Table of Contents

Volume 10, Issue 3

  February 1, 2011

  Pages 359 - 550

View covers archive

 Issue Catalogue (MARC XML)

EDITORIALS: CELL CYCLE FEATURES

Open Access Article

Aneuploidy in cancer: Sudden or sequential?

David Gisselsson
Pages 359 - 361
http://dx.doi.org/10.4161/cc.10.3.14518
Abstract | PDF

Comment on: Gisselsson D, et al. Proc Natl Acad Sci USA 2010; 107:20489-93.

Open Access Article

Transforming blood vessels into bone

Damian Medici and Bjorn R. Olsen
Pages 362 - 363
http://dx.doi.org/10.4161/cc.10.3.14519
Abstract | PDF

Comment on: Medici D, et al. Nat Med 2010; 16:1400-6.

Open Access Article

An example of functional interaction between NFAT5/TonEBP and Nuclear Factor-κB by hypertonic stress: Aquaporin-2 transcription

Udo Hasler
Pages 364 - 365
http://dx.doi.org/10.4161/cc.10.3.14520
Abstract | PDF

Comment on: Roth I, et al. Mol Biol Cell 2010; 21:3459-74.

Open Access Article

You’d better catch that Wnt: Primitive hematopoiesis requires canonical Wnt signaling

Hong Thi Tran and Kris Vleminckx
Pages 366 - 367
http://dx.doi.org/10.4161/cc.10.3.14521
Abstract | PDF

Comment on: Tran HT, et al. Proc Natl Acad Sci USA 2010; 107:16160-5.

Open Access Article

It never rains but it pours: Potential role of butyrophilins in inhibiting anti-tumor immune responses

Juan R. Cubillos-Ruiz and Jose R. Conejo-Garcia
Pages 368 - 369
http://dx.doi.org/10.4161/cc.10.3.14565
Abstract | PDF

Feature on: Cubillos-Ruiz JR, et al. Oncotarget 2010; 1:329-338.

Open Access Article

Role of nucleosomes in mitotic bookmarking

Theresa K. Kelly and Peter A. Jones
Pages 370 - 371
http://dx.doi.org/10.4161/cc.10.3.14734
Abstract | PDF

Feature on: Kelly TK, et al. Mol Cell 2010; 39:901-11.

Open Access Article

This message was inspected by Upf1: 3’UTR length sensing in mRNA quality control

J. Robert Hogg
Pages 372 - 373
http://dx.doi.org/10.4161/cc.10.3.14735
Abstract | PDF

Feature on: Hogg JR, Goff SP. Upf1 senses 3'UTR length to potentiate mRNA decay. Cell. 2010; 143:379-89.




CELL CYCLE NEWS & VIEWS

Open Access Article

More than MAX: Discovering the Myc interactome

Manpreet Kalkat, Amanda R. Wasylishen, Sam S. Kim and Linda Penn
Pages 374 - 375
http://dx.doi.org/10.4161/cc.10.3.14645
Abstract | PDF

Comment on: Agrawal P, et al. Cell Cycle 2010; 9:4908-4921.

Open Access Article

Loss of CC3/TIP30 allows tumor cells to cope with low glucose

Pierre Sonveaux
Page 376
http://dx.doi.org/10.4161/cc.10.3.14646
Abstract | PDF

Comment on: Chen V, et al. Cell Cycle 2010; 9:4941-4953.

Open Access Article

BRCA1, microRNAs and cancer predisposition: Challenging the dogma

Maria Inês Almeida, Rui M. Reis and George A. Calin
Page 377
http://dx.doi.org/10.4161/cc.10.3.14738
Abstract | PDF

Comment on: Pelletier C, et al. Cell Cycle 2011; 10:90–1
 

Open Access Article

PKCε paves the way for prostate cancer

Alakananda Basu
Page 378
http://dx.doi.org/10.4161/cc.10.3.14739
Abstract | PDF

Comment on: Benavides F, et al. Cell Cycle 2011; 10:268-77
 

Open Access Article

A tale of three PKCs: Epsilon emerges as a driver of pre-neoplastic phenotypes

Karen E. Knudsen
Page 379
http://dx.doi.org/10.4161/cc.10.3.14740
Full Text | PDF




