Table of Contents

Volume 4, Issue 7

  July 2005

  Pages 851 - 989

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 Issue Catalogue (MARC XML)

EXTRA VIEWS

Open Access Article

Inhibition of c-fms by Imatinib: Expanding the Spectrum of Treatment

Andrea L. Dewar, Andrew C.W. Zannettino, Timothy P. Hughes and A. Bruce Lyons
Pages 851 - 853
http://dx.doi.org/10.4161/cc.4.7.1788
Abstract | PDF

Imatinib is a selective protein tyrosine kinase inhibitor currently used in the treatment of chronic myeloid leukaemia (CML). It specifically suppresses the growth of bcr-abl expressing CML progenitor cells by blocking the ATP-binding site of the kinase domain of bcr-abl. Imatinib also inhibits the c-abl, platelet derived growth factor receptor (PDGFR), abl-related gene and stem cell factor receptor, c-kit, protein tyrosine kinases. It is through inhibition of c-kit that imatinib is also used clinically in the treatment of gastrointestinal stromal tumours. We have recently demonstrated that imatinib also specifically targets the macrophage colony stimulating factor receptor, c-fms, at therapeutic concentrations. Although this finding has important implications with regard to potential side effects in patients currently receiving imatinib therapy, these results suggest that imatinib may also be useful in the treatment of diseases where c-fms is implicated. This includes breast and ovarian cancer and inflammatory conditions such as rheumatoid arthritis. We also speculate that imatinib may be used in diseases where bone destruction occurs due to excessive osteoclast activity, such as in the haematologic malignancy, multiple myeloma.

Open Access Article

Targeted Gene Delivery by Intravenous Injection of Retroviral Vectors

Kouki Morizono and Irvin S.Y. Chen
Pages 854 - 856
http://dx.doi.org/10.4161/cc.4.7.1789
Abstract | PDF

Specifically and effectively directing a therapeutic gene to its intended site of action is a critical issue for translation of basic genomics to clinical gene therapy. Delivering gene therapy vectors to specific cells or tissues through intravenous injection is the most desirable method for this purpose. In 2001, we reported successful targeted gene transduction in vitro utilizing both oncoretroviral and lentiviral vectors pseudotyped with a chimeric Sindbis virus envelope (ZZ SINDBIS). However, these pseudotypes mediated non-specific gene transduction to liver and spleen in vivo. To address this problem we generated the modified ZZ SINDBIS (termed m168) with significantly less non-specific infectivity. To investigate the ability of m168 pseudotyped lentiviral vector to mediate targeted gene transduction in vivo, we utilized a metastatic tumor model by using mouse melanoma cells engineered to express human P-glycoprotein. We administered the m168 pseudotyped vector conjugated with anti-P-glycoprotein antibody into the mice intravenously to target metastatic melanoma. The m168 pseudotyped vector selectively infected metastatic melanoma cells demonstrating successful targeted gene transduction in vivo. Targeting technology based upon m168 can be further modified for application not only to cancer but also potentially to genetic, neurologic, infectious and immune diseases, thereby expanding the future application of gene therapy.

Open Access Article

MDM2 as a Critical Effector of the MYCN Oncogene in Tumorigenesis

Andrew Slack and Jason M. Shohet
Pages 857 - 860
http://dx.doi.org/10.4161/cc.4.7.1790
Abstract | PDF

The MYCN oncogene plays an important role in the pathogenesis of neuroblastoma. It is amplified in more than 30% of high-risk cases and over expression induces neuroblastoma in transgenic mice. MYCN amplification/overexpression is found in many types of cancers including neuroblastoma, medulloblastoma and other aggressive tumors of neuroectodermal origin as well as in rhadomyosarcoma and small cell lung cancers. MYCN exerts its oncogenic effects through transcriptional regulation of numerous target genes. We have recently characterized the p53 inhibitor MDM2 (HDM2) as one such target in MYCN amplified neuroblastoma cell lines. Conditional expression of MYCN yields elevated MDM2 mRNA and protein. MYCN inhibition leads to diminished MDM2, stabilized p53 and apoptosis. As the primary negative regulator of p53, MDM2 is critically regulated in normal cells to ensure adequate p53 activity in response to damage or stress. Additionally, MDM2 regulates many p53 independent processes pertinent to oncogenesis. We propose that increased MDM2 levels downstream of MYCN are tumorigenic secondary to disruption of multiple p53 dependent and independent mechanisms controlling genomic stability, apoptopsis and cell cycle progression. Further research into the MYCN / MDM2 regulated pathways will provide insight into the pathogenesis of MYCN-driven tumors and provide targets for novel therapeutic interventions.

