Table of Contents

Volume 11, Issue 13

  July 1, 2012

  Pages 2409 - 2580

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 Issue Catalogue (MARC XML)

EDITORIALS: CELL CYCLE FEATURES

Open Access Article

Regulation of USP7/HAUSP in response to DNA damage: Yet another role for ATM

Svetlana V. Khoronenkova and Grigory L. Dianov
Pages 2409 - 2410
http://dx.doi.org/10.4161/cc.20800
Abstract | Full Text | PDF

Comment on: Khoronenkova SV, et al. Mol Cell 2012; 45:801-13.

Open Access Article

Human pluripotency: A difficult state to make smart choices

Shravanti Rampalli and Mickie Bhatia
Pages 2411 - 2412
http://dx.doi.org/10.4161/cc.20801
Abstract | Full Text | PDF

Comment on: Hong SH, et al. Cell Stem Cell 2011; 9:24-36.

Open Access Article

HIF-1 and its antagonist Cited2: Regulators of HSC quiescence

Jinwei Du and Yu-Chung Yang
Pages 2413 - 2414
http://dx.doi.org/10.4161/cc.20803
Abstract | Full Text | PDF

Comment on: Du J, et al. Blood 2012; 119:2789-98.

Open Access Article

A way to invade: A story of ErbB2 and lysosomes

Bo Rafn and Tuula Kallunki
Pages 2415 - 2416
http://dx.doi.org/10.4161/cc.20860
Abstract | Full Text | PDF

Comment on: Rafn B, et al. Mol Cell 2012; 45:764-76.




CELL CYCLE NEWS & VIEWS

Open Access Article

Inhibition of IκB kinase in Notch signaling activates FOXO3a

Keqiang Ye
Page 2417
http://dx.doi.org/10.4161/cc.21067
Abstract | Full Text | PDF

Comment on: Buontempo F, et al. Cell Cycle 2012; 11:2467-75.

Open Access Article

One stone, two birds: CDK9-directed activation of UBE2A regulates monoubiquitination of both H2B and PCNA

Hui Zhang and David S. Yu
Page 2418
http://dx.doi.org/10.4161/cc.21068
Abstract | Full Text | PDF

Comment on: Shchebet A, et al. Cell Cycle 2012; 11:2122-7.

Open Access Article

Osh6 links yeast vacuolar functions to lifespan extension and TOR

Daniel Wuttke and João Pedro de Magalhães
Page 2419
http://dx.doi.org/10.4161/cc.21069
Abstract | Full Text | PDF

Comment on: Gebre S, et al. Cell Cycle 2012; 11:2176-88.

Open Access Article

Creative destruction of the microtubule array

Peter W. Baas and Wenqian Yu
Pages 2420 - 2421
http://dx.doi.org/10.4161/cc.21070
Abstract | Full Text | PDF

Comment on: Mukherjee S, et al. Cell Cycle 2012; 11:2359-66.




EXTRA VIEWS

Polo-like kinase 1 directs the AMPK-mediated activation of myosin regulatory light chain at the cytokinetic cleavage furrow independently of energy balance

Alejandro Vazquez-Martin, Sílvia Cufí, Cristina Oliveras-Ferraros and Javier A. Menendez
Pages 2422 - 2426
http://dx.doi.org/10.4161/cc.20438
Abstract | Full Text | PDF

It has been recently proposed that AMP-activated protein kinase (AMPK) might indirectly promote the phosphorylation of MRLC (myosin II regulatory light chain) at Ser19 to regulate the transition from metaphase to anaphase and the completion of cytokinesis. Although these findings provide biochemical support for our earlier observations showing that the active form of the α catalytic AMPK subunit associates dynamically with essential mitotic regulators, several important issues remained unexplored. Does glucose starvation alter the ability of AMPK to bind to the mitotic apparatus and travel from centrosomes to the spindle midzone during mitosis and cytokinesis? Does AMPK activate MRLC exclusively at the cleavage furrow during cytokinesis? What is the mitosis-specific stimulus that activates the mito-cytokinetic AMPK/MRLC axis regardless of energy deprivation? First, we confirm that exogenous glucose deprivation fails to alter the previously described distribution of phospho-AMPKα^Thr172 in all of the mitotic phases and does not disrupt its apparent association with the mitotic spindle and other structures involved in cell division. Second, we establish for the first time that phospho-AMPKα^Thr172 colocalizes exclusively with Ser19-phosphorylated MRLC at the cleavage furrow of dividing cells, a previously unvisualized interaction between phospho-AMPKα^Thr172 and phospho-MRLC^Ser19 that occurs in cleavage furrows, intercellular bridges and the midbody during cell division that appears to occur irrespective of glucose availability. Third, we reveal for the first time that the inhibition of AMPK mitotic activity in response to PLK1 inhibition completely prevents the co-localization of phospho-AMPKα^Thr172 and phospho-MRLC^Ser19 during the final stages of cytokinesis and midbody ring formation. Because PLK1 inhibition efficiently suppresses the AMPK-mediated activation of MRLC at the cytokinetic cleavage furrow, we propose a previously unrecognized role for AMPK in ensuring that cytokinesis occurs at the proper place and time by establishing a molecular dialog between PLK1 and MRLC in an energy-independent manner.

