Commentary: ATG5: A distinct role in the nucleus

Both apoptotic and autophagic pathways are activated in cells during anticancer treatment using DNA-damaging agents. Thus, the outcome is balanced between apoptotic cell death and enhanced autophagy, with the possibility of prolonged cell survival. It seems intuitively obvious that this survival mechanism might interfere with the desired tumor cell killing. We addressed this question by tipping the balance in favor of autophagy, using etoposide or cisplatin at low, sublethal doses. Over 4 days, only a little apoptosis was observed, but both drugs sharply increased autophagic flux. Surprisingly, cells underwent a cell cycle arrest at G₂/M, followed later by mitotic catastrophe with formation of multipolar spindles, missegregated chromosomes, or enlarged, irregular, sometimes multiple nuclei. Why? The answer is that even a low level of DNA damage not only upregulates autophagy, but also provokes the recruitment of an autophagy-related protein, ATG5, to the nucleus, where it binds BIRC5/survivin, thereby interfering with correct assembly of the chromosome passenger complex needed for cytokinesis.     

Podoverine A—a novel microtubule destabilizing natural product from the Podophyllum species

Natural products represent compound classes with high chemical and structural diversity and various biological activities. Libraries based on natural products are valuable starting point in the search for novel biologically active substances. Here we report on the identification of the natural product podoverine A from the plant Podophyllum versipelle Hance as a novel tubulin-acting agent. A natural product compound collection was subjected to a high-content screen that monitors changes in cytoskeleton and DNA and podoverine A was identified as inhibitor of mitosis. This natural product causes mitotic arrest and inhibits microtubule polymerization in vitro and in cells by targeting the vinca binding site on tubulin.     

Targeting mitosis‐regulating genes in cisplatin‐sensitive and ‐resistant melanoma cells: A live‐cell RNAi screen displays differential nucleus‐derived phenotypes

Chemoresistance in malignant melanoma remains an unresolved clinical issue. In the search for novel molecular targets, a live‐cell high‐content RNAi screen based on gene expression data was performed in cisplatin‐sensitive and cisplatin‐resistant MeWo melanoma cells, Mel‐28 cells and a melanocyte cell line. Cells were exposed to 91 siRNAs and distinct nucleus‐derived phenotypes such as cell division, cell death and migration phenotypes were detected by time‐lapse microscopy over 60 h. Using this approach, cisplatin‐sensitive and cisplatin‐resistant melanoma cells were compared by automated image analysis and visual inspection. In cisplatin‐sensitive MeWo melanoma cells, 14 genes were identified that showed distinct phenotype abnormalities after exposure to gene‐specific siRNAs. In cisplatin‐resistant MeWo cells, five genes were detected. Nine genes were detected whose knock‐down led to differential nuclear phenotypes in cisplatin‐sensitive and ‐resistant cells. In Mel‐28 cells, nine genes were identified which induced nuclear phenotypes including all eight genes which were identified in cisplatin‐resistant MeWo cells. An analogous RNAi screen on melanocytes revealed no detectable phenotype abnormalities after RNAi. Pathway analysis showed in cisplatin‐sensitive MeWo cells and Mel‐28 cells an enrichment of at least three genes in major mitotic pathways. We hereby show that siRNA screening may help to identify tumor‐specific genes leading to phenotype abnormalities. These genes may serve as potential therapeutic targets in the treatment of melanoma.     

ATG5

Both apoptotic and autophagic pathways are activated in cells during anticancer treatment using DNA-damaging agents. Thus, the outcome is balanced between apoptotic cell death and enhanced autophagy, with the possibility of prolonged cell survival. It seems intuitively obvious that this survival mechanism might interfere with the desired tumor cell killing. We addressed this question by tipping the balance in favor of autophagy, using etoposide or cisplatin at low, sublethal doses. Over 4 days, only a little apoptosis was observed, but both drugs sharply increased autophagic flux. Surprisingly, cells underwent a cell cycle arrest at G₂/M, followed later by mitotic catastrophe with formation of multipolar spindles, missegregated chromosomes, or enlarged, irregular, sometimes multiple nuclei. Why? The answer is that even a low level of DNA damage not only upregulates autophagy, but also provokes the recruitment of an autophagy-related protein, ATG5, to the nucleus, where it binds BIRC5/survivin, thereby interfering with correct assembly of the chromosome passenger complex needed for cytokinesis.     

