Amino acids regulate expression of antizyme-1 to modulate ornithine decarboxylase activity

Target of Rapamycin Mediated Ornithine Decarboxylase Antizyme Modulate Intracellular Putrescine and Ganoderic Acid Content in Ganoderma lucidum

Putrescine (Put) has been shown to play an important regulatory role in cell growth in organisms. As the primary center regulating the homeostasis of polyamine (PA) content, ornithine decarboxylase antizyme (AZ) can regulate PA content through feedback. Nevertheless, the regulatory mechanism of Put is poorly understood in fungi. Here, our analysis showed that GlAZ had a modulate effect on intracellular Put content by interacting with ornithine decarboxylase (ODC) proteins and reducing its intracellular protein levels. In addition, GlAZ upregulated the metabolic pathway of ganoderic acid (GA) biosynthesis in Ganoderma lucidum by modulating the intracellular Put content. However, a target of rapamycin (TOR) was found to promote the accumulation of intracellular Put after the GlTOR inhibitor Rap was added exogenously, and unbiased analyses demonstrated that GlTOR may promote Put production through its inhibitory effect on the level of GlAZ protein in GlTOR-GlAZ-cosilenced strains. The effect of TOR on fungal secondary metabolism was further explored, and the content of GA in the GlTOR-silenced strain after the exogenous addition of the inhibitor Rap was significantly increased compared with that in the untreated wild-type (WT) strain. Silencing of TOR in the GlTOR-silenced strains caused an increase in GA content, which returned to the WT state after replenishing Put. Moreover, the content of GA in GlTOR-GlAZ-cosilenced strains was also not different from that in the WT strain. Consequently, these results strongly indicate that GlTOR affects G. lucidum GA biosynthesis via GlAZ. IMPORTANCE Research on antizyme (AZ) in fungi has focused on the mechanism by which AZ inhibits ornithine decarboxylase (ODC). Moreover, there are existing reports on the regulation of AZ protein translation by TOR. However, little is known about the mechanisms that influence AZ in fungal secondary metabolism. Here, both intracellular Put content and GA biosynthesis in G. lucidum were shown to be regulated through protein interactions between GlAZ and GlODC. Furthermore, exploration of upstream regulators of GlAZ suggested that GlAZ was regulated by the upstream protein GlTOR, which affected intracellular Put levels and ganoderic acid (GA) biosynthesis. The results of our work contribute to the understanding of the upstream regulation of Put and provide new insights into PA regulatory systems and secondary metabolism in fungi.

Is Glyceryl Trinitrate, a Nitric Oxide Donor Responsible for Ameliorating the Chemical-Induced Tissue Injury In Vivo?

Oxidative stress induced by well-known toxins including ferric nitrilotriacetate (Fe-NTA), carbon tetrachloride (CCl₄) and thioacetamide (TAA) has been attributed to causing tissue injury in the liver and kidney. In this study, the effect of glyceryl trinitrate (GTN), a donor of nitric oxide and NG-nitroarginine methyl ester (l-NAME), a nitric oxide inhibitor on TAA-induced hepatic oxidative stress, GSH and GSH-dependent enzymes, serum transaminases and tumor promotion markers such as ornithine decarboxylase (ODC) activity and [³H]-thymidine incorporation in rats were examined. The animals were divided into seven groups consisting of six healthy rats per group. The six rats were injected intraperitoneally with TAA to evaluate its toxic effect, improvement in its toxic effect if any, or worsening in its toxic effect if any, when given in combination with GTN or l-NAME. The single necrogenic dose of TAA administration caused a significant change in the levels of both hepatic and serum enzymes such as glutathione S-transferase (GST), glutathione reductase (GR), glutathione peroxidase (GPx), γ-glutamyl transpeptidase (GGT), glucose 6-phosphate dehydrogenase (G6PD), alanine aminotransferase (AST) and aspartate aminotransferase (ALT). In addition, treatment with TAA also augmented malondialdehyde (MDA), ornithine decarboxylase (ODC) activity and [³H]-thymidine incorporation in rats liver. Concomitantly, TAA treatment depleted the levels of GSH. However, most of these changes were alleviated by the treatment of animals with GTN dose-dependently. The protective effect of GTN against TAA was also confirmed histopathologically. The present data confirmed our earlier findings with other oxidants including Fe-NTA and CCl₄. The GTN showed no change whatsoever when administered alone, however when it was given along with TAA then it showed protection thereby contributing towards defending the role against oxidants-induced organ toxicity. Overall, GTN may contribute to protection against TAA-induced oxidative stress, toxicity, and proliferative response in the liver, according to our findings.

