Table of Contents

Volume 9, Issue 9

  May 1, 2010

  Pages 1661 - 1856

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 Issue Catalogue (MARC XML)

EDITORIALS: CELL CYCLE FEATURES

Open Access Article

Escape from targeted inhibition: The dark side of kinase inhibitor therapy

Jill Wykosky, Akitake Mukasa, Frank Furnari and Webster K. Cavenee
Pages 1661 - 1662
http://dx.doi.org/10.4161/cc.9.9.11592
Abstract | PDF

Comment on: Mukasa A, et al. Proc Natl Acad Sci USA 2010; 107:2616-21.

Open Access Article

Complex transcriptional regulatory networks around the retinoblastoma tumor suppressor gene

Deborah L. Burkhart and Julien Sage
Pages 1663 - 1664
http://dx.doi.org/10.4161/cc.9.9.11593
Abstract | PDF

Comment on: Burkhart DL, et al. Mol Cell Biol 2010; In press.

Open Access Article

Hsp90 inhibitors: A potential treatment for latent EBV infection?

Xiaoping Sun and Shannon C. Kenney
Pages 1665 - 1666
http://dx.doi.org/10.4161/cc.9.9.11594
Abstract | PDF

Comment on: Sun X, et al. Proc Natl Acad Sci USA 2010; 107:3146-51.

Open Access Article

The cell cycle and Wnt

Gary Davidson
Pages 1667 - 1668
http://dx.doi.org/10.4161/cc.9.9.11595
Abstract | PDF

Comment on: Davidson G, et al. Dev Cell 2009; 17:788-99.

Open Access Article

A new puzzling role of p53 in mouse embryonic stem cells

Mangmang Li and Jing Huang
Pages 1669 - 1670
http://dx.doi.org/10.4161/cc.9.9.11596
Abstract | PDF

Comment on: Lee KH, et al. Proc Natl Acad Sci USA 2010; 107:69-74.

Open Access Article

Finding time: A daily clock in yeast

Martha Merrow and Margien Raven
Pages 1671 - 1672
http://dx.doi.org/10.4161/cc.9.9.11624
Abstract | PDF

Comment on: Eelderink-Chen Z, et al. Proc Natl Acad Sci USA 2010; 107:2043-7.

Open Access Article

mTOR signaling in the control of activation of primordial follicles

Deepak Adhikari and Kui Liu
Pages 1673 - 1674
http://dx.doi.org/10.4161/cc.9.9.11626
Abstract | PDF

Comment on: Adhikari D, et al. Mol Hum Reprod 2009; 15:765-70.

Open Access Article

Importance of cofilin oxidation for oxidant-induced apoptosis

Stéphanie Zdanov, Fábio Klamt and Emily Shacter
Pages 1675 - 1677
http://dx.doi.org/10.4161/cc.9.9.11650
Abstract | PDF

Comment on: Klamt F, et al. Nat Cell Biol 2009; 11:1241-6.




NEWS & VIEWS

Open Access Article

Dissecting the role of INCENP-Aurora B in spindle assembly checkpoint function, chromosomal alignment and cytokinesis

Roland P. Piekorz
Pages 1678 - 1683
http://dx.doi.org/10.4161/cc.9.9.11514
Abstract | PDF

Comment on: Becker M, et al. Cell Cycle 2010; 9:1360–72.

Open Access Article

Unraveling the relationship between n-myc and Focal Adhesion Kinase (FAK) in neuroblastoma?

Mary Beth Madonna
Pages 1678 - 1683
http://dx.doi.org/10.4161/cc.9.9.11591
Abstract | PDF

Comment on: Beierle EA, et al. Cell Cycle 2010; 9:1005–15.

Open Access Article

The replisome: A nanomachine or a dynamic dance of protein partners?

Gulfem D. Guler and Ellen Fanning
Pages 1678 - 1683
http://dx.doi.org/10.4161/cc.9.9.11622
Abstract | PDF

Comment on: Wawrousek K, et al. Cell Cycle 2010; 9:1156–66.

Open Access Article

Integrins open the way to epithelial-mesenchymal transitions

Aristidis Moustakas
Pages 1678 - 1683
http://dx.doi.org/10.4161/cc.9.9.11623
Abstract | PDF

Comment on: Bianchi A, et al. Cell Cycle 2010; 9:1647–59.

Open Access Article

Canonical Hedgehog signaling drives proangiogenic responses in endothelial cells

C. Arnold Spek, Maarten F. Bijlsma and Karla C.S. Queiroz
Pages 1678 - 1683
http://dx.doi.org/10.4161/cc.9.9.11653
Abstract | PDF

Comment on: Chinchilla P, et al. Cell Cycle 2010; 9:570–9.




