Telomere instability and cancer

Telomeres are required to preserve genome integrity, chromosome stability, nuclear architecture and chromosome pairing during meiosis. Given that telomerase activity is limiting or absent in most somatic tissues, shortening of telomeres during development and aging is the rule. In vitro, telomere length operates as a mechanism to prevent uncontrolled cell growth and therefore defines the proliferation potential of a cell. In vitro, in somatic cells that have lost proliferation control, shortening of telomeres becomes the main source of genome instability leading to genetic or epigenetic changes that may allow cells to become immortal and to acquire tumor phenotypes. In vivo, mice models have indisputably shown both the protective and the promoting role of very short telomeres in cancer development. In humans, although telomere shortening and other types of telomere dysfunction probably contribute to the genome instability often detected in tumors, the specific contributions of such instability to the development of cancer remain largely undetermined.     

EBNA1 may prolong G(2)/M phase and sensitize HER2/neu-overexpressing ovarian cancer cells to both topoisomerase II-targeting and paclitaxel drugs

We have shown previously that the Epstein-Barr virus nuclear antigen-1 (EBNA1) can act as a transforming suppressor in the HER2/neu-overexpressing ovarian cancer cells. In the present study, by using flow cytometric analysis, we demonstrate that EBNA1 could prolong G(2)/M phase and sensitize to Taxol-induced apoptosis in the EBNA1-expressing ovarian cancer cell stable transfectants. In addition, EBNA1 could also significantly increase topoisomerase IIalpha protein expression, indicating that the up-regulation of topoisomerase IIalpha may be one of the mechanisms by which EBNA1 enhances the sensitivity of ovarian cancer cells to topoisomerase II-targeting anticancer drugs, such as VP-16 and Adriamycin. These data suggest that EBNA1 not only prolongs cell cycle at G(2)/M phase and up-regulates topoisomerase IIalpha expression in HER2/neu-overexpressing ovarian cancer cells, but also increases cellular apoptosis through sensitization of cancer cells to topoisomerase II-directing anticancer drugs.     

Tumorigenicity of interleukin-2 (IL-2)-cDNA-transfected L1210 lymphoma and its in vivo variants is modulated by changes in IL-2 expression; potential therapeutic implications

Summary To study parameters that affect the tumorigenicity of L1210 lymphoma we have analyzed the structure of MHC class I antigens of this tumor. In addition this tumor was transfected with interleukin-2 (IL-2) cDNA in order to determine the effects of high concentrations of IL-2 within the tumor environment. The nucleotide sequence of the class I K^d, D^d and L^d mRNAs from this tumor showed that the encoded amino acid sequence of the corresponding antigens is normal, thus suggesting that the tumorigenicity of L1210 lymphoma is not due to defective antigen presentation to tumor-specific cytotoxic T cells. In contrast, induction of IL-2 expression by cDNA transfection led to loss of tumorigenicity of the IL-2-secreting tumor cells. However, a fraction of long-term-surviving mice developed progressively growing variant tumors that showed substantial decrease or loss of IL-2 expression. These results suggest that IL-2 secretion by tumors is suicidal but, because of tumor heterogeneity, IL-2-loss-variant tumors may arise that are able to escape the immune defenses of the host. The observed consistent loss of IL-2 expression in variant tumors implies that specific targeting of large quantities of IL-2 to tumor cells may be a valuable approach to immunotherapy of cancer. In addition we find that under specific gamma ray irradiation IL-2-secreting tumor cells lose their ability to multiply yet continue to secrete IL-2 at levels equivalent to those secreted by unirradiated cells. Such IL-2-secreting irradiated tumor cells were found to be superior immunogens in comparison to the irradiated parental tumor cells, suggesting their use as tumor vaccines.     

Inhibition of rat C6 glioblastoma tumor growth by expression of insulin-like growth factor I receptor antisense mRNA

 The expression of insulin-like growth factor I receptor (IGF-IR) antisense mRNA inhibits the growth of C6 rat glioblastoma cells both in vitro and in vivo [Cancer Res (1994) 54: 2218]. Moreover, the injection of C6 cells expressing an antisense mRNA to the IGF-IR into syngeneic rats prevents subsequent wild-type tumorigenesis and induces regression of established tumors. For the study of immune function in syngeneic rats, C6 cells expressing either IGF-IR sense or IGF-IR antisense mRNA were injected and splenic lymphocyte function analyzed in vitro after 2 weeks. Cytotoxic, CD8⁺ lymphocytes from animals injected with IGF-IR antisense cells, but not from those treated with IGF-IR sense cells, proliferated in vitro in response to wild-type C6 cells. Wild-type C6 cells or IGF-IR-sense-RNA-expressing cells rapidly formed tumors upon subcutaneous injection into athymic nude mice. IGF-IR antisense cells were weakly tumorigenic, exhibiting a six- to tenfold increase in tumor latency. Injection of IGF-IR antisense C6 cells mildly delayed the development of wild-type tumors, and did not induce the regression of established wild-type C6 tumors in athymic nude mice. Thus, these findings demonstrate the stimulation of a cellular immune response in rats following the injection of IGF-IR antisense cells. However, studies of athymic nude mice indicate that expression of IGF-IR antisense mRNA also inhibits C6 cells tumorigenicity by additional mechanisms. Received: 27 January 1995 / Accepted: 15 November 1995     

诱导多能干细胞技术的优化及其应用前景

诱导多能干细胞(induced pluripotent stem cells, iPSCs)是类似胚胎干细胞的一种细胞类型,可以通过对已分化的体细胞进行诱导重编程获得,具有自我更新能力和多潜能性,在体外疾病模型的建立、移植替代治疗、发育学等方面有广阔的应用前景,但致瘤性、转化率低、疾病模型拟合度差等缺点限制着iPS技术在临床和科研上的推广。对近几年诱导多能干细胞技术优化方面取得的新进展进行综述,重点阐述降低致瘤性和提高转化率的几种方法及iPS在临床和科研上的应用前景。     

Suppression of proliferation,tumorigenicity and metastasis of lung cancer cells after their transduction by interferon-beta gene in baculovirus vector

BackgroundGene therapy represents an interesting alternative treatment for cancers. Interferon-beta is well known as a multifunctional cytokine that provides antiviral, antiproliferative, antiangiogenic and immunomodulating effects. For this reason introduction of this cytokine gene in baculovirus vector is seen as a rather promising tool for anticancer therapy.AimInvestigation of biological behavior in vitro and in vivo of lung cancer cells modified by interferon-beta gene which was introduced into the cells in vitro with baculovirus vector.Materials and MethodsStudies were performed on mouse Lewis lung carcinoma cells as the tumor model (LL cell line). Transductions of cells by recombinant baculoviruses, in vitro and in vivo analysis of tumor cell biology and immunocytochemical method have been used.ResultsThe study of various in vitro biological parameters of LL cancer cells transduced by recombinant baculovirus with interferon gene demonstrated that the transduction of cells is accompanied by significant inhibition of their proliferation and ability to form colonies in semisolid agar. Also, transduction of LL cells with interferon gene inhibited their tumorigenicity, i.e. the ability to cause formation of tumors and metastases in lungs of mice in vivo. Anti-tumor activity of recombinant interferon is realized via high level of its local production in tumors, induced by LL carcinoma cells, transduced with recombinant interferon-beta gene. Recombinant baculovirus without interferon gene did not influence significantly on tumorigenicity and metastatic ability of lung cancer cells.ConclusionsIntroduction of interferon-beta gene in Lewis lung carcinoma cells in vitro in recombinant baculovirus leads to inhibition of their proliferation potential and malignant behavior in vitro, tumorigenicity and metastatic activity in vivo.     

DNA methylation-regulated miR-193a-3p dictates resistance of hepatocellular carcinoma to 5-fluorouracil via repression of SRSF2 expression

Chemoresistance prevents effective cancer therapy and is rarely predictable prior to treatment, particularly for hepatocellular carcinoma (HCC). Following the chemoresistance profiling of eight HCC cell lines to each of nine chemotherapeutics, two cell lines (QGY-7703 as a sensitive and SMMC-7721 as a resistant cell line to 5-fluorouracil (5-FU) treatment) were systematically studied for mechanistic insights underpinning HCC 5-FU chemoresistance. Genomic profiling at both DNA methylation and microRNA (miR) levels and subsequent mechanistic studies illustrate a new mechanism for how DNA methylation-regulated miR-193a-3p dictates the 5-FU resistance of HCC cells via repression of serine/arginine-rich splicing factor 2 (SRSF2) expression. In turn, SRSF2 preferentially up-regulates the proapoptotic splicing form of caspase 2 (CASP2L) and sensitizes HCC cells to 5-FU. Forced changes of miR-193a-3p level reverse all of the phenotypic features examined, including cell proliferation, cell cycle progression, and 5-FU sensitivity, in cell culture and in nude mice. Importantly, the siRNA-mediated repression of SRSF2 phenocopies all of the miR-193a-3p mimic-triggered changes in QGY-7703. This newly identified miR-193a-3p-SRSF2 axis highlights a new set of companion diagnostics required for optimal 5-FU therapy of HCC, which involve assaying both the DNA methylation state of the miR-193a gene and the expression of miR-193a-3p and SRSF2 and the relative level of the proapoptotic versus antiapoptotic splicing forms of caspase 2 in clinical samples.     

β1,4-Galactosyltransferase V regulates self-renewal of glioma-initiating cell

Glioma results from unregulated expansion of a self-renewing glioma-initiating cell population. The regulatory pathways which are essential for sustaining the self-renewal of glioma-initiating cells remain largely unknown. Cell surface N-linked oligosaccharides play functional roles in determining cell fate and are associated with glioma malignancy. Previously, we have reported that β1,4-galactosyltransferase V (β1,4GalT V) effectively galactosylates the GlcNAcβ1→6Man arm of the highly branched N-glycans and positively regulates glioma cell growth. Here, we show that decreasing the expression of β1,4GalT V by RNA interference in glioma cells attenuated the formation of polylactosamine and inhibited the ability of tumor formation in vivo. Down-regulation of β1,4GalT V depleted CD133-positive cells in glioma xenograft, and inhibited the self-renewal capacity and the tumorigenic potential of glioma-initiating cells. These data reveal a critical role of β1,4GalT V in the self-renewal and tumorigenicity of glioma-initiating cells, and indicate that manipulating β1,4GalT V expression may have therapeutic potential for the treatment of malignant glioma.     

Semiparametric Bayes Multiple Testing: Applications to Tumor Data

Summary In National Toxicology Program (NTP) studies, investigators want to assess whether a test agent is carcinogenic overall and specific to certain tumor types, while estimating the dose‐response profiles. Because there are potentially correlations among the tumors, a joint inference is preferred to separate univariate analyses for each tumor type. In this regard, we propose a random effect logistic model with a matrix of coefficients representing log‐odds ratios for the adjacent dose groups for tumors at different sites. We propose appropriate nonparametric priors for these coefficients to characterize the correlations and to allow borrowing of information across different dose groups and tumor types. Global and local hypotheses can be easily evaluated by summarizing the output of a single Monte Carlo Markov chain (MCMC). Two multiple testing procedures are applied for testing local hypotheses based on the posterior probabilities of local alternatives. Simulation studies are conducted and an NTP tumor data set is analyzed illustrating the proposed approach.