Table of Contents

Volume 8, Issue 24

  December 15, 2009

  Pages 4003 - 4181

View covers archive

 Issue Catalogue (MARC XML)

EDITORIALS: CELL CYCLE FEATURES

Open Access Article

Arginine methylation as a molecular signature of the Piwi small RNA pathway

Vasily V. Vagin, Gregory J. Hannon and Alexei A. Aravin
Pages 4003 - 4004
http://dx.doi.org/10.4161/cc.8.24.10146
PDF

Open Access Article

SADB kinases license centrosome replication

Ana C. Carrera and María Alvarado-Kristensson
Pages 4005 - 4006
http://dx.doi.org/10.4161/cc.8.24.10178
Abstract | PDF

Comment on: Alvarado-Kristensson M, et al. Nat Cell Biol 2009; 11:1081-92.

Open Access Article

Revealing human disease genes through analysis of the yeast mitochondrial proteome

Huai-Xiang Hao and Jared Rutter
Pages 4007 - 4008
http://dx.doi.org/10.4161/cc.8.24.10205
Abstract | PDF

Comment on: Hao HX, et al. Science 2009; 325:1139-42.

Open Access Article

“Micro”-management of DNA repair genes by hypoxia

Meredith E. Crosby, Peter M. Glazer and Mircea Ivan
Pages 4009 - 4010
http://dx.doi.org/10.4161/cc.8.24.10211
Abstract | PDF

Comment on: Crosby et al. Cancer Research 2009.

Open Access Article

ADARs have effects beyond RNA editing

Bret S.E. Heale, Liam P. Keegan and Mary A. O’Connell
Pages 4011 - 4012
http://dx.doi.org/10.4161/cc.8.24.10214
Abstract | PDF

Comment on: Heale BS, et al. EMBO J 2009; In press.


Open Access Article

RNA viruses hijack the mRNA decay machinery to multiply

Nicoletta Scheller and Juana Díez
Pages 4013 - 4014
http://dx.doi.org/10.4161/cc.8.24.10223
Abstract | PDF

Comment on: Scheller N, et al. Proc Natl Acad Sci USA 2009; 106:13517-22.

Open Access Article

Circadian clock and the concept of homeostasis

Olivier Bonny and Dmitri Firsov
Pages 4015 - 4016
http://dx.doi.org/10.4161/cc.8.24.10224
Abstract | PDF

Comment on: Mercier Zuber A, et al. Proc Natl Acad Sci U S A 2009; In press.

Open Access Article

Over the barrier and through the blood: To CNS delivery we go

Kevin D. Foust and Brian K. Kaspar
Pages 4017 - 4018
http://dx.doi.org/10.4161/cc.8.24.10245
Abstract | PDF

Comment on: Foust KD, et al. Nat Biotechnol 2009; 27:59-65.

Open Access Article

Instruction of lineage choice by hematopoietic cytokines

Michael A. Rieger and Timm Schroeder
Pages 4019 - 4020
http://dx.doi.org/10.4161/cc.8.24.10261
Abstract | PDF

Comment on: Rieger MA, et al. Hematopoietic cytokines can instruct lineage choice. Science 2009; 325:217-8.

Open Access Article

Lysosomal enhancement: A CLEAR answer to cellular degradative needs

Marco Sardiello and Andrea Ballabio
Pages 4021 - 4022
http://dx.doi.org/10.4161/cc.8.24.10263
Abstract | PDF

Comment on: Sardiello M, et al. A gene network regulating lysosomal biogenesis and function. Science 2009; 325:473-7.




CELL CYCLE NEWS & VIEWS

Open Access Article

Control of RNA polymerases I and III by the TOR signaling pathway

Magdalena Boguta
Pages 4023 - 4028
http://dx.doi.org/10.4161/cc.8.24.10534
Abstract | PDF

Comment on: Sch9 partially mediates TORC1 signaling to control ribosomal RNA synthesis. Wei Y, et al. Cell Cycle 2009; 8:In this issue.


Open Access Article

New tricks from an old drug: A role for quinacrine in anti-cancer therapy?

Cindy H. Chau and William D. Figg
Pages 4023 - 4028
http://dx.doi.org/10.4161/cc.8.24.10473
Abstract | PDF

Comment on: Anti-malaria drug blocks proteotoxic stress response: Anti-cancer implications. Neznanov N, et al. Cell Cycle 2009; 8:In press.


