A novel form of constitutively active farnesylated Akt1 prevents mammary epithelial cells from anoikis and suppresses chemotherapy-induced apoptosis

Protein kinase B/Akt has been described as a central mediator of anti-apoptotic signals transduced by the PI3 kinase. Although the role of Akt in the suppression of apoptosis is well elucidated, a potential function of Akt in tumorigenesis and chemoresistance is less intensively documented. In this study, we describe the construction of a novel form of constitutively active Akt1, which relies on the deletion of its pleckstrin homology domain and the insertion of a C-terminal farnesylation sequence. Stable cell lines were generated with MCF10A mammary epithelial cells and A549 human NSCLC cells expressing constitutively active Akt1. Enigneered MCF10A cells were rendered resistant towards apoptosis resulting from loss of cellular substrate attachment (anoikis). We investigated the chemosensitivity of A549 cells expressing farnesylated Akt vs control cells. A profoundly decreased sensitivity towards Mitoxantrone and cisplatin was observed in cells expressing farnesylated Akt. No significant difference in sensitivity however was observed upon treatment with cell cycle specific chemotherapeutic agents like paclitaxel. Our data suggest, that Akt is a central mediator in the suppression of anoikis and modulation of chemotherapy-induced apoptosis. Therefore it represents a promising target for small molecule inhibitors to shift the apoptotic threshold in cancer cells after treatment with standard chemotherapy.     

Cisplatin increases B-cell-lymphoma-2 expression via activation of protein kinase C and Akt2 in endometrial cancer cells

Hypoxia is known to play important roles in the development and progression of tumors. We previously demonstrated that S100A4, a critical molecule for metastasis, was upregulated in ovarian cancer cells. Therefore, we examined the mechanisms of the upregulation of S100A4 expression in ovarian carcinoma cells, with particular attention paid to the effects of hypoxia. The expression levels of S100A4 were found to be correlated with the invasiveness of ovarian carcinoma cells in vitro and in vivo, and the upregulation of S100A4 expression was associated with hypomethylation of CpG sites in the first intron of S100A4 in ovarian carcinoma cell lines and tissues. The expression of S100A4 was increased under hypoxia and was associated with elevated invasiveness, which was inhibited by S100A4 small interfering RNA (siRNA). In addition, exposure to hypoxia reduced the methylation of hypoxia-response elements (HRE) of the S100A4 gene in a time-dependent fashion, in association with the increased binding of HIF-1α to a methylation-free HRE in ovarian carcinoma cells. These results indicate that hypoxia-induced hypomethylation plays an essential role in S100A4 overexpression and the epigenetic transformation of ovarian carcinoma cells into the "metastatic phenotype."     

Enhancement of cisplatin-induced apoptosis by infection with adeno-associated virus type 2.

The non-pathogenic human adeno-associated virus, AAV, has been shown to sensitize human cancer cells and experimental tumors towards the action of chemotherapeutic agents such as cisplatin. Since chemotherapeutic drugs mainly involve the induction of apoptosis, we investigated whether 1 possible mechanism of AAV-mediated sensitization of human tumor cells may result from an enhancement of cisplatin-induced apoptosis. In HeLa and A549 cells, infection with AAV type 2 (AAV-2) increased cisplatin-induced DNA fragmentation but had no cytotoxic effect by itself. This enhanced apoptosis appeared to be mediated at least in part by a component of the viral capsid since empty or UV-inactivated AAV-2 particles were also able to boost cisplatin-induced DNA fragmentation. Interestingly, these effects were not observed after infection with AAV type 5 (AAV-5) or the autonomous parvovirus, H-1. AAV-2-mediated enhancement of apoptosis was not associated with a modification of the expression of CD95 ligand, CD95 receptor or other death receptors, as shown by RT-PCR and RNase protection assay. In contrast, using the mitochondrial fluorescent dye, JC-1 in flow cytometry, AAV-2 infection was found to further reduce the mitochondrial transmembrane potential after treatment with cisplatin in a caspase-independent manner, suggesting that increase of apoptosis by AAV-2 occurred at the mitochondrial level. In contrast, in cells of the small cell lung cancer line, P693, an enhancement of cisplatin-induced DNA fragmentation was not observed after infection with AAV-2. In these cells, sensitization to cisplatin-toxicity was associated with cell cycle arrest in G2/M. The data indicate that in the absence of viral gene expression, AAV-2-mediated sensitization to cisplatin involves multiple cellular pathways promoting cell death signals in a cell type-dependent manner. The results further support that AAV-2 particles may be appropriate adjuvants for improving cancer chemotherapy and may also have consequences regarding AAV-2-based vectors for gene therapy.     

