Defects In Cell Viability Research Articles

MSCs-derived exosomes containing miR-486-5p attenuate cerebral ischemia and reperfusion (I/R) injury

ObjectivesThis study aims to investigate the impact of mesenchymal stem cell (MSC)-derived exosomes (Exo) on cerebral ischemia and reperfusion (I/R) injury, along with the underlying mechanism. MethodsAn animal model of cerebral ischemia was induced using middle cerebral artery occlusion (MCAO), and a cell model utilizing Neuro‐2a cells was established through oxygen-glucose deprivation/reoxygenation (OGD/R). Exosomes isolated from mouse MSCs were administered to mice or used to stimulate Neuro‐2a cells. Exosomes from MSCs transfected with miR-NC, miR-486-5p mimics, miR-486-5p inhibitor, or phosphatase and tensin homolog (PTEN) short hairpin RNAs (sh-PTEN) were employed to stimulate Neuro‐2a cells. The regulatory axis of miR-486-5p and PTEN was confirmed through rescue experiments. ResultsExo-miR-486-5p mimics alleviated cerebral I/R injury, improving neurological deficits and reducing the infarct ratio. Furthermore, Exo-miR-486-5p mimics attenuated OGD/R-induced defects in cell viability and inhibited apoptosis in Neuro‐2a cells. These mimics also reduced levels of lactate dehydrogenase (LDH) and malondialdehyde (MDA) while enhancing superoxide dismutase (SOD) activity, both in brain tissue homogenates of mice and cell supernatants. Mechanistically, PTEN was identified as a target of miR-486-5p, and the downregulation of PTEN notably elevated Exo-miR-486-inhibitor-induced reductions in cell viability while mitigating cell apoptosis. ConclusionThe results of this study demonstrate the potential of exosomes derived from MSCs to protect against cerebral I/R injury via the miR-486-5p and PTEN axis.

Escherichia coli B-Strains Are Intrinsically Resistant to Colistin and Not Suitable for Characterization and Identification of mcr Genes.

Antimicrobial resistance is an increasing threat to human and animal health. Due to the rise of multi-, extensive, and pandrug resistance, last resort antibiotics, such as colistin, are extremely important in human medicine. While the distribution of colistin resistance genes can be tracked through sequencing methods, phenotypic characterization of putative antimicrobial resistance (AMR) genes is still important to confirm the phenotype conferred by different genes. While heterologous expression of AMR genes (e.g., in Escherichia coli) is a common approach, so far, no standard methods for heterologous expression and characterization of mcr genes exist. E. coli B-strains, designed for optimum protein expression, are frequently utilized. Here, we report that four E. coli B-strains are intrinsically resistant to colistin (MIC 8-16 μg/mL). The three tested B-strains that encode T7 RNA polymerase show growth defects when transformed with empty or mcr-expressing pET17b plasmids and grown in the presence of IPTG; K-12 or B-strains without T7 RNA polymerase do not show these growth defects. E. coli SHuffle T7 express carrying empty pET17b also skips wells in colistin MIC assays in the presence of IPTG. These phenotypes could explain why B-strains were erroneously reported as colistin susceptible. Analysis of existing genome data identified one nonsynonymous change in each pmrA and pmrB in all four E. coli B-strains; the E121K change in PmrB has previously been linked to intrinsic colistin resistance. We conclude that E. coli B-strains are not appropriate heterologous expression hosts for identification and characterization of mcr genes. IMPORTANCE Given the rise in multidrug, extensive drug, and pandrug resistance in bacteria and the increasing use of colistin to treat human infections, occurrence of mcr genes threatens human health, and characterization of these resistance genes becomes more important. We show that three commonly used heterologous expression strains are intrinsically resistant to colistin. This is important because these strains have previously been used to characterize and identify new mobile colistin resistance (mcr) genes. We also show that expression plasmids (i.e., pET17b) without inserts cause cell viability defects when carried by B-strains with T7 RNA polymerase and grown in the presence of IPTG. Our findings are important as they will facilitate improved selection of heterologous strains and plasmid combinations for characterizing AMR genes, which will be particularly important with a shift to Culture-independent diagnostic tests where bacterial isolates become increasingly less available for characterization.

