Table of Contents

Volume 11, Issue 19

  October 1, 2012

  Pages 3519 - 3703

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 Issue Catalogue (MARC XML)

EDITORIALS: CELL CYCLE FEATURES

Open Access Article

Cdk7: Open questions beyond the prevailing model

Miguel Ganuza and David Santamaría
Pages 3519 - 3520
http://dx.doi.org/10.4161/cc.21888
Abstract | Full Text | PDF

Comment on: Ganuza M, et al. EMBO J 2012; 31:2498-510.

Open Access Article

Rejuvenating regeneration: Metformin activates endogenous adult stem cells

Javier A. Menendez and Alejandro Vazquez-Martin
Pages 3521 - 3522
http://dx.doi.org/10.4161/cc.21878
Abstract | Full Text | PDF

Comment on: Wang J, et al. Cell Stem Cell 2012; 11:23-35.

Open Access Article

p85β increases phosphoinositide 3-kinase activity and accelerates tumor progression

Ana González-García and Ana C. Carrera
Pages 3523 - 3524
http://dx.doi.org/10.4161/cc.21961
Abstract | Full Text | PDF

Comment on: Cortés I, et al. Proc Natl Acad Sci USA 2012; 109:11318-23.

Open Access Article

DEC1 and MIC-1: New players of p53-dependent cell fate decision

Yingjuan Qian, Yong-Sam Jung and Xinbin Chen
Pages 3525 - 3526
http://dx.doi.org/10.4161/cc.21962
Abstract | Full Text | PDF

Comment on: Qian Y, et al. Proc Natl Acad Sci USA 2012; 109:11300-5.

Open Access Article

What limits meiotic crossovers?

Wayne Crismani and Raphaël Mercier
Pages 3527 - 3528
http://dx.doi.org/10.4161/cc.21963
Abstract | Full Text | PDF

Comment on: Crismani W, et al. Science 2012; 336:1588-90.

Open Access Article

Signaling dynamics and embryonic development

Aryeh Warmflash, Eric D. Siggia and Ali H. Brivanlou
Pages 3529 - 3530
http://dx.doi.org/10.4161/cc.21964
Abstract | Full Text | PDF

Comment on: Warmflash A, et al. Proc Natl Acad Sci USA 2012; 109:E1947-56.




CELL CYCLE NEWS & VIEWS

Open Access Article

Chronological and replicative lifespan in yeast: Do they meet in the middle?

Michael Polymenis and Brian K. Kennedy
Page 3531
http://dx.doi.org/10.4161/cc.22041
Abstract | Full Text | PDF

Comment on: Murakami C, et al. Cell Cycle 2012; 11:3087-96.

Open Access Article

Acetic acid and acidification accelerate chronological and replicative aging in yeast

Mario G. Mirisola and Valter D. Longo
Pages 3532 - 3533
http://dx.doi.org/10.4161/cc.22042
Abstract | Full Text | PDF

Comment on: Murakami C, et al. Cell Cycle 2012; 11:3087-96.

Open Access Article

Cyclin D1 goes metabolic: Dual functions of cyclin D1 in regulating lipogenesis

Karen E. Knudsen
Page 3534
http://dx.doi.org/10.4161/cc.22039
Abstract | Full Text | PDF

Comment on: Hanse EA, et al. Cell Cycle 2012; 11:2681-90.

Open Access Article

A role for protein phosphatase 4 in regulating non-homologous end-joining

Anthony J. Davis and David J. Chen
Page 3535
http://dx.doi.org/10.4161/cc.22040
Abstract | Full Text | PDF

Comment on: Liu J, et al. Cell Cycle 2012; 11:2643-9.




