Table of Contents

Volume 5, Issue 2

  January 16, 2006

  Pages 125 - 217

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 Issue Catalogue (MARC XML)

EXTRA VIEWS

Open Access Article

Turning the Replication Checkpoint On and Off


Pages 125 - 128
http://dx.doi.org/10.4161/cc.5.2.2308
Abstract | PDF

The replication checkpoint monitors the progress of DNA replication forks during S phase, and delays the firing of later replication origins when active replication forks are stalled due to collisions with damaged or abnormally structured DNA. Key components of the replication checkpoint pathway are the apical protein kinase, ATR, and its downstream target kinase, Chk1. Defects in either ATR or Chk1 function result in loss of DNA replication fidelity and cell viability, even in the absence of extrinsic genotoxic stress. Moreover, several clinically important antitumor agents, such as the camptothecins (CPTs), exert their antitumor effects by interfering with DNA replication, and hence the therapeutic response to these drugs is intimately related to signaling through the replication checkpoint. A recent report from this laboratory adds a new facet to the regulatory mechanisms that control the function and duration of checkpoint signaling through the ATR-Chk1 pathway. The results indicate that replication stress induced by a variety of agents, including CPT and deep hypoxia, triggers the ubiquitin-dependent degradation of the checkpoint kinase Chk1 in both normal and transformed human cells. This review provides an overview of the study’s major findings, together with their implications for both replication checkpoint function and tumor responsiveness to CPT and related anticancer drugs.

Open Access Article

Less REST, More Vascular Disease? Regulation of Cell Cycle and Migration of Vascular Smooth Muscle Cells

Alex Cheong, Ian C. Wood and David J. Beech
Pages 129 - 131
http://dx.doi.org/10.4161/cc.5.2.2310
Abstract | PDF

Neointimal hyperplasia and atherosclerosis are cardiovascular abnormalities resulting in heart attacks and strokes – major causes of death and disability in societies with a western-style diet. Both are contributed to significantly by a phase of enhanced cell cycle activity and migration of vascular smooth muscle cells. Here we describe how this activity is associated with a switch in the types of ion channel controlling trans-membrane ion transport. In particular we stress the de novo expression of the KCa3.1 potassium channel when the cells proliferate, but we also review evidence of changes in other ion channels. The molecular mechanisms governing such switches in ion transport have been unknown until we recently showed down-regulation of the repressive REST transcription factor is an important step. Here we explain and expand the hypothesis that REST-regulation of ion transport has a previously unrecognised role in cell proliferation.

Open Access Article

CUTL1: A Key Mediator of TGFβ-Induced Tumor Invasion

Patrick Michl and Julian Downward
Pages 132 - 134
http://dx.doi.org/10.4161/cc.5.2.2311
Abstract | PDF

The TGFβ pathway plays a dual role in human carcinogenesis. On one hand, TGFβ is well known for its ability to inhibit epithelial cell proliferation and promote apoptosis. However, many advanced cancers acquire resistance to the growth-inhibitory effects of TGFβ and respond to it instead with promotion of proliferation, invasion and tumor progression. The homeobox transcription factor CUTL1, also known as CCAAT displacement protein, CDP or Cux-1, is involved in the control of normal embryonic development and differentiation. Recently, we found that CUTL1 is a transcriptional target of TGFβ and is an important mediator of the TGFβ-induced cell migration and invasion. In addition, CUTL1 is highly expressed in various epithelial cancers and seems to negatively correlate with tumor differentiation and patient survival. Therefore we postulate that CUTL1 might be a key mediator of the tumor-promoting effects of TGFβ in advanced cancers.

Open Access Article

Brain Tumors Provide New Clues to the Source of Cancer Stem Cells: Does Oncology Recapitulate Ontogeny?

Richard J. Gilbertson
Pages 135 - 137
http://dx.doi.org/10.4161/cc.5.2.2319
Abstract | PDF

Recent studies of leukemia and solid tumors have provided compelling evidence for the existence of cancer stem cells, but the origin of these cells remains a matter of considerable debate. By comparing the gene expression profiles of ependymomas with those of cells in the normal developing nervous system, we were able to pinpoint radial glia as candidate stem cells of this brain tumor. These data suggest strongly that ependymomas arise directly from transformed radial glia and they provide a novel method that could be used to map the cell of origin of other types of cancer.