Recurrent non-severe hypoglycemia aggravates cognitive decline in diabetes and induces mitochondrial dysfunction in cultured astrocytes

The present study aimed to determine the relationship between astrocytes and recurrent non-severe hypoglycemia (RH)2 -associated cognitive decline in diabetes. RH induced cognitive impairment and neuronal cell death in the cerebral cortex of diabetic mice, accompanied by excessive activation of astrocytes. Levels of the neurotrophins BDNF and GDNF, together with BDNF and GDNF- related signaling, were downregulated by RH. In vitro, recurrent low glucose (RLG)3 impaired cell viability and induced apoptosis of high-glucose cultured astrocytes. Accumulating mitochondrial ROS and dysregulated mitochondrial functions, including abnormal morphology, decreased membrane potential, downregulated ATP levels, and disrupted bioenergetic status, were observed in these cells. SS-31 mediated protection of mitochondrial functions reversed RLG-induced cell viability defects and neurotrophin production. These findings demonstrate that RH induced astrocyte overactivation and mitochondrial dysfunction, leading to astrocyte-derived neurotrophin disturbance, which might contribute to diabetic cognitive decline. Targeting astrocyte mitochondria might represent a neuroprotective therapy for hypoglycemia-associated neurodegeneration in diabetes.

PEPCK-M recoups tumor cell anabolic potential in a PKC-\u03b6-dependent manner

BackgroundMitochondrial phosphoenolpyruvate carboxykinase (PEPCK-M; PCK2) is expressed in all cancer types examined and in neuroprogenitor cells. The gene is upregulated by amino acid limitation and ER-stress in an ATF4-dependent manner, and its activity modulates the PEP/Ca2+ signaling axis, providing clear arguments for a functional relationship with metabolic adaptations for cell survival. Despite its potential relevance to cancer metabolism, the mechanisms responsible for its pro-survival activity have not been completely elucidated.Methods[U-13C]glutamine and [U-13C]glucose labeling of glycolytic and TCA cycle intermediates and their anabolic end-products was evaluated quantitatively using LC/MS and GC/MS in conditions of abundant glucose and glucose limitation in loss-of-function (shRNA) and gain-of-function (lentiviral constitutive overexpression) HeLa cervix carcinoma cell models. Cell viability was assessed in conjunction with various glucose concentrations and in xenografts in vivo.ResultsPEPCK-M levels linearly correlated with [U-13C]glutamine label abundance in most glycolytic and TCA cycle intermediate pools under nutritional stress. In particular, serine, glycine, and proline metabolism, and the anabolic potential of the cell, were sensitive to PEPCK-M activity. Therefore, cell viability defects could be rescued by supplementing with an excess of those amino acids. PEPCK-M silenced or inhibited cells in the presence of abundant glucose showed limited growth secondary to TCA cycle blockade and increased ROS.In limiting glucose conditions, downregulation of PKC-ζ tumor suppressor has been shown to enhance survival. Consistently, HeLa cells also sustained a survival advantage when PKC-ζ tumor suppressor was downregulated using shRNA, but this advantage was abolished in the absence of PEPCK-M, as its inhibition restores cell growth to control levels. The relationship between these two pathways is also highlighted by the anti-correlation observed between PEPCK-M and PKC-ζ protein levels in all clones tested, suggesting co-regulation in the absence of glucose. Finally, PEPCK-M loss negatively impacted on anchorage-independent colony formation and xenograft growth in vivo.ConclusionsAll in all, our data suggest that PEPCK-M might participate in the mechanisms to regulate proteostasis in the anabolic and stalling phases of tumor growth. We provide molecular clues into the clinical relevance of PEPCK-M as a mechanism of evasion of cancer cells in conditions of nutrient stress.

Delineating FtsQ-mediated regulation of cell division in Mycobacterium tuberculosis

Identifying and characterizing the individual contributors to bacterial cellular elongation and division will improve our understanding of their impact on cell growth and division. Here, we delineated the role of ftsQ, a terminal gene of the highly conserved division cell wall (dcw) operon, in growth, survival, and cell length maintenance in the human pathogen Mycobacterium tuberculosis (Mtb). We found that FtsQ overexpression significantly increases the cell length and number of multiseptate cells. FtsQ depletion in Mtb resulted in cells that were shorter than WT cells during the initial growth stages (4 days after FtsQ depletion) but were longer than WT cells at later stages (10 days after FtsQ depletion) and compromised the survival in vitro and in differentiated THP1 macrophages. Overexpression of N- and C-terminal FtsQ regions altered the cell length, and the C-terminal domain alone complemented the FtsQ depletion phenotype. MS analyses suggested robust FtsQ phosphorylation on Thr-24, and although phosphoablative and -mimetic mutants rescued the FtsQ depletion-associated cell viability defects, they failed to complement the cell length defects. MS and coimmunoprecipitation experiments identified 63 FtsQ-interacting partners, and we show that the interaction of FtsQ with the recently identified cell division protein SepIVA is independent of FtsQ phosphorylation and suggests a role of FtsQ in modulating cell division. FtsQ exhibited predominantly septal localization in both the presence and absence of SepIVA. Our results suggest a role for FtsQ in modulating the length, division, and survival of Mtb cells both in vitro and in the host.

