Table of Contents

Volume 8, Issue 22

  November 15, 2009

  Pages 3611 - 3785

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 Issue Catalogue (MARC XML)

EDITORIALS: CELL CYCLE FEATURES

Open Access Article

Yin and yang: Cancer-implicated miRNAs that have it both ways

Jason T. Huse and Eric C. Holland
Pages 3611 - 3612
http://dx.doi.org/10.4161/cc.8.22.9893
Abstract | PDF

Comment on: Huse JT, et al. Genes Dev 2009; 23:1327-37. AND Kota J, et al. Cell 2009; 137:1005-17.

Open Access Article

microRNA cascade in diabetic kidney disease: Big impact initiated by a small RNA

Mitsuo Kato and Rama Natarajan
Pages 3613 - 3614
http://dx.doi.org/10.4161/cc.8.22.9816
Abstract | PDF

Comment on: Kato M, et al. Nat Cell Biol 2009; 11:881–9.

Open Access Article

Sniffing out cancer using “chemical nose” sensors

Vincent M. Rotello
Pages 3615 - 3616
http://dx.doi.org/10.4161/cc.8.22.9915
Abstract | PDF

Comment on: Bajaj A, et al. Proc Nat Acad Sci 2009; 106:10912-16.

Open Access Article

DNA damage response to eroded telomeres

Michael Lisby and Vincent Géli
Pages 3617 - 3618
http://dx.doi.org/10.4161/cc.8.22.9945
Abstract | PDF

Comment on: Abdallah P, et al. Nat Cell Biol 2009; 11:988-93.

Open Access Article

Double-trouble in mitosis caused by von Hippel-Lindau tumor-suppressor protein inactivation

Claudio R. Thoma, Alberto Toso, Patrick Meraldi and Wilhelm Krek
Pages 3619 - 3620
http://dx.doi.org/10.4161/cc.8.22.9907
Abstract | PDF

Comment on: Thoma CR, et al. Nat Cell Biol 2009; 11:994-1001.


Open Access Article

The regulation of human reproduction by p53 and its pathway

Wenwei Hu, Zhaohui Feng and Arnold J. Levine
Pages 3621 - 3622
http://dx.doi.org/10.4161/cc.8.22.9938
Abstract | PDF

Comment on: Kang HJ, et al. Proc Natl Acad Sci U S A 2009; 106:9761-6.

Open Access Article

SharING out the roles in replicatING DNA

Delphine Larrieu and Rémy Pedeux
Pages 3623 - 3624
http://dx.doi.org/10.4161/cc.8.22.9947
Abstract | PDF

Comment on: Larrieu D, et al. EMBO Rep 2009; 10:1168-74.

Open Access Article

p21^Cip1 regulation by ERK2: A post-translational mechanism that relays a proliferation signal

Chae Young Hwang and Ki-Sun Kwon
Pages 3625 - 3626
http://dx.doi.org/10.4161/cc.8.22.9958
Abstract | PDF

Comment on: Hwang CY, et al. Mol Cell Biol 2009; 29:3379-89.

Open Access Article

microRNAs gain magnitude in muscle

Colin G. Crist and Margaret Buckingham
Pages 3627 - 3628
http://dx.doi.org/10.4161/cc.8.22.9960
Abstract | PDF

Comment on: Crist CG, et al. Proc Natl Acad Sci USA 2009; 106:13383-7.

Open Access Article

Pathogenic role of interleukin-21 in psoriasis

Roberta Caruso, Antonio Costanzo and Giovanni Monteleone
Pages 3629 - 3630
http://dx.doi.org/10.4161/cc.8.22.9964
Abstract | PDF

Comment on: Caruso R, et al. Nat Med 2009; 15:1013-5.




CELL CYCLE NEWS & VIEWS

Open Access Article

Targeting protein interactions of p53 for therapeutic intervention: Success in a frustrated landscape

Tom L. Blundell and Victor M. Bolanos-Garcia
Pages 3631 - 3635
http://dx.doi.org/10.4161/cc.8.22.10311
Abstract | PDF

Comment on: Design of a novel MDM2 binding peptide based on the p53 family. Madhumalar A, et al. Cell Cycle 2009; 8:2828-36.