Open Access Article

Defining Cell Lineages in the Prostate Epithelium

Sabina Signoretti and Massimo Loda
Pages 138 - 141
http://dx.doi.org/10.4161/cc.5.2.2340
Abstract | PDF

Understanding the stages of cell differentiation in the normal prostate epithelium is essential for the identification of the cell type(s) involved in prostatic carcinogenesis. Prostate glands are composed of three types of epithelial cells (i.e. basal, secretory and neuroendocrine) but the hierarchical relations among these cell types have been long controversial. We have recently developed a novel system to define prostate epithelial cell lineages in vivo. We find that, during normal prostate organogenesis, terminally differentiated secretory cells derive from p63-positive basal cells, which thus represent/include prostate stem cells. Future studies will determine if p63-positive basal cells retain stem cells capabilities in the adult prostate epithelium.

Open Access Article

Mammalian Gene Expression Program Resiliency: The Roles of Multiple Coactivator Mechanisms in Hypoxia–Responsive Transcription

Lawryn H. Kasper and Paul K. Brindle
Pages 142 - 146
http://dx.doi.org/10.4161/cc.5.2.2353
Abstract | PDF

Abstract. CBP and its paralog p300 (CBP/p300 collectively) are transcriptional coactivators that are among the most interconnected proteins in the mammalian proteinprotein “interactome”, with over 315 described interaction partners. CBP/p300 are protein/histone acetyltransferases, but most of the protein-binding domains of CBP/p300 are unique to these two coactivators, indicating that CBP/p300 should be highly limiting. The CH1 domain of CBP/p300 was considered essential for most, if not all, hypoxia-inducible transcription by binding to hypoxia-inducible-factor-1? (HIF-1?). Mutating CH1 had little effect, however, on the hypoxia-induced transcription of the HIFtarget genes Higd1a, Egln1 (prolyl-hydroxylase), Bnip3 (Bcl2-interacting-protein-3), and Pfkl (phosphofructokinase). In contrast, HIF-targets Pgf (placental growth factor) and Egln3 were strongly affected by the CH1 mutation, while Stc1 (stanniocalcin-1) and Slc2a1 (glucose-transporter-1) were moderately affected. HIF targets were also dependent on coactivation mechanisms that are sensitive to trichostatin A (TSAS). Paradoxically, TSA inhibits histone deacetylases (HDACs) that are usually associated with transcriptional repression, implying that HDACs can also function as coactivators. Thus, activator-specific transcription in mammals requires seemingly unrelated coactivator mechanisms, and individual target genes vary in their requirements for each mechanism. Gene expression program resiliency is therefore coupled with gene specific regulation by avoiding uniform reliance on a “keystone” coactivator interaction.

Open Access Article

Translational Regulation of TRAIL Sensitivity

Amith Panner, Andrew T. Parsa and Russell O. Pieper
Pages 147 - 150
http://dx.doi.org/10.4161/cc.5.2.2359
Abstract | PDF

TNF-related apoptosis-inducing ligand (TRAIL) is a peptide that induces apoptosis to varying degrees in tumor cells, but not in normal cells. While TRAIL sensitivity in tumors has been linked to c-myc- and MEK/Erk-induced enhancement of caspase activation, our recent study identified a third input controlling TRAIL sensitivity, namely the Akt-mTOR pathway. We showed that instead of enhancing TRAIL sensitivity, Akt expression, acting through mTOR and the mTOR targets S6 kinase and eIF-4E, selectively enhances translation of the anti-apoptotic protein FLIPs and confers TRAIL resistance. In this perspective article we will discuss the linkage of the AktmTOR pathway to other regulators of TRAIL sensitivity, its importance in controlling a broader range of apoptotic events, its utility in predicting TRAIL responsiveness, and its potential manipulation for therapeutic benefit.