Abstract 2524: MiR-124 suppresses p62 and p65/NFkB to regulate autophagy, inflammation and cell death in KRAS mutant mesenchymal NSCLC cells

Abstract Background KRAS mutant non-small cell lung cancers (NSCLC) are molecularly and histologically diverse. Epithelial-like cells are more KRAS dependent, whereas mesenchymal-like cells are less KRAS dependent. These two subtypes are designated KE (epithelial) and KM (mesenchymal), respectively. A KE versus KM subtype transcriptional signature reveals specific modes of KRAS dependent survival signaling in the KE subtype. This KRAS dependency signature is significantly enriched with predicted microRNA (miRNA) target genes of miR-205 and miR-34b/c. MiRNAs can function as tumor suppressors by coordinately regulating multiple oncogenic signaling pathways. The role of deregulated miRNA function in mediating the survival of KM versus KE NSCLC cells has not been investigated to date. Methods Differential miRNA expression in KRAS mutant cell lines was determined using Taqman low-density qPCR arrays (TLDA). Functional miRNA reconstitution experiments of downregulated miRNAs were performed in a panel of KM cell lines. Effects on apoptosis and autophagy were performed by Western blotting, immunofluorescence and live cell microscopy and caspase assays. The molecular targets of miR-124 were computationally identified by TargetScan or miRWalk and experimentally verified using 3’UTR luciferase-based assays. Functional rescue of miRNA-dependent cell viability defects was determined by ectopic predicted target gene expression. Results Comparison of KE to KM cells yielded a KE-KM miRNA subtype classifier/signature. This signature revealed a number of silenced or suppressed miRNAs in KM cell lines, including members of the miR-200 family. MiR-200 and miR-205 reconstitution in KM cells modulated epithelial plasticity by Zeb1 protein suppression and increased E-cadherin levels. Reconstitution of miR-124, miR-625 and miR-518-3p in KM cells caused pronounced loss of cell viability. Furthermore, miR-124 caused autolysosome maturation defects. We identified SQSTM1/p62, TRAF6 and RELA/p65 as key predicted targets of miR-124. MiR-124 reconstitution in KM cells caused decreased p62, TRAF6 and p65 protein levels. The effect of miR-124 on p62 expression was verified using a Luciferase-p62-3’UTR reporter construct. Overexpression of p62 in KM cells rescued the cell viability defects caused by miR-124. Conclusion These studies implicate miR-124 as a context-dependent tumor suppressor miRNA in KM subtype cells. MiR-124 directly suppresses expression of SQSTM1/p62 to promote defects in autolysosome maturation. In parallel, miR-124 suppresses RELA/ p65 and in some cases, TRAF6, to alter expression levels of several cytokines. Thus, miR-124 coordinately regulates autophagy and inflammation to disrupt the finely-tuned balance between pro and anti-inflammatory signals, resulting in cytotoxic effects in a specific subtype of mesenchymal-like KRAS mutant NSCLC cells. Citation Format: Anita K. Mehta, Kevin Hua, William Whipple, Mihn-Thuy Nguyen, Rushika M. Perera, Johanns Haybaeck, Joanne Weidhass, Jeffrey Settleman, Anurag Singh. MiR-124 suppresses p62 and p65/NFkB to regulate autophagy, inflammation and cell death in KRAS mutant mesenchymal NSCLC cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2524. doi:10.1158/1538-7445.AM2017-2524

Abstract 1180: The TCA cycle transferase DLST is critical for MYC-mediated leukemogenesis

