Table of Contents

Volume 9, Issue 21

  November 1, 2010

  Pages 4251 - 4415

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 Issue Catalogue (MARC XML)

EDITORIALS: CELL CYCLE FEATURES

Open Access Article

Regulation of cardiomyocyte proliferation by Foxp1

Yuzhen Wang and Edward E. Morrisey
Pages 4251 - 4252
http://dx.doi.org/10.4161/cc.9.21.13924
Abstract | PDF

Comment on: Zhang Y, et al. Genes Dev 2010; 24:1746-57.

Open Access Article

Rewiring of glycolysis in cancer cell metabolism

Jason W. Locasale, Matthew G. Vander Heiden and Lewis C. Cantley
Page 4253
http://dx.doi.org/10.4161/cc.9.21.13925
Abstract | PDF

Comment on: Vander Heiden MG, et al. Science 2010; 329:1492-9.

Open Access Article

Cell survival in tough times: The mitochondrial recovery plan

Stephen W.G. Tait and Douglas R. Green
Pages 4254 - 4255
http://dx.doi.org/10.4161/cc.9.21.13962
Abstract | PDF

Comment on: Tait SW, et al. Dev Cell. 2010; 18:802-13.




SPECIAL FEATURE ON INTERDISCIPLINARY RESEARCH

Open Access Article

Shifting senescence into quiescence by turning up p53

Manuel Serrano
Pages 4256 - 4257
http://dx.doi.org/10.4161/cc.9.21.13785
Abstract | PDF

Comment on: Leontieva OV, et al. Cell Cycle 2010; 9:4323–7.




CELL CYCLE NEWS & VIEWS

Open Access Article

Prevention of merotelic chromosome attachments by the monopolin complex

Dannel McCollum
Pages 4258 - 4265
http://dx.doi.org/10.4161/cc.9.21.13526
Abstract | PDF

Comment on: Rumpf C, et al. Cell Cycle 2010; 9:3997–4004.

Open Access Article

Ribosomal protein L37 and the p53 network

Lilyn Daftuar, Yan Zhu and Carol Prives

http://dx.doi.org/10.4161/cc.9.21.13527
Abstract | PDF

Comment on: Llanos S, et al. Cell Cycle 2010; 9:4005–2.

Open Access Article

The role of FAN1 nuclease in the Fanconi anemia pathway

Maria Castella and Toshiyasu Taniguchi

http://dx.doi.org/10.4161/cc.9.21.13529
Abstract | PDF

Comment on: Shereda RD, et al. Cell Cycle 2010; 9:3977–83.

Open Access Article

Arrestin' the hedgehog: Shh limits its own signaling via β-Arrestin1

Paul S. Knoepfler

http://dx.doi.org/10.4161/cc.9.21.13530
Abstract | PDF

Comment on: Parathath SR, et al. Cell Cycle 2010; 9:4013–24.

Open Access Article

A new FAN of the stalled replication fork

Maureen E. Hoatlin

http://dx.doi.org/10.4161/cc.9.21.13602
Abstract | PDF

 

Comment on: Shereda RD, et al. Cell Cycle 2010; 9:3977–83.

Open Access Article

Purα and nucleotide excision repair system: Implications in cellular response to ultraviolet C radiation-induced DNA damage and chemoresistance in malignant cells

Gaetano Romano and Antonio Giordano

http://dx.doi.org/10.4161/cc.9.21.13605
Abstract | PDF

Comment on: Kaminski R, et al. Cell Cycle 2010; 9:4164–73.

Open Access Article

p53: The pivot between cell cycle arrest and senescence

Raffaela Santoro and Giovanni Blandino

http://dx.doi.org/10.4161/cc.9.21.13853
Abstract | PDF

Comment on: Leontieva et al. Cell Cycle 2010; 9:4323–7.

Open Access Article

Greatwall in control of recovery

René H. Medema

http://dx.doi.org/10.4161/cc.9.21.13890
Abstract | PDF

Comment on: Peng A, et al. Cell Cycle 2010; 9:4364–9.