EXTRA VIEWS

Open Access Article

SKI promotes Smad3 linker phosphorylations associated with the tumor-promoting trait of TGF-β

Qiushi Lin, Dahu Chen, Nikolai A. Timchenko and Estela E. Medrano
Pages 1684 - 1689
http://dx.doi.org/10.4161/cc.9.9.11292
Abstract | PDF

The transcriptional co-regulator SKI is a potent inhibitor of TGF-β-growth inhibitory signals. SKI binds to receptor-activated Smads in the nucleus, forming repressor complexes containing HDACs, mSin3, NCoR, and other protein partners. Alternatively, SKI binds to activated Smads in the cytoplasm, preventing their nuclear translocation. SKI is necessary for anchorage-independent growth of melanoma cells in vitro, and most important, for human melanoma xenograft growth in vivo. We recently identified a novel role of SKI in TGF-β signaling. SKI promotes the switch of Smad3 from repressor of proliferation to activator of oncogenesis by facilitating phosphorylations in the linker domain. High levels of endogenous SKI are required by the tumor promoting trait of TGF-β to induce expression of the plasminogen-activator inhibitor-1 (PAI-1), sustained expression of C-Myc and for aborting upregulation of p21^Waf-1. Here we discuss how SKI diversifies and amplifies its functions by associating with multiple protein partners and by promoting Smad3 linker phosphorylation(s) in response to TGF-β signaling in melanoma cells.

Open Access Article

A functional link between Polo-like kinase 1 and the mammalian Target-Of-Rapamycin pathway?

Annelies G. Renner, Laurent Créancier, Cédric Dos Santos, Camille Fialin, Christian Recher, Christian Bailly, Anna Kruczynski, Bernard Payrastre and Stéphane Manenti
Pages 1690 - 1696
http://dx.doi.org/10.4161/cc.9.9.11295
Abstract | PDF

Polo like kinase-1 is a key effector of cell division and its over-expression in several cancers is often linked with negative prognostic. We recently described that Plk1 is over-expressed in acute myeloid leukemia, and that its inhibition selectively reduces the proliferation of leukemic cells. Here, we report that Plk1 inhibition or depletion using pharmacological and siRNA approaches decreased the phosphorylation of two mTOR substrates in AML cells. In HCT116 cells, inducible expression of a constitutively active form of Plk1 leads to activation of mTOR, as shown by increased phosphorylation of its 4E-BP1 and RPS6 down-stream targets. In addition, HCT116 cells over-expressing the active form of Plk1 were characterized by abnormal growth that could be reversed by rapamycin, a specific inhibitor of the TORC1 complex. Altogether these data suggest the existence of a molecular and functional link between the Plk1 mitotic kinase and the mTOR pathway. Given the different established functions of Plk1 and mTOR during the cell cycle, we will discuss the possible meaning of this functional relationship.

Open Access Article

CYCLINg through transcription: Post-translational modifications of P-TEFb regulate transcription elongation

Sungyoo Cho, Sebastian Schroeder and Melanie Ott
Pages 1697 - 1705
http://dx.doi.org/10.4161/cc.9.9.11346
Abstract | PDF

The cyclin T/CDK9 complex, also called positive transcription elongation factor b (P-TEFb) phosphorylates the C-terminal domain of the large fragment of the RNA polymerase II. This action is a hallmark of the transition from transcription initiation to elongation. P-TEFb is itself modified by phosphorylation and ubiquitination. Recently, the core components of P-TEFb, cyclin T1 and the CDK9 proteins, were identified as novel substrates of histone acetyltransferases. Here, we review how posttranslational modifications regulate the activity of the P-TEFb complex and discuss how acetylation of the complex optimizes transcription elongation in the context of other posttranslational modifications.

Open Access Article

GAMT joins the p53 network: Branching into metabolism

Takao Ide, Kiki Chu, Stuart A. Aaronson and Sam W. Lee
Pages 1706 - 1710
http://dx.doi.org/10.4161/cc.9.9.11473
Abstract | PDF

The p53 protein functions to prevent tumor development by restricting proliferation, motility and survival of abnormal or stressed cells. In addition to well-established roles, recent discoveries indicate a role for p53 in the regulation of pathways involved in energy metabolism. The metabolic functions of p53 can inhibit the shift to glycolysis that is characteristically seen in cancer cells, while favoring the energy production by mitochondrial oxidative phosphorylation. Identification of guanidinoacetate methyltransferase (GAMT) as a new p53 target connects p53 to creatine metabolism critical in the regulation of ATP homeostasis. The involvement of GAMT in both genotoxic and metabolic stress-induced apoptosis, as well as the requirement of p53-dependent up-regulation of GAMT in glucose starvation-mediated fatty acid oxidation (FAO), demonstrate a further role of p53 in coordinating stress response with changes in cellular metabolism. Such activities of p53 would help to bring a better understanding of how cancer cells acquire unique metabolic features to maintain their own survival and proliferation, and might provide interesting clues toward the development of novel therapies.