Aurora-A induces cell survival and chemoresistance by activation of Akt through a p53-dependent manner in ovarian cancer cells

Aurora-A is frequently altered in epithelial malignancies. Overexpressing Aurora-A induces centrosome amplification and G2/M cell cycle progression. We have previously shown elevated level of Aurora-A in ovarian cancer and activation of telomerase by Aurora-A in human mammary and ovarian epithelia. Here we report that Aurora-A protects ovarian cancer cells from apoptosis induced by chemotherapeutic agent and activates Akt pathway in a p53-dependent manner. Ectopic expression of Aurora-A renders cells resistant to cisplatin (CDDP), etoposide and paclitaxel-induced apoptosis and stimulates Akt1 and Akt2 activity in wild-type p53 but not p53-null ovarian cancer cells. Aurora-A inhibits cytochrome C release and Bax conformational change induced by CDDP. Knockdown of Aurora-A by RNAi sensitizes cells to CDDP-induced apoptosis and decreases phospho-Akt level in wild-type p53 cells. Reintroduction of p53 decreases Akt1 and Akt2 activation and restores CDDP sensitivity in p53-null but not p53-null-Aurora-A cells. Inhibition of Akt by small molecule inhibitor, API-2, overcomes the effects of Aurora-A-on cell survival and Bax mitochondrial translocation. Taken collectively, these data indicate that Aurora-A activates Akt and induces chemoresistance in a p53-dependent manner and that inhibition of Akt may be an effective means of overcoming Aurora-A-associated chemoresistance in ovarian cancer cells expressing wild-type p53.     

Sensitisation for cisplatin-induced apoptosis by isothiocyanate E-4IB leads to signalling pathways alterations

A new synthetic isothiocyanate (ITC) derivative, ethyl 4-isothiocyanatobutanoate (E-4IB), appeared to be an effective modulator of cellular proliferation and potent inducer of apoptosis. In cooperation with cisplatin, this compound exerted synergistic effects in human ovarian carcinoma A2780 cells. In the present study we investigated in more detail E4IB-sensitisation for cisplatin-induced apoptosis. Sequential administration of both cytostatic agents led to increased intracellular platinum accumulation, glutathione level depletion and mitochondrial membrane potential dissipation. These events were accompanied with poly (ADP-ribosyl) polymerase cleavage, stimulation of caspase-3 activity, upregulation of p53, FasL and Gadd45alpha, cyclin B1 downregulation and an increase in mitogen-activated protein kinases JNK, ERK and p38 phosphorylation as well as PI3K level alterations. The presented results might have implications for developing new strategies aimed at therapeutic benefit of natural or synthetic ITCs in cooperation with various anticancer drugs.     

Low expression of MYCN promotes cisplatin resistance by suppressing cisplatin-induced apoptosis in epithelial ovarian cancer