Open Access Article

When DNA damage goes invisible

Francis Rodier and Judith Campisi
Pages 3631 - 3635
http://dx.doi.org/10.4161/cc.8.22.10190
Abstract | PDF

Comment on: DNA damage foci in mitosis are devoid of 53BP1. Nelson G, et al. Cell Cycle 2009; In press.

Open Access Article

Revealing the hidden relationship between nucleosomes and splicing

Craig D. Kaplan
Pages 3631 - 3635
http://dx.doi.org/10.4161/cc.8.22.10289
Abstract | PDF

Comment on: Nucleosomes are preferentially positioned at exons in somatic and sperm cells. Nahkuri S, et al. Cell Cycle 2009; 8:3420-4.

Open Access Article

Intriguing novel abilities of Nutlin-3A: Induction of cellular quiescence as opposed to cellular senescence—Implications for chemotherapy

Linda S. Steelman and James A. McCubrey
Pages 3631 - 3635
http://dx.doi.org/10.4161/cc.8.22.10165
Abstract | PDF

Comment on: Cellular quiescence caused by the Mdm2 inhibitor nutlin-3a. Korotchkina LG, et al. Cell Cycle 2009; 8:3777-81.




EXTRA VIEWS

Open Access Article

Insights into the function of the human P-TEFb component CDK9 in the regulation of chromatin modifications and co-transcriptional mRNA processing

Judith Pirngruber, Andrei Shchebet and Steven A. Johnsen
Pages 3636 - 3642
http://dx.doi.org/10.4161/cc.8.22.9890
Abstract | PDF

Cyclin-dependent kinase-9 (CDK9) was originally characterized as a transcription elongation factor which regulates RNA Polymerase II (RNAPII) activity following transcriptional initiation. However, recent evidence from a number of studies have shown that CDK9 plays an important role in regulating not only RNAPII activity but also co-transcriptional histone modification and mRNA processing events such as splicing and 3' end processing. Importantly, our previous work and the work presented here demonstrate that CDK9 functions to guide a complex network of chromatin modifications including histone H2B monoubiquitination (H2Bub1), H3 lysine 4 trimethylation (H3K4me3) and H3K36me3. This function appears to be dependent upon not only the phosphorylation of the RNA Polymerase II C-terminal domain but also upon other CDK9 targets such as the Suppressor of Ty Homolog-5 (SUPT5H), Negative Elongation Factor-E (NELF-E) and probably the human Rad6 homolog UBE2A. We provide a working model by which CDK9 may control co-transcriptional replication-dependent histone mRNA 3' end processing in an H2Bub1 and H3K4me3-dependent manner and uncover new and important differences between the functions of human CDK9 and its yeast counterparts Ctk1 and Bur1.

Open Access Article

Geometric control of the cell cycle

Sophie G. Martin
Pages 3643 - 3647
http://dx.doi.org/10.4161/cc.8.22.9891
Abstract | PDF

How do cells sense their own size and shape? And how does this information regulate progression of the cell cycle? Our group, in parallel to that of Paul Nurse, have recently demonstrated that fission yeast cells use a novel geometry-sensing mechanism to couple cell length perception with entry into mitosis. These rod-shaped cells measure their own length by using a medially-placed sensor, Cdr2, that reads a protein gradient emanating from cell tips, Pom1, to control entry into mitosis. Budding yeast cells use a similar molecular sensor to delay entry into mitosis in response to defects in bud morphogenesis. Metazoan cells also modulate cell proliferation in response to their own shape by sensing tension. Here I discuss the recent results obtained for the fission yeast system and compare them to the strategies used by these other organisms to perceive their own morphology.

Open Access Article

Hacking RNA: Hakai promotes tumorigenesis by enhancing the RNA-binding function of PSF

Angélica Figueroa, Yasuyuki Fujita and Myriam Gorospe
Pages 3648 - 3651
http://dx.doi.org/10.4161/cc.8.22.9909
Abstract | PDF

Hakai, an E3 ubiquitin ligase for the E-cadherin complex, plays a crucial role in lowering cell-cell contacts in epithelial cells, a hallmark feature of tumor progression.  Recently, Hakai was also found to interact with PSF (PTB-associated splicing factor).  While PSF can function as a DNA-binding protein with a tumor suppressive function, its association with Hakai promotes PSF’s RNA-binding ability and post-transcriptional influence on target mRNAs.  Hakai overexpression enhanced the binding of PSF to mRNAs encoding cancer-related proteins, while knockdown of Hakai reduced the RNA-binding ability of PSF. Furthermore, the knockdown of PSF suppressed Hakai-induced cell proliferation.  Thus, Hakai can affect the oncogenic phenotype both by altering E-cadherin-based intercellular adhesions and by increasing PSF’s ability to bind RNAs that promote cancer-related gene expression.

