the metabolism of cancer cells. Taking this into account, the aim of this study was to explore metabolic effects of this polyphenol in colon cancer.MethodsOxygen consumption, ATP levels, Western blotting and other molecular biology techniques were carried out to characterize the metabolic signature of RSV in SW620 colon cancer cells.ResultsParadoxically, the cytotoxic effects of RSV were associated with an increase in oxygen consumption supported by mitochondrial biogenesis and increased fatty acid oxidation. This partial reversion of the Warburg effect was followed by hyperpolarization of mitochondrial membrane and ROS production, leading to an increased apoptosis.ConclusionsOur results propose that the anticancer mechanisms of RSV could reside in targeting cancer cell metabolism, promoting mitochondrial electron transport chain overload and, ultimately, increasing ROS production.General significanceThese results shed new light into the anticancer mechanism of RSV supporting the ability of this compound in potentiating the effects of chemotherapy.     

ROS-mediated activation of AKT induces apoptosis via pVHL in prostate cancer cells

Reactive oxygen species (ROS) play a central role in oxidative stress, which leads to the onset of diseases, such as cancer. Furthermore, ROS contributes to the delicate balance between tumor cell survival and death. However, the mechanisms by which tumor cells decide to elicit survival or death signals during oxidative stress are not completely understood. We have previously reported that ROS enhanced tumorigenic functions in prostate cancer cells, such as transendothelial migration and invasion, which depended on CXCR4 and AKT signaling. Here, we report a novel mechanism by which ROS facilitated cell death through activation of AKT. We initially observed that ROS enhanced the expression of phosphorylated AKT (p-AKT) in 22Rv1 human prostate cancer cells. The tumor suppressor PTEN, a negative regulator of AKT signaling, was rendered catalytically inactive through oxidation by ROS, although the expression levels remained consistent. Despite these events, cells still underwent apoptosis. Further investigation into apoptosis revealed that expression of the tumor suppressor pVHL increased, and contains a target site for p-AKT phosphorylation. pVHL and p-AKT associated in vitro, and knockdown of pVHL rescued HIF1α expression and the cells from apoptosis. Collectively, our study suggests that in the context of oxidative stress, p-AKT facilitated apoptosis by inducing pVHL function.     

Cytosolic pro-apoptotic SPIKE induces mitochondrial apoptosis in cancer

Proteins of the BCL-2 family are important regulators of apoptosis. The BCL-2 family includes three main subgroups: the anti-apoptotic group, such as BCL-2, BCL-XL, BCL-W, and MCL-1; multi-domain pro-apoptotic BAX, BAK; and pro-apoptotic “BH3-only” BIK, PUMA, NOXA, BID, BAD, and SPIKE. SPIKE, a rare pro-apoptotic protein, is highly conserved throughout the evolution, including Caenorhabditis elegans, whose expression is downregulated in certain tumors, including kidney, lung, and breast.In the literature, SPIKE was proposed to interact with BAP31 and prevent BCL-XL from binding to BAP31. Here, we utilized the Position Weight Matrix method to identify SPIKE to be a BH3-only pro-apoptotic protein mainly localized in the cytosol of all cancer cell lines tested. Overexpression of SPIKE weakly induced apoptosis in comparison to the known BH3-only pro-apoptotic protein BIK. SPIKE promoted mitochondrial cytochrome c release, the activation of caspase 3, and the caspase cleavage of caspase’s downstream substrates BAP31 and p130CAS. Although the informatics analysis of SPIKE implicates this protein as a member of the BH3-only BCL-2 subfamily, its role in apoptosis remains to be elucidated.     

Bone morphogenetic protein-9 induces apoptosis in prostate cancer cells, the role of prostate apoptosis response-4

Bone morphogenetic proteins (BMP) have been implicated in the development of bone metastases in prostate cancer. In this study, we investigated the role which BMP-9 played in prostate cancer and found that the expression of BMP-9 was decreased or absent in prostate cancer, particularly in the foci of higher grade disease. We further investigated the influence of BMP-9 on the biological behaviors of prostate cancer cells. The forced overexpression of BMP-9 prevented the in vitro growth, cell-matrix adhesion, invasion, and migration of prostate cancer cells. We also elucidated that BMP-9 induced apoptosis in PC-3 cells through the up-regulation of prostate apoptosis response-4. Among the receptors which have been implicated in the signaling of BMP-9, BMPR-IB and BMPR-II have also been implicated in the development and progression of prostate cancer. Knockdown of BMPR-IB or BMPR-II using respective hammerhead ribozyme transgenes could promote cell growth in vitro. We also found that BMPR-II is indispensable for the Smad-dependent signal transduction by BMP-9 in PC-3 cells, in which Smad-1 was phosphorylated and translocated from the cytoplasm into the nuclei. Taken together, BMP-9 inhibits the growth of prostate cancer cells due to the induced apoptosis, which is related to an up-regulation of prostate apoptosis response-4 through a Smad-dependent pathway. BMP-9 could also prevent the migration and invasiveness of prostate cancer. This suggests that BMP-9 may function as a tumor suppressor and apoptosis regulator in prostate cancer.     