Open Access Article

Chromosome missegregation causes colon cancer by APC loss of heterozygosity

Darren J. Baker and Jan M. van Deursen
Pages 1711 - 1716
http://dx.doi.org/10.4161/cc.9.9.11314
Abstract | PDF

A longstanding hypothesis in the field of cancer biology is that aneuploidy causes cancer by promoting loss of chromosomes that contain tumor suppressor genes. By crossing aneuploidy-prone Bub1 hypomorphic mice onto a heterozygous null background for p53, we provided conclusive evidence for this idea.1 Surprisingly, the tumors that developed in this model had not just lost the chromosome 11 copy harboring wildtype p53, but had also gained an extra copy of chromosome 11 bearing the p53 null allele. Here we report that a similar chromosome-reshuffling blueprint drives colonic tumorigenesis in Bub1 hypomorphic mice that are heterozygous for ApcMin, but now involving chromosome 18. These extended studies highlight that in order for whole chromosome instability to drive tumorigenesis, it needs to establish tumor suppressor gene loss of heterozygosity while retaining two copies of the other genes on the chromosome. Additional restrictions seem to apply to whole chromosome instability as a cancer causing mechanism, which will be discussed in this paper.




PERSPECTIVES

Open Access Article

MicroRNAs in neurodegenerative disorders

Eunsung Junn and M. Maral Mouradian
Pages 1717 - 1721
http://dx.doi.org/10.4161/cc.9.9.11296
Abstract | PDF

MicroRNAs (miRNAs) are endogenous, small, noncoding RNAs regulating eukaryotic gene expression at the post-transcriptional level. During the last decade, considerable advances have been made in our understanding the biogenesis of miRNAs, the molecular mechanisms by which they regulate gene expression and their functional role in various physiological situations. miRNAs are abundant in the brain where they have crucial roles in development and synaptic plasticity. Accumulating evidence from postmortem brain analyses and animal model studies has begun to suggest that miRNA dysfunction contributes to neurodegenerative disorders. Here, we discuss several examples of investigations demonstrating the role of miRNAs in neurodegenerative disorders. As the expression of disease-causing genes is regulated by certain miRNA(s), changes in these miRNAs could lead to the accumulation of disease-causing proteins, and subsequently to neuronal dysfunction and death. Detailed understanding of these mechanisms can provide potential new therapeutic approaches to slow down or halt the progression of neurodegenerative diseases.

Open Access Article

A therapeutic role for targeting c-Myc/Hif-1- dependent signaling pathways

Klaus Podar and Kenneth C. Anderson
Pages 1722 - 1728
http://dx.doi.org/10.4161/cc.9.9.11358
Abstract | PDF

Deregulated c-Myc occurs in ~30% of human cancers. Similarly, hypoxia- inducible factor (HIF) is commonly overexpressed in a variety of human malignancies. Under physiologic conditions, HIF inhibits c-Myc activity; however, when deregulated oncogenic c-Myc collaborates with HIF in inducing the expression of VEGF, PDK1, and hexokinase 2. Most of the knowledge of HIF derives from studies investigating a role of HIF under hypoxic conditions, however, HIF-1α stabilization is also found in normoxic conditions. Specifically, under hypoxic conditions Hif-1- mediated regulation of oncogenic c-Myc plays a pivotal role in conferring metabolic advantages to tumor cells as well as adaptation to the tumorigenic micromilieu. In addition, our own results show that under normoxic conditions oncogenic c-Myc is required for constitutive high Hif-1 protein levels and activity in Multiple Myeloma (MM) cells thereby influencing VEGF secretion and angiogenic activity within the bone marrow microenvironment. Further studies are needed to delineate the functional relevance of HIF, MYC, and the HIF-MYC collaboration in MM and other malignancies, also integrating the tumor microenvironment and the cellular context. Importantly, first studies already demonstrate promising preclinical results of novel agents, predominantly small molecules, which target c-Myc, HIF or both.

Open Access Article

Cyclin I-Cdk5 governs survival in post-mitotic cells

Paul T. Brinkkoetter, Jeffrey W. Pippin and Stuart J. Shankland
Pages 1729 - 1731
http://dx.doi.org/10.4161/cc.9.9.11471
Abstract | PDF

Cdk5 has long been recognized to play an important role in development, maturation and apoptosis of post-mitotic and terminally differentiated cells. Activation of Cdk5 is tightly regulated by specific activators. Cyclin I was recently characterized as the first cyclin protein that binds to and activates Cdk5. Cyclin I-Cdk5 activates the MEK-ERK pathway and results in increased Bcl-2 and Bcl-XL mRNA and protein levels. Lack of cyclin I renders podocytes more susceptible to apoptosis. Interestingly, activation of Cdk5 by p35 is also involved in the podocytes’ response to injury. In the absence of p35, podocytes are more prone to undergo apoptosis. Here, we propose a new model where Cdk5 plays a central role in the cellular response machinery against injury-induced apoptosis of post-mitotic cells. While cyclin I-Cdk5 regulates Bcl-2 family proteins through activation of the MEK-ERK pathway, p35-Cdk5 directly phosphorylates and stabilizes Bcl-2.




