Table of Contents

Volume 10, Issue 20

  October 15, 2011

  Pages 3409 - 3610

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 Issue Catalogue (MARC XML)

EDITORIALS: CELL CYCLE FEATURES

Open Access Article

Actomyosin contractililty: Force power drives tumor growth

Michael S. Samuel and Michael F. Olson
Pages 3409 - 3410
http://dx.doi.org/10.4161/cc.10.20.17722
Abstract | PDF

Comment on: Samuel MS et al. Cancer Cell 2011; 19:776-91.

Open Access Article

A self-propelled biological process: Plk1-dependent, product-activated feed-forward mechanism

Jung-Eun Park, Raymond L. Erikson and Kyung S. Lee
Pages 3411 - 3412
http://dx.doi.org/10.4161/cc.10.20.17522
Abstract | Full Text | PDF

Comment on : Park JE, et al. Proc Natl Acad Sci USA 2011; 108:8200-05.

Open Access Article

Essential protein interactions within the replisome regulate DNA replication

Huidong Zhang, Seung-Joo Lee and Charles C. Richardson
Pages 3413 - 3414
http://dx.doi.org/10.4161/cc.10.20.17523
Abstract | PDF

Comment on: Zhang H, et al. Proc Natl Acad Sci USA 2011; 108:9372-7.

Open Access Article

mTOR in podocyte function: Is rapamycin good for diabetic nephropathy?

Min-Kan Lu, Xing-Guo Gong and Kun-Liang Guan
Pages 3415 - 3416
http://dx.doi.org/10.4161/cc.10.20.17686
Abstract | PDF

Comment on: Inoki K, et al. J Clin Invest 2011; 121:2181–2196 and Gödel M, et al. J Clin Invest 2011; 121:2197–2209

Open Access Article

Ribosome biogenesis and p53: Who is regulating whom?

Dragomir B. Krastev and Frank Buchholz
Pages 3417 - 3418
http://dx.doi.org/10.4161/cc.10.20.17687
Abstract | PDF

Comment on: Krastev DB, et al. Nat Cell Biol 2011; 13:809-18.

Open Access Article

(H)if blood stem cells gO₂ sleep: What can wake them up?

Matilda Rehn and Jörg Cammenga
Pages 3419 - 3420
http://dx.doi.org/10.4161/cc.10.20.17690
Abstract | PDF

Comment on: Rehn M, et al. Blood 2011; 118:1534-43.

Open Access Article

Lineage reprogramming: A shortcut to generating functional neurons from fibroblasts

Shane Grealish, Johan Jakobsson and Malin Parmar
Pages 3421 - 3422
http://dx.doi.org/10.4161/cc.10.20.17691
Abstract | PDF

Comment on: Pfisterer U, et al. Proc Natl Sci USA 2011; 108:10343-8.

Open Access Article

A novel role for Activation-induced cytidinedeaminase: Central B-cell tolerance

Masayuki Kuraoka and Garnett Kelsoe
Pages 3423 - 3424
http://dx.doi.org/10.4161/cc.10.20.17693
Abstract | PDF

Comment on: Kuraoka M, et al. Proc Natl Acad Sci USA 2011; 108:11560-5




CELL CYCLE NEWS & VIEWS

Open Access Article

Redundancy in response to DNA damage: The key to protection of genome integrity

Zbigniew Darzynkiewicz
Page 3425
http://dx.doi.org/10.4161/cc.10.20.17525
Abstract | PDF

Comment on: Ciznadija D, et al. Cell Cycle 2011; 10:2714-23.

Open Access Article

Lamins reach out to novel functions in DNA damage repair

Andreas Brachner and Roland Foisner
Page 3426
http://dx.doi.org/10.4161/cc.10.20.17526
Abstract | PDF

Comment on: Redwood AB, et al. Cell Cycle 2011; 10:2550-61.

Open Access Article

New role for Spinophilin in tumor suppression

Ignacio Palmero
Page 3427
http://dx.doi.org/10.4161/cc.10.20.17527
Abstract | PDF

Comment on: Ferrer I, et al. Cell Cycle 2011; 10:2751-62.

Open Access Article

Prostate cancer: JunD, Gadd45a and Gadd45g as therapeutic targets

Dan A. Liebermann and Barbara Hoffman
Page 3428
http://dx.doi.org/10.4161/cc.10.20.17528
Abstract | PDF

Comment on: Zerbini L, et al. Cell Cycle 2011; 10: 2584-92.

