Table of Contents

Volume 10, Issue 1

  January 1, 2011

  Pages 1 - 168

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 Issue Catalogue (MARC XML)

EDITORIALS: CELL CYCLE FEATURES

Open Access Article

Could TCTP contribute to Armin Braun's paradigm of tumor reversion in plants?

Robert Amson, Jacek Z. Kubiak, Marc Van Montagu and Adam Telerman
Page 1
http://dx.doi.org/10.4161/cc.10.1.14288
Abstract | PDF

Comment on: Brioudes F, et al. Proc Natl Acad Sci USA 2010; 107:16384-9.

Open Access Article

Probing the complexity of miRNA expression across hematopoiesis

Oleh I. Petriv, Carl L. Hansen, R. Keith Humphries and Florian Kuchenbauer
Pages 2 - 3
http://dx.doi.org/10.4161/cc.10.1.14289
Abstract | PDF

Comment on: Petriv OI, et al. Proc Natl Acad Sci USA 2010; 107:15443-8.

Open Access Article

Costimulating epithelial γδ T Cells

Deborah A. Witherden and Wendy L. Havran
Pages 4 - 5
http://dx.doi.org/10.4161/cc.10.1.14290
Abstract | PDF

Comment on: Witherden DA, et al. Science 2010; 329:1205-10.

Open Access Article

The NFκB paradox: RelB induces and inhibits gene expression

Lisa A. Madge and Michael J. May
Pages 6 - 7
http://dx.doi.org/10.4161/cc.10.1.14291
Abstract | PDF

Comment on: Madge LA, et al. J Biol Chem 2010; 285:38069–77.

Open Access Article

Central role for cAMP signaling in pigmentation and UV resistance

John D’Orazio and David E. Fisher
Pages 8 - 9
http://dx.doi.org/10.4161/cc.10.1.14292
Abstract | PDF

Comment on: Khaled M, et al. Genes Dev 2010; 24:2276-81.

Open Access Article

CD47 applies the brakes to angiogenesis via vascular endothelial growth factor receptor-2

Sukhbir Kaur and David D. Roberts
Pages 10 - 12
http://dx.doi.org/10.4161/cc.10.1.14324
Abstract | PDF

Comment on: Kaur S, et al. J Biol Chem 2010; 285:38923–32.

Open Access Article

Cell death by sugar: Bittersweet TOR

Giovambattista Pani
Pages 13 - 14
http://dx.doi.org/10.4161/cc.10.1.14325
Abstract | PDF

Comment on: Panieri E, et al. Aging 2010; 2:487-503.




CELL CYCLE NEWS & VIEWS

Open Access Article

Function following form: Functional differentiation of mammary epithelial cells requires laminin-induced polarization of PI3-kinase

Derek C. Radisky
Pages 15 - 22
http://dx.doi.org/10.4161/cc.10.1.14218
Abstract | PDF

Comment on: Xu R, et al. Cell Cycle 2010; 9:4315-4322.

Open Access Article

Refreshed but vulnerable: Yeast daughter cells are more sensitive to stress than young mothers

Miguel Coelho and Iva M. Tolić-Nørrelykke

http://dx.doi.org/10.4161/cc.10.1.14220
Abstract | PDF

Comment on: Knorre DA, et al. Cell Cycle 2010; 9:4501-5.

Open Access Article

Phosphorylation of Histone H3 in 1- and 2-cell embryos

Simon I.R. Lane and Keith T. Jones

http://dx.doi.org/10.4161/cc.10.1.14221
Abstract | PDF

Comment on: Teperek-Tkacz M, et al. Cell Cycle 2010; 9:4674–87.

Open Access Article

Linking Nek6 to p53-induced senescence

Min-Jean Yin

http://dx.doi.org/10.4161/cc.10.1.14222
Abstract | PDF

Comment on: Jee HJ, et al. Cell Cycle 2010; 9:4703–10.

Open Access Article

Aurora kinase roles in idiosyncratic mitoses: The same, but different

Karen Schindler

http://dx.doi.org/10.4161/cc.10.1.14250
Abstract | PDF

Comment on: Teperek-Tkacz M, et al. Cell Cycle 2010; 9:4674–87.

Open Access Article

A role for Nek6 kinase activity in preventing senescence?