Centromere fragmentation is a common mitotic defect of S and G2 checkpoint override

DNA damaging agents, including those used in the clinic, activate cell cycle checkpoints, which blocks entry into mitosis. Given that checkpoint override results in cell death via mitotic catastrophe, inhibitors of the DNA damage checkpoint are actively being pursued as chemosensitization agents. Here we explored the effects of gemcitabine in combination with Chk1 inhibitors in a panel of pancreatic cancer cell lines and found variable abilities to override the S phase checkpoint. In cells that were able to enter mitosis, the chromatin was extensively fragmented, as assessed by metaphase spreads and Comet assay. Notably, electron microscopy and high-resolution light microscopy showed that the kinetochores and centromeres appeared to be detached from the chromatin mass, in a manner reminiscent of mitosis with unreplicated genomes (MUGs). Cell lines that were unable to override the S phase checkpoint were able to override a G₂ arrest induced by the alkylator MMS or the topoisomerase II inhibitors doxorubicin or etoposide. Interestingly, checkpoint override from the topoisomerase II inhibitors generated fragmented kinetochores (MUGs) due to unreplicated centromeres. Our studies show that kinetochore and centromere fragmentation is a defining feature of checkpoint override and suggests that loss of cell viability is due in part to acentric genomes. Furthermore, given the greater efficacy of forcing cells into premature mitosis from topoisomerase II-mediated arrest as compared with gemcitabine-mediated arrest, topoisomerase II inhibitors maybe more suitable when used in combination with checkpoint inhibitors.     

Catastrophe Risk Analysis: A Financial Perspective

This article examines how catastrophe events affect risk analysis from a financial perspective. Data from different industries such as Advanced Sustainable Performance Indices, gold, energy, real estate, and insurance were collected and analyzed. The performance of these funds was compared by using various financial ratios. Then we tested the stock selecting and market timing abilities. We also assessed whether a particular catastrophe event has affected stock prices by analysis of two event studies, the 9/11 terrorist attacks in the United States and the collapse through bankruptcy of Lehman Brothers. We examined how an asset portfolio performs under catastrophic events and under the situation of adding Advanced Sustainable Performance Indices into an investor's portfolio basket. We found that the 9/11 terrorist attacks affected the Dow Jones Real Estate Index's prices a lot. Lehman Brothers' bankruptcy filing had a positive impact on the CBOE Gold Index, and had a large impact on the Fidelity US Bond Index. The ASPI Index in our optimization problem gave us better diversification. From our analysis, we conclude that portfolio diversification is a good way to hedge against catastrophic risk.     

Mitotic inheritance of DNA methylation: more than just copy and paste

Decades of investigation on DNA methylation have led to deeper insights into its metabolic mechanisms and biological functions.This understanding was fueled by the recent development of genome editing tools and our improved capacity for analyzing the global DNA methylome in mammalian cells.This review focuses on the maintenance of DNA methylation patterns during mitotic cell division.We discuss the latest discoveries of the mechanisms for the inheritance of DNA methylation as a stable epigenetic memory.We also highlight recent evidence showing the rapid turnover of DNA methylation as a dynamic gene regulatory mechanism.A body of work has shown that altered DNA methylomes are common features in aging and disease.We discuss the potential links between methylation maintenance mechanisms and diseaseassociated methylation changes.     

Mud binds the kinesin-14 Ncd in Drosophila

Maintenance of proper mitotic spindle structure is necessary for error-free chromosome segregation and cell division. Spindle assembly is controlled by force-generating kinesin motors that contribute to its geometry and bipolarity, and balancing motor-dependent forces between opposing kinesins is critical to the integrity of this process. Non-claret dysjunctional (Ncd), a Drosophila kinesin-14 member, crosslinks and slides microtubule minus-ends to focus spindle poles and sustain bipolarity. However, mechanisms that regulate Ncd activity during mitosis are underappreciated. Here, we identify Mushroom body defect (Mud), the fly ortholog of human NuMA, as a direct Ncd binding partner. We demonstrate this interaction involves a short coiled-coil domain within Mud (Mud^CC) binding the N-terminal, non-motor microtubule-binding domain of Ncd (Ncd^nMBD). We further show that the C-terminal ATPase motor domain of Ncd (Ncd^CTm) directly interacts with Ncd^nMBD as well. Mud binding competes against this self-association and also increases Ncd^nMBD microtubule binding in vitro. Our results describe an interaction between two spindle-associated proteins and suggest a potentially new mode of minus-end motor protein regulation at mitotic spindle poles.     

Types of potentials in a mitotic spindle

The dynamics of a mitotic spindle is very important to understand if the functioning of mitosis has to be understood and defined very accurately. There are a number of forces involved in such a process. Despite of the fact that there have been numerous studies done on the functioning of a mitotic spindle, there is still not a very precise understanding of this system and how it behaves. This study aims at understanding and expressing all the possible potentials which might be responsible in a mitotic spindle and its mechanism.