Nicotinamide adenine dinucleotide, a metabolic regulator of transcription, longevity and disease

ATP-Citrate Lyase Links Cellular Metabolism to Histone Acetylation

Modification of chromatin structure is usually thought of as a global, relatively nonspecific way of modulating gene expression. However, Wellen et al. (p. 1076 ; see the Perspective by Rathmell and Newgard ) demonstrate that such regulation helps link growth factor–stimulated increases in metabolism to appropriate changes in gene expression. Adenosine triphosphate (ATP)–citrate lyase (ACL), which converts citrate to acetyl–coenzyme A (CoA) in the mitochondria of mammalian cells during metabolism of glucose, was also found to be present in the nucleus, where it might regulate activity of histone acetyl transferases (HATs) by controlling the availability of acetyl-CoA. Indeed, depletion of ACL from cultured human colon carcinoma cells specifically decreased histone acetylation in the nucleus, but appeared not to affect the overall amount of acetylation of proteins in the cells. Loss of ACL in cultured mouse 3T3-L1 cells diminished the increase in histone acetylation normally associated with hormone-stimulated differentiation of these cells and inhibited the increase in expression of specific genes, such as that encoding the Glut4 glucose transporter. Thus, ACL may help cells link metabolic activity to changes in gene expression.

ATP-Citrate Lyase Links Cellular Metabolism to Histone Acetylation

Modification of chromatin structure is usually thought of as a global, relatively nonspecific way of modulating gene expression. However, Wellen et al. (p. 1076 ; see the Perspective by Rathmell and Newgard ) demonstrate that such regulation helps link growth factor–stimulated increases in metabolism to appropriate changes in gene expression. Adenosine triphosphate (ATP)–citrate lyase (ACL), which converts citrate to acetyl–coenzyme A (CoA) in the mitochondria of mammalian cells during metabolism of glucose, was also found to be present in the nucleus, where it might regulate activity of histone acetyl transferases (HATs) by controlling the availability of acetyl-CoA. Indeed, depletion of ACL from cultured human colon carcinoma cells specifically decreased histone acetylation in the nucleus, but appeared not to affect the overall amount of acetylation of proteins in the cells. Loss of ACL in cultured mouse 3T3-L1 cells diminished the increase in histone acetylation normally associated with hormone-stimulated differentiation of these cells and inhibited the increase in expression of specific genes, such as that encoding the Glut4 glucose transporter. Thus, ACL may help cells link metabolic activity to changes in gene expression.

ATP-Citrate Lyase Links Cellular Metabolism to Histone Acetylation

Modification of chromatin structure is usually thought of as a global, relatively nonspecific way of modulating gene expression. However, Wellen et al. (p. 1076 ; see the Perspective by Rathmell and Newgard ) demonstrate that such regulation helps link growth factor–stimulated increases in metabolism to appropriate changes in gene expression. Adenosine triphosphate (ATP)–citrate lyase (ACL), which converts citrate to acetyl–coenzyme A (CoA) in the mitochondria of mammalian cells during metabolism of glucose, was also found to be present in the nucleus, where it might regulate activity of histone acetyl transferases (HATs) by controlling the availability of acetyl-CoA. Indeed, depletion of ACL from cultured human colon carcinoma cells specifically decreased histone acetylation in the nucleus, but appeared not to affect the overall amount of acetylation of proteins in the cells. Loss of ACL in cultured mouse 3T3-L1 cells diminished the increase in histone acetylation normally associated with hormone-stimulated differentiation of these cells and inhibited the increase in expression of specific genes, such as that encoding the Glut4 glucose transporter. Thus, ACL may help cells link metabolic activity to changes in gene expression.

ATP-Citrate Lyase Links Cellular Metabolism to Histone Acetylation

Modification of chromatin structure is usually thought of as a global, relatively nonspecific way of modulating gene expression. However, Wellen et al. (p. 1076 ; see the Perspective by Rathmell and Newgard ) demonstrate that such regulation helps link growth factor–stimulated increases in metabolism to appropriate changes in gene expression. Adenosine triphosphate (ATP)–citrate lyase (ACL), which converts citrate to acetyl–coenzyme A (CoA) in the mitochondria of mammalian cells during metabolism of glucose, was also found to be present in the nucleus, where it might regulate activity of histone acetyl transferases (HATs) by controlling the availability of acetyl-CoA. Indeed, depletion of ACL from cultured human colon carcinoma cells specifically decreased histone acetylation in the nucleus, but appeared not to affect the overall amount of acetylation of proteins in the cells. Loss of ACL in cultured mouse 3T3-L1 cells diminished the increase in histone acetylation normally associated with hormone-stimulated differentiation of these cells and inhibited the increase in expression of specific genes, such as that encoding the Glut4 glucose transporter. Thus, ACL may help cells link metabolic activity to changes in gene expression.

ATP-Citrate Lyase Links Cellular Metabolism to Histone Acetylation

Modification of chromatin structure is usually thought of as a global, relatively nonspecific way of modulating gene expression. However, Wellen et al. (p. 1076 ; see the Perspective by Rathmell and Newgard ) demonstrate that such regulation helps link growth factor–stimulated increases in metabolism to appropriate changes in gene expression. Adenosine triphosphate (ATP)–citrate lyase (ACL), which converts citrate to acetyl–coenzyme A (CoA) in the mitochondria of mammalian cells during metabolism of glucose, was also found to be present in the nucleus, where it might regulate activity of histone acetyl transferases (HATs) by controlling the availability of acetyl-CoA. Indeed, depletion of ACL from cultured human colon carcinoma cells specifically decreased histone acetylation in the nucleus, but appeared not to affect the overall amount of acetylation of proteins in the cells. Loss of ACL in cultured mouse 3T3-L1 cells diminished the increase in histone acetylation normally associated with hormone-stimulated differentiation of these cells and inhibited the increase in expression of specific genes, such as that encoding the Glut4 glucose transporter. Thus, ACL may help cells link metabolic activity to changes in gene expression.