EXTRA VIEWS

Open Access Article

Screening for modulators of cisplatin sensitivity: Unbiased screens reveal common themes

Jeroen H. Nijwening, Hendrik J. Kuiken and Roderick L. Beijersbergen
Pages 380 - 386
http://dx.doi.org/10.4161/cc.10.3.14642
Abstract | PDF

Cisplatin is a widely used chemotherapeutic agent to treat a variety of solid tumors. The cytotoxic mode of action of cisplatin is mediated by inducing conformational changes in DNA including intra- and inter-strand crosslink adducts. Recognition of these adducts results in the activation of the DNA damage response resulting in cell cycle arrest, repair, and potentially, apoptosis. Despite the clinical efficacy of cisplatin, many tumors are either intrinsically resistant or acquire resistance during treatment. The identification of cisplatin drug response modulators can help us understand these resistance mechanisms, provide biomarkers for treatment strategies, or provide drug targets for combination therapy. Here we discuss functional genetic screens, including one performed by us, set up to identify genes whose inhibition results in increased sensitivity to cisplatin. In summary, the validated genes identified in these screens mainly operate in DNA damage response including nucleotide excision repair, translesion synthesis, and homologous recombination.

Open Access Article

Human Cdc14A becomes a cell cycle gene in controlling Cdk1 activity at the G₂/M transition

Maria P. Sacristán, Sara Ovejero and Avelino Bueno
Pages 387 - 391
http://dx.doi.org/10.4161/cc.10.3.14643
Abstract | PDF

Cdc14 belongs to a dual-specificity phosphatase family highly conserved through evolution that preferentially reverses CDK (Cyclin dependent kinases) –dependent phosphorylation events. In the yeast Saccharomyces cerevisiae, Cdc14 is an essential regulator of late mitotic events and exit from mitosis by counteracting CDK activity at the end of mitosis. However, many studies have shown that Cdc14 is dispensable for exiting mitosis in all other model systems analyzed. In fission yeast, the Cdc14 homologue Flp1/Clp1 regulates the stability of the mitotic inducer Cdc25 at the end of mitosis to ensure Cdk1 inactivation before cytokinesis. We have recently reported that human Cdc14A, the Cdc14 isoform located at the centrosomes during interphase, down-regulates Cdc25 activity at the G2/M transition to prevent premature activation of Cdk1-Cyclin B1 complexes and untimely entry into mitosis. Here we speculate about new molecular mechanisms for Cdc14A and discuss the current evidence suggesting that Cdc14 phosphatase plays a role in cell cycle control in higher eukaryotes.

Open Access Article

Gene positioning is regulated by phosphorylation of the nuclear pore complex by Cdk1

Donna Garvey Brickner and Jason H. Brickner
Pages 392 - 395
http://dx.doi.org/10.4161/cc.10.3.14644
Abstract | PDF

In yeast, many genes are targeted to the nuclear periphery through interaction with the Nuclear Pore Complex upon activation. Targeting requires nucleoporin proteins and DNA elements in the promoters of these genes. We have recently found that targeting is regulated through the cell cycle. Immediately following the initiation of DNA replication, active genes lose peripheral localization for ~30 minutes. This regulation is mediated by cyclic phosphorylation of a nucleoporin by Cdk1. Some genes that are targeted to the nuclear periphery upon activation remain at the nuclear periphery after repression, a phenomenon called transcriptional memory. Curiously, the mechanism that regulates localization of active genes to the nuclear periphery does not regulate the localization of the same genes after repression, suggesting that these genes are targeted by two distinct mechanisms. Finally, the localization of other parts of the genome that localize at the nuclear periphery seem to be regulated by a distinct mechanism, suggesting that the spatial organization of the genome is tightly coupled to the progression of the cell cycle.