Polyamines and related signaling pathways in cancer

Polyamines are aliphatic compounds with more than two amino groups that play various important roles in human cells. In cancer, polyamine metabolism dysfunction often occurs, and regulatory mechanisms of polyamine. This review summarizes the existing research on the metabolism and transport of polyamines to study the association of oncogenes and related signaling pathways with polyamines in tumor cells. Drugs that regulate enzymes have been developed for cancer treatment, and in the future, more attention should be paid to treatment strategies that simultaneously modulate polyamine metabolism and carcinogenic signaling pathways. In addition, the polyamine pathway is a potential target for cancer chemoprevention. As an irreversible suicide inhibitor of the ornithine decarboxylase (a vital enzyme of polyamine synthesis), Difluoro-methylornithine had been shown to have the chemoprevention effect on cancer. Therefore, we summarized and analyzed the chemoprophylaxis effect of the difluoromethylornithine in this systematic review.

Dietary and Gut Microbiota Polyamines in Obesity- and Age-Related Diseases

The polyamines putrescine, spermidine, and spermine are widely distributed polycationic compounds essential for cellular functions. Intracellular polyamine pools are tightly regulated by a complex regulatory mechanism involving de novo biosynthesis, catabolism, and transport across the plasma membrane. In mammals, both the production of polyamines and their uptake from the extracellular space are controlled by a set of proteins named antizymes and antizyme inhibitors. Dysregulation of polyamine levels has been implicated in a variety of human pathologies, especially cancer. Additionally, decreases in the intracellular and circulating polyamine levels during aging have been reported. The differences in the polyamine content existing among tissues are mainly due to the endogenous polyamine metabolism. In addition, a part of the tissue polyamines has its origin in the diet or their production by the intestinal microbiome. Emerging evidence has suggested that exogenous polyamines (either orally administrated or synthetized by the gut microbiota) are able to induce longevity in mice, and that spermidine supplementation exerts cardioprotective effects in animal models. Furthermore, the administration of either spermidine or spermine has been shown to be effective for improving glucose homeostasis and insulin sensitivity and reducing adiposity and hepatic fat accumulation in diet-induced obesity mouse models. The exogenous addition of agmatine, a cationic molecule produced through arginine decarboxylation by bacteria and plants, also exerts significant effects on glucose metabolism in obese models, as well as cardioprotective effects. In this review, we will discuss some aspects of polyamine metabolism and transport, how diet can affect circulating and local polyamine levels, and how the modulation of either polyamine intake or polyamine production by gut microbiota can be used for potential therapeutic purposes.

The effect of dietary asparagine supplementation on energy metabolism in liver of weaning pigs when challenged with lipopolysaccharide

Objective

This experiment was conducted to investigate whether asparagine (Asn) could improve liver energy status in weaning pigs when challenged with lipopolysaccharide.

Methods

Forty-eight weaned pigs (Duroc×Large White×Landrace, 8.12±0.56 kg) were assigned to four treatments: i) CTRL, piglets received a control diet and injected with sterile 0.9% NaCl solution; ii) lipopolysaccharide challenged control (LPSCC), piglets received the same control diet and injected with Escherichia coli LPS; iii) lipopolysaccharide (LPS)+0.5% Asn, piglets received a 0.5% Asn diet and injected with LPS; and iv) LPS+1.0% Asn, piglets received a 1.0% Asn diet and injected with LPS. All piglets were fed the experimental diets for 19 d. On d 20, the pigs were injected intraperitoneally with Escherichia coli LPS at 100 μg/kg body weights or the same volume of 0.9% NaCl solution based on the assigned treatments. Then the pigs were slaughtered at 4 h and 24 h after LPS or saline injection, and the liver samples were collected.

Results

At 24 h after LPS challenge, dietary supplementation with 0.5% Asn increased ATP concentration (quadratic, p<0.05), and had a tendency to increase adenylate energy charges and reduce AMP/ATP ratio (quadratic, p<0.1) in liver. In addition, Asn increased the liver mRNA expression of pyruvate kinase, pyruvate dehydrogenase, citrate synthase, and isocitrate dehydrogenase β (linear, p<0.05; quadratic, p<0.05), and had a tendency to increase the mRNA expression of hexokinase 2 (linear, p<0.1). Moreover, Asn increased liver phosphorylated AMP-activated protein kinase (pAMPK)/total AMP-activated protein kinase (tAMPK) ratio (linear, p<0.05; quadratic, p<0.05). However, at 4 h after LPS challenge, Asn supplementation had no effect on these parameters.