EXTRA VIEWS

Open Access Article

Cdc5 blocks in vivo Rad53 activity, but not in situ activity (ISA)

Jaime Lopez-Mosqueda, Genevieve M. Vidanes and David Toczyski
Pages 4266 - 4268
http://dx.doi.org/10.4161/cc.9.21.13637
Abstract | PDF

DNA damage promotes the activation of a signal transduction cascade referred to as the DNA damage checkpoint. This pathway initiates with the Mec1/ATR kinase, which then phosphorylates the Rad53/Chk2 kinase. Mec1 phosphorylation of Rad53 is then thought to promote Rad53 autophosphorylation, ultimately leading to a fully active Rad53 molecule that can go on to phosphorylate substrates important for DNA damage resistance. In the absence of DNA repair, this checkpoint is eventually down-regulated in a Cdc5-dependent process referred to as checkpoint adaptation. Recently, we showed that overexpression of Cdc5 leads to checkpoint inactivation and loss of the strong electrophoretic shift associated with Rad53 inactivation. Interestingly, this same overexpression did not strongly inhibit Rad53 autophosphorylation activity as measured by the in situ assay (ISA). The ISA involves incubating the re-natured Rad53 protein with γ 32P labeled ATP after electrophoresis and Western blotting. Using a newly identified Rad53 target, we show that despite strong ISA activity, Rad53 does not maintain phosphorylation of this substrate. We hypothesize that, during adaptation, Rad53 may be in a unique state in which it maintains some Mec1 phosphorylation, but does not have the auto-phosphorylations required for full activity towards exogenous substrates.

Open Access Article

PUMA-mediated tumor suppression: A tale of two stories

Verena Labi and Andreas Villunger
Pages 4269 - 4275
http://dx.doi.org/10.4161/cc.9.21.13666
Abstract | PDF

Several recent studies provided evidence that PUMA, a pro-apoptotic member of the BH3-only protein subgroup of the Bcl-2 family, is critical for restricting survival and recovery of different cell types, including those of the hematopoietic system, after g-irradiation (IR)-triggered DNA damage. According to its pro-apoptotic function downstream of p53, PUMA is considered to act as a tumor suppressor. While this expectation was met in a model of oncogene-driven lymphomagenesis or carcinogen-driven tumor formation in the gut, studies on IR-driven tumor formation revealed surprising new insights into the role of p53-triggered and PUMA-mediated apoptosis in tumorigenesis and stem cell homeostasis.

Open Access Article

Repeat element-driven activation of proto-oncogenes in human malignancies

Björn Lamprecht, Constanze Bonifer and Stephan Mathas
Pages 4276 - 4281
http://dx.doi.org/10.4161/cc.9.21.13682
Abstract | PDF

Recent data demonstrated that the aberrant activity of endogenous repetitive elements of the DNA in humans can drive the expression of proto-oncogenes. This article summarizes these results and gives an outlook on the impact of these findings on the pathogenesis and therapy of human cancer.

Open Access Article

Redundancy and variation in the ubiquitin-mediated proteolytic targeting of a transcription factor

Eric M. Rubenstein and Mark Hochstrasser
Pages 4282 - 4285
http://dx.doi.org/10.4161/cc.9.21.13741
Abstract | PDF

As central components of the intricate networks of eukaryotic gene regulation, transcription factors are frequent targets of ubiquitin-dependent proteolysis. A well-known example is the budding yeast MATa2 (a2) transcriptional repressor, which functions as a master regulator of cell-type determination. Degradation of a2 by the ubiquitin-proteasome system is necessary for a phenotypic switch from one cell type to another. A surprisingly complex set of ubiquitin-protein conjugation mechanisms are involved. One pathway utilizes an integral-membrane ubiquitin ligase (E3) that also functions in endoplasmic reticulum-associated degradation (ERAD). Recently, we showed that a second a2 ubiquitylation pathway uses a heterodimeric E3 that, while able to bind the ubiquitin-like protein SUMO, directly recognizes non-sumoylated a2. Other transcription factors are now also known to be ubiquitylated by multiple mechanisms; as many as a dozen E3s have been implicated in degradation of the human p53 tumor suppressor, for example. We discuss general issues of redundancy and mechanistic variation in protein modification by ubiquitin.