ATP-Citrate Lyase Links Cellular Metabolism to Histone Acetylation

Modification of chromatin structure is usually thought of as a global, relatively nonspecific way of modulating gene expression. However, Wellen et al. (p. 1076 ; see the Perspective by Rathmell and Newgard ) demonstrate that such regulation helps link growth factor–stimulated increases in metabolism to appropriate changes in gene expression. Adenosine triphosphate (ATP)–citrate lyase (ACL), which converts citrate to acetyl–coenzyme A (CoA) in the mitochondria of mammalian cells during metabolism of glucose, was also found to be present in the nucleus, where it might regulate activity of histone acetyl transferases (HATs) by controlling the availability of acetyl-CoA. Indeed, depletion of ACL from cultured human colon carcinoma cells specifically decreased histone acetylation in the nucleus, but appeared not to affect the overall amount of acetylation of proteins in the cells. Loss of ACL in cultured mouse 3T3-L1 cells diminished the increase in histone acetylation normally associated with hormone-stimulated differentiation of these cells and inhibited the increase in expression of specific genes, such as that encoding the Glut4 glucose transporter. Thus, ACL may help cells link metabolic activity to changes in gene expression.

ATP-Citrate Lyase Links Cellular Metabolism to Histone Acetylation

Modification of chromatin structure is usually thought of as a global, relatively nonspecific way of modulating gene expression. However, Wellen et al. (p. 1076 ; see the Perspective by Rathmell and Newgard ) demonstrate that such regulation helps link growth factor–stimulated increases in metabolism to appropriate changes in gene expression. Adenosine triphosphate (ATP)–citrate lyase (ACL), which converts citrate to acetyl–coenzyme A (CoA) in the mitochondria of mammalian cells during metabolism of glucose, was also found to be present in the nucleus, where it might regulate activity of histone acetyl transferases (HATs) by controlling the availability of acetyl-CoA. Indeed, depletion of ACL from cultured human colon carcinoma cells specifically decreased histone acetylation in the nucleus, but appeared not to affect the overall amount of acetylation of proteins in the cells. Loss of ACL in cultured mouse 3T3-L1 cells diminished the increase in histone acetylation normally associated with hormone-stimulated differentiation of these cells and inhibited the increase in expression of specific genes, such as that encoding the Glut4 glucose transporter. Thus, ACL may help cells link metabolic activity to changes in gene expression.

ATP-Citrate Lyase Links Cellular Metabolism to Histone Acetylation

Modification of chromatin structure is usually thought of as a global, relatively nonspecific way of modulating gene expression. However, Wellen et al. (p. 1076 ; see the Perspective by Rathmell and Newgard ) demonstrate that such regulation helps link growth factor–stimulated increases in metabolism to appropriate changes in gene expression. Adenosine triphosphate (ATP)–citrate lyase (ACL), which converts citrate to acetyl–coenzyme A (CoA) in the mitochondria of mammalian cells during metabolism of glucose, was also found to be present in the nucleus, where it might regulate activity of histone acetyl transferases (HATs) by controlling the availability of acetyl-CoA. Indeed, depletion of ACL from cultured human colon carcinoma cells specifically decreased histone acetylation in the nucleus, but appeared not to affect the overall amount of acetylation of proteins in the cells. Loss of ACL in cultured mouse 3T3-L1 cells diminished the increase in histone acetylation normally associated with hormone-stimulated differentiation of these cells and inhibited the increase in expression of specific genes, such as that encoding the Glut4 glucose transporter. Thus, ACL may help cells link metabolic activity to changes in gene expression.

ATP-Citrate Lyase Links Cellular Metabolism to Histone Acetylation

Modification of chromatin structure is usually thought of as a global, relatively nonspecific way of modulating gene expression. However, Wellen et al. (p. 1076 ; see the Perspective by Rathmell and Newgard ) demonstrate that such regulation helps link growth factor–stimulated increases in metabolism to appropriate changes in gene expression. Adenosine triphosphate (ATP)–citrate lyase (ACL), which converts citrate to acetyl–coenzyme A (CoA) in the mitochondria of mammalian cells during metabolism of glucose, was also found to be present in the nucleus, where it might regulate activity of histone acetyl transferases (HATs) by controlling the availability of acetyl-CoA. Indeed, depletion of ACL from cultured human colon carcinoma cells specifically decreased histone acetylation in the nucleus, but appeared not to affect the overall amount of acetylation of proteins in the cells. Loss of ACL in cultured mouse 3T3-L1 cells diminished the increase in histone acetylation normally associated with hormone-stimulated differentiation of these cells and inhibited the increase in expression of specific genes, such as that encoding the Glut4 glucose transporter. Thus, ACL may help cells link metabolic activity to changes in gene expression.

ATP-Citrate Lyase Links Cellular Metabolism to Histone Acetylation

Modification of chromatin structure is usually thought of as a global, relatively nonspecific way of modulating gene expression. However, Wellen et al. (p. 1076 ; see the Perspective by Rathmell and Newgard ) demonstrate that such regulation helps link growth factor–stimulated increases in metabolism to appropriate changes in gene expression. Adenosine triphosphate (ATP)–citrate lyase (ACL), which converts citrate to acetyl–coenzyme A (CoA) in the mitochondria of mammalian cells during metabolism of glucose, was also found to be present in the nucleus, where it might regulate activity of histone acetyl transferases (HATs) by controlling the availability of acetyl-CoA. Indeed, depletion of ACL from cultured human colon carcinoma cells specifically decreased histone acetylation in the nucleus, but appeared not to affect the overall amount of acetylation of proteins in the cells. Loss of ACL in cultured mouse 3T3-L1 cells diminished the increase in histone acetylation normally associated with hormone-stimulated differentiation of these cells and inhibited the increase in expression of specific genes, such as that encoding the Glut4 glucose transporter. Thus, ACL may help cells link metabolic activity to changes in gene expression.

ATP-Citrate Lyase Links Cellular Metabolism to Histone Acetylation

Modification of chromatin structure is usually thought of as a global, relatively nonspecific way of modulating gene expression. However, Wellen et al. (p. 1076 ; see the Perspective by Rathmell and Newgard ) demonstrate that such regulation helps link growth factor–stimulated increases in metabolism to appropriate changes in gene expression. Adenosine triphosphate (ATP)–citrate lyase (ACL), which converts citrate to acetyl–coenzyme A (CoA) in the mitochondria of mammalian cells during metabolism of glucose, was also found to be present in the nucleus, where it might regulate activity of histone acetyl transferases (HATs) by controlling the availability of acetyl-CoA. Indeed, depletion of ACL from cultured human colon carcinoma cells specifically decreased histone acetylation in the nucleus, but appeared not to affect the overall amount of acetylation of proteins in the cells. Loss of ACL in cultured mouse 3T3-L1 cells diminished the increase in histone acetylation normally associated with hormone-stimulated differentiation of these cells and inhibited the increase in expression of specific genes, such as that encoding the Glut4 glucose transporter. Thus, ACL may help cells link metabolic activity to changes in gene expression.