Abstract The proto-oncogene MYC has been implicated in the pathogenesis of many human cancers, including hematological and solid malignancies1. In the majority of T-ALL cases, MYC is aberrantly expressed downstream of activated NOTCH1 mutations. Despite the pivotal role of MYC in the pathogenesis of T-cell acute lymphoblastic leukemia (T-ALL) and many other cancers, the mechanisms underlying MYC-mediated tumorigenesis remain inadequately understood2. Here we utilized a well-characterized zebrafish model of Myc-induced T-ALL for genetic studies to identify novel genes contributing to disease onset. We found that heterozygous inactivation of a tricarboxylic acid (TCA) cycle enzyme, dihydrolipoamide S-succinyltransferase (Dlst), significantly delayed tumor onset. Concordant with our zebrafish results, RNAi knockdown of DLST led to decreased cell viability and induction of apoptosis in human T-ALL cell lines. DLST is the E2 transferase of the -ketoglutarate dehydrogenase complex (KGDHC), which converts -ketoglutarate (-KG) to succinyl-CoA in the TCA cycle3. Polar metabolomics profiling revealed that the TCA cycle was disrupted by DLST knockdown in human T-ALL cells, as demonstrated by an accumulation of -KG and its precursor glutamine, as well as a loss of succinyl-CoA. Addition of succinate, the downstream TCA cycle intermediate, to human T-ALL cells was sufficient to rescue defects in cell viability caused by DLST inactivation. Taken together, our studies identify DLST as an important mediator of MYC-driven leukemogenesis and provide compelling evidence for the metabolic dependence of T-ALL cells on the TCA cycle. 1. Nesbit CE, Tersak JM, Prochownik EV. MYC oncogenes and human neoplastic disease. Oncogene 1999 May 13; 18(19): 3004-3016. 2. Sharma VM, Calvo JA, Draheim KM, Cunningham LA, Hermance N, Beverly L, et al. Notch1 contributes to mouse T-cell leukemia by directly inducing the expression of c-myc. Molecular and cellular biology 2006 Nov; 26(21): 8022-8031. 3. Sheu KF, Blass JP. The alpha-ketoglutarate dehydrogenase complex. Ann N Y Acad Sci 1999; 893: 61-78. Citation Format: Nicole Anderson, Dun Li, H.L. Peng, Marc Mansour, Fabrice Laroche, Evisa Gjini, Daniel Helman, Itrat Harrold, Le Meng, Takaomi Sanda, Adam Amsterdam, Donna Neuberg, Travis Denton, Anurag Singh, A Thomas Look, Hui Feng. The TCA cycle transferase DLST is critical for MYC-mediated leukemogenesis. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1180.

Optimized expression and purification of biophysical quantities of Lac repressor and Lac repressor regulatory domain

The recombinant production of Lac repressor (LacI) in Escherichia coli is complicated by its ubiquitous use as a regulatory element in commercially-available expression vectors and host strains. While LacI-regulated expression systems are often used to produce recombinant LacI, the product can be heterogeneous and unsuitable for some studies. Alternative approaches include using unregulated vectors which typically suffer from low yield or vectors with promoters induced by metabolically active sugars which can dilute isotope labels necessary for certain biophysical studies. Here, an optimized expression system and isolation protocol for producing various constructs of LacI is introduced which eliminates these complications. The expression vector is an adaptation of the pASK backbone wherein expression of the lacI gene is regulated by an anhydrotetracyline inducible tetA promoter and the host strain lacks the lacI gene. Typical yields in highly deuterated minimal medium are nearly 2-fold greater than those previously reported. Notably, the new expression system is also able to produce the isolated regulatory domain of LacI without co-expression of the full-length protein and without any defects in cell viability, eliminating the inconvenient requirement for strict monitoring of cell densities during pre-culturing. Typical yields in highly deuterated minimal medium are significantly greater than those previously reported. Characterization by solution NMR shows that LacI constructs produced using this expression system are highly homogenous and functionally active.

Redox Imbalance Underlies the Fitness Defect Associated with Inactivation of the Pta-AckA Pathway in Staphylococcus aureus.

The phosphotransacetylase-acetate kinase (Pta-AckA) pathway is thought to be a vital ATP generating pathway for Staphylococcus aureus. Disruption of the Pta-AckA pathway during overflow metabolism causes significant reduction in growth rate and viability, albeit not due to intracellular ATP depletion. Here, we demonstrate that toxicity associated with inactivation of the Pta-AckA pathway resulted from an altered intracellular redox environment. Growth of the pta and ackA mutants under anaerobic conditions partially restored cell viability. NMR metabolomics analyses and (13)C6-glucose metabolism tracing experiments revealed the activity of multiple pathways that promote redox (NADH/NAD(+)) turnover to be enhanced in the pta and ackA mutants during anaerobic growth. Restoration of redox homeostasis in the pta mutant by overexpressing l- lactate dehydrogenase partially restored its viability under aerobic conditions. Together, our findings suggest that during overflow metabolism, the Pta-AckA pathway plays a critical role in preventing cell viability defects by promoting intracellular redox homeostasis.