Conclusion

The present study indicated that Asn could improve the energy metabolism in injured liver at the late stage of LPS challenge.

OAZ1 knockdown enhances viability and inhibits ER and LHR transcriptions of granulosa cells in geese

An increasing number of studies suggest that ornithine decarboxylase antizyme 1 (OAZ1), which is regarded as a tumor suppressor gene, regulates follicular development, ovulation, and steroidogenesis. The granulosa cells in the ovary play a critical role in these ovarian functions. However, the action of OAZ1 mediating physiological functions of granulosa cells is obscure. OAZ1 knockdown in granulosa cells of geese was carried out in the current study. The effect of OAZ1 knockdown on polyamine metabolism, cell proliferation, apoptosis, and hormone receptor transcription of primary granulosa cells in geese was measured. The viability of granulosa cells transfected with the shRNA OAZ1 at 48 h was significantly higher than the control (p<0.05). The level of putrescine and spermidine in granulosa cells down-regulating OAZ1 was 7.04- and 2.11- fold higher compared with the control, respectively (p<0.05). The CCND1, SMAD1, and BCL-2 mRNA expression levels in granulosa cells down-regulating OAZ1 were each significantly higher than the control, respectively (p<0.05), whereas the PCNA and CASPASE 3 expression levels were significantly lower than the control (p<0.05). The estradiol concentration, ER and LHR mRNA expression levels were significantly lower in granulosa cells down-regulating OAZ1 compared with the control (p<0.05). Taken together, our results indicated that OAZ1 knockdown elevated the putrescine and spermidine contents and enhanced granulosa cell viability and inhibited ER and LHR transcriptions of granulosa cells in geese.

Pharmacogenetic influence of eNOS gene variant on endothelial and glucose metabolism responses to L-arginine supplementation: Post hoc analysis of the L-arginine trial

OBJECTIVE

To evaluate whether variants of the eNOS gene are associated with endothelial and metabolic responses to L-arginine (L-arg) supplementation.

MATERIAL AND METHODS

We examined a single nucleotide polymorphism of the eNOS gene (rs753482-A>C) to investigate the effects of this variant on endothelial function (EF), colony-forming unit-endothelial cell (CFU-EC) number, asymmetric-dimethylarginine (ADMA) level, insulin sensitivity index (ISI), and insulin secretion (IS) in a post hoc analysis of the L-arg trial. The L-arg trial (6.4 g/day for 18 months) was a single-center, randomized, double-blind, parallel-group, placebo-controlled, phase III trial in individuals with impaired glucose tolerance and metabolic syndrome. followed by a 12-month extended follow-up period after termination of the study drug (NCT 00917449).

RESULTS

At baseline, EF, CFU-EC numbers, ADMA levels, and ISI were impaired in subjects carrying minor allele C (both heterozygotes, AC and homozygotes, CC) as compared to subjects carrying major allele A (homozygotes, AA) (p<0.01). Compared to placebo, L-arg increased EF, CFU-EC numbers, and ISI, and improved ADMA levels and IS (p<0.01). The greatest improvements were found in AA subjects treated with L-arg, while the worst results were found in AC+CC subjects treated with placebo. In the placebo-treated subjects, EF, CFU-EC, ISI, and IS were significantly lower and ADMA was significantly higher in AC+CC subjects than in AA subjects.

CONCLUSIONS

Treatment with L-arg induced similar improvements in EF, CFU-EC numbers, ADMA levels, ISI, and IS in both AA subjects and AC+CC subjects. The presence of minor allele resulted in the worst prognosis in terms of EF, CFU-EC numbers, ADMA levels, ISI, and IS during the 30-month observation period.