ATP-Citrate Lyase Links Cellular Metabolism to Histone Acetylation

Modification of chromatin structure is usually thought of as a global, relatively nonspecific way of modulating gene expression. However, Wellen et al. (p. 1076 ; see the Perspective by Rathmell and Newgard ) demonstrate that such regulation helps link growth factor–stimulated increases in metabolism to appropriate changes in gene expression. Adenosine triphosphate (ATP)–citrate lyase (ACL), which converts citrate to acetyl–coenzyme A (CoA) in the mitochondria of mammalian cells during metabolism of glucose, was also found to be present in the nucleus, where it might regulate activity of histone acetyl transferases (HATs) by controlling the availability of acetyl-CoA. Indeed, depletion of ACL from cultured human colon carcinoma cells specifically decreased histone acetylation in the nucleus, but appeared not to affect the overall amount of acetylation of proteins in the cells. Loss of ACL in cultured mouse 3T3-L1 cells diminished the increase in histone acetylation normally associated with hormone-stimulated differentiation of these cells and inhibited the increase in expression of specific genes, such as that encoding the Glut4 glucose transporter. Thus, ACL may help cells link metabolic activity to changes in gene expression.

ATP-Citrate Lyase Links Cellular Metabolism to Histone Acetylation

Modification of chromatin structure is usually thought of as a global, relatively nonspecific way of modulating gene expression. However, Wellen et al. (p. 1076 ; see the Perspective by Rathmell and Newgard ) demonstrate that such regulation helps link growth factor–stimulated increases in metabolism to appropriate changes in gene expression. Adenosine triphosphate (ATP)–citrate lyase (ACL), which converts citrate to acetyl–coenzyme A (CoA) in the mitochondria of mammalian cells during metabolism of glucose, was also found to be present in the nucleus, where it might regulate activity of histone acetyl transferases (HATs) by controlling the availability of acetyl-CoA. Indeed, depletion of ACL from cultured human colon carcinoma cells specifically decreased histone acetylation in the nucleus, but appeared not to affect the overall amount of acetylation of proteins in the cells. Loss of ACL in cultured mouse 3T3-L1 cells diminished the increase in histone acetylation normally associated with hormone-stimulated differentiation of these cells and inhibited the increase in expression of specific genes, such as that encoding the Glut4 glucose transporter. Thus, ACL may help cells link metabolic activity to changes in gene expression.

ATP-Citrate Lyase Links Cellular Metabolism to Histone Acetylation

Modification of chromatin structure is usually thought of as a global, relatively nonspecific way of modulating gene expression. However, Wellen et al. (p. 1076 ; see the Perspective by Rathmell and Newgard ) demonstrate that such regulation helps link growth factor–stimulated increases in metabolism to appropriate changes in gene expression. Adenosine triphosphate (ATP)–citrate lyase (ACL), which converts citrate to acetyl–coenzyme A (CoA) in the mitochondria of mammalian cells during metabolism of glucose, was also found to be present in the nucleus, where it might regulate activity of histone acetyl transferases (HATs) by controlling the availability of acetyl-CoA. Indeed, depletion of ACL from cultured human colon carcinoma cells specifically decreased histone acetylation in the nucleus, but appeared not to affect the overall amount of acetylation of proteins in the cells. Loss of ACL in cultured mouse 3T3-L1 cells diminished the increase in histone acetylation normally associated with hormone-stimulated differentiation of these cells and inhibited the increase in expression of specific genes, such as that encoding the Glut4 glucose transporter. Thus, ACL may help cells link metabolic activity to changes in gene expression.

ATP-Citrate Lyase Links Cellular Metabolism to Histone Acetylation

Modification of chromatin structure is usually thought of as a global, relatively nonspecific way of modulating gene expression. However, Wellen et al. (p. 1076 ; see the Perspective by Rathmell and Newgard ) demonstrate that such regulation helps link growth factor–stimulated increases in metabolism to appropriate changes in gene expression. Adenosine triphosphate (ATP)–citrate lyase (ACL), which converts citrate to acetyl–coenzyme A (CoA) in the mitochondria of mammalian cells during metabolism of glucose, was also found to be present in the nucleus, where it might regulate activity of histone acetyl transferases (HATs) by controlling the availability of acetyl-CoA. Indeed, depletion of ACL from cultured human colon carcinoma cells specifically decreased histone acetylation in the nucleus, but appeared not to affect the overall amount of acetylation of proteins in the cells. Loss of ACL in cultured mouse 3T3-L1 cells diminished the increase in histone acetylation normally associated with hormone-stimulated differentiation of these cells and inhibited the increase in expression of specific genes, such as that encoding the Glut4 glucose transporter. Thus, ACL may help cells link metabolic activity to changes in gene expression.

ATP-Citrate Lyase Links Cellular Metabolism to Histone Acetylation

Modification of chromatin structure is usually thought of as a global, relatively nonspecific way of modulating gene expression. However, Wellen et al. (p. 1076 ; see the Perspective by Rathmell and Newgard ) demonstrate that such regulation helps link growth factor–stimulated increases in metabolism to appropriate changes in gene expression. Adenosine triphosphate (ATP)–citrate lyase (ACL), which converts citrate to acetyl–coenzyme A (CoA) in the mitochondria of mammalian cells during metabolism of glucose, was also found to be present in the nucleus, where it might regulate activity of histone acetyl transferases (HATs) by controlling the availability of acetyl-CoA. Indeed, depletion of ACL from cultured human colon carcinoma cells specifically decreased histone acetylation in the nucleus, but appeared not to affect the overall amount of acetylation of proteins in the cells. Loss of ACL in cultured mouse 3T3-L1 cells diminished the increase in histone acetylation normally associated with hormone-stimulated differentiation of these cells and inhibited the increase in expression of specific genes, such as that encoding the Glut4 glucose transporter. Thus, ACL may help cells link metabolic activity to changes in gene expression.