Open Access Article

Systematically linking drug susceptibility to cancer genome aberrations

Martin L. Sos and Roman K. Thomas
Pages 3652 - 3656
http://dx.doi.org/10.4161/cc.8.22.9936
Abstract | PDF

Genetic aberrations (lesions) govern the transformation of previously normal cells into cancer cells by changing key signaling pathways within the cells that control cellular proliferation, differentiation and survival. Such lesions are thus considered prime molecular targets for cancer therapy. While some notable examples underscore the clinical relevance of this connection between genetics and drug response, there is a lack of analytical approaches to provide such novel “drug-mutation” combinations in a broad and unbiased fashion. We have therefore collected a panel of genetically and phenotypically characterized non-small cell lung cancer (NSCLC) cell lines to systematically screen for drug susceptibility of NSCLC as a function of genetic lesions. We found such genetic lesions to predict activity of geldanamycin-derived Hsp90 inhibitors as well as of the clinically approved SRC/ABL-inhibitor dasatinib. This work may therefore help advancing our understanding of critical oncogenic pathway dependencies and may impact future drug development by defining drug-susceptible patient populations.

Open Access Article

Protective roles of matrix metalloproteinases: From mouse models to human cancer

Carlos López-Otín, Lavanya H. Palavalli and Yardena Samuels
Pages 3657 - 3662
http://dx.doi.org/10.4161/cc.8.22.9956
Abstract | PDF

Matrix metalloproteinases (MMPs) have long been linked to cancer progression owing to their ability to breakdown tissue barriers for metastatic spread. Accordingly, multiple studies have examined the potential value of these enzymes as targets for cancer therapy. Unfortunately, most clinical trials with MMP inhibitors have yielded negative results which has made necessary to re-evaluate the role of these proteases in cancer. Recent works mainly based on the use of mouse models deficient in specific MMPs have revealed that these enzymes play many roles in cancer distinct from matrix destruction, influencing early steps of tumor evolution, and expanding their pro-tumorigenic properties. However, these in vivo studies have also shown that, unexpectedly, some MMP family members like MMP8 may have paradoxical anti-tumor functions. Nevertheless, the final validation of these MMPs as bona fide tumor suppressors requested the identification of the putative genetic or epigenetic changes underlying their inactivation during cancer development. To this purpose, very recent large-scale genomic studies have explored the possibility that MMPs could be genetically altered in a panel of human malignant tumors from different sources. These studies have demonstrated that MMP8 is a frequently mutated gene in human melanoma. Functional analysis of the identified mutations has confirmed that all of them lead to the loss-of-function of MMP8 and enhance the progression of melanoma, thus providing definitive evidence that MMP8 is a tumor-suppressor gene. Parallel studies have extended these findings to other MMP-related metalloproteinases such as ADAMTS15, which has been found to be genetically inactivated in human colorectal cancer. This review describes the identification and validation of some MMPs and related enzymes as anti-tumor proteases and speculates about the molecular mechanisms underlying their protective roles in tumor development. Finally, the review explores the clinical applications derived from the identification of MMPs that favor the host instead of the tumor.

Open Access Article

Epigenetic alterations in a murine model for chronic lymphocytic leukemia

Shih-Shih Chen, Mara H. Sherman, Erin Hertlein, Amy J. Johnson, Michael A. Teitell, John C. Byrd and Christoph Plass
Pages 3663 - 3667
http://dx.doi.org/10.4161/cc.8.22.9957
Abstract | PDF