EXTRA VIEWS

Open Access Article

Interactions of pro-apoptotic BH3 proteins with anti-apoptotic Bcl-2 family proteins measured in live MCF-7 cells using FLIM FRET

Qian Liu, Brian Leber and David W. Andrews
Pages 3536 - 3542
http://dx.doi.org/10.4161/cc.21462
Abstract | Full Text | PDF

Increased interactions between pro-apoptotic BH3-only proteins and anti-apoptotic Bcl-2 family proteins at mitochondria result in tumor initiation, progression and resistance to traditional chemotherapy. Drugs that mimic the BH3 region are expected to release BH3-only proteins from anti-apoptotic proteins, inducing apoptosis in some cancer cells and sensitizing others to chemotherapy. Recently, we applied fluorescence lifetime imaging microscopy and fluorescence resonance energy transfer to measure protein:protein interactions for the Bcl-2 family of proteins in live MCF-7 cells using fluorescent fusion proteins. While the BH3-proteins bound to Bcl-XL and Bcl-2, the BH3 mimetic ABT-737 inhibited binding of only Bad and tBid, but not Bim. We have extended our studies by investigating ABT-263, a clinical drug based on ABT-737. We show that the inhibitory effects and pattern of the two drugs are comparable for both Bcl-XL and Bcl-2. Furthermore, we show that mutation of a conserved residue in the BH3 region in Bad and tBid disrupted their interactions with Bcl-XL and Bcl-2, while the corresponding BimEL mutant showed no decrease in binding to these anti-apoptotic proteins. Therefore, in MCF-7 cells, Bim has unique binding properties compared with other BH3-only proteins that resist displacement from Bcl-XL and Bcl-2 by BH3 mimetics.

Open Access Article

Transcriptional targeting by microRNA-Polycomb complexes: A novel route in cell fate determination

Giuseppe Zardo, Alberto Ciolfi, Laura Vian, Monia Billi, Serena Racanicchi, Francesco Grignani and Clara Nervi
Pages 3543 - 3549
http://dx.doi.org/10.4161/cc.21468
Abstract | Full Text | PDF

Advances in the understanding of the epigenetic events underlying the regulation of developmental genes expression and cell lineage commitment are revealing novel regulatory networks. These also involve distinct components of the epigenetic pathways, including chromatin histone modification, DNA methylation, repression by polycomb complexes and microRNAs. Changes in chromatin structure, DNA methylation status and microRNA expression levels represent flexible, reversible and heritable mechanisms for the maintenance of stem cell states and cell fate decisions. We recently provided novel evidence showing that microRNAs, besides determining the post-transcriptional gene silencing of their targets, also bind to evolutionarily conserved complementary genomic seed-matches present on target gene promoters. At these sites, microRNAs can function as a critical interface between chromatin remodeling complexes and the genome for transcriptional gene silencing. Here, we discuss our novel findings supporting a role of the transcriptional chromatin targeting by polycomb-microRNA complexes in lineage fate determination of human hematopoietic cells.

How to keep proliferative neural stem/progenitor cells: A critical role of asymmetric inheritance of cyclin D2

Yuji Tsunekawa and Noriko Osumi
Pages 3550 - 3554
http://dx.doi.org/10.4161/cc.21500
Abstract | Full Text | PDF

It has long been argued that cell cycle regulators such as cyclins, cyclin-dependent kinases and their inhibitors affect the fate of neuronal progenitor cells. Recently, we identified that cyclin D2, which localizes at the basal tip of the radial glial cell (i.e., the neural progenitor in the developing neocortex), functions to give differential cell fates to its daughter cells just after cell division. This basally biased localization is due to transportation of cyclin D2 mRNA via its unique cis-regulatory sequence and local translation into cyclin D2 protein at the basal endfoot. During division of the neural progenitor cells, cyclin D2 protein is inherited by the daughter cell that retain the basal process, resulting in asymmetric distribution of cyclin D2 protein between the two daughter cells. Cyclin D2 is similarly localized in the human fetal cortical primordium, suggesting a common mechanism for the maintenance of neural progenitors and a possible scenario in evolution of primate brains. Here we introduce our recent findings and discuss how cyclin D2 functions in mammalian brain development and evolution.

