Multiple Defects of Cell Cycle Checkpoints in U937-ASPI3K, an U937 Cell Mutant Stably Expressing Anti-Sense ATM Gene cDNA

(Ataxia-telangiectasia mutated gene (ATM) functions in control of cell cycle checkpoints in responding to DNA damage and protects cells from undergoing apoptosis. Knock-out within tumor cells of endogenous ATM will achieve therapeutic benefits and enable a better understanding of the decisive mechanisms of cell death or survival in response to DNA damaging agents. ) In present paper, we sought to characterize the cell cycle checkpoint profiles in U937-ASPI3K, a U937 cell mutant that was previously established with endogenous ATM knock-out phenotype. Syn- chronized U937-ASPI3K was exposed to 137Cs irradiation, G1, S. G2/M cell cycle checkpoint pro- files were evaluated by determining cell cycle kinetics, p53/p21 protein, cyclin dependent kinase 2 (CDK2) and p34CDC2 kinase activity in response to irradiation. U937-ASPI3K exhibited multiple defects in cell cycle checkpoints as defined by failing to arrest cells upon irradiation. The accumulation of cellular p53/p21 protein and inhibition of CDK kinase was also abolished in U937-ASPI3K. It was concluded that the stable expression of anti-sense PI3K cDNA fragment completely abolished multiple cell cycle checkpoints in U937-ASPI3K, and hence U937-ASPI3K with an AT-like phenotype could serves as a valuable model system for investigating the signal transduction pathway in responding to DNA damaging-based cancer therapy.

The role of NBS1 in DNA double strand break repair, telomere stability, and cell cycle checkpoint control

The genomes of eukaryotic cells are under continuous assault by environmental agents and endogenous metabolic byproducts. Damage induced in DNA usually leads to a cascade of cellular events, the DNA damage response. Failure of the DNA damage response can lead to development of malignancy by reducing the efficiency and fidelity of DNA repair. The NBS1 protein is a component of the MRE11/RAD50/NBS 1 complex （MRN） that plays a critical role in the cellular response to DNA damage and the maintenance of chromosomal integrity. Mutations in the NBS1 gene are responsible for Nijmegen breakage syndrome （NBS）, a hereditary disorder that imparts an increased predisposition to development of malignancy. The phenotypic characteristics of cells isolated from NBS patients point to a deficiency in the repair of DNA double strand breaks. Here, we review the current knowledge of the role of NBS1 in the DNA damage response. Emphasis is placed on the role of NBS1 in the DNA double strand repair, modulation of the DNA damage sensing and signaling, cell cycle checkpoint control and maintenance oftelomere stability.

Cell cycle regulation through primary cilium:A long-forgotten story

Protruded from cytomembrane,primary cilium is a widespread cell organelle that can be found in almost all cell types in Mammalia.Because of its comprehensive requirement in various cellular activities and various functions in different organs,primary cilium has been a valuable research area of human pathology research since the turn of the millennium.And the potential application of the interaction between primary cilia and cell cycle regulation may be the most promising direction as many primary cilium-caused diseases are found to be caused by cell cycle dysregulation resulted from primary cilia defects.Therefore,a deep understanding of the interaction between primary cilia and the cell cycle is in great need.Hence in this review,we mainly described how the interaction between primary cilia and cell cycle proceeds and demonstrated three hypotheses raised from much different research.These hypotheses include(1)Primary cilium as a cellular signaling hub to regulate the cell cycle,(2)Primary cilium as a reservoir of cell cycle regulation-related factors,and(3)Primary cilium as a cell cycle checkpoint or a brake.Nonetheless,we also call for more attention on research of interaction between cell cycle and primary cilia and tried to point out some possible research directions for those who are interested.

Prevention of DNA re-replication in eukaryotic cells

DNA replication is a highly regulated process involving a number of licensing and replication factors that function in a carefully orchestrated manner to faithfully replicate DNA during every cell cycle.Loss of proper licensing control leads to deregulated DNA replication including DNA re-replication,which can cause genome instability and tumorigenesis.Eukaryotic organisms have established several conserved mechanisms to prevent DNA re-replication and to counteract its potentially harmful effects.These mechanisms include tightly controlled regulation of licensing factors and activation of cell cycle and DNA damage checkpoints.Deregulated licensing control and its associated compromised checkpoints have both been observed in tumor cells,indicating that proper functioning of these pathways is essential for maintaining genome stability.In this review,we discuss the regulatory mechanisms of licensing control,the deleterious consequences when both licensing and checkpoints are compromised,and present possible mechanisms to prevent re-replication in order to maintain genome stability.

Qilan preparation(芪蓝颗粒) inhibits proliferation and induces apoptosis by down-regulating microRNA-21 in humaqin Tca8113 tongue squamous cell carcinoma cells

OBJECTIVE: The aim of this study was to examine the antitumor effects of Qilan preparation(芪蓝颗粒) on oral squamous cell carcinoma(OSCC) in vitro and to investigate its underlying mechanisms of action. METHODS: Cell proliferation, cell cycle distribution and apoptosis were examined using cell counting kit-8(CCK8) and flow cytometry(FCM). The expression of PTEN and PDCD4 were determined by western blot. Changes in miR-21 levels were quantified using Taq Man stem-loop real-time PCR. After miR-21 was transiently transfected into Tca8113 cells using Lipofectamine?3000, cell proliferation, apoptosis and miR-21 and PDCD4 expression levels were measured. RESULTS: Qilan preparation inhibited Tca8113 cell growth in a dose-and time-dependent manner by inducing apoptosis and cell cycle arrest in S-phase, decreasing miR-21 levels and increasing PTEN and PDCD4 expression. Mi R-21 overexpression reversed the Qilan preparation-induced suppression of cell proliferation and induction of apoptosis while also blocking the increase in PDCD4.CONCLUSIONS: Our study revealed, for the first time, the ability of Qilan preparation to suppress TSCC cell growth and elucidated that Qilan preparation elicits its anti-cancer actions via either the miR-21/PDCD4 or PTEN pathway.

Functional role of ATM in the cellular response to DNA damage

Ataxia-telangiectasia mutated(ATM)plays a key role in regulating the cellular response to ionizing radiation.The tumor-suppressor gene ATM,mutations in which cause the human genetic disease ataxia telangiecta-sia,encodes a key protein kinase that controls the cellular response to double-stranded breaks.Activation of ATM results in phosphorylation of many downstream targets that modulate numerous damage response pathways,most notably cell cycle checkpoints.Here,we highlight some of the new developments in thefield in our understanding of the mechanism of activation of ATM and its signaling pathways,explore whether DNA double-strand breaks are the sole activators of ATM and ATM-dependent signaling pathways,and address some of the prominent,unanswered questions related to ATM and its function.The scope of this article is to provide a brief overview of the recent literature on this subject and to raise questions that could be addressed in future studies.

Downregulation of Notch-regulated Ankyrin Repeat Protein Exerts Antitumor Activities against Growth of Thyroid Cancer

Background： The Notch-regulated ankyrin repeat protein （NRARP） is recently found to promote proliferation of breast cancer cells. The role of NRARP in carcinogenesis deserves extensive investigations. This study attempted to investigate the expression of NRARP in thyroid cancer tissues and assess the influence of NRARP on cell proliferation, apoptosis, cell cycle, and invasion in thyroid cancer. Methods： Thirty-four cases with thyroid cancer were collected from the Department of General Surgery, Xinhua Hospital, Shanghai ]iao Tong University School of Medicine between 2011 and 2012. lmmunohistochemistry was used to detect the level of N RARP in cancer tissues. Lentivirus carrying NRARP-shRNA （Lenti-NRARP-shRNA） was applied to down-regulate NRARP expression. Cell viability was tested after treatment with Lenti-NRARP-shRNA using 3-（4,5-dimethylthiazol-2-yl）-2,5-diphenyltetrazolium bromide assay. Apoptosis and cell cycle distribution were determined by flow cytometry. Cell invasion was tested using Transwell invasion assay. In addition, expressions of several cell cycle-associated and apoptosis-associated proteins were examined using Western blotting after transfection. Student＇s t-test, one-way analysis of variance （ANOVA）, or Kaplan Meier were used to analyze the differences between two group or three groups. Results： N RARP was highly expressed in thyroid cancer tissues. Lenti-NRARP-shRNA showed significantly inhibitory activities against cell growth at a multiplicity of infection of l 0 or higher （P 〈 0.05）. Lenti-NRARP-shRNA-induced G 1 arrest （BHTl 01 ： 72.57% ± 5.32%; g305C： 75.45% ± 5.26%） by promoting p21 expression, induced apoptosis by promoting bax expression and suppressing bcl-2 expression, and inhibited cell invasion by suppressing matrix metalloproteinase-9 expression. Conclusion： Downregulation of NRARP expression exerts significant antitumor activities against cell growth and invasion of thyroid cancer, that suggests a potential role of NRARP in thyroid cancer targeted therapy.

The role of RAD9 in tumorigenesis

RAD9 regulates multiple cellular processes that influence genomic integrity,and for at least some of its functions the protein acts as part of a heterotrimeric complex bound to HUS1 and RAD1 proteins.RAD9 participates in DNA repair,including base excision repair,homologous recombination repair and mismatch repair,multiple cell cycle phase checkpoints and apoptosis.In addition,functions including the transactivation of downstream target genes,immunoglobulin class switch recombination,as well as 3′–5′exonuclease activity have been reported.Aberrant RAD9 expression has been linked to breast,lung,thyroid,skin and prostate tumorigenesis,and a cause–effect relationship has been demonstrated for the latter two.Interestingly,human RAD9 overproduction correlates with prostate cancer whereas deletion of Mrad9,the corresponding mouse gene,in keratinocytes leads to skin cancer.These results reveal that RAD9 protein can function as an oncogene or tumor suppressor,and aberrantly high or low levels can have deleterious health consequences.It is not clear which of the many functions of RAD9 is critical for carcinogenesis,but several alternatives are considered herein and implications for the development of novel cancer therapies based on these findings are examined.