Limit Cell Growth Research Articles

Evaluation of ∆2-pioglitazone, an analogue of pioglitazone, on colon cancer cell survival: Evidence of drug treatment association with autophagy and activation of the Nrf2/Keap1 pathway.

Thiazolidinediones have been shown to exhibit anti-proliferative effects against cancer cells derived from diverse tissue origins both in vivo and in vitro. We studied the anti-proliferative impact of 5-{4-(2-(5-ethyl-pyridin-2-yl)-ethoxy)-benzylidene}-thiazolidine-2,4-dione (∆2-pioglitazone), an analogue of pioglitazone, which binds to the nuclear peroxisome proliferator activated receptor-γ without activating it, on human adenocarcinoma-derived HT29 and HCT116 cells. In HTC116 cells, exposure to ∆2-pioglitazone reduced cell growth, but HT29 cells reached the plateau phase of growth after three days. ∆2-pioglitazone treatment did not trigger cells to enter apoptosis but enhanced the autophagy process. The effect of ∆2-pioglitazone treatment was related to the increase of oxygen and nitric oxide-derived species production and decreased glutathione content. Moreover, pre-treatment with an antioxidant before addition of ∆2-pioglitazone limited cell growth inhibition, reduced the production of reactive species and attenuated autophagy within the cells. The impact of the drug was associated with activation of the Nrf2/Keap1 pathway as demonstrated by the increased protein content of several antioxidant enzymes, notably heme-oxygenase-1.

The expression of the tumour suppressor HBP1 is down-regulated by growth factors via the PI3K/PKB/FOXO pathway.

Growth factors inactivate the FOXO (forkhead box O) transcription factors through PI3K (phosphoinositide 3-kinase) and PKB (protein kinase B). By comparing microarray data from multiple model systems, we identified HBP1 (high-mobility group-box protein 1) as a novel downstream target of this pathway. HBP1 mRNA was down-regulated by PDGF (platelet-derived growth factor), FGF (fibroblast growth factor), PI3K and PKB, whereas it was up-regulated by FOXO factors. This observation was confirmed in human and murine fibroblasts as well as in cell lines derived from leukaemia, breast adenocarcinoma and colon carcinoma. Bioinformatics analysis led to the identification of a conserved consensus FOXO-binding site in the HBP1 promoter. By luciferase activity assay and ChIP, we demonstrated that FOXO bound to this site and regulated the HBP1 promoter activity in a PI3K-dependent manner. Silencing of HBP1 by shRNA increased the proliferation of human fibroblasts in response to growth factors, suggesting that HBP1 limits cell growth. Finally, by analysing a transcriptomics dataset from The Cancer Genome Atlas, we observed that HBP1 expression was lower in breast tumours that had lost FOXO expression. In conclusion, HBP1 is a novel target of the PI3K/FOXO pathway and controls cell proliferation in response to growth factors.

TBC1D7Mutations are Associated with Intellectual Disability, Macrocrania, Patellar Dislocation, and Celiac Disease

TBC1D7 forms a complex with TSC1 and TSC2 that inhibits mTORC1 signaling and limits cell growth. Mutations in TBC1D7 were reported in a family with intellectual disability (ID) and macrocrania. Using exome sequencing, we identified two sisters homozygote for the novel c.17_20delAGAG, p.R7TfsX21 TBC1D7 truncating mutation. In addition to the already described macrocephaly and mild ID, they share osteoarticular defects, patella dislocation, behavioral abnormalities, psychosis, learning difficulties, celiac disease, prognathism, myopia, and astigmatism. Consistent with a loss-of-function of TBC1D7, the patient's cell lines show an increase in the phosphorylation of 4EBP1, a direct downstream target of mTORC1 and a delay in the initiation of the autophagy process. This second family allows enlarging the phenotypic spectrum associated with TBC1D7 mutations and defining a TBC1D7 syndrome. Our work reinforces the involvement of TBC1D7 in the regulation of mTORC1 pathways and suggests an altered control of autophagy as possible cause of this disease.