CEP192 interacts physically and functionally with the K63-deubiquitinase CYLD to promote mitotic spindle assembly

Maria Ana Gomez-Ferreria, Mikhail Bashkurov, Michael Mullin, Anne-Claude Gingras and Laurence Pelletier
Pages 3555 - 3558
http://dx.doi.org/10.4161/cc.21574
Abstract | Full Text | PDF

CEP192 is a centrosome protein that plays a critical role in centrosome biogenesis and function in mammals, Drosophila and C. elegans.^1-6 Moreover, CEP192-depleted cells arrest in mitosis with disorganized microtubules, suggesting that CEP192’s function in spindle assembly goes beyond its role in centrosome activity and pointing to a potentially more direct role in the regulation of the mitotic microtubule landscape.⁷ To better understand CEP192 function in mitosis, we used mass spectrometry to identify CEP192-interacting proteins. We previously reported that CEP192 interacts with NEDD1, a protein that associates with the γ-tubulin ring complex (γ-TuRC) and regulates its phosphorylation status during mitosis.⁸ Additionally, within the array of proteins that interact with CEP192, we identified the microtubule binding K63-deubiquitinase CYLD. Further analyses show that co-depletion of CYLD alleviates the bipolar spindle assembly defects observed in CEP192-depleted cells. This functional relationship exposes an intriguing role for CYLD in spindle formation and raises the tantalizing possibility that CEP192 promotes robust mitotic spindle assembly by regulating K63-polyubiquitin-mediated signaling through CYLD.




PERSPECTIVE

Toll-like receptors, signaling adapters and regulation of the pro-inflammatory response by PI3K

Ty Dale Troutman, J. Fernando Bazan and Chandrashekhar Pasare
Pages 3559 - 3567
http://dx.doi.org/10.4161/cc.21572
Abstract | Full Text | PDF

TLRs are a family of pattern recognition receptors that recognize conserved molecular structures/products from a wide variety of microbes. Following recognition of ligands, TLRs recruit signaling adapters to initiate a pro-inflammatory signaling cascade culminating in the activation of several transcription factor families. Additionally, TLR signals lead to activation of PI3K, affecting many aspects of the cellular response, including cell survival, proliferation and regulation of the pro-inflammatory response. The recent discovery of BCAP as a TLR signaling adaptor, crucial for linking TLRs to PI3K activation, allows new questions of the importance of PI3K activation downstream of TLRs. Here, we summarize the current understanding of signaling pathways activated by TLRs and provide our perspective on TLR mediated activation of PI3K and its impact on regulating cellular processes.




REPORTS

Open Access Article

Familial partial lipodystrophy, mandibuloacral dysplasia and restrictive dermopathy feature barrier-to-autointegration factor (BAF) nuclear redistribution

Cristina Capanni, Stefano Squarzoni, Vittoria Cenni, Maria Rosaria D’Apice, Alessandra Gambineri, Giuseppe Novelli, Manfred Wehnert, Renato Pasquali, Nadir M. Maraldi and Giovanna Lattanzi
Pages 3568 - 3577
http://dx.doi.org/10.4161/cc.21869
Abstract | Full Text | PDF

Prelamin A processing impairment is a common feature of a restricted group of rare genetic alterations/disorders associated with a wide range of clinical phenotypes. Changes in histone posttranslational modifications, alterations in non-histone chromatin proteins and chromatin disorganization have been specifically linked to impairment of specific, distinct prelamin A processing steps, but the molecular mechanism involved in these processes is not yet understood . In this study, we show that the accumulation of wild-type prelamin A detected in restrictive dermopathy (RD), as well as the accumulation of mutated forms of prelamin A identified in familial partial lipodystrophy (FPLD) and mandibuloacral dysplasia (MADA), affect the nuclear localization of barrier-to-autointegration factor (BAF), a protein able to link lamin A precursor to chromatin remodeling functions. Our findings, in accordance with previously described results, support the hypothesis of a prelamin A involvement in BAF nuclear recruitment and suggest BAF-prelamin A complex as a protein platform usually activated in prelamin A-accumulating diseases. Finally, we demonstrate the involvement of the inner nuclear membrane protein emerin in the proper localization of BAF-prelamin A complex.