Open Access Article

DNA damage response in the absence of DNA lesions continued…

Tibor Pankotai, Anne Sophie Hoffbeck, Charlene Boumendil and Evi Soutoglou
Pages 4023 - 4028
http://dx.doi.org/10.4161/cc.8.24.10564
Abstract | PDF

Comment on: Pseudo-DNA damage response in senescent cells. Pospelova TV, et al. Cell Cycle 2009; 8:In this issue.


Open Access Article

Defining the ERAD connection: Assembly required

Richard N. Sifers
Pages 4023 - 4028
http://dx.doi.org/10.4161/cc.8.24.10494
Abstract | PDF

Comment on: Int6 and Moe1 interact with Cdc48 to regulate ERAD and proper chromosome segregation. Otero JH, et al. Cell Cycle 2010; 9:In press.


Open Access Article

Transdifferentiation of endogenous cells: Cell therapy without the cells

Ian Rogers
Pages 4023 - 4028
http://dx.doi.org/10.4161/cc.8.24.10512
Abstract | PDF

Comment on: Sex steroid-mediated reprogramming of vascular smooth muscle cells to stem cellsamd neurons: Possible utilization of sex steroid combinations for regenerative treatment without utilization of in vitro developed stem cells. Bukovsky A. Cell Cycle 2009; 8:In this issue.





EXTRA VIEWS

Open Access Article

Cell cycle regulators in the control of metabolism

Emilie Blanchet, Jean-Sébastien Annicotte and Lluis Fajas
Pages 4029 - 4031
http://dx.doi.org/10.4161/cc.8.24.10110
Abstract | PDF

We recently showed that the CDK4-pRB-E2F1 cell cycle regulators directly regulate the expression of Kir6.2, which is a key component of the K_ATP channel involved in the regulation of glucose-induced insulin secretion. There is enough evidence to indicate that the CDK4-pRB-E2F1 regulatory pathway is involved in general glucose homeostasis, and metabolism. In this article we discuss which are the metabolic implications of these findings.

Open Access Article

Regulation of protein stability by GSK3 mediated phosphorylation

Chong Xu, Nam-Gyun Kim and Barry M. Gumbiner
Pages 4032 - 4039
http://dx.doi.org/10.4161/cc.8.24.10111
Abstract | PDF

Glycogen synthase kinase-3 (GSK3) plays important roles in numerous signaling pathways that regulate a variety of cellular processes including cell proliferation, differentiation, apoptosis and embryonic development. In the canonical Wnt signaling pathway, GSK3 phosphorylation mediates proteasomal targeting and degradation of β-catenin via the destruction complex. We recently reported a biochemical screen that discovered multiple additional protein substrates whose stability is regulated by Wnt signaling and/or GSK3 and these have important implications for Wnt/GSK3 regulation of different cellular processes.1 In this article, we also present a bio-informatics based screen for proteins whose stability may be controlled by GSK3 and β-Trcp, the SCF E3 ubiquitin ligase that is responsible for β-catenin degradation in the Wnt signaling pathway. Furthermore, we review various GSK3 regulated proteolysis substrates described in the literature. We propose that GSK3 phosphorylation dependent proteolysis is a widespread mechanism that the cell employs to regulate a variety of cell processes in response to signals.

Open Access Article

Antiangiogenic agents and HIF-1 inhibitors meet at the crossroads

Annamaria Rapisarda, Robert H. Shoemaker and Giovanni Melillo
Pages 4040 - 4043
http://dx.doi.org/10.4161/cc.8.24.10145
Abstract | PDF

Novel molecularly targeted therapies aim at exploiting oncogenic and non-oncogenic alterations that epitomize potential vulnerable aspects of tumorigenesis, with the hope to ultimately target cancer cells and spare normal tissues.  Hypoxia, a decrease in tissue oxygen levels, is a feature of the tumor micro-environment that has attracted considerable interest for its potential contribution to increasing the tumorigenicity of cancer cells, by selecting more aggressive and metastatic clones and by activating pathways that contribute to cancer cells survival, all of which may have important therapeutic implications.  In this article, we discuss how two therapeutic strategies, which have been developed over the last few years to target aspects dependent on or associated with intratumor hypoxia, may provide the rationale for a novel combination strategy aimed at blocking compensatory circuits that maintain cancer cells survival and propagate the cancer phenotype.  We hypothesized that concurrent inhibition of HIF-1 and VEGF, which are mechanistically linked to intratumor hypoxia, represents a logical therapeutic combination that may find applications in a number of solid tumors, irrespective of their underlying genetic alterations.  Indeed, intrinsic limitations of HIF-1 inhibitors and mechanisms of acquired resistance to anti-VEGF therapies may counterbalance each other in combination approaches that block vicious compensatory pathways exploited by cancer cells to overcome environmental stresses.