Open Access Article

Geminin Regulates Multiple Steps of the Chromosome Inheritance Cycle

Kiku-e K. Tachibana and Erich A. Nigg
Pages 151 - 154
http://dx.doi.org/10.4161/cc.5.2.2363
Abstract | PDF

Centrosome duplication like DNA replication must occur exactly once per cell cycle to maintain genomic stability. Cell fusion and microinjection assays gave rise to the concept of “licensing” and uncovered nuclear-intrinsic blocks to over-replication and recently also centrosome-intrinsic blocks to overduplication. The chromatin licence has been defined in molecular terms as the pre-replication complex (pre-RC) antagonised by its regulator geminin. Geminin prevents pre-RC assembly and over-replication in S and G2 phases. However, the mechanisms that limit centrosome duplication including a potential centrosome licence remain poorly understood. Here, we discuss our recent data demonstrating that loss of the licensing inhibitor geminin causes centrosome overduplication in addition to genomic over-replication. We present further evidence that geminin is an inhibitor of centrosome duplication. Therefore, geminin is involved in regulating multiple steps of the chromosome inheritance cycle, including DNA replication, centrosome duplication and chromosome segregation.

Open Access Article

Epigenomics: Mapping the Methylome


Pages 155 - 158
http://dx.doi.org/10.4161/cc.5.2.2367
Abstract | PDF

DNA methylation is integral to normal development and disease processes. However, the genomic distribution of methylated sequences – the methylome – is poorly understood. We have recently developed a platform technology for rapid assessment of methylation status throughout the human genome in a high-resolution, high-throughput manner. This is achieved by coupling a methylated DNA immunoprecipitation (MeDIP) method for isolating methyl cytosine rich fragments with array-based comparative genomic hybridization (array CGH). Using a combination of whole genome tiling path BAC arrays and CpG island microarrays, DNA methylation profiles are obtained simultaneously at both genome-wide and locus-specific levels. A comparison between male and female DNA using MeDIP-array CGH revealed unexpected hypomethylation of the inactive x-chromosome in gene-poor regions. Furthermore, comparisons between cancer and non-cancer cell types yielded differential methylation patterns that link genetic and epigenetic instability offering a new approach to decipher misregulation in cancer. Finally, we provide new data showing epigenomic instability in lung cancer cells with concurrent regions of genetic and epigenetic alterations harbouring known oncogenes.




PERSPECTIVES

Open Access Article

Exploiting the Compromised Spindle Assembly Checkpoint Function of Tumor Cells: Dawn on the Horizon?

Marc Schmidt and Rene H. Medema
Pages 159 - 163
http://dx.doi.org/10.4161/cc.5.2.2309
Abstract | PDF

Aneuploidy is a frequent property of cancer cells that arises as a consequence of chromosomal instability (CIN). A major safeguard mechanism protecting cells from CIN is the spindle assembly checkpoint. This checkpoint surveys proper attachment of chromosomes to the mitotic spindle and effectively suppresses erroneous chromosome segregation by delaying mitotic progression until proper spindle-chromosome interactions have been established. Several lines of evidence suggest that the development of aneuploidy may be a gradual process that in many cases could result from subtle spindle checkpoint defects that occur during tumorgenesis and steadily weaken spindle checkpoint function. Here we discuss the evidence for this concept and address the question whether normal somatic cells and tumor cells could perhaps exhibit differences in spindle checkpoint regulation that allow the design of more specific anti-tumor strategies that effectively kill tumor cells but spare normal cells.

Open Access Article

Assessing the Link between BACH1 and BRCA1 in the FA Pathway

Sharon B. Cantor and Paul R. Andreassen
Pages 164 - 167
http://dx.doi.org/10.4161/cc.5.2.2338
Abstract | PDF

The BACH1 helicase was initially identified by its direct binding to BRCA1 and, thus, was linked to hereditary breast cancer. More recently, BACH1 was identified as the gene defective in the J complementation group of Fanconi anemia (FA). FA is a multigenetic disorder characterized by cellular sensitivity to crosslinkers and chromosome instability. Because FANCD2 monoubiquitination is intact in BACH1 deficient cells, BACH1 appears to act downstream in the FA pathway akin to BRCA2/FANCD1. Interestingly, while BRCA1 has various interactions with FA proteins it has not been identified as an FA gene. As the race to uncover the last few unknown FA complementation groups comes to an end, future work will be required to uncover how these gene products function to combat the effects of DNA damage and maintain genomic stability. In particular, it remains elusive whether BRCA1 is functionally linked to the FA pathway through its interaction with BACH1/FANCJ. This review focuses on a model for the connection of BRCA1 to BACH1 in the FA pathway. We predict that BRCA1 regulates the BACH1 helicase activity to coordinate the timely displacement of Rad51 from nucleofilaments, promoting error free repair and ultimately maintaining chromosomal integrity.

Open Access Article

Control of Hepatic Differentiation by Activin/TGFβ Signaling

Frédéric Clotman and Frédéric P. Lemaigre
Pages 168 - 171
http://dx.doi.org/10.4161/cc.5.2.2341
Abstract | PDF

During liver development, liver progenitors called hepatoblasts differentiate into hepatocytes or biliary cells. Recently, we showed that the segregation between hepatocytes and biliary cells is dependent on a gradient of Activin/TGFβ signaling, and that Activin/TGFβ signaling is controlled in fetal liver by transcription factors of the Onecut family. Here, we discuss candidate factors possibly involved in the formation of the Activin/TGFβ signaling gradient, how this gradient could integrate into a network of signaling pathways modulating hepatoblast differentiation, and the implications for human liver disease and therapy.

Open Access Article

The MicroRNA Pathway Plays a Regulatory Role in Stem Cell Division

H.R. Shcherbata, S. Hatfield, E.J. Ward, S. Reynolds, K.A. Fischer and H. Ruohola-Baker
Pages 172 - 175
http://dx.doi.org/10.4161/cc.5.2.2343
Abstract | PDF

One of the key characteristics of stem cells is their capacity for self-renewal for long periods of time. In this respect, stem cells are similar to cancer cells, which also have the ability to escape cell cycle stop signals. Therefore, a critical question in stem cell and cancer biology is how cell division is regulated in these cell types. In this review, we summarize recent progress and describe future challenges to understanding the role the microRNA pathway plays in regulating mechanisms controlling stem cell division.




REVIEW

Open Access Article

TAZ: A β-Catenin-like Molecule that Regulates Mesenchymal Stem Cell Differentiation

Jeong-Ho Hong and Michael B. Yaffe
Pages 176 - 179
http://dx.doi.org/10.4161/cc.5.2.2362
Abstract | PDF

Regulating the switch between proliferation and differentiation of mesenchymal stem cells is critical for the development of normal tissues, and the prevention of tumors. How mesenchymal stem cells exit from the cell cycle and differentiate into alternative cell fates such as bone, fat, and muscle, is incompletely understood. We recently discovered that a WW domain-containing molecule, TAZ, functions as a transcriptional modulator to stimulate bone development while simultaneous blocking the differentiation of mesenchymal stem cells into fat. These developmental effects occur through direct interaction between TAZ and the transcription factors Runx2 and PPARα, resulting in transcriptional enhancement and repression, respectively of selective programs of gene expression. We propose that TAZ, as well as a highly related molecule YAP, are functionally, though not structurally, similar to β-catenin and integrate extracellular, membrane, and cytoskeletal-derived signals to influence mesenchymal stem cell fate.




BRIEF REPORT

Open Access Article

Differential Regulation of D-Type Cyclins in the Mouse Intestine


Pages 180 - 183
http://dx.doi.org/10.4161/cc.5.2.2306
Abstract | PDF

The intestinal epithelium undergoes continuous rapid renewal throughout adult life. To examine contributions of D-type cyclins to proliferation in the intestine, we examined D-type cyclin expression in the mouse proximal and distal small intestine and colon. Cyclin D1 was expressed throughout the small and large intestine. In contrast, cyclin D2 and D3 protein levels were not readily detectable in the duodenum. Levels of RNAs encoding all three D-type cyclins were higher in the ileum and colon than in the duodenum. Immunohistochemistry revealed that cyclin D1 and D2 are expressed in colonic epithelial cells, with cyclin D2 being more restricted to the proliferative zone. Expression of cyclin D1 and D2 was detected in conditionally immortalized young adult mouse colon (YAMC) cells and in a colon epithelial cell line derived from the ApcMin/+ mouse (IMCE cells), with higher basal levels of both cyclins in the IMCE cells. In an experimental model of colitis, levels of cyclin D1 mRNA increased significantly, and cyclin D1 protein was localized to both epithelial cells and inflammatory cells in the colon. The individual D-type cyclins may make different contributions to proliferation, disease and development of cancer in the intestine.