Open Access Article

New insights into 5q- syndrome as a ribosomopathy

Jillian L. Barlow, Lesley F. Drynan, Nicola L. Trim, Wendy N. Erber, Alan J. Warren and Andrew N.J. McKenzie
Pages 4286 - 4293
http://dx.doi.org/10.4161/cc.9.21.13742
Abstract | PDF

Myelodysplastic Syndromes (MDS) are a heterogeneous group of acquired clonal bone marrow disorders, characterised by ineffective haematopoiesis.  The mechanisms underlying many of these blood disorders have remained elusive due to the difficulty in pinpointing specific gene mutations or haploinsufficencies, which can occur within large deleted regions.   However, there is an increasing interest in the classification of some of these diseases as ribosomopathies.  Indeed, studies have implicated Ribosomal Protein (RP) S14 as a strong candidate for haploinsufficiency in 5q- syndrome, a particular form of MDS.  Recently, two novel mouse models have provided evidence for the involvement of both RPS14 and the p53 pathway, and specific miRNAs in 5q- syndrome.  In this review we will discuss: 5q- syndrome mouse models, the possible mechanisms underlying this blood disorder with respect to the candidate genes, and comparisons with other ribosomopathies, and the involvement of the p53 pathway in these diseases.




PERSPECTIVE

Open Access Article

Could STAT3 provide a link between respiration and cell cycle progression?

Peter E. Shaw
Pages 4294 - 4296
http://dx.doi.org/10.4161/cc.9.21.13677
Abstract | PDF

Maintaining the intracellular environment is important for the survival and proliferation of eukaryotic cells. How a cell regulates its redox potential during fluctuations in the generation of intracellular reactive oxygen species and exposure to extracellular oxidants is unclear. The recent findings that Signal Transducer and Activator of Transcription 3 (STAT3) regulates mitochondrial respiration and can be oxidised directly by peroxide to form multimers may have revealed features of a homeostatic mechanism coupling cell cycle progression to the intracellular redox potential.




REVIEW

Open Access Article

The autophagic tumor stroma model of cancer or “battery-operated tumor growth”: A simple solution to the autophagy paradox

Ubaldo E. Martinez-Outschoorn, Diana Whitaker-Menezes, Stephanos Pavlides, Barbara Chiavarina, Gloria Bonuccelli, Casey Trimmer, Aristotelis Tsirigos, Gemma Migneco, Agnieszka K. Witkiewicz, Renee M. Balliet, Isabelle Mercier, Chengwang Wang, Neal Flomenberg, Anthony Howell, Zhao Lin, Jaime Caro, Richard G. Pestell, Federica Sotgia and Michael P. Lisanti
Pages 4297 - 4306
http://dx.doi.org/10.4161/cc.9.21.13817
Abstract | PDF