 

Open Access Article

TET proteins in malignant hematopoiesis

Saskia M.C. Langemeijer, Mariam G. Aslanyan and Joop H. Jansen
Pages 4044 - 4048
http://dx.doi.org/10.4161/cc.8.24.10239
Abstract | PDF

Differentiation of hematopoietic stem cells into mature blood cells is a multistage process. During each stage, both extrinsic and intrinsic factors coordinate the expression of the genes required for the cell to adopt a particular fate. Disturbance of this accurately balanced system can lead to a variety of hematopoietic disorders. In hematopoietic malignancies, the activity of genes involved in the key processes of proliferation, apoptosis and differentiation are affected, resulting in clonal expansion of aberrant cells. Clonal disorders of erythroid, myeloid and megakaryocytic cells are combined in the group of the myeloid malignancies. Diagnosis of these malignancies is based on morphological, immunophenotypic and, with increasing importance, genetic parameters. Effective and specific treatment strategies remain subject for further development. Insight into the genes and pathways implicated in the pathogenesis of myeloid malignancies will contribute to the design of targeted therapies.

Open Access Article

Normal and oncogenic roles for microRNAs in the developing brain

Africa Fernandez-L, Paul A. Northcott, Michael D. Taylor and Anna M. Kenney
Pages 4049 - 4054
http://dx.doi.org/10.4161/cc.8.24.10243
Abstract | PDF

MicroRNAS (miRNAs) are small endogenous non-coding RNAs that play important roles in many different biological processes including proliferation, differentiation and apoptosis through silencing of target genes. Emerging evidence indicates that miRNAs are key players in mammalian development that, when altered, contribute to tumorigenesis. However, only a few studies to date have focused on the role of miRNAs in medulloblastoma, the most common malignant pediatric brain tumor. These tumors arise in the cerebellum and may attribute their origins to deregulated proliferation of neural progenitor cells during development. Understanding the interplay between normal brain development and medulloblastoma pathogenesis is necessary in order for more efficient, less toxic targeted therapies to be developed and implemented. MiRNA expression profiling of both mouse and human medulloblastomas has led to the identification of signatures correlating with the molecular subgroups of medulloblastoma, tumor diagnosis and response to treatment, as well as novel targets of potential clinical relevance. This review summarizes the recent miRNA literature in both medulloblastoma and normal brain development.




PERSPECTIVE

Open Access Article

TOR-driven aging: Speeding car without brakes

Mikhail V. Blagosklonny
Pages 4055 - 4059
http://dx.doi.org/10.4161/cc.8.24.10310
Abstract | PDF

This article discusses that the traditional analogy of an aging organism with a rusting (albeit self-repairing) car is misleading. The true analogy is a speeding car that enters a low-speed zone and damages itself because it does not and cannot slow down. For such a car without brakes (and actually without a driver), aging from rusting never occurs. Using simple analogies (although turning gerontology upside down), this article discusses the origin of aging, how overactivation of the mTOR (Target of Rapamycin) pathway causes aging, why aging causes damage (organ damage) not damage causes aging, the link between aging and age-related diseases, slow aging versus aging tolerance and suppression of aging with rapamycin.




REVIEWS

Open Access Article

Oncogenic ILK, tumor suppression and all that JNK

Adam David Durbin, Gregory Edward Hannigan and David Malkin
Pages 4060 - 4066
http://dx.doi.org/10.4161/cc.8.24.10093
Abstract | PDF

In neoplastic cells, proteins exert either pro or anti-tumorigenic functions. However, some proteins exhibit both properties, commonly dependent on specific aberrations occurring in a tumor-specific context. Recently, we demonstrated that the integrin-linked kinase (ILK), generally characterized as an oncogenic protein kinase, functions as a tumor suppressor protein in vitro and in vivo in the aggressive pediatric tumor, rhabdomyosarcoma (RMS). Other studies have similarly demonstrated both growth and tumor suppressive functions for ILK in normal and transformed tissues. The mechanism of ILK tumor suppression in RMS relies on expression levels of another kinase, the c-jun amino terminal kinase-1 (JNK1). These findings support a model in which ILK tumor suppression is mediated in part by elevated JNK1 expression, and indicate both a rationale for stratification of patients to receive anti-ILK therapies, and a need to better understand the context in which ILK displays its seemingly contradictory functions. This review discusses the complex roles of ILK in tumorigenesis, and offers arguments to harness ILK and JNK signaling as novel targets for anti-cancer therapy.