ATP-Citrate Lyase Links Cellular Metabolism to Histone Acetylation

Modification of chromatin structure is usually thought of as a global, relatively nonspecific way of modulating gene expression. However, Wellen et al. (p. 1076 ; see the Perspective by Rathmell and Newgard ) demonstrate that such regulation helps link growth factor–stimulated increases in metabolism to appropriate changes in gene expression. Adenosine triphosphate (ATP)–citrate lyase (ACL), which converts citrate to acetyl–coenzyme A (CoA) in the mitochondria of mammalian cells during metabolism of glucose, was also found to be present in the nucleus, where it might regulate activity of histone acetyl transferases (HATs) by controlling the availability of acetyl-CoA. Indeed, depletion of ACL from cultured human colon carcinoma cells specifically decreased histone acetylation in the nucleus, but appeared not to affect the overall amount of acetylation of proteins in the cells. Loss of ACL in cultured mouse 3T3-L1 cells diminished the increase in histone acetylation normally associated with hormone-stimulated differentiation of these cells and inhibited the increase in expression of specific genes, such as that encoding the Glut4 glucose transporter. Thus, ACL may help cells link metabolic activity to changes in gene expression.

Assimilation of endogenous nicotinamide riboside is essential for calorie restriction-mediated life span extension in Saccharomyces cerevisiae

NAD(+) (nicotinamide adenine dinucleotide) is an essential cofactor involved in various biological processes including calorie restriction-mediated life span extension. Administration of nicotinamide riboside (NmR) has been shown to ameliorate deficiencies related to aberrant NAD(+) metabolism in both yeast and mammalian cells. However, the biological role of endogenous NmR remains unclear. Here we demonstrate that salvaging endogenous NmR is an integral part of NAD(+) metabolism. A balanced NmR salvage cycle is essential for calorie restriction-induced life span extension and stress resistance in yeast. Our results also suggest that partitioning of the pyridine nucleotide flux between the classical salvage cycle and the NmR salvage branch might be modulated by the NAD(+)-dependent Sir2 deacetylase. Furthermore, two novel deamidation steps leading to nicotinic acid mononucleotide and nicotinic acid riboside production are also uncovered that further underscore the complexity and flexibility of NAD(+) metabolism. In addition, utilization of extracellular nicotinamide mononucleotide requires prior conversion to NmR mediated by a periplasmic phosphatase Pho5. Conversion to NmR may thus represent a strategy for the transport and assimilation of large nonpermeable NAD(+) precursors. Together, our studies provide a molecular basis for how NAD(+) homeostasis factors confer metabolic flexibility.

The yeast PNC1 longevity gene is up-regulated by mRNA mistranslation

Translation fidelity is critical for protein synthesis and to ensure correct cell functioning. Mutations in the protein synthesis machinery or environmental factors that increase synthesis of mistranslated proteins result in cell death and degeneration and are associated with neurodegenerative diseases, cancer and with an increasing number of mitochondrial disorders. Remarkably, mRNA mistranslation plays critical roles in the evolution of the genetic code, can be beneficial under stress conditions in yeast and in Escherichia coli and is an important source of peptides for MHC class I complex in dendritic cells. Despite this, its biology has been overlooked over the years due to technical difficulties in its detection and quantification. In order to shed new light on the biological relevance of mistranslation we have generated codon misreading in Saccharomyces cerevisiae using drugs and tRNA engineering methodologies. Surprisingly, such mistranslation up-regulated the longevity gene PNC1. Similar results were also obtained in cells grown in the presence of amino acid analogues that promote protein misfolding. The overall data showed that PNC1 is a biomarker of mRNA mistranslation and protein misfolding and that PNC1-GFP fusions can be used to monitor these two important biological phenomena in vivo in an easy manner, thus opening new avenues to understand their biological relevance.

Nampt: linking NAD biology, metabolism and cancer

Nicotinamide phosphoribosyltransferase (Nampt) converts nicotinamide to nicotinamide mononucleotide (NMN), a key nicotinamide adenine dinucleotide (NAD) intermediate. Previously identified as a cytokine pre-B-cell colony-enhancing factor and controversially claimed as an insulin-mimetic hormone visfatin, Nampt has recently drawn much attention in several fields, including NAD biology, metabolism and inflammation. As a NAD biosynthetic enzyme, Nampt regulates the activity of NAD-consuming enzymes such as sirtuins and influences a variety of metabolic and stress responses. Nampt also plays an important part in regulating insulin secretion in pancreatic beta-cells. Nampt seems to have another function as an immunomodulatory cytokine and, therefore, has a role in inflammation. This review summarizes these various functional aspects of Nampt and discusses its potential roles in diseases, including type 2 diabetes and cancer.

Regulation of active site coupling in glutamine-dependent NAD(+) synthetase

NAD(+) is an essential metabolite both as a cofactor in energy metabolism and redox homeostasis and as a regulator of cellular processes. In contrast to humans, Mycobacterium tuberculosis NAD(+) biosynthesis is absolutely dependent on the activity of a multifunctional glutamine-dependent NAD(+) synthetase, which catalyzes the ATP-dependent formation of NAD(+) at the synthetase domain using ammonia derived from L-glutamine in the glutaminase domain. Here we report the kinetics and structural characterization of M. tuberculosis NAD(+) synthetase. The kinetics data strongly suggest tightly coupled regulation of the catalytic activities. The structure, the first of a glutamine-dependent NAD(+) synthetase, reveals a homooctameric subunit organization suggesting a tight dependence of catalysis on the quaternary structure, a 40-A intersubunit ammonia tunnel and structural elements that may be involved in the transfer of information between catalytic sites.

Determination of NAD(+) and NADH in a single cell under hydrogen peroxide stress by capillary electrophoresis

A capillary electrophoresis (CE) method based on an enzymatic cycling reaction is developed to determine both NAD(+) and NADH in a single cell in a single run. The detection limit can reach down to 0.2 amol of NAD(+) and 1 amol of NADH with a homemade capillary electrophoresis laser-induced fluorescence (CE-LIF) setup. This method shows good reproducibility and specificity. After an intact cell is injected into the capillary and lysed using a Tesla coil, intracellular NAD(+) and NADH were separated, incubated with the cycling buffer, and quantified by recording the amount of fluorescent product generated. Cellular NAD(+) and NADH levels of a rat myoblast cell line were determined using this method. Both NAD(+) and NADH levels decreased when the cells were exposed to oxidative stress induced by H(2)O(2). This may be due to the activation of the DNA repair enzyme, poly(ADP-ribose) polymerase, in response to the oxidative damage imposed on DNA, since pretreatment of the cells with an inhibitor of these enzymes prevented the reduction of cellular NAD(+) and NADH levels.