NK cells, hypoxia and trophoblast cell differentiation

Damayanti Chakraborty, M.A. Karim Rumi and Michael J. Soares
Pages 2427 - 2430
http://dx.doi.org/10.4161/cc.20542
Abstract | Full Text | PDF

Hemochorial placentation is characterized by extensive remodeling of the maternal vasculature, converting them to flaccid low resistance vessels. This process greatly facilitates exchange of nutrients and gases between the mother and the fetus. Two key modulators that orchestrate these vascular changes have been identified at the maternal fetal interface, natural killer (NK) cells and invasive trophoblast cells. Hypoxia-inducible factor (HIF) transcription factors direct cellular responses to low oxygen, influencing trophoblast lineage commitment and promoting development of the invasive trophoblast lineage. This short review focuses on role of NK cells on uterine spiral artery development and subsequent modulation of oxygen tensions at the maternal fetal interface.

Open Access Article

Differential regulation of embryonic and adult β cell replication

Uma Gunasekaran, Courtney W. Hudgens, Brian T. Wright, Matthew F. Maulis and Maureen Gannon
Pages 2431 - 2442
http://dx.doi.org/10.4161/cc.20545
Abstract | Full Text | PDF

Diabetes results from an inadequate functional β cell mass, either due to autoimmune destruction (Type 1 diabetes) or insulin resistance combined with β cell failure (Type 2 diabetes). Strategies to enhance β cell regeneration or increase cell proliferation could improve outcomes for patients with diabetes. Research conducted over the past several years has revealed that factors regulating embryonic β cell mass expansion differ from those regulating replication of β cells post-weaning. This article aims to compare and contrast factors known to control embryonic and postnatal β cell replication. In addition, we explore the possibility that connective tissue growth factor (CTGF) could increase adult β cell replication. We have already shown that CTGF is required for embryonic β cell proliferation and is sufficient to induce replication of embryonic β cells. Here we examine whether adult β cell replication and expansion of β cell mass can be enhanced by increased CTGF expression in mature β cells.




REVIEWS

Phospho-specific Smad3 signaling: Impact on breast oncogenesis

Elizabeth Tarasewicz and Jacqueline S. Jeruss
Pages 2443 - 2451
http://dx.doi.org/10.4161/cc.20546
Abstract | Full Text | PDF

Members of the TGFβ superfamily are known to exert a myriad of physiologic and pathologic growth controlling influences on mammary development and oncogenesis. In epithelial cells, TGFβ signaling inhibits cell growth through cytostatic and pro-apoptotic activities but can also induce cancer cell EMT and, thus, has a dichotomous role in breast cancer biology. Mechanisms governing this switch are the subject of active investigation. Smad3 is a critical intracellular mediator of TGFβ signaling regulated through phosphorylation by the TGFβ receptor complex at the C terminus. Smad3 is also a substrate for several other kinases that phosphorylate additional sites within the Smad protein. This discovery has expanded the understanding of the significance and complexity of TGFβ signaling through Smads. This review highlights recent advances revealing the critical role of phospho-specific Smad3 in malignancy and illustrates the potential prognostic and therapeutic impact of Smad3 phospho-isoforms in breast cancer.