The role of autophagy in tumorigenesis is controversial. Both autophagy inhibitors (chloroquine) and autophagy promoters (rapamycin) block tumorigenesis by unknown mechanism(s). This is called the “Autophagy Paradox”. We have recently reported a simple solution to this paradox. We demonstrated that epithelial cancer cells use oxidative stress to induce autophagy in the tumor microenvironment. As a consequence, the autophagic tumor stroma generates recycled nutrients that can then be used as chemical building blocks by anabolic epithelial cancer cells. This model results in a net energy transfer from the tumor stroma to epithelial cancer cells (an energy imbalance), thereby promoting tumor growth. This net energy transfer is both unilateral and vectorial, from the tumor stroma to the epithelial cancer cells, representing a true host-parasite relationship. We have termed this new paradigm “The Autophagic Tumor Stroma Model of Cancer Cell Metabolism” or “Battery-Operated Tumor Growth”. In this sense, autophagy in the tumor stroma serves as a “battery” to fuel tumor growth, progression, and metastasis, independently of angiogenesis. Using this model, the systemic induction of autophagy will prevent epithelial cancer cells from using recycled nutrients, while the systemic inhibiton of autophagy will prevent stromal cells from producing recycled nutrients—both effectively “starving” cancer cells. We discuss the idea that tumor cells could become resistant to the systemic induction of autophagy, by the up-regulation of natural endogenous autophagy inhibitors in cancer cells. Alternatively, tumor cells could also become resistant to the systemic induction of autophagy, by the genetic silencing/deletion of pro-autophagic molecules, such as Beclin1. If autophagy resistance develops in cancer cells, then the systemic inhibition of autophagy would provide a therapeutic solution to this type of drug resistance, as it would still target autophagy in the tumor stroma. As such, an anti-cancer therapy that combines the alternating use of both autophagy promoters and autophagy inhibitors would be expected to prevent the onset of drug resistance. We also discuss why anti-angiogenic therapy has been found to promote tumor recurrence, progression, and metastasis. More specifically, anti-angiogenic therapy would induce autophagy in the tumor stroma via the induction of stromal hypoxia, thereby converting a non-aggressive tumor type to a “lethal” aggressive tumor phenotype. Thus, uncoupling the metabolic parasitic relationship between cancer cells and an autophagic tumor stroma may hold great promise for anti-cancer therapy. Finally, we believe that autophagy in the tumor stroma is the local microscopic counterpart of systemic wasting (cancer-associated cachexia), which is associated with advanced and metastatic cancers. Cachexia in cancer patients is not due to decreased energy intake, but instead involves an increased basal metabolic rate and increased energy expenditures, resulting in a negative energy balance. Importantly, when tumors were surgically excised, this increased metabolic rate returned to normal levels. This view of cachexia, resulting in energy transfer to the tumor, is consistent with our hypothesis. So, cancer-associated cachexia may start locally as stromal autophagy, and then spread systemically. As such, stromal autophagy may be the requisite precursor of systemic cancer-associated cachexia.




REPORTS

Open Access Article

p27^Kip1, a double-edged sword in Shh-mediated medulloblastoma: Tumor accelerator and suppressor

Bobby Bhatia, Arfa Malik, Africa Fernandez-L and Anna M. Kenney
Pages 4307 - 4314
http://dx.doi.org/10.4161/cc.9.21.13441
Abstract | PDF

Medulloblastoma, a brain tumor arising in the cerebellum, is the most common solid childhood malignancy.  The current standard of care for medulloblastoma leaves survivors with life-long side effects.  Gaining insight into mechanisms regulating transformation of medulloblastoma cells-of-origin may lead to development of better treatments for these tumors.  Cerebellar granule neuron precursors (CGNPs) are proposed cells-of-origin for certain classes of medulloblastoma, specifically those marked by aberrant Sonic hedgehog (Shh) signaling pathway activation.  CGNPs require signaling by Shh for proliferation during brain development.  In mitogen-stimulated cells, nuclear localized cyclin dependent kinase (cdk) inhibitor p27 (Kip1) functions as a checkpoint control at the G1- to S-phase transition by inhibiting cdk2.  Recent studies have suggested cytoplasmically localized p27^kip1 acquires oncogenic functions.  Here, we show that p27^Kip1 is cytoplasmically localized in CGNPs and mouse Shh-mediated medulloblastomas.  Tranasgenic mice bearing an activating mutation in the Shh pathway and lacking one or both p27^Kip1 alleles have accelerated tumor incidence compared to mice bearing both p27^Kip1 alleles.  Interestingly, mice heterozygous for p27^Kip1 have decreased survival latency compared to p27^Kip1-null animals.  Our data indicate that this may reflect the requirement for at least one copy of p27^Kip1 for recruiting cyclin D/cdk4/6 to promote cell cycle progression yet insufficient expression in the heterozygous or null state to inhibit cyclin E/cdk2.  Finally, we find that mis-localized p27^Kip1 may play a positive role in motility in medulloblastoma cells.  Together, our data indicate that the dosage of p27^Kip1 plays a role in cell cycle progression and tumor suppression in Shh-mediated medulloblastoma expansion.