Redox responses in yeast to acetate as the carbon source

Following a shift to medium with acetate as the carbon source, a parental yeast strain exhibited a transient moderate 20% reduction in total cellular [NAD(+)+NADH] but showed a approximately 10-fold increase in the ratio of [NAD(+)]:[NADH] after 36h. A mutant strain (idhDelta) lacking the tricarboxylic acid cycle enzyme isocitrate dehydrogenase had 50% higher cellular levels of [NAD(+)+NADH] relative to the parental strain but exhibited similar changes in cofactor concentrations following a shift to acetate medium, despite an inability to grow on that carbon source; essentially all of the cofactor was in the oxidized form within 36h. The salvage pathway for NAD(H) biosynthesis was found to be particularly important for viability during early transition of the parental strain to stationary phase in acetate medium. However, oxygen consumption was not affected, suggesting that the NAD(H) produced during this time may support other cellular functions. The idhDelta mutant exhibited increased flux through the salvage pathway in acetate medium but was dependent on the de novo pathway for viability. Long-term chronological lifespans of the parental and idhDelta strains were similar, but viability of the mutant strain was dependent on both pathways for NAD(H) biosynthesis.

Therapeutic potential of SIRT1 and NAMPT-mediated NAD biosynthesis in type 2 diabetes

Both genetic and environmental factors contribute to the pathogenesis of type 2 diabetes, and it is critical to understand the interplay between these factors in the regulation of insulin secretion and insulin sensitivity to develop effective therapeutic interventions for type 2 diabetes. For the past several years, studies on the mammalian NAD-dependent protein deacetylase SIRT1 and systemic NAD biosynthesis mediated by nicotinamide phosphoribosyltransferase (NAMPT) have demonstrated that these two regulatory components together play a critical role in the regulation of glucose homeostasis, particularly in the regulation of glucose-stimulated insulin secretion in pancreatic beta cells. These components also contribute to the age-associated decline in beta cell function, which has been suggested to be one of the major contributing factors to the pathogenesis of type 2 diabetes. In this review article, the roles of SIRT1 and NAMPT-mediated systemic NAD biosynthesis in glucose homeostasis and the pathophysiology of type 2 diabetes will be summarized, and their potential as effective targets for the treatment and prevention of type 2 diabetes will be discussed.

Glycolytic enzyme inhibitors in cancer treatment

BACKGROUND

The radio- and chemotherapeutics currently used for the treatment of cancer are widely known to be characterized by a low therapeutic index. An interesting approach to overcoming some of the limits of these techniques is the exploitation of the so-called Warburg effect, which typically characterizes neoplastic cells. Interestingly, this feature has already been utilized with good results, but only for diagnostic purposes (PET and SPECT). From a pharmacological point of view, drugs able to perturb cancer cell metabolism, specifically at the level of glycolysis, may display interesting therapeutic activities in cancer.

OBJECTIVE

The pharmacological actions of these glycolytic enzyme inhibitors, based primarily on ATP depletion, could include: i) amelioration of drug selectivity by exploiting the particular glycolysis addiction of cancer cell; ii) inhibition of energetic and anabolic processes; iii) reduction of hypoxia-linked cancer-cell resistance; iv) reduction of ATP-dependent multi-drug resistance; and v) cytotoxic synergism with conventional cancer treatments.

CONCLUSION

Several glycolytic inhibitors are currently in preclinical and clinical development. Their clinical value as anticancer agents, above all in terms of therapeutic index, strictly depends on a careful reevaluation of the pathophyiological role of the unique metabolism of cancer cells in general and of Warburg effect in particular.

Single sample extraction protocol for the quantification of NAD and NADH redox states in Saccharomyces cerevisiae

A robust redox extraction protocol for quantitative and reproducible metabolite isolation and recovery has been developed for simultaneous measurement of nicotinamide adenine dinucleotide (NAD) and its reduced form, NADH, from Saccharomyces cerevisiae. Following culture in liquid media, yeast cells were harvested by centrifugation and then lysed under nonoxidizing conditions by bead blasting in ice-cold, nitrogen-saturated 50 mM ammonium acetate. To enable protein denaturation, ice cold nitrogen-saturated CH(3)CN/50 mM ammonium acetate (3:1 v/v) was added to the cell lysates. Chloroform extractions were performed on supernatants to remove organic solvent. Samples were lyophilized and resuspended in 50 mM ammonium acetate. NAD and NADH were separated by HPLC and quantified using UV-Vis absorbance detection. NAD and NADH levels were evaluated in yeast grown under normal (2% glucose) and calorie restricted (0.5% glucose) conditions. Results demonstrate that it is possible to perform a single preparation to reliably and robustly quantitate both NAD and NADH contents in the same sample. Robustness of the protocol suggests it will be (i) applicable to quantification of these metabolites in other cell cultures; and (ii) amenable to isotope labeling strategies to determine the relative contribution of specific metabolic pathways to total NAD and NADH levels in cell cultures.

Promotion of cellular NAD(+) anabolism: therapeutic potential for oxidative stress in ageing and Alzheimer's disease

Oxidative imbalance is a prominent feature in Alzheimer's disease and ageing. Increased levels of reactive oxygen species (ROS) can result in disordered cellular metabolism due to lipid peroxdation, protein-cross linking, DNA damage and the depletion of nicotinamide adenine dinucleotide (NAD(+)). NAD(+) is a ubiquitous pyridine nucleotide that plays an essential role in important biological reactions., from ATP production and secondary messenger signaling, to transcriptional regulation and DNA repair. Chronic oxidative stress may be associated with NAD(+) depletion and a subsequent decrease in metabolic regulation and cell viability. Hence, therapies targeted toward maintaining intracellular NAD(+) pools may prove efficacious in the protection of age-dependent cellular damage, in general, and neurodegeneration in chronic central nervous system inflammatory diseases such as Alzheimer's disease, in particular.

Use of the electrochromic behaviour of lanthanide phthalocyanine films for nicotinamide adenine dinucleotide detection

Electrochromic properties of spun films of bis[octakis(hexylthio)phthalocyaninato] dysprosium(III) were investigated for determining nicotinamide adenine dinucleotide hydride (NADH) in water solutions. A spin-coated film deposited on indium tin oxide electrode displays only one redox couple (at E1/2=0.78V). The films of [(C6H13S)8Pc]2Dy were modified chemically or electrochemically for the detection of reduced NADH in water solution. The modified film in the oxidized ([(C6H13S)8Pc]2Dy)+ form is believed to be reduced to its neutral form on interaction with NADH.