Open Access Article

The sweet secrets of p27^kip1 regulation and function in cell migration

Eric Fearon
Page 3429
http://dx.doi.org/10.4161/cc.10.20.17529
Abstract | PDF

Comment on: Nagano Y, et al. Cell Cycle 2011; 10:2593-603.

Open Access Article

p21 regulates the cell cycle…or the other way around?

Juliana Speroni and Vanesa Gottifredi
Page 3430
http://dx.doi.org/10.4161/cc.10.20.17530
Abstract | PDF

Comment on: Ciznadija D, et al. Cell Cycle 2011; 10:2714-23.

Open Access Article

Caveolin-1: Would-be Achilles’ heel of tumor microenvironment?

Saori Furuta, Cyrus M. Ghajar and Mina J. Bissell
Page 3431
http://dx.doi.org/10.4161/cc.10.20.17648
Abstract | PDF

Comment on: Witkiewicz AK, et al. Cell Cycle 2011; 10:1794-809

Open Access Article

Small cell lung cancer: New insights into origins

David MacPherson
Page 3432
http://dx.doi.org/10.4161/cc.10.20.17664
Abstract | PDF

Comment on: Park K, et al. Cell Cycle 2011; 10:2806-15.

Open Access Article

Targeting JunD: A potential strategy to counteract hormone-refractory prostate cancer

Devanand Sarkar, Xiang-Yang Wang and Paul B. Fisher
Page 3433
http://dx.doi.org/10.4161/cc.10.20.17668
Abstract | PDF

Comment on: Zerbini LF, et al. Cell Cycle 2011; 10:2583–91

Open Access Article

Multiple roles of ELG1 with different interactions determine various cellular processes

Jennifer McCulley and Kyungjae Myung
Page 3434
http://dx.doi.org/10.4161/cc.10.20.17670
Abstract | PDF

Comment on: Parnas O, et al. Cell Cycle 2011; 10:2894-903




EXTRA VIEWS

Open Access Article

Cell cycle phosphorylation of mitotic exit network (MEN) proteins

Michele H. Jones, Jamie M. Keck, Catherine C. L. Wong, Tao Xu, John R. Yates and Mark Winey
Pages 3435 - 3440
http://dx.doi.org/10.4161/cc.10.20.17790
Abstract | PDF

Phosphorylation of proteins is an important mechanism used to regulate most cellular processes. Recently, we completed an extensive phosphoproteomic analysis of the core proteins that constitute the Saccharomyces cerevisiae centrosome. Here, we present a study of phosphorylation sites found on the mitotic exit network (MEN) proteins, most of which are associated with the cytoplasmic face of the centrosome. We identified 55 sites on Bfa1, Cdc5, Cdc14 and Cdc15. Eight sites lie in cyclin-dependent kinase motifs (Cdk, S/T-P), and 22 sites are completely conserved within fungi. More than half of the sites were found in centrosomes from mitotic cells, possibly in preparation for their roles in mitotic exit. Finally, we report phosphorylation site information for other important cell cycle and regulatory proteins.

Open Access Article

Translational control by 80S formation and 60S availability: The central role of eIF6, a rate limiting factor in cell cycle progression and tumorigenesis

Daniela Brina, Stefano Grosso, Annarita Miluzio and Stefano Biffo
Pages 3441 - 3446
http://dx.doi.org/10.4161/cc.10.20.17796
Abstract | PDF

Ribosome biogenesis and translation can be simplified as the processes of generating ribosomes and their use for decoding mRNA into a protein. Ribosome biogenesis has been efficiently studied in unicellular organisms like the budding yeast, allowing us a deep and basic knowledge of this process in growing cells. Translation has been modeled in vitro and in unicellular organisms. These studies have given us an important insight into the mechanisms and evolutionarily conserved aspects of ribosome biology. However, we advocate the need of the direct study of these processes in multicellular organisms. Analysis of ribosome biogenesis and translation in vivo in Metazoa and mammalian models is emerging and unveils the unexpected consequences of perturbed ribosome biogenesis and translation. Here, we will describe how one factor, eIF6, plays a crucial role both in the generation of the large ribosomal subunit and its availability for translation. From there, we will make specific conclusions on the physiological relevance of eIF6 in 80S formation, cell cycle progression and disease, raising the point that the control of gene expression may occur at the unexpected level of the large ribosomal subunit. In the future, the modulation of eIF6 binding to the 60S may be pharmacologically exploited to reduce the growth of cancer cells or ameliorate the phenotype of SDS syndrome.

