Significant role of Psf3 expression in non‐small‐cell lung cancer

The GINS complex associates with cell division cycle (Cdc) protein 45 and mini‐chromosome maintenance (Mcm) proteins 2–7 to form the Cdc45–Mcm–GINS (CMG) complex, which is essential for DNA duplication. One member of the GINS complex is Psf3. We previously found that increased Psf3 expression was strongly associated with poor survival in lung adenocarcinoma. Here, we investigated the role of Psf3 expression in non‐small‐cell lung cancer (NSCLC). We verified Psf3 expression in human NSCLC tissues (180 patients) and cell lines. Immunohistochemical analysis revealed that the overexpression of Psf3 was significantly associated with vessel invasion (P = 0.016), lymphatic invasion (P = 0.002), and pleural invasion (P = 0.036). The overall survival rate in patients with Psf3 overexpression was significantly lower than that in patients without Psf3 overexpression (P = 0.006). Multivariate survival analysis revealed Psf3 expression to be an independent risk factor for an unfavorable outcome (P = 0.049). A proximal ligation assay showed interactions between Psf3 and other CMG components (such as Mcm2 and Cdc45) in both NSCLC specimens and cell lines, indicating that Psf3 acted as the CMG complex, which could lead to excessive proliferation. Knockdown of Psf3 inhibited the proliferation of both cell lines by delaying the S phase, which revealed that Psf3 played an important role in cancer proliferation. Thus, Psf3 acted as the CMG complex, promoting excessive proliferation. These results suggest that Psf3 inhibition might be a therapeutic target for NSCLC with Psf3 overexpression.     

Survivin stable knockdown by siRNA inhibits tumor cell growth and angiogenesis in breast and cervical cancers

Increased resistance to apoptosis is a hallmark of many tumor cells. Survivin, a member of IAP family protein, is expressed in many human cancers and plays an important role in protecting cells from apoptosis. Here we show that vector-based small interfering RNAs (siRNA) stably knockdown survivin expression in several cancer cell lines, leading to increased apoptotic rate in response to different proapoptotic stimuli, such as doxorubicin or TNF-alpha. The apoptotic susceptibility was dependent on divergent levels of survivin expression. The stable transfectants exhibited abnormal morphology, suppressed cell growth, enhanced spontaneous apoptosis and cell cycle hindrance. Furthermore, in nude mice xenografts of survivin-positive tumors, cells expressing survivin-targeted siRNAs exhibited decreased tumor formation and reduced angiogenesis. Results from these studies: (1) provide direct evidence that intracellular silencing of survivin by siRNA sensitizes human tumor cells to apoptosis; (2) define survivin as a promising molecular target for cancer therapy; and (3) suggest the potential applicability of survivin-targeted siRNA for treating human tumors, probably in combination with chemotherapy.     

Integrative Functional Genomics Analysis of Sustained Polyploidy Phenotypes in Breast Cancer Cells Identifies an Oncogenic Profile for GINS2

Aneuploidy is among the most obvious differences between normal and cancer cells. However, mechanisms contributing to development and maintenance of aneuploid cell growth are diverse and incompletely understood. Functional genomics analyses have shown that aneuploidy in cancer cells is correlated with diffuse gene expression signatures and aneuploidy can arise by a variety of mechanisms, including cytokinesis failures, DNA endoreplication, and possibly through polyploid intermediate states. To identify molecular processes contributing to development of aneuploidy, we used a cell spot microarray technique to identify genes inducing polyploidy and/or allowing maintenance of polyploid cell growth in breast cancer cells. Of 5760 human genes screened, 177 were found to induce severe DNA content alterations on prolonged transient silencing. Association with response to DNA damage stimulus and DNA repair was found to be the most enriched cellular processes among the candidate genes. Functional validation analysis of these genes highlighted GINS2 as the highest ranking candidate inducing polyploidy, accumulation of endogenous DNA damage, and impairing cell proliferation on inhibition. The cell growth inhibition and induction of polyploidy by suppression of GINS2 was verified in a panel of breast cancer cell lines. Bioinformatic analysis of published gene expression and DNA copy number studies of clinical breast tumors suggested GINS2 to be associated with the aggressive characteristics of a subgroup of breast cancers in vivo. In addition, nuclear GINS2 protein levels distinguished actively proliferating cancer cells suggesting potential use of GINS2 staining as a biomarker of cell proliferation as well as a potential therapeutic target.     