Open Access Article

Repair of Ischemic Heart Disease with Novel Bone Marrow-Derived Multipotent Stem Cells

Namho Lee, Tina Thorne, Douglas W. Losordo and Young-sup Yoon
Pages 861 - 864
http://dx.doi.org/10.4161/cc.4.7.1799
Abstract | PDF

Congestive heart failure is a growing, worldwide epidemic. The major causes of heart failure are related to irreversible damage resulting from myocardial infarction (heart attack). The long-standing axiom has been that the myocardium has a limited capacity for self-repair or regeneration; and the irreversible loss of cardiac muscle and accompanying contraction and fibrosis of myocardial scar tissue, sets into play a series of events, namely, progressive ventricular remodeling of nonischemic myocardium that ultimately leads to progressive heart failure. The loss of cardiomyocyte survival cues is associated with diverse pathways for heart failure, underscoring the importance of maintaining the number of viable cardiomyocytes during heart failure progression. Currently, no medication or procedure used clinically has shown efficacy in replacing the myocardial scar with functioning contractile tissue. Therefore, given the major morbidity and mortality associated with myocardial infarction and heart failure, new approaches have been sought to address the principal pathophysiologic deficits responsible for these conditions, resulting from the loss of cardiomyocytes and viable blood vessels. Recently, the identification of stem cells from bone marrow capable of contributing to tissue regeneration has ignited significant interest in the possibility that cell therapy could be employed therapeutically for the repair of damaged myocardium. In this review, we will discuss the currently available bone marrow-derived stem progenitor cells for myocardial repair and focus on the advantages of using recently identified novel bone marrow-derived multipotent stem cells (BMSC)

Open Access Article

Li-Fraumeni Syndrome: a p53 Family Affair

Tomoo Iwakuma, Guillermina Lozano and Elsa R. Flores
Pages 865 - 867
http://dx.doi.org/10.4161/cc.4.7.1800
Abstract | PDF

The p53 alterations frequently found in human tumors are missense mutations in the DNA binding domain. These p53 mutations have been shown to have gain-of-function or dominant negative properties in multiple experiments. The consequences of these p53 mutations at physiological levels on the development of a tumor were unclear. Using mouse models, three recent papers have shed light on the mechanisms of mutant p53 and its family members, p63 and p73, in tumorigenesis. Interestingly, the p53 point mutant mice had a similar phenotype to p53 family compound mutant mice suggesting that there is an interplay between the p53 family members in tumorigenesis and Li-Fraumeni syndrome.

Open Access Article

Smc5-Smc6 Complex Preserves Nucleolar Integrity in S. cerevisiae

Jordi Torres-Rosell, Félix Machín and Luis Aragón
Pages 868 - 872
http://dx.doi.org/10.4161/cc.4.7.1825
Abstract | PDF

As a baton in a relay race, intact genomes need to be smoothly passed onto daughter cells every cell generation. Cohesin and condensin are multiprotein complexes involved in chromosome segregation during mitosis, they perform the crucial function of organizing and compacting chromosomes into pairs to facilitate their equal distribution in anaphase. Both complexes share a core of similar origin, containing a heterodimer formed by members of the conserved chromosomal ATPase family named Smc. A third complex containing Smc proteins at its core, the Smc5-Smc6 complex, previously known to be involved in DNA repair has recently been shown to contribute to chromosome segregation during anaphase. Smc5-Smc6 plays a role in the disjunction of repetitive regions. Here, we present results further supporting the importance of Smc5-Smc6 in maintaining the integrity of the repetitive ribosomal DNA (rDNA) locus, the largest repetitive region of the budding yeast genome.