REVIEWS

Open Access Article

The paradox of tumor-associated neutrophils: Fueling tumor growth with cytotoxic substances

A. McGarry Houghton
Pages 1732 - 1737
http://dx.doi.org/10.4161/cc.9.9.11297
Abstract | PDF

Human cancers are comprised of numerous cell types including neutrophils. Although often ignored, neutrophils are frequently present at sites of tumorigenesis including the kidney, breast, colon, and lung. These cells possess substances such as reactive oxygen species and proteinases that are capable of modifying tumor growth and invasiveness. This review addresses recent reports describing both pro-host and pro-tumor roles for neutrophils and neutrophil-derived substances and will examine the alterations in neutrophil behavior that explain this apparent biological discrepancy. Unfortunately, with the exception of investigator driven manipulation of neutrophil function, these cells function overwhelmingly against the host in the setting of cancer. Many cancers are capable of recruiting neutrophils to sites of tumorigenesis where they enhance tumor growth. Identification of the neutrophil-derived substances that promote tumor growth may yield novel therapeutic approaches to inhibit cancer progression. Alternatively, strategies designed to generate highly activated and cytotoxic neutrophils within the tumor microenvironment may provide a means to unleash the tumoricidal potential of the host’s innate immune response.

Open Access Article

Targeting gastrin releasing peptide receptors: New options for the therapy and diagnosis of cancer

Florian Hohla and Andrew V. Schally
Pages 1738 - 1741
http://dx.doi.org/10.4161/cc.9.9.11347
Abstract | PDF

Gastrin-releasing peptide (GRP), the mammalian bombesin (BN), appears to be involved in the growth of several neoplasms. BN/GRP receptors (BN/GRP-Rs) are expressed in a variety of cancer cells and have limited distribution in normal human tissue. Thus inhibition of BN/GRP-Rs represents an attractive target for pharmacological treatment of some human malignancies. This review will focus on intracellular signaling pathways, which have been characterized to mediate BN/GRP-dependent receptor biological effects as well as on various approaches to target BN/GRP-Rs for therapeutic and diagnostic interventions in human malignancies.

Open Access Article

Inching over hurdles: How DNA helicases move on crowded lattices

Maria Spies and Taekjip Ha
Pages 1742 - 1749
http://dx.doi.org/10.4161/cc.9.9.11469
Abstract | PDF

Many of the genome maintenance transactions require continuous progression of molecular motors along single or double stranded DNA (dsDNA) molecule. DNA, however, is rarely found in the cell in its bare form. Structural proteins organize dsDNA and control its accessibility to molecular machines of DNA replication, repair, recombination, and transcription. Single-stranded DNA (ssDNA) is sequestered by ssDNA binding proteins, which protect it from degradation, modification and undesired transactions. Appreciation of how molecular machines compete with these stationary blocks and with each other for the access to DNA is important for our understanding of the mechanisms underlying genome maintenance. This understanding in turn establishes the molecular basis of various human diseases resulting from defects in molecular motors and their ability to navigate in crowded intracellular environments. By building upon our recent finding that it is possible for a helicase translocating on ssDNA to bypass a stationary bound protein without displacing it, we discuss potential outcomes of collisions between DNA helicases and ssDNA binding proteins. We then propose that the selective ability of some helicases to bypass or displace a specific ssDNA binding protein may be important for activation of these enzymes for particular DNA maintenance tasks.




SPOTLIGHT ON COHESIN AT THE SPINDLE POLE

Open Access Article

Cohesin: It’s not just for chromosomes anymore

Laura A. Simmons Kovacs and Steven B. Haase
Pages 1750 - 1753
http://dx.doi.org/10.4161/cc.9.9.11792
Abstract | PDF

The centrosome is the microtubule organizing center important for the establishment of the mitotic spindle in animal cells.  In mitosis, cells normally contain two centrosomes, one for each pole of the bipolar spindle.  If a cell acquires additional centrosomes, it has the potential to build a multi-polar spindle which could lead to catastrophic errors in chromosome segregation.  Although such an event is unlikely to produce viable daughter cells, an increase in centrosome number has been shown to cause chromosome instability and produce anneuploid daughter cells ^1-3.  Accordingly, supernumerary centrosomes have been found in a variety of human cancers and accumulation of additional centrosomes has been associated with the process of tumorigenesis ^{1, 4-9}.  Despite the obvious importance of regulating centrosome number, relatively little is known about how centrosome duplication is regulated.  Perhaps surprisingly, several recent studies, including three articles in this issue of Cell Cycle, implicate proteins involved in the regulation of chromosome cohesion in the maintenance of centrosome number during mitosis ^10-14.  Here we will discuss these findings and what they may tell us about the regulation of centrosome number.