Open Access Article

Laminin regulates PI3K basal localization and activation to sustain STAT5 activation

Ren Xu, Virginia A. Spencer, Dinah Levy Groesser and Mina J. Bissell
Pages 4315 - 4322
http://dx.doi.org/10.4161/cc.9.21.13578
Abstract | PDF

Extracellular matrix (ECM) is a key regulator of tissue morphogenesis and functional differentiation in the mammary gland.  We showed recently that laminin-111 (LN1) together with prolactin induces b-casein expression in mammary epithelial cells (MECs) by sustaining STAT5 activation.  Others have shown that Rac1 is required for integrin-mediated STAT5 activation, but molecules upstream of Rac1 remain to be elucidated.  Here, we show that exposure to three-dimensional (3D) laminin-rich ECM (LrECM) gels changes the localization of phosphoinositide 3-kinase (PI3K) in MECs from diffuse to basal accompanied with the activation of PI3K-Rac1 signaling pathway.  We show by co-immunoprecipitation that Rac1 associates with STAT5, and that LrECM treatment enhances this interaction.  Blocking PI3K with LY294002 inhibits LrECM-dependent Rac1 activation, attenuates sustained STAT5 phosphorylation, and blocks ß-casein gene transcription.  These results indicate that PI3K is a key mediator of the LN1-induced signaling cascade which controls the activity of transcription factors essential for tissue-specific gene expression.

Open Access Article

Weak p53 permits senescence during cell cycle arrest

Olga V. Leontieva, Andrei V. Gudkov and Mikhail V. Blagosklonny
Pages 4323 - 4327
http://dx.doi.org/10.4161/cc.9.21.13584
Abstract | PDF

Cell cycle arrest coupled with hyper-active mTOR leads to cellular senescence. While arresting cell cycle, high levels of p53 can inhibit mTOR (in some cell lines), thus causing reversible quiescence instead of senescence. Nutlin-3a-induced p53 inhibited mTOR and thus caused quiescence in WI-38 cells. In contrast, while arresting cell cycle, the DNA-damaging drug doxorubicin (DOX) did not inhibit mTOR and caused senescence. Super-induction of p53 by either nutlin-3a or high concentrations of DOX (high-DOX) prevented low-DOX-induced senescence, converting it into quiescence. This explains why in order to cause senescence, DNA damaging drugs must be used at low concentrations, which arrest cell cycle but do not induce p53 at levels sufficient to suppress mTOR. Noteworthy, very prolonged treatment with nutlin-3a also caused senescence preventable by rapamycin. In RPE cells, low concentrations of nutlin-3a caused a semi-senescent morphology. Higher concentrations of nutlin-3a inhibited mTOR and caused quiescent morphology. We conclude that low p53 levels during prolonged cell cycle arrest tend to cause senescence, whereas high levels of p53 tend to cause either quiescence or cell death.

Open Access Article

Cis-interactions between non-coding ribosomal spacers dependent on RNAP-II separate RNAP-I and RNAP-III transcription domains

María Mayan and Luis Aragón
Pages 4328 - 4337
http://dx.doi.org/10.4161/cc.9.21.13591
Abstract | PDF

Ribosome biogenesis requires transcription of structural RNAs. In budding yeast, ribosomal units contain both 35S and 5S RNA genes separated by intergenic spacer sequences (IGS) that are transcribed by RNAP-II. IGS transcripts cause instability by promoting unequal sister chromatid recombination between repeats and are thus rapidly degraded by the exosome. Whether RNAP-II within IGS regions plays any functional role is unknown. Here we demonstrate that the bulk of RNAP-II bound to IGS sites is blocked for elongation and hence remains in a poised or stalled configuration. We describe a novel role for these stalled RNAP-II complexes in the formation of cis-interactions between the IGS of rDNA. We show that this function separates 35S and 5S RNA genes into polymerase-specific chromatin loops and demonstrate that removal of stalled RNAP-II complexes causes displacement of RNAP-III from the 5S gene region and transcriptional downregulation of 5S rRNA by spreading of RNAP-I. We conclude that stalled RNAP-II plays an active role in the cis-organisation of ribosomal repeats providing domains of polymerase specificity in the nucleolar transcription environment.