Orc2 protects ORCA from ubiquitin-mediated degradation

Zhen Shen and Supriya G. Prasanth
Pages 3578 - 3589
http://dx.doi.org/10.4161/cc.21870
Abstract | Full Text | PDF

Origin recognition complex (ORC) is highly dynamic, with several ORC subunits getting posttranslationally modified by phosphorylation or ubiquitination in a cell cycle-dependent manner. We have previously demonstrated that a WD repeat containing protein ORC-associated (ORCA/LRWD1) stabilizes the ORC on chromatin and facilitates pre-RC assembly. Further, ORCA levels are cell cycle-regulated, with highest levels during G₁, and progressively decreasing during S phase, but the mechanism remains to be elucidated. We now demonstrate that ORCA is polyubiquitinated in vivo, with elevated ubiquitination observed at the G₁/S boundary. ORCA utilizes lysine-48 (K48) ubiquitin linkage, suggesting that ORCA ubiquitination mediates its regulated degradation. Ubiquitinated ORCA is re-localized in the form of nuclear aggregates and is predominantly associated with chromatin. We demonstrate that ORCA associates with the E3 ubiquitin ligase Cul4A-Ddb1. ORCA is ubiquitinated at the WD40 repeat domain, a region that is also recognized by Orc2. Furthermore, Orc2 associates only with the non-ubiquitinated form of ORCA, and Orc2 depletion results in the proteasome-mediated destabilization of ORCA. Based on the results, we suggest that Orc2 protects ORCA from ubiquitin-mediated degradation in vivo.

Drosha mediates destabilization of Lin28 mRNA targets

Chong Qiao, Jing Ma, Jie Xu, Mingyi Xie, Wei Ma and Yingqun Huang
Pages 3590 - 3598
http://dx.doi.org/10.4161/cc.21871
Abstract | Full Text | PDF

Lin28 plays important roles in development, stem cell maintenance, oncogenesis and metabolism. As an RNA-binding protein, it blocks the biogenesis primarily of let-7 family miRNAs and also promotes translation of a cohort of mRNAs involved in cell growth, metabolism and pluripotency, likely through recognition of distinct sequence and structural motifs within mRNAs. Here, we show that one such motif, shared by multiple Lin28-responsive elements (LREs) present in Lin28 mRNA targets also participates in a Drosha-dependent regulation and may contribute to destabilization of its cognate mRNAs. We further show that the same mutations in the LREs known to abolish Lin28 binding and stimulation of translation also abrogate Drosha-dependent mRNA destabilization, and that this effect is independent of miRNAs, uncovering a previously unsuspected coupling between Drosha-dependent destabilization and Lin28-mediated regulation. Thus, Lin28-dependent stimulation of translation of target mRNAs may, in part, serve to compensate for their intrinsic instability, thereby ensuring optimal levels of expression of genes critical for cell viability, metabolism and pluripotency.