Epithelial ovarian cancer (EOC) is the most common cause of gynecological cancer-associated mortality. Cisplatin is one of the most effective chemotherapeutic drugs used in EOC; however, its use can lead to relapse due to cisplatin resistance. MYCN sensitizes neuroblastoma to undergo cisplatin-induced apoptosis. However, to the best of our knowledge, there have been no studies to date on the association between MYCN and cisplatin resistance in EOC. Therefore, the present study assessed this association. Datasets from The Cancer Genome Atlas database were used. The overall survival (OS) of patients receiving platin-based therapy was analyzed using Kaplan-Meier Plotter software. RNA sequencing data of 300 patients with EOC were downloaded from cBioportal. The co-expressed genes were subjected to ‘Kyoto Encyclopedia of Genes and Genomes’ analysis using DAVID software. For gene set enrichment analysis, the expression matrix was separated according to the median expression of MYCN, which was selected for hallmark gene set enrichment. Immunohistochemistry was used to assess MYCN expression in EOC tissue. Western blotting was used to evaluate MYCN, p53, Bax and Bcl-2 protein expression levels in EOC cells. Cell viability and apoptosis were assessed using Cell Counting Kit-8 and flow cytometry, respectively. The results demonstrated that MYCN upregulation was associated with increased cisplatin sensitivity and prolonged OS of patients with EOC and patients receiving platin-based therapy. Cisplatin downregulated MYCN expression in cisplatin-sensitive, but not resistant, EOC cells. The genes co-expressed with MYCN were primarily involved in pathways involved in ‘chemotherapeutic resistance’ and ‘apoptosis’. MYCN enriched the apoptosis and p53 signaling pathways in hallmark gene sets. Cells in which MYCN was knocked down demonstrated significantly increased cisplatin resistance; however, MYCN overexpression in cisplatin-resistant cells restored cisplatin sensitivity. Collectively, the present study demonstrated that MYCN downregulation promoted cisplatin resistance by suppressing cisplatin-induced apoptosis in EOC.     

Calpain-mediated pathway dominates cisplatin-induced apoptosis in human lung adenocarcinoma cells as determined by real-time single cell analysis

Cisplatin is an efficient anticancer agent. Cisplatin-based chemotherapy is believed to involve different signal transduction pathways, among which calpain activation has been proposed as an important factor in the induced apoptosis. In our study, based on real-time single cell analysis, we investigated the molecular involvement of calpain in cisplatin-induced apoptosis in living human lung adenocarcinoma cells. After cisplatin treatment, calpain was activated, resulting in Bid cleavage at 4-5 hr, followed by Bid translocation and cytochrome c release, leading to cell death. Calpeptin and PD150606, specific inhibitors of calpain, blocked Bid activation completely; however, cytochrome c release was delayed by more than 2 hr, which was associated with the delay of caspase-3 activation and cell death. Remarkably, calpain-mediated release of cytochrome c and cell death was significantly compromised in the Bid knockdown cells. Z-IETD-fmk and Z-VDVAD-fmk were used to block the activation of caspase-8 and caspase-2, respectively; however, the progression of apoptosis were not affected, suggesting that caspase-8 and caspase-2 were not involved in this experimental model. Taken together, the data demonstrate that calpain mediated cisplatin-induced apoptosis in human lung adenocarcinoma cells through activating Bid, which then regulated the mitochondrial apoptotic pathway. The delays of cytochrome c release, caspase-3 activation and subsequent cell death by inactivating calpain or silencing Bid exclude other earlier or parallel pathways, strongly suggesting that the calpain-mediated pathway is the kinetically earliest one, which dominates the cisplatin-induced apoptosis.     

Akt/c-Myc通路对胃癌细胞化疗效果的影响

背景与目的：Akt信号通路是调节原癌基因c-myc蛋白表达水平的主要机制之一,Akt信号通路激活后可降低胃癌细胞的化疗敏感性。然而,目前对Akt/c-Myc通路在胃癌化疗过程中的作用尚不明确。因此,本课题通过观察Akt/c-Myc信号通路对胃癌细胞化疗效果的影响并探讨其作用机制。方法：依托泊苷作用于胃癌SGC7901和BGC823细胞,MTT法检测细胞的生存率;分别采用流式细胞仪和Hoechst33258荧光染色法检测细胞周期分布和凋亡;Akt活性的检测采用非放射性蛋白激酶活性分析法;Western印迹法检测c-Myc和p-AktSer473蛋白的表达水平;RT-PCR法检测c-MycmRNA的表达;同时观察PI3-K/Akt通路抑制剂Wortmannin对依托泊苷诱导的上述变化的影响。结果：依托泊苷呈时间-剂量依赖性抑制SGC7901和BGC823细胞的生长,明显诱导细胞的凋亡;同时上调SGC7901和BGC823细胞中Akt活性及p-AktSer473蛋白表达水平,并增强c-Myc蛋白和mRNA的表达。Wortmannin可明显增强依托泊苷的细胞生长抑制作用并提高细胞的凋亡水平;抑制依托泊苷诱导的c-Myc蛋白的表达,但对c-MycmRNA表达没有明显的影响。结论：依托泊苷激活SGC7901和BGC823细胞中的Akt信号通路,并上调c-Myc蛋白的表达水平而影响胃癌的化疗效果。Akt信号通路可能主要是通过转录后调节来调控c-Myc蛋白的水平。     