Open Access Article

βTrCP-dependent degradation of CDC25B phosphatase at the metaphase-anaphase transition is a pre-requisite for correct mitotic exit

Yann Thomas, Olivier Coux and Véronique Baldin
Pages 4338 - 4350
http://dx.doi.org/10.4161/cc.9.21.13593
Abstract | PDF

The dual-specificity phosphatase CDC25B, a key regulator of CDK/Cyclin complexes, is considered as the starter of mitosis. It is an unstable protein, degraded by the proteasome, but often over-expressed in various human cancers. Based on experiments carried out in Xenopus eggs, and on video microscopy studies in mammalian cells, it has been proposed that human CDC25B degradation is dependent of the F-box protein bTrCP, but the involvement of this latter protein was not formally demonstrated yet. Here, we show that indeed, in mammalian cells, bTrCP participates to CDC25B turn-over, and is required for the complete degradation of CDC25B at the metaphase-anaphase transition. Using a stabilized mutant of CDC25B, which cannot interact anymore with bTrCP, we further show that, during late phases of mitosis, reduced degradation of CDC25B leads to an extended window of expression of the protein, which in turn induces a delay in mitosis exit and entails mitotic defects such as chromosomes missegregation. These findings show that a dysfunction in the rapid and precisely controlled degradation of CDC25B at the metaphase-anaphase transition is sufficient to cause genomic instability and suggest that, in human tissues, pathologic stabilization or untimed expression of CDC25B could contribute to tumorigenesis.

Open Access Article

Chromatin unfolding by Cdt1 regulates MCM loading via opposing functions of HBO1 and HDAC11-geminin

Philip G. Wong, Michele A. Glozak, Thinh V. Cao, Cyrus Vaziri, Edward Seto and Mark G. Alexandrow
Pages 4351 - 4363
http://dx.doi.org/10.4161/cc.9.21.13596
Abstract | PDF

The efficiency of metazoan origins of DNA replication is known to be enhanced by histone acetylation near origins. Although this correlates with increased MCM recruitment, the mechanism by which such acetylation regulates MCM loading is unknown. We show here that Cdt1 induces large scale chromatin decondensation that is required for MCM recruitment. This process occurs in G1, is suppressed by Geminin, and requires HBO1 HAT activity and histone H4 modifications. HDAC11, which binds Cdt1 and replication origins during S-phase, potently inhibits Cdt1-induced chromatin unfolding and re-replication, suppresses MCM loading, and binds Cdt1 more efficiently in the presence of Geminin. We also demonstrate that chromatin at endogenous origins is more accessible in G1 relative to S-phase. These results provide evidence that histone acetylation promotes MCM loading via enhanced chromatin accessibility. This process is regulated positively by Cdt1 and HBO1 in G1 and repressed by Geminin-HDAC11 association with Cdt1 in S-phase, and represents a novel form of replication licensing control.

Open Access Article

A novel role for Greatwall kinase in recovery from DNA damage

Aimin Peng, Tomomi M. Yamamoto, Michael L. Goldberg and James L. Maller
Pages 4364 - 4369
http://dx.doi.org/10.4161/cc.9.21.13632
Abstract | PDF

Activation of the DNA damage response (DDR) is critical for genomic integrity and tumor suppression. The occurrence of DNA damage quickly evokes the DDR through ATM/ATR-dependent signal transduction, which promotes DNA repair and activates the checkpoint to halt cell cycle progression (Halazonetis et al., 2008; Motoyama and Naka, 2004; Zhou and Elledge, 2000). The "turn off" process of the DDR upon satisfaction of DNA repair, also known as "checkpoint recovery", involves deactivation of DDR elements, but the mechanism is poorly understood. Greatwall kinase (Gwl) has been identified as a key element in the G2/M transition (Archambault et al., 2007; Jackson, 2006; Zhao et al., 2008; Yu et al., 2004; Yu et al., 2006; Zhao et al., 2006) and helps maintain M phase through inhibition of PP2A/B55δ (Burgess et al., 2010; Castilho et al., 2009; Goldberg, 2010; Lorca et al., 2010; Vigneron et al., 2009), the principal phosphatase for Cdk-phosphorylated substrates. Here we show that Gwl also promotes recovery from DNA damage and is itself directly inhibited by the DNA damage response (DDR). In Xenopus egg extracts, immunodepletion of Gwl increased the DDR to damaged DNA, whereas addition of wild type, but not kinase dead Gwl, inhibited the DDR. The removal of damaged DNA from egg extracts leads to recovery from checkpoint arrest and entry into mitosis, a process impaired by Gwl depletion and enhanced by Gwl over-expression. Moreover, activation of Cdk1 after the removal of damaged DNA is regulated by Gwl. Collectively, these results defines Gwl as a new regulator of the DDR, which plays an important role in recovery from DNA