Open Access Article

DDB2 (Damaged-DNA binding protein 2) in nucleotide excision repair and DNA damage response

Tanya Stoyanova, Nilotpal Roy, Dragana Kopanja, Pradip Raychaudhuri and Srilata Bagchi
Pages 4067 - 4071
http://dx.doi.org/10.4161/cc.8.24.10109
Abstract | PDF

DDB2 was identified as a protein involved in the Nucleotide Excision Repair (NER), a major DNA repair mechanism that repairs UV damage to prevent accumulation of mutations and tumorigenesis. However, recent studies indicated additional functions of DDB2 in the DNA damage response pathway. Herein, we discuss the proposed mechanisms by which DDB2 activates NER and programmed cell death upon DNA damage through its E3 ligase activity.

Open Access Article

Peroxiredoxin 1 and its role in cell signaling

Carola A. Neumann, Juxiang Cao and Yefim Manevich
Pages 4072 - 4078
http://dx.doi.org/10.4161/cc.8.24.10242
Abstract | PDF

Peroxiredoxins (Prdxs) are a family of small (22-27kDa) non-seleno peroxidases currently known to possess six mammalian isoforms. Although their individual roles in cellular redox regulation and antioxidant protection are quite distinct, they all catalyze peroxide reduction of H2O2, organic hydroperoxides and peroxynitrite. They are found to be expressed ubiquitously and in high levels, suggesting that they are both an ancient and important enzyme family. Prdxs can be divided into three major subclasses: typical 2-cysteine (2-Cys) Prdxs (Prdx1-4), atypical 2-Cys Prdx (Prdx 5) and 1-Cys Prdx (Prdx 6). Recent evidence suggests that 2-Cys peroxiredoxins are more than “just simple peroxidases”. This hypothesis has been discussed elegantly in recent review articles, considering “over”-oxidation of the protonated thiolate peroxidatic cysteine and post-translational modification of Prdxs as processes initiating a mechanistic switch from peroxidase to chaperon function. The process of over-oxidation of the peroxidatic cysteine (CP) occurs during catalysis in the presence of thioredoxin (Trx), thus rendering the sulfenic moiety to sulfinic acid , which can be reduced by sulfiredoxin (Srx). However, further oxidation to sulfonic acid is believed to promote Prdx degradation or, as recently shown, the formation of oligomeric peroxidase-inactive chaperones10 with questionable H2O2-scavenging capacity. In the light of this and given that Prdx1 has recently been shown by us and by others to interact directly with signaling molecules, we will explore the possibility that H2O2 regulates signaling in the cell in a temporal and spatial fashion via oxidizing Prdx1. Therefore, this review will focus on H2O2 modulating cell signaling via Prdxs by discussing: a) the activity of Prdxs towards H2O2; b) sub cellular localization and availability of other peroxidases, such as catalase or glutathione peroxidases; c) the availability of Prdxs reducing systems such as thioredoxin and sulfiredoxin and lastly, d) Prdx1 interacting signaling molecules.




REPORTS

Open Access Article

Sex steroid-mediated reprogramming of vascular smooth muscle cells to stem cells and neurons: Possible utilization of sex steroid combinations for regenerative treatment without utilization of in vitro developed stem cells

Antonin Bukovsky
Pages 4079 - 4084
http://dx.doi.org/10.4161/cc.8.24.10147
Abstract | PDF

Previous work from our laboratory demonstrated that sex steroid combinations, but not individual sex steroids alone, cause transdifferentiation of ovarian epithelial cells - ovarian surface epithelium (OSE) and follicular granulosa cells - into neural stem cells (NSC) and differentiating neurons. In the present study we have chosen primary culture of human vascular smooth muscle cells (SMC), a non-epithelial mesenchymal cells in order to test them as a control cell type regarding their morphology and expression of NSC and neuronal markers. Utilization of estradiol (E2), progesterone (PG) or testosterone (TS) alone did not induce the emergence of neurons from the vascular SMC. However, the treatment with sex steroid combinations (PG+TS or E2+PG+TS) caused transdifferentiation into neural/neuronal type cells. By immunohistochemistry, these cells exhibited strong expression of stem cell markers and neural/neuronal glycoconjugates SSEA-1, SSEA-4, Thy-1, NeuN and NCAM. In the Neurobasal/B27 medium both, the OSE and vascular SMC also transdifferentiated into neuronal cells. Western blot analysis has shown significant increase of NeuN 48-kDa species after E2+PG or PG+TS treatment. Secretion of E2 increased significantly in vascular SMC cultures pretreated with TS, PG or TS+PG. Unlike OSE cells, the vascular SMC accompany as pericytes all vessels, including CNS microvasculature. We also observed that sex steroid combinations could produce SMC stem type cells which differentiated within a few days back to mature vascular SMC. This is of potential interest for the vascular regenerative medicine. Altogether, our observations suggest that sex steroid combinations could induce in vivo improvement of neurodegenerative, traumatic and ischemic neurological disorders and vascular diseases via their effect on resident pluripotent vascular SMC, i.e. without a need of in vitro developed stem cells.