Interaction of polyamines and mTOR signaling in the synthesis of antizyme (AZ)

Tissue polyamine levels are largely determined by the activity of ornithine decarboxylase (ODC, EC 4.1.17), which catalyzes the conversion of ornithine to the diamine putrescine. The activity of the enzyme is primarily regulated by a negative feedback mechanism involving ODC antizyme (AZ). Our previous studies demonstrated that AZ synthesis is stimulated by the absence of amino acids, the levels of which are sensed by the mTOR complex containing TORC1, which is stimulated by amino acids and inhibited by their absence, and TORC2 the function of which is not well defined. Polyamines, which cause a +1 ribosomal frameshift during the translation of AZ mRNA are required to increase AZ synthesis in both the presence and absence of amino acids. Amino acid starvation increases TORC2 activity. We have demonstrated that mTORC2 activity is necessary for AZ synthesis in the absence of amino acids. Tuberous sclerosis protein (TSC), a negative regulator of mTOR function regulates the activities of both the TORC1 and TORC2. TSC2 knockdown increased mTORC1 activity with concomitant inhibition of mTORC2 activity eliminating AZ induction in the absence of amino acids as well as that induced by spermidine. Thus, these results clearly demonstrate that in addition to polyamines, mTORC2 activity is necessary for AZ synthesis. Moreover, our results support a role for mTORC2 in the synthesis of a specific protein, AZ, which regulates growth of intestinal epithelial cells.

Polyamine-independent Expression of Caenorhabditis elegans Antizyme

Degradation of ornithine decarboxylase, the rate-limiting enzyme of polyamine biosynthesis, is promoted by the protein antizyme. Expression of antizyme is positively regulated by rising polyamine concentrations that induce a +1 translational frameshift required for production of the full-length protein. Antizyme itself is negatively regulated by the antizyme inhibitor. In our study, the regulation of Caenorhabditis elegans antizyme was investigated, and the antizyme inhibitor was identified. By applying a novel GFP-based method to monitor antizyme frameshifting in vivo, we show that the induction of translational frameshifting also occurs under stressful conditions. Interestingly, during starvation, the initiation of frameshifting was independent of polyamine concentrations. Because frameshifting was also prevalent in a polyamine auxotroph double mutant, a polyamine-independent regulation of antizyme frameshifting is suggested. Polyamine-independent induction of antizyme expression was found to be negatively regulated by the peptide transporter PEPT-1, as well as the target of rapamycin, but not by the daf-2 insulin signaling pathway. Stress-dependent expression of C. elegans antizyme occurred morely slowly than expression in response to increased polyamine levels, pointing to a more general reaction to unfavorable conditions and a diversion away from proliferation and reproduction toward conservation of energy. Interestingly, antizyme expression was found to drastically increase in aging individuals in a postreproductive manner. Although knockdown of antizyme did not affect the lifespan of C. elegans, knockdown of the antizyme inhibitor led to a significant reduction in lifespan. This is most likely caused by an increase in antizyme-mediated degradation of ornithine decarboxylase-1 and a resulting reduction in cellular polyamine levels.

A Nascent Peptide Signal Responsive to Endogenous Levels of Polyamines Acts to Stimulate Regulatory Frameshifting on Antizyme mRNA

The protein antizyme is a negative regulator of cellular polyamine concentrations from yeast to mammals. Synthesis of functional antizyme requires programmed +1 ribosomal frameshifting at the 3′ end of the first of two partially overlapping ORFs. The frameshift is the sensor and effector in an autoregulatory circuit. Except for Saccharomyces cerevisiae antizyme mRNA, the frameshift site alone only supports low levels of frameshifting. The high levels usually observed depend on the presence of cis-acting stimulatory elements located 5′ and 3′ of the frameshift site. Antizyme genes from different evolutionary branches have evolved different stimulatory elements. Prior and new multiple alignments of fungal antizyme mRNA sequences from the Agaricomycetes class of Basidiomycota show a distinct pattern of conservation 5′ of the frameshift site consistent with a function at the amino acid level. As shown here when tested in Schizosaccharomyces pombe and mammalian HEK293T cells, the 5′ part of this conserved sequence acts at the nascent peptide level to stimulate the frameshifting, without involving stalling detectable by toe-printing. However, the peptide is only part of the signal. The 3′ part of the stimulator functions largely independently and acts at least mostly at the nucleotide level. When polyamine levels were varied, the stimulatory effect was seen to be especially responsive in the endogenous polyamine concentration range, and this effect may be more general. A conserved RNA secondary structure 3′ of the frameshift site has weaker stimulatory and polyamine sensitizing effects on frameshifting.