Open Access Article

Rfc5p regulates alternate RFC complex functions in sister chromatid pairing reactions in budding yeast

Marie E. Maradeo, Anisha Garg and Robert V. Skibbens
Pages 4370 - 4378
http://dx.doi.org/10.4161/cc.9.21.13634
Abstract | PDF

Sister chromatid pairing reactions, termed cohesion establishment, occur during S-phase and appear to be regulated by Replication Factor C (RFC) complexes. For instance, RFCs that contain Ctf18p exhibit pro-establishment activities while those that contain Elg1p exhibit anti-establishment activities. It remains unknown whether Ctf18p-RFC and Elg1p-RFC functions are simply opposing or instead reveal complicated and non-parallel regulatory mechanisms. To better understand the nature of these novel pathways, we analyzed the small RFC subunit Rfc5p that is common to both Ctf18p-RFC and Elg1p-RFC. Despite this commonality, the data show that diminished Rfc5p function rescues ctf7/eco1 mutant cell phenotypes, revealing that Rfc5p promotes anti-establishment activities. This rescue is specific to establishment pathways in that rfc5-1 greatly accentuates growth defects when expressed in scc2 (deposition), mcd1/scc1 or smc3 (cohesion maintenance) mutated cells. Our results reveal for the first time a role for small RFC subunits in directing RFC complex functions - in this case towards anti-establishment pathways. We further report that Pds5p exhibits both establishment and anti-establishment functions in cohesion. This duality suggests that categorizations of establishment and anti-establishment activities require further examination.

Open Access Article

FGF inhibits the activity of the cyclin B1/CDK1 kinase to induce a transient G₂ arrest in RCS chondrocytes

Tri Tran, Victoria Kolupaeva and Claudio Basilico
Pages 4379 - 4386
http://dx.doi.org/10.4161/cc.9.21.13671
Abstract | PDF

Fibroblast growth factors (FGFs) negatively regulate long bone development by inhibiting the proliferation of chondrocytes that accumulate in the G1 phase of the cycle following FGF treatment. Here we report that FGF also causes a striking but transient delay in mitotic entry in RCS chondrocytes by inactivating the cyclin B1-associated CDK1(CDC2) kinase. As a consequence of this inactivation, cells accumulate in the G2 phase of the cycle for the first 4-6 hours of the treatment. Cyclin B1/CDK1 activity is then restored and cells reach a G1 arrest. The reduced cyclin B1/CDK1 activity was accompanied by increased CDK1 inhibitory phosphorylation, likely caused by increased activity and expression of the Myt1 kinase. FGF1 also caused dephosphorylation of the CDC25C phosphatase, that however appears due the inactivation of cyclin B1/CDK1 complex in the CDK1 feedback loop, and not the activation of specific phosphatases. The inactivation of the cyclin B1/CDK1 complex is a direct effect of FGF signaling, and not a consequence of the G2 arrest as it can be observed also in cells blocked at mitosis by Nocodazole. The Chk1 and ATM/ATR kinase are known to play essential roles in the G2 checkpoint induced by DNA damage/genotoxic stress, but inhibition of Chk1 or ATM/ATR not only did not prevent, but rather potentiated the FGF-induced G2 arrest. Additionally our results indicate that the transient G2 arrest is induced by FGF in RCS cell through mechanisms that are independent of the G1 arrest, and that the G2 block is not strictly required for the sustained G1 arrest but may provide a pausing mechanism that allows the FGF response to be fully established.