REPORTS

Open Access Article

E2F3a Stimulates Proliferation, p53-Independent Apoptosis and Carcinogenesis in a Transgenic Mouse Model

Qiwei X. Paulson, Mark J. McArthur and David G. Johnson
Pages 184 - 190
http://dx.doi.org/10.4161/cc.5.2.2307
Abstract | PDF

Mutation or inactivation of the retinoblastoma (Rb) tumor suppressor occurs in most human tumors and results in the deregulation of several members of the E2F family of transcription factors. Among the E2F family, E2F3 has been implicated as a key regulator of cell proliferation and E2F3 gene amplification and overexpression is detected in some human tumors. To study the role of E2F3 in tumor development, we established a transgenic mouse model expressing E2F3a in a number of epithelial tissues via a keratin 5 (K5) promoter. Transgenic expression of E2F3a leads to hyperproliferation, hyperplasia and increased levels of p53-independent apoptosis in transgenic epidermis. Consistent with data from human cancers, the E2F3a transgene is found to have a weak oncogenic activity on its own and to significantly enhance the response to a skin carcinogenesis protocol. The phenotype of K5 E2F3a transgenic mice is distinct from similar transgenic mice expressing E2F1 or E2F4. In particular, E2F3a has a unique apoptotic activity and lacks the tumor suppressive property of E2F1 in this model system.

Open Access Article

Dual-Color-Coded Imaging of Viable Circulating Prostate Carcinoma Cells Reveals Genetic Exchange between Tumor Cells In Vivo, Contributing to Highly Metastatic Phenotypes

Gennadi V. Glinsky, Anna B. Glinskii, Olga Berezovskaya, Brian A. Smith, Ping Jiang, Xiao-Ming Li, Meng Yang and Robert M. Hoffman
Pages 191 - 197
http://dx.doi.org/10.4161/cc.5.2.2320
Abstract | PDF

Color-coded imaging analysis revealed yellow fluorescent metastasis precursor cells that were readily recognized in the blood of tumor-bearing mice after mixtures of red fluorescent protein (RFP)- and green fluorescent protein (GFP)-expressing PC-3 human prostate carcinoma cells were implanted in the nude mouse prostate and metastasized. The yellow fluorescent cells were purified from the blood of nude mice to 99% homogeneity by FACS, expanded in culture, and re-implanted in the prostate of nude mice. The yellow fluorescent phenotype was heritable and stably maintained by tumor cells for many generations in vitro and in vivo. In the animals implanted with the yellow-fluorescing cells, 100% developed aggressive metastatic cancer. Lung metastases were demonstrated in 100% of the animals as early as four weeks after injection of the yellow-fluorescing cells in the mouse prostate. In contrast, when the GFP- and RFP-expressing parental cells were inoculated into the mouse prostate separately, none of the animals developed lung metastasis. All animals had almost exclusively yellow fluorescent cells in the blood and bone marrow. These results are consistent with the idea that spontaneous genetic exchange between tumor cells in vivo contributes to genomic instability and creation of highly metastatic cells.

Open Access Article

Regulation of Separase in Meiosis: Separase is Activated at the Metaphase I-II Transition in Xenopus Oocytes during Meiosis

Heng-Yu Fan, Qing-Yuan Sun and Hui Zou
Pages 198 - 204
http://dx.doi.org/10.4161/cc.5.2.2321
Abstract | PDF