Open Access Article

An update on cohesin function as a ‘molecular glue’ on chromosomes and spindles

Richard W. Wong
Pages 1754 - 1758
http://dx.doi.org/10.4161/cc.9.9.11806
Abstract | PDF

One of the critical events in mitosis is proper sister chromatid cohesion, which is mediated by a protein complex called cohesin. The cohesin complex is best known for its role in tethering the sister DNA molecules. This review summarizes recent progress in understanding the functions of cohesin, and of its major subunits, SMC1, SMC3, Scc1 and Scc3. It is now clear that cohesin also plays crucial roles in controlling transcription and gene expression, DNA damage repair and spindle pole formation; functions that are beyond the traditional view of cohesin as a 'molecular glue' that holds sister chromosomes together.

Open Access Article

Determinants of Rad21 localization at the centrosome in human cells

Juan F. Giménez-Abián, Laura A. Díaz-Martínez, Nicole A. Beauchene, Wei-Shan Hsu, Hung-Ji Tsai and Duncan J. Clarke
Pages 1759 - 1763
http://dx.doi.org/10.4161/cc.9.9.11523
Abstract | PDF

Cohesin proteins help maintain the physical associations between sister chromatids that arise in S-phase and are removed in anaphase. Recent studies found that cohesins also localize to the centrosomes, the organelles that organize the mitotic bipolar spindle. We find that the cohesin protein Rad21 localizes to centrosomes in a manner that is dependent upon known regulators of sister chromatid cohesion as well as regulators of centrosome function. These data suggest that Rad21 functions at the centrosome and that the regulators of Rad21 coordinate the centrosome and chromosomal functions of cohesin.

Open Access Article

Cohesin is needed for bipolar mitosis in human cells

Laura A. Díaz-Martínez, Nicole A. Beauchene, Katherine Furniss, Pedro Esponda, Juan F. Giménez-Abián and Duncan J. Clarke
Pages 1764 - 1773
http://dx.doi.org/10.4161/cc.9.9.11525
Abstract | PDF

Multi-polar mitosis is strongly linked with aggressive cancers and it is a histological diagnostic of tumor-grade. However, factors that cause chromosomes to segregate to more than two spindle poles are not well understood. Here we show that cohesins Rad21, Smc1 and Smc3 are required for bipolar mitosis in human cells. After Rad21 depletion, chromosomes align at the metaphase plate and bipolar spindles assemble in most cases, but in anaphase the separated chromatids segregate to multiple poles. Time-lapse microscopy revealed that the spindle poles often become split in Rad21-depleted metaphase cells. Interestingly, exogenous expression of non-cleavable Rad21 results in multi-polar anaphase. Since cohesins are present at the spindle poles in mitosis, these data are consistent with a non-chromosomal function of cohesin.

Open Access Article

Rad21 is required for centrosome integrity in human cells independently of its role in chromosome cohesion

Nicole A. Beauchene, Laura A. Díaz-Martínez, Katherine Furniss, Wei-Shan Hsu, Hung-Ji Tsai, Chris Chamberlain, Pedro Esponda, Juan F. Giménez-Abián and Duncan J. Clarke
Pages 1774 - 1780
http://dx.doi.org/10.4161/cc.9.9.11524
Abstract | PDF

Classically, chromosomal functions in DNA repair and sister chromatid association have been assigned to the cohesin proteins. More recent studies have provided evidence that cohesins also localize to the centrosomes, which organize the bipolar spindle during mitosis. Depletion of cohesin proteins is associated with multi-polar mitosis in which spindle pole integrity is compromised. However, the spindle pole defects after cohesin depletion could be an indirect consequence of a chromosomal cohesion defect which might impact centrosome integrity via alterations to the spindle microtubule network. Here we show that the cohesin Rad21 is required for centrosome integrity independently of its role as a chromosomal cohesin. Thus, Rad21 may promote accurate chromosome transmission not only by virtue of its function as a chromosomal cohesin, but also because it is required for centrosome function.




REPORTS

Open Access Article

The Raf/MEK/ERK pathway can govern drug resistance, apoptosis and sensitivity to targeted therapy

Stephen L. Abrams, Linda S. Steelman, John G. Shelton, Ellis W.T. Wong, William H. Chappell, Jörg Bäsecke, Franca Stivala, Marco Donia, Ferdinando Nicoletti, Massimo Libra, Alberto M. Martelli and James A. McCubrey
Pages 1781 - 1791
http://dx.doi.org/10.4161/cc.9.9.11483
Abstract | PDF

The effects of the Raf/MEK/ERK and PI3K/PTEN/Akt/mTOR signaling pathways on proliferation, drug resistance, prevention of apoptosis and sensitivity to signal transduction inhibitors were examined in  FL/DAkt-1:ER*(Myr⁺)+DRaf-1:AR cells which are conditionally-transformed to grow in response to Raf and Akt activation. Drug resistant cells were isolated from FL/DAkt-1:ER*(Myr⁺)+DRaf-1:AR cells in the presence of doxorubicin. Activation of Raf-1, in the drug resistant FL/DAkt-1:ER*(Myr⁺)+DRaf-1:AR cells, increased the IC₅₀ for doxorubicin 80-fold, whereas activation of Akt-1, by itself, had no effect on the doxorubicin IC₅₀. However, Akt-1 activation enhanced cell proliferation and clonogenicity in the presence of chemotherapeutic drugs. Thus the Raf/MEK/ERK pathway had profound effects on the sensitivity to chemotherapeutic drugs, and Akt-1 activation was required for the long term growth of these cells as well as resistance to chemotherapeutic drugs. The effects of doxorubicin on the induction of apoptosis in the drug resistant cells were enhanced by addition of either mTOR and MEK inhibitors. These results indicate that targeting the Raf/MEK/ERK and PI3K/Akt/mTOR pathways may be an effective approach for therapeutic intervention in drug resistant cancers that have mutations activating these cascades.




Open Access Article

Substrate degradation by the anaphase promoting complex occurs during mitotic slippage

Jinho Lee, Jin Ah Kim, Robert L. Margolis and Rati Fotedar
Pages 1792 - 1801
http://dx.doi.org/10.4161/cc.9.9.11519
Abstract | PDF

Microtubule targeting drugs are successful in chemotherapy because they indefinitely activate the spindle assembly checkpoint.  The spindle assembly checkpoint monitors proper attachment of all kinetochores to microtubules and tension between the kinetochores of sister chromatids to prevent premature anaphase entry.  To this end, the activated spindle assembly checkpoint suppresses the E3 ubiquitin ligase activity of the anaphase-promoting complex (APC).  In the continued presence of conditions that activate the spindle assembly checkpoint, cells eventually escape from mitosis by "slippage".  It has not been directly tested whether APC activation accompanies slippage. Using cells blocked in mitosis with the microtubule assembly inhibitor nocodazole, we show that mitotic APC substrates are degraded upon mitotic slippage.  To confirm that APC is normally activated upon mitotic slippage we have found that knockdown of Cdc20 and Cdh1, two mitotic activators of APC, prevents the degradation of APC substrates during mitotic slippage. Knockdown of Cdc20 and Cdh1 prevents the degradation of APC substrates during mitotic slippage. We provide the first direct demonstration that despite conditions that activate the spindle checkpoint, APC is indeed activated upon mitotic slippage of cells to interphase cells.  Activation of the spindle checkpoint by microtubule targeting drugs used in chemotherapy may not indefinitely prevent APC activation.

Open Access Article

High-throughput knockout screen in Schizosaccharomyces pombe identifies a novel gene required for efficient homolog disjunction during meiosis I

Cornelia Rumpf, Lubos Cipak, Maria Novatchkova, Zhang Li, Silvia Polakova, Andrej Dudas, Ines Kovacikova, Eva Miadokova, Gustav Ammerer and Juraj Gregan
Pages 1802 - 1808
http://dx.doi.org/10.4161/cc.9.9.11526
Abstract | PDF

Meiosis is the process which produces haploid gametes from diploid precursor cells. This reduction of chromosome number is achieved by two successive divisions. Whereas homologs segregate during meiosis I, sister chromatids segregate during meiosis II. To identify novel proteins required for proper segregation of chromosomes during meiosis, we applied a high-throughput knockout technique to delete 87 S. pombe genes whose expression is upregulated during meiosis and analyzed the mutant phenotypes. Using this approach, we identified a new protein, Dil1, which is required to prevent meiosis I homolog non-disjunction. We show that Dil1 acts in the dynein pathway to promote oscillatory nuclear movement during meiosis.

Open Access Article

miR-129 regulates cell proliferation by downregulating Cdk6 expression

Junjie Wu, Jun Qian, Chun Li, Letty Kwok, Feng Cheng, Peijun Liu, Catalina Perdomo, Darrell Kotton, Cyrus Vaziri, Christina Anderlind, Avrum Spira, Wellington V. Cardoso and Jining Lü
Pages 1809 - 1818
http://dx.doi.org/10.4161/cc.9.9.11535
Abstract | PDF

Reduced expression of miR-129 has been reported in multiple tumor cell lines and in primary tumors including medulloblastoma, undifferentiated gastric cancers, lung adenocarcinoma, endometrial cancer and colorectal carcinoma. There is also recent evidence of an antiproliferative activity of miR-129 in tumor cell lines. Still, little is known about how miR-129 regulates cell proliferation. Here we found that lentiviral-mediated over-expression of miR-129 in mouse lung epithelial cells (E10 cells) results in significant G1 phase arrest that eventually leads to cell death. miR-129 induce G1 phase arrest in multiple human lung adenocarcinoma cell lines, suggesting miR-129 targeting of G1/S phase-specific regulators. Interestingly, we show that Cdk6, a kinase involved in G1-S transition, is a direct target of miR-129. We also found the down-regulation of three other cell cycle-related novel targets of miR-129, including Erk1, Erk2 and protein kinase C epsilon (Prkce). We further show that among these targets, only Cdk6 is functionally relevant. Restoring expression of Cdk6, but not Prkce partially rescues the cell growth arrest and cell death phenotype that results from miR-129 over-expression. Together, our data indicate that miR-129 plays an important role in regulating cell proliferation by downregulation of Cdk6.