Open Access Article

Insulin resistance due to nutrient excess: Is it a consequence of AMPK downregulation?

Asish K. Saha, X. Julia Xu, Thomas W. Balon, Amanda Brandon, Edward W. Kraegen and Neil B. Ruderman
Pages 3447 - 3451
http://dx.doi.org/10.4161/cc.10.20.17886
Abstract | PDF

It has long been known that excesses of glucose and branched chain amino acids, such as leucine, lead to insulin resistance in skeletal muscle. A recent study in incubated rat muscle suggests that both molecules may do so by virtue of their ability to downregulate the fuel sensing and signaling enzyme AMP-activated protein kinase (AMPK) and activate mTOR/p70S6 kinase (p70S6K) signaling. The results also demonstrated that inhibition of mTOR/p70S6K with rapamycin prevented the development of insulin resistance but had no effect on AMPK activity (Thr172 phosphorylation of its catalytic subunit). In contrast, activation of AMPK by both AICAR and α-lipoic acid led to the phosphorylation of specific molecules that diminished both mTOR/p70S6K signaling and insulin resistance. These findings suggest that downregulation of AMPK precedes mTOR/p70S6K activation in mediating glucose and leucine-induced insulin resistance, although the mechanism by which it does so remains to be determined. Also requiring study is how an excess of the two nutrients leads to AMPK downregulation.

Open Access Article

Bioenergy sensing in the brain: The role of AMP-activated protein kinase in neuronal metabolism, development and neurological diseases

Stephen Amato and Heng-Ye Man
Pages 3452 - 3460
http://dx.doi.org/10.4161/cc.10.20.17953
Abstract | PDF

Bioenergy homeostasis constitutes one of the most crucial foundations upon which other cellular and organismal processes may be executed. AMP-activated protein kinase (AMPK) has been shown to be the key player in the regulation of energy metabolism, and thus is becoming the focus of research on obesity, diabetes and other metabolic disorders. However, its role in the brain, the most energy-consuming organ in our body, has only recently been studied and appreciated. Widely expressed in the brain, AMPK activity is tightly coupled to the energy status at both neuronal and whole-body levels. Importantly, AMPK signaling is intimately implicated in multiple aspects of brain development and function including neuronal proliferation, migration, morphogenesis and synaptic communication, as well as in pathological conditions such as neuronal cell death, energy depletion and neurodegenerative disorders.

Open Access Article

RUNX1 and its understudied role in breast cancer

Kevin A. Janes
Pages 3461 - 3465
http://dx.doi.org/10.4161/cc.10.20.18029
Abstract | PDF

The transcription factor Runt-related transcription factor 1 (RUNX1) is critical for the earliest steps of hematopoiesis. RUNX1 was originally identified as a gene fusion in acute myeloid leukemia (AML) and thus has garnered heavy attention as a tumor suppressor in hematopoietic malignancies. However, RUNX1 is also strongly expressed in breast epithelia and may be misregulated during tumorigenesis. Here, I discuss our recent work implicating RUNX1 in proliferation control during breast epithelial-acinar morphogenesis. My goal is to place these findings in the context of a handful of other reports, which together argue that RUNX1 could act as a tumor suppressor gene in breast cancer. Testing this hypothesis requires focused in vivo studies, because the major commercial platform for global mRNA expression profiling does not reliably reflect RUNX1 levels. Our in vitro results indicate that hyperproliferation in RUNX1-deficient breast epithelia relies on another family of transcription factors, the Forkhead box O (FOXO) proteins. FOXOs could, therefore, represent a synthetic-lethal target for RUNX1-deficient tumors if the hypothesized link to breast cancer is correct.




REVIEWS

Open Access Article

Endocrine pancreas development in zebrafish

Zahra Tehrani and Shuo Lin
Pages 3466 - 3472
http://dx.doi.org/10.4161/cc.10.20.17764
Abstract | PDF

Type 1 diabetes results from the autoimmune destruction of insulin-producing pancreatic β cells. Current efforts to cure diabetes are aimed at replenishing damaged cells by generating a new supply of β cells in vitro. The most promising strategy for achieving this goal is to differentiate embryonic stem (ES) cells by sequentially exposing them to signaling molecules that they would normally encounter in vivo. This approach requires a thorough understanding of the temporal sequence of the signaling events underlying pancreatic β-cell induction during embryonic development. The zebrafish system has emerged as a powerful tool in the study of pancreas development. In this review, we provide a temporal summary of pancreas development in zebrafish with a special focus on the formation of pancreatic β cells.