Separase is a cysteine protease conserved in all eukaryotes and functions to remove the sister chromatid cohesion in anaphase by cleaving the SCC1 subunit of the cohesin complex. The regulation of separase activity as the degradation of its inhibitor, securin, and the downregulation of the inhibitory phosphorylation has never been directly investigated in the meiotic cell cycle of vertebrates. In this study, we cloned the full-length gene encoding Xenopus separase from an oocyte cDNA library. Purified xSeparase can cleave the human ?- kleisin subunit of cohesin in vitro but cannot bind with hSecurin when these two proteins are co-expressed in 293T cells. Similar to its human counterpart, xSeparase cleaves itself upon activation but at a single site. The cleavage site is conserved with one of the three selfcleavage sites in hSeparase. Using self-cleavage as a reporter for its activation, we demonstrated that xSeparase was transiently activated between the two meioses and may be involved in the homologous chromosome separation, as observed in other organisms. Taking the advantage of the inability of xSecurin to interact with hSeparase, we demonstrated that the CSF extract re-inhibit both full-length and auto-cleaved hSeparase, indicating that phosphorylation inhibition of separase does occur under the physiological condition. In addition, we found that the endogenous xSecurin was accumulated in response to progesterone-induced oocyte maturation, and was degraded at both the anaphase I and II in an APC/C-dependent manner.

Open Access Article

Connecting p63 to Cellular Proliferation: The Example of the Adenosine Deaminase Target Gene

Elisabetta Sbisà, Giuseppe Mastropasqua, Kostantinos Lefkimmiatis, Mariano Francesco Caratozzolo, Anna Maria D’Erchia and Apollonia Tullo
Pages 205 - 212
http://dx.doi.org/10.4161/cc.5.2.2361
Abstract | PDF

An unresolved issue regards the role of p73 and p63, the two homologs of the p53 oncosuppressor gene, in normal cells and in tumour development. Specific target genes for each protein need to be identified and characterized in order to understand the specific role of each protein in tumour initiation and progression as well as in oncosuppression and development. We tested whether p63 is implicated in transcriptional events related to sustaining cell proliferation by transactivation of antiapoptotic and cell survival target genes such as Adenosine Deaminase (ADA), an important gene involved in cell proliferation. We demonstrate that ADA is a direct target gene of p63 isoforms. In human keratinocytes, the rate of proliferation and the high level of ADA transcript diminished upon elimination of p63 by small interfering RNA. Reporter assays and chromatin immunoprecipitation experiments indicate a physical interaction of p63 with the two putative p53 binding sites we identified in the ADA gene. Moreover, in response to p53 stabilization and ?Np63 downregulation in normal keratinocytes after U.V. treatment, we found a change in the transcriptional pattern of the p53 family target genes, consistent with the different roles played by p53 and p63 in tumour suppression and cellular proliferation. In fact p53 upregulation determined an increase in p21, which in turn mediated the cell cycle arrest, while the downregulation of ?Np63 determined a marked decrease in ADA transcript. The experiments reported here support the hypothesis that TAp63 and ?Np63 might contribute to tumour genesis not exclusively by antagonizing p53, but by conferring a proliferative potential on cancer cells through the transactivation of target genes indispensable for cell division, such as the Adenosine Deaminase gene.

Open Access Article

Protein Kinase A(PKA)-Restrictcive and PKA-Permissive Phases of Oocyte Maturation

Jing Wang, Winnie Li Cao and X. Johné Liu
Pages 213 - 217
http://dx.doi.org/10.4161/cc.5.2.2365
Abstract | PDF

Substantial evidence has indicated that cAMP-dependent protein kinase (protein kinase A or PKA) plays a critical role in maintaining meiotic prophase arrest in vertebrate oocytes. However, PKA activity dynamic and its physiological substrate profile remain poorly defined. We have recently developed a novel PKA substrate construct which we employ to monitor PKA activity in live oocytes. In the current study, we have employed biochemical and imaging analyses of single cells to determine PKA activity dynamics during oocyte maturation and to investigate the consequence of re-activation of PKA during oocyte maturation. We demonstrated here that progesterone caused a rapid and permanent inhibition of PKA during the entire maturation process. However, artificial reactivation of endogenous PKA had differential consequences, depending on the timing of PKA reactivation. Reactivation of endogenous PKA at any time prior to GVBD inhibited progesterone-induced GVBD. PKA reactivation at GVBD, or thereafter, did not interfere with meiosis I to meiosis II transition, nor did it interfere with metaphase II arrest. These results demonstrate for the first time a PKA-restricted phase and a PKA-permissive phase during oocyte maturation.