The TCA cycle transferase DLST is important for MYC-mediated leukemogenesis.

Despite the pivotal role of MYC in the pathogenesis of T-cell acute lymphoblastic leukemia (T-ALL) and many other cancers, the mechanisms underlying MYC-mediated tumorigenesis remain inadequately understood. Here we utilized a well-characterized zebrafish model of Myc-induced T-ALL for genetic studies to identify novel genes contributing to disease onset. We found that heterozygous inactivation of a tricarboxylic acid (TCA) cycle enzyme, dihydrolipoamide S-succinyltransferase (Dlst), significantly delayed tumor onset in zebrafish without detectable effects on fish development. DLST is the E2 transferase of the α-ketoglutarate (α-KG) dehydrogenase complex (KGDHC), which converts α-KG to succinyl-CoA in the TCA cycle. RNAi knockdown of DLST led to decreased cell viability and induction of apoptosis in human T-ALL cell lines. Polar metabolomics profiling revealed that the TCA cycle was disrupted by DLST knockdown in human T-ALL cells, as demonstrated by an accumulation of α-KG and a decrease of succinyl-CoA. Addition of succinate, the downstream TCA cycle intermediate, to human T-ALL cells was sufficient to rescue defects in cell viability caused by DLST inactivation. Together, our studies uncovered an important role for DLST in MYC-mediated leukemogenesis and demonstrated the metabolic dependence of T-lymphoblasts on the TCA cycle, thus providing implications for targeted therapy.

Abstract LB-C02: A KRAS dependency microRNA signature reveals a p62/Sqstm1-centered autophagy network regulated by mir-124

Abstract Background Non-small cell lung cancer (NSCLC) is derived from broncho-alveolar epithelial cells. NSCLCs frequently harbor mutations in the KRAS oncogene, yet only a subset of NSCLC cell lines depend on KRAS for sustained survival signaling. Cells that are more epithelial are highly KRAS dependent, whereas mesenchymal-like cells are KRAS independent for cell survival signaling. KRAS mutations are commonly associated with resistance to anti-cancer therapeutics. An important drug resistance mechanism is altered cellular plasticity, via a process known as epithelial-to-mesenchymal transition (EMT). Here, we aimed to identify and elucidate a KRAS dependent microRNA (miRNA) signaling network in epithelial cancer cells that modulates malignant growth and proliferation as well as cellular plasticity in NSCLC. Methods Differential miRNA expression in 6 KRAS mutant NSCLC cell lines (3 KRAS independent versus 3 KRAS dependent) was determined using Taqman low-density qPCR arrays (TLDA). To explore the functional relevance of differentially regulated miRNAs, gain-of-function studies by reconstitution experiments were performed using miRNA mimics in a panel of six KRAS independent cell lines. The molecular targets of mir-124-2 were computationally identified by TargetScan or miRWalk and experimentally verified using 3'UTR luciferase-based assays. Functional rescue of cell viability defects was determined by forced expression of GFP-p62/Sqstm1 in KRAS independent lung cancer cell lines. Results We identified a distinct differential miRNA expression profile in KRAS dependent versus KRAS independent NSCLC cells. This KRAS dependency miRNA signature included members of the mir-200 family, mir-34c and mir-205. Mir-200 and mir-205 reconstitution in KRAS independent cells modulated epithelial plasticity by down regulating Zeb1 protein expression and, thereby, increasing E-cadherin levels. Ectopic introduction of a subset of miRNAs in KRAS independent cells caused a consistent and pronounced loss of cell viability in all cell lines tested, including mir124, mir-625 and mir-518-3p. Ectopic expression of mir124 in KRAS independent cells caused cell viability defects by inducing apoptosis and autophagy. Using bioinformatics databases, we isolated p62/Sqstm1 and REL-A as key predicted targets of mir124-2. Mir-124-2 reconstitution in KRAS independent NSCLC cell lines caused decreased p62/Sqstm1 and REL-A protein expression levels. The effect of mir-124 on p62/Sqstm1 expression was verified using a p62-3'UTR-Luciferase construct. Overexpression of GFP-p62 in KRAS independent cells rescued the cell viability defects by mir124-2. Conclusion MiR-124 expression is down regulated in KRAS independent NSCLC cells. Reintroduction of mir124-2 induces cell viability defects in part, by targeting p62/Sqstm1 and REL-A. We conclude that, mir-124 down regulates p62/Sqstm1 expression to activate autophagic flux. This leads to down regulation of the NFκB pathway and subsequent reduction in expression of pro-survival genes such as IL-6 and IL-1β. Taken together, mir124-2 acts as a tumor suppressor in KRAS mutant NSCLC cells and provides a mechanistic link between activation of autophagy and control of proinflammatory signaling in NSCLC cell survival. Overexpression of mir124-2 might be of potential therapeutic value for the treatment of KRAS mutant NSCLC. Citation Format: ANITA K. MEHTA, Kevin Hua, William Whipple, Minh-Thuy Nguyen, Stephanie Bartley, Margaret McGuiness, Jeff Settleman, Joanne Weidhaas, Anurag Singh. A KRAS dependency microRNA signature reveals a p62/Sqstm1-centered autophagy network regulated by mir-124. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr LB-C02.