Tetrandrine induces apoptosis by activating reactive oxygen species and repressing Akt activity in human hepatocellular carcinoma

Tetrandrine, a bisbenzylisoquinoline alkaloid component of broadly used traditional Chinese medicine, has antitumor effects against some cancers. In our study, we investigated the effects of tetrandrine on the human hepatocellular carcinoma (HCC) in vitro and in vivo. The results showed that tetrandrine effectively induced apoptosis of liver cancer cell in a dose- and time-dependent manner accompanied by alteration of cell morphology, chromatin fragmentation and caspase activation. Tetrandrine treatment also induced intracellular accumulation of reactive oxygen species (ROS), and ROS scavengers (LNAC and GSH) completely blocked the effects of tetrandrine-induced apoptosis, suggesting that the generation of ROS plays an important role in tetrandrine-induced apoptosis. Although the activities of JNK and ERK were inhibited significantly by tetrandrine treatment, JNK and ERK are not involved in the tetrandrine-induced apoptosis. In contrast, Akt activity was found to be closely related to tetrandrine-induced apoptosis. The data demonstrated that Akt activity inhibitor LY294002 synergistically promoted tetrandrine-induced apoptosis of HCC, whereas ectopic expression of Akt contrastly abrogated partial of the tetrandrine-induced apoptosis. These data suggest that Akt signal is the downstream event of ROS generation in the tetrandrine-induced HCC cell apoptosis. Moreover, the results of xenograft in nude mice were consistent with that of the in vitro studies. Therefore, our data suggest that tetrandrine may be a promising agent for the treatment of HCC as a regulator of ROS/Akt pathway.     

Akt promotes cisplatin resistance in human ovarian cancer cells through inhibition of p53 phosphorylation and nuclear function

Resistance to cisplatin-based chemotherapy is a major cause of treatment failure in human ovarian cancer. Wild-type TP53 status is often, but not always, associated with cisplatin sensitivity, suggesting that additional factors may be involved. Overexpression/activation of the phosphatidylinositol-3-kinase/Akt pathway is commonly observed in ovarian cancer, and Akt activation is a determinant of chemoresistance in ovarian cancer cells, an effect that may be due, in part, to its inhibitory actions on p53-dependent apoptosis. To that end, we examined the role and regulation of p53 in chemosensitive ovarian cancer cells, as well as in their chemoresistant counterparts, and investigated if and how Akt influences this pathway. Cisplatin induced apoptosis in chemosensitive, but not chemoresistant cells, and this was inhibited by downregulation of p53. Cisplatin upregulated PUMA in a p53-dependent manner, and the presence of PUMA was necessary, but not sufficient for cisplatin-induced apoptosis. p53 was phosphorylated on numerous N-terminal residues, including Ser15, Ser20, in response to cisplatin in chemosensitive, but not chemoresistant cells. Furthermore, activation of Akt inhibited the cisplatin-induced upregulation of PUMA, and suppressed cisplatin-induced p53 phosphorylation, while inhibition of Akt increased total and phospho-p53 contents and sensitized p53 wild-type, chemoresistant cells to cisplatin-induced apoptosis. Finally, mutation of Ser15 and/or Ser20, but not of Ser37, to alanine significantly attenuated the ability of p53 to facilitate CDDP-induced apoptosis, and this was independent of PUMA expression. These results support the hypothesis that p53 is a determinant of CDDP sensitivity, and suggest that Akt contributes to chemoresistance, in part, by attenuating p53-mediated PUMA upregulation and phosphorylation of p53, which are essential, but independent determinants of sensitivity to CDDP-induced apoptosis.     

Biological and chemical inhibitors of NF-kappaB sensitize SiHa cells to cisplatin-induced apoptosis

Cisplatin, a chemotherapeutic agent, is known to induce apoptosis of cancer cells. We examined the role of NF-kappaB during cisplatin-induced apoptosis in two human cervical cancer cell lines, HeLa and SiHa, known to differ in their response to cisplatin treatment. We found that SiHa cells were relatively more resistant than HeLa cells to the cytotoxic effects induced by cisplatin as measured by MTT assays. HeLa cells were more sensitive to the apoptotic effects induced by cisplatin as shown by increases in annexin staining, DNA fragmentation, and loss of mitochondrial membrane potential. Similarly the activities of caspases 3, 8, and 9 and cleavage of PARP induced by cisplatin were more in HeLa than SiHa cells. Cisplatin induced NF-kappaB DNA binding activity in HeLa and SiHa cells but not in primary cervical cells and the active DNA binding complex in SiHa cells consists of p50 and RelA heterodimers. However, when NF-kappaB DNA binding activity was blocked by chemical (curcumin, PDTC, or salicylic acid) or biological inhibitors (NIK-KM or IKK-beta DN), the cell viability was less in SiHa cells with cisplatin treatment, but these effects were not observed in HeLa cells. Similarly upon treatment with cisplatin SiHa cells had more activation of caspases compared to that seen in HeLa cells under conditions of NF-kappaB inhibition by biological or chemical inhibitors. These results suggest that NF-kappaB may contribute to the resistance of human cervical cancer cells to cisplatin and highlight the potential use of combination therapy involving cisplatin and NF-kappaB inhibitors.     

Retaining MKP1 expression and attenuating JNK-mediated apoptosis by RIP1 for cisplatin resistance through miR-940 inhibition

The elucidation of chemoresistance mechanisms is important to improve cancer patient survival. In this report, we investigated the role and mechanism through which receptor-interacting protein 1 (RIP1), a mediator in cell survival and death signaling, participates in cancer''s response to chemotherapy. In lung cancer cells, knockdown of RIP1 substantially increased cisplatin-induced apoptotic cytotoxicity, which was associated with robust JNK activation. The expression of the JNK inactivating phosphatase, MKP1, was substantially reduced in RIP1 knockdown cells. Although MKP1 protein stability was not altered by RIP1 suppression, the synthesis rate of MKP1 was dramatically reduced in RIP1-suppressed cells. Furthermore, we found that the expression of miR-940 was substantially increased in RIP1 knockdown cells. Knockdown of miR-940 restored MKP1 expression and attenuated cisplatin-induced JNK activation and cytotoxicity. Importantly, ectopic expression of MKP1 effectively attenuated cisplatin-induced JNK activation and cytotoxicity. In addition, activation of the JNK upstream signaling kinase, MKK4, was also potentiated in RIP1 knockdown cells. Altogether, our results suggest that RIP1 contributes to cisplatin resistance by suppressing JNK activation that involves releasing miR-940-mediated inhibition of MKP1 and suppressing activation of MKK4. Intervention targeting the RIP1/miR-940/MKP1/JNK pathway may be used to sensitize platinum-based chemotherapy.     

HtrA1 sensitizes ovarian cancer cells to cisplatin-induced cytotoxicity by targeting XIAP for degradation

HtrA1, a member of serine protease family, has been previously found to be involved in resistance to chemotherapy in ovarian cancer although the underlying mechanism is not clear. Using mixture-based oriented peptide library approach, previously we identified X-linked inhibitor of apoptosis protein (XIAP), a member of the inhibitor of apoptosis proteins family, as a potential substrate of HtrA1. The aim of our work is to investigate the link between HtrA1 and XIAP proteins and their relationships with chemoresistance in ovarian cancer. Our results showed that recombinant XIAP was degraded by purified wild-type HtrA1 but not mutant HtrA1 in vitro. Consistent with the in vitro data, coimmunoprecipitation assays showed that HtrA1 and XIAP formed a protein complex in vivo. Ectopic expression of HtrA1 led to decreased level of XIAP in OV167 and OV202 ovarian cancer cells, while knockdown of HtrA1 resulted in increased level of XIAP in SKOV3 ovarian cancer cells. Furthermore, overexpression of HtrA1 in OV202 cells promoted cell sensitivity to cisplatin-induced apoptosis that could be reversed by increased expression of XIAP. The cleavage of XIAP induced by HtrA1 was enhanced by cisplatin treatment. Taken together, our experiments have identified XIAP as a novel substrate of HtrA1 and the degradation of XIAP by HtrA1 contributes to cell response to chemotherapy, suggesting that restoring the expression of HtrA1 may be a promising treatment strategy for ovarian cancer.     