Open Access Article

Multiple faces of FoxM1 transcription factor: Lessons from transgenic mouse models

Tanya V. Kalin, Vladimir Ustiyan and Vladimir V. Kalinichenko
Pages 396 - 405
http://dx.doi.org/10.4161/cc.10.3.14709
Abstract | PDF

FoxM1 transcription factor (previously called HFH-11B, Trident, FoxM1b, Win, and MPP2) is expressed in actively dividing cells and critical for cell cycle progression. FoxM1 expression is induced in a variety of tissues during embryogenesis, and Foxm1^-/- mice exhibit embryonic lethal phenotype due to multiple abnormalities in the liver, heart, lung and blood vessels. FoxM1 levels are dramatically decreased in adult tissues, but FoxM1 expression is re-activated during organ injury and numerous cancers. In this review, we discussed the role of FoxM1 in different cell lineages using recent data from transgenic mouse models with conditional “gain-of-function” and “loss-of-function” of FoxM1, as well as tissue samples from human patients. In addition, we provided experimental data showing additional sites of FoxM1 expression in the mouse embryo. Novel cell-autonomous roles of FoxM1 in embryonic development, organ injury and cancer formation in vivo were analyzed. Potential application of these findings for the diagnosis and treatment of human diseases were discussed.

Open Access Article

Distinct and redundant functions of histone deacetylases HDAC1 and HDAC2 in proliferation and tumorigenesis

Jennifer Jurkin, Gordin Zupkovitz, Sabine Lagger, Reinhard Grausenburger, Astrid Hagelkruys, Lukas Kenner and Christian Seiser
Pages 406 - 412
http://dx.doi.org/10.4161/cc.10.3.14712
Abstract | PDF

Histone deacetylases (HDACs) are negative regulators of gene expression and have been implicated in tumorigenesis and tumor progression. Therefore, HDACs are promising targets for anti-tumor drugs. However, the relevant isoforms of the 18 members encompassing HDAC family have not been identified. Studies utilizing either gene targeting or knockdown approaches reveal both specific and redundant functions of the closely related class I deacetylases HDAC1 and HDAC2 in the control of proliferation and differentiation. Combined ablation of HDAC1 and HDAC2 in different cell types led to a severe proliferation defects or enhanced apoptosis supporting the idea that both enzymes are relevant targets for tumor therapy. In a recent study on the role of HDAC1 in teratoma formation we have reported a novel and surprising function of HDAC1 in tumorigenesis. In this tumor model HDAC1 attenuates proliferation during teratoma formation. In the present work we discuss new findings on redundant and unique functions of HDAC1 and HDAC2 as regulators of proliferation and tumorigenesis and potential implications for applications of HDAC inhibitors as therapeutic drugs.




PERSPECTIVES

Open Access Article

Selective targeting of histone methylation

Abul BMMK Islam, William F. Richter, Nuria Lopez-Bigas and Elizaveta V. Benevolenskaya
Pages 413 - 424
http://dx.doi.org/10.4161/cc.10.3.14705
Abstract | PDF

Histones are post-translationally modified by multiple histone-modifying enzymes, which in turn influences gene expression. Much of the work in the field to date has focused on genetic, biochemical and structural characterization of these enzymes. The most recent genome-wide methods provide insights into specific recruitment of histone-modifying enzymes in vivo and, therefore, onto mechanisms of establishing a differential expression pattern. Here we focus on the recruitment mechanisms of the enzymes involved in the placement of two contrasting histone marks, histone H3 lysine 4 (H3K4) methylation and histone H3 lysine 27 (H3K27) methylation. We describe distribution of their binding sites and show that recruitment of different histone-modifying proteins can be coordinated, opposed, or alternating. Specifically, genomic sites of the H3K4 histone demethylase KDM5A become accessible to its homolog KDM5B in cells with a lowered KDM5A level. The currently available data on recruitment of H3K4/H3K27 modifying enzymes suggests that the formed protein complexes are targeted in a sequential and temporal manner, but that additional, still unknown, interactions contribute to targeting specificity.