Open Access Article

Mobilization of bone marrow stem cells with StemEnhance® improves muscle regeneration in cardiotoxin-induced muscle injury

Christian Drapeau, Donna Antarr, Huaiyu Ma, Zhijian Yang, Li Tang, Robert M. Hoffman and David J. Schaeffer
Pages 1819 - 1823
http://dx.doi.org/10.4161/cc.9.9.11540
Abstract | PDF

Bone marrow-derived stem cells have the ability to migrate to sites of tissue damage and participate in tissue regeneration. The number of circulating stem cells has been shown to be a key parameter in this process. Therefore, stimulating the mobilization of bone marrow stem cells may accelerate tissue regeneration in various animal models of injury. In this study we investigated the effect of the bone marrow stem cells mobilizer StemEnhance (SE), a water-soluble extract of the cyanophyta Aphanizomenon flos-aquae (AFA), on hematopoietic recovery after myeloablation as well as recovery from cardiotoxin-induced injury of the anterior tibialis muscle in mice. Control and SE-treated female mice were irradiated, and then transplanted with GFP+ bone marrow stem cells and allowed to recover. Immediately after transplant, animals were gavaged daily with 300 mg/kg of SE in PBS or a PBS control. After hematopoietic recovery (23 days), mice were injected with cardiotoxin in the anterior tibialis muscle. Five weeks later, the anterior tibialis muscles were analyzed for incorporation of GFP+ bone marrow-derived cells using fluorescence imaging. SE significantly enhanced recovery from cardiotoxin-injury. However, StemEnhance did not affect the growth of the animal and did not affect hematopoietic recovery after myeloablation, when compared to control. This study suggests that inducing mobilization of stem cells from the bone marrow is a strategy for muscle regeneration.

Open Access Article

Dietary n-3 polyunsaturated fatty acids fail to reduce prostate tumorigenesis in the PB-ErbB-2 x Pten^+/- preclinical mouse model

Sarada Vissapragada, Anup Ghosh, Lymor Ringer, Paul Sirajuddin, Patricia Salinas, Amanda Brophy, Daniel Peaceman, Bhaskar Kallakury, Partha P. Banerjee, Stanley T. Fricke, William Helfrich, Yi Chien Lee, Richard Pestell, Philipp Scherer, Herbert B. Tanowitz, Maria Laura Avantaggiati, Leena Hilakivi-Clarke, Michael P. Lisanti, Olga C. Rodriguez and Chris Albanese
Pages 1824 - 1829
http://dx.doi.org/10.4161/cc.9.9.11542
Abstract | PDF

Diet and obesity, and their associated metabolic alterations, are some of the fastest-growing causes of disease and death in America. Findings from epidemiological studies correlating obesity, the sources of dietary fat and prostate cancer (PCa) are conflicting. We have previously shown that 15% of PB-ErbB-2 x pten^+/- mice developed PCa and exhibited increased phosphorylated 4E-BP1, but not the key PI3-kinase intermediary phospho-protein, mTOR, when maintained on unrefined mouse chow. We report herein that 100% of animals fed refined, westernized AIN-93-based diets containing corn oil developed PCa by 12 months of age. Increases in visceral fat and mTOR activation in the tumors were also observed. Furthermore, nuclear cyclin E levels were significantly induced by the AIN-93-corn oil-based diets versus chow. Replacing 50% of the corn oil with menhaden oil, with 21% of its triglycerides being n-3 PUFA’s, had no effect on tumorigenesis, fat deposition, cyclin E or mTOR. Phosphorylated BAD levels were similar in the tumors of mice in all three diets. Our data demonstrated that in the context of our preclinical model, components of crude chow, but not dietary n-3 PUFAs, protect against PCa progression. In addition, these data establish phosphorylated mTOR, nuclear cyclin E and visceral fat deposits as possible biomarkers of increased dietary risk for PCa.