Open Access Article

Acute lymphoblastic leukemia and developmental biology: A crucial interrelationship

Elena Campos-Sanchez, Amparo Toboso-Navasa, Isabel Romero-Camarero, Marcos Barajas-Diego, Isidro Sánchez-García and César Cobaleda
Pages 3473 - 3486
http://dx.doi.org/10.4161/cc.10.20.17779
Abstract | PDF

The latest scientific findings in the field of cancer research are redefining our understanding of the molecular and cellular basis of the disease, moving the emphasis toward the study of the mechanisms underlying the alteration of the normal processes of cellular differentiation. The concepts best exemplifying this new vision are those of cancer stem cells and tumoral reprogramming. The study of the biology of acute lymphoblastic leukemias (ALLs) has provided seminal experimental evidence supporting these new points of view. Furthermore, in the case of B cells, it has been shown that all the stages of their normal development show a tremendous degree of plasticity, allowing them to be reprogrammed to other cellular types, either normal or leukemic. Here we revise the most recent discoveries in the fields of B-cell developmental plasticity and B-ALL research and discuss their interrelationships and their implications for our understanding of the biology of the disease.




REPORTS

Open Access Article

FBXL2 is a ubiquitin E3 ligase subunit that triggers mitotic arrest

Bill B. Chen, Jennifer R. Glasser, Tiffany A. Coon and Rama K. Mallampalli
Pages 3487 - 3494
http://dx.doi.org/10.4161/cc.10.20.17742
Abstract | PDF

Mitotic progression is regulated by ubiquitin E3 ligase complexes to carefully orchestrate eukaryotic cell division. Here, we show that a relatively new E3 ligase component belonging to the SCF (Skip-Cullin1-F-box protein) E3 ligase family, SCF^FBXL2, impairs cell proliferation by mediating cyclin D3 polyubiquitination and degradation. Both cyclin D3 and FBXL2 colocalize within the centrosome. FBXL2 overexpression led to G₂/M-phase arrest in transformed epithelia, resulting in the appearance of supernumerary centrosomes, tetraploidy and nuclei where condensed chromosomes are arranged on circular monopolar spindles typical of mitotic arrest. RNAi-mediated knockdown of cyclin D3 recapitulated effects of SCF^FBXL2 expression. SCF^FBXL2 impaired the ability of cyclin D3 to associate with centrosomal assembly proteins [Aurora A, polo-like kinase 4 (Plk4), CDK11]. Thus, these results suggest a role for SCF^FBXL2 in regulating the fidelity of cellular division.

Open Access Article

The H2B ubiquitin ligase RNF40 cooperates with SUPT16H to induce dynamic changes in chromatin structure during DNA double-strand break repair

Vijayalakshmi Kari, Andrei Shchebet, Heinz Neumann and Steven A. Johnsen
Pages 3495 - 3504
http://dx.doi.org/10.4161/cc.10.20.17769
Abstract | PDF

Many anticancer therapies function largely by inducing DNA double-strand breaks (DSBs) or altering the ability of cancer cells to repair them. Proper and timely DNA repair requires dynamic changes in chromatin assembly and disassembly characterized by histone H3 lysine 56 acetylation (H3K56ac) and phosphorylation of the variant histone H2AX (γH2AX). Similarly, histone H2B monoubiquitination (H2Bub1) functions in DNA repair, but its role in controlling dynamic changes in chromatin structure following DSBs and the histone chaperone complexes involved remain unknown. Therefore, we investigated the role of the H2B ubiquitin ligase RNF40 in the DSB response. We show that RNF40 depletion results in sustained H2AX phosphorylation and a decrease in rapid cell cycle checkpoint activation. Furthermore, RNF40 knockdown resulted in decreased H3K56ac and decreased recruitment of the facilitates chromatin transcription (FACT) complex to chromatin following DSB. Knockdown of the FACT component suppressor of Ty homolog-16 (SUPT16H) phenocopied the effects of RNF40 knockdown on both γH2AX and H3K56ac following DSB induction. Consistently, both RNF40 and SUPT16H were required for proper DNA end resection and timely DNA repair, suggesting that H2Bub1 and FACT cooperate to increase chromatin dynamics, which facilitates proper checkpoint activation and timely DNA repair. These results provide important mechanistic insights into the tumor suppressor function of H2Bub1 and provide a rational basis for pursuing H2Bub1-based therapies in conjunction with traditional chemo- and radiotherapy.