Liquid perfluorochemical-supported hybrid cell culture system for proliferation of chondrocytes on fibrous polylactide scaffolds

CP5 bovine chondrocytes were cultured on biodegradable electrospun fibrous polylactide (PLA) scaffolds placed on a flexible interface formed between two immiscible liquid phases: (1) hydrophobic perfluorochemical (PFC) and (2) aqueous culture medium, as a new way of cartilage implant development. Robust and intensive growth of CP5 cells was achieved in our hybrid liquid–solid–liquid culture system consisting of the fibrous PLA scaffolds in contrast to limited growth of the CP5 cells in traditional culture system with PLA scaffold placed on solid surface. The multicellular aggregates of CP5 cells covered the surface of PLA scaffolds and the chondrocytes migrated through and overgrew internal fibers of the scaffolds. Our hybrid culture system simultaneously allows the adhesion of adherent CP5 cells to fibers of PLA scaffolds as well as, due to use of phase of PFC, enhances the mass transfer in the case of supplying/removing of respiratory gases, i.e., O2 and CO2. Our flexible (independent of vessel shape) system is simple, ready-to-use and may utilize a variety of polymer-based scaffolds traditionally proposed for implant development.

Preliminary studies of cell culture strategies for bioprocess development based on HEK293 cells

Background The use of human embryonic kidney cells (HEK293) for recombinant protein or virus production has gained relevance along the last years. They are specially recommended for transient gene expression and adenovirus or adeno-associated virus generation [1,2]. To achieve high volumetric productivities towards bioprocess optimization, the concentration of biocatalizer (i.e. animal cells) must be enhanced. The limits for cell growth are mainly related to the accumulation of metabolic by-products, or the depletion of nutrients [3]; therefore, cell cultures strategies must be developed. In this work, we have explored Punctual Feeding and Media Replacement cell culture strategies to over perform the limit on Xvmax encountered on batch culture mode. Finally, we scaled up cell culture in order to control other parameters (i.e. pO2) that could be limiting cell growth.

The Use of Chemostats in Microbial Systems Biology

Cells regulate their rate of growth in response to signals from the external world. As the cell grows, diverse cellular processes must be coordinated including macromolecular synthesis, metabolism and ultimately, commitment to the cell division cycle. The chemostat, a method of experimentally controlling cell growth rate, provides a powerful means of systematically studying how growth rate impacts cellular processes - including gene expression and metabolism - and the regulatory networks that control the rate of cell growth. When maintained for hundreds of generations chemostats can be used to study adaptive evolution of microbes in environmental conditions that limit cell growth. We describe the principle of chemostat cultures, demonstrate their operation and provide examples of their various applications. Following a period of disuse after their introduction in the middle of the twentieth century, the convergence of genome-scale methodologies with a renewed interest in the regulation of cell growth and the molecular basis of adaptive evolution is stimulating a renaissance in the use of chemostats in biological research.

The Use of Chemostats in Microbial Systems Biology

Cells regulate their rate of growth in response to signals from the external world. As the cell grows, diverse cellular processes must be coordinated including macromolecular synthesis, metabolism and ultimately, commitment to the cell division cycle. The chemostat, a method of experimentally controlling cell growth rate, provides a powerful means of systematically studying how growth rate impacts cellular processes - including gene expression and metabolism - and the regulatory networks that control the rate of cell growth. When maintained for hundreds of generations chemostats can be used to study adaptive evolution of microbes in environmental conditions that limit cell growth. We describe the principle of chemostat cultures, demonstrate their operation and provide examples of their various applications. Following a period of disuse after their introduction in the middle of the twentieth century, the convergence of genome-scale methodologies with a renewed interest in the regulation of cell growth and the molecular basis of adaptive evolution is stimulating a renaissance in the use of chemostats in biological research.