猪丁型冠状病毒诱导的细胞线粒体凋亡

猪丁型冠状病毒(Porcine deltacoronavirus,PDCoV)是一种新型的猪肠道致病性冠状病毒,可引起猪群剧烈腹泻及呕吐,但致病机制尚不清楚。本研究检测了PDCoV感染诱导的细胞凋亡。Caspase酶活性检测显示,在PDCoV感染的细胞中,caspase 3、caspase 8和caspase 9的活性随病毒感染量的增多而显著提高,类似的现象未能在紫外灭活病毒感染的细胞中观察到,表明PDCoV感染可同时激活内源性与外源性细胞凋亡通路,并暗示细胞凋亡的诱导依赖于病毒复制。为深入探究PDCoV诱导的内源性细胞凋亡,分别检测胞浆和线粒体中细胞色素C与凋亡诱导因子。结果显示,与正常细胞相比,PDCoV感染细胞从线粒体释放到胞浆的细胞色素C显著增多,且其释放量随着感染时间的延长而增多,而凋亡诱导因子始终定位于线粒体,提示PDCoV感染通过促使线粒体膜间隙的细胞色素C进入胞浆而启动caspase依赖的线粒体凋亡通路。本研究初步揭示了PDCoV诱导细胞凋亡的机制。     

Isoliquiritigenin (ISL) inhibits ErbB3 signaling in prostate cancer cells

Isoliquiritigenin (ISL), a flavonoid found in licorice, shallot, and bean sprouts, has been identified as a potent anti-tumor promoting agent. We previously demonstrated that ISL reduces cell proliferation and induces apoptosis in DU145 human prostate cancer cells and MAT-LyLu (MLL) rat prostate cancer cells. Overexpression of members of the ErbB receptor family is a frequently observed event in several human cancers, and ErbB receptors currently constitute the primary targets of anticancer strategies. In order to elucidate the mechanisms underlying the ISL regulation of prostate cancer cell proliferation, the present study attempted to determine whether ISL inhibits heregulin (HRG)-beta-induced ErbB3 signaling. DU145 and MLL cells were cultured in serum-free medium with ISL and/or HRG-beta. Exogenous HRG-beta alone was shown to effect an increase in the numbers of viable cells, whereas HRG-beta did not counteract the ISL-induced growth inhibition. ISL reduced the protein and mRNA levels of ErbB3 in a dose-dependent manner, but exerted no effect on HRG protein levels. Immunoprecipitation/Western blot studies indicated that ISL inhibited the HRG-beta-induced tyrosine phosphorylation of ErbB3, the recruitment of the p85 regulatory subunit of phosphatidylinositol 3-kinase (PI3K) to ErbB3, and Akt phosphorylation in DU145 cells. These results indicate that ISL inhibits the proliferation of prostate cancer cells, at least in part, via the inhibition of ErbB3 signaling and the PI3K/Akt pathway.     

Genistein induces apoptosis of RPE-J cells by opening mitochondrial PTP

Although previous studies demonstrated that genistein-induced apoptosis of various cell types including RPE-J cells, the involvement of mitochondrial events in such types of apoptosis has not been demonstrated to date. In this investigation of genistein-induced apoptosis of RPE-J cells, genistein induced the reduction of the mitochondrial membrane potential and the release of cytochrome c to cytosol. A mitochondrial permeability transition pore (PTP) blocker bongkrekic acid prevented the reduction of the mitochondrial membrane potential and cytochrome c release, and consequently abolished caspase-3 activation, nuclear condensation, and DNA fragmentation. On the other hand, zVAD-fmk did not inhibit the mitochondrial event such as the reduction of the mitochondrial membrane potential and cytochrome c release although it prevented caspase-3 activation, nuclear condensation, and DNA fragmentation. Taken together, genistein induces apoptosis of RPE-J cells by opening the mitochondrial PTP, and the mitochondrial event in this type of apoptosis is caused independently of caspase.     