Open Access Article

Effects of conditional depletion of topoisomerase II on cell cycle progression in mammalian cells

Ruth E. Gonzalez, Chang-Uk Lim, Kelly Cole, Christine Hanko Bianchini, Gary P. Schools, Brian E. Davis, Ikuo Wada, Igor B. Roninson and Eugenia V. Broude
Pages 3505 - 3514
http://dx.doi.org/10.4161/cc.10.20.17778
Abstract | PDF

Topoisomerase II (Topo II) that decatenates newly synthesized DNA is targeted by many anticancer drugs. Some of these drugs stabilize intermediate complexes of DNA with Topo II and others act as catalytic inhibitors of Topo II. Simultaneous depletion of Topo IIα and Topo IIβ, the two isoforms of mammalian Topo II, prevents cell growth and normal mitosis, but the role of Topo II in other phases of mammalian cell cycle has not yet been elucidated. We have developed a derivative of p53-suppressed human cells with constitutive depletion of Topo IIβ and doxycycline-regulated conditional depletion of Topo IIα. The effects of Topo II depletion on cell cycle progression were analyzed by time-lapse video microscopy, pulse-chase flow cytometry and mitotic morphology. Topo II depletion increased the duration of the cell cycle and mitosis, interfered with chromosome condensation and sister chromatid segregation and led to frequent failure of cell division, ending in either cell death or restitution of polyploid cells. Topo II depletion did not change the rate of DNA replication but increased the duration of G₂. These results define the effects of decreased Topo II activity, rather than intermediate complex stabilization, on the mammalian cell cycle.

Open Access Article

MG132 inhibition of proteasome blocks high-dose UV irradiation-induced apoptosis

Ling Zhang, Jennifer J. Hu and Feng Gong
Pages 3515 - 3518
http://dx.doi.org/10.4161/cc.10.20.17789
Abstract | PDF

The 26S proteasome, a multicatalytic enzyme complex, is the main intracellular proteolytic system involved in the degradation of ubiquitinated proteins. The ability of proteasome inhibitors to induce apoptosis has been exploited in the recent development of chemotherapeutic agents. Here, we show that inhibition of proteasome by MG132 blocks DNA damage-induced apoptosis. Blockage of apoptosis by MG132 correlates with p53 stabilization and upregulation of p21/WAF1, a p53 transcriptional target. Surprisingly, in the absence of MG132, robust apoptosis induced by a high dose of UV irradiation correlate with rapid p53 degradation. This is in sharp contrast to p53 stabilization when cells were exposed to lower levels of UV irradiation. Our findings highlight a scenario in which severe UV damage can induce rapid p53 degradation by the proteasome. Importantly, these data suggest that the 26S proteasome plays a key role in promoting apoptosis induced by high doses of UV irradiation.

Open Access Article

Molecular cloning and characterization of mitogen-activated protein kinase 2 in Toxoplasma gondii

Huan Huang, Yan Fen, Yi Bao, Hattie Lee, Michael P. Lisanti, Herbert Tanowitz and Louis M Weiss
Pages 3519 - 3526
http://dx.doi.org/10.4161/cc.10.20.17791
Abstract | PDF

Mitogen-activated protein kinase (MAPK) pathways are major signal transduction systems by which eukaryotic cells convert environmental cues to intracellular events, such as cell proliferation and differentiation. Toxoplasma gondii is an obligate intracellular protozoan that is both a human and animal pathogen. This Apicomplexan causes significant morbidity and mortality in immune-competent and immune-compromised hosts. In humans, the most common manifestations of T. gondii infections are chorioretinitis in congenital infection and encephalitis in immune-compromised patients, such as patients with advanced AIDS. We have identified a T. gondii homolog of the MAPK family that we have called TgMAPK2. Sequence analyses demonstrated that TgMAPK2 has homology with lower eukaryotic ERK2 but has significant differences from mammalian ERK2. TgMAPK2 has an open reading frame of 2,037 bp, 678 amino acids, and its molecular weight is 73.1 kDa. It contains the typical 12 subdomains of a MAPK and has a TDY motif in the dual phosphorylation and activation subdomains. This suggests that TgMAPK2 may play an important role in stress response. recombinant TgMAPK2 was catalytically active and was not inhibited by a human ERK2 inhibitor, FR180204. A partial TgMAPK2 lacking the ATP-binding motifs GxGxxGxV was successfully regulated by a ligand-controlled destabilization domain (ddFKBP) expression vector system in T. gondii. Since TgMAPK2 is significantly different from its mammalian counterpart, it may be useful as a drug target. This work establishes a foundation for further study for this unique kinase.