Early stages in the development of chronic lymphocytic leukemia (CLL) have not been explored mainly due to the inability to study normal B-cells en route to transformation. In order to determine such early events of leukemogenesis, we have used a well established mouse model for CLL. Over-expression of human TCL1, a known CLL oncogene in murine B-cells leads to the development of mature CD19+/CD5+/IgM+ clonal leukemia with a disease phenotype similar to that seen in human CLL. Herein, we review our recent study using this TCL1-driven mouse model for CLL and corresponding human CLL samples in a cross-species epigenomics approach to address the timing and relevance of epigenetic events occurring during leukemogenesis. We demonstrated that the mouse model recapitulates the epigenetic events that have been reported for human CLL, affirming the power and validity of this mouse model to study early epigenetic events in cancer progression. Epigenetic alterations are detected as early as three months after birth, far before disease manifests at about 11 months of age. These mice undergo NFkB repressor complex mediated inactivation of the transcription factor Foxd3, whose targets become aberrantly methylated and silenced in mouse and human CLL. Overall, our data suggest the accumulated epigenetic alterations during CLL pathogenesis as a consequence of gene silencing through TCL1 and NFkB repressor complex, suggesting the relevance for NFκB as a therapeutic target in CLL.

Open Access Article

Regulation of p53: TRIM24 enters the RING

Abhinav K. Jain and Michelle Craig Barton
Pages 3668 - 3674
http://dx.doi.org/10.4161/cc.8.22.9979
Abstract | PDF

Negative regulation of p53 in normal, unstressed cells maintains levels of this tumor suppressor below a threshold for cell cycle arrest or apoptosis, and is rapidly reversed in the face of cellular stresses to permit p53 response. Recently, we created a new mouse and stem cell model by knock-in addition of an epitope tag at Trp53.  Biochemical purification of endogenous, tagged p53-protein complexes from mouse embryonic stem cells, and peptide analysis by mass spectrometry, revealed a new RING-domain E3-ubiquitin ligase TRIM24 that targets p53 for degradation. Depletion of TRIM24, formerly named TIF1α, in tumor-derived cells induces p53-dependent apoptosis.  In Drosophila, bonus is a single copy gene homologous to the mammalian Tif1 family.  Mosaic deletion of bonus induces cell death in vivo, which is rescued by depletion of D-p53. Bonus is the first identified regulator of p53 protein levels in Drosophila, which lacks an ortholog of Mdm2.  TRIM24/bonus may be the ancestral precursor of the large group of mammalian E3-ligases that target p53 for ubiquitin modification.  Understanding the specific roles that these numerous E3-ligases have in the hierarchy of p53-regulation remains a challenge for the field.  We discuss various scenarios for selectivity in choice of E3-ligase targeting p53 for degradation.

Open Access Article

Genetic manipulations reveal dynamic cell and gene functions: Cre-ating a new view of myogenesis

David A. Hutcheson and Gabrielle Kardon
Pages 3675 - 3678
http://dx.doi.org/10.4161/cc.8.22.9992
Abstract | PDF

Development of multicellular organisms is temporally and spatially complex. The Cre/loxP and Flp/FRT systems for genetic manipulation in mammals now enable researchers to explicitly examine in vivo the temporal and spatial role of cells and genes during development via cell lineage and ablation studies and conditional gene inactivation and activation. Recently we have used these methods to genetically dissect the role of Pax3+ and Pax7+ progenitor populations and the function of β-catenin, an important regulator of myogenesis, in vertebrate limb myogenesis. Our lineage and ablation studies of Pax3+ and Pax7+ progenitors revealed surprising insights into myogenesis not apparent from Pax3 and Pax7 expression and functional studies. In addition, conditional inactivation and activation of β-catenin in different progenitor populations and their progeny demonstrated that β-catenin plays several cell-autonomous roles in myogenesis. Our studies highlight the hierarchical (i.e. genes versus cells), temporal, and spatial complexity of development and demonstrate that manipulations of both cells and genes will be required to obtain a full understanding of the development of multicellular organisms.