Skp2在恶性肿瘤侵袭转移中的作用

SCF(Skpl-Cullinl-F-box)复合物是一大类泛素连接酶E3.S期激酶相关蛋白2(S-phase kinase associated protein 2,Skp2)是F盒蛋白家庭成员之一.研究表明Skp2主要参与细胞周期的调控,与多种恶性肿瘤的发生、发展密切相关.近年研究发现,Skp2在肿瘤的侵袭、转移中也扮演着重要的角色.Skp2可以通过调控RhoA、基质金属蛋白酶MMP-2、MMP-9的表达和活性以及E-cadherin的降解从而促进肿瘤细胞的侵袭和转移.本文就近几年Skp2在肿瘤侵袭、转移中的作用进行综述.     

人类泛素耦联酶E2C与肿瘤的关系

人类泛素耦联酶E2C(UBE2C)属于泛素.蛋白酶体途径的E2酶家族,其通过调控cyclinA和cyclin B的周期性变化在维持细胞周期的正常运转中起着重要作用.UBE2C通过其N末端来控制细胞周期末期促进复合物(APC)的激活阈值,并加强对APC检查点的调节,而UBE2C的细胞周期依赖性表达又受APC的调控.UBE2C在多种肿瘤细胞株和组织中高表达,与肿瘤的发生、增殖、转化以及恶性程度密切相关,可作为肿瘤的诊断和治疗的新靶点.     

人类泛素耦联酶E2C与肿瘤的关系

人类泛素耦联酶E2C(UBE2C)属于泛素.蛋白酶体途径的E2酶家族,其通过调控cyclinA和cyclin B的周期性变化在维持细胞周期的正常运转中起着重要作用.UBE2C通过其N末端来控制细胞周期末期促进复合物(APC)的激活阈值,并加强对APC检查点的调节,而UBE2C的细胞周期依赖性表达又受APC的调控.UBE2C在多种肿瘤细胞株和组织中高表达,与肿瘤的发生、增殖、转化以及恶性程度密切相关,可作为肿瘤的诊断和治疗的新靶点.     

染色质解旋酶DNA结合蛋白与肿瘤关系的研究进展

染色质解旋酶DNA结合蛋白5（CHD5）属于染色质重塑酶,其既能重塑染色质促进基因转录,又能正向调控p53/p19arf控制细胞增殖、凋亡和衰老。目前,已经在神经母细胞瘤、胶质瘤、乳腺癌、肺癌等多种肿瘤中发现CHD5的缺失并发现其低表达与肿瘤的发生、发展、预后情况有关。在多种肿瘤中,CHD5基因出现单链或双链缺失,以及高甲基化现象,导致其表达下调。可见,CHD5通过遗传学和表观遗传学机制共同控制肿瘤进展,在肿瘤的发生发展中发挥重要作用。     

PTEN: a new guardian of the genome

The phosphatase and tensin homolog deleted on chromosome 10 (PTEN) tumor suppressor is a phosphatase that antagonizes the phosphoinositol-3-kinase/AKT signaling pathway and suppresses cell survival as well as cell proliferation. PTEN is the second most frequently mutated gene in human cancer after p53. Germline mutations of PTEN have been found in cancer susceptibility syndromes, such as Cowden syndrome, in which over 80% of patients have mutations of PTEN. Homozygous deletion of Pten causes embryonic lethality, suggesting that PTEN is essential for embryonic development. Mice heterozygous for Pten develop spontaneous tumors in a variety of organs comparable with the spectrum of its mutations in human cancer. The mechanisms of PTEN functions in tumor suppression are currently under intense investigation. Recent studies demonstrate that PTEN plays an essential role in the maintenance of chromosomal stability and that loss of PTEN leads to massive alterations of chromosomes. The tumor suppressor p53 is known as a guardian of the genome that mediates the cellular response to environmental stress, leading to cell cycle arrest or cell death. Through completely different mechanisms, PTEN also protects the genome from instability. Thus, we propose that PTEN is a new guardian of the genome. In this review, we will discuss new discoveries on the role of PTEN in tumor suppression and explore mechanisms by which PTEN maintains genomic stability.     