Open Access Article

Generation of a set of conditional analog-sensitive alleles of essential protein kinases in the fission yeast Schizosaccharomyces pombe

Lubos Cipak, Chao Zhang, Ines Kovacikova, Cornelia Rumpf, Eva Miadokova, Kevan M. Shokat and Juraj Gregan
Pages 3527 - 3532
http://dx.doi.org/10.4161/cc.10.20.17792
Abstract | Full Text | PDF

The genome of the fission yeast Schizosaccharomyces pombe encodes for 17 protein kinases that are essential for viability. Studies of the essential kinases often require the use of mutant strains carrying conditional alleles. To inactivate these kinases conditionally, we applied a recently developed chemical genetic strategy. The mutation of a single residue in the ATP-binding pocket confers sensitivity to small-molecule inhibitors, allowing for specific inactivation of the modified kinase. Using this approach, we constructed conditional analog-sensitive alleles of 13 essential protein kinases in the fission yeast S. pombe.

Open Access Article

Modulated microtubule dynamics enable Hklp2/Kif15 to assemble bipolar spindles

Stefan Florian and Thomas U. Mayer
Pages 3533 - 3544
http://dx.doi.org/10.4161/cc.10.20.17817
Abstract | PDF

Activity of the sliding motor Eg5 and coordinated microtubule dynamics are both essential for mitotic spindle pole separation. It is still a matter of controversy if changes in microtubule dynamics can compensate inhibition of Eg5 activity and re-enable bipolarization. Using a consistent live cell-imaging approach, we show that perturbation of microtubule dynamics can compensate inhibition of Eg5 through a spindle formation process reminiscent of meiosis: In Eg5-inhibited mammalian somatic cells, alteration of microtubule dynamics through depletion of TOGp or low doses of nocodazole induces the formation of multiple acentrosomal spindle poles which pass through an intermediate multipolar state followed by bipolarization. Pole separation depends on Hklp2/Kif15, an otherwise dispensable plus end-directed spindle motor and results in spindles with two centrosomal poles. Once bipolar, spindles do not rely on altered microtubule dynamics to maintain their bipolarity anymore and are functional in chromosome segregation. We conclude that altered microtubule dynamics enable Hklp2/Kif15 to replace Eg5 in pole separation through a mechanism involving the formation of acentrosomal poles. Our observations suggest that combination chemotherapy regimens involving microtubule-targeting drugs and Eg5 inhibitors might be less effective than expected.

Open Access Article

Differential epithelium DNA damage response to ATM and DNA-PK pathway inhibition in human prostate tissue culture

Zhewei Zhang, Zhiming Yang, Sari Jäämaa, Hester Liu, Laxmi G. Pellakuru, Tsuyoshi Iwata, Taija M. af Hällström, Angelo M. De Marzo and Marikki Laiho
Pages 3545 - 3553
http://dx.doi.org/10.4161/cc.10.20.17841
Abstract | PDF

The ability of cells to respond and repair DNA damage is fundamental for the maintenance of genomic integrity. Ex vivo culturing of surgery-derived human tissues has provided a significant advancement to assess DNA damage response (DDR) in the context of normal cytoarchitecture in a non-proliferating tissue. Here, we assess the dependency of prostate epithelium DDR on ATM and DNA-PKcs, the major kinases responsible for damage detection and repair by nonhomologous end-joining (NHEJ), respectively. DNA damage was caused by ionizing radiation (IR) and cytotoxic drugs, cultured tissues were treated with ATM and DNA-PK inhibitors, and DDR was assessed by phosphorylation of ATM and its targets H2AX and KAP1, a heterochromatin binding protein. Phosphorylation of H2AX and KAP1 was fast, transient and fully dependent on ATM, but these responses were moderate in luminal cells. In contrast, DNA-PKcs was phosphorylated in both luminal and basal cells, suggesting that DNA-PK-dependent repair was also activated in the luminal cells despite the diminished H2AX and KAP1 responses. These results indicate that prostate epithelial cell types have constitutively dissimilar responses to DNA damage. We correlate the altered damage response to the differential chromatin state of the cells. These findings are relevant in understanding how the epithelium senses and responds to DNA damage.