PERSPECTIVES

Open Access Article

AMPK: Evidence for an energy-sensing cytokinetic tumor suppressor

Alejandro Vazquez-Martin, Cristina Oliveras-Ferraros, Eugeni López-Bonet and Javier A. Menendez
Pages 3679 - 3683
http://dx.doi.org/10.4161/cc.8.22.9905
Abstract | PDF

The AMP-activated protein kinase (AMPK) system, an evolutionary conserved low-energy checkpoint, functions as a canonical suppressor of cell proliferation. Proliferating cells, however, should also ensure a proper spatio-temporal bond between AMPK-sensed cell’s metabolic status and cell division. A crucial linkage between cell proliferation and AMPK-interpreted cell bioenergetics appears to take place during the M-phase of the cell cycle. A recent description of a physical interplay between the active form the α-catalytic AMPK subunit with essential mitotic regulators in the centrosome and midbody has provided direct evidence that tumor-suppressive properties for AMPK closely relate to its ability to exquisitely coordinate sensing of energy resources and the fundamental biological process of genome division during mitosis and cytokinesis. Based on recent findings in our laboratory observing abortive cytokinesis followed by nuclear shape reorganization, mitotic catastrophe, polyploidization events, and cell giantism in p53-null cancer cells pharmacologically manipulated to exhibit sustained activation of AMPK, we now propose that AMPK is a novel and biologically significant participant with a tumor suppressive activity in the mitotic/cytokinetic phase of the cell cycle. In this scenario, molecular co-evolution of the energy-sensing cytokinetic tumor suppressor AMPK within the chronic biophysical constraints of the tumor microenvironment may inherently promote a continuous generation of structural and numerical changes in chromosomes favoring generation of nascent tumor cells and/or tumor-initiating cells over tumor cell death.

Open Access Article

The role of mTORC1 pathway in intestinal tumorigenesis

Teruaki Fujishita, Masahiro Aoki and Makoto M. Taketo
Pages 3684 - 3687
http://dx.doi.org/10.4161/cc.8.22.9946
Abstract | PDF

Activation of the mTORC1 pathway has been implicated in many types of cancer, and several mTORC1 inhibitors are currently under clinical trials for treating various cancer patients. Notably, Temsirolimus has recently been approved for treatment of advanced renal cell carcinoma. However, the role of mTORC1 pathway in colorectal tumorigenesis remains largely unknown. We have recently found that the mTORC1 pathway is activated in intestinal adenomas of Apc mutant mice, accompanied by an elevated level of mTOR protein, and that treatment with RAD001, an mTORC1 inhibitor, suppresses the growth of these polyps. Our results suggest an important role of mTORC1 pathway in colorectal cancer, as well as a therapeutic possibility for mTORC1 inhibitors in its treatment.




REVIEWS

Open Access Article

Covalent modifications of histones during mitosis and meiosis

Dazhong Xu, Jingxiang Bai, Qing Duan, Max Costa and Wei Dai
Pages 3688 - 3694
http://dx.doi.org/10.4161/cc.8.22.9908
Abstract | PDF

Higher order chromosome structures are the hallmark of mitotic and meiotic cells. Chromatin condensation and compaction are essential for rapid chromosome congression and accurate chromosome segregation during cell division. The core histones possess tails at their amino-termini. These tails, which extend from the surface of the nucleosomes, are highly dynamic and subject to an extensive array of covalent modifications.  Modified histone tails play an important role, not only in the folding of nucleosomal arrays into higher order chromatin structures but also are crucial role in gene regulation. The combination of these distinct covalent modifications of histones constitutes “the histone code” that regulates various cellular processes, including mitotic and meiotic progression.

Open Access Article

ATX-LPA receptor axis in inflammation and cancer

Shuying Liu, Mandi Murph, Nattapon Panupinthu and Gordon B. Mills
Pages 3695 - 3701
http://dx.doi.org/10.4161/cc.8.22.9937
Abstract | PDF

Lysophosphatidic acid (LPA, 1- or 2-acyl-sn-glycerol 3-phosphate) mediates a plethora of physiological and pathological activities via interactions with a series of high affinity G protein-coupled receptors (GPCR). Both LPA receptor family members and autotaxin (ATX/LysoPLD), the primary LPA-producing enzyme, are aberrantly expressed in many human breast cancers and several other cancer lineages. Using transgenic mice expressing either an LPA receptor or ATX, we recently demonstrated that the ATX-LPA receptor axis plays a causal role in breast tumorigenesis and cancerrelated inflammation, further validating the ATX-LPA receptor axis as a rich therapeutic target in cancer.