Open Access Article

Sch9 partially mediates TORC1 signaling to control ribosomal RNA synthesis

Yuehua Wei and X.F. Steven Zheng
Pages 4085 - 4090
http://dx.doi.org/10.4161/cc.8.24.10170
Abstract | PDF

TORC1 is a central regulator of ribosomal RNA synthesis. Here we report that Sch9 partially mediates TORC1 signaling to regulate Pol I– and Pol III–dependent transcription. Mechanistically, Sch9 is involved in hyperphosphorylation and cytoplasmic localization of Maf1, and for optimal synthesis of rRNAs and tRNAs. Interestingly, sch9Δ does not affect Maf1 basal phosphorylation and nucleolar localization. In addition, TORC1 is still capable of regulating rRNAs and tRNAs in the absence of Sch9. Moreover, the hyperactive Sch9(2D3E) mutant does not confer significant rapamycin resistance in cell growth. Together, these observations indicate that Sch9 is involved in optimal regulation of ribosome biogenesis by TORC1, but is dispensable for the essential aspects of ribosome biogenesis and cell growth, suggesting that TORC1 controls cell growth through Sch9–dependent and independent mechanisms.

Open Access Article

C. elegans mitotic cyclins have distinct as well as overlapping functions in chromosome segregation

Monique van der Voet, Monique Lorson, Dayalan G. Srinivasan, Karen L. Bennett and Sander van den Heuvel
Pages 4091 - 4102
http://dx.doi.org/10.4161/cc.8.24.10171
Abstract | PDF

Mitotic cyclins in association with the Cdk1 protein kinase regulate progression through mitosis in all eukaryotes. Here, we address to what extent mitotic cyclins in the nematode Caenorhabditis elegans provide overlapping functions or distinct biological activities. C. elegans expresses a single A-type cyclin (CYA-1), three typical B-type cyclins (CYB-1, CYB-2.1 and CYB-2.2), and one B3-subfamily member (CYB-3). While we observed clear redundancies between the cyb genes, cyb-1 and cyb-3 also contribute specific essential functions in meiosis and mitosis. CYB-1 and CYB-3 show similar temporal and spatial expression, both cyclins localize prominently to the nucleus, and both associate with CDK-1 and display histone H1 kinase activity in vitro. We demonstrate that inhibition of cyb-1 by RNAi interferes with chromosome congression and causes aneuploidy. In contrast, cyb-3(RNAi) embryos fail to initiate sister chromatid separation. Inhibition of both cyclins simultaneously results in a much earlier and more dramatic arrest. However, only the combination of cyb-1, cyb-3 and cyb-2.1/cyb-2.2 RNAi fully resembles cdk-1 inhibition. This combination of redundant and specific phenotypes supports that in vivo phosphorylation of certain Cdk targets can be achieved by multiple Cdk1/cyclin complexes, while phosphorylation of other targets requires a unique Cdk1/cyclin combination.

Open Access Article

The Polyhomeotic protein induces hyperplastic tissue overgrowth through the activation of the JAK/STAT pathway

Inma González, Rocío Simón and Ana Busturia
Pages 4103 - 4111
http://dx.doi.org/10.4161/cc.8.24.10212
Abstract | PDF