Identification of novel metastasis suppressor signaling pathways for breast cancer

Andy J. Minn, Elena Bevilacqua, Jieun Yun and Marsha Rich Rosner
Pages 2452 - 2457
http://dx.doi.org/10.4161/cc.20624
Abstract | Full Text | PDF

Cancer lethality is mainly caused by metastasis. Therefore, understanding the nature of the genes involved in this process has become a priority. Given the heterogeneity of mutations in cancer cells, considerable focus has been directed toward characterizing metastasis genes in the context of relevant signaling pathways rather than treating genes as independent and equal entities. One signaling cascade implicated in the regulation of cell growth, invasion and metastasis is the MAP kinase pathway. Raf kinase inhibitory protein (RKIP) functions as an inhibitor of the MAP kinase pathway and is a metastasis suppressor in different cancer models. By utilizing statistical analysis of clinical data integrated with experimental validation, we recently identified components of the RKIP signaling pathway relevant to breast cancer metastasis. Using the RKIP pathway as an example, we show how prior biological knowledge can be efficiently combined with genome-wide patient data to identify gene regulatory mechanisms that control metastasis.




REPORTS

The histone acetyltransferase PCAF regulates p21 transcription through stress-induced acetylation of histone H3

Ian M. Love, Pedja Sekaric, Dingding Shi, Steven R. Grossman and Elliot J. Androphy
Pages 2458 - 2466
http://dx.doi.org/10.4161/cc.20864
Abstract | Full Text | PDF

The activity of p53 as a tumor suppressor primarily depends on its ability to transactivate specific target genes in response to genotoxic and other potentially mutagenic stresses. Several histone acetyl transferases (HATs), including p300, CBP, PCAF and GCN5 have been implicated in the activation of p53-dependent transcription of the cyclin-dependent kinase (cdk) inhibitor p21 as well as other target genes. Here we show that PCAF, but not CBP or p300, is a critical regulator of p53-dependent p21 expression in response to multiple p53-activating stresses. PCAF was required for the transcriptional activation of p21 in response to exogenous p53 in p53-null cells, nutlin-3, DNA damaging agents and p14ARF expression, suggesting a broad requirement for PCAF in p53 signaling to p21 after stress. Importantly, cells lacking PCAF failed to undergo cell cycle arrest in response to nutlin-3 treatment or p14ARF expression, consistent with a physiologically important role for PCAF in this p53 function. Surprisingly, the role for PCAF in induction of p21 was independent of p53 lysine 320 acetylation, a previously suggested target of PCAF-mediated acetylation. Though p21 promoter occupancy by p53 was not altered by PCAF knockdown, activation of p21 transcription required an intact PCAF HAT domain, and induction of chromatin marks acetyl-H3K9 and acetyl-H3K14 at the p21 promoter by p53 was dependent upon physiologic levels of PCAF. Together, our experiments indicate that PCAF is required for stress-responsive histone 3 acetylation at the p21 promoter, p53-directed transcription of p21 and the resultant growth arrest.

Activity of the selective IκB kinase inhibitor BMS-345541 against T-cell acute lymphoblastic leukemia: Involvement of FOXO3a

Francesca Buontempo, Francesca Chiarini, Daniela Bressanin, Giovanna Tabellini, Fraia Melchionda, Andrea Pession, Milena Fini, Luca M. Neri, James A. McCubrey and Alberto M. Martelli
Pages 2467 - 2475
http://dx.doi.org/10.4161/cc.20859
Abstract | Full Text | PDF

Several lines of evidence suggest that the IκB kinase (IKK)/nuclear factor-κB (NFκB) axis is required for viability of leukemic cells and is a predictor of relapse in T-cell acute lymphoblastic leukemia (T-ALL). Moreover, many anticancer agents induce NFκB nuclear translocation and activation of its target genes, which counteract cellular resistance to chemotherapeutic drugs. Therefore, the design and the study of IKK-specific drugs is crucial to inhibit tumor cell proliferation and to prevent cancer drug-resistance. Here, we report the anti-proliferative effects induced by BMS-345541 (a highly selective IKK inhibitor) in three Notch1-mutated T-ALL cell lines and in T-ALL primary cells from pediatric patients. BMS-345541 induced apoptosis and an accumulation of cells in the G₂/M phase of the cell cycle via inhibition of IKK/NFκB signaling. We also report that T-ALL cells treated with BMS-345541 displayed nuclear translocation of FOXO3a and restoration of its functions, including control of p21^Cip1 expression levels. We demonstrated that FOXO3a subcellular re-distribution is independent of AKT and ERK 1/2 signaling, speculating that in T-ALL the loss of FOXO3a tumor suppressor function could be due to deregulation of IKK, as has been previously demonstrated in other cancer types.

It is well known that, differently from p53, FOXO3a mutations have not yet been found in human tumors, which makes therapeutics activating FOXO3a more appealing than others. For these features, BMS-345541 could be used alone or in combination with traditional therapies in the treatment of T-ALL.

Separase-dependent cleavage of pericentrin B is necessary and sufficient for centriole disengagement during mitosis

Kwanwoo Lee and Kunsoo Rhee
Pages 2476 - 2485
http://dx.doi.org/10.4161/cc.20878
Abstract | Full Text | PDF

Centriole disengagement is considered an essential step for licensing a new round of centriole duplication in the next cell cycle. Separase is critical for centriole disengagement. Here, we showed that pericentrin B (PCNTB) is specifically cleaved by separase at the exit of mitosis. The cleavage-resistant PCNTB mutant blocks the centriole disengagement and duplication. We also observed that an artificial cleavage of PCNTB during M phase induced premature disengagement of centrioles. Based on these results, we concluded that the separase-dependent cleavage of PCNTB is necessary and sufficient for centriole disengagement during mitosis.

Lin28 regulates HER2 and promotes malignancy through multiple mechanisms

Chen Feng, Veronique Neumeister, Wei Ma, Jie Xu, Lingeng Lu, Jennifer Bordeaux, Nita J. Maihle, David L. Rimm and Yingqun Huang
Pages 2486 - 2494
http://dx.doi.org/10.4161/cc.20893
Abstract | Full Text | PDF

The RNA binding protein Lin28 and its paralog Lin28B are associated with advanced human malignancies. Blocking the biogenesis of let-7 miRNA, a tumor suppressor, by Lin28/Lin28B has been thought to underlie their roles in cancer. Here we report that the mRNA for the human epidermal growth factor receptor 2 (HER2), a HER-family receptor tyrosine kinase known to play a critical role in cell proliferation and survival and also a major therapeutic target in breast cancer, is among several targets of Lin28 regulation. We show that Lin28 stimulates HER2 expression at the posttranscriptional level, and that enforced Lin28 expression promotes cancer cell growth via multiple mechanisms. Consistent with its pleiotropic role in regulating gene expression, Lin28 overexpression in primary breast tumors is a powerful predictor of poor prognosis, representing the first report on the impact of Lin28 expression on clinical outcome in human cancer. While revealing another layer of regulation of HER2 expression in addition to gene amplification, our studies also suggest novel mechanistic insights linking Lin28 expression to disease outcome and imply that targeting multiple pathways is a common mechanistic theme of Lin28-mediated regulation in cancer.

MiR-138 suppressed nasopharyngeal carcinoma growth and tumorigenesis by targeting the CCND1 oncogene

Xia Liu, Xiao-Bin Lv, Xiao-Pai Wang, Yi Sang, Shuangbing Xu, Kaishun Hu, Mansi Wu, Yi Liang, Pan Liu, Jianjun Tang, Wen-Hua Lu, Qi-Sheng Feng, Li-Zhen Chen, Chao-Nan Qian, Jin-Xin Bei, Tiebang Kang and Yi-Xin Zeng
Pages 2495 - 2506
http://dx.doi.org/10.4161/cc.20898
Abstract | Full Text | PDF

The microRNA miR-138 is dysregulated in several human cancers, but the underlying mechanism remains largely unknown. Here, we report that miR-138 is commonly underexpressed in nasopharyngeal carcinoma (NPC) specimens and NPC cell lines. The ectopic expression of miR-138 dramatically suppressed cell proliferation and colony formation in vitro and inhibited tumorigenesis in vivo. Moreover, we identified the cyclin D1 (CCND1) gene as a novel direct target of miR-138. In consistent with the knocked-down expression of CCND1, overexpression of miR-138 inhibited cell growth and cell cycle progression in NPC cells. Furthermore, CCND1 was widely upregulated in NPC tumors, and its mRNA levels were inversely correlated with miR-138 expression. Taken together, our findings suggest that miR-138 might be a tumor suppressor in NPC, which is exerted partially by inhibiting CCND1 expression. The identification of functional miR-138 in NPC and its direct link to CCND1 might provide good candidates for developing diagnostic markers and therapeutic applications for NPC.