METHODOLOGICAL REPORT

Open Access Article

Evaluation of p63 and p73 antibodies for cross-reactivity

Jennifer M. Rosenbluth, Kimberly Johnson, Luojia Tang, Tracy Triplett and Jennifer A. Pietenpol
Pages 3702 - 3706
http://dx.doi.org/10.4161/cc.8.22.10036
Abstract | PDF

The tumor suppressor p53 is commonly mutated in human cancers.  However, two homologs of p53, p63 and p73, are frequently over-expressed in tumors and are associated with tumor subtypes, clinical outcomes, and responses to therapy.  There are many isoforms of p53, p63, and p73 (the p53 family).  Proper detection of and discrimination between the members of this tumor suppressor family in human tissues is of critical importance to cancer research and clinical care.  In this study, we assessed the specificity of several commercially available and newly generated p73 antibodies, focusing on antibodies that distinguish between the TAp73 and ∆Np73 isoforms by Western analysis, immunohistochemistry, and immunofluorescence.  In addition, we found that the pan-p63 and pan-p73 antibodies tested cross-react with p73 and p63 respectively.  The results of this study have important implications for analysis of p63 and p73 expression and co-expression in human tumors, and for potential use of these reagents in molecular diagnostics and therapeutic decision-making.




REPORTS

Open Access Article

A theoretical model for p53 dynamics: Identifying optimal therapeutic strategy for its activation and stabilization

Do-Hyun Kim, Kyoohyoung Rho and Sunghoon Kim
Pages 3707 - 3716
http://dx.doi.org/10.4161/cc.8.22.10023
Abstract | PDF

The activation and stabilization of tumor suppressor p53 are very important in preventing cells from becoming cancerous. Hence, many experimental works have been carried out to investigate p53’s dynamics through its interactions with other proteins and its therapeutic applications for the treatment of cancers. In this work, by analyzing a theoretical model, we attempt to search for an optimal therapeutic strategy that guarantees the activation and stabilization of p53. For this purpose, we introduce a new mathematical model including oncogene activation and ARF, which are recognized as crucial for tumor suppression but have not yet been considered in most theoretical works. Through mathematical modeling and numerical simulations, we confirm several important properties of p53 dynamics: the role of the oncogene-mediated activation of ARF as an important factor for the activation and stabilization of p53, the necessity of time delays in negative feedback loops to guarantee sustained p53 oscillations, and the digital behavior of p53 pulses. Furthermore, we propose that the binding of ARF to Mdm2 and enhancing the degradation of Mdm2 is an efficient strategy for therapeutic targeting, which may assure the activation and stabilization of p53.

Open Access Article

Cell nonhomologous end joining capacity controls SAF-A phosphorylation by DNA-PK in response to DNA double-strand breaks inducers

Sébastien Britton, Carine Froment, Philippe Frit, Bernard Monsarrat, Bernard Salles and Patrick Calsou
Pages 3717 - 3722
http://dx.doi.org/10.4161/cc.8.22.10025
Abstract | PDF

Aiming to identify novel phosphorylation sites in response to DNA double-strand breaks (DSB) inducers, we have isolated a phosphorylation site on KU70. Unexpectedly, a rabbit antiserum raised against this site cross-reacted with a 120 kDa protein in cells treated by DNA DSB inducers. We identified this protein as SAF-A/hnRNP U, an abundant and essential nuclear protein containing regions binding DNA or RNA. The phosphorylation site was mapped at S59 position in a sequence context favoring a "S-hydrophobic" consensus model for DNA-PK phosphorylation site in vivo. This site was exclusively phosphorylated by DNA-PK in response to DNA DSB inducers. In addition, the extent and duration of this phosphorylation was in inverse correlation with the capacity of the cells to repair DSB by nonhomologous end joining. These results bring a new link between the hnRNP family and the DNA damage response. Additionaly, the mapped phospho-site on SAF-A might serve as a potential bio-marker for DNA-PK activity in academic studies and clinical analyses of DNA-PK activators or inhibitors.