Abstract 5526: Inhibition of the histone methyl transferase EZH2 causes viability defects in multiple myeloma

Abstract Histone lysine methylation, which is dynamically regulated by methyltransferases and demethylases, plays an important role in the establishment and maintenance of chromatin structure and thereby contributes to the control of gene expression. The development of small molecule methyltransferase and demethylase inhibitors provides an approach to manipulate transcriptional programs, and thus potentially allow interference with aberrant cellular states as observed in cancer. The histone methyltransferase Enhancer of Zeste Homologue 2 (EZH2) is a component of the Polycomb Repressive Complex 2. It mediates trimethylation of lysine 27 on histone 3 (H3K27me3), which leads to transcriptional repression. EZH2 has been widely implicated in cancer and inhibition of its catalytic activity provides a novel therapeutic approach to treat human cancers. Constellation has identified, characterized and optimized potent, selective and reversible EZH2 small molecule inhibitors as well as studied the biological impact of such inhibition. We have previously shown that pharmacological inhibition of EZH2 causes selective lymphoma cell viability defects with cell lines harboring EZH2 mutations being the most sensitive. The discovery of small molecules that specifically inhibit EZH2 has enabled us to look for other disease indications that might be dependent on EZH2 for survival. We carried out a long term cell viability screen in ∼75 cell lines across several different hematological malignancies using an EZH2 inhibitor. About 30% of all tested Mutliple Myeloma and Plasmacytoma cell lines showed a time-dependent phenotypic response. In these cell lines H3K27me3 levels were effectively reduced in a dose dependent manner within 4 days of compound treatment which was followed by the induction of apoptotsis at later time points. EZH2 inhibitors also achieved tumor growth inhibition in a Multiple Myeloma subcutaneous xenograft model. To understand the underlying molecular mechanism of EZH2 inhibitor sensitivity in Multiple Myeloma, genome-wide mapping of EZH2 and H3K27me3 sites in the absence and presence of the compound have been performed in conjunction with gene expression profiling and the results will be discussed. In conclusion, we identified Multiple Myeloma as a disease modality where EZH2 inhibition leads to cell viability defects both in vitro and in vivo. Citation Format: Shilpi Arora, Vidya Balasubramanian, Kaylyn Williamson, Victor Gehling, Chris Nasveschuk, Rishi Vaswani, Jennifer Busby, Shivani Garapaty, Priya Iyer, Feng Zhao, Robert Campbell, Richard Cummings, Jim Audia, JC Harmange, Brian Albrecht, Andrew Cook, Les Dakin, Emmanuel Normant, Patrick Trojer. Inhibition of the histone methyl transferase EZH2 causes viability defects in multiple myeloma. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5526. doi:10.1158/1538-7445.AM2014-5526

FTT0831c/FTL_0325 Contributes to Francisella tularensis Cell Division, Maintenance of Cell Shape, and Structural Integrity