Polyamine metabolism is sensitive to glycolysis inhibition in human neuroblastoma cells

Polyamines are essential for cell proliferation, and their levels are elevated in many human tumors. The oncogene n-myc is known to potentiate polyamine metabolism. Neuroblastoma, the most frequent extracranial solid tumor in children, harbors the amplification of n-myc oncogene in 25% of the cases, and it is associated with treatment failure and poor prognosis. We evaluated several metabolic features of the human neuroblastoma cell lines Kelly, IMR-32, and SK-N-SH. We further investigated the effects of glycolysis impairment in polyamine metabolism in these cell lines. A previously unknown linkage between glycolysis impairment and polyamine reduction is unveiled. We show that glycolysis inhibition is able to trigger signaling events leading to the reduction of N-Myc protein levels and a subsequent decrease of both ornithine decarboxylase expression and polyamine levels, accompanied by cell cycle blockade preceding cell death. New anti-tumor strategies could take advantage of the direct relationship between glucose deprivation and polyamine metabolism impairment, leading to cell death, and its apparent dependence on n-myc. Combined therapies targeting glucose metabolism and polyamine synthesis could be effective in the treatment of n-myc-expressing tumors.

Modulation of intestinal epithelial cell proliferation, migration, and differentiation in vitro by Astragalus polysaccharides

Previous studies have shown that Astragalus polysaccharides (APS) can be used to treat general gastrointestinal disturbances including intestinal mucosal injury. However, the mechanism by which APS mediate this effect is unclear. In the present study, the effects of APS on proliferation, migration, and differentiation of intestinal epithelial cells (IEC-6) were assessed using an in vitro wounding model and colorimetric thiazolyl blue (MTT) assays. The effect of APS on IEC-6 cell differentiation was observed using a light microscope and scanning electron microscope, and the expression of differentiation-specific markers of IEC-6 cells, such as cytokeratin 18 (CK18), alkaline phosphatase (ALP), tight junction protein ZO-2, and sucrase-isomaltase (SI), was determined by immunofluorescence assay (IFA) and real-time PCR. In addition, APS-induced signaling pathways in IEC-6 cells were characterized. Our results indicated that APS significantly enhance migration and proliferation of IEC-6 cells in vitro. APS-treated IEC-6 cells have numerous microvilli on their apical surface and also highly express CK18, ALP, ZO-2, and SI. Moreover, APS-treated IEC-6 cells, in which the activity and expression level of ornithine decarboxylase (ODC) were significantly elevated, also exhibited an increase in cellular putrescine, whereas no significant increase in TGF-β levels was observed. These findings suggest that APS may enhance intestinal epithelial cell proliferation, migration, and differentiation in vitro by stimulating ODC gene expression and activity and putrescine production, independent of TGF-β. Exogenous administration of APS may provide a new approach for modulating intestinal epithelial wound restitution in vivo.

Antizyme (AZ) regulates intestinal cell growth independent of polyamines

Since antizyme (AZ) is known to inhibit cell proliferation and to increase apoptosis, the question arises as to whether these effects occur independently of polyamines. Intestinal epithelial cells (IEC-6) were grown in control medium and medium containing 5 mM difluoromethylornithine (DFMO) to inhibit ODC, DFMO + 5 µM spermidine (SPD), DFMO + 5 µM spermine (SPM), or DFMO + 10 µM putrescine (PUT) for 4 days and various parameters of growth were measured along with AZ levels. Cell counts were significantly decreased and mean doubling times were significantly increased by DFMO. Putrescine restored growth in the presence of DFMO. However, both SPD and SPM when added with DFMO caused a much greater inhibition of growth than did DFMO alone, and both of these polyamines caused a dramatic increase in AZ. The addition of SPD or SPM to media containing DFMO + PUT significantly inhibited growth and caused a significant increase in AZ. IEC-6 cells transfected with AZ-siRNA grew more than twice as rapidly as either control cells or those incubated with DFMO, indicating that removal of AZ increases growth in cells in which polyamine synthesis is inhibited as well as in control cells. In a separate experiment, the addition of SPD increased AZ levels and inhibited growth of cells incubated with DFMO by 50%. The addition of 10 mM asparagine (ASN) prevented the increase in AZ and restored growth to control levels. These results show that cell growth in the presence or absence of ODC activity and in the presence or absence of polyamines depends only on the levels of AZ. Therefore, the effects of AZ on cell growth are independent of polyamines.