Open Access Article

Chemotherapy induces ATP release from tumor cells

Isabelle Martins, Antoine Tesniere, Oliver Kepp, Mickaël Michaud, Frederic Schlemmer, Laura Senovilla, Claire Séror, Didier Métivier, Jean-Luc Perfettini, Laurence Zitvogel and Guido Kroemer
Pages 3723 - 3728
http://dx.doi.org/10.4161/cc.8.22.10026
Abstract | PDF

Chemotherapy can induce anticancer immune responses. In contrast to a widely extended prejudice, apoptotic cell death is often more efficient in eliciting a protective anticancer immune response than necrotic cell death. Recently, we have found that purinergic receptors of the P2X7 type are required for the anticancer immune response induced by chemotherapy. ATP is the endogenous ligand that has the highest affinity for P2X7. Therefore, we investigated the capacity of a panel of chemotherapeutic agents to induce ATP release from cancer cells. Here, we describe that multiple distinct anticancer drugs reduce the intracellular concentration of ATP before and during the manifestation of apoptotic characteristics such as the dissipation of the mitochondrial transmembrane potential and the exposure of phosphatidylserine residues on the plasma membrane. Indeed, as apoptosis progresses, intracellular ATP concentrations decrease, although even advanced-stage apoptotic cells still contain sizeable ATP levels. Only when cells enter secondary necrosis, the ATP concentration falls to undetectable levels. Concomitantly, a wide range of chemotherapeutic agents causes the release of ATP into the extracellular space as they induce tumor cell death. Hence, ATP release is a general correlate of apoptotic cell death induced by conventional anticancer therapies.

Open Access Article

microRNAs regulate human embryonic stem cell division

Junlin Qi, Jenn-Yah Yu, Halyna R. Shcherbata, Julie Mathieu, Amy Jia Wang, Sudeshna Seal, Wenyu Zhou, Bradford M. Stadler, David Bourgin, Linlin Wang, Angel Nelson, Carol Ware, Christopher Raymond, Lee P. Lim, Jill Magnus, Irena Ivanovska, Robert Diaz, Alexey Ball, Michele Cleary and Hannele Ruohola-Baker
Pages 3729 - 3741
http://dx.doi.org/10.4161/cc.8.22.10033
Abstract | PDF

RNA interference-mediated suppression of DICER and DROSHA in human embryonic stem cells (hESCs) attenuates cell proliferation, supporting a role for an intact microRNA (miRNA) pathway in the control of hESC cell division.  Normal cell growth can be partially restored by introduction of the mature miRNAs miR-195 and miR-372. These miRNAs regulate two tumor suppressor genes, respectively: WEE1, which encodes a negative G2/M kinase modulator of the cycB/CDK complex and CDKN1A, which encodes p21, a cycE/CDK cyclin dependent kinase inhibitor that regulates the G1/S transition.  We show that in wild-type hESCs, WEE1 levels control the rate of hESC division, whereas p21 levels must be maintained at a low level for hESC division to proceed.  These data support a model for hESC cell cycle control in which miRNAs regulate negative cell cycle modulators at two phases of the cell cycle to ensure proper replenishment of the stem cell population.

Supplemental information can be found here.

Open Access Article

Cep55 stabilization is required for normal execution of cytokinesis

Armando van der Horst, Jacinta Simmons and Kum Kum Khanna
Pages 3742 - 3749
http://dx.doi.org/10.4161/cc.8.22.10047
Abstract | PDF

Cep55 is a mitotic phosphoprotein that plays an important role in cytokinesis, the final stage of cell division during which physical separation of the two daughter cells is accomplished. We recently demonstrated that the peptidyl-prolyl isomerase Pin1 regulates this cell cycle event by enhancing the Plk1-dependent phosphorylation of Cep55. We show here that Cep55 is stabilized post-translationally during mitosis and that siRNA-mediated knockdown of Pin1 prevents this stabilization. Consistent with this, Cep55 is unstable in Pin1 knockout mouse embryonic fibroblasts. Moreover, mutation of the Pin1 binding sites in Cep55 reduces its stability during mitosis. Mutation of the Plk1 phosphorylation site also lowers Cep55 stability, whereas overexpression of Plk1 increases Cep55 levels, in keeping with Pin1 regulating Plk1-mediated phosphorylation of Cep55. Importantly, expression of wild-type Cep55 at levels similar to that of the phosphorylation mutants only partially reverts the cytokinesis defect induced by depletion of Cep55, indicating that inadequate levels of Cep55 prevent proper execution of cytokinesis. Taken together, these data provide more insight into the regulation of the final stages of cell division. As cytokinesis defects can cause chromosomal instability, knowledge about the processes that regulate normal cytokinesis adds to our understanding of events that lead to tumorigenesis.