Andrew M. Fry

http://dx.doi.org/10.4161/cc.10.1.14251
Abstract | PDF

Comment on: Jee HJ, et al. Cell Cycle 2010; 9:4703–10.

Open Access Article

C. elegans seam cells as stem cells: Wnt signaling and casein kinase Iα regulate asymmetric cell divisions in an epidermal progenitor cell type

David M. Eisenmann

http://dx.doi.org/10.4161/cc.10.1.14329
Abstract | PDF

Comment on: Banerjee D, et al. Cell Cycle 2010; 9:4748-65.

Open Access Article

The importance of being in the right place at the right time: Overexpression of Cdk2 and its ortholog Ime2 are toxic to S. cerevisiae

David Stuart

http://dx.doi.org/10.4161/cc.10.1.14330
Abstract | PDF

Comment on: Szwarcwort-Cohen M, et al. Cell Cycle 2010; 9:4711-19.




EXTRA VIEWS

Open Access Article

Is post-transcriptional stabilization, splicing and translation of selective mRNAs a key to the DNA damage response?

H. Christian Reinhardt, Ian G. Cannell, Sandra Morandell and Michael B. Yaffe
Pages 23 - 27
http://dx.doi.org/10.4161/cc.10.1.14351
Abstract | PDF

In response to DNA damage, cells activate a complex, kinase-based signaling network that consist of two components - a rapid phosphorylation-driven signaling cascade that results in immediate inhibition of Cdk/cyclin complexes to arrest the cell cycle along with recruitment of repair machinery to damaged DNA, followed by a delayed transcriptional response that promotes cell cycle arrest through the induction of Cdk inhibitors, such as p21. In recent years a third layer of complexity has emerged that involves post-transcriptional control of mRNA stability, splicing, and translation as a critical part of the DNA damage response.  Here, we describe recent work implicating DNA damage-dependent modification of RNA-binding proteins that are responsible for some of these mRNA effects, highlighting recent work on post-transcriptional regulation of the cell cycle checkpoint protein/apoptosis inducer Gadd45a by the checkpoint kinase MAPKAP Kinase-2.

Open Access Article

A role for cdk9-cyclin k in maintaining genome integrity

David S. Yu and David Cortez
Pages 28 - 32
http://dx.doi.org/10.4161/cc.10.1.14364
Abstract | PDF

Cyclin-dependent kinase 9 (CDK9), with its cyclin T regulatory subunit, is a component of the positive transcription elongation factor b (P-TEFb) complex, which stimulates transcription elongation and also functions in co-transcriptional histone modification, mRNA processing, and mRNA export.  CDK9 also binds to cyclin K but the function of this CDK9-cyclin K complex is less clear.  We and others have recently shown that CDK9 functions directly in maintaining genome integrity.  This activity is restricted to CDK9-cyclin K.  Depletion of CDK9 or its cyclin K but not cyclin T regulatory subunit impairs cell cycle recovery in response to replication stress and induces spontanous DNA damage in replicating cells.  CDK9-cyclin K also interacts with ATR and other DNA damage response and DNA repair proteins.  CDK9 accumulates on chromatin and limits the amount of single-stranded DNA in response to replication stress.  Collectively, these data are consistent with a model in which CDK9 responds to replication stress by localizing to chromatin to reduce the breakdown of stalled replication forks and promote recovery from replication arrest.  The direct role of CDK9-cyclin K in pathways that maintain genome integrity in response to replication stress appear to be evolutionarily conserved.

Open Access Article

Beyond effector caspase inhibition: Bcl2L12 neutralizes p53 signaling in glioblastoma

Alexander H. Stegh and Ronald A. DePinho
Pages 33 - 38
http://dx.doi.org/10.4161/cc.10.1.14365
Abstract | PDF