Open Access Article

A New Perp in the Lineup: Linking p63 and Desmosomal Adhesion

Rebecca A. Ihrie and Laura D. Attardi
Pages 873 - 876
http://dx.doi.org/10.4161/cc.4.7.1836
Abstract | PDF

The process of stratified epithelial development depends upon a transcriptional program directed by the p53-related transcription factor p63. p63 is required for the commitment of the ectoderm to stratification and for the completion of terminal differentiation in stratified epithelia, and mutations in p63 have been identified in multiple developmental disorders affecting ectoderm-derived tissues. Recent work from our laboratory has determined that the p53 target gene Perp is required for the integrity of the stratified epithelia specified by p63, and that expression of Perp in these structures depends on the presence of p63. In these tissues, Perp is a critical component of the desmosome, a cell-cell adhesion complex whose constituents are frequently mutated in human diseases affecting the skin and hair. Perp’s position downstream of p63 and p53, as well as its essential role in normal desmosome function, suggest that it, like other adhesion proteins, may be a target for mutation in human blistering diseases or cancer.

Open Access Article

Hsp70-2 is Required for Tumor Cell Growth and Survival

Mads Daugaard, Marja Jäättelä and Mikkel Rohde
Pages 877 - 880
http://dx.doi.org/10.4161/cc.4.7.1838
Abstract | PDF

Heat shock protein 70 (Hsp70) family consists of at least eight chaperone proteins that differ from each other by their pattern of expression and intracellular localization. Whereas ample experimental and clinico-pathological data has implicated the major stress-inducible Hsp70-1 as a protein required for cancer cell survival, the study of the other family members has been limited by the lack of experimental tools to differentiate between the highly homologous family members. This limitation has been recently overcome by the RNA interference technology that for the first time allows targeted knockdown of the individual Hsp70 family members. Data based on this technology has revealed that also Hsp70-2, a protein essential for spermatogenesis, is required for cancer cell growth and survival. Remarkably, the highly homologous Hsp70 proteins enhance cancer cell growth and survival by distinct molecular mechanisms.

Open Access Article

Genetic Instability: The Dark Side of THE Hypoxic Response

Kenneth K.W. To, Minori Koshiji, Stefanie Hammer and L. Eric Huang
Pages 881 - 882
http://dx.doi.org/10.4161/cc.4.7.1839
Abstract | PDF

Under low oxygen tension, the activated transcription factor HIF-1? upregulates an array of hypoxia-inducible genes via heterodimerization with ARNT and binding to the hypoxia-responsive element in the promoter. Alternatively, HIF-1? regulates hypoxia-responsive genes by functionally antagonizing the oncoprotein Myc via protein-protein interactions. This so-called HIF-1?–Myc mechanism apparently not only accounts for the gene up-regulation, but also for the gene down-regulation during hypoxia, depending upon the active and repressive nature of Myc in gene expression. Indeed, our recent study demonstrated that both mismatch repair genes, MSH2 and MSH6, are inhibited by this mechanism in a p53-dependent manner. In particular, the constitutively bound transcription factor Sp1 serves as a molecular switch by recruiting HIF-1? in hypoxia to displace the transcription activator Myc from the promoter. Therefore, our findings shed light on the mechanisms underlying hypoxia-induced genetic instability, an “adverse” effect of the hypoxic response, and yet a germane process to tumor survival and progression.




PERSPECTIVES

Open Access Article

Adenovirus Overrides Cellular Checkpoints for Protein Translation

Clodagh C. O’Shea, Serah Choi, Frank McCormick and David Stokoe
Pages 883 - 888
http://dx.doi.org/10.4161/cc.4.7.1791
Abstract | PDF

mTOR is a critical regulator of protein translation, and plays an important role in controlling cellular replication. Recent studies indicate that nutrient and growth factor mediated activation of mTOR is deregulated in human cancer, and therefore represents an attractive tumor target. However, activation of mTOR is a complex process that is not yet fully understood. DNA viruses and tumor cells often perturb similar cellular pathways to facilitate their replication. In a recent study, we used adenovirus as a novel tool to probe the mechanisms underlying the inappropriate activation of mTOR in quiescent primary cells. These studies revealed that adenovirus encodes two viral proteins, E4-ORF1 and E4-ORF4, which activate mTOR, even in the absence of nutrient/growth factor signals, and which play a role in promoting viral replication. E4-ORF1 mimics growth factor signaling to mTOR by activating PI3-kinase, whereas E4-ORF4, which binds and relocalizes PP2A, can substitute for glucose mediated activation of mTOR. We discuss insights from this study, together with the similarities that may exist between viruses and tumor cells with respect to the mechanistic and functional requirements for mTOR activation in driving their aberrant DNA replication.