Open Access Article

Unexpected role of nucleoporins in coordination of cell cycle progression

Hiroshi Nakano, Wei Wang, Chieko Hashizume, Tatsuyoshi Funasaka, Hiroshi Sato and Richard W. Wong
Pages 425 - 433
http://dx.doi.org/10.4161/cc.10.3.14721
Abstract | PDF

Many human cancers have irregular chromosome content, a condition known as aneuploidy. Several nuclear pore proteins (nucleoporins/Nups) that mediate transport of RNA or macromolecules into and out of the nucleus have been implicated in mitosis. These nucleoporins are involved in molecular networks that function in a variety of mitotic processes, including chromosome condensation, sister chromatid cohesion, kinetochore assembly and spindle formation. An alteration in the concentration of Nups inside cells often causes aneuploidy. In this review, we discuss this sprouting area and the possible functions of Nups during mitosis.




REVIEWS

Open Access Article

Recent advances in cloning herpesviral genomes as infectious bacterial artificial chromosomes

Fuchun Zhou and Shou-Jiang Gao
Pages 434 - 440
http://dx.doi.org/10.4161/cc.10.3.14708
Abstract | PDF

Herpesviruses are common but important pathogens in humans and animals. These viruses have large complex genomes encoding genes with diverse functions in different phases of their life cycle and associated diseases. In the last decade, genomes of herpesviruses cloned as infectious bacterial artificial chromosomes (BACs) have become powerful tools for delineating the functions of viral genes and understanding the pathogenesis of their associated diseases. Here we review the history of herpesviral genetics and recent advances in methods for cloning herpesviral genomes as infectious BACs.

Open Access Article

MicroRNAs in skeletal myogenesis

Yejing Ge and Jie Chen
Pages 441 - 448
http://dx.doi.org/10.4161/cc.10.3.14710
Abstract | PDF

MicroRNAs (miRNAs) have emerged as critical regulators of numerous biological processes by modulating gene expression at the post-transcriptional level. It has become increasingly clear that almost all aspects of skeletal muscle development involve regulation by miRNAs. Many of these miRNAs have distinct expression profiles in skeletal muscles, under the regulation by the myogenic program. In the last few years the field has seen a rapid expansion of our knowledge of myogenic miRNAs that target a wide range of muscle genes to coordinately control the myogenic process. In this review we provide an up-to-date list of reported myogenic miRNAs and survey their expression patterns, regulation of biogenesis, and gene targets in skeletal muscles. Emerging themes of miRNA regulation in the context of skeletal myogenesis will also be discussed.

Open Access Article

Spindly switch controls anaphase: Spindly and RZZ functions in chromosome attachment and mitotic checkpoint control

Marin Barisic and Stephan Geley
Pages 449 - 456
http://dx.doi.org/10.4161/cc.10.3.14759
Abstract | PDF

Spindly is a coiled-coil domain containing protein, also known as CCDC99, that is an important regulator of the mitotic checkpoint. It belongs to a functionally conserved family of proteins that controls the localization and function of cytoplasmic dynein at kinetochores. At kinetochores Spindly interacts with the RZZ (Rod/ZW10/Zwilch) complex and is required for the recruitment of cytoplasmic dynein to kinetochores. Loss of Spindly results in loss of kinetochore dynein functions, which impairs poleward chromosome movements and mitotic checkpoint inactivation. In addition, Spindly regulates the establishment of stable microtubule attachments via regulation of the RZZ complex. Thus, Spindly couples dynein-mediated poleward chromosome movements to the establishment of stable microtubule attachments and subsequent mitotic checkpoint inactivation and provides an important switch for the control of mitosis.




REPORTS

Open Access Article

Senescence-associated heterochromatin foci are dispensable for cellular senescence, occur in a cell type- and insult-dependent manner and follow expression of p16^ink4a

Martin Kosar, Jirina Bartkova, Sona Hubackova, Zdenek Hodny, Jiri Lukas and Jiri Bartek
Pages 457 - 468
http://dx.doi.org/10.4161/cc.10.3.14707
Abstract | PDF