Chetomin induces apoptosis in human triple-negative breast cancer cells by promoting calcium overload and mitochondrial dysfunction

Human triple-negative breast cancer (TNBC) is poorly diagnosed and unresponsive to conventional hormone therapy. Chetomin (CHET), a fungal metabolite synthesized by Chaetomium cochliodes, has been reported as a promising anticancer and antiangiogenic agent but the complete molecular mechanism of its anticancer potential remains to be elucidated. In our study, we explored the anti-neoplastic action of CHET on TNBC cells. Cytotoxicity studies were performed in human TNBC cells viz. MDA-MB-231 and MDA-MB-468 cells by Sulforhodamine B assay. It exhibited antiproliferative response and induced apoptosis in both the cell types. Cell cycle analysis revealed that it increases the sub G0/G1 phase cell population. Modulation of mitochondrial membrane potential, activation of caspase 3/7 and a remarkable increase in the expression of cleaved PARP and increased chromatin condensation was observed after CHET treatment in MDA-MB-231 and MDA-MB-468 cells. Additionally, an elevated level of intracellular Ca²⁺ played an important role in CHET mediated cell death response. Calcium overload in mitochondria led to release of cytochrome c which in turn triggered caspase-3 mediated cell death. Inhibition of calcium signalling using BAPTA-AM reduced apoptosis confirming the involvement of calcium signalling in CHET induced cell death. Chetomin also inhibited PI3K/mTOR cell survival pathway in human TNBC cells. The overall findings suggest that Chetomin inhibited the growth of human TNBC cells by caspase-dependent apoptosis and modulation of PI3K/mTOR signalling and could be used as a novel chemotherapeutic agent for the treatment of human TNBC in future.     

Hispolon induces apoptosis in human gastric cancer cells through a ROS-mediated mitochondrial pathway

Severe side effects and complications such as gastrointestinal and hematological toxicities because of current anticancer drugs are major problems in the clinical management of gastric cancer, which highlights the urgent need for novel effective and less toxic therapeutic approaches. Hispolon, an active polyphenol compound, is known to possess potent antineoplastic and antiviral properties. In this study, we investigated the efficacy of hispolon in human gastric cancer cells and explored the cell death mechanism. Hispolon induced ROS-mediated apoptosis in gastric cancer cells and was more toxic toward gastric cancer cells than toward normal gastric cells, suggesting greater susceptibility of the malignant cells. The mechanism of hispolon-induced apoptosis was that hispolon abrogated the glutathione antioxidant system and caused massive ROS accumulation in gastric cancer cells. Excessive ROS caused oxidative damage to the mitochondrial membranes and impaired the membrane integrity, leading to cytochrome c release, caspase activation, and apoptosis. Furthermore, hispolon potentiated the cytotoxicity of chemotherapeutic agents used in the clinical management of gastric cancer. These results suggest that hispolon could be useful for the treatment of gastric cancer either as a single agent or in combination with other anticancer agents.     

Adenovirus-mediated expression of Fas ligand induces apoptosis of human prostate cancer cells

Several laboratories have reported on the apoptotic potentials of human prostate cancer (PC) cell lines in response to crosslinking of Fas (CD95/APO-1) with agonistic anti-Fas antibodies. We have re-evaluated the apoptotic potentials of seven human PC cell lines using the natural Fas ligand (FasL) in place of agonistic antibody. First, PC cell lines were tested in a standard cytotoxicity assay with a transfected cell line that stably expresses human FasL. Next, we developed an adenoviral expression system employing 293 cells that stably express crmA, a poxvirus inhibitor of apoptosis, to analyze the effects of FasL when expressed internally by the PC cell lines. Our data suggest that the apoptotic potentials of these cell lines were greatly underestimated in previous studies utilizing agonistic anti-Fas antibodies. Lastly, adenoviral-mediated expression of FasL prevented growth and induced regression of two human PC cell lines in immunodeficient mice. These preliminary in vivo results suggest a potential use for adenovirus encoding FasL as a gene therapy for PC.     

Adenosine induces apoptosis in human liver cancer cells through ROS production and mitochondrial dysfunction

Mitochondria are the most important sensor for apoptosis. Extracellular adenosine is well reported to induce apoptosis of tumor cells. Here we found that extracellular adenosine suppresses the cell growth by induction of apoptosis in BEL-7404 liver cancer cells, and identified a novel mechanism that extracellular adenosine triggers apoptosis by increasing Reactive Oxygen Species (ROS) production and mitochondrial membrane dysfunction in the cells. We observed that adenosine increases ROS production, activates c-Caspase-8 and -9 and Caspase effectors, c-Caspase-3 and c-PARP, induces accumulation of apoptosis regulator Bak, decreases Bcl-xL and Mcl-1, and causes the mitochondrial membrane dysfunction and the release of DIABLO, Cytochrome C, and AIF from mitochondria to cytoplasm in the cells; ROS inhibitor, NAC significantly reduces adenosine-induced ROS production; it also shows the same degree of blocking adenosine-induced loss of mitochondrial membrane potential (MMP) and apoptosis. Our study first observed that adenosine increases ROS production in tumor cells and identified the positive feedback loop for ROS-mediated mitochondrial membrane dysfunction which amplifies the death signals in the cells. Our findings indicated ROS production and mitochondrial dysfunction play a key role in adenosine-induced apoptosis of 7404 cells.     