Open Access Article

The role of miR-31 and its target gene SATB2 in cancer-associated fibroblasts

Olga Aprelikova, Xiang Yu, John Palla, Bih-Rong Wei, Simone John, Ming Yi, Robert Stephens, R. Mark Simpson, John I. Risinger, Amir Jazaeri and John Niederhuber
Pages 4387 - 4398
http://dx.doi.org/10.4161/cc.9.21.13674
Abstract | PDF

It is well established that there is a dynamic relationship between the expanding tumor and the host surrounding tissue. Cancer-associated fibroblasts (CAFs), the most common cellular population found in the tumor microenvironment, supporting tumor growth and dissemination. Here, we set out to determine the factors that may be involved in dramatic alteration of gene expression pattern in CAFs, focusing on microRNA and transcriptional regulators. We established matched pairs of human CAFs isolated from endometrial cancer and normal endometrial fibroblasts.  MicroRNA and mRNA analyses identified differential expression of 11 microRNAs, with miR-31 being the most downregulated microRNA in CAFs (p=0.007). We examined several putative miR-31 target genes identified by microarray analysis and demonstrated that miR-31 directly targets the homeobox gene SATB2, which is responsible for chromatin remodeling and regulation of gene expression, and was significantly elevated in CAFs. The functional relevance of miR-31 and SATB2 were tested in in vitro models of endometrial cancer.  Overexpression of miR-31 significantly impaired the ability of CAFs to stimulate tumor cell migration and invasion, without affecting tumor cell proliferation. Genetic manipulation of SATB2 levels in normal fibroblasts or CAFs showed that, reciprocally to miR-31, SATB2 increased tumor cell migration and invasion, while knock-down of endogenous SATB2 in CAFs reversed this phenotype. Introduction of SATB2 into normal fibroblasts stimulated expression of a number of genes involved in cell invasion, migration and scattering. These findings provide new insights into tumor-stroma interaction and document that miR

Open Access Article

Identification of novel factors involved in or regulating initiation of DNA replication by a genome-wide phenotypic screen in Saccharomyces cerevisiae

Lijuan Ma, Yuanliang Zhai, Daorong Feng, Tsz-choi Chan, Yongjun Lu, Xinrong Fu, Jiafeng Wang, Yanhong Chen, Jianna Li, Ke Xu and Chun Liang
Pages 4399 - 4410
http://dx.doi.org/10.4161/cc.9.21.13679
Abstract | PDF

DNA replication in eukaryotic cells is tightly regulated to ensure faithful inheritance of the genetic material. While the replicators, replication origins and many replication-initiation proteins in Saccharomyces cerevisiae have been identified and extensively studied, the detailed mechanism that controls the initiation of DNA replication is still not well understood. It is likely that some factors involved in or regulating the initiation of DNA replication have not been discovered. To identify novel DNA replication-initiation proteins and their regulators, we developed a sensitive and comprehensive phenotypic screen by combining several established genetic strategies including plasmid loss assays with plasmids containing a single versus multiple replication origins and colony color sectoring assays. We isolated dozen of mutants in previously known initiation proteins and identified several novel factors, including Ctf1p Ctf3p, Ctf4p, Ctf18p, Adk1p and Cdc60p, whose mutants lose plasmid containing a single replication origin at high rates but lose plasmid carrying multiple replication origins at lower rates. We also show that overexpression of replication initiation proteins causes synthetic dosage lethality or growth defects in ctf1 and ctf18 mutants and that Ctf1p and Ctf18p physically interact with ORC, Cdt1p and MCM proteins. Furthermore, depletion of both Ctf1p and Ctf18p prevents S phase entry, retards S phase progression, and reduces pre-RC formation during the M-to-G1 transition. These data suggest that Ctf1p and Ctf18p together play important roles in regulating the initiation of DNA replication.




LETTERS TO THE EDITOR

Open Access Article

Rarity of AKT1 and AKT3 E17K mutations in squamous cell carcinoma of lung

Hongdo Do, Renato Salemi, Carmel Murone, Paul L. Mitchell and Alexander Dobrovic
Pages 4411 - 4412
http://dx.doi.org/10.4161/cc.9.21.13654
PDF

Open Access Article

Chromosomes kiss and tell: Long-range chromosome contacts modulate replication termination

Shikha Laloraya
Pages 4413 - 4415
http://dx.doi.org/10.4161/cc.9.21.13872
PDF