Open Access Article

Romidepsin (FK228/depsipeptide) controls growth and induces apoptosis in neuroblastoma tumor cells

Jyoti Panicker, Zhijie Li, Christine McMahon, Caroline Sizer, Kenneth Steadman, Richard Piekarz, Susan E. Bates and Carol J. Thiele
Pages 1830 - 1838
http://dx.doi.org/10.4161/cc.9.9.11543
Abstract | PDF

As histone deacetylase inhibitors such as romidepsin (depsipeptide, FK228) complete successful Phase I clinical trials in pediatric solid tumors, it is important that their mechanisms of action are delineated in order to inform the development of subsequent clinical trials as single agents or in combination therapies. In this study, we evaluate the effect of romidepsin as a single agent on a number of different neuroblastoma (NB) cell lines. We find that the growth of 6/6 human NB tumor cell lines but not an immortalized fibroblast cell line (NIH3T3) is inhibited by romidepsin (IC50 = 1-6.5 ng/ml) after 72 h of treatment. Romidepsin shows selective dose-dependent cytotoxicity in both single copy and N-myc amplified NB cell lines, in cell lines with wild-type or mutant p53 and those containing Alk mutations. The decrease in cell proliferation is accompanied by caspase-dependent apoptosis as shown by PARP cleavage, an accumulation of cells in the sub-G1 phase of the cell cycle and the ability of a pan-caspase inhibitor to reduce cell death. Romidepsin inhibits the growth of subcutaneous NB xenografts in a dose dependent manner in immunocompromised mice. Furthermore, romidepsin induces expression of genes such as p21 and expression of p75 and NTRK (TrkA) which are more highly expressed in the tumors from NB patients that have a good prognosis. These studies support continued investigations into the therapeutic activity of romidepsin in NB.

Open Access Article

Enhancing therapeutic efficacy by targeting non-oncogene addicted cells with combinations of signal transduction inhibitors and chemotherapy

Stephen L. Abrams, Linda S. Steelman, John G. Shelton, William Chappell, Jörg Bäsecke, Franca Stivala, Marco Donia, Ferdinando Nicoletti, Ferdinando Nicoletti, Massimo Libra , Alberto M. Martelli and James A. McCubrey
Pages 1839 - 1846
http://dx.doi.org/10.4161/cc.9.9.11544
Abstract | PDF

The effects of inhibition of the Raf/MEK/ERK and PI3K/Akt/mTOR signaling pathways and chemotherapeutic drugs on cell cycle progression and drug sensitivity were examined in cytokine-dependent FL5.12 hematopoietic cells. We examined their effects, as these cells resemble normal hematopoietic precursor cells as they do not exhibit “oncogene-addicted” growth, while they do display “cytokine-addicted” proliferation as cytokine removal resulted in apoptosis in greater than 80% of the cells within 48 hrs. When cytokine-dependent FL5.12 cells were cultured in the presence of IL-3, which stimulated multiple proliferation and anti-apoptotic cascades, MEK, PI3K and mTOR inhibitors transiently suppressed but did not totally inhibit cell cycle progression or induce apoptosis while chemotherapeutic drugs such as doxorubicin and paclitaxel were more effective in inducing cell cycle arrest and apoptosis. Doxorubicin induced a G1 block, while paclitaxel triggered a G2/M block. Doxorubicin was more effective in inducing cell death than paclitaxel. Furthermore the effects of doxorubicin could be enhanced by addition of MEK, PI3K or mTOR inhibitors. Cytokine-dependent cells which proliferate in vitro and are not “oncogene-addicted” may represent a pre-malignant stage, more refractory to treatment with targeted therapy. However, these cells are sensitive to chemotherapeutic drugs. It is important to develop methods to inhibit the growth of such cytokine-dependent cells as they may resemble the leukemia stem cell and other cancer initiating cells. These results demonstrate the enhanced effectiveness of targeting early hematopoietic progenitor cells with combinations of chemotherapeutic drugs and signal transduction inhibitors.

Open Access Article

Rescue of the apoptotic-inducing function of mutant p53 by small molecule RITA

Carolyn Y. Zhao, Vera Grinkevich, Fedor Nikulenkov, Wenjie Bao and Galina Selivanova
Pages 1847 - 1855
http://dx.doi.org/10.4161/cc.9.9.11545
Abstract | PDF

Expression of mutant p53 correlates with poor prognosis in many tumors, therefore strategies aimed at reactivation of mutant p53 are likely to provide important benefits for treatment of tumors that are resistant to chemotherapy and radiotherapy. We have previously identified and characterized a small molecule RITA that binds p53 and induces a conformational change which prevents the binding to p53 of several inhibitors, including its own destructor MDM2. In this way, RITA rescues the tumor suppression function of wild type p53. Here, we demonstrate that RITA suppressed the growth and induced apoptosis in human tumor cell lines of a diverse origin carrying mutant p53 proteins. RITA restored transcriptional transactivation and transrepression function of several hot spot p53 mutants. The ability of RITA to rescue the activity of different p53 mutants suggests the generic mechanism of action. Thus, RITA is a promising lead for the development of anti-cancer drugs that reactivate the tumor suppressor function of p53 in cancer cells irrespective whether they express mutant or wild type p53.




LETTER TO THE EDITOR

Open Access Article

Hyperglycemia and hypoxia inducible factor (HIF): A multifaceted story

Sergiu-Bogdan Catrina, Ileana Ruxandra Botusan and Vivekananda Gupta Sunkari
Page 1856
http://dx.doi.org/10.4161/cc.9.9.11308
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