Combined inhibition of Chk1 and Wee1: In vitro synergistic effect translates to tumor growth inhibition in vivo

Laura Carrassa, Rosaria Chilà, Monica Lupi, Francesca Ricci, Cinzia Celenza, Marco Mazzoletti, Massimo Broggini and Giovanna Damia
Pages 2507 - 2517
http://dx.doi.org/10.4161/cc.20899
Abstract | Full Text | PDF

Targeting Chk1 protein kinase can enhance the antitumor effects of radio- and chemotherapy. Recent evidence disclosed a role of Chk1 in unperturbed cell proliferation and survival, implying that Chk1 inhibitors could also be effective as single agents in tumors with a specific genetic background. To identify genes in synthetic lethality with Chk1, we did a high-throughput screening using a siRNA library directed against 719 human protein kinases in the human ovarian cancer cell line OVCAR-5, resistant to Chk1 inhibitors. Wee1 tyrosine kinase was the most significant gene in synthetic lethality with Chk1. Treatment with non-toxic concentrations of a Chk1 inhibitor (PF-00477736) and a Wee1 inhibitor (MK-1775) confirmed the marked synergistic effect in various human cancer cell lines (breast, ovarian, colon, prostate), independently of the p53 status. Detailed molecular analysis showed that the combination caused cancer cells to undergo premature mitosis before the end of DNA replication, with damaged DNA leading to cell death partly by apoptosis. In vivo treatment of mice bearing OVCAR-5 xenografts with the combination of Chk1 and Wee1 inhibitors led to greater tumor growth inhibition than with the inhibitors used as single agents with no toxicity. These data provide a strong rationale for the clinical investigation of the combination of a Chk1 and a Wee1 inhibitor.

Combination of gastrin-releasing peptide antagonist with cytotoxic agents produces synergistic inhibition of growth of human experimental colon cancers

Ferenc G. Rick, Stefan Buchholz, Andrew V. Schally, Luca Szalontay, Awtar Krishan, Christian Datz, Andreas Stadlmayr, Elmar Aigner, Roberto Perez, Stephan Seitz, Norman L. Block and Florian Hohla
Pages 2518 - 2525
http://dx.doi.org/10.4161/cc.20900
Abstract | Full Text | PDF

We investigated the efficacy of a powerful antagonist of bombesin/gastrin-releasing peptide (BN/GRP) RC-3940-II administered as a single agent or in combination with cytotoxic agents on the growth of HT-29, HCT-116 and HCT-15 human colon cancer in vitro and in vivo. GRP-receptor mRNA and protein were found in all three cell lines tested. Exposure of HT-29 cells to 10 μM RC-3940-II led to an increase in the number of cells blocked in S phase and G₂/M and cells with lower G₀/G₁ DNA content. Similar changes on the cell cycle traverse of HT-29 cells could also be seen at lower concentrations of RC-3940-II (1 μM) after pretreatment with 100 nM GRP (14–27), indicating a dose-dependent mechanism of action based on the blockage of BN/GRP induced proliferation of tumor cells at lower concentrations.

Daily in vivo treatment with BN/GRP antagonist RC-3940-II decreased the volume of HT-29, HCT-116 and HCT-15 tumors xenografted into athymic nude mice by 25 to 67% (p < 0.005). Combined treatment with RC-3940-II and chemotherapeutic agents 5-FU and irinotecan resulted in a synergistic tumor growth suppression of HT-29, HCT-116 and HCT-15 xenografts by 43% to 78%. In HT-29 and HCT-116 xenografts the inhibition for the combinations of RC-3940-II and irinotecan vs. single substances (p < 0.05) was significantly greater.

These findings support the use of RC-3940-II as an anticancer agent and may help to design clinical trials using RC-3940-II in combinations with cytotoxic agents.

S-phase sensing of DNA-protein crosslinks triggers TopBP1-independent ATR activation and p53-mediated cell death by formaldehyde

Victor Chun-Lam Wong, Haley L. Cash, Jessica L. Morse, Shan Lu and Anatoly Zhitkovich
Pages 2526 - 2537
http://dx.doi.org/10.4161/cc.20905
Abstract | Full Text | PDF