Featured Article - FREE

CDK inhibitors (p16/p19/p21) induce senescence and autophagy in cancer-associated fibroblasts, “fueling” tumor growth via paracrine interactions, without an increase in neo-angiogenesis

Claudia Capparelli, Barbara Chiavarina, Diana Whitaker-Menezes, Timothy G. Pestell, Richard G. Pestell, James Hulit, Sebastiano Andò, Anthony Howell, Ubaldo E. Martinez-Outschoorn, Federica Sotgia and Michael P. Lisanti
Pages 3599 - 3610
http://dx.doi.org/10.4161/cc.21884
Abstract | Full Text | PDF

Here, we investigated the compartment-specific role of cell cycle arrest and senescence in breast cancer tumor growth. For this purpose, we generated a number of hTERT-immortalized senescent fibroblast cell lines overexpressing CDK inhibitors, such as p16(INK4A), p19(ARF) or p21(WAF1/CIP1). Interestingly, all these senescent fibroblast cell lines showed evidence of increased susceptibility toward the induction of autophagy (either at baseline or after starvation), as well as significant mitochondrial dysfunction. Most importantly, these senescent fibroblasts also dramatically promoted tumor growth (up to ~2-fold), without any comparable increases in tumor angiogenesis. Conversely, we generated human breast cancer cells (MDA-MB-231 cells) overexpressing CDK inhibitors, namely p16(INK4A) or p21(WAF1/CIP1). Senescent MDA-MB-231 cells also showed increased expression of markers of cell cycle arrest and autophagy, including β-galactosidase, as predicted. Senescent MDA-MB-231 cells had retarded tumor growth, with up to a near 2-fold reduction in tumor volume. Thus, the effects of CDK inhibitors are compartment-specific and are related to their metabolic effects, which results in the induction of autophagy and mitochondrial dysfunction. Finally, induction of cell cycle arrest with specific inhibitors (PD0332991) or cellular stressors [hydrogen peroxide (H₂O₂) or starvation] indicated that the onset of autophagy and senescence are inextricably linked biological processes. The compartment-specific induction of senescence (and hence autophagy) may be a new therapeutic target that could be exploited for the successful treatment of human breast cancer patients.

Identification of a novel function of the clathrin-coated structure at the plasma membrane in facilitating GM-CSF receptor-mediated activation of JAK2

Ping-Hung Chen, Fan-Ching Chien, Sue-Ping Lee, Woan-Eng Chan, I-Hsuan Lin, Chun-Shan Liu, Fang-Jen Lee, Jiann-Shiun Lai, Peilin Chen, Hsin-Fang Yang-Yen and Jeffrey Jong-Young Yen
Pages 3611 - 3626
http://dx.doi.org/10.4161/cc.21920
Abstract | Full Text | PDF

It is well known that ligand binding to the high-affinity GM-CSF receptor (GMR) activates JAK2. However, how and where this event occurs in a cellular environment remains unclear. Here, we demonstrate that clathrin- but not lipid raft-mediated endocytosis is crucial for GMR signaling. Knockdown expression of clathrin heavy chain or intersectin 2 (ITSN2) attenuated GMR-mediated activation of JAK2, whereas inhibiting clathrin-coated pits or plagues to bud off the membrane by the dominant-negative mutant of dynamin enhanced such event. Moreover, unlike the wild-type receptor, an ITSN2-non-binding mutant of GMR defective in targeting to clathrin-coated pits or plagues [collectively referred to as clathrin-coated structures (CCSs) here] failed to activate JAK2 at such locations. Additional experiments demonstrate that ligand treatment not only enhanced JAK2/GMR association at CCSs, but also induced a conformational change of JAK2 which is required for JAK2 to be activated by CCS-localized CK2. Interestingly, ligand-independent activation of the oncogenic mutant of JAK2 (JAK2V617F) also requires the targeting of this mutant to CCSs. But JAK2V617F seems to be constitutively in an open conformation for CK2 activation. Together, this study reveals a novel functional role of CCSs in GMR signaling and the oncogenesis of JAK2V617F.

The stress-activated protein kinases p38α/β and JNK1/2 cooperate with Chk1 to inhibit mitotic entry upon DNA replication arrest

Alba Llopis, Noelia Salvador, Amaia Ercilla, Sandra Guaita-Esteruelas, Ivan del Barco Barrantes, Jalaj Gupta, Matthias Gaestel, Roger J. Davis, Angel R. Nebreda and Neus Agell
Pages 3627 - 3637
http://dx.doi.org/10.4161/cc.21917
Abstract | Full Text | PDF

Accurate DNA replication is crucial for the maintenance of genome integrity. To this aim, cells have evolved complex surveillance mechanisms to prevent mitotic entry in the presence of partially replicated DNA. ATR and Chk1 are key elements in the signal transduction pathways of DNA replication checkpoint; however, other kinases also make significant contributions. We show here that the stress kinases p38 and JNK are activated when DNA replication is blocked, and that their activity allows S/M, but not G₂/M, checkpoint maintenance when Chk1 is inhibited. Activation of both kinases by DNA replication inhibition is not mediated by the caffeine-sensitive kinases ATR or ATM. Phosphorylation of MKK3/6 and MKK4, p38 and JNK upstream kinases was also observed upon DNA replication inhibition. Using a genetic approach, we dissected the p38 pathway and showed that both p38α and p38β isoforms collaborate to inhibit mitotic entry. We further defined MKK3/6 and MK2/3 as the key upstream and downstream elements in the p38 signaling cascade after replication arrest. Accordingly, we found that the stress signaling pathways collaborate with Chk1 to keep cyclin B1/Cdk1 complexes inactive when DNA replication is inhibited, thereby preventing cell cycle progression when DNA replication is stalled. Our results show a complex response to replication stress, where multiple pathways are activated and fulfill overlapping roles to prevent mitotic entry with unreplicated DNA.

Recognition mechanism of p63 by the E3 ligase Itch: Novel strategy in the study and inhibition of this interaction

Alessia Bellomaria, Gaetano Barbato, Gerry Melino, Maurizio Paci and Sonia Melino
Pages 3638 - 3648
http://dx.doi.org/10.4161/cc.21918
Abstract | Full Text | PDF

The HECT-containing E3 ubiquitin ligase Itch mediates the degradation of several proteins, including p63 and p73, involved in cell specification and fate. Itch contains four WW domains, which are essential for recognition on the target substrate, which contains a short proline-rich sequence. Several signaling complexes containing these domains have been associated with human diseases such as muscular dystrophy, Alzheimer’s or Huntington’s diseases. To gain further insight into the structural determinants of the Itch-WW2 domain, we investigated its interaction with p63. We assigned, by 3D heteronuclear NMR experiments, the backbone and side chains of the uniformly ¹³C-¹⁵N-labeled Itch-WW2. In vitro interaction of Itch-WW2 domain with p63 was studied using its interactive p63 peptide, pep63. Pep63 is an 18-mer peptide corresponding to the region from 534–551 residue of p63, encompassing the PPxY motif that interacts with the Itch-WW domains, and we identified the residues involved in this molecular recognition. Moreover, here, a strategy of stabilization of the conformation of the PPxY peptide has been adopted, increasing the WW-ligand binding. We demonstrated that cyclization of pep63 leads to an increase of both the biological stability of the peptide and of the WW-ligand complex. Stable metal-binding complexes of the pep63 have been also obtained, and localized oxidative damage on Itch-WW2 domain has been induced, demonstrating the possibility of use of metal-pep63 complexes as models for the design of metal drugs to inhibit the Itch-WW-p63 recognition in vivo. Thus, our data suggest a novel strategy to study and inhibit the recognition mechanism of Itch E3-ligase.