Open Access Article

Dissection of cell context-dependent interactions between HBx and p53 family members in regulation of apoptosis: A role for HBV-induced HCC

Susanne Knoll, Katharina Fürst, Saijo Thomas, Sergio Villanueva Baselga, Anja Stoll, Stephanie Schaefer and Brigitte M. Pützer
Pages 3554 - 3565
http://dx.doi.org/10.4161/cc.10.20.17856
Abstract | PDF

Chronic hepatitis B virus (HBV) infection is the major risk for hepatocellular carcinomas (HCC). HBV X protein (HBx) and p53 tumor suppressor family interactions may be crucial for HCC induction. We compared p53 and p73 interactions with HBx in normal and HCC tumor cell lines differing in their p53 status. In the latter, HBx was pro-apoptotic but exhibited opposite effects in non-tumor cells. In these normal cells, p53 and p73 were retained in the cytoplasm. In hepatoma cells, however, HBx led to nuclear translocation of p53 and p73, followed by enhanced transactivation of p53-dependent promoters. The nuclear transfer of p53, but not of p73, was abrogated by protein kinase C inhibitor Gö6976. HBx overexpression in HCC cells led to strong p53 phosphorylation at Ser15, but not in non-tumor cells. Our results define ATM kinase as mediator for HBx-induced p53 phosphorylation. While HBx promotes cell death in p53/p73-positive hepatoma cells also in presence of increased levels of the oncogenic ΔTAp73 isoform, it significantly potentiates ΔTAp73-mediated proliferation and malignant transformation of fibroblasts. Our data suggest that prevention of apoptosis in normal cells by HBx through inhibition of pro-apoptotic p53 family members via direct interaction and coaction with anti-apoptotic ΔTAp73 seems to be the key element in the decision in favor of cell survival. The complex cell context-dependent interactions between p53 family members and HBx in the regulation of apoptosis may be essential in HBV-induced HCC and anticancer therapy.

Open Access Article

Identification and modeling of a phosphatase-like domain in a tRNA 2′-O-ribosyl phosphate transferase Rit1p

Anna Czerwoniec and Janusz M. Bujnicki
Pages 3566 - 3570
http://dx.doi.org/10.4161/cc.10.20.17857
Abstract | Full Text | PDF

Cytoplasmic initiator tRNAs from plants and fungi are excluded from participating in translational elongation by the presence of a unique 2'-phosphoribosyl modification of purine 64, introduced posttranscriptionally by the enzyme Rit1p. Members of the Rit1p family show no obvious similarity to other proteins or domains, there is no structural information available to guide experimental analyses, and the mechanism of action of this enzyme remains a mystery. Using protein fold recognition, we identified a phosphatase-like domain in the C-terminal part of Rit1p. A comparative model of the C-terminal domain was constructed and used to predict the function of conserved residues and to propose the mechanism of action of Rit1p. The model will facilitate experimental analyses of Rit1p and its interactions with the initiator tRNA substrate.

Open Access Article

Networks of intergenic long-range enhancers and snpRNAs drive castration-resistant phenotype of prostate cancer and contribute to pathogenesis of multiple common human disorders

Anna B. Glinskii, Shuang Ma, Jun Ma, Denise Grant, Chang-Uk Lim, Ian Guest, Stewart Sell, Ralph Buttyan and Gennadi V. Glinsky
Pages 3571 - 3597
http://dx.doi.org/10.4161/cc.10.20.17842
Abstract | PDF

The mechanistic relevance of intergenic disease-associated genetic loci (IDAGL) containing highly statistically significant disease-linked SNPs remains unknown. Here, we present experimental and clinical evidence supporting the importantance of the role of IDAGL in human diseases. A targeted RT-PCR screen coupled with sequencing of purified PCR products detects widespread transcription at multiple IDAGL and identifies 96 small noncoding trans-regulatory RNAs of ~100–300 nt in length containing SNPs (snpRNAs) associated with 21 common disorders. Multiple independent lines of experimental evidence support functionality of snpRNAs by documenting their cell type-specific expression and evolutionary conservation of sequences, genomic coordinates and biological effects. Chromatin state signatures, expression profiling experiments and luciferase reporter assays demonstrate that many IDAGL are Polycomb-regulated long-range enhancers. Expression of snpRNAs in human and mouse cells markedly affects cellular behavior and induces allele-specific clinically relevant phenotypic changes: NLRP1-locus snpRNAs rs2670660 exert regulatory effects on monocyte/macrophage transdifferentiation, induce prostate cancer (PC) susceptibility snpRNAs and transform low-malignancy hormone-dependent human PC cells into highly malignant androgen-independent PC. Q-PCR analysis and luciferase reporter assays demonstrate that snpRNA sequences represent allele-specific “decoy” targets of microRNAs that function as SNP allele-specific modifiers of microRNA expression and activity. We demonstrate that trans-acting RNA molecules facilitating resistance to androgen depletion (RAD) in vitro and castration-resistant phenotype (CRP) in vivo of PC contain intergenic 8q24-locus SNP variants (rs1447295; rs16901979; rs6983267) that were recently linked with increased risk of PC. Q-PCR analysis of clinical samples reveals markedly increased and highly concordant (r = 0.896; p < 0.0001) snpRNA expression levels in tumor tissues compared with the adjacent normal prostate [122-fold and 45-fold in Gleason 7 tumors (p = 0.03); 370-fold and 127-fold in Gleason 8 tumors (p = 0.0001) for NLRP1-locus and 8q24-locus snpRNAs, respectively]. Our experiments indicate that RAD and CR phenotype of human PC cells can be triggered by ncRNA molecules transcribed from the NLRP1-locus intergenic enhancer at 17p13 and by downstream activation of the 8q24-locus snpRNAs. Our results define the IDAGL at 17p13 and 8q24 as candidate regulatory loci of RAD and CR phenotypes of PC, reveal previously unknown molecular links between the innate immunity/inflammasome system and development of hormone-independent PC and identify novel molecular and genetic targets with diagnostic and therapeutic potentials, exploration of which should be highly beneficial for personalized clinical management of PC.

Open Access Article

Chk2 deficiency in Myc overexpressing lymphoma cells elicits a synergistic lethal response in combination with PARP inhibition

Andreas Höglund, Kerstin Strömvall, Yongmei Li, Linus Plym Forshell and Jonas A. Nilsson
Pages 3598 - 3607
http://dx.doi.org/10.4161/cc.10.20.17887
Abstract | Full Text | PDF

Myc is a transcription factor frequently found deregulated in human cancer. The Myc-mediated cellular transformation process is associated with fast proliferative cells and inherent genomic instability, giving rise to malignant, invasive neoplasms with poor prognosis for survival. Transcription-independent functions of Myc include stimulation of replication. Excessive Myc expression stimulates a replication-associated DNA damage response that signals via the phosphoinositide-3-kinase (PI3K)-related protein kinases (PIKKs) ATM and ATR. These, in turn, activate the DNA damage transducers Chk1 and Chk2. Here, we show that Myc can stimulate Chek2 transcript indirectly in vitro as well as in B cells of λ-Myc transgenic mice or in the intestine of Apc^Min mice. However, Chk2 is dispensable for Myc’s ability to transform cells in vitro and for the survival of established lymphoma cells from λ-Myc transgenic mice. Chk2 deficiency induces polyploidy and slow growth, but the cells are viable and protected against DNA damage. Furthermore, inhibition of both Chk1/Chk2 with AZD7762 induces cell death and significantly delays disease progression of transplanted lymphoma cells in vivo. DNA damage recruits PARP family members to sites of DNA breaks that, in turn, facilitate the induction of DNA repair. Strikingly, combining Chk2 and PARP inhibition elicits a synergistic lethal response in the context of Myc overexpression. Our data indicates that only certain types of chemotherapy would give rise to a synergistic lethal response in combination with specific Chk2 inhibitors, which will be important if Chk2 inhibitors enter the clinic.




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Open Access Article

mTOR protein localization is cell cycle-regulated

Margit Rosner and Markus Hengstschläger
Pages 3608 - 3610
http://dx.doi.org/10.4161/cc.10.20.17855
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