Molecular crowding limits translation and cell growth

Bacterial growth is crucially dependent on protein synthesis and thus on the cellular abundance of ribosomes and related proteins. Here, we show that the slow diffusion of the bulky tRNA complexes in the crowded cytoplasm imposes a physical limit on the speed of translation, which ultimately limits the rate of cell growth. To study the required allocation of ancillary translational proteins to alleviate the effect of molecular crowding, we develop a model for cell growth based on a coarse-grained partitioning of the proteome. We find that coregulation of ribosome- and tRNA-affiliated proteins is consistent with measured growth-rate dependencies and results in near-optimal allocation over a broad range of growth rates. The analysis further resolves a long-standing controversy in bacterial growth physiology concerning the growth-rate dependence of translation speed and serves as a caution against premature identification of phenomenological parameters with mechanistic processes.

Inhibition of Nit1 Decreases Growth of K-Ras-Driven Tumors

Inhibition of Nit1 Decreases Growth of K-Ras-Driven Tumors

Quorum Quenching Enzymes and Their Application in Degrading Signal Molecules to Block Quorum Sensing-Dependent Infection

With the emergence of antibiotic-resistant strains of bacteria, the available options for treating bacterial infections have become very limited, and the search for a novel general antibacterial therapy has received much greater attention. Quorum quenching can be used to control disease in a quorum sensing system by triggering the pathogenic phenotype. The interference with the quorum sensing system by the quorum quenching enzyme is a potential strategy for replacing traditional antibiotics because the quorum quenching strategy does not aim to kill the pathogen or limit cell growth but to shut down the expression of the pathogenic gene. Quorum quenching enzymes have been identified in quorum sensing and non-quorum sensing microbes, including lactonase, acylase, oxidoreductase and paraoxonase. Lactonase is widely conserved in a range of bacterial species and has variable substrate spectra. The existence of quorum quenching enzymes in the quorum sensing microbes can attenuate their quorum sensing, leading to blocking unnecessary gene expression and pathogenic phenotypes. In this review, we discuss the physiological function of quorum quenching enzymes in bacterial infection and elucidate the enzymatic protection in quorum sensing systems for host diseases and their application in resistance against microbial diseases.

FGFR3 has tumor suppressor properties in cells with epithelial phenotype

BackgroundDue to frequent mutations in certain cancers, FGFR3 gene is considered as an oncogene. However, in some normal tissues, FGFR3 can limit cell growth and promote cell differentiation. Thus, FGFR3 action appears paradoxical.ResultsFGFR3 expression was forced in pancreatic cell lines. The receptor exerted dual effects: it suppressed tumor growth in pancreatic epithelial-like cells and had oncogenic properties in pancreatic mesenchymal-like cells. Distinct exclusive pathways were activated, STATs in epithelial-like cells and MAP Kinases in mesenchymal-like cells. Both FGFR3 splice variants had similar effects and used the same intracellular signaling. In human pancreatic carcinoma tissues, levels of FGFR3 dropped in tumors.ConclusionIn tumors from epithelial origin, FGFR3 signal can limit tumor growth, explaining why the 4p16.3 locus bearing FGFR3 is frequently lost and why activating mutations of FGFR3 in benign or low grade tumors of epithelial origin are associated with good prognosis. The new hypothesis that FGFR3 can harbor both tumor suppressive and oncogenic properties is crucial in the context of targeted therapies involving specific tyrosine kinase inhibitors (TKIs). TKIs against FGFR3 might result in adverse effects if used in the wrong cell context.

Disruption of TBC1D7, a subunit of the TSC1-TSC2 protein complex, in intellectual disability and megalencephaly

BackgroundMutations in TSC1 or TSC2 cause the tuberous sclerosis complex (TSC), a disorder characterised by the development of hamartomas or benign tumours in various organs as well as the variable...

Pyruvate kinase M2 expression, but not pyruvate kinase activity, is up-regulated in a grade-specific manner in human glioma.