Epigenetic mechanisms controlling cellular proliferation are essential to animal development. Moreover, altered levels of expression of the epigenetic regulator proteins are associated with the development and progression of human diseases like cancer. We have studied the effects of high levels of Polyhomeotic (PH) protein, a member of the Polycomb Group (PcG), during the proliferation of the imaginal discs in Drosophila. Over expression of PH protein causes induction of proliferation, accompanied with induction of JNK-dependent apoptosis. As a result, massive hyperplastic overgrowth is produced and the corresponding differentiated tissues show phenotypes related with mis-regulation of homeotic gene expression. We have found that high levels of PH up-regulate the JAK/STAT pathway through the de-repression of Unpaired (UPD), the extracellular ligand of the Drosophila JAK/STAT signalling cascade. Moreover, inactivation of the JAK/STAT pathway in the presence of a large amount of PH protein greatly reduces the tissue overgrowth, demonstrating a functional role of JAK/STAT in PH-induced hyperplasia. Finally, we have observed that decapentaplegic and d-myc, two growth genes and putative targets of the JAK/STAT pathway, are also over expressed in the PH-induced tumors. We propose that during normal development, the PcG proteins act to maintain inactive the JAK/STAT pathway. Upon cellular stress, changes in the levels of PcG proteins expression are induced and JAK/STAT is activated leading to tumor development. Our results show a functional relationship between the PcG gene expression and the JAK/STAT pathway, both of which are found to be perturbed in tumorigenesis.

Open Access Article

Pseudo-DNA damage response in senescent cells

Tatyana V. Pospelova, Zoya N. Demidenko, Elena I. Bukreeva, Valery A. Pospelov, Andrei V. Gudkov and Mikhail V. Blagosklonny
Pages 4112 - 4118
http://dx.doi.org/10.4161/cc.8.24.10215
Abstract | PDF

Cellular senescence is currently viewed as a response to DNA damage. In this report, we showed that non-damaging agents such as sodium butyrate-induced p21 and ectopic expression of either p21 or p16 cause cellular senescence without detectable DNA breaks. Nevertheless, senescent cells displayed components of DNA damage response (DDR) such as γH2AX foci and uniform nuclear staining for p-ATM. Importantly, there was no accumulation of 53BP1 in γH2AX foci of senescent cells. Consistently, comet assay failed to detect DNA damage. Rapamycin, an inhibitor of mTOR, which was shown to suppress cellular senescence, decreased γH2AX foci formation. Thus, cellular senescence leads to activation of atypical DDR without detectable DNA damage. Pseudo-DDR may be a marker of general over-activation of senescent cells.

Open Access Article

Interplay between BMP4 and IL-7 in human intrathymic precursor cells

Alberto Varas, Rosa Sacedón, Laura Hidalgo, Víctor G. Martínez, Jaris Valencia, Teresa Cejalvo, Agustín Zapata, Carmen Hernández-López and Angeles Vicente
Pages 4119 - 4126
http://dx.doi.org/10.4161/cc.8.24.10149
Abstract | PDF

Bone morphogenetic proteins (BMPs) play a pivotal role during vertebrate embryogenesis and organogenesis, and have also been described to function in regulating cell fate and determination in self-renewing tissues in adults. Recent results have demonstrated that the different components of the BMP2/4 signaling pathway are expressed in the human thymus. In this study, we provide evidence that BMP4 and IL-7 interplay is important in the maintenance of the human thymic progenitor population. Intrathymic CD34⁺ cells express BMP receptors (BMPRIA, BMPRIB, ActRIA, BMPRII), signal transduction molecules (Smad1, 5, 8 and 4), and produce BMP4. Neutralization of endogenous BMP4 by treatment with the antagonist Noggin reduces thymic precursor cell survival, and the addition of exogenous BMP4 decreases their proliferation. The treatment of chimeric human-mouse fetal thymus organ cultures with BMP4 inhibits cell expansion, arrests thymocyte differentiation, and leads to the accumulation of human CD34⁺ precursor cells. This effect is mainly attributed to the ability of BMP4 to counteract the IL-7-induced proliferation and differentiation of CD34⁺ cells. BMP4 down-regulates in the precursor cell population the expression of CD127 and inhibits the IL-7-dependent STAT5 phosphorylation. In addition, BMP signaling is promoted by IL-7. Our results also demonstrate that in thymic progenitors BMPs act downstream of Sonic Hedgehog, previously described to function as a maintenance factor for human intrathymic CD34⁺ precursor cells.

Open Access Article

A perspective of promoter architecture from the CCAAT box

Diletta Dolfini, Federico Zambelli, Giulio Pavesi and Roberto Mantovani
Pages 4127 - 4137
http://dx.doi.org/10.4161/cc.8.24.10240
Abstract | PDF

The CCAAT box is an important promoter element regulated by NF-Y, a conserved trimer with histone-like features. We describe a new Position Specific Frequency Matrix (PSFM): we derived from 328 NF-Y promoters from the literature the p-CCAAT, and refined it by analysing  ChIP on chip data (g-CCAAT). Interestingly, g-CCAAT- has distinct features, such as variations within the CCAAT pentanucleotide. We validated the NF-Y-dependency of several promoters with functional assays. We examined the presence of these PSFMs in all human promoters and detail a number of parameters of CCAAT boxes: position, orientation, distance from TSS, presence of TATA, CpG islands and enrichments of nearby TF elements. The CCAAT genes fall into different GO categories, with cell-cycle and chromatin/transcription specifically enriched. Additional findings surfaced: (i) the CCAAT-TATA combination, often mentioned in textbooks, is an exception, rather than the rule. CCAAT promoters are less precise in terms of TSS. (ii) There is a good correlation between CCAAT and CpG islands; (iii) selective TFs sites are enriched in CCAAT promoters, with precise stereoalignements of some of them. In conclusion, the new features of the CCAAT box and the link with the neighbouring elements will help in the functional classification of promoters.

Open Access Article

A serine cluster mediates BMAL1-dependent CLOCK phosphorylation and degradation

Mary L. Spengler, Karen K. Kuropatwinski, Molly Schumer and Marina Antoch
Pages 4138 - 4146
http://dx.doi.org/10.4161/cc.8.24.10273
Abstract | PDF

The circadian clock regulates biological processes from gene expression to organism behavior in a precise, sustained rhythm that is generated at the unicellular level by coordinated function of interlocked transcriptional feedback loops and post-translational modifications of core clock proteins. CLOCK phosphorylation regulates transcriptional activity, cellular localization and stability; however little is known about the specific residues and enzymes involved. We have identified a conserved cluster of serines that include, Ser431, which is a prerequisite phosphorylation site for the generation of BMAL dependent phospho-primed CLOCK and for the potential GSK-3 phosphorylation at Ser427. Mutational analysis and protein stability assays indicate that this serine cluster functions as a phospho-degron. Through the use of GSK-3 activators/inhibitors and kinase assays, we demonstrate that GSK-3β regulates the degron-site by increasing CLOCK phosphorylation/degradation, which correlates with an increase in the expression of CLOCK responsive promoters. Stabilization of phospho-deficient CLOCK delays the phase of oscillation in synchronized fibroblasts. This investigation begins the characterization of a complex phospho-regulatory site that controls the degradation of CLOCK, a core transcription factor that is essential for circadian behavior.

Open Access Article

C. elegans sym-1 is a downstream target of the Hunchback-like-1 developmental timing transcription factor

Ryusuke Niwa, Kazumasa Hada, Kouichi Moliyama, Ryosuke L. Ohniwa, Yi-Meng Tan, Katherine Olsson Carter, Woo Chi, Valerie Reinke and Frank J. Slack
Pages 4147 - 4154
http://dx.doi.org/10.4161/cc.8.24.10292
Abstract | PDF

In the nematode Caenorhabditis elegans, the let-7 microRNA (miRNA) and its family members control the timing of key developmental events in part by directly regulating expression of hunchback-like-1 (hbl-1). C. elegans hbl-1 mutants display multiple developmental timing deficiencies, including cell cycle defects during larval development. While hbl-1 is predicted to encode a transcriptional regulator, downstream targets of HBL-1 have not been fully elucidated. Here we report using microarray analysis to uncover genes downstream of HBL-1. We established a transgenic strain that over-expresses hbl-1 under the control of the heat shock promoter. Heat shock-induced hbl-1 over-expression led to retarded hypodermal structures at the adult stage, opposite to the effect seen in loss of function (lf) hbl-1 mutants. The microarray screen identified numerous potential genes that are up-regulated or down-regulated by HBL-1, including sym-1, which encodes a leucine-rich repeat protein with a signal sequence. We found an increase in sym-1 transcription in the heat shock-induced hbl-1 over-expression strain, while loss of hbl-1 function caused a decrease in sym-1 expression levels. Furthermore, we found that sym-1(lf) modified the hypodermal abnormalities in hbl-1 mutants. Given that SYM-1 is a protein secreted from hypodermal cells to the surrounding cuticle, we propose that the adult-specific cuticular structures may be under the temporal control of HBL-1 through regulation of sym-1 transcription.

Open Access Article

Small molecule screening reveals a transcription-independent pro-survival function of androgen receptor in castration-resistant prostate cancer

Natalia V. Narizhneva, Natalia D. Tararova, Petro Ryabokon, Inna Shyshynova, Anatoly Prokvolit, Pavel G. Komarov, Andrei A. Purmal, Andrei V. Gudkov and Katerina V. Gurova
Pages 4155 - 4167
http://dx.doi.org/10.4161/cc.8.24.10316
Abstract | PDF

In prostate cancer (PCa) patients, initial responsiveness to androgen deprivation therapy is frequently followed by relapse due to development of treatment-resistant androgen-independent PCa. This is typically associated with acquisition of mutations in AR that allow activity as a transcription factor in the absence of  ligand, indicating that androgen-independent PCa remains dependent on AR function. Our strategy to effectively target AR in androgen-independent PCa involved using a cell-based readout to isolate small molecules that inhibit AR transactivation function through mechanisms other than modulation of ligand binding. A number of the identified inhibitors were toxic to AR-expressing PCa cells regardless of their androgen dependence.  Among these, some only suppressed PCa cell growth (ARTIS), while others induced cell death (ARTIK).  ARTIK, but not ARTIS, compounds caused disappearance of AR protein from treated cells. siRNA against AR behaved like ARTIK compounds, while a dominant negative AR mutant that prevents AR-mediated transactivation but does not eliminate the protein showed only a growth suppressive effect. These observations reveal a transcription-independent function of AR that is essential for PCa cell viability and, therefore, is an ideal target for anti-PCa treatment. Indeed, several of the identified AR inhibitors demonstrated in vivo efficacy in mouse models of PCa and are candidates for pharmacologic optimization.

Open Access Article

The p53 target Plk2 interacts with TSC proteins impacting mTOR signaling, tumor growth, and chemosensitivity under hypoxic conditions

Elizabeth M. Matthew, Lori S. Hart, Aristotelis Astrinidis, Arunasalam Navaraj, Nathan G. Dolloff, David T. Dicker, Elizabeth P. Henske and Wafik S. El-Deiry
Pages 4168 - 4175
http://dx.doi.org/10.4161/cc.8.24.10800
Abstract | PDF

Tuberous sclerosis complex 1 (TSC1) inhibits mammalian target of rapamycin (mTOR), a central promotor of cell growth and proliferation.  The protein product of the TSC1 gene, hamartin (referred to as TSC1) is known to interact with Polo-like kinase 1 (Plk1) in a cell cycle regulated, phosphorylation-dependent manner. We hypothesized that the p53 target gene, Plk2, is a tumor suppressor, mediating its tumor suppressor function through interactions with TSC1 that facilitate TSC1/2 restraint of mTOR under hypoxic stress.  We found that human lung tumor cells deficient in Plk2 grew larger than control tumors, and that Plk2 interacts with endogenous TSC1 protein.  Additionally, C-terminal Plk2-GST fusion protein bound both TSC1 and TSC2 proteins.   TSC1 levels were elevated in response to Adriamycin and cells transiently over-expressing Plk2 demonstrated decreased phosphorylation of the downstream target of mTOR, ribosomal protein p70S6 kinase during hypoxia.  Plk2 levels were inversely correlated with cytoplasmic p70S6K phosphorylation. Plk2 levels did not increase in response to DNA damage (Adriamycin, CPT-11) when HCT 116 and H460 cells were exposed to hypoxia. TSC1-deficient mouse embryonic fibroblasts with TSC1 added back demonstrated decreased S6K phosphorylation, which was further decreased when Plk2 was transiently over-expressed.  Interestingly, under normoxia, Plk2 deficient tumor cells demonstrated increased apoptosis in response to various chemotherapeutic agents including CPT-11 but increased resistance to apoptotic death after CPT-11 treatment under hypoxia, and tumor xenografts comprised of these Plk2-deficient cells were resistant to CPT-11.  Our results point to a novel Plk2-TSC1 interaction with effects on mTOR signaling during hypoxia, and tumor growth that may enable targeting Plk2 signaling in cancer therapy.




LETTERS TO THE EDITOR

Open Access Article

Cell type-specific regulation of a replication origin residing within an AT-rich/LINE-1-rich isochore

Gennady Kholodii, Olga Dantsevich, Gleb Korobov and Vyacheslav Tarantul
Pages 4176 - 4178
http://dx.doi.org/10.4161/cc.8.24.10151
PDF

Open Access Article

Spontaneous bone loss in RIP-iNOS transgenic mouse: A mouse model for diabetes-mediated osteopenia/osteoporosis

Qing-Sheng Mi, Sheng-Li Yan, Zai-Zhao Wang, Ke-Hong Ding, Changgui Li, Luan Wang, Li Zhou, Yasuhiko Yamamoto, Hiroshi Yamamoto, Hiroshi Okamoto and Carlos Isales
Pages 4179 - 4181
http://dx.doi.org/10.4161/cc.8.24.10152
PDF