Cellular senescence, an irreversible proliferation arrest evoked by stresses such as oncogene activation, telomere dysfunction, or diverse genotoxic insults, has been implicated in tumor suppression and aging. Primary human fibroblasts undergoing oncogene-induced or replicative senescence are known to form senescence-associated heterochromatin foci (SAHF), nuclear DNA domains stained densely by DAPI and enriched for histone modifications including lysine9-trimethylated histone H3. While cellular senescence occurs also in premalignant human lesions, it is unclear how universal is SAHF formation among various cell types, under diverse stresses, and whether SAHF occur in vivo. Here, we report that human primary fibroblasts (BJ and MRC-5) and primary keratinocytes undergoing replicative senescence, or premature senescence induced by oncogenic H-Ras, diverse chemotherapeutics and bacterial cytolethal distending toxin, show differential capacity to form SAHF. Whereas all tested cell types formed SAHF in response to activated H-Ras, only MRC-5, but not BJ fibroblasts or keratinocytes, formed SAHF under senescence induced by etoposide, doxorubicin, hydroxyurea, bacterial intoxication or telomere attrition. In addition, DAPI-defined SAHF were detected on paraffin sections of Ras-transformed cultured fibroblasts, but not human lesions at various stages of tumorigenesis. Overall, our results indicate that unlike the widely present DNA damage response marker γH2AX, SAHF is not a common feature of cellular senescence. Whereas SAHF formation is shared by diverse cultured cell types under oncogenic stress, SAHF are cell-type-restricted under genotoxin-induced and replicative senescence. Furthermore, while the DNA/DAPI-defined SAHF formation in cultured cells parallels enhanced expression of p16^ink4a, such ‘prototypic’ SAHF are not observed in tissues, including premalignant lesions, irrespective of enhanced p16^ink4a and other features of cellular senescence.

Open Access Article

CtIP interacts with TopBP1 and Nbs1 in the response to double-stranded DNA breaks (DSBs) in Xenopus egg extracts

Juan S. Ramírez-Lugo, Hae Yong Yoo, Su Jin Yoon and William G. Dunphy
Pages 469 - 480
http://dx.doi.org/10.4161/cc.10.3.14711
Abstract | PDF

In the presence of double-stranded DNA breaks (DSBs), the activation of ATR is achieved by the ability of ATM to phosphorylate TopBP1 on serine 1131, which leads to an enhancement of the interaction between ATR and TopBP1. In Xenopus egg extracts, the Mre11-Rad50-Nbs1 (MRN) complex is additionally required to bridge ATM and TopBP1 together. In this report, we show that CtIP, which is recruited to DSB-containing chromatin, interacts with both TopBP1 and Nbs1 in a damage-dependent manner. An N-terminal region containing the first two BRCT repeats of TopBP1 is essential for the interaction with CtIP. Furthermore, two distinct regions in the N-terminus of CtIP participate in establishing the association between CtIP and TopBP1. The first region includes two adjacent putative ATM/ATR phosphorylation sites on serines 273 and 275. Secondly, binding is diminished when an MRN-binding region spanning residues 25–48 is deleted, indicative of a role for the MRN complex in mediating this interaction. This was further evidenced by a decrease in the interaction between CtIP and TopBP1 in Nbs1-depleted extracts and a reciprocal decrease in the binding of Nbs1 to TopBP1 in the absence of CtIP, suggestive of the formation of a complex containing CtIP, TopBP1, and the MRN complex. When CtIP is immunodepleted from egg extracts, the activation of the response to DSBs is compromised and the levels of ATR, TopBP1, and Nbs1 on damaged chromatin are reduced. Thus, CtIP interacts with TopBP1 in a damage-stimulated, MRN-dependent manner during the activation of ATR in response to DSBs.

Open Access Article

ATM-dependent ERK signaling via AKT in response to DNA double-strand breaks

Ashraf Khalil, Rhiannon N. Morgan, Bret R. Adams, Sarah E. Golding, Seth M. Dever, Elizabeth Rosenberg, Lawrence F. Povirk and Kristoffer Valerie
Pages 481 - 491
http://dx.doi.org/10.4161/cc.10.3.14713
Abstract | PDF