Matrine inhibits proliferation and induces apoptosis via BID-mediated mitochondrial pathway in esophageal cancer cells

Matrine, as a member of Sophora family, is an alkaloid found in plants, and produces plethora pharmacological effects, including anti-cancer effects. However, the mechanism involved remains largely unknown. This study is conducted to investigate the anti-cancer mechanisms of matrine in human esophageal cancer in vitro and in vivo. In human esophageal cancer cell Eca-109, matrine significantly decreased the cell viability in a dose-dependent manner, and induced apoptosis as well as cell cycle arrest in G0/G1 phase by up-regulation of P53 and P21. The expression of several apoptosis-related proteins in cells and tumor tissues were evaluated by Western blot analysis. We found that matrine induced cell apoptosis by down-regulation of the ratio of BCL-2/BID and increasing activation of caspase-9. Further studies indicated that matrine induced apoptosis of Eca-109 was through the mitochondria-mediated internal pathway, but not by death receptor-mediated extrinsic apoptotic pathway, which was confirmed by the fact that Bid translocated from the nucleus to mitochondria during the process of the apoptosis induced by matrine. In vivo study found that matrine effectively inhibited the tumor formation of Eca-109 cells in nude mice. Our study suggests that matrine could serve as a potential novel agent from natural products to treat esophageal cancer.     

Physiologically attainable concentrations of lycopene induce mitochondrial apoptosis in LNCaP human prostate cancer cells

Prostate cancer is the second leading cause of cancer deaths among men in the United States. Studies show that people with diets rich in tomato-based foods have reduced risks of cancer, viz., prostate cancer. This is attributed, in part, to lycopene, the most abundant carotenoid in tomatoes. Thus, we studied the effect of lycopene at physiologically attainable concentrations on apoptosis, cellular proliferation, and necrosis in LNCaP human prostate cancer cells. Cells at 37 degrees C and >80% confluency were treated with media alone (0.32% tetrahydrofuran vehicle) or with increasing concentrations (0.3-3.0 microM) of lycopene overnight. After washing monolayers, analyses by high-performance liquid chromatography (HPLC) showed that cellular accumulation of lycopene was 5.5 +/- 0.8, 14.0 +/- 3.2, and 36.7 +/- 12.3 pmole/10(6) cells for 0.3, 1.0, and 3.0 muM, respectively, and not detected in control cells. Lycopene did not alter cellular proliferation because bromodeoxyuridine (BrdU) incorporation and cell numbers were identical among groups. However, results of a 3[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay showed that mitochondrial function decreased 61%-83% with increasing concentrations of lycopene (P < 0.001). Cytotoxicity and necrosis did not contribute to this effect because lactate dehydrogenase (LDH) release (1.5%-1.8%) and trypan blue exclusion (89%-93%) were similar. Subsequently, we demonstrated that increasing concentrations of lycopene significantly (P < 0.05) reduced mitochondrial transmembrane potential, induced the release of mitochondrial cytochrome c, and increased annexin V binding, confirming induction of apoptosis. Thus, lycopene at physiologically relevant concentrations did not affect cellular proliferation or promote necrosis but clearly altered mitochondrial function and induced apoptosis in LNCaP human prostate cancer cells.     

Microcin J25-Ga induces apoptosis in mammalian cells by inhibiting mitochondrial RNA-polymerase

MccJ25, an antimicrobial peptide, was unable to cause apoptosis of COS-7 cells in spite of inducing reactive-oxygen species overproduction as well as cytochrome c release from isolated mitochondria. Surprisingly, MccJ25-Ga, an amidated variant of MccJ25 that displays similar anti-mitochondrial effects, did induce apoptosis in COS-7. The only difference found between the activities of these peptides was the unpredicted inhibition of mitochondrial RNA synthesis by MccJ25-Ga. These results led us to hypothesize that both mitochondrial RNA polymerase and mitochondrial membrane might be the molecular targets of MccJ25-Ga in mitochondria and this combined effect may lead to apoptosis.