Open Access Article

Epigenetic Control of Replication Origins

Jing Zhou, Charles Chau, Zhong Deng, William Stedman and Paul M. Lieberman
Pages 889 - 892
http://dx.doi.org/10.4161/cc.4.7.1823
Abstract | PDF

Efficient duplication of the eukaryotic genome requires the spatial and temporal coordination of numerous replication origins on each chromosome. Epigenetic factors, like chromatin environment, can have profound effects on origin site selection, utilization frequency, and cell cycle firing time. Precisely how chromatin contributes to origin site selection and timing is not completely understood. Recently, we reported on the cell cycle changes in chromatin structure at the plasmid replication origins of Epstein-Barr Virus (EBV) and Kaposi’s Sarcoma-Associated Herpesvirus (KSHV)1,2. These studies and others suggest that cell cycle changes in histone modification and nucleosome remodeling regulate pre-replication factor assembly and initiation of DNA replication at origins. We discuss how these studies of viral origins may provide important insights into epigenetic control of cellular chromosome origins.

Open Access Article

Cell Division and Hematopoietic Stem Cells: Not Always Exhausting

Carl R. Walkley, Grant A. McArthur and Louise E. Purton
Pages 893 - 896
http://dx.doi.org/10.4161/cc.4.7.1831
Abstract | PDF

Pluripotent hematopoietic stem cells (HSCs) sustain blood cell production throughout an individual’s lifespan through complex processes supported by self-renewal, differentiation, senescence or cell death decisions of the HSCs. These decisions are tightly regulated under homeostatic conditions, allowing both the continuous generation of progenitors and mature cells in addition to the maintenance and replenishment of the HSC pool. Several recent studies have provided insights into some of the key molecular mechanisms regulating these different cell fate decisions. One of the emerging themes of these studies is that of the importance of cell cycle regulators in the maintenance of HSCs.

Open Access Article

The Jak/Stat Pathway: A Novel Way to Regulate PI3K Activity

Kathrine Abell and Christine J. Watson
Pages 897 - 900
http://dx.doi.org/10.4161/cc.4.7.1837
Abstract | PDF

Phosphoinositide 3-kinases (PI3Ks) have been grouped into three major classes that have different substrate specificities. Class IA PI3Ks consist of a catalytic and a regulatory subunit and have multiple isoforms that arise from different subunit combinations. The role of two of the small regulatory subunits, p55? and p50?, is poorly understood. We have now identified a novel function for these subunits and have shown that their expression is specifically induced in the involuting mouse mammary gland where they are involved in the downregulation of PI3K signalling and Akt/PKB activity. This abrogation of survival signalling thru Akt/PKB and its downstream targets is essential for the induction of apoptosis. The switch from lactation to involution is associated with activation of the transcription factor Stat3, by the cytokine LIF. Stat3 is essential for the induction of apoptosis and, in the absence of Stat3 or LIF, expression of the p55? and p50? subunits is abrogated. Surprisingly, Stat3 is a direct regulator of p55? and p50? expression, as demonstrated using ChIP assays, and therefore these subunits are not splicing isoforms as previously thought. An important implication of our results is that the p55? and p50? small regulatory subunits are regulated independently of the larger p85? subunit, and have an essential role in Stat3-mediated apoptosis in mammary gland.




REVIEWS

Open Access Article

Circadian Clock Genes as Modulators of Sensitivity to Genotoxic Stress

Marina P. Antoch, Roman V. Kondratov and Joseph S. Takahashi
Pages 901 - 907
http://dx.doi.org/10.4161/cc.4.7.1792
Abstract | PDF

A broad variety of organisms display circadian rhythms (i.e. oscillations with 24-hr periodicities) in many aspects of their behavior, physiology and metabolism. These rhythms are under genetic control and are generated endogenously at the cellular level. In mammals, the core molecular mechanism of the oscillator consists of two transcriptional activators, CLOCK and BMAL1, and their transcriptional targets, CRYPTOCHROME (CRY) and PERIOD (PER). The CRY and PER proteins function as negative regulators of CLOCK/BMAL1 activity, thus forming the major circadian autoregulatory feedback loop. It is believed that the circadian clock system regulates daily variations in output physiology and metabolism through periodic activation/repression of the set of clock-controlled genes that are involved in various metabolic pathways. Importantly, circadian-controlled pathways include those that determine in vivo responses to genotoxic stress. By using circadian mutant mice deficient in different components of the molecular clock system, we have established genetic models that correspond with the two opposite extremes of circadian cycle as reflected by the activity of the CLOCK/BMAL1 transactivation complex. Comparison of the in vivo responses of these mutants to the chemotherapeutic drug, cyclophosphamide (CY), has established a direct correlation between drug toxicity and the functional status of the CLOCK/BMAL1 transcriptional complex. We have also demonstrated that CLOCK/BMAL1 modulates sensitivity to drug-induced toxicity by controlling B cell responses to active CY metabolites. These results suggest that the sensitivity of cells to genotoxic stress induced by anticancer therapy may be modulated by CLOCK/BMAL1 transcriptional activity. Further elucidation of the molecular mechanisms of circadian control as well as identification of specific pharmacological modulators of CLOCK/BMAL1 activity are likely to lead to the development of new anti-cancer treatment schedules with increased therapeutic index and reduced morbidity.

Open Access Article

Triple Layer Control: Phosphorylation, Acetylation and Ubiquitination of FOXO Proteins

Peter K. Vogt, Hao Jiang and Masahiro Aoki
Pages 908 - 913
http://dx.doi.org/10.4161/cc.4.7.1796
Abstract | PDF

FOXO proteins are transcriptional regulators that control cell cycle progression, DNA repair, apoptosis, and defense against oxidative damage. These divergent functions of FOXO proteins are regulated by signal-induced, post-translational modifications. Phosphorylation of cytoplasmic FOXO at specific sites by JNK initiates translocation into the nucleus. Acetylation and deacetylation of nuclear FOXO affects the selection of transcriptional programs that are controlled by FOXO proteins. Activation of Akt by growth factors results in phosphorylation of nuclear FOXO at specific sites followed by additional phosphorylations mediated by other kinases. Akt-dependent phosphorylation reduces the DNA-binding activity of FOXO, interferes with binding to the co-activators p300/CBP, and inactivates the FOXO nuclear translocation signal. The Akt-phosphorylated FOXO is exported from the nucleus in a CRM1- and 14-3-3-dependent process. Cytoplasmic, Akt-phosphorylated FOXO interacts with the ubiquitin ligase Skp2 and is targeted for proteasomal degradation. The nuclear-cytoplasmic “FOXO shuttle” is driven by stress signals that result in nuclear import and FOXO transcriptional activity and growth signals that initiate nuclear export and proteasomal degradation of FOXO.

Open Access Article

TRAIL: At the Center of Drugable Anti-Tumor Pathways

Nicole Clarke, Angela Nebbioso, Lucia Altucci and Hinrich Gronemeyer
Pages 914 - 918
http://dx.doi.org/10.4161/cc.4.7.1822
Abstract | PDF

Molecular analysis, in vivo and in vitro has identified TRAIL as a central component of anti-cancer networks in the cell. More recently, TRAIL has been shown to be involved in the selective apoptosis of AML cells by histone deacetylase inhibitors (HDACi). Here we summarize findings that the TRAIL pathway is a key factor in the apoptotic action of HDACi, as well as, retinoids and retinoid-combinations.