Malignant gliomas are the most common and lethal primary central nervous system cancer. Glioblastoma mutliforme (GBM), the most aggressive of these neoplasms, are generally lethal within 2 years of diagnosis due in part to the intense apoptosis resistance of its cancer cells, hence poor therapeutic response to conventional and targeted therapies.  Twenty years of research has uncovered key genetic events involved in disease initiation and progression, foremost the Tp53 tumor suppressor that is mutated or deleted in 35% of GBM. The prime importance of p53 signaling for gliomapathogenesis is further evidenced by epistatic genetic events targeting additional pathway components including deletion of p14^Arf (CDKN2A) and amplification of the p53-degrading ubiquitin ligases MDM2 and MDM4.  Recent studies have identified and validated Bcl2-Like 12 (Bcl2L12) as a potent glioma oncoprotein with multiple strategic points in apoptosis regulatory networks, i.e. effector caspases and the p53 tumor suppressor. Bcl2L12 resides in both the cytoplasm and nucleus.  In the cytoplasm, Bcl2L12 functions to inhibit caspases 3 and 7, in the nucleus, Bcl2L12 forms a complex with p53, modestly reduces p53 protein stability and prevents its binding to selected target gene promoter (e.g. p21, DR5, Noxa and PUMA), thereby inhibiting p53-directed transcriptomic changes upon DNA damage. Proteomic and multidimensional oncogenomic analyses confirmed a Bcl2L12-p53 signaling axis in GBM, as Bcl2L12 exhibited predominant genomic amplification, elevated mRNA and protein levels in GBM tumors with uncompromised p53 function. On the cell biological level, Bcl2L12 exerts robust inhibition of p53-dependent senescence and apoptosis processes in glioma cells. These multi-leveled studies establish Bcl2L12 as an important oncoprotein acting at the intersection of nuclear p53 and cytoplasmic caspase signaling and point to pharmacological disruption of the Bcl2L12:p53 complex as a promising novel therapeutic strategy for the enhanced treatment of GBM.

Open Access Article

Context-dependent regulation of Musashi-mediated mRNA translation and cell cycle regulation.

Melanie C. MacNicol, Chad E. Cragle and Angus M. MacNicol
Pages 39 - 44
http://dx.doi.org/10.4161/cc.10.1.14388
Abstract | PDF

Musashi-mediated mRNA translational control has been implicated in the promotion of physiological and pathological stem cell proliferation. During self-renewal of mammalian stem cells, Musashi has been proposed to act to repress the translation of mRNAs encoding inhibitors of cell cycle progression. By contrast, in maturing Xenopus oocytes Musashi activates translation of target mRNAs that encode proteins promoting cell cycle progression. The mechanisms directing Musashi to differentially control mRNA translation in mammalian stem cells and Xenopus oocytes is unknown. In this study, we demonstrate that the mechanisms defining Musashi function lie within the cellular context. Specifically, we show that murine Musashi acts as an activator of translation in maturing Xenopus oocytes while Xenopus Musashi functions as a repressor of target mRNA translation in mammalian cells. We further demonstrate that within the context of a primary mammalian neural stem/progenitor cell, Musashi can be converted from a repressor of mRNA translation to an activator of translation in response to extracellular stimuli. We present current models of Musashi-mediated mRNA translational control and discuss possible mechanisms for regulating Musashi function. An understanding of these mechanisms presents exciting possibilities for development of therapeutic targets to control physiological and pathological stem cell proliferation.

Open Access Article

PCL2 modulates gene regulatory networks controlling self-renewal and commitment in embryonic stem cells

Emily Walker, Janet L. Manias, Wing Y. Chang and William L. Stanford
Pages 45 - 51
http://dx.doi.org/10.4161/cc.10.1.14389
Abstract | PDF

Recent reports have better elucidated the components of the Polycomb Repressive Complex 2 (PRC2) and its functional role in embryonic stem cells (ESCs) and their differentiated derivatives. The depletion of a newly described mammalian PRC2 associated protein, PCL2, leads to an increase in ESC self-renewal and a delay in differentiation, a phenotype similar to knockouts of the core PRC2 members. Genomic and cell biology data suggest that PCL2 is important in cell fate decisions and may play a role in recruitment of PRC2 to target genes and histone methylation. Importantly, depletion of PCL2 in ESCs leads to a decrease in 3meH3K27 at the proximal promoter regions of pluripotency transcription factors Tbx3, Klf4, Foxd3 and a concomitant increase in gene expression. These proteins subsequently activate expression of Oct4, Nanog and Sox2 through a feed-forward gene regulatory circuit, altering the core pluripotency network and driving cell fate decisions towards self-renewal. We propose a model whereby alteration of the epigenetic state of Tbx3, Klf4, and Foxd3 results in the enforced expression of the pluripotency network, preventing differentiation.




PERSPECTIVES

Open Access Article

Substrate-specific regulation of ubiquitination by the anaphase-promoting complex

Ling Song and Michael Rape
Pages 52 - 56
http://dx.doi.org/10.4161/cc.10.1.14387
Abstract | PDF

By orchestrating the sequential degradation of a large number of cell cycle regulators, the ubiquitin ligase anaphase-promoting complex (APC/C) is essential for proliferation in all eukaryotes. The correct timing of APC/C-dependent substrate degradation, a critical feature of progression through mitosis, was long known to be controlled by mechanisms targeting the core APC/C-machinery. Recent experiments, however, have revealed an important contribution of substrate-specific regulation of the APC/C to achieve accurate cell division. In this perspective, we describe different mechanisms of substrate-specific APC/C-regulation and discuss their importance for cell division.

Open Access Article

Reviewing once more the c-myc and Ras collaboration: Converging at the cyclin D1-CDK4 complex and challenging basic concepts of cancer biology

Chenguang Wang, Michael P. Lisanti and D. Joshua Liao
Pages 57 - 67
http://dx.doi.org/10.4161/cc.10.1.14449
Abstract | PDF

The c-myc is a proto-oncogene that manifests aberrant expression at high frequencies in most types of human cancer. C-myc gene amplifications are often observed in various cancers as well. Ample studies have also proved that c-myc has a potent oncogenicity, which can be further enhanced by collaborations with other oncogenes such as Bcl-2 and activated Ras. Studies on the collaborations of c-myc with Ras or other genes in oncogenicity have established several basic concepts and have disclosed their underlying mechanisms of tumor biology, including “immortalization” and “transformation”. In many cases, these collaborations may converge at the cyclin D1-CDK4 complex. In the meantime, however, many results from studies on the c-myc, Ras and cyclin D1-CDK4 also challenge these basic concepts of tumor biology and suggest to us that the immortalized status of cells should be emphasized. Stricter criteria and definitions for a malignantly transformed status and a benign status of cells in culture also need to be established to facilitate our study of the mechanisms for tumor formation and to better link up in vitro data with animal results and eventually with human cancer pathology.




REVIEW

Open Access Article

A new regulator of the cell cycle: The PR-Set7 histone methyltransferase

Shumin Wu and Judd C. Rice
Pages 68 - 72
http://dx.doi.org/10.4161/cc.10.1.14363
Abstract | PDF

The ability of eukaryotes to alter chromatin structure and function is modulated, in part, by histone-modifying enzymes and the post-translational modifications they create.  One of these enzymes, PR-Set7/Set8/KMT5a, is the sole histone methyltransferase responsible for the monomethylation of histone H4 lysine 20 (H4K20me1) in higher eukaryotes.  Both PR-Set7 and H4K20me1 were previously found to be tightly cell cycle regulated suggesting that they play an important, although unknown, role in cell cycle progression.  Several recent reports reveal that PR-Set7 abundance is dynamically regulated during different cell cycle phases by distinct enzymes including cdk1/cyclinB, Cdc14, SCF^Skp2, CRL4^cdt2 and APC^cdh1.  Importantly, these reports demonstrate that inappropriate levels of PR-Set7 result in profound cell cycle defects including the inability to initiate S phase, the re-replication of DNA and the improper timing of mitotic progression.  Here, we summarize the significance of these new findings, raise some important questions that require further investigation and explore several possibilities of how PR-Set7 and methylated H4K20 may likely function as novel regulators of the cell cycle.




REPORTS

Open Access Article

PACSIN 2 represses cellular migration through direct association with cyclin D1 but not its alternate splice form cyclin D1b

Hui Meng, Lifeng Tian, Jie Zhou, Zhiping Li, Xuanmao Jiao, Wayne W. Li, Markus Plomann, Zhishun Xu, Michael P. Lisanti, Chenguang Wang and Richard G. Pestell
Pages 73 - 81
http://dx.doi.org/10.4161/cc.10.1.14243
Abstract | PDF

Cyclin D1 overexpression is a common feature of many human malignancies. Genomic deletion analysis has demonstrated a key role for cyclin D1 in cellular proliferation, angiogenesis, and cellular migration. To investigate the mechanisms contributing to cyclin D1 functions, we purified cyclin D1a-associated complexes by affinity chromatography and identified the PACSIN 2 (protein kinase C and casein kinase substrate in neurons 2) protein by mass spectrometry. The PACSIN 2, but not the related PACSIN 1 and 3, directly bound wild-type cyclin D1 (cyclin D1a) at the carboxyl terminus, and failed to bind cyclin D1b, the alternative splicing variant of cyclin D1. PACSIN 2 knockdown induced cellular migration and reduced cell spreading in LNCaP cells expressing cyclin D1a. In cyclin D1^-/- mouse embryonic fibroblasts (MEFs), cyclin D1a, but not cyclin D1b, reduced the cell spreading to a polarized morphology. siPACSIN 2 had no effect on cellular migration of cyclin D1^-/- MEFs. Cyclin D1a restored the migratory ability of cyclin D1^-/- MEFs, which was further enhanced by knocking down PACSIN 2 with siRNA. The cyclin D1-associated protein, PACSIN 2, regulates cell spreading and migration, which are dependent on cyclin D1 expression.

Open Access Article

Chemical states of the N-terminal “lid” of MDM2 regulate p53 binding: Simulations reveal complexities of modulation

Shubhra Ghosh Dastidar, Devanathan Raghunathan, Judith Nicholson, Ted R. Hupp, David P. Lane and Chandra S. Verma
Pages 82 - 89
http://dx.doi.org/10.4161/cc.10.1.14345
Abstract | PDF

Phosphorylation of S17 in the N-terminal "lid" of MDM2 (residues 1-24) is proposed to regulate the binding of p53. The lid is composed of an intrinsically disordered peptide motif that is not resolved in the crystal structure of the MDM2 N-terminal domain.  Molecular dynamics simulations of MDM2 provide novel insight into how the lid undergoes complex dynamics depending on its phosphorylation state that have not been revealed by NMR analyses. The difference in charges between the phosphate and the phosphomimetic 'Asp' and the change in shape from tetrahedral to planar are manifested in differences in strengths and durations of interactions that appear to modulate access of the binding site to ligands and peptides differentially. These findings unveil the complexities that underlie protein-protein interactions and reconcile some differences between the biochemical and NMR data suggesting that lid mutation or deletion can change the specific activity of MDM2 and provide concepts for future approaches to evaluate the effects of S17 modification on p53 binding.

Open Access Article

Rare BRCA1 haplotypes including 3’UTR SNPs associated with breast cancer risk

Cory Pelletier, William C. Speed, Trupti Paranjape, Katie Keane, Rachel Blitzblau, Antoinette Hollestelle, Kyan Safavi, Ans van den Ouweland, Daniel Zelterman, Frank J. Slack, Kenneth K. Kidd and Joanne B. Weidhaas
Pages 90 - 99
http://dx.doi.org/10.4161/cc.10.1.14359
Abstract | PDF

Genetic markers identifying women at an increased risk of developing breast cancer exist, yet the majority of inherited risk remains elusive.  While numerous BRCA1 coding sequence mutations are associated with breast cancer risk, BRCA1 mutations account for less then 5% of breast cancer risk.  Since 3' untranslated region (3'UTR) polymorphisms disrupting microRNA (miRNA) binding can be functional and can act as genetic markers of cancer risk, we tested the hypothesis that such polymorphisms in the 3'UTR of BRCA1 and haplotypes containing these functional polymorphisms may be associated with breast cancer risk.  We sequenced the BRCA1 3'UTR from breast cancer patients to identify miRNA disrupting polymorphisms.  We further evaluated haplotypes of this region including the identified 3'UTR variants in a large population of controls and breast cancer patients (n=221) with known breast cancer subtypes and ethnicities.  We identified three 3'UTR variants in BRCA1 that are polymorphic in breast cancer populations, and haplotype analysis including these variants revealed that breast cancer patients harbor five rare haplotypes not generally found among controls (9.50% for breast cancer chromosomes, 0.11% for control chromosomes, p=0.0001).  Three of these rare haplotypes contain the rs8176318 BRCA1 3'UTR functional variant.  These haplotypes are not biomarkers for BRCA1 coding mutations, as they are found rarely in BRCA1 mutant breast cancer patients (1/129 patients= 0.78%). These rare BRCA1 haplotypes and 3'UTR SNPs may represent new genetic markers of breast cancer risk.

Open Access Article

Downregulation of uPAR inhibits migration, invasion, proliferation, FAK/PI3K/Akt signaling and induces senescence in papillary thyroid carcinoma cells

Theodore S. Nowicki, Hong Zhao, Zbigniew Darzynkiewicz, Augustine Moscatello, Edward Shin, Stimson Schantz, Raj K. Tiwari and Jan Geliebter
Pages 100 - 107
http://dx.doi.org/10.4161/cc.10.1.14362
Abstract | PDF

Papillary thyroid carcinoma (PTC) is the most common endocrine and thyroid malignancy.  The urokinase plasminogen activator receptor (uPAR) plays an important role in cancer pathogenesis, including breakdown of the extracellular matrix, invasion, and metastasis.  Additionally, there is increasing evidence that uPAR also promotes tumorigenesis via the modulation of multiple signaling pathways.  BRAFV600E, the most common initial genetic mutation in PTC, leads to ERK1/2 hyperphosphorylation, which has been shown in numerous cancers to induce uPAR.  Treatment of the BRAFV600E-positive PTC cell line, BCPAP, with the MEK/ERK inhibitor U0126 reduced uPAR RNA levels by 90%.  siRNA-mediated down-regulation of uPAR in BCPAP cells resulted in greatly decreased activity in the focal adhesion kinase (FAK)/phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway.  This phenomenon was concurrent with drastically reduced proliferation rates and decreased clonigenic survival, as well as demonstrated senescence-associated nuclear morphology and induction of b-galactosidase activity. uPAR-knockdown BCPAP cells also displayed greatly reduced migration and invasion rates, as well as a complete loss of the cells' ability to augment their invasiveness following plasminogen supplementation. Taken together, these data provide new evidence of a novel role for uPAR induction (as a consequence of constitutive ERK1/2 activation) as a central component in PTC pathogenesis, and highlight the potential of uPAR as a therapeutic target.

Open Access Article

DNA-RNA hybrids contribute to the replication dependent genomic instability induced by Omcg1 deficiency

Martin Houlard, Jérôme Artus, Teddy Léguillier, Sandrine Vandormael-Pournin and Michel Cohen-Tannoudji
Pages 108 - 117
http://dx.doi.org/10.4161/cc.10.1.14379
Abstract | PDF

During S phase, the replisome has to overcome many physical obstacles that can cause replication fork stalling and compromise genome integrity. Transcription is an important source of replicative stress and consequently, maintenance of genome integrity requires the protection of chromosomes from the deleterious effects arising from the interaction between nascent RNAs and template DNA, leading to stable DNA-RNA hybrids (R-loop) formation. We previously reported the essential role of Omcg1 (Ovum Mutant Candidate Gene) for cell cycle progression during early embryonic development. Here, we show that OMCG1 is a target of the cell cycle checkpoint kinases ATR/ATM and is essential for S phase progression in mouse embryonic fibroblasts. Using a conditional gene inactivation strategy, we demonstrate that OMCG1 depletion impairs cell viability as a consequence of DSB formation, checkpoint activation and replication fork collapse. We also show that no chromosome breaks were generated in non-cycling Omcg1-deficient cells. Furthermore, increased RNaseH expression significantly alleviated genomic instability in deficient fibroblasts suggesting that cotranscriptional R-loops formation contributes to the genesis of replication-dependent DSBs in these cells. Together with recent reports describing its participation to complexes involved in cotanscriptional processes, our results suggest that OMCG1 plays a role in the tight coupling between mRNA processing pathways and maintenance of genome integrity during cell cycle progression.

Open Access Article

An inhibitor of cyclin-dependent kinases suppresses TLR signaling and increases the susceptibility of cancer patients to herpes viridae

Mustapha Zoubir, Caroline Flament, Abdelaziz Gdoura, Rastilav Bahleda, Elena Litvinova, Vassili Soumelis, Rosa Conforti, Sophie Viaud, Jean-Charles Soria, Guido Kroemer, Laurence Zitvogel and Nathalie Chaput
Pages 118 - 126
http://dx.doi.org/10.4161/cc.10.1.14445
Abstract | PDF

Cyclin-dependent kinase (CDK) inhibitors have been considered as excellent drug candidates for cancer therapy owing to their potential capacity to restore cell cycle control. The first generation of CDK inhibitors showed modest clinical advantages that could be attributed to off-target effects preventing them from reaching therapeutic concentrations. A phase I dose-escalation study using the second generation multi-CDK inhibitor PHA-793887 was conducted on a total of 19 patients with advanced refractory malignancies in two sites in Europe: the University of Leeds and St. James’s Institute of Oncology, Leeds, UK, and the Institut Gustave Roussy, Villeujf, France (IGR). Fifteen patients were treated at IGR. Six among these patients manifested the reactivation of herpes virus replication. In vitro experiments revealed that PHA-793887 severely impaired signaling by toll-like receptors (such as TLR3, TLR4 and TLR9) in dendritic cells (DC), thus suppressing the production of multiple cytokines (type 1 interferon, interleukin-6,-10, -12, and tumor necrosis factor- α) by mature DC, as well as the DC-stimulated production of interferon-γ by natural killer cells. Pharmacological inhibition of glycogen synthase-3β (GSK-3β), one of the off-targets of PHA-793887, did not cause such immunological defects. Altogether, these data underscore a hitherto unsuspected immunosuppressive effect of PHA-793887.

Open Access Article

Ubiquitin-mediated protein degradation and methylation-induced gene silencing cooperate in the inactivation of the INK4/ARF locus in Burkitt lymphoma cell lines

Annalisa Roberti, Flavio Rizzolio, Chiara Lucchetti, Laurence de Leval and Antonio Giordano
Pages 127 - 134
http://dx.doi.org/10.4161/cc.10.1.14446
Abstract | PDF

Burkitt lymphoma is one of the most aggressive tumors affecting humans. Together with the characteristic chromosomal translocation that constitutively activates the c-Myc oncogene, alterations in cellular tumor suppressor pathways are additionally required in order to allow the cells to overcome anti-oncogenic barriers and proliferate in an uncontrolled manner. The INK4a/ARF locus on chromosome 9p21 is considered a safeguard locus since it encodes the two important tumor suppressor proteins, p14^ARF and p16^INK4a. By regulating the p53 and Rb pathways p14^ARF and p16^INK4a respectively act as pro-apoptotic and cell cycle inhibitor proteins. The importance of the INK4a/ARF locus has been well documented in several human tumors as well as in Burkitt lymphoma. Although the mechanisms responsible for the transcriptional regulation of the INK4a/ARF locus have been thoroughly characterized, less is known about its posttranscriptional control. In this study we found that p16^INK4a and p14^Arf are concurrently inactivated in a panel of BL cell lines. We demonstrate that along with the epigenetic silencing of the p16INK4a gene, the complete inactivation of the locus is achieved by the improper turnover of INK4/ARF proteins by the ubiquitin-proteasome system (UPS), as the proteasome inhibitor MG-132 blocks p14^ARF degradation and induces a dramatic stabilization of the p16^INK4a protein. We establish that the simultaneous deregulation of both DNA methylation patterns and the ubiquitin-dependent proteolysis system is required to completely inactive the INK4/ARF locus, opening new prospects for the understanding and treatment of Burkitt lymphoma.

Open Access Article

Trophinin-mediated cell adhesion induces apoptosis of human endometrial epithelial cells through PKC-δ

Naoaki Tamura, Kazuhiro Sugihara, Tomoya O. Akama and Michiko N. Fukuda
Pages 135 - 143
http://dx.doi.org/10.4161/cc.10.1.14448
Abstract | PDF

Trophinin is an intrinsic membrane protein expressed in trophectoderm cells of embryos and in uterine epithelial cells. Trophinin potentially mediates apical cell adhesion at human embryo implantation sites through trophinin-trophinin binding in these two cell types. Trophinin-mediated cell adhesion activates trophectoderm cells for invasion, whereas the effect of adhesion on maternal side is not known. We show that addition of GWRQ peptide, a previously established peptide that mimics trophinin-mediated cell adhesion, to human endometrial epithelial cells expressing trophinin induces their apoptosis. FAS involvement was excluded, as GWRQ did not bind to FAS, and FAS knockdown did not alter GWRQ-induced apoptosis. Immunoblotting analyses of protein kinases revealed an elevation of PKC-d protein in GWRQ-bound endometrial epithelial cells. In the absence of GWRQ, PKC-d associated with trophinin and remained cytoplasmic, but after GWRQ binding to the trophinin extracellular domain, PKC-d became tyrosine phosphorylated, dissociated from trophinin, and entered the nucleus. In PKC-d knockdown endometrial cells, GWRQ did not induce apoptosis.

Open Access Article

Cell size and growth rate are major determinants of replicative lifespan

Jingye Yang, Huzefa Dungrawala, Hui Hua, Arkadi Manukyan, Lesley Abraham, Wesley Lane, Holly Mead, Jill Wright and Brandt L. Schneider
Pages 144 - 155
http://dx.doi.org/10.4161/cc.10.1.14455
Abstract | PDF

Yeast cells, like mammalian cells, enlarge steadily as they age. Unabated cell growth can promote cellular senescence; however, the significance of the relationship between size and cellular lifespan is not well understood. Herein, we report a genetic link between cell size, growth rate and lifespan. Mutations that increase cell size concomitantly increase growth rate and decrease lifespan. As a result, large cells grow, divide and age dramatically faster than small cells. Conversely, small cell mutants age slowly and are long-lived. Investigation of the mechanisms involved suggests that attainment of a maximal size modulates lifespan. Indeed, cumulative results revealed that life expectancy is size-dependent, and that the rate at which cells age is determined in large part by the amount of cell growth per generation.

Open Access Article

Quantitative evidence for early life fitness defects from 32 longevity-associated alleles in yeast

Joe R. Delaney, Christopher J. Murakami, Brady Olsen, Brian K. Kennedy and Matt Kaeberlein
Pages 156 - 165
http://dx.doi.org/10.4161/cc.10.1.14457
Abstract | PDF

Reduced fecundity has been associated with some alleles that enhance longevity in invertebrate and mammalian models. This observation has been suggested to support the antagonistic pleiotropy theory of aging, which predicts that alleles of some genes promoting fitness early in life have detrimental effects later in life that limit survival. In only a few cases, however, has the relative fitness of long-lived mutants been quantified through direct competition with the wild type genotype. Here we report the first comprehensive analysis of longevity/fitness trade-offs by measuring the relative fitness of 49 long-lived yeast variants in a direct competition assay with wild type cells. We find that 32 (65%) of these variants show a significant defect in fitness in this competition assay. In 26 (81%) of these cases, this reduction in fitness can be partially accounted for by reduced maximal growth rate during early life, usually resulting from a G0/G1-specific cell cycle defect. A majority of the less fit longevity-enhancing variants are associated with reduced mRNA translation. These findings are therefore consistent with the idea that enhanced longevity often comes with a fitness cost and suggest that this cost is often associated with variation in a subset of longevity factors, such as those regulating mRNA translation, growth, and reproduction.




LETTER TO THE EDITOR

Open Access Article

Menin controls the concentration of retinoblastoma protein

Dina Ivo, Laetitia Corset, Laura Desbourdes, Patrick Gaudray and Günther Weber
Pages 166 - 168
http://dx.doi.org/10.4161/cc.10.1.14447
Abstract | PDF

Menin, the protein encoded by the Multiple Endocrine Neoplasia type 1 gene, is involved in the cell cycle control through its participation in functional dynamics of chromatin and regulation of transcription. RB, the protein of the retinoblastoma gene RB1, controls the progression of the cell cycle and is regulated in its activity by means of a feedback by phosphorylation. Studies in double heterozygous knockout mice for Men1 and the Retinoblastoma gene Rb1 have recently indicated that both genes may be implicated in the same pathways. In the course of our studies on Menin, we found that after suppression or in absence of Menin, RB1 expression was strongly reduced in a posttranscriptional manner. Under conditions of growth arrest, the hyperphosphorylated form of RB was most strongly affected, whereas its hypophosphorylated form was less or not at all reduced. Our findings confirm the hypothesis that the pathways of two tumor suppressor genes are connected.