Combined inhibition of Wee1 and Hsp90 activates intrinsic apoptosis in cancer cells

Aki Iwai, Dimitra Bourboulia, Mehdi Mollapour, Sandra Jensen-Taubman, Sunmin Lee, Alison C. Donnelly, Soichiro Yoshida, Naoto Miyajima, Shinji Tsutsumi, Armine K. Smith, David Sun, Xiaolin Wu, Brian S. Blagg, Jane B. Trepel, William G. Stetler-Stevenson and Len Neckers
Pages 3649 - 3655
http://dx.doi.org/10.4161/cc.21926
Abstract | Full Text | PDF

Heat shock protein 90 (Hsp90) is an essential, evolutionarily conserved molecular chaperone. Cancer cells rely on Hsp90 to chaperone mutated and/or activated oncoproteins, and its involvement in numerous signaling pathways makes it an attractive target for drug development. Surprisingly, however, the impact of Hsp90 inhibitors on cancer cells is frequently cytostatic in nature, and efforts to enhance the antitumor activity of Hsp90 inhibitors in the clinic remain a significant challenge. In agreement with previous data obtained using Wee1 siRNA, we show that dual pharmacologic inhibition of Wee1 tyrosine kinase and Hsp90 causes cancer cells to undergo apoptosis in vitro and in vivo. Gene expression profiling revealed that induction of the intrinsic apoptotic pathway by this drug combination coincided with transcriptional downregulation of Survivin and Wee1, an outcome not seen in cells treated separately with either agent. At the translational level, expression of these two proteins, as well as activated Akt, was completely abrogated. These data support the hypothesis that Wee1 inhibition sensitizes cancer cells to Hsp90 inhibitors; they establish combined Wee1/Hsp90 inhibition as a novel therapeutic strategy; and they provide a mechanistic rationale for enhancing the pro-apoptotic activity of Hsp90 inhibitors.

Increased tRNA modification and gene-specific codon usage regulate cell cycle progression during the DNA damage response

Ashish Patil, Madhu Dyavaiah, Fraulin Joseph, John P. Rooney, Clement T.Y. Chan, Peter C. Dedon and Thomas J. Begley
Pages 3656 - 3665
http://dx.doi.org/10.4161/cc.21919
Abstract | Full Text | PDF

S-phase and DNA damage promote increased ribonucleotide reductase (RNR) activity. Translation of RNR1 has been linked to the wobble uridine modifying enzyme tRNA methyltransferase 9 (Trm9). We predicted that changes in tRNA modification would translationally regulate RNR1 after DNA damage to promote cell cycle progression. In support, we demonstrate that the Trm9-dependent tRNA modification 5-methoxycarbonylmethyluridine (mcm⁵U) is increased in hydroxyurea (HU)-induced S-phase cells, relative to G₁ and G₂, and that mcm⁵U is one of 16 tRNA modifications whose levels oscillate during the cell cycle. Codon-reporter data matches the mcm⁵U increase to Trm9 and the efficient translation of AGA codons and RNR1. Further, we show that in trm9Δ cells reduced Rnr1 protein levels cause delayed transition into S-phase after damage. Codon re-engineering of RNR1 increased the number of trm9Δ cells that have transitioned into S-phase 1 h after DNA damage and that have increased Rnr1 protein levels, similar to that of wild-type cells expressing native RNR1. Our data supports a model in which codon usage and tRNA modification are regulatory components of the DNA damage response, with both playing vital roles in cell cycle progression.

VDAC3 regulates centriole assembly by targeting Mps1 to centrosomes

Shubhra Majumder, Mark Slabodnick, Amanda Pike, Joseph Marquardt and Harold A. Fisk
Pages 3666 - 3678
http://dx.doi.org/10.4161/cc.21927
Abstract | Full Text | PDF

Centrioles are duplicated during S-phase to generate the two centrosomes that serve as mitotic spindle poles during mitosis. The centrosomal pool of the Mps1 kinase is important for centriole assembly, but how Mps1 is delivered to centrosomes is unknown. Here we have identified a centrosome localization domain within Mps1 and identified the mitochondrial porin VDAC3 as a protein that binds to this region of Mps1. Moreover, we show that VDAC3 is present at the mother centriole and modulates centriole assembly by recruiting Mps1 to centrosomes.