Normal tissues express the M1 isoform of pyruvate kinase (PK) that helps generate and funnel pyruvate into the mitochondria for ATP production. Tumors, in contrast, express the less active PKM2 isoform, which limits pyruvate production and spares glycolytic intermediates for the generation of macromolecules needed for proliferation. Although high PKM2 expression and low PK activity are considered defining features of tumors, very little is known about how PKM expression and PK activity change along the continuum from low grade to high grade tumors, and how these changes relate to tumor growth. To address this issue, we measured PKM isoform expression and PK activity in normal brain, neural progenitor cells, and in a series of over 100 astrocytomas ranging from benign grade I pilocytic astrocytomas to highly aggressive grade IV glioblastoma multiforme (GBM). All glioma exhibited comparably reduced levels of PKM1 expression and PK activity relative to normal brain. In contrast, while grade I-III gliomas all had modestly increased levels of PKM2 RNA and protein expression relative to normal brain, GBM, regardless of whether they arose de novo or progressed from lower grade tumors, showed a 3–5 fold further increase in PKM2 RNA and protein expression. Low levels of PKM1 expression and PK activity were important for cell growth as PKM1 over-expression and the accompanying increases in PK activity slowed the growth of GBM cells. The increased expression of PKM2, however, was also important, because shRNA-mediated PKM2 knockdown decreased total PKM2 and the already low levels of PK activity, but paradoxically also limited cell growth in vitro and in vivo. These results show that pyruvate kinase M expression, but not pyruvate kinase activity, is regulated in a grade-specific manner in glioma, but that changes in both PK activity and PKM2 expression contribute to growth of GBM.

LKB1 tumor suppressor regulates AMP kinase/mTOR-independent cell growth and proliferation via the phosphorylation of Yap

The liver kinase B1 (LKB1) tumor suppressor inhibits cell growth through its regulation of cellular metabolism and apical-basal polarity. The best understood mechanism whereby LKB1 limits cell growth is through activation of the AMP-activated-protein-kinase/mammalian-target-of-rapamycin (AMPK/mTOR) pathway to control metabolism. As LKB1 is also required for polarized epithelial cells to resist hyperplasia, it is anticipated to function through additional mechanisms. Recently, Yes-associated protein (Yap) has emerged as a transcriptional co-activator that modulates tissue homeostasis in response to cell-cell contact. Thus this study examined a possible connection between Yap and LKB1. Restoration of LKB1 expression in HeLa cells, which lack this tumor suppressor, or short-hairpin RNA knockdown of LKB1 in NTERT immortalized keratinocytes, demonstrated that LKB1 promotes Yap phosphorylation, nuclear exclusion and proteasomal degradation. The ability of phosphorylation-defective Yap mutants to rescue LKB1 phenotypes, such as reduced cell proliferation and cell size, suggest that Yap inhibition contributes to LKB1 tumor suppressor function(s). However, failure of Lats1/2 knockdown to suppress LKB1-mediated Yap regulation suggested that LKB1 signals to Yap via a non-canonical pathway. Additionally, LKB1 inhibited Yap independently of either AMPK or mTOR activation. These findings reveal a novel mechanism whereby LKB1 may restrict cancer cell growth via the inhibition of Yap.

TBC1D7 Is a Third Subunit of the TSC1-TSC2 Complex Upstream of mTORC1

The tuberous sclerosis complex (TSC) tumor suppressors form the TSC1-TSC2 complex, which limits cell growth in response to poor growth conditions. Through its GTPase-activating protein (GAP) activity toward Rheb, this complex inhibits the mechanistic target of rapamycin (mTOR) complex 1 (mTORC1), a key promoter of cell growth. Here, we identify and biochemically characterize TBC1D7 as a stably associated and ubiquitous third core subunit of the TSC1-TSC2 complex. We demonstrate that the TSC1-TSC2-TBC1D7 (TSC-TBC) complex is the functional complex that senses specific cellular growth conditions and possesses Rheb-GAP activity. Sequencing analyses of samples from TSC patients suggest that TBC1D7 is unlikely to represent TSC3. TBC1D7 knockdown decreases the association of TSC1 and TSC2 leading to decreased Rheb-GAP activity, without effects on the localization of TSC2 to the lysosome. Like the other TSC-TBC components, TBC1D7 knockdown results in increased mTORC1 signaling, delayed induction of autophagy, and enhanced cell growth under poor growth conditions.