Open Access Article

High resolution imaging of changes in the structure and spatial organization of chromatin, γ-H2A.X and the MRN complex within etoposide-induced DNA repair foci

Graham Dellaire, Rosemarie Kepkay and David P. Bazett-Jones
Pages 3750 - 3769
http://dx.doi.org/10.4161/cc.8.22.10065
Abstract | PDF

The focal accumulation of DNA repair factors, including the MRE11/Rad50/NBS1 (MRN) complex and the phospho-histone variant γ-H2A.X, is a key cytological feature of the DNA damage response (DDR). Although these foci have been extensively studied by light microscopy, there is comparatively little known regarding their ultrastructure. Using correlative light microscopy and electron spectroscopic imaging (LM/ESI) we have characterized the ultrastructure of chromatin and DNA repair foci within the nuclei of normal human fibroblasts in response to DNA double-strand breaks (DSBs). The induction of DNA DSBs by etoposide leads to a global decrease in chromatin density, which is accompanied by the formation of invaginations of the nuclear envelope as revealed by live-cell microscopy. Using LM/ESI and the immunogold localization of γ-H2A.X and MRE11 within repair foci, we also observed decondensed 10nm chromatin fibers within repair foci and the accumulation of large non-chromosomal protein complexes over three hours recovery from etoposide. At 18 h after etoposide treatment, we observed a close juxtapositioning of PML nuclear bodies and late repair foci of γ-H2A.X, which exhibited a highly organized chromatin arrangement distinct from earlier repair foci. Finally, the dual immunogold labeling of MRE11 with either γ-H2A.X or NBS1 revealed that γ-H2A.X and the MRN complex are sub-compartmentalized within repair foci at the sub-micron scale. Together these data provide the first ultrastructural comparison of γ-H2A.X and MRN DNA repair foci, which are structurally dynamic over time and strikingly similar in organization.

Open Access Article

Anosmin-1 involved in neuronal cell migration is hypoxia inducible and cancer regulated

Bixi Jian, Chandrasekharam N. Nagineni, Sreelatha Meleth, William Grizzle, Kirby Bland, Irshad Chaudry and Raghavan Raju
Pages 3770 - 3776
http://dx.doi.org/10.4161/cc.8.22.10066
Abstract | PDF

Functional expression of KAL1 gene is critical in the migration of GnRH neurons from the olfactory placode to the hypothalamus in embryogenesis. This gene thus far has not been shown to play a functional role in any other physiological or pathological process either in the developed brain or in peripheral tissues. We show here that KAL1 gene expression is decreased in early stage and increased in later stages of cancers. Screening of colon, lung and ovarian cancer cDNA panels indicated significant decrease in KAL1 expression in comparison to corresponding uninvolved tissues. However, KAL1 expression increased with the progression of cancer from early (I and II) stages to later (III and IV) stages of the cancer. There was a direct correlation between the TGF-β and KAL1 expression in colon cancer cDNA. Using colon cancer cell lines, we showed that TGF-β induces KAL1 gene expression and secretion of anosmin-1 protein (KAL1 coded protein). We further report that hypoxia induces anosmin-1 expression; anosmin-1 protects cancer cells from apoptosis activated by hypoxia and increases cancer cell mobility. Using siRNA technique we found that KAL1 expression following hypoxia is hypoxia-inducible factor (HIF-1) α dependent. Our results suggest that KAL1 gene expression plays an important role in cancer metastasis and protection from apoptosis.

Open Access Article

Cellular quiescence caused by the Mdm2 inhibitor Nutlin-3A

Lioubov G. Korotchkina, Zoya N. Demidenko, Andrei V. Gudkov and Mikhail V. Blagosklonny
Pages 3777 - 3781
http://dx.doi.org/10.4161/cc.8.22.10121
Abstract | PDF

Cellular senescence is characterized by irreversible loss of proliferative potential and a large, flat cell morphology. Ectopic p21and doxorubicin induced cellular senescence in HT1080 and WI-38-tert cell lines. In the same cell lines, the Mdm2 inhibitor nutlin-3a induced p53 but, unexpectedly, caused quiescence (reversible arrest) with a small cell morphology. We discuss that Mdm antagonists could be used in combination with chemotherapy to reversibly arrest normal cells, thus protecting them during chemotherapy of cancer (cyclotherapy).




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