Glutamine depletion and glucose depletion trigger growth inhibition via distinctive gene expression reprogramming

Shuo Qie, Dongming Liang, Chengqian Yin, Weiting Gu, Meng Meng, Chenguang Wang and Nianli Sang
Pages 3679 - 3690
http://dx.doi.org/10.4161/cc.21944
Abstract | Full Text | PDF

Glutamine (Gln) and glucose (Glc) represent two important nutrients for proliferating cells, consistent with the observations that oncogenic processes are associated with enhanced glycolysis and glutaminolysis. Gln depletion and Glc depletion have been shown to trigger growth arrest and eventually cell death. Solid tumors often outgrow the blood supply, resulting in ischemia, which is associated with hypoxia and nutrient insufficiency. Whereas oxygen-sensing and adaptive mechanisms to hypoxia have been well-studied, how cells directly sense and respond to Gln and Glc insufficiency remains unclear. Using mRNA profiling techniques, we compared the gene expression profiles of acute Gln-depleted cells, Glc-depleted cells and cells adapted to Gln depletion. Here we report the global changes of the gene expression in those cells cultured under the defined nutrient conditions. Analysis of mRNA profiling data revealed that Gln and Glc depletion triggered dramatic gene expression reprogramming. Either Gln or Glc deletion leads to changes of the expression of cell cycle genes, but these conditions have distinctive effects on transcription regulators and gene expression profiles. Moreover, Gln and Glc depletion triggered distinguishable ER-stress responses. The gene expression patterns support that Gln and Glc have distinctive metabolic roles in supporting cell survival and proliferation, and cells use different mechanisms to sense and respond to Gln and Glc insufficiency. Our mRNA profiling database provides a resource for further investigating the nutrient-sensing mechanisms and potential effects of Glc and Gln abundance on the biological behaviors of cells.

Identification of an estrogen-regulated circadian mechanism necessary for breast acinar morphogenesis

Stefano Rossetti, Francesca Corlazzoli, Alex Gregorski, Nurul Hidayah A. Azmi and Nicoletta Sacchi
Pages 3691 - 3700
http://dx.doi.org/10.4161/cc.21946
Abstract | Full Text | PDF

Altered estrogen receptor α (ERA) signaling and altered circadian rhythms are both features of breast cancer. By using a method to entrain circadian oscillations in human cultured cells, we recently reported that the expression of key clock genes oscillates in a circadian fashion in ERA-positive breast epithelial cells but not in breast cancer cells, regardless of their ERA status. Moreover, we reported that ERA mRNA oscillates in a circadian fashion in ERA-positive breast epithelial cells, but not in ERA-positive breast cancer cells. By using ERA-positive HME1 breast epithelial cells, which can be both entrained in vitro and can form mammary gland-like acinar structures in three-dimensional (3D) culture, first we identified a circuit encompassing ERA and an estrogen-regulated loop consisting of two circadian clock genes, PER2 and BMAL1. Further, we demonstrated that this estrogen-regulated circuit is necessary for breast epithelial acinar morphogenesis. Disruption of this circuit due to ERA-knockdown, negatively affects the estrogen-sustained circadian PER2-BMAL1 mechanism as well as the formation of 3D HME1 acini. Conversely, knockdown of either PER2 or BMAL1, by hampering the PER2-BMAL1 loop of the circadian clock, negatively affects ERA circadian oscillations and 3D breast acinar morphogenesis. To our knowledge, this study provides the first evidence of the implication of an ERA-circadian clock mechanism in the breast acinar morphogenetic process.




LETTER TO THE EDITOR

New light on p27^kip1 in breast cancer

Barbara Belletti and Gustavo Baldassarre
Pages 3701 - 3702
http://dx.doi.org/10.4161/cc.21573
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ERRATUM

Open Access Article

Erratum to Ponassi R, et al. Cell Cycle Volume 7, Issue 20; pp. 3211-24

Raffaella Ponassi and 27 others
Page 3703
http://dx.doi.org/10.4161/cc.22288
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