Ionizing radiation (IR) triggers many signaling pathways primarily originating from either damaged DNA or non-nuclear sources such as growth factor receptors. Thus, to study the DNA damage-induced signaling component alone by irradiation would be a challenge. To generate DNA double-strand breaks (DSBs) and minimize non-nuclear signaling, human cancer cells having bromodeoxyuridine (BrdU) - substituted DNA were treated with the photosensitizer Hoechst 33258 followed by long wavelength UV (UV-A) treatment (BrdU photolysis). BrdU photolysis resulted in well-controlled, dose- dependent generation of DSBs equivalent to radiation doses between 0.2 - 20 Gy, as determined by pulsed-field gel electrophoresis, and accompanied by dose-dependent ATM (ser-1981), H2AX (ser-139), Chk2 (thr-68), and p53 (ser-15) phosphorylation. Interestingly, low levels (≤2 Gy equivalents) of BrdU photolysis stimulated ERK phosphorylation whereas higher (>2 Gy eq.) resulted in ERK dephosphorylation. ERK phosphorylation was ATM-dependent whereas dephosphorylation was ATM-independent. The ATM-dependent increase in ERK phosphorylation was also seen when DSBs were generated by transfection of cells with an EcoRI expression plasmid or by electroporation of EcoRI enzyme. Furthermore, AKT was critical for transmitting the DSB signal to ERK. Altogether, our results show that low levels of DSBs trigger ATM- and AKT-dependent ERK pro-survival signaling and increased cell proliferation whereas higher levels result in ERK dephosphorylation consistent with a dose-dependent switch from pro-survival to anti-survival signaling.

Open Access Article

In vitro and in vivo anticancer action of Saquinavir-NO, a novel nitric oxide-derivative of the protease inhibitor saquinavir, on hormone resistant prostate cancer cells

Marco Donia, Danijela Maksimovic-Ivanic, Sanja Mijatovic, Marija Mojic, Djordje Miljkovic, Gordana Timotijevic, Paolo Fagone, Salvatore Caponnetto, Yousef Al-Abed, James A. McCubrey, Stanislava Stosic-Grujicic and Ferdinando Nicoletti
Pages 492 - 499
http://dx.doi.org/10.4161/cc.10.3.14727
Abstract | PDF

The NO-derivative of the HIV protease inhibitor saquinavir (Saq-NO) is a nontoxic variant of the parental drug with enhanced anticancer activity on several cell lines. However, it is still unclear whether the p53 status of the target cell might influence the sensitivity to Saq-NO. In this study we evaluated the in vitro and in vivo activity of Saq-NO on the p53-deficient hormone resistant prostate cancer PC-3 cells. We demonstrate that the absence of functional p53 is not essential for the capacity of Saq-NO to reduce prostate cancer cell growth. In contrast to its previously described cytostatic action in B16 and C6 cell lines, Saq-NO exerted cytotoxic effects in PC-3 cells leading to dominant induction of apoptosis and enhanced production of proapoptotic Bim. In addition, differently from saquinavir, Saq-NO restored TRAIL sensitivity that was correlated with increased expression of DR5 independent from ROS/RNS production and YY1 repression. NF-κB activation may be responsible of the Saq-NO induced DR5 expression. Moreover, Saq-NO but not saquinavir, exerted synergistic activity with conventional cytostatic therapy. In agreement with these in vitro studies, Saq-NO inhibited the in vivo growth of PC-3 cells xenotransplants to a greater extent than the parental compound. Taken together, these data indicate that Saq-NO possesses powerful and suitable in vitro and in vivo chemotherapeutic potential to be further studied as a novel drug for the treatment of prostate cancer in the clinical setting.

Open Access Article

A new in vitro system for activating the cell cycle checkpoint

Jingna Wang, Staci Engle and Youwei Zhang
Pages 500 - 506
http://dx.doi.org/10.4161/cc.10.3.14753
Abstract | PDF

