The specific amino acid requirements of a human carcinoma cell (Stain HeLa) in tissue culture

The Fate of Glutamine in Human Metabolism. The Interplay with Glucose in Proliferating Cells

Genome-scale models of metabolism (GEM) are used to study how metabolism varies in different physiological conditions. However, the great number of reactions involved in GEM makes it difficult to understand these variations. In order to have a more understandable tool, we developed a reduced metabolic model of central carbon and nitrogen metabolism, C2M2N with 77 reactions, 54 internal metabolites, and 3 compartments, taking into account the actual stoichiometry of the reactions, including the stoichiometric role of the cofactors and the irreversibility of some reactions. In order to model oxidative phosphorylation (OXPHOS) functioning, the proton gradient through the inner mitochondrial membrane is represented by two pseudometabolites DPH (∆pH) and DPSI (∆ψ). To illustrate the interest of such a reduced and quantitative model of metabolism in mammalian cells, we used flux balance analysis (FBA) to study all the possible fates of glutamine in metabolism. Our analysis shows that glutamine can supply carbon sources for cell energy production and can be used as carbon and nitrogen sources to synthesize essential metabolites. Finally, we studied the interplay between glucose and glutamine for the formation of cell biomass according to ammonia microenvironment. We then propose a quantitative analysis of the Warburg effect.

The Fate of Glutamine in Human Metabolism. The Interplay with Glucose in Proliferating Cells

Genome-scale models of metabolism (GEM) are used to study how metabolism varies in different physiological conditions. However, the great number of reactions involved in GEM makes it difficult to understand these variations. In order to have a more understandable tool, we developed a reduced metabolic model of central carbon and nitrogen metabolism, C2M2N with 77 reactions, 54 internal metabolites, and 3 compartments, taking into account the actual stoichiometry of the reactions, including the stoichiometric role of the cofactors and the irreversibility of some reactions. In order to model oxidative phosphorylation (OXPHOS) functioning, the proton gradient through the inner mitochondrial membrane is represented by two pseudometabolites DPH (∆pH) and DPSI (∆ψ). To illustrate the interest of such a reduced and quantitative model of metabolism in mammalian cells, we used flux balance analysis (FBA) to study all the possible fates of glutamine in metabolism. Our analysis shows that glutamine can supply carbon sources for cell energy production and can be used as carbon and nitrogen sources to synthesize essential metabolites. Finally, we studied the interplay between glucose and glutamine for the formation of cell biomass according to ammonia microenvironment. We then propose a quantitative analysis of the Warburg effect.

Cancer Metabolism Drives a Stromal Regenerative Response

The metabolic reprogramming associated with malignant transformation has led to a growing appreciation of the nutrients required to support anabolic cell growth. Less well studied is how cancer cells satisfy those demands in vivo, where they are dispersed within a complex microenvironment. Tumor-associated stromal components can support tumor growth by providing nutrients that supplement those provided by the local vasculature. These non-malignant stromal cells are phenotypically similar to those that accumulate during wound healing. Owing to their immediate proximity, stromal cells are inevitably affected by the metabolic activity of their cancerous neighbors. Until recently, a role for tumor cell metabolism in influencing the cell fate decisions of neighboring stromal cells has been underappreciated. Here, we propose that metabolites consumed and released by tumor cells act as paracrine factors that regulate the non-malignant cellular composition of a developing tumor by driving stromal cells toward a regenerative response that supports tumor growth.

The development of the concept of ferroptosis

The term ferroptosis was coined in 2012 to describe an iron-dependent regulated form of cell death caused by the accumulation of lipid-based reactive oxygen species; this type of cell death was found to have molecular characteristics distinct from other forms of regulated cell death. Features of ferroptosis have been observed periodically over the last several decades, but these molecular features were not recognized as evidence of a distinct form of cell death until recently. Here, we describe the history of observations consistent with the current definition of ferroptosis, as well as the advances that contributed to the emergence of the concept of ferroptosis. We also discuss recent implications and applications of manipulations of the ferroptotic death pathway.

The Role for Myc in Coordinating Glycolysis, Oxidative Phosphorylation, Glutaminolysis, and Fatty Acid Metabolism in Normal and Neoplastic Tissues

That cancer cells show patterns of metabolism different from normal cells has been known for over 50 years. Yet, it is only in the past decade or so that an appreciation of the benefits of these changes has begun to emerge. Altered cancer cell metabolism was initially attributed to defective mitochondria. However, we now realize that most cancers do not have mitochondrial mutations and that normal cells can transiently adopt cancer-like metabolism during periods of rapid proliferation. Indeed, an encompassing, albeit somewhat simplified, conceptual framework to explain both normal and cancer cell metabolism rests on several simple premises. First, the metabolic pathways used by cancer cells and their normal counterparts are the same. Second, normal quiescent cells use their metabolic pathways and the energy they generate largely to maintain cellular health and organelle turnover and, in some cases, to provide secreted products necessary for the survival of the intact organism. By contrast, undifferentiated cancer cells minimize the latter functions and devote their energy to producing the anabolic substrates necessary to maintain high rates of unremitting cellular proliferation. Third, as a result of the uncontrolled proliferation of cancer cells, a larger fraction of the metabolic intermediates normally used by quiescent cells purely as a source of energy are instead channeled into competing proliferation-focused and energy-consuming anabolic pathways. Fourth, cancer cell clones with the most plastic and rapidly adaptable metabolism will eventually outcompete their less well-adapted brethren during tumor progression and evolution. This attribute becomes increasingly important as tumors grow and as their individual cells compete in a constantly changing and inimical environment marked by nutrient, oxygen, and growth factor deficits. Here, we review some of the metabolic pathways whose importance has gained center stage for tumor growth, particularly those under the control of the c-Myc (Myc) oncoprotein. We discuss how these pathways differ functionally between quiescent and proliferating normal cells, how they are kidnapped and corrupted during the course of transformation, and consider potential therapeutic strategies that take advantage of common features of neoplastic and metabolic disorders.

The Central Role of Amino Acids in Cancer Redox Homeostasis: Vulnerability Points of the Cancer Redox Code

A fine balance in reactive oxygen species (ROS) production and removal is of utmost importance for homeostasis of all cells and especially in highly proliferating cells that encounter increased ROS production due to enhanced metabolism. Consequently, increased production of these highly reactive molecules requires coupling with increased antioxidant defense production within cells. This coupling is observed in cancer cells that allocate significant energy reserves to maintain their intracellular redox balance. Glutathione (GSH), as a first line of defense, represents the most important, non-enzymatic antioxidant component together with the NADPH/NADP⁺ couple, which ensures the maintenance of the pool of reduced GSH. In this review, the central role of amino acids (AAs) in the maintenance of redox homeostasis in cancer, through GSH synthesis (cysteine, glutamate, and glycine), and nicotinamide adenine dinucleotide (phosphate) production (serine, and glutamine/glutamate) are illustrated. Special emphasis is placed on the importance of AA transporters known to be upregulated in cancers (such as system x_c-light chain and alanine-serine-cysteine transporter 2) in the maintenance of AA homeostasis, and thus indirectly, the redox homeostasis of cancer cells. The role of the ROS varies (often described as a "two-edged sword") during the processes of carcinogenesis, metastasis, and cancer treatment. Therefore, the context-dependent role of specific AAs in the initiation, progression, and dissemination of cancer, as well as in the redox-dependent sensitivity/resistance of the neoplastic cells to chemotherapy are highlighted.

Presence of a consensus DNA motif at nearby DNA sequence of the mutation susceptible CG nucleotides

Complexity in tissues affected by cancer arises from somatic mutations and epigenetic modifications in the genome. The mutation susceptible hotspots present within the genome indicate a non-random nature and/or a position specific selection of mutation. An association exists between the occurrence of mutations and epigenetic DNA methylation. This study is primarily aimed at determining mutation status, and identifying a signature for predicting mutation prone zones of tumor suppressor (TS) genes. Nearby sequences from the top five positions having a higher mutation frequency in each gene of 42 TS genes were selected from a cosmic database and were considered as mutation prone zones. The conserved motifs present in the mutation prone DNA fragments were identified. Molecular docking studies were done to determine putative interactions between the identified conserved motifs and enzyme methyltransferase DNMT1. Collective analysis of 42 TS genes found GC as the most commonly replaced and AT as the most commonly formed residues after mutation. Analysis of the top 5 mutated positions of each gene (210 DNA segments for 42 TS genes) identified that CG nucleotides of the amino acid codons (e.g., Arginine) are most susceptible to mutation, and found a consensus DNA "T/AGC/GAGGA/TG" sequence present in these mutation prone DNA segments. Similar to TS genes, analysis of 54 oncogenes not only found CG nucleotides of the amino acid Arg as the most susceptible to mutation, but also identified the presence of similar consensus DNA motifs in the mutation prone DNA fragments (270 DNA segments for 54 oncogenes) of oncogenes. Docking studies depicted that, upon binding of DNMT1 methylates to this consensus DNA motif (C residues of CpG islands), mutation was likely to occur. Thus, this study proposes that DNMT1 mediated methylation in chromosomal DNA may decrease if a foreign DNA segment containing this consensus sequence along with CG nucleotides is exogenously introduced to dividing cancer cells.

Targeting Metabolism for Cancer Therapy

Metabolic reprogramming contributes to tumor development and introduces metabolic liabilities that can be exploited to treat cancer. Chemotherapies targeting metabolism have been effective cancer treatments for decades, and the success of these therapies demonstrates that a therapeutic window exists to target malignant metabolism. New insights into the differential metabolic dependencies of tumors have provided novel therapeutic strategies to exploit altered metabolism, some of which are being evaluated in preclinical models or clinical trials. Here, we review our current understanding of cancer metabolism and discuss how this might guide treatments targeting the metabolic requirements of tumor cells.

Simultaneous tracing of carbon and nitrogen isotopes in human cells

Stable isotope tracing is a powerful method for interrogating metabolic enzyme activities across the metabolic network of living cells. However, most studies of mammalian cells have used (13)C-labeled tracers only and focused on reactions in central carbon metabolism. Cellular metabolism, however, involves other biologically important elements, including nitrogen, hydrogen, oxygen, phosphate and sulfur. Tracing stable isotopes of such elements may help shed light on poorly understood metabolic pathways. Here, we demonstrate the use of high-resolution mass spectrometry to simultaneously trace carbon and nitrogen metabolism in human cells cultured with (13)C- and (15)N-labeled glucose and glutamine. To facilitate interpretation of the complex isotopomer data generated, we extend current methods for metabolic flux analysis to handle multivariate mass isotopomer distributions (MMIDs). We find that observed MMIDs are broadly consistent with known biochemical pathways. Whereas measured (13)C MIDs were informative for central carbon metabolism, (15)N isotopes provided evidence for nitrogen-carrying reactions in amino acid and nucleotide metabolism. This computational and experimental methodology expands the scope of metabolic flux analysis beyond carbon metabolism, and may prove important to understanding metabolic phenotypes in health and disease.

Physiologic Medium Rewires Cellular Metabolism and Reveals Uric Acid as an Endogenous Inhibitor of UMP Synthase

A complex interplay of environmental factors impacts the metabolism of human cells, but neither traditional culture media nor mouse plasma mimic the metabolite composition of human plasma. Here, we developed a culture medium with polar metabolite concentrations comparable to those of human plasma (human plasma-like medium [HPLM]). Culture in HPLM, relative to that in traditional media, had widespread effects on cellular metabolism, including on the metabolome, redox state, and glucose utilization. Among the most prominent was an inhibition of de novo pyrimidine synthesis-an effect traced to uric acid, which is 10-fold higher in the blood of humans than of mice and other non-primates. We find that uric acid directly inhibits uridine monophosphate synthase (UMPS) and consequently reduces the sensitivity of cancer cells to the chemotherapeutic agent 5-fluorouracil. Thus, media that better recapitulates the composition of human plasma reveals unforeseen metabolic wiring and regulation, suggesting that HPLM should be of broad utility.

Widespread Use of Misidentified Cell Line KB (HeLa): Incorrect Attribution and Its Impact Revealed through Mining the Scientific Literature

Continuous cell lines are widely used, but can result in invalid, irreproducible research data. Cell line misidentification is a common problem that can be detected by authentication testing; however, misidentified cell lines continue to be used in publications. Here we explore the impact of one misidentified cell line, KB (HeLa), on the scientific literature. We identified 574 articles between 2000 and 2014 that provided an incorrect attribution for KB, in accordance with its false identity as oral epidermoid carcinoma, but only 57 articles that provided a correct attribution for KB, as HeLa or cervical adenocarcinoma. Statistical analysis of 57 correct and 171 incorrect articles showed that the number of citations to these articles increased over time. Content analysis of 200 citing articles showed there was a tendency to describe the cell line in accordance with the description in the cited paper. Analysis of journal impact factor showed no significant difference between correct and incorrect groups. Articles using KB or citing that usage were most frequently published in the subject areas of pharmacology, pharmacy, oncology, and medicinal chemistry. These findings are important for science policy and support the need for journals to require authentication testing as a condition of publication. Cancer Res; 77(11); 2784-8. ©2017 AACR.

Animal-cell culture media: History, characteristics, and current issues

Background

Cell culture technology has spread prolifically within a century, a variety of culture media has been designed. This review goes through the history, characteristics and current issues of animal‐cell culture media.

Methods

A literature search was performed on PubMed and Google Scholar between 1880 and May 2016 using appropriate keywords.

Results

At the dawn of cell culture technology, the major components of media were naturally derived products such as serum. The field then gradually shifted to the use of chemical‐based synthetic media because naturally derived ingredients have their disadvantages such as large batch‐to‐batch variation. Today, industrially important cells can be cultured in synthetic media. Nevertheless, the combinations and concentrations of the components in these media remain to be optimized. In addition, serum‐containing media are still in general use in the field of basic research. In the fields of assisted reproductive technologies and regenerative medicine, some of the medium components are naturally derived in nearly all instances.

Conclusions

Further improvements of culture media are desirable, which will certainly contribute to a reduction in the experimental variation, enhance productivity among biopharmaceuticals, improve treatment outcomes of assisted reproductive technologies, and facilitate implementation and popularization of regenerative medicine.

Differential regulation of metabolic pathways by androgen receptor (AR) and its constitutively active splice variant, AR-V7, in prostate cancer cells

Metastatic prostate cancer (PCa) is primarily an androgen-dependent disease, which is treated with androgen deprivation therapy (ADT). Tumors usually develop resistance (castration-resistant PCa [CRPC]), but remain androgen receptor (AR) dependent. Numerous mechanisms for AR-dependent resistance have been identified including expression of constitutively active AR splice variants lacking the hormone-binding domain. Recent clinical studies show that expression of the best-characterized AR variant, AR-V7, correlates with resistance to ADT and poor outcome. Whether AR-V7 is simply a constitutively active substitute for AR or has novel gene targets that cause unique downstream changes is unresolved. Several studies have shown that AR activation alters cell metabolism. Using LNCaP cells with inducible expression of AR-V7 as a model system, we found that AR-V7 stimulated growth, migration, and glycolysis measured by ECAR (extracellular acidification rate) similar to AR. However, further analyses using metabolomics and metabolic flux assays revealed several differences. Whereas AR increased citrate levels, AR-V7 reduced citrate mirroring metabolic shifts observed in CRPC patients. Flux analyses indicate that the low citrate is a result of enhanced utilization rather than a failure to synthesize citrate. Moreover, flux assays suggested that compared to AR, AR-V7 exhibits increased dependence on glutaminolysis and reductive carboxylation to produce some of the TCA (tricarboxylic acid cycle) metabolites. These findings suggest that these unique actions represent potential therapeutic targets.

Arginine deprivation using pegylated arginine deiminase has activity against primary acute myeloid leukemia cells in vivo

The strategy of enzymatic degradation of amino acids to deprive malignant cells of important nutrients is an established component of induction therapy of acute lymphoblastic leukemia. Here we show that acute myeloid leukemia (AML) cells from most patients with AML are deficient in a critical enzyme required for arginine synthesis, argininosuccinate synthetase-1 (ASS1). Thus, these ASS1-deficient AML cells are dependent on importing extracellular arginine. We therefore investigated the effect of plasma arginine deprivation using pegylated arginine deiminase (ADI-PEG 20) against primary AMLs in a xenograft model and in vitro. ADI-PEG 20 alone induced responses in 19 of 38 AMLs in vitro and 3 of 6 AMLs in vivo, leading to caspase activation in sensitive AMLs. ADI-PEG 20-resistant AMLs showed higher relative expression of ASS1 than sensitive AMLs. This suggests that the resistant AMLs survive by producing arginine through this metabolic pathway and ASS1 expression could be used as a biomarker for response. Sensitive AMLs showed more avid uptake of arginine from the extracellular environment consistent with their auxotrophy for arginine. The combination of ADI-PEG 20 and cytarabine chemotherapy was more effective than either treatment alone resulting in responses in 6 of 6 AMLs tested in vivo. Our data show that arginine deprivation is a reasonable strategy in AML that paves the way for clinical trials.

Famine versus feast: understanding the metabolism of tumors in vivo

To fuel unregulated proliferation, cancer cells alter metabolism to support macromolecule biosynthesis. Cell culture studies have revealed how different oncogenic mutations and nutrients impact metabolism. Glucose and glutamine are the primary fuels used in vitro; however, recent studies have suggested that utilization of other amino acids as well as lipids and protein can also be important to cancer cells. Early investigations of tumor metabolism are translating these findings to the biology of whole tumors and suggest that additional complexity exists beyond nutrient availability alone in vivo. Whole-body metabolism and tumor heterogeneity also influence the metabolism of tumor cells, and successful targeting of metabolism for cancer therapy will require an understanding of tumor metabolism in vivo.

Inositol synthesis regulates the activation of GSK-3α in neuronal cells

The synthesis of inositol provides precursors of inositol lipids and inositol phosphates that are pivotal for cell signaling. Mood stabilizers lithium and valproic acid, used for treating bipolar disorder, cause cellular inositol depletion, which has been proposed as a therapeutic mechanism of action of both drugs. Despite the importance of inositol, the requirement for inositol synthesis in neuronal cells is not well understood. Here, we examined inositol effects on proliferation of SK-N-SH neuroblastoma cells. The essential role of inositol synthesis in proliferation is underscored by the findings that exogenous inositol was dispensable for proliferation, and inhibition of inositol synthesis decreased proliferation. Interestingly, the inhibition of inositol synthesis by knocking down INO1, which encodes inositol-3-phosphate synthase, the rate-limiting enzyme of inositol synthesis, led to the inactivation of GSK-3α by increasing the inhibitory phosphorylation of this kinase. Similarly, the mood stabilizer valproic acid effected transient decreases in intracellular inositol, leading to inactivation of GSK-3α. As GSK-3 inhibition has been proposed as a likely therapeutic mechanism of action, the finding that inhibition of inositol synthesis results in the inactivation of GSK-3α suggests a unifying hypothesis for mechanism of mood-stabilizing drugs. Inositol is an essential metabolite that serves as a precursor for inositol lipids and inositol phosphates. We report that inhibition of the rate-limiting enzyme of inositol synthesis leads to the inactivation of glycogen synthase kinase (GSK) 3α by increasing inhibitory phosphorylation of this kinase. These findings have implications for the therapeutic mechanisms of mood stabilizers and suggest that inositol synthesis and GSK 3α activity are intrinsically related.

Factors causing compositional changes in soy protein hydrolysates and effects on cell culture functionality

Soy protein hydrolysates significantly enhance cell growth and recombinant protein production in cell cultures. The extent of this enhancement in cell growth and IgG production is known to vary from batch to batch. This can be due to differences in the abundance of different classes of compounds (e.g., peptide content), the quality of these compounds (e.g., glycated peptides), or the presence of specific compounds (e.g., furosine). These quantitative and qualitative differences between batches of hydrolysates result from variation in the seed composition and seed/meal processing. Although a considerable amount of literature is available that describes these factors, this knowledge has not been combined in an overview yet. The aim of this review is to identify the most dominant factors that affect hydrolysate composition and functionality. Although there is a limited influence of variation in the seed composition, the overview shows that the qualitative changes in hydrolysate composition result in the formation of minor compounds (e.g., Maillard reaction products). In pure systems, these compounds have a profound effect on the cell culture functionality. This suggests that the presence of these compounds in soy protein hydrolysates may affect hydrolysate functionality as well. This influence on the functionality can be of direct or indirect nature. For instance, some minor compounds (e.g., Maillard reaction products) are cytotoxic, whereas other compounds (e.g., phytates) suppress protein hydrolysis during hydrolysate production, resulting in altered peptide composition, and, thus, affect the functionality.

How does cancer cell metabolism affect tumor migration and invasion?

Cancer metastasis is the major cause of cancer-associated death. Accordingly, identification of the regulatory mechanisms that control whether or not tumor cells become "directed walkers" is a crucial issue of cancer research. The deregulation of cell migration during cancer progression determines the capacity of tumor cells to escape from the primary tumors and invade adjacent tissues to finally form metastases. The ability to switch from a predominantly oxidative metabolism to glycolysis and the production of lactate even when oxygen is plentiful is a key characteristic of cancer cells. This metabolic switch, known as the Warburg effect, was first described in 1920s, and affected not only tumor cell growth but also tumor cell migration. In this review, we will focus on the recent studies on how cancer cell metabolism affects tumor cell migration and invasion. Understanding the new aspects on molecular mechanisms and signaling pathways controlling tumor cell migration is critical for development of therapeutic strategies for cancer patients.

The PI3K, metabolic, and autophagy networks: interactive partners in cellular health and disease

A fundamental imperative for mammalian cells is to coordinate cell metabolism and growth with environmentally induced stress. This review focuses on three highly integrated networks-the phosphoinositide 3-kinase (PI3K) signaling cascade, intermediate metabolism, and autophagy-that work together to maintain cellular homeostasis under basal conditions and to drive cell-mass accumulation and cell cycle progression in the presence of appropriate mitogenic stimuli. Dysfunction within any one of these networks results in compensatory responses from the other networks. These responses underpin several pathologies associated with major human diseases such as cancer. We discuss the PI3K, metabolism, and autophagy networks and provide selected insights into internetwork cross-talk mechanisms. In recognition of the extensive interactions observed in both healthy and diseased cells, we propose that the three networks be merged into a "metabolism-signaling supernetwork." A detailed understanding of this supernetwork will facilitate the development of novel therapies for cancer and other complex diseases.

Serum-free media in hybridoma culture and monoclonal antibody production

The replacement of serum in hybridoma cultures is considered. The focus is on the effects of serum-free media on hybridoma growth and monoclonal antibody secretion. Comparative literature data with serum supplemented cultures are discussed with an analysis of serum-free formulations and selection rules for the serum-free ingredients. In general, serum-free media which are "lipid rich" can sustain cell growth rates approaching that of serum supplemented cultures. Specific antibody secretion rate, however, is usually higher in serum-free media, irrespective of the lipid content.

Metabolic reprogramming in cancer: unraveling the role of glutamine in tumorigenesis

Increased glutaminolysis is now recognized as a key feature of the metabolic profile of cancer cells, along with increased aerobic glycolysis (the Warburg effect). In this review, we discuss the roles of glutamine in contributing to the core metabolism of proliferating cells by supporting energy production and biosynthesis. We address how oncogenes and tumor suppressors regulate glutamine metabolism and how cells coordinate glucose and glutamine as nutrient sources. Finally, we highlight the novel therapeutic and imaging applications that are emerging as a result of our improved understanding of the role of glutamine metabolism in cancer.

The metabolic switch and its regulation in cancer cells

The primary features of cancer are maintained via intrinsically modified metabolic activity, which is characterized by enhanced nutrient supply, energy production, and biosynthetic activity to synthesize a variety of macromolecular components during each passage through the cell cycle. This metabolic shift in transformed cells, as compared with non-proliferating cells, involves aberrant activation of aerobic glycolysis, de novo lipid biosynthesis and glutamine-dependent anaplerosis to fuel robust cell growth and proliferation. Here, we discuss the unique metabolic characteristics of cancer, the constitutive regulation of metabolism through a variety of signal transduction pathways and/or enzymes involved in metabolic reprogramming in cancer cells, and their implications in cancer diagnosis and therapy.

COMPARATIVE STUDIES IN ROUS SARCOMA WITH VIRUS, TUMOR CELLS, AND CHICK EMBRYO CELLS TRANSFORMED IN VITRO BY VIRUS : I. PRODUCTION OF MUCOPOLYSACCHARIDES

The chick embryo fibroblast infected by Rous sarcoma virus in vitro acquires the capacity to produce the acid mucopolysaccharides which are found in the tumors caused by this virus and which are also produced by tumor cells in vitro. The transformed cell acquires synthetic as well as morphologic, metabolic, and proliferative properties characteristic of Rous sarcoma tumor cells in vivo and in vitro and the transformed cell may be analogous to the tumor cell produced by virus infection in vivo.

THE EFFECT OF DIPHTHERIA TOXIN ON THE METABOLISM OF HELA CELLS : II. EFFECT ON NUCLEIC ACID METABOLISM

The effect of toxin on the incorporation of uridine and thymidine into nucleic acids was investigated. P³² orthophosphate incorporation into the nucleoside phosphate fraction was also investigated. No early effect of toxin on nucleic acid synthesis was evident and only a slight effect of toxin on nucleoside phosphate formation was found prior to 1.5 hours after toxin addition. Both these processes, however, were found to be sensitive to dinitrophenol. These results are interpreted as indicating that toxin does not act by a general uncoupling of oxidation from phosphorylation. Other possible mechanisms of toxin action are proposed.

Effect of ascorbic acid on bone marrow-derived mesenchymal stem cell proliferation and differentiation

Mesenchymal stem cells (MSCs) derived from bone marrow are an important tool in tissue engineering and cell-based therapies because of their multipotent capacity. Majority of studies on MSCs have investigated the roles of growth factors, cytokines, and hormones. Antioxidants such as ascorbic acid can be used to expand MSCs while preserving their differentiation ability. Moreover, ascorbic acid can also stimulate MSC proliferation without reciprocal loss of phenotype and differentiation potency. In this study, we evaluated the effects of ascorbic acid on the proliferation, differentiation, extracellular matrix (ECM) secretion of MSCs. The MSCs were cultured in media containing various concentrations (0-500 microM) of L-ascorbate-2-phosphate (Asc-2-P) for 2 weeks, following which they were differentiated into adipocytes and osteoblasts. Ascorbic acid stimulated ECM secretion (collagen and glycosaminoglycan) and cell proliferation. Moreover, the phenotypes of the experimental groups as well as the differentiation potential of MSCs remained unchanged. The apparent absence of decreased cell density or morphologic change is consistent with the toxicity observed with 5-250 microM concentrations of Asc-2-P. The results demonstrate that MSC proliferation or differentiation depends on ascorbic acid concentration.

Branched-chain amino acids and immunity

Although there has been great interest in the effects of amino acids on immune function, little is known about the impact of changes in BCAA availability on the ability of the immune system to function. Human immune cells incorporate BCAA into proteins and are able to oxidize BCAA. The immune system exists to protect the host from pathogenic invaders and from other noxious insults. Upon infection, there is a marked increase in demand for substrates by the immune system; these substrates provide energy and are the precursors for the synthesis of new cells, effector molecules, and protective molecules. Cell culture studies show that BCAA are absolutely essential for lymphocytes to synthesize protein, RNA, and DNA and to divide in response to stimulation. In mice, dietary BCAA restriction impairs several aspects of the immune function and increases the susceptibility to pathogens. Postsurgical or septic patients given BCAA intravenously showed improved immunity and this may relate to improved outcome. BCAAs are therefore absolutely essential for lymphocyte responsiveness and are necessary to support other immune cell functions. However, many aspects of BCAA and its effects on immune function have been understudied or not studied at all. More research is needed to understand the extent of the immune system's requirement for BCAA. It is likely that the essentiality of BCAA for the function of immune cells relates to protein synthesis.

Intracellular localization of type 4 adenovirus. I. Cellular fractionation studies

HeLa cells infected with types 1 or 4 adenovirus were separated into cytoplasmic and nuclear fractions by mechanical disruption and differential centrifugation and the quantity of infectious virus in each was determined. The results showed that the majority of infectious virus of both types could be isolated in the cytoplasmic fraction. It was not possible to explain the large amount of type 4 virus in the cytoplasmic fraction by the number of nuclei disrupted in the fractionation procedure, but the amount of type 1 virus in the cytoplasmic fraction could have been contributed by disrupted nuclei. This suggested that there might be a basic difference in the intracellular formation of the two types of virus. The intracellular distribution of complement-fixing antigen was similar to that of infectious virus in type 4-infected cells. Technical difficulties, inherent in cellular fractionation studies, were encountered but did not appear to explain the results obtained.

Studies of mouse polyoma virus infection. 1. Procedures for quantitation and detection of virus

Three procedures have been compared for usefulness in titration and detection of polyoma virus: production of cytopathic effect (CPE) in mouse embryo tissue culture, production of HI antibody after inoculation into weanling mice (MAP test), and production of tumors in suckling hamsters during a 3 to 5 week observation period. The tissue culture and mouse antibody production tests were generally comparable in sensitivity, reproducibility, and time required to obtain results. Titration by tumor production in suckling hamsters was not suitable for quantitation because of marked variation in susceptibility among animals. Virus was detected in tissues of normal mice from spontaneously infected colonies by either production of CPE in mouse embryo tissue culture or by the MAP test; virus was found in organs of 15 (58 per cent) of 26 mice with antibody, and 2 (8 per cent) of 24 mice without antibody.

The effect of diphtheria toxin on the metabolism of HeLa cells

The effect of diphtheria toxin on certain metabolic processes in growing HeLa cells has been described. It was found that both aerobic respiration and glycolysis are insensitive to toxin action. The incorporation of S³⁵-methionine was found to be completely inhibited by toxin prior to the appearance of any visible cell damage. It was also observed that toxin levels above 0.3 Lf per ml. had no further effect on the kinetics of inhibition of methionine uptake. The kinetics of intoxication were studied by adding diphtheria antitoxin to a partially intoxicated culture at various times and measuring the resulting rate of methionine uptake. Low temperatures were found to block intoxication. Using this information, data were obtained suggesting that the initial step in the process of intoxication consists of a rapid adsorption of toxin by the cell. The kinetics of toxin action on protein synthesis were compared with those of cyanide and 2,4-DNP. Diphtheria toxin eliminates completely any methionine uptake remaining after exposure of the cell to either of these respiratory inhibitors. The significance of these results is discussed.

Studies of mouse polyoma virus infection. III. Distribution of antibodies in laboratory mouse colonies

Eight mouse colonies were surveyed for prevalence of antibody to mouse polyoma virus. Frequency of HI antibody varied from 0 to 84 per cent in adult mice in different colonies. Antibody was infrequent in mice less than 3 months of age, and increased in frequency with age. There was no evidence that infection was specific for particular mouse strains. The highest frequency of infection was found in colonies in which breeding mice are housed in proximity to mice inoculated with polyoma virus or passage tumors, and within an infected colony, the incidence of infection was greatest in rooms housing mice inoculated with polyoma virus. Mice from a colony free of antibody became infected when held in room or cage contact with virus-inoculated mice, but at very low rates except in mothers of inoculated litters. These results were interpreted as indicating that artificial contamination of the environment is an important factor in determining the prevalence of infection in the colonies observed. There was no correlation between polyoma infection and spontaneous leukemia in AK. mice.

Characterization of a factor formed in the course of adenovirus infection of tissue cultures causing detachment of cells from glass

Infectious tissue culture fluids of the majority of serotypes of adenovirus at low dilutions detach HeLa or KB cells from glass surfaces within a few hours after inoculation. A reproducible method for testing cell detachment was devised. The factor present in infectious tissue culture fluids and responsible for cell detachment is trypsin-sensitive and non-dialyzable; it is smaller and more resistant to the effect of heat or ultraviolet light than the infectious virus particle. Cell detachment activity was found to be temperature-dependent, and the cell-detaching titer of infectious tissue culture fluids was not affected by repeated exposure to HeLa cells. Inhibition of cell detachment by human or rabbit sera was observed only when other antibodies to adenovirus antigens were also present, but the antibody inhibiting cell detachment could not be correlated quantitatively with complement-fixing or homologous neutralizing antibody.