The p53 upregulated modulator of apoptosis (PUMA) chemosensitizes intrinsically resistant ovarian cancer cells to cisplatin by lowering the threshold set by Bcl-x(L) and Mcl-1.

Ovarian cancer is the number one cause of death from gynecologic malignancy. A defective p53 pathway is a hallmark of ovarian carcinoma. The p53 mutation correlates significantly with resistance to platinum-based chemotherapy, early relapse and shortened overall survival in ovarian cancer patients. PUMA (p53 upregulated modulator of apoptosis), a BH3-only Bcl-2 family protein, was recently identified as a transcriptional target of p53 and a potent apoptosis inducer in various cancer cells. In this study, we showed that the induction of PUMA by cisplatin was abolished in p53-deficient SKOV3 cells. Elevated expression of PUMA-induced apoptosis and sensitized A2780s and SKOV3 ovarian cancer cells to cisplatin, and the combination of PUMA and low-dose cisplatin, significantly suppressed xenograft tumor growth in vivo through enhanced induction of apoptosis compared with treatment with PUMA or cisplatin alone. The effects of PUMA were mediated by enhanced caspase activation and release of cytochrome c and Smac (second mitochondria-derived activator of caspase) into the cytosol. Furthermore, PUMA chemosensitized intrinsically resistant SKOV3 cells to cisplatin through downregulation of B-cell lymphoma-extra large (Bcl-x(L)) and myeloid cell leukemia sequence 1 (Mcl-1). PUMA-mediated Bcl-x(L) downregulation mainly happened at the transcription level, whereas PUMA-induced Mcl-1 down-regulation was associated with caspase-dependent cleavage and proteasome-mediated degradation. To our knowledge, these data suggest a new mechanism by which overexpression of PUMA enhances sensitivity of SKOV3 cells to cisplatin by lowering the threshold set simultaneously by Bcl-x(L) and Mcl-1. Taken together, our findings indicate that PUMA is an important modulator of therapeutic responses of ovarian cancer cells and is potentially useful as a chemosensitizer in ovarian cancer therapy.

[Cloning, subcellular localization and in situ detection of Xenopus laevis beta-synnclein gene].

OBJECTIVE: To clone Xenopus laevis beta-synuclein gene (xSYNB) and study the subcellular localization of xSYNB protein. METHODS: According to the xSYNB cDNA sequence published in GenBank, a pair of primers were designed. The encoding region of xSYNB gene from the adult Xenopus laevis brain was amplified by RT-PCR, and then was cloned into pGEM-T Easy vector. The resulting recombinant plasmid was named as TA-xSYNB. The xSYNB cDNA was further subcloned into the pEGFP-N1 vector, and the resulting recombinant expression plasmid pEGFPN1-xSYNB was transfected into HEK293 cells to analyze the subcellular localization of xSYNB. The whole-mount in situ hybridization of embryos were used to identify the expression localization of xSYNB. RESULTS: The recombinant expression plasmid pEGFPN1-xSYNB was successfully constructed. The results of green fluorescence detection suggested that xSYNB gene was mainly expressed in the cytoplasm, and the results of in situ hybridization suggested that xSYNB gene was mainly expressed in the brain of embryo. CONCLUSION: The xSYNB gene may play a role in the development of the nervous system of Xenopus laevis.

[Suppression of colon cancer in murine model by recombinant human endostatin adenovirus and cisplatin].

OBJECTIVE: To investigate the efficacy, side effect and anti-tumor mechanism of recombinant human endostatin adenovirus (Ad-hE) and cisplatin on murine colon cancer. METHODS: Mice with CT26 colon cancer were randomly divided into 5 groups, being given Ad-hE via tail vein, cisplatin (Cis) intraperitoneally, Ad-hE plus cisplatin (Ad-hE+Cis), empty adenovirus (Ad-N), and saline (NS), respectively. The therapeutic effect and side effect of the treatments and the angiogenesis and apoptosis of tumor cells were observed. RESULTS: Ad-hE + Cis suppressed the growth of lung metastatic tumor and prolonged survival time of the murine CT26 colon cancer model. The anti-tumor activity was associated with decreased microvessel density and increased apoptosis of tumor cells. CONCLUSION: Recombinant human endostatin adenovirus enhances the anti-tumor activity of cisplatin without increasing toxicity.

Long-term stable expression of antisense cDNA of cyclin B1 profoundly inhibits the proliferation of tumor cells and suppresses tumorigenicity in implanted mice.

BACKGROUND: Cyclin B1 (CLB1) is necessary for mitotic initiation in mammalian cells and plays important roles in cancer development. Therefore, a potential strategy in cancer therapy is to suppress the activity of CLB1 by delivering antisense constructs of CLB1 into tumor cells. In previous CLB1 studies, antisense constructs with a short half life were often used and these constructs might not persistently inhibit CLB1. METHODS: We successfully created a recombinant plasmid encoding the full-length antisense cDNA of mouse cyclin B1 (AS-mCLB1) and transfected this construct to the murine Lewis lung carcinoma (LL/2) and CT-26 colon carcinoma (CT-26) cells. We isolated clones of LL/2 and CT-26 transfectants with stable expression of AS-mCLB1. Reverse transcriptional polymerase chain reaction (RT-PCR) and Western blot were applied to detect the expression of the mRNA and protein levels of CLB1. To further test the efficacy of this strategy in vivo, AS-mCLB1-expressing LL/2 and CT-26 transfectants were implanted into mice. RESULTS: We found the expression of the mRNA and protein levels of CLB1 decrease in these transfectants. The inhibition of CLB1 caused prominent G1 arrest, abnormal morphology, retarded cell growth and an increase in apoptosis. In AS-mCLB1-expressing LL/2 and CT-26 transfectants implanted mice, tumorigenicity was effectively suppressed compared with the controls. In addition, the expression of AS-mCLB1 also significantly increases the survival duration of implanted animals. CONCLUSION: AS-mCLB1 is likely to be useful in future cancer therapy, which may be associated with its ability to down-regulate the expression of CLB1 and then induce G1arrest and apoptosis in tumor cells.

MicroRNA-1 promotes apoptosis of hepatocarcinoma cells by targeting apoptosis inhibitor-5 (API-5).

Although microRNA-1 (miR-1) is a known liver cancer suppressor, the role of miR-1 in apoptosis of hepatoma cells has remained largely unknown. Our study shows that ectopic miR-1 overexpression induced apoptosis of liver hepatocellular carcinoma (HepG2) cells. Apoptosis inhibitor 5 (API-5) was found to be a potential regulator of miR-1 induced apoptosis, using a bioinformatics approach. Furthermore, an inverse relationship between miR-1 and API-5 expression was observed in human liver cancer tissues and adjacent normal liver tissues. Negative regulation of API-5 expression by miR-1 was demonstrated to promote apoptosis of HepG2 cells. Our study provides a novel regulatory mechanism of miR-1 in the apoptosis of hepatoma cells.

NOXA-induced alterations in the Bax/Smac axis enhance sensitivity of ovarian cancer cells to cisplatin.

Ovarian cancer is the most common cause of death from gynecologic malignancy. Deregulation of p53 and/or p73-associated apoptotic pathways contribute to the platinum-based resistance in ovarian cancer. NOXA, a pro-apoptotic BH3-only protein, is identified as a transcription target of p53 and/or p73. In this study, we found that genetic variants of Bcl-2 proteins exist among cisplatin-sensitive and -resistant ovarian cancer cells, and the responses of NOXA and Bax to cisplatin are regulated mainly by p53. We further evaluated the effect of NOXA on cisplatin. NOXA induced apoptosis and sensitized A2780s and SKOV3 cells to cisplatin in vitro and in vivo. The effects were mediated by elevated Bax expression, enhanced caspase activation, release of Cyt C and Smac into the cytosol. Furthermore, gene silencing of Bax or Smac significantly attenuated NOXA and/or cisplatin-induced apoptosis in chemosensitive A2780s cells, whereas overexpression of Bax or addition of Smac-N7 peptide significantly increased NOXA and/or cisplatin-induced apoptosis in chemoresistant SKOV3 cells. To our knowledge, these data suggest a new mechanism by which NOXA chemosensitized ovarian cancer cells to cisplatin by inducing alterations in the Bax/Smac axis. Taken together, our findings show that NOXA is potentially useful as a chemosensitizer in ovarian cancer therapy.

PNAS-4, a novel pro-apoptotic gene, can potentiate antineoplastic effects of cisplatin.

PURPOSE: PNAS-4, a novel pro-apoptotic gene activated during the early response to DNA damage, can inhibit proliferation via apoptosis when overexpressed in some tumor cells. The objectives of this study were to determine whether PNAS-4 could enhance apoptosis induced by cisplatin besides its induction of apoptosis, and to evaluate the usefulness of combined treatment with mouse PNAS-4 (mPNAS-4) gene therapy and low-dose cisplatin chemotherapy in the inhibition of tumor growth in colon carcinoma (CT26) and Lewis lung carcinoma (LL/2) murine models. METHODS: In this study, the in vitro growth-inhibitory and pro-apoptotic effects of PNAS-4 and/or cisplatin on CT26, LL/2, and SKOV3 cancer cells were assessed by MTT assay, flow cytometric analysis, DNA fragmentation, and morphological analysis, respectively. The in vivo antitumor activity of combined treatment with mPNAS-4 gene therapy and low-dose cisplatin were evaluated in the inhibition of tumor growth in colon carcinoma (CT26) and Lewis lung carcinoma (LL/2) murine models. Tumor volume and survival time were observed. Induction of apoptosis was also assessed in tumor tissues. RESULTS: In vitro, PNAS-4 inhibited proliferation of colon carcinoma (CT26), Lewis lung carcinoma (LL/2) and human ovarian cancer (SKOV3) cell lines via apoptosis, and significantly enhanced the apoptosis of CT26, LL/2, and SKOV3 cells induced by cisplatin. In vivo systemic administration of expression plasmid encoding mPNAS-4 (pcDNA3.1-mPS) and cisplatin, significantly decreased tumor growth through increased tumor cell apoptosis compared to treatment with mPNAS-4 or cisplatin alone. CONCLUSIONS: Our data suggests that the combined treatment with mPNAS-4 plus cisplatin may augment the induction of apoptosis in tumor cells in vitro and in vivo, and that the augmented antitumor activity in vivo may result from the increased induction of apoptosis. The present study may provide a novel way to augment the antitumor efficacy of cytotoxic chemotherapy.

[Mechanism study of antisense cyclin B1 in tumorigenesis inhibition using proteomic technique].

BACKGROUND & OBJECTIVE: Previous researches showed that down-regulating the expression of cyclin B1 in tumor cells by RNA interference may inhibit tumorigenesis, but the mechanism remains to be clarified. This study was to reveal the molecular mechanism of antisense cyclin B1 in tumorigenesis inhibition by comparative proteomic technique. METHODS: A recombinant plasmid containing the full-length antisense cDNA of mouse cyclin B1 was transfected into mouse colon carcinoma cell line CT26. Total proteins of transfected cells and control cells were extracted and separated by two-dimensional gel electrophoresis (2-DE). The differential expression proteins were analyzed with PDQuest software, and identified using matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF-MS) and Mascot database searching. The 2 differential proteins with the highest confidence of the peptides were selected and verified by Western blot. RESULTS: Seven differentially expressed proteins were identified: Axin2, CCTtheta, DR5, and HPCM27 were up-regulated in transfected cells, while RFP17, mKIAA1195, and LOC77035 were down-regulated. The expression abundance differences of Axin2 and DR5, with the highest confidence, were verified by Western blot. CONCLUSIONS: Several proteins expressed differentially in CT26 cells after transfection of antisense cyclin B1, which take part in some signal pathways in cell proliferation, differentiation, migration, apoptosis, and transcriptional control. The antitumor effect of antisense cyclin B1 may relate to the interplay of the above proteins.

Induction of apoptosis by phenylisocyanate derivative of quercetin: involvement of heat shock protein.

Quercetin, a widely distributed bioflavonoid, inhibits the growth of various tumor cells. The present study was designed to investigate whether a novel quercetin derivative [phenylisocyanate of quercetin (PHICNQ)] exerts antitumor activity against K562 and CT26 tumor cell lines by inducing apoptosis, and to examine the possible mechanism in the phenomenon. The cell proliferation assay of K562 and CT26 tumor cells was determined by the trypan blue dye exclusion test. Apoptosis of PHICNQ-treated cells was determined by morphological analysis, agarose gel DNA electrophoresis and quantitated by flow cytometry after staining with propidium iodide. Cell cycle was evaluated by flow cytometry. The expression of heat shock protein 70 was checked by Western blot analysis. Our results showed that PHICNQ inhibited the proliferation of K562 and CT26 cells in a dose-dependent and time-dependent manner. PHICNQ was 308- and 73-fold more active on CT26 and K562 cells than quercetin, respectively. In addition to this cytostatic effect, treatment of K562 and CT26 tumor cells with PHICNQ induced apoptosis. PHICNQ treatment downregulated the expression of heat shock protein 70 more dramatically than quercetin treatment. These results suggest that PHICNQ is a more powerful antiproliferative derivative than quercetin, with cytostatic and apoptotic effects on K562 and CT26 tumor cells. PHICNQ may trigger apoptosis in tumor cells through inhibition of heat shock protein 70 synthesis and expression.