Open Access Article

Effector Proteins for Methylated Histones: An Expanding Family

Jeremy A. Daniel, Marilyn G. Pray-Grant and Patrick A. Grant
Pages 919 - 926
http://dx.doi.org/10.4161/cc.4.7.1824
Abstract | PDF

Methylation of histone lysine residues in eukaryotic chromatin has been an exciting area of research ever since the first histone methyltransferase enzyme, Suv39h, was found to methylate lysine 9 of histone H3 in 2000 1. Only a year later, the HP1 chromodomain polypeptide was identified as a recognition module for this histone modification 2, 3. Similar to bromodomain-containing proteins that recognize histone acetylation sites and subsequently stabilize large complexes to chromatin, effector proteins can also be recruited and stabilized by histone methylation. Although histone acetylation generally correlates with active transcription, histone methylation is associated with both the activation and silencing of transcription, depending on which lysine residue is modified. The list of proteins that may in fact directly associate with specific methylated histone lysines is expanding. Since the finding of HP1, many additional proteins have been shown to bind methylated histone residues. For instance, Polycomb, Chd1, 53BP1, and Crb2/Rad9 proteins all associate with methylated chromatin in a unique manner governed by their respective recognition motifs. Here we highlight recent data on the recognition specificity and biological significance of proteins that associate with methylated histone lysines.




BRIEF REPORT

Open Access Article

PTEN Loss Inhibits CHK1 to Cause Double Stranded-DNA Breaks in Cells

Janusz Puc and Ramon Parsons
Pages 927 - 929
http://dx.doi.org/10.4161/cc.4.7.1795
Abstract | PDF

CHK1 is an essential kinase involved in the regulation of the cell cycle progression and preservation of genomic integrity. Inhibition of CHK1 leads to the accumulation of double-stranded DNA breaks. Loss of PTEN impairs CHK1-mediated checkpoint activation due to cytoplasmic sequestration of ubiquitinated CHK1. Here, we provide evidence that another consequence of reduced CHK1 function in PTEN deficient cells is the accumulation of double-stranded DNA breaks. Moreover, we show that the site of CHK1 ubiquitination (K274) is near the site of AKT phosphorylation (S280). Overall, these data demonstrate that lack of PTEN generates DNA damage due to inappropriate inactivation of CHK1. DNA damage due to the loss of PTEN is likely to stimulate tumor development.




REPORTS

Open Access Article

Regulation of E2F-1 after DNA Damage by p300-Mediated Acetylation and Ubiquitination

Laura Galbiati, Ramiro Mendoza-Maldonado, Maria Ines Gutierrez and Mauro Giacca
Pages 930 - 939
http://dx.doi.org/10.4161/cc.4.7.1784
Abstract | PDF

Here we report a novel, non-competitive mechanism that links acetylation and ubiquitination, in which the association of transcription factor E2F-1 with the cellular co-activator and acetyltransferase p300 determines its acetylation and subsequent ubiquitination. By using an antibody specifically recognizing the acetylated form of E2F-1 (AcE2F-1), we found that, after DNA damage, AcE2F-1 accumulates in the cells in a time-dependent manner, and that acetylation is increased by the expression of p300. Remarkably, the same DNA damaging conditions also induce the accumulation of ubiquitinated E2F-1, an event that is again markedly stimulated by p300 overexpression. The effects of p300 on E2F-1 ubiquitination require the integrity of the HAT domain of p300 and of the three acetylated lysines in E2F-1. Of note, p300-induced E2F-1 ubiquitination does not depend on the p45Skp2 E3 ligase, since it does not extend to other p45Skp2 targets and also occurs with an E2F-1 mutant devoid of the p45Skp2-binding domain but still retaining the acetylated region. Finally, p300-induced E2F-1 ubiquitination is not influenced by RB.

Open Access Article

Ras and the Rho Effector Cla4 Collaborate to Target and Anchor Lte1 at the Bud Cortex

Anupama Seshan and Angelika Amon
Pages 940 - 946
http://dx.doi.org/10.4161/cc.4.7.1785
Abstract | PDF

Lte1, a protein important for exit from mitosis, localizes to the bud cortex as soon as the bud forms and remains there until cells exit from mitosis. Ras, the Rho GTPase Cdc42 and its effector the protein kinase Cla4 are required for Lte1’s association with the bud cortex. Here we investigate how Ras, and the Cdc42 effector Cla4 regulate the localization of Lte1. We find that Ras2 and Lte1 associate in stages of the cell cycle when Lte1 is phosphorylated and associated with the bud cortex and that this association requires CLA4. Additionally, RAS1 and RAS2 are required for CLA4-dependent Lte1 phosphorylation. Our findings suggest that Cla4-dependent phosphorylation promotes the initial association of Lte1 with Ras at the bud cortex and that Ras is required to stabilize phosphorylated forms of Lte1 at the bud cortex. Our results also raise the interesting possibility that the localization of Lte1 affects the protein’s ability to promote mitotic exit.