Functional Asymmetries of Proteasome Translocase Pore

Degradation by proteasomes involves coupled translocation and unfolding of its protein substrates. Six distinct but paralogous proteasome ATPase proteins, Rpt1 to -6, form a heterohexameric ring that acts on substrates. An axially positioned loop (Ar-Φ loop) moves in concert with ATP hydrolysis, engages substrate, and propels it into a proteolytic chamber. The aromatic (Ar) residue of the Ar-Φ loop in all six Rpts of S. cerevisiae is tyrosine; this amino acid is thought to have important functional contacts with substrate. Six yeast strains were constructed and characterized in which Tyr was individually mutated to Ala. The mutant cells were viable and had distinct phenotypes. rpt3, rpt4, and rpt5 Tyr/Ala mutants, which cluster on one side of the ATPase hexamer, were substantially impaired in their capacity to degrade substrates. In contrast, rpt1, rpt2, and rpt6 mutants equaled or exceeded wild type in degradation activity. However, rpt1 and rpt6 mutants had defects that limited cell growth or viability under conditions that stressed the ubiquitin proteasome system. In contrast, the rpt3 mutant grew faster than wild type and to a smaller size, a defect that has previously been associated with misregulation of G1 cyclins. This rpt3 phenotype probably results from altered degradation of cell cycle regulatory proteins. Finally, mutation of five of the Rpt subunits increased proteasome ATPase activity, implying bidirectional coupling between the Ar-Φ loop and the ATP hydrolysis site. The present observations assign specific functions to individual Rpt proteins and provide insights into the diverse roles of the axial loops of individual proteasome ATPases.

Abstract LB-29: LKB1 tumor suppressor regulates AMP kinase/mTOR-independent cell growth and proliferation via the phosphorylation of Yap

Abstract The liver kinase B1 (LKB1) tumor suppressor inhibits cell growth through its regulation of cellular metabolism and apical-basal polarity. The best understood mechanism whereby LKB1 limits cell growth is through activation of the AMP-activated-protein-kinase/mammalian-target-of-rapamycin (AMPK/mTOR) pathway to control metabolism. Since LKB1 is also required for polarized epithelial cells to resist hyperplasia it is anticipated to function through additional mechanisms. Recently, Yes-associated protein (Yap) has emerged as a transcriptional co-activator that modulates tissue homeostasis in response to cell-cell contact. Thus this study examines a possible connection between Yap and LKB1. Restoration of LKB1 expression in HeLa cells, which lack this tumor suppressor, or shRNA knockdown of LKB1 in 293T cells, demonstrated that LKB1 promotes Yap phosphorylation, nuclear exclusion, and proteasomal degradation. The ability of phosphorylation-defective Yap mutants to rescue LKB1 phenotypes, such as reduced cell proliferation and cell size, suggest that Yap inhibition contributes to LKB1 tumor suppressor function(s). Interestingly, LKB1 inhibited Yap independently of either AMPK or mTOR activation. These findings reveal a novel mechanism whereby LKB1 may restrict cancer cell growth via the inhibition of Yap. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-29. doi:1538-7445.AM2012-LB-29

Abstract 3954: mTOR inhibitor increases radiation sensitivity in a radiation-resistance cancer cells through induction of cellular senescence

Abstract Autophagy is frequently activated in cancer cells resistant to ionizing radiation and is considered to limit the efficacy of radiotherapy as a prosurvival mechanism. In autophagy signaling, mTOR is an important target for enhancing the therapeutic effect of radiation since inhibiting mTOR limits cell growth and decreases cell proliferation, while increasing autophagy. However, the mode of these actions has remained poorly understood. Here, using radioresistant carcinoma cells, we investigated the mechanism by which the enhanced autophagy flux through the mTOR inhibition overcomes radioresistance of cancer cells subjected to irradiation. AMC-HN-9 cells triggered robust cellular proliferation, and induced cell arrest and autophagy activation in an irradiation dose-dependent manner, showing that adoption of an autophagy mode serves as a survival strategy against radiation. Interestingly, however, the potentiation of radiation-induced autophagy by concomitant inhibition of mTOR activity with mTOR inhibitors (rapamycin or PP242) reduced rather than enhanced cell survival and cell proliferation. Notably, mTOR inhibition in radiation-exposed cells was accompanied by senescence features, including the increased senescence-associated β-galactosidase (SA α-gal) activity and heterochromatin formation and irreversible growth arrest. Stress-induced senescence was associated with suppression of Rb-mediated E2F target genes. The results of this study show that the mTOR-dependent induction of autophagy can maintain a growth-arrested state in radioresistant cancer cells and increase radiosensitivity. It indicates that cellular senescence induced by mTOR inhibitor is a promising interventional strategy for enhancing the therapeutic efficacy in cancer cells refractory to irradiation Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3954. doi:1538-7445.AM2012-3954