OCT4 spliced variants are highly expressed in brain cancer tissues and inhibition of OCT4B1 causes G2/M arrest in brain cancer cells

The new claim about the origin of cancer known as Cancer Stem Cell theory states that a somatic differentiated cell can dedifferentiated or reprogrammed for regaining the cancer cell features. It has been recently shown that expression of stemness factors such as Oct4, Sox2, Nanog and Klf4, in a variety of somatic cancers can leads to development of tumorogenesis. Here, the expression of Oct4 variants were evaluated in brain tumor tissues by quantitative RT-PCR and immunohistochemical (IHC) analysis. In next phase of our study, the expression of Oct4B1 was knock-down in brain cancer cell lines and its effect on cell cycle was assessed. Finally, in order to get insights into sequence-structure-function relationships of Oct4 isofroms, their sequences were analysed using bioinformatic tools. Our data revealed that all three variants of Oct4 are expressed in different types of brain cancer. The expression level of Oct4B1, in contast to Oct4B, was much higher in high-grade brain tumors compared with low-grade ones. In line with qPCR, the expression of Oct4A and B isofroms was confirmed with IHC in different types of brain tumors. Moreover, as a result of the suppression of Oct4B1 expression, the brain cancer cells were arrested in G2/M phase of cell cycle. Bioinfromatics data indicated that the predicted Oct4B1 protein have DNA binding properties. All together, our findings suggest that Oct4B1 has a potential role in tumorigenesis of brain cancer and can be considered as a new tumor marker with potential value in diagnosis and treatment of brain cancer.     

Notch信号通路与消化系统肿瘤相关性的研究进展

Notch信号是一种遗传进化上高度保守,反映相邻细胞间通信作用的一种信号通路,其不仅在细胞正常发育、分化增殖和凋亡中起着重要的作用,而且与多种肿瘤的发生和发展具有相关性.食管鳞状细胞癌的发生常伴随Notch-1的低表达,但食管腺癌的发生却与Notch信号的高表达相关,且高表达的Notch信号对胃癌形成具有促进作用,其表达量提高的程度预示胃癌形成风险的高低.结肠癌中Notch-1表达的升高与病理分级、淋巴转移和病程相关,而Nctch配体Dll-4可促进结肠癌中新生血管的生成有助于癌细胞的转移和远端浸润,与之相反的是Notch-2却可能起到抑制结肠癌生长的作用.总之,目前Notch信号多被视为致癌因素,可促进肿瘤的生长,但在某些肿瘤中也能够诱导肿瘤细胞分化、抑制肿瘤细胞的增殖,表现为致癌与抑癌两种截然相反的作用.应用γ-分泌酶抑制剂(γ-secretase inhibitor,GSI)、小RNA干扰技术和单克隆抗体等方法阻断Notch信号通路,将成为肿瘤治疗的一个新方向.     

Lats2, a putative tumor suppressor,inhibits G1/S transition

Lats2 is a new member of the Lats tumor suppressor family. The human LATS2 gene is located at chromosome 13q11-12, which has been shown to be a hot spot (67%) for LOH in nonsmall cell lung cancer. In order to understand the function of LATS2 in the control of tumor development, we ectopically expressed mouse Lats2 via retroviral infection in NIH3T3/v-ras cells to examine whether Lats2 plays a role in suppressing tumor development and regulating cell proliferation. We have found that ectopic expression of Lats2 in NIH3T3/v-ras cells suppresses development of tumors in athymic nude mice and inhibits proliferation of NIH3T3/v-ras cells in an in vitro assay. Cell cycle profile analysis demonstrated that ectopic expression of Lats2 inhibited the G1/S transition. Further mechanistic studies revealed that cyclin E/CDK2 kinase activity was downregulated in Lats2-transduced NIH3T3/v-ras cells, while other cell cycle regulators controlling the G1/S transition were not affected. We have also shown that LATS2 kinase activity and two LATS conserved domains (LCDs) are required for Lats2 to suppress tumorigenicity and to inhibit cell growth. In addition, the LATS2 protein is cytoplasmic during interphase in NIH3T3 cells, while it becomes localized to the mitotic apparatus during mitosis. Finally, we propose a model in which a combination of mammalian Lats2 and Lats1 control cell proliferation by negatively regulating different cell cycle check points.     

PTPRO基因甲基化与肿瘤的研究进展

PTPRO基因是蛋白酪氨酸磷酸酶PTPs家族成员之一,是细胞增殖、分化、代谢、细胞与细胞间通讯、基因转录以及细胞存活等重要信号通路的媒介,参与细胞生长、分化、分裂周期、癌基因转化等多种过程,是新近发现的一个潜在抑癌基因,其在癌症发生机制中的作用是目前研究的热点.多项研究发现在多种恶性肿瘤组织中均存在PTPRO基因低表达,而且与其甲基化水平呈负相关,并指出PTPRO基因甲基化状态的检测具有重要的临床意义,有望成为临床早期诊断及疾病监控的生物学指标,而逆转PTPRO基因的甲基化则可能为癌症治疗提供新的方向.因此,PTPRO基因甲基化在肿瘤的发生发展过程中发挥着重要作用.     

Small-molecule targeting of translation initiation for cancer therapy

Translation initiation plays a critical role in the regulation of cell growth and tumorigenesis. We report here that inhibiting translation initiation through induction of eIF2α phosphorylation by small-molecular-weight compounds restricts the availability of the eIF2·GTP·Met-tRNA_i ternary complex and abrogates the proliferation of cancer cells in vitro and tumor growth in vivo. Restricting the availability of the ternary complex preferentially down-regulates the expression of growth-promoting proteins and up-regulates the expression of ER stress response genes in cancer cells as well as in tumors excised from either animal models of human cancer or cancer patients. These findings provide the first direct evidence for translational control of gene-specific expression by small molecules in vivo and indicate that translation initiation factors are bona fide targets for development of mechanism-specific anti-cancer agents.     

CPS1调节恶性肿瘤发生发展的研究进展

氨基甲酰磷酸合成酶1（carbamoyl phosphate synthetase 1,CPS1）在生理状态下是肝脏特异性蛋白,表达于肝脏线粒体内,催化尿素循环第一步反应,是肝脏发挥解毒功能的关键酶之一,其表达和活性受多因素调控。病理状态下,CPS1在原发性肝癌、非小细胞肺癌、小肠癌、结直肠癌、脑胶质瘤、膀胱癌等恶性肿瘤中亦存在不同程度的上调或下调,并在不同肿瘤中发挥不同功能,主要通过调节物质代谢参与肿瘤发生、发展并影响患者预后。本文针对CPS1蛋白结构和功能、表达和调控以及CPS1在肿瘤发生发展过程中的作用进行文献综述。     

Hexokinase 2 overexpression promotes the proliferation and survival of laryngeal squamous cell carcinoma

Proliferating cancer cells preferentially use anaerobic glycolysis rather than oxidative phosphorylation for energy production. Hexokinase 2 (HK2) is highly expressed in many malignant cells and is necessary for anaerobic glycolysis. The role of HK2 in laryngeal squamous cell carcinoma (LSCC) is unknown. In this study, the expression of HK2 in LSCC was investigated and the effect of inhibiting HK2 expression with small hairpin RNA (shRNA) on tumor growth was investigated. Using immunohistochemistry, HK2 expression was assessed in LSCC tissues. Human laryngeal carcinoma Hep-2 cells were stably transfected with a plasmid expressing HK2 shRNA (pGenesil-1.1-HK2) and were compared to control cells with respect to the cell cycle, cell viability, apoptosis, and their ability to form xenograft tumors. HK2 expression was significantly higher in LSCC than in papilloma or glottis polypus. Tumor samples of higher T, N, and TNM stage often had stronger HK2 staining. HK2 shRNA reduced HK2 mRNA, protein levels, and HK activity in Hep-2 cells. HK2 cells expressing shRNA demonstrated a higher G0–G1 ratio, increased apoptosis, and reduced viability. Xenograft tumors derived from cells expressing HK2 shRNA were smaller and had lower proliferation than those from untransfected or control-plasmid-transfected cells. In conclusion, depletion of HK2 expression resulted in reduced xenograft tumor development likely by reducing proliferation, altering the cell cycle, reducing cell viability and activating apoptosis. These data suggest that HK2 plays an important role in the development of LSCC and represents a potential therapeutic target for LSCC.     

Targeting mTORC2 inhibits colon cancer cell proliferation in vitro and tumor formation in vivo

The mammalian target of rapamycin (mTOR), which exists in two functionally distinct complexes, mTORC1 and mTORC2 plays an important role in tumor growth. Whereas the role of mTORC1 has been well characterized in this process, little is known about the functions of mTORC2 in cancer progression. In this study, we explored the specific role of mTORC2 in colon cancer using a short hairpin RNA expression system to silence the mTORC2-associated protein rictor. We found that downregulation of rictor in HT29 and LS174T colon cancer cells significantly reduced cell proliferation. Knockdown of rictor also resulted in a G1 arrest as observed by cell cycle analysis. We further observed that LS174T cells deficient for rictor failed to form tumors in a nude mice xenograft model. Taken together, these results show that the inhibition of mTORC2 reduces colon cancer cell proliferation in vitro and tumor xenograft formation in vivo. They also suggest that specifically targeting mTORC2 may provide a novel treatment strategy for colorectal cancer.