Open Access Article

Evolution of Eukaryotic Cysteine Sulfinic Acid Reductase, Sulfiredoxin (Srx), from Bacterial Chromosome Partitioning Protein ParB

Malay K. Basu and Eugene V. Koonin
Pages 947 - 952
http://dx.doi.org/10.4161/cc.4.7.1786
Abstract | PDF

Sufiredoxin (Srx) is a sulfinic acid reductase, a recently identified eukaryotic enzyme, which is involved in the reduction of the hyperoxidized sulfinic acid form of the catalytic cysteine of 2-Cys peroxiredoxins (Prx). This reaction contributes to the oxidative stress response and H202 mediated signaling. We show that Srx has significant sequence and structural similarity to a functionally unrelated protein, ParB, a DNA-binding protein with a helix-turn-helix (HTH) domain which is involved in chromosome partitioning in bacteria. Sequence comparison and phylogenetic analysis of the Srx and ParB protein families suggest that Srx evolved via truncation of ParB, which removed the entire C-terminal half of the protein, including the HTH domain, and a substitution of cysteine for a glutamic acid in a highly conserved structural motif of ParB. The latter substitution apparently created the sulfinic acid reductase catalytic site. Evolution of a redox enzyme from a DNA-binding protein, with retention of highly significant sequence similarity, is unusual, even when compared to functional switches accompanying recruitment of other prokaryotic proteins for new functions in eukaryotes.

Open Access Article

RGS14 is a Microtubule-Associated Protein

Luke Martin-McCaffrey, Francis S. Willard, Agnieszka Pajak, Lina Dagnino, David P. Siderovski and Sudhir J.A. D’Souza
Pages 953 - 960
http://dx.doi.org/10.4161/cc.4.7.1787
Abstract | PDF

Heterotrimeric G-proteins and their regulators are emerging as important players in modulating microtubule polymerization dynamics and in spindle force generation during cell division in C. elegans, D. melanogaster, and mammals. We recently demonstrated that RGS14 is required for completion of the first mitotic division of the mouse embryo, and that it regulates microtubule organization in vivo. Here, we demonstrate that RGS14 is a microtubule associated protein and a component of the mitotic spindle that may regulate microtubule polymerization and spindle organization. Taxol-stabilized tubulin, but not depolymerized tubulin co-immunoprecipitates with RGS14 from cell extracts. Furthermore, RGS14 co-purifies with tubulin from porcine brain following multiple rounds of microtubule polymerization/depolymerization and binds directly to microtubules formed in vitro from pure tubulin (KD=1.3 +/- 0.3 ?M). Both RGS14 and G?i1 in the presence of exogenous GTP promote tubulin polymerization, which is dependent on additional microtubule associated proteins. However, preincubation of RGS14 with G?i1-GDP precludes either from promoting microtubule polymerization, suggesting that a functional GTP/GDP cycle is necessary. Finally, we show that RGS14 is a component of mitotic asters formed in vitro from HeLa cell extracts and that depletion of RGS14 from cell extracts blocks aster formation. Collectively, these results show that RGS14 is a microtubule associated protein that may modulate microtubule dynamics and spindle formation.