The Francisella FTT0831c/FTL_0325 gene encodes amino acid motifs to suggest it is a lipoprotein and that it may interact with the bacterial cell wall as a member of the OmpA-like protein family. Previous studies have suggested that FTT0831c is surface exposed and required for virulence of Francisella tularensis by subverting the host innate immune response (M. Mahawar et al., J. Biol. Chem. 287:25216-25229, 2012). We also found that FTT0831c is required for murine pathogenesis and intramacrophage growth of Schu S4, but we propose a different model to account for the proinflammatory nature of the resultant mutants. First, inactivation of FTL_0325 from live vaccine strain (LVS) or FTT0831c from Schu S4 resulted in temperature-dependent defects in cell viability and morphology. Loss of FTT0831c was also associated with an unusual defect in lipopolysaccharide O-antigen synthesis, but loss of FTL_0325 was not. Full restoration of these properties was observed in complemented strains expressing FTT0831c in trans, but not in strains lacking the OmpA motif, suggesting that cell wall contact is required. Finally, growth of the LVS FTL_0325 mutant in Mueller-Hinton broth at 37°C resulted in the appearance of membrane blebs at the poles and midpoint, prior to the formation of enlarged round cells that showed evidence of compromised cellular membranes. Taken together, these data are more consistent with the known structural role of OmpA-like proteins in linking the OM to the cell wall and, as such, maintenance of structural integrity preventing altered surface exposure or release of Toll-like receptor 2 agonists during rapid growth of Francisella in vitro and in vivo.

Abstract 4621: The histone methyltransferase EZH2 catalytic activity is required for cell growth in diffuse large B-cell lymphoma.

Abstract Lysine methyltransferases and demethylases were identified as transcriptional co-regulators functioning by either preserving particular chromatin methylation states or by controlling placement and removal of histone lysine methylation marks to promote dynamic changes in gene expression. The development of small molecule methyltransferase and demethylase inhibitors provides a novel approach to affect the regulation of transcription, and thus potentially allowing interference with aberrant transcriptional programs as observed, for instance, in cancer. Enhancer of Zeste Homolog 2 (EZH2), the major histone H3 lysine 27 (K27) methyltransferase, is widely implicated in tumor progression. The presence of a recurrent mutation of a single tyrosine residue in the EZH2 catalytic domain in germinal center B-cell like diffuse large B-cell lymphoma (GCB-DLBCL) and follicular lymphoma suggests that these cancers might be dependent on altered EZH2 molecular function, the mutation facilitating the conversion of an H3K27 di-methylated to a tri-methylated state. Inhibition of the EZH2 catalytic activity will provide a new therapeutic approach to treat human cancers, especially lymphomas carrying activating mutations. Constellation has identified, characterized and optimized potent, selective and reversible EZH2 small molecule inhibitors as well as studied the biological impact of such inhibition. We find that pharmacological inhibition of EZH2 causes selective cell viability defects with cell lines harboring EZH2 mutations being the most sensitive. Our EZH2 inhibitors potently engage the target in vivo and exhibit efficacy in lymphoma xenograft models. Genome-wide mapping of EZH2 and H3K27me3 sites in the absence and presence of the compound revealed that the EZH2 inhibitor caused significant changes to the local chromatin modification landscape, however only a subset of these alterations translated into gene expression changes. The discovery of additional contexts that define sensitivity to EZH2 inhibitors will be discussed. Citation Format: James E. Audia, Patrick Trojer, Shivani Garapaty, Fei Lan, Vidya Balasubramanian, Eric Chan, Charles Hatton, Robert Campbell, Richard Cummings, Emmanuel Normant, Barbara Bryant, Brian Albrecht, Jean Christophe Harmange, Les Dakin, Victor Gehling, Chris Nasveschuk, Rishi Vaswani, Andrew Cook. The histone methyltransferase EZH2 catalytic activity is required for cell growth in diffuse large B-cell lymphoma. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4621. doi:10.1158/1538-7445.AM2013-4621

542 The Experimental Anti-cancer Drug Mitochondrially-targeted Vitamin E Succinate Inhibits Mitochondrial Transcription

domain in germinal center B-cell like diffuse large B-cell lymphoma (GCBDLBCL) and follicular lymphoma suggests that these cancers might be dependent on altered EZH2 molecular function, the mutation facilitating the conversion of a H3K27 di-methylated to a tri-methylated state. Inhibition of the EZH2 catalytic activity will provide a new therapeutic approach to treat human cancers, especially lymphomas carrying activating mutations. Constellation has identified, characterized and optimized potent, selective and reversible EZH2 small molecule inhibitors as well as studied the biological impact of such inhibition. We find that pharmacological inhibition of EZH2 causes cell viability defects with cell lines harboring EZH2 mutations being the most sensitive. Genome-wide mapping of EZH2 and H3K27me3 sites in the absence and presence of the compound revealed that the EZH2 inhibitor caused significant changes to the local chromatin modification landscape, however only a subset of these alterations translated into gene expression changes. The EZH2-controlled gene signature and the functional impact of altered expression on GCBDLBCL cell survival will be discussed.