In response to DNA damage, cells launch elegant networks of genome surveillance mechanisms, called cell cycle checkpoints, to detect and repair damaged DNA to maintain the genome stability. Key components of cell cycle checkpoints are two PI3K-related protein kinases (PIKK), ATR and ATM, which participate in both sensing the DNA damage and transducing the damage signal through phosphorylating two target protein kinases, Chk1 and Chk2, respectively. However, how exactly cell cycle checkpoints are activated, maintained, and terminated are not completely understood. Given the complexity of the cell cycle checkpoint signaling and the cellular environment, systems that can faithfully mimic the cell cycle checkpoint activation in vitro, such as the Xenopus egg extracts, are of extreme value in dissecting the precise molecular mechanisms underlying DNA damage response. Here we describe that the well-established in vitro transcription and translation (IVTNT) system has the capability to induce protein phosphorylation of substrates for ATR or ATM, including Chk1, Rad17, and ATM itself. These phosphorylation events highly mimic those occurring in cells when treated with DNA damaging agents. Our results demonstrate that the IVTNT system could be developed into a novel in vitro system to facilitating the dissecting of mechanisms leading to cell cycle checkpoint activation in vivo.

Open Access Article

MicroRNA expression analysis in triple-negative (ER, PR and Her2/neu) breast cancer

Jelena Radojicic, Apostolos Zaravinos, Thomas Vrekoussis, Maria Kafousi, Demetrios A. Spandidos and Efstathios N. Stathopoulos
Pages 507 - 517
http://dx.doi.org/10.4161/cc.10.3.14754
Abstract | PDF

miRNAs are small, regulatory molecules approximately 21-24 nucleotides in length. They function at the post-transcriptional level by controlling the expression of more than 50% of human protein-coding genes and play an essential role in cell signaling pathways. The objective of the present study was to explore the expression profile of oncomiRs and tumor-suppressor miRs, and to define their possible correlations in triple-negative (ER, PR and Her2/neu) primary breast cancers. Forty-nine primary triple-negative breast cancer cases, along with 34 matched tumor-associated normal samples were investigated for the expression of 9 miRNAs using qPCR. Relationships between the expression of miR-10b, miR-21, miR-122a, miR-145, miR-205, miR-210, miR-221, miR-222 and miR-296 and the pathologic features of the tumors were examined, as were the influences of miR expression on patient overall and cancer-specific survival. miR-21, miR-210 and miR-221 were significantly overexpressed, whereas miR-10b, miR-145, miR-205, miR-122a were significantly underexpressed in the triple-negative primary breast cancers. Significant correlations among all of the studied miRs were scored both in the breast cancer and control tissue. Expression of miR-222 and miR-296 did not exhibit any significant difference between the breast cancer and normal tissue. There was a non-significant trend for high expression levels of the microRNAs, miR-21, miR-210, miR-221 and miR-222, to be associated with worse patient disease-free and overall survival. miR-21, miR-210 and miR-221 expression plays a significant role in triple- negative primary breast cancers.

Open Access Article

CREG1 enhances p16^INK4a-induced cellular senescence

Benchamart Moolmuang and Michael A. Tainsky
Pages 518 - 530
http://dx.doi.org/10.4161/cc.10.3.14756
Abstract | PDF

Cellular senescence is an irreversible growth arrest that is activated in normal cells upon shortening of telomere and other cellular stresses. Bypassing cellular senescence is a necessary step for cells to become immortal during oncogenic transformation. During the spontaneous immortalization of Li-Fraumeni Syndrome (LFS) fibroblasts, we found that CREG1 (Cellular Repressor of E1A-stimulated Genes 1) expression was decreased during immortalization and increased in senescence. Moreover, we found that repression of CREG1 expression occurs via an epigenetic mechanism, promoter DNA methylation. Ectopic expression of CREG1 in the immortal LFS cell lines decreases cell proliferation but does not directly induce senescence. We confirmed this in osteosarcoma and fibrosarcoma cancer cell lines, cancers commonly seen in Li-Fraumeni Syndrome. In addition, we found that p16^INK4a is also downregulated in immortal cells and that coexpression of CREG1 and p16^INK4a, an inhibitor of CDK4/6 and Rb phosphorylation, has a greater effect than either CREG1 and p16^INK4a alone to reduce cell growth, induce cell cycle arrest and cellular senescence in immortal LFS fibroblasts, osteosarcoma and fibrosarcoma cell lines. Moreover, cooperation of CREG1 and p16^INK4a inhibits the expression of cyclin A and cyclin B by inhibiting promoter activity thereby decreasing mRNA and protein levels; these proteins are required for S-phase entry and G2/M transition. In conclusion, this is the first evidence to demonstrate that CREG1 enhances p16^INK4a–induced senescence by transcriptional repression of cell cycle-regulated genes.