Open Access Article

Crm1-Mediated Nuclear Export of Cdc14 is Required for the Completion of Cytokinesis in Budding Yeast

Joshua Bembenek, Jungseog Kang, Cornelia Kurischko, Bing Li, Jesse R. Raab, Kenneth D. Belanger, Francis C. Luca and Hongtao Yu
Pages 961 - 971
http://dx.doi.org/10.4161/cc.4.7.1798
Abstract | PDF

The mitotic exit network (MEN) controls the exit from mitosis in budding yeast. The proline-directed phosphatase, Cdc14p, is a key component of MEN and promotes mitotic exit by activating the degradation of Clb2p and by reversing Cdk-mediated mitotic phosphorylation. Cdc14p is sequestered in the nucleolus during much of the cell cycle and is released in anaphase from the nucleolus to the nucleoplasm and cytoplasm to perform its functions. Release of Cdc14p from the nucleolus during anaphase is well understood. In contrast, less is known about the mechanism by which Cdc14p is released from the nucleus to the cytoplasm. Here we show that Cdc14p contains a leucine-rich nuclear export signal (NES) that interacts with Crm1p physically. Mutations in the NES of Cdc14p allow Clb2p degradation and mitotic exit, but cause abnormal morphology and cytokinesis defects at non-permissive temperatures. Cdc14p localizes to the bud neck, among other cytoplasmic structures, following its release from the nucleolus in late anaphase. This bud neck localization of Cdc14p is disrupted by mutations in its NES and by the leptomycin B-mediated inhibition of Crm1p. Our results suggest a requirement for Crm1p-dependent nuclear export of Cdc14p in coordinating mitotic exit and cytokinesis in budding yeast.

Open Access Article

Mad3/BubR1 Phosphorylation during Spindle Checkpoint Activation Depends on both Polo and Aurora Kinases in Budding Yeast

Giulia Rancati, Valentina Crispo, Giovanna Lucchini and Simonetta Piatti
Pages 972 - 980
http://dx.doi.org/10.4161/cc.4.7.1829
Abstract | PDF

During mitosis the spindle assembly checkpoint (SAC) delays the onset of anaphase and mitotic exit until all chromosomes are bipolarly attached to spindle fibers. Both lack of attachment due to spindle/kinetochore defects and lack of tension across kinetochores generate the “wait anaphase” signal transmitted by the SAC, which involves the evolutionarily conserved Mad1, Mad2, Mad3/BubR1, Bub1, Bub3 and Mps1 proteins, and inhibits the activity of the ubiquitin ligase Cdc20/APC, that promotes both sister chromatid dissociation in anaphase and mitotic exit. In particular, Mad3/BubR1 is directly implicated, together with Mad2, in Cdc20 inactivation in both human and yeast cells, suggesting that its activity is likely finely regulated. We show that budding yeast Mad3, like its human orthologue BubR1, is a phosphoprotein that is hyperphosphorylated during mitosis and when SAC activation is triggered by microtubule depolymerizing agents, kinetochore defects or lack of kinetochore tension. In vivo Mad3 phosphorylation depends on the Polo kinase Cdc5 and, to a minor extent, the Aurora B kinase Ipl1. Accordingly, replacing with alanines five serine residues belonging to Polo kinase-dependent putative phosphorylation sites dramatically reduces Mad3 phosphorylation, suggesting that Mad3 is likely an in vivo target of Cdc5.

Open Access Article

Methylation of MRE11 Regulates its Nuclear Compartmentalization

François-Michel Boisvert, Michael J. Hendzel, Jean-Yves Masson and Stéphane Richard
Pages 981 - 989
http://dx.doi.org/10.4161/cc.4.7.1830
Abstract | PDF

The cellular response to DNA damage includes the orderly recruitment of many protein complexes to DNA lesions. The MRE11-RAD50-NBS1 (MRN) complex is well known to localize early to sites of DNA damage, but the post-translational modifications required to mobilize it to DNA damage sites are poorly understood. Recently, we have shown that MRE11 is arginine methylated in a C-terminal glycine-arginine rich (GAR) domain by protein arginine methyltransferase 1 (PRMT1). Arginine methylation is required for the exonuclease activity of MRE11 and the intra-S phase DNA damage response. Herein, we report that cells treated with methylase inhibitors failed to relocalize MRE11 from PML nuclear bodies to sites of DNA damage and formed few ?- H2AX foci. We also demonstrate that PRMT1 is a component of PML nuclear bodies where it co-localizes with MRE11. Using cellular fractionation, we demonstrate that methylated MRE11 is predominantly associated with nuclear structures and that MRE11 methylated arginines were required for this association. These results suggest that MRE11 methylation regulates its association with nuclear structures such as PML nuclear bodies and sites of DNA damage.