Glaucoma-associated WDR36 variants encode functional defects in a yeast model system

Primary open-angle glaucoma (POAG) is a leading cause of blindness worldwide. POAG is associated with a characteristic progression of changes to ocular morphology and degeneration at the optic nerve head with the loss of visual fields. Physical mapping efforts identified genomic loci in which to search for causative POAG gene mutations. WDR36, at locus GLC1G, was initially identified as a gene with a low frequency of non-synonymous sequence variations that were exclusive to adult-onset POAG patients. It has since been shown that rare WDR36 sequence variants are also present in the normal population at similarly low frequencies. The lack of a consistent genotype:phenotype correlation prompted us to investigate the functional consequences of WDR36 sequence variations. WDR36 is involved in rRNA processing, a critical step in ribosome biogenesis, and is very similar to yeast Utp21p which is a member of the small subunit (SSU) processome complex responsible for maturation of 18S rRNA. We, therefore, developed a yeast model system to test the functional and phenotypic consequences of POAG-associated sequence variants introduced into UTP21. Alone, the POAG variants did not produce any significant defects in cell viability or rRNA processing. However, when combined with disruption of STI1 (which synthetically interacts with UTP21), 5 of the 11 tested variants had increased or decreased cell viability which corresponded to reduced or elevated levels of pre-rRNA, respectively. These results demonstrate that, in the correct genetic background, WDR36 sequence variants can lead to an altered cellular phenotype, supporting the theory that WDR36 participates in polygenic forms of glaucoma.

Small GTPase Rho5 is a functional homologue of Rho1, which controls cell shape and septation in fission yeast

The small GTPase Rho1 plays an essential role in controlling the organization of the actin cytoskeleton and synthesis of the cell wall in the fission yeast Schizosaccharomyces pombe. Here we studied the role of Rho5 whose primary structure is very similar to that of Rho1. It was found that elevated expression of Rho5 was able to compensate for the lethality of cells lacking Rho1. Rho5 was localized to the ends of interphase cells and the mid-region of mitotic cells. Overexpression of Rho5 caused depolarization of F-actin patches and abnormal formation of the cell wall, as did Rho1. Although rho5 + was not essential for maintaining the cell shape, rho1 rho5-double null cells showed more severe defects in cell viability than rho1-null cells. Thus, it is likely that Rho5 has an overlapping function with Rho1 in controlling cell growth and division in S. pombe.

Maternal Control of Development at the Midblastula Transition and beyond: Mutants from the Zebrafish II

Many maternal factors in the oocyte persist in the embryo. They are required to initiate zygotic transcription but also function beyond this stage, where they interact with zygotic gene products during embryonic development. In a four-generation screen in the zebrafish, we identified 47 maternal-effect and five paternal-effect mutants that manifest their phenotypes at the time of, or after, zygotic genome activation. We propagated a subset of 13 mutations that cause developmental arrest at the midblastula transition, defects in cell viability, embryonic morphogenesis, and establishment of the embryonic body plan. This diverse group of mutants, many not previously observed in vertebrates, demonstrates a substantial maternal contribution to the “zygotic” period of embryogenesis and a surprising degree of paternal control. These mutants provide powerful tools to dissect the maternal and paternal control of vertebrate embryogenesis.

Analysis of the autonomy of imaginal disc defects in a small-disc mutant of Drosophila melanogaster

Lethal mutations which cause imaginal disc abnormalities in Drosophila melanogaster identify genes whose function is necessary for normal disc development, and these mutant genes may be used as probes of the role of their wild-type alleles in normal development. It is crucial to the interpretation of the disc phenotype of such mutants to know which abnormalities are autonomous (caused by expression of the mutant gene in imaginal cells) and which are nonautonomous (indirectly caused, for example, by expression of the mutant gene in larval cells). We chose for study l(3)c21R (3-67.8), a late-larval lethal mutation with a complex phenotype, to test the adequacy of available techniques for assessing autonomy. We employed surgical and genetic techniques to determine the imaginal cell autonomy of the defects in cell viability, growth, and differentiation in c21R discs. The imaginal cell viability defect is nonautonomous. The disc growth and differentiation defects are autonomous; however, in genetic mosaics these two autonomous defects are separable. These results show that c21R belongs to the class of mutations which affect both larval and imaginal cells. In combination, the available methods were adequate to resolve the issue of autonomy in this complex case. However, in isolation several of the methods could have led to incomplete or misleading interpretations. This emphasizes that to analyze any developmental mutant it is necessary to examine the issue of autonomy from several points of view.