Sirtuins: novel targets for metabolic disease in drug development

Calorie restriction extends lifespan and produces a metabolic profile desirable for treating diseases such as type 2 diabetes. SIRT1, an NAD(+)-dependent deacetylase, is a principal modulator of pathways downstream of calorie restriction that produces beneficial effects on glucose homeostasis and insulin sensitivity. Activation of SIRT1 leads to enhanced activity of multiple proteins, including peroxisome proliferator-activated receptor coactivator-1alpha (PGC-1alpha) and FOXO which helps to mediate some of the in vitro and in vivo effects of sirtuins. Resveratrol, a polyphenolic SIRT1 activator, mimics the effects of calorie restriction in lower organisms and in mice fed a high-fat diet ameliorates insulin resistance. In this review, we summarize recent research advances in unveiling the molecular mechanisms that underpin sirtuin as therapeutic candidates and discuss the possibility of using resveratrol as potential drug for treatment of diabetes.

The malate-aspartate NADH shuttle components are novel metabolic longevity regulators required for calorie restriction-mediated life span extension in yeast

Recent studies suggest that increased mitochondrial metabolism and the concomitant decrease in NADH levels mediate calorie restriction (CR)-induced life span extension. The mitochondrial inner membrane is impermeable to NAD (nicotinamide adenine dinucleotide, oxidized form) and NADH, and it is unclear how CR relays increased mitochondrial metabolism to multiple cellular pathways that reside in spatially distinct compartments. Here we show that the mitochondrial components of the malate-aspartate NADH shuttle (Mdh1 [malate dehydrogenase] and Aat1 [aspartate amino transferase]) and the glycerol-3-phosphate shuttle (Gut2, glycerol-3-phosphate dehydrogenase) are novel longevity factors in the CR pathway in yeast. Overexpressing Mdh1, Aat1, and Gut2 extend life span and do not synergize with CR. Mdh1 and Aat1 overexpressions require both respiration and the Sir2 family to extend life span. The mdh1Deltaaat1Delta double mutation blocks CR-mediated life span extension and also prevents the characteristic decrease in the NADH levels in the cytosolic/nuclear pool, suggesting that the malate-aspartate shuttle plays a major role in the activation of the downstream targets of CR such as Sir2. Overexpression of the NADH shuttles may also extend life span by increasing the metabolic fitness of the cells. Together, these data suggest that CR may extend life span and ameliorate age-associated metabolic diseases by activating components of the NADH shuttles.

Mechanisms underlying caloric restriction and lifespan regulation: implications for vascular aging

This review focuses on the emerging evidence that attenuation of the production of reactive oxygen species and inhibition of inflammatory pathways play a central role in the antiaging cardiovascular effects of caloric restriction. Particular emphasis is placed on the potential role of the plasma membrane redox system in caloric restriction-induced pathways responsible for sensing oxidative stress and increasing cellular oxidative stress resistance. We propose that caloric restriction increases bioavailability of NO, decreases vascular reactive oxygen species generation, activates the Nrf2/antioxidant response element pathway, inducing reactive oxygen species detoxification systems, exerts antiinflammatory effects, and, thereby, suppresses initiation/progression of vascular disease that accompany aging.

Identification of a subunit of NADH-dehydrogenase as a p49/STRAP-binding protein

Background

The p49/STRAP (or SRFBP1) protein was recently identified in our laboratory as a cofactor of serum response factor that contributes to the regulation of SRF target genes in the heart.

Results

In the present study, we report that NDUFAB1, a nuclear encoded subunit of NADH dehydrogenase, represented the majority of the cDNA clones that interacted with p49/STRAP in multiple screenings using the yeast two-hybrid system. The p49/STRAP and NDUFAB1 proteins interacted and co-localized with each other in the cell. The p49/STRAP protein contains four classic nuclear localization sequence motifs, and it was observed to be present predominantly in the nucleus. Overexpression of p49/STRAP altered the intracellular level of NAD, and reduced the NAD/NADH ratio. Overexpression of p49/STRAP also induced the deacetylation of serum response factor.

Conclusion

These data suggest that p49/STRAP plays a role in the regulation of intracellular processes such as cardiac cellular metabolism, gene expression, and possibly aging.

Nampt/PBEF/Visfatin regulates insulin secretion in beta cells as a systemic NAD biosynthetic enzyme

Intracellular nicotinamide phosphoribosyltransferase (iNampt) is an essential enzyme in the NAD biosynthetic pathway. An extracellular form of this protein (eNampt) has been reported to act as a cytokine named PBEF or an insulin-mimetic hormone named visfatin, but its physiological relevance remains controversial. Here we show that eNampt does not exert insulin-mimetic effects in vitro or in vivo but rather exhibits robust NAD biosynthetic activity. Haplodeficiency and chemical inhibition of Nampt cause defects in NAD biosynthesis and glucose-stimulated insulin secretion in pancreatic islets in vivo and in vitro. These defects are corrected by administration of nicotinamide mononucleotide (NMN), a product of the Nampt reaction. A high concentration of NMN is present in mouse plasma, and plasma eNampt and NMN levels are reduced in Nampt heterozygous females. Our results demonstrate that Nampt-mediated systemic NAD biosynthesis is critical for beta cell function, suggesting a vital framework for the regulation of glucose homeostasis.

Energy metabolism, altered proteins, sirtuins and ageing: converging mechanisms?

The predominant molecular symptom of ageing is the accumulation of altered gene products. Nutritional studies show that ageing in animals can be significantly influenced by dietary restriction. Genetics has revealed that ageing may be controlled by changes in intracellular NAD/NADH ratio regulating sirtuin activity. Physiological and other approaches indicate that mitochondria may also regulate ageing. A mechanism is proposed which links diet, exercise and mitochondria-dependent changes in NAD/NADH ratio to intracellular generation of altered proteins. It is suggested that ad libitum feeding conditions decrease NAD availability which also decreases metabolism of the triose phosphate glycolytic intermediates, glyceraldehyde-3-phosphate and dihydroxyacetone-phosphate, which can spontaneously decompose into methylglyoxal (MG). MG is a highly toxic glycating agent and a major source of protein advanced-glycosylation end-products (AGEs). MG and AGEs can induce mitochondrial dysfunction and formation of reactive oxygen species (ROS), as well as affect gene expression and intracellular signalling. In dietary restriction–induced fasting, NADH would be oxidised and NAD regenerated via mitochondrial action. This would not only activate sirtuins and extend lifespan but also suppress MG formation. This proposal can also explain the apparent paradox whereby increased aerobic activity suppresses formation of glycoxidized proteins and extends lifespan. Variation in mitochondrial DNA composition and consequent mutation rate, arising from dietary-controlled differences in DNA precursor ratios, could also contribute to tissue differences in age-related mitochondrial dysfunction.

Study the oxidative injury of yeast cells by NADH autofluorescence

Autofluorescence has an advantage over the extrinsic fluorescence of an unperturbed environment during investigation, especially in complex system such as biological cells and tissues. NADH is an important fluorescent substance in living cells. The time courses of intracellular NADH autofluorescence in the process of yeast cells exposed to H(2)O(2) and ONOO(-) have been recorded in detail in this work. In the presence of different amounts of H(2)O(2) and ONOO(-), necrosis, apoptosis and reversible injury are initiated in yeast cells, which are confirmed by acridine orange/ethidum bromide and Annexin V/propidium iodide staining. It is found that intracellular NADH content increases momently in the beginning of the apoptotic process and then decreases continually till the cell dies. The most remarkable difference between the apoptotic and the necrotic process is that the NADH content in the latter case changes much more sharply. Further in the case of reversible injury, the time course of intracellular NADH content is completely different from the above two pathways of cell death. It just decreases to some degree firstly and then resumes to the original level. Based on the role of NADH in mitochondrial respiratory chain, the time course of intracellular NADH content is believed to have reflected the response of mitochondrial redox state to oxidative stress. Thus, it is found that the mitochondrial redox state changes differently in different pathways of oxidative injury in yeast cells.

The power to reduce: pyridine nucleotides--small molecules with a multitude of functions

The pyridine nucleotides NAD and NADP play vital roles in metabolic conversions as signal transducers and in cellular defence systems. Both coenzymes participate as electron carriers in energy transduction and biosynthetic processes. Their oxidized forms, NAD+ and NADP+, have been identified as important elements of regulatory pathways. In particular, NAD+ serves as a substrate for ADP-ribosylation reactions and for the Sir2 family of NAD+-dependent protein deacetylases as well as a precursor of the calcium mobilizing molecule cADPr (cyclic ADP-ribose). The conversions of NADP+ into the 2'-phosphorylated form of cADPr or to its nicotinic acid derivative, NAADP, also result in the formation of potent intracellular calcium-signalling agents. Perhaps, the most critical function of NADP is in the maintenance of a pool of reducing equivalents which is essential to counteract oxidative damage and for other detoxifying reactions. It is well known that the NADPH/NADP+ ratio is usually kept high, in favour of the reduced form. Research within the past few years has revealed important insights into how the NADPH pool is generated and maintained in different subcellular compartments. Moreover, tremendous progress in the molecular characterization of NAD kinases has established these enzymes as vital factors for cell survival. In the present review, we summarize recent advances in the understanding of the biosynthesis and signalling functions of NAD(P) and highlight the new insights into the molecular mechanisms of NADPH generation and their roles in cell physiology.

The regulation of nicotinamide adenine dinucleotide biosynthesis by Nampt/PBEF/visfatin in mammals

PURPOSE OF REVIEW

Nicotinamide adenine dinucleotide (NAD) is a classic coenzyme in cellular redox reactions. Recently, NAD biochemistry has also been implicated in a broader range of biological functions in mammals, but the regulation of NAD biosynthesis has been poorly investigated. Recent progress in the field of NAD biochemistry has fueled new interest in the NAD biosynthetic pathways from its precursors and their physiological roles in metabolism. This review summarizes the latest knowledge on the NAD biosynthetic pathways and focuses on one of the key NAD biosynthetic enzymes, namely, nicotinamide phosphoribosyltransferase.

RECENT FINDINGS

Mammals predominantly use nicotinamide rather than nicotinic acid as a precursor for NAD biosynthesis. Nicotinamide phosphoribosyltransferase (Nampt) is the rate-limiting enzyme that converts nicotinamide to nicotinamide mononucleotide in the NAD biosynthetic pathway from nicotinamide in mammals. The same protein has also been identified as a cytokine (pre-B-cell colony-enhancing factor or PBEF) or an insulin-mimetic hormone (visfatin).

SUMMARY

We propose that the presumed multiple effects of Nampt/PBEF/visfatin may be entirely explained by its role as an intra and extracellular NAD biosynthetic enzyme. We also propose a new model of Namp/PBEF/visfatin-mediated systemic NAD biosynthesis and its possible physiological significance. Our model provides an important insight into developing preventive/therapeutic interventions for metabolic complications, such as obesity and diabetes.

Visfatin/pre-B-cell colony-enhancing factor: a protein with various suggested functions

Pre-B-cell colony-enhancing factor (PBEF) was recently found in high levels in visceral fat, and was therefore renamed visfatin. This new adipocytokine exerts insulin-mimetic effects in mice and in cultured cells by binding to and activating the insulin receptor. Despite some recent studies on this topic, the proposed role of visfatin in metabolism remains largely unknown. Initially, PBEF/visfatin was discovered as a cytokine for the differentiation of B-cells. Pre-B-cell colony-enhancing factor was also shown to inhibit apoptosis of neutrophils in sepsis and was discussed as a novel biomarker for acute lung injury (ALI). Although PBEF is missing a signal sequence, its secretion and function as a molecule involved in the regulation of inflammatory processes was reported in several studies. Investigations of PBEF/visfatin in gestational membranes suggest a function in the physiologic and pathologic pathways leading to labor. Furthermore, it was found upregulated in colorectal cancer and was brought into connection with the regulation of the cell cycle. Intra-cellular, PBEF/visfatin acts as a cytosolic enzyme involved in nicotinamide adenine dinucleotide (NAD) synthesis. This activity was shown to be important for vascular smooth muscle cell (SMC) maturation, indicating a possible involvement in vascular pathology. The important physiologic role of PBEF/visfatin is also underlined by its evolutionary highly conserved gene in different species. This review summarizes the current knowledge of the various functions of PBEF/visfatin towards involvements in pathophysiology of several diseases.

Sirtuins: the 'magnificent seven', function, metabolism and longevity

The sirtuin family of histone deacetylases (HDACs) was named after their homology to the Saccharomyces cerevisiae gene silent information regulator 2 (Sir2). In the yeast, Sir2 has been shown to mediate the effects of calorie restriction on the extension of life span and high levels of Sir2 activity promote longevity. Like their yeast homologs, the mammalian sirtuins (SIRT1-7) are class III HDACs and require NAD(+) as a cofactor to deacetylate substrates ranging from histones to transcriptional regulators. Through this activity, sirtuins are shown to regulate important biological processes ranging from apoptosis, adipocyte and muscle differentiation, and energy expenditure to gluconeogenesis. We review here the current knowledge regarding the role of sirtuins in metabolism, longevity, and discuss the possible therapeutic applications that could result from the understanding of their function in different organs and pathologies.

SIRT1 and endocrine signaling

Sirtuins (Sir2-related enzymes) are a recently discovered class of NAD(+)-dependent protein deacetylases that regulate gene expression in a variety of organisms by deacetylation of modified lysine residues on histones, transcription factors and other proteins. Conservation of sirtuin regulation of the insulin-insulin-like growth factor I signaling pathway has been observed for Caenorhabditis elegans and mammals, indicating an ancient role for sirtuins in the modulation of organism adaptations to nutritional intake. The human sirtuin SIRT1 regulates a number of transcription factors that modulate endocrine signaling, including peroxisome proliferator-activated receptor gamma, peroxisome proliferator-activated receptor gamma coactivator 1alpha, forkhead-box transcription factors and p53.

Analysis of Arabidopsis growth factor gene 1 (GFG1) encoding a nudix hydrolase during oxidative signaling

Maintenance of pyridine nucleotide homeostasis is vital for normal growth and development of plants and animals. We demonstrate that Arabidopsis Growth Factor Gene 1 (GFG1; At4g12720) encoding a nudix hydrolase, is an NADH pyrophosphatase and ADP-ribose pyrophosphatase. The affinity for NADH and ADP-ribose indicates that this enzyme could serve as a connection between sensing cellular redox changes and downstream signaling. GFG1 transcript levels were rapidly and transiently induced during both biotic stresses imposed by avirulent pathogens and abiotic stresses like ozone and osmoticum. T-DNA knock out plants of GFG1 gene, gfg1-1, exhibit pleiotropic phenotypes such as reduced size, increased levels of reactive oxygen species and NADH, microscopic cell death, constitutive expression of pathogenesis-related genes and enhanced resistance to bacterial pathogens. The recombinant protein failed to complement the mutator deficiency in SBMutT- strain of Escherichia coli, suggesting this protein may not play a role in sanitizing the nucleotide pool. Based on rapid transcriptional changes in response to various stresses, substrate specificity of the enzyme, and analysis of the knock out mutant, we propose that GFG1 is a key gene linking cellular metabolism and oxidative signaling.

Ligand-induced domain rearrangement of fatty acid beta-oxidation multienzyme complex

The quaternary structure of a fatty acid beta-oxidation multienzyme complex, catalyzing three sequential reactions, was investigated by X-ray crystallographic and small-angle X-ray solution scattering analyses. X-ray crystallography revealed an intermediate structure of the complex among the previously reported structures. However, the theoretical scattering curves calculated from the crystal structures remarkably disagree with the experimental profiles. Instead, an ensemble of the atomic models, which were all calculated by rigid-body optimization, reasonably explained the experimental data. These structures significantly differ from those in the crystals, but they maintain the substrate binding pocket at the domain boundary. Comparisons among these structures indicated that binding of 3-hydroxyhexadecanoyl-CoA or nicotinamide adenine dinucleotide induces domain rearrangements in the complex. The conformational changes suggest the structural events occurring during the chain reaction catalyzed by the multienzyme complex.

Activation of the adenylyl cyclase/protein kinase A pathway facilitates neural release of beta-nicotinamide adenine dinucleotide in canine mesenteric artery

Using high performance liquid chromatography techniques with fluorescence detection we demonstrate that overflow of beta-nicotinamide adenine dinucleotide evoked by electrical field stimulation (16 Hz, 0.3 ms) in the canine isolated mesenteric artery is increased by the activators of adenylyl cyclase (AC) forskolin and calcitonin gene-related peptide (CGRP), by dibutyryl cAMP, and by the inhibitors of phosphodiesterases III and IV milrinone and rolipram. The enhancing effect of forskolin is abolished by the AC inhibitor MDL 12,330A and by protein kinase A (PKA) inhibitors peptide 14-22 amide and 4-cyano-3-methylisoquinoline. Therefore, activation of the AC/cAMP/PKA pathway enhances the release of beta-NAD+ from perivascular nerve terminals.

Effects of lactate dehydrogenase suppression and glycerol-3-phosphate dehydrogenase overexpression on cellular metabolism

In order to conduct a physiological functional study of lactate dehydrogenase (LDH) and glycerol-3-phosphate dehydrogenase (GPDH), we engineered a CHO dhfr(-) cell, by overexpressing either the anti-sense LDH-A RNA (anti-LDH cells) or GPDH (GP3 cells), or both (GP3/anti-LDH cells). LDH activity in the cell cytosol, and lactate content and pHe change in the growth media were found to decrease according to the order: cell lines GP3/anti-LDH > anti-LDH > GP3 > CHO. Intracellular ATP contents, representing the extent of respiration rate, also decreased, according to a rank order as follows: GP3 > CHO > GP3/anti-LDH > anti-LDH. We also attempted to identify and characterize any physiological changes occurring in the cells which harbored diverse metabolic pathways. First, anti-LDH cells with heightened respiration rates were found to display a higher degree of sensitivity to the prooxidant tert-butyl hydroperoxide (tBOOH), and the mitochondrial complex III inhibitor, antimycin A, than the GPDH-expressing cells (GP3 and GP3/anti-LDH), which have a lower respiration rate. Second, the anti-sense LDH-A RNA-expressing cells (anti-LDH and GP3/anti-LDH) evidenced a higher degree of resistance to apoptosis by cell-cell contact inhibition, and a faster doubling time ( approximately 19 h compared with approximately 26 h) than the CHO and GP3 cells. Additionally, cell growth in an extended culture under HCO(3) (-)-free conditions to induce a steep acidification could be maintained with the anti-sense LDH-A RNA-expressing cells, but could not be maintained with the CHO and GP3 cells. Third, we observed that the most appropriate cell line for the optical production of a certain therapeutic protein (Tissue-Plasminogen Activator) was the GP3/anti-LDH cells. Collectively, our data indicate a variety of physiological roles for LDH and GPDH, including cellular acidosis, oxidoresistance, apoptosis by both acidosis and cell-cell contact inhibition, cell growth, and the generation of recombinant proteins.