We examined genotoxic signaling and cell fate decisions in response to a potent DNA-protein crosslinker formaldehyde (FA). DNA-protein crosslinks (DPC) are poorly understood lesions produced by bifunctional carcinogens and several cancer drugs. FA-treated human cells showed a rapid activation of ATR kinase that preferentially targeted the p53 transcription factor at low doses and CHK1 kinase at more severe damage, producing bell-shaped and sublinear responses, respectively. CHK1 phosphorylation was transient, and its loss was accompanied by increased p53 accumulation and Ser15 phosphorylation. Activation of p53 was insensitive to inhibition of mismatch repair and nucleotide and base excision repair, excluding the role of small DNA adducts in this response. The p53-targeted signaling was transcription-independent, absent in quiescent cells and specific to S-phase in cycling populations. Unlike other S-phase stressors, FA-activated p53 was functional transcriptionally, promoted apoptosis in lung epithelial cells and caused senescence in normal lung fibroblasts. FA did not induce ATR, RAD1 or RPA foci, and p53 phosphorylation was TopBP1-independent, indicating a noncanonical mode of ATR activation. Replication arrest by FA caused a dissociation of ATR from a chromatin-loaded MCM helicase but no PCNA monoubiquitination associated with stalled polymerases. These results suggest that unlike typical DNA adducts that stall DNA polymerases, replication inhibition by bulkier DPC largely results from blocking upstream MCM helicase, which prevents accumulation of ssDNA. Overall, our findings indicate that S-phase-specific, TopBP1-independent activation of the ATR-p53 axis is a critical stress response to FA-DPC, which has implications for understanding of FA carcinogenesis.

Open Access Article

A novel ubiquitin mark at the N-terminal tail of histone H2As targeted by RNF168 ubiquitin ligase

Marco Gatti, Sabrina Pinato, Elena Maspero, Paolo Soffientini, Simona Polo and Lorenza Penengo
Pages 2538 - 2544
http://dx.doi.org/10.4161/cc.20919
Abstract | Full Text | PDF

Ubiquitination of histones plays a critical role in the regulation of several processes within the nucleus, including maintenance of genome stability and transcriptional regulation. The only known ubiquitination site on histones is represented by a conserved Lys residue located at the C terminus of the protein. Here, we describe a novel ubiquitin mark at the N-terminal tail of histone H2As consisting of two Lys residues at positions 13 and 15 (K13/K15). This “bidentate” site is a target of the DNA damage response (DDR) ubiquitin ligases RNF8 and RNF168. Histone mutants lacking the K13/K15 site impair RNF168- and DNA damage-dependent ubiquitination. Conversely, inactivation of the canonical C-terminal site prevents the constitutive monoubiquitination of histone H2As but does not abolish the ubiquitination induced by RNF168. A ubiquitination-defective mutant is obtained by inactivating both the N- and the C-terminal sites, suggesting that these are unique, non-redundant acceptors of ubiquitination on histone H2As. This unprecedented result implies that RNF168 generates a qualitatively different Ub mark on chromatin.

Open Access Article

Two-compartment tumor metabolism: Autophagy in the tumor microenvironment and oxidative mitochondrial metabolism (OXPHOS) in cancer cells

Ahmed F. Salem, Diana Whitaker-Menezes, Zhao Lin, Ubaldo E. Martinez-Outschoorn, Herbert B. Tanowitz, Mazhar Salim Al-Zoubi, Anthony Howell, Richard G. Pestell, Federica Sotgia and Michael P. Lisanti
Pages 2545 - 2559
http://dx.doi.org/10.4161/cc.20920
Abstract | Full Text | PDF

Previously, we proposed a new paradigm to explain the compartment-specific role of autophagy in tumor metabolism. In this model, autophagy and mitochondrial dysfunction in the tumor stroma promotes cellular catabolism, which results in the production of recycled nutrients. These chemical building blocks and high-energy “fuels” would then drive the anabolic growth of tumors, via autophagy resistance and oxidative mitochondrial metabolism in cancer cells. We have termed this new form of stromal-epithelial metabolic coupling: “two-compartment tumor metabolism.” Here, we stringently tested this energy-transfer hypothesis, by genetically creating (1) constitutively autophagic fibroblasts, with mitochondrial dysfunction or (2) autophagy-resistant cancer cells, with increased mitochondrial function. Autophagic fibroblasts were generated by stably overexpressing key target genes that lead to AMP-kinase activation, such as DRAM and LKB1. Autophagy-resistant cancer cells were derived by overexpressing GOLPH3, which functionally promotes mitochondrial biogenesis. As predicted, DRAM and LKB1 overexpressing fibroblasts were constitutively autophagic and effectively promoted tumor growth. We validated that autophagic fibroblasts showed mitochondrial dysfunction, with increased production of mitochondrial fuels (L-lactate and ketone body accumulation). Conversely, GOLPH3 overexpressing breast cancer cells were autophagy-resistant, and showed signs of increased mitochondrial biogenesis and function, which resulted in increased tumor growth. Thus, autophagy in the tumor stroma and oxidative mitochondrial metabolism (OXPHOS) in cancer cells can both dramatically promote tumor growth, independently of tumor angiogenesis. For the first time, our current studies also link the DNA damage response in the tumor microenvironment with “Warburg-like” cancer metabolism, as DRAM is a DNA damage/repair target gene.

Overexpression of cyclin E/CDK2 complexes overcomes FGF-induced cell cycle arrest in the presence of hypophosphorylated Rb proteins

Victoria Kolupaeva and Claudio Basilico
Pages 2557 - 2566
http://dx.doi.org/10.4161/cc.20944
Abstract | Full Text | PDF

FGF signaling inhibits chondrocyte proliferation and requires the function of the p107 and p130 members of the Rb protein family to execute growth arrest. p107 dephosphorylation plays a critical role in the chondrocyte response to FGF, as overexpression of cyclin D1/CDK4 complexes (the major p107 kinase) in rat chondrosarcoma (RCS) cells overcomes FGF-induced p107 dephosphorylation and growth arrest. In cells overexpressing cyclin D1/CDK4, FGF-induced downregulation of cyclin E/CDK2 activity was absent. To examine the role of cyclin E/CDK2 complexes in mediating FGF-induced growth arrest, this kinase was overexpressed in RCS cells. FGF-induced dephosphorylation of either p107 or p130 was not prevented by overexpressing cyclin E/CDK2 complexes. Unexpectedly, however, FGF-treated cells exhibited sustained proliferation even in the presence of hypophosphorylated p107 and p130. Both pocket proteins were able to form repressive complexes with E2F4 and E2F5 but these repressors were not translocated into the nucleus and therefore were unable to occupy their respective target DNA sites. Overexpressed cyclin E/CDK2 molecules were stably associated with p107 and p130 in FGF-treated cells in the context of E2F repressive complexes. Taken together, our data suggest a novel mechanism by which cyclin E/CDK2 complexes can promote cell cycle progression in the presence of dephosphorylated Rb proteins and provide a novel insight into the key Retinoblastoma/E2F/cyclin E pathway. Our data also highlight the importance of E2F4/p130 complexes for FGF-mediated growth arrest in chondrocytes.

Tetraploidization increases sensitivity to Aurora B kinase inhibition

Miriam Marxer, Charles E. Foucar, Wing Yu Man, Yu Chen, Hoi Tang Ma and Randy Y.C. Poon
Pages 2567 - 2577
http://dx.doi.org/10.4161/cc.20947
Abstract | Full Text | PDF

Aurora kinases are overexpressed in many cancers and are targets for anticancer drugs. The yeast homolog of Aurora B kinase, IPL1, was found to be a ploidy-specific lethality gene. Given that polyploidization is a common feature of many cancers, we hypothesized polyploidization also sensitizes mammalian cells to inhibition of Aurora kinases. Using two models of apparent diploid vs. tetraploid cell lines (one based on the hepatocellular carcinoma cell line Hep3B and another on untransformed mouse fibroblasts), we found that tetraploid cells were more sensitive to Aurora B inhibition than their diploid counterparts. Apoptosis could be induced in tetraploid cells by two different Aurora B inhibitors. Furthermore, tetraploid cells were sensitive to Aurora B inhibition but were not affected by Aurora A inhibition. Interestingly, the underlying mechanism was due to mitotic slippage and the subsequent excessive genome reduplication. In support of this, abolition of cytokinesis with dihydrocytochalasin B resulted in similar effects on tetraploid cells as Aurora B inhibition. These results indicate that inhibition of Aurora B or cytokinesis can promote apoptosis effectively in polyploid cancer cells.




LETTER TO THE EDITOR

Decreased efficiency of MSH6 mRNA polyadenylation linked to a 20-base-pair duplication in Lynch syndrome families

Adrien Decorsière, Christine Toulas, Françoise Fouque, Anne-Françoise Tilkin-Mariamé, Janick Selves, Rosine Guimbaud, Edith Chipoulet, Caroline Delmas, Jean-Marc Rey, Pascal Pujol, Gilles Favre, Stefania Millevoi and Stéphan Vagner
Pages 2578 - 2580
http://dx.doi.org/10.4161/cc.20625
Full Text | PDF