Geldanamycin decreases Raf-1 and Akt levels and induces apoptosis in neuroblastomas

Neuroblastomas are the most common extracranial solid tumors of childhood. These tumors are associated with an overall poor prognosis, particularly for advanced stage disease. The benzoquinone ansamycin antibiotic, geldanamycin (GA), exhibits potent antitumor activity in certain cancer cell lines by destabilizing important signal transduction proteins (e.g., Raf-1 and Akt). The purpose of our study was to determine whether GA can alter the expression of Raf-1 and Akt, which have been shown to be critical for neuronal cell survival, and induce apoptosis of neuroblastoma cells. Human neuroblastoma cells (SH-SY5Y, SK-N-SH and LAN-1) were treated with GA for a variable period of time. Cell viability was assessed with MTT assays. Apoptosis was assessed with DNA fragmentation ELISA, TUNEL-flow cytometric assay, Western blot and caspase activities. We found that GA decreases cell viability and induces apoptosis in the SH-SY5Y human neuroblastoma cell line. These effects were mediated through activation of caspase-9 and -3, mitochondrial release of cytochrome c and subsequent PARP cleavage. GA-induced apoptosis was associated with a reduction in the level and activity of Raf-1 and Akt. The importance of these proteins was further demonstrated by induction of apoptosis in SH-SY5Y cells by a combination of U0126 (MEK1/2 inhibitor) and LY294002 (an inhibitor of PI3K). Similar to SH-SY5Y cells, other human neuroblastoma cells (SK-N-SH and LAN-1) were sensitive to the effects of GA-induced apoptosis. Taken together, our findings suggest that GA may be a novel therapeutic agent, which may be effective in the treatment of neuroblastomas.     

Cisplatin-dependent upregulation of death receptors 4 and 5 augments induction of apoptosis by TNF-related apoptosis-inducing ligand against esophageal squamous cell carcinoma

TNF-related apoptosis-inducing ligand (TRAIL) is a member of the TNF superfamily known to induce apoptosis in a variety of cancers. The purpose of our study was to examine the effects of TRAIL in combination with cisplatin against esophageal squamous cell carcinoma (ESCC) cell lines in vitro and in vivo, and to elucidate underlying molecular mechanisms. Expression profiles of TRAIL receptors were investigated in 19 ESCC (KYSE) cell lines using RT-PCR. Crystal violet staining assays were performed to reveal the sensitivity against TRAIL. Flow cytometric analyses of apoptosis induction and TRAIL receptor expression were performed. Furthermore, Western blot was used to clarify the apoptosis pathway involved, and a nude-mouse xenograft model was used to show effects in vivo. Results show that death receptors (DR) 4 and 5 were expressed in 100% of the cell lines, and 79% (15/19) expressed 4 TRAIL receptors. There was only 1 cell line without decoy receptor expression. Eighteen cell lines were resistant to TRAIL, but in some, the combination treatment with cisplatin could overcome this resistance. They underwent apoptosis via activation of caspase-8 and -3, and cisplatin-dependent upregulation of DR4 and 5 was detected. Furthermore, pretreatment with cisplatin followed by TRAIL resulted in significant tumoricidal effects. Finally, systemic administration of TRAIL with cisplatin synergistically suppressed tumor growth of ESCC xenografts in nude mice. These results provide a significance of cisplatin-induced upregulation of death receptors as apoptosis-inducing machinery, and it was suggested that sequential administration of cisplatin and TRAIL might be a feasible chemotherapeutic regimen against ESCC.