Physiological effects of free fatty acid production in genetically engineered Synechococcus elongatus PCC 7942

The direct conversion of carbon dioxide into biofuels by photosynthetic microorganisms is a promising alternative energy solution. In this study, a model cyanobacterium, Synechococcus elongatus PCC 7942, is engineered to produce free fatty acids (FFA), potential biodiesel precursors, via gene knockout of the FFA-recycling acyl-ACP synthetase and expression of a thioesterase for release of the FFA. Similar to previous efforts, the engineered strains produce and excrete FFA, but the yields are too low for large-scale production. While other efforts have applied additional metabolic engineering strategies in an attempt to boost FFA production, we focus on characterizing the engineered strains to identify the physiological effects that limit cell growth and FFA synthesis. The strains engineered for FFA-production show reduced photosynthetic yields, chlorophyll-a degradation, and changes in the cellular localization of the light-harvesting pigments, phycocyanin and allophycocyanin. Possible causes of these physiological effects are also identified. The addition of exogenous linolenic acid, a polyunsaturated FFA, to cultures of S. elongatus 7942 yielded a physiological response similar to that observed in the FFA-producing strains with only one notable difference. In addition, the lipid constituents of the cell and thylakoid membranes in the FFA-producing strains show changes in both the relative amounts of lipid components and the degree of saturation of the fatty acid side chains. These changes in lipid composition may affect membrane integrity and structure, the binding and diffusion of phycobilisomes, and the activity of membrane-bound enzymes including those involved in photosynthesis. Thus, the toxicity of unsaturated FFA and changes in membrane composition may be responsible for the physiological effects observed in FFA-producing S. elongatus 7942. These issues must be addressed to enable the high yields of FFA synthesis necessary for large-scale biofuel production.

Antiproliferative Effects of Vitamin D, DHA and 5‐ Fluorourocil on Breast Cancer

It is well documented that both vitamin D and DHA have antiproliferative effects on a variety of human cancer cells, including breast cancer. Research also shows that a combination approach to cancer treatment is often more effective than any one treatment alone. The purpose of our research was to determine whether the combination of vitamin D (calcitriol) and DHA would slow the progression of human MCF‐7 breast cancer cells more than when they were added alone. We also sought to determine whether these compounds would increase the sensitivity of cells to the antimetabolite chemotherapy drug, 5‐Fluorourocil which is commonly used in the treatment of breast cancer. If either calcitriol or DHA are able to enhance the effects of a chemoptherapeutic agent, it could translate into a lower drug requirement for the patient. This would be beneficial due to the undesirable side effects patients typically experience when taking cytotoxic drugs. In this study, human mammary epithelial cells, MCF‐7s, were treated with 25μM DHA, 100 nM calcitriol, and 15μM 5‐Fluorourocil alone and in multiple combinations for 48 hrs. Cells were then assessed for viability using a fluorescence assay. At 100 nM, calcitriol was ineffective in slowing cell growth. In contrast, both 5‐Fluorourocil and DHA slowed growth significantly. Combining calcitriol and DHA treatments did not improve cell outcome more than treating cells separately. Interestingly, DHA was just as effective as 5‐Fluorourocil in limiting cell growth. Combining cell treatments did not appear to be any more effective than treating cells with only one compound. These results suggest that DHA alone may be just as efficacious as 5‐Fluorourocil in slowing breast cancer progression and may thus offer a dietary approach to breast cancer treatment. This research is supported by the Office of Graduate Research, Central Washington University.