Spermidine, a sensor for antizyme 1 expression regulates intracellular polyamine homeostasis

Although intracellular polyamine levels are highly regulated, it is unclear whether intracellular putrescine (PUT), spermidine (SPD), or spermine (SPM) levels act as a sensor to regulate their synthesis or uptake. Polyamines have been shown to induce AZ1 expression through a unique +1 frameshifting mechanism. However, under physiological conditions which particular polyamine induces AZ1, and thereby ODC activity, is unknown due to their inter-conversion. In this study we demonstrate that SPD regulates AZ1 expression under physiological conditions in IEC-6 cells. PUT and SPD showed potent induction of AZ1 within 4 h in serum-starved confluent cells grown in DMEM (control) medium. Unlike control cells, PUT failed to induce AZ1 in cells grown in DFMO containing medium; however, SPD caused a robust AZ1 induction in these cells. SPM showed very little effect on AZ1 expression in both the control and polyamine-depleted cells. Only SPD induced AZ1 when S-adenosylmethionine decarboxylase (SAMDC) and/or ODC were inhibited. Surprisingly, addition of DENSpm along with DFMO restored AZ1 induction by putrescine in polyamine-depleted cells suggesting that the increased SSAT activity in response to DENSpm converted SPM to SPD, leading to the expression of AZ1. This study shows that intracellular SPD levels controls AZ1 synthesis.

Regulation of intestinal mucosal growth by amino acids

Amino acids, especially glutamine (GLN) have been known for many years to stimulate the growth of small intestinal mucosa. Polyamines are also required for optimal mucosal growth, and the inhibition of ornithine decarboxylase (ODC), the first rate-limiting enzyme in polyamine synthesis, blocks growth. Certain amino acids, primarily asparagine (ASN) and GLN stimulate ODC activity in a solution of physiological salts. More importantly, their presence is also required before growth factors and hormones such as epidermal growth factor and insulin are able to increase ODC activity. ODC activity is inhibited by antizyme-1 (AZ) whose synthesis is stimulated by polyamines, thus, providing a negative feedback regulation of the enzyme. In the absence of amino acids mammalian target of rapamycin complex 1 (mTORC1) is inhibited, whereas, mTORC2 is stimulated leading to the inhibition of global protein synthesis but increasing the synthesis of AZ via a cap-independent mechanism. These data, therefore, explain why ASN or GLN is essential for the activation of ODC. Interestingly, in a number of papers, AZ has been shown to inhibit cell proliferation, stimulate apoptosis, or increase autophagy. Each of these activities results in decreased cellular growth. AZ binds to and accelerates the degradation of ODC and other proteins shown to regulate proliferation and cell death, such as Aurora-A, Cyclin D1, and Smad1. The correlation between the stimulation of ODC activity and the absence of AZ as influenced by amino acids is high. Not only do amino acids such as ASN and GLN stimulate ODC while inhibiting AZ synthesis, but also amino acids such as lysine, valine, and ornithine, which inhibit ODC activity, increase the synthesis of AZ. The question remaining to be answered is whether AZ inhibits growth directly or whether it acts by decreasing the availability of polyamines to the dividing cells. In either case, evidence strongly suggests that the regulation of AZ synthesis is the mechanism through which amino acids influence the growth of intestinal mucosa. This brief article reviews the experiments leading to the information presented above. We also present evidence from the literature that AZ acts directly to inhibit cell proliferation and increase the rate of apoptosis. Finally, we discuss future experiments that will determine the role of AZ in the regulation of intestinal mucosal growth by amino acids.

Dietary requirements of "nutritionally non-essential amino acids" by animals and humans

Amino acids are necessary for the survival, growth, development, reproduction and health of all organisms. They were traditionally classified as nutritionally essential or non-essential for mammals, birds and fish based on nitrogen balance or growth. It was assumed that all "non-essential amino acids (NEAA)" were synthesized sufficiently in the body to meet the needs for maximal growth and health. However, there has been no compelling experimental evidence to support this assumption over the past century. NEAA (e.g., glutamine, glutamate, proline, glycine and arginine) play important roles in regulating gene expression, cell signaling, antioxidative responses, neurotransmission, and immunity. Additionally, glutamate, glutamine and aspartate are major metabolic fuels for the small intestine to maintain its digestive function and protect its mucosal integrity. Therefore, based on new research findings, NEAA should be taken into consideