A novel dual signaling axis for NSP 5a3a induced apoptosis in head and neck carcinoma

NSP 5a3a is a novel structural protein found to be over-expressed in certain cancer cell lines in-vitro such as Hela, Saos-2, and MCF-7 while barely detectable levels in normal body tissues except for Testis. This particular isoform has been known to interact with cyto- nuclear proteins B23, known to be involved in multi-faceted cellular processes such as cell division, apoptosis, ribosome biogenesis, and rRNA processing, as well as with hnRNP-L, known to be involved with RNA metabolism and rRNA processing. A previous preliminary investigation of NSP 5a3a as a potential target in Head and Neck Carcinoma revealed a novel p73 dependent mechanism through which NSP 5a3a induced apoptosis in Head and Neck cell lines when over-expressed in-vitro. Our present investigation further elucidated a novel dual axis signaling point by which NSP 5a3a induces apoptosis in Head and Neck cell line HN30 through p73-DAXX and TRAF2-TRADD. Interestingly, this novel mechanism appears independent of canonical caspases involved in the intrinsic mitochondrial pathway as well as those in the death receptor pathway thru TRAF2 and TRADD.     

Targeted cancer therapy with ribosome biogenesis inhibitors: a real possibility?

The effects of many chemotherapeutic drugs on ribosome biogenesis have been underestimated for a long time. Indeed, many drugs currently used for cancer treatment – and which are known to either damage DNA or hinder DNA synthesis – have been shown to exert their toxic action mainly by inhibiting rRNA synthesis or maturation. Moreover, there are new drugs that have been proposed recently for cancer chemotherapy, which only hinder ribosome biogenesis without any genotoxic activity. Even though ribosome biogenesis occurs in both normal and cancer cells, whether resting or proliferating, there is evidence that the selective inhibition of ribosome biogenesis may, in some instances, result in a selective damage to neoplastic cells. The higher sensitivity of cancer cells to inhibitors of rRNA synthesis appears to be the consequence of either the loss of the mechanisms controlling the cell cycle progression or the acquisition of activating oncogene and inactivating tumor suppressor gene mutations that up-regulate the ribosome biogenesis rate. This article reviews those cancer cell characteristics on which the selective cancer cell cytotoxicity induced by the inhibitors of ribosome biogenesis is based.     

RNA helicase DDX5 is a p53-independent target of ARF that participates in ribosome biogenesis

The p19ARF tumor suppressor limits ribosome biogenesis and responds to hyperproliferative signals to activate the p53 checkpoint response. Although its activation of p53 has been well characterized, the role of ARF in restraining nucleolar ribosome production is poorly understood. Here we report the use of a mass spectroscopic analysis to identify protein changes within the nucleoli of Arf-deficient mouse cells. Through this approach, we discovered that ARF limited the nucleolar localization of the RNA helicase DDX5, which promotes the synthesis and maturation of rRNA, ultimately increasing ribosome output and proliferation. ARF inhibited the interaction between DDX5 and nucleophosmin (NPM), preventing association of DDX5 with the rDNA promoter and nuclear pre-ribosomes. In addition, Arf-deficient cells transformed by oncogenic RasV12 were addicted to DDX5, because reduction of DDX5 was sufficient to impair RasV12-driven colony formation in soft agar and tumor growth in mice. Taken together, our findings indicate that DDX5 is a key p53-independent target of the ARF tumor suppressor and is a novel non-oncogene participant in ribosome biogenesis.     

Functional analysis of a novel glioma antigen,EFTUD1

Background

A cDNA library made from 2 glioma cell lines, U87MG and T98G, was screened by serological identification of antigens by recombinant cDNA expression (SEREX) using serum from a glioblastoma patient. Elongation factor Tu GTP binding domain containing protein 1 (EFTUD1), which is required for ribosome biogenesis, was identified. A cancer microarray database showed overexpression of EFTUD1 in gliomas, suggesting that EFTUD1 is a candidate molecular target for gliomas.

Methods

EFTUD1 expression in glioma cell lines and glioma tissue was assessed by Western blot, quantitative PCR, and immunohistochemistry. The effect on ribosome biogenesis, cell growth, cell cycle, and induction of apoptosis and autophagy in glioma cells during the downregulation of EFTUD1 was investigated. To reveal the role of autophagy, the autophagy-blocker, chloroquine (CQ), was used in glioma cells downregulating EFTUD1. The effect of combining CQ with EFTUD1 inhibition in glioma cells was analyzed.

Results

EFTUD1 expression in glioma cell lines and tissue was higher than in normal brain tissue. Downregulating EFTUD1 induced G1 cell-cycle arrest and apoptosis, leading to reduced glioma cell proliferation. The mechanism underlying this antitumor effect was impaired ribosome biogenesis via EFTUD1 inhibition. Additionally, protective autophagy was induced by glioma cells as an adaptive response to EFTUD1 inhibition. The antitumor effect induced by the combined treatment was significantly higher than that of either EFTUD1 inhibition or CQ alone.

Conclusion

These results suggest that EFTUD1 represents a novel therapeutic target and that the combination of EFTUD1 inhibition with autophagy blockade may be effective in the treatment of gliomas.     

In vitro and in vivo analysis of the interaction between 5.8S rRNA and ARF protein reveal a new difference between murine p19ARF and human p14ARF

Both human and murine ARF proteins have been recently reported to impair rRNA maturation and ribosomes biogenesis through a p53-independent pathway. A specific interaction has been established between 5.8S rRNA and the murine p19ARF specie. We report here, by use of both in vitro and ChIP-RNA assays, the absence of any interaction between the human p14ARF and the homologous 5.8S rRNA. Our data are not consistent with the involvement of a 5.8S-p14ARF complex in ribosome biogenesis in man. Rather they suggest that the human protein does not require such an interaction to achieve a similar function. This result is a new argument in favour of functional differences between human and murine ARF proteins.     

TRAIL induces apoptosis in oral squamous carcinoma cells: a crosstalk with oncogenic Ras regulated cell surface expression of death receptor 5

TNF-related apoptosis inducing ligand (TRAIL) induces apoptosis through its death receptors (DRs) 4 and/or 5 expressed on the surface of target cells. The selectivity of TRAIL towards cancer cells has promoted clinical evaluation of recombinant human TRAIL (rhTRAIL) and its agonistic antibodies in treating several major human cancers including colon and non-Hodgkin''s lymphoma. However, little is known about their ability in killing oral squamous cell carcinoma (OSCC) cells. In this study, we tested the apoptotic responses of a panel of seven human OSCC cell lines (HN31, HN30, HN12, HN6, HN4, Cal27, and OSCC3) to rhTRAIL and monoclonal antibodies against DR4 or DR5. We found that rhTRAIL is a potent inducer of apoptosis in most of the oral cancer cell lines tested both in vitro and in vivo. We also showed that DR5 was expressed on the surface of the tested cell lines which correlated with the cellular susceptibility to apoptosis induced by rhTRAIL and anti-DR5 antibody. By contrast, little or no DR4 was detected on the surface of OSCC3 and HN6 cells rendering cellular resistance to DR4 antibody and a reduced sensitivity to rhTRAIL. Notably, the overall TRAIL sensitivity correlated well with the levels of endogenous active Ras in the cell lines tested. Expression of a constitutively active Ras mutant (RasV12) in OSCC3 cells selectively upregulated surface expression of DR5, but not DR4, and restored TRAIL sensitivity. Our findings could have implications for the use of TRAIL receptor targeted therapies in the treatment of human OSCC tumors particularly the ones harboring constitutively active Ras mutant.     

沉默lncRNA HOTTIP通过上调miR-663a表达增加非小细胞肺癌细胞系放射敏感性

目的 探讨lncRNA HOTTIP通过调控miR-663a表达对4个非小细胞肺癌细胞系放射敏感性影响。方法 用0、2、4、6、8 Gy分别照射H838、H157、A549、H1299细胞系,采用克隆形成实验检测细胞存活情况。qRT-PCR检测细胞中HOTTIP和miR-663a表达水平。以A549、H1299细胞为研究对象,沉默HOTTIP表达、过表达miR-663a后用克隆形成实验检测细胞存活情况。流式细胞术检测细胞凋亡情况,Western blot检测Cleaved caspase-3、Cleaved PARP和γ-H2AX表达。双荧光素酶报告基因实验和qRT-PCR检测验证HOTTIP和miR-663a的靶向关系。结果 HOTTIP在放射耐受的H157、A549、H1299细胞中表达上调,miR-663a表达下调。沉默HOTTIP或过表达miR-663a均可抑制A549、H1299细胞存活(放射增敏比分别为1.562、1.507),促进Cleaved caspase-3、Cleaved PARP和γ-H2AX表达,促进放射照射诱导细胞凋亡。miR-663a是HOTTIP的靶基因,HOTTIP可负性调控miR-663a的表达。抑制miR-663a表达可逆转沉默HOTTIP对肺癌细胞系放射敏感性的影响。结论 沉默HOTTIP通过上调miR-663a表达,抑制肺癌细胞系存活,促进其凋亡,从而提高肺癌细胞系的放射敏感性。     

miR-486-5p对胃癌细胞株SGC7901生物学行为的影响

背景与目的：既往研究表明微小RNA-486-5p(miR-486-5p)在多种肿瘤的进展中起重要作用,但其在胃癌中作用的研究较少,本研究旨在探讨miR-486-5p对胃癌细胞株SGC7901增殖、凋亡及迁移能力的影响。方法：使用实时定量PCR(quantification real-time PCR,qRT-PCR)检测胃癌细胞株SGC7901及胃黏膜上皮细胞GES-1中miR-486-5p的表达,构建miR-486-5p过表达质粒,使用脂质体法瞬时转染胃癌细胞株SGC7901,qRT-PCR检测转染细胞后miR-486-5p的表达丰度,噻唑蓝(MTT)法及流式细胞仪检测细胞的增殖及凋亡情况,Transwell小室迁移实验检测细胞的迁移能力。结果：miR-486-5p在SGC7901细胞中表达明显下调,SGC7901细胞转染miR-486-5p过表达质粒后,miR-486-5p表达明显上调,细胞增殖、迁移能力降低,凋亡率增高,差异均有统计学意义(P<0.05)。结论：miR-486-5p可抑制胃癌细胞株SGC7901的增殖和迁移。     

Oncogenic AKTivation of translation as a therapeutic target

The AKT signalling pathway is a major regulator of protein synthesis that impinges on multiple cellular processes frequently altered in cancer, such as proliferation, cell growth, survival, and angiogenesis. AKT controls protein synthesis by regulating the multistep process of mRNA translation at every stage from ribosome biogenesis to translation initiation and elongation. Recent studies have highlighted the ability of oncogenic AKT to drive cellular transformation by altering gene expression at the translational level. Oncogenic AKT signalling leads to both global changes in protein synthesis as well as specific changes in the translation of select mRNAs. New and developing technologies are significantly advancing our ability to identify and functionally group these translationally controlled mRNAs into gene networks based on their modes of regulation. How oncogenic AKT activates ribosome biogenesis, translation initiation, and translational elongation to regulate these translational networks is an ongoing area of research. Currently, the majority of therapeutics targeting translational control are focused on blocking translation initiation through inhibition of eIF4E hyperactivity. However, it will be important to determine whether combined inhibition of ribosome biogenesis, translation initiation, and translation elongation can demonstrate improved therapeutic efficacy in tumours driven by oncogenic AKT.     

A new PICTure of nucleolar stress

Cell growth demands new protein synthesis, which requires nucleolar ribosomal functions. Ribosome biogenesis consumes a large proportion of the cell's resources and energy, and so is tightly regulated through an intricate signaling network to guarantee fidelity. Thus, events that impair ribosome biogenesis cause nucleolar stress. In response to this stress, several nucleolar ribosomal proteins (RPs) translocate to the nucleoplasm and bind to MDM2. MDM2‐mediated ubiquitination and degradation of the tumor suppressor p53 is then blocked, resulting in p53 accumulation and the induction of p53‐dependent cell cycle arrest and apoptosis. Nucleolar stress is therefore a quality control surveillance mechanism that monitors the synthesis and assembly of the rRNA and protein components of ribosomes. Although nucleolar stress signaling pathways have been extensively analyzed, critical questions remain about their regulatory mechanisms. For example, how do RPs translocate from the nucleolus to the nucleoplasm to exert their functions, and do these p53‐regulating RPs influence the prognosis of human cancer patients? Our laboratory recently identified the nucleolar protein PICT1 as a novel regulator of nucleolar stress. PICT1 sequesters the ribosomal protein RPL11 in the nucleolus, preventing it from binding to MDM2. MDM2 is then free to degrade p53, favoring tumor cell growth. Accordingly, the level of PICT1 in a tumor is becoming a useful prognostic marker for human cancers. This review summarizes the evidence that links nucleolar stress to tumorigenesis, and casts PICT1 as an oncogenic player in human cancer biology. (Cancer Sci 2012; 103: 632–637)     

Translocation of Bax to mitochondria induces apoptotic cell death in indole-3-carbinol (I3C) treated breast cancer cells

Epidemiological studies have suggested that the consumption of fruits and vegetables that provide several classes of compounds, including Indole-3-carbinol (I3C), may have chemopreventive activity against breast cancer. Several in vitro and in vivo animal studies also provide convincing evidence for the anti-tumor activity of I3C, however, the molecular mechanism(s) by which I3C exerts its biological effects on breast cancer cells has not been fully elucidated. In this study, we investigated the effects of I3C in Her-2/neu over-expressing MDA-MB-435 breast cancer cells and compared these results with parental cells transfected with control vector. We focused our investigation in elucidating the molecular mechanism(s) by which I3C induces apoptosis in breast cancer cells. Our data show that I3C inhibits breast cancer cell growth in a dose dependent manner in Her-2/neu over-expressing and in normal Her-2/neu expressing cells. Induction of apoptosis was also observed in these cell lines when treated with I3C, as measured by poly (ADPribose) polymerase (PARP) and caspase-3 activation. In addition, we found that I3C up-regulates Bax, down-regulates Bcl-2 and, thereby, increased the ratio of Bax to Bcl-2 favoring apoptosis. These results suggest that the alteration in the expression of these genes may play an important role in mediating the biological effects of I3C. Moreover, we also show the cellular localization of Bax by confocal microscopy, which showed diffuse distribution of Bax throughout the cytoplasmic compartment in breast cancer cells in control culture. However, in I3C treated cells, Bax showed a punctate pattern of distribution that was localized in the mitochondria. From these results, we conclude that the over-expression and translocation of Bax to mitochondria causes mitochondrial depolarization and activation of caspases, which may be one of the mechanism(s) by which I3C induces apoptotic processes in I3C treated breast cancer cells. Overall, our present data provide a novel molecular mechanism(s) by which I3C elicits its biological effects on both Her-2/neu over-expressing and with normal Her-2/neu expressing breast cancer cells, suggesting that I3C could be an effective agent in inducing apoptosis in breast cancer cells.     

Aberrant ribosome biogenesis activates c-Myc and ASK1 pathways resulting in p53-dependent G1 arrest

The largest energy consumer in the cell is the ribosome biogenesis whose aberrancy elicits various diseases in humans. It has been recently revealed that p53 induction, along with cell cycle arrest, is related with abnormal ribosome biogenesis, but the exact mechanism still remains unknown. In this study, we have found that aberrant ribosome biogenesis activates two parallel cellular pathways, c-Myc and ASK1/p38, which result in p53 induction and G1 arrest. The c-Myc stabilizes p53 by rpL11-mediated HDM2 inhibition, and ASK1/p38 activates p53 by phosphorylation on serine 15 and 33. Our studies demonstrate the relationship between these two pathways and p53 induction. The changes caused by impaired ribosomal stress, such as p53 induction and G1 arrest, were completely disappeared by inhibition of either pathway. These findings suggest a monitoring mechanism of c-Myc and ASK1/p38 against abnormal ribosome biogenesis through controlling the stability and activity of p53 protein.     

Changes in p21WAF1, pRb, Mdm-2, Bax and Bcl-2 expression in cervical cancer cell lines transfected with a p53 expressing adenovirus

The aim of this study was to provide some insights into the molecular mechanisms involved in p53-dependent apoptosis and growth arrest. Changes in the levels of p53 protein and proteins regulated by p53 were studied in relation to events of the cell cycle and apoptosis in cervical cancer cell lines upon transfection with a p53 expressing adenovirus (Ad5-p53). The post-transfection level of p53 protein in SiHa cells was found to be unchanged during the 24-48 h period. In contrast, the level of p21WAF1 protein was shown to increase to its highest level at 24 h, and decreased gradually up to 48 h after the Ad5-p53 transfection. We further noted that the increase of p21WAF1 was accompanied by G1 arrest at 24 h and the decrease of p21WAF1 was associated with apoptosis at 36-48 h after transfection. An anti-p21WAF1 antibody cross-reactive protein band of approximately 14 kDa was observed in HeLa and C-33A cells when these cells were committed to apoptosis upon Ad5-p53 transfection. In SiHa cells, phosphorylation of pRb was inhibited during the early stage of Ad5-p53 transfection. This was followed by the cleavage of pRb. However, Ad5-p53 transfection did not change the levels of Bax and Bcl-2 proteins. Our results suggested that, Bax and Bcl-2 may not be important for the apoptosis of these cells, whereas cleavage of Rb, and the decrease of p21WAF1 could play important roles in p53-dependent apoptosis.