Open Access Article

CK1ε targets Cdc25A for ubiquitin-mediated proteolysis under normal conditions and in response to checkpoint activation

Shunfu Piao, Su-Jin Lee, Yongbin Xu, Jungsug Gwak, Sangtaek Oh, Bum-Joon Park and Nam-Chul Ha
Pages 531 - 537
http://dx.doi.org/10.4161/cc.10.3.14757
Abstract | PDF

Cdc25A phosphatase, which is essential in cell cycle progression, is degraded by the proteasome throughout interphase and in response to genotoxic stress. Phosphorylation of Cdc25A on Ser82 in the DSG motif is important in the recognition by β-TrCP, resulting in targeting of Cdc25A for ubiquitination. Chk1 is known to phosphorylate Cdc25A on Ser76, and NEK11 or CK1α relays phosphorylation of Cdc25A to Ser82 in a hierarchical manner. In this study, we found that CK1ε has unique enzymatic activity on the serine residue in the DSG motif using a β-catenin N-terminal region as a substrate. We then examined whether CK1ε has activity on the DSG motif of Cdc25A. We found CK1ε directly phosphorylated Ser82 without any prior phosphorylation of Cdc25A, and depletion of CK1ε stabilized the cellular Cdc25A in 293 cells. Moreover, we found that CK1ε also has activity as a relaying kinase like NEK11 or CK1α when the cell is exposed to DNA damage. Taken together, our results indicate that CK1ε regulates the cellular levels of Cdc25A in parallel with Chk1-dependent Cdc25A degradation, contributing to the precise control of cell division.

Open Access Article

Threonine 48 in the BIR domain of survivin is critical to its mitotic and anti-apoptotic activities and can be phosphorylated by CK2 in vitro

Rachel M.A. Barrett, Rita Colnaghi and Sally P. Wheatley
Pages 538 - 548
http://dx.doi.org/10.4161/cc.10.3.14758
Abstract | PDF

In this study we report that the protein kinase CK2 phosphorylates survivin specifically on threonine 48 (T48) within its BIR domain, and that T48 is critical to both the mitotic and anti-apoptotic roles of survivin. Interestingly, during mitosis T48 mutants localise normally, but are unable to support cell growth when endogenous survivin is removed by siRNA. In addition, while overexpression of survivin normally confers inhibition of TRAIL-mediated apoptosis, this protection is abolished by mutation of T48. Furthermore in interphase cells depletion of endogenous survivin causes redistribution of T48 mutants from the cytoplasm to the nucleus and treatment of cells expressing survivin-GFP with the CK2 inhibitor TBB phenocopies this nuclear redistribution. Finally, we show T48 mutants have increased affinity for borealin, and that this association and cell proliferation can be restored by introduction of a second mutation at T97. To our knowledge these data are the first to identify T48 as a key regulatory site on survivin, and CK2 as a mediator of its mitotic and anti-apoptotic functions.




LETTER TO THE EDITOR

Open Access Article

A model for discrete spindle elongation

Ming Yang and Yixing Wang
Pages 549 - 550
http://dx.doi.org/10.4161/cc.10.3.14760
Abstract | PDF

It is not understood how spindles elongate by discrete lengths of approximately 0.7 µm or multiples of 0.7 µm during anaphase B of the cell cycle. Here, we report that GTP-tubulin segments (newly synthesized segments) on microtubules have discrete lengths of approximately 0.35 µm or multiples of 0.35 µm. Because two sets of microtubules, namely anti-parallel interpolar microtubules, contribute to spindle elongation, the total lengths of the GTP-tubulin segments on their plus ends should be 0.7 µm or multiples of 0.7 µm. Microtubule synthesis in such discrete lengths is thus hypothesized to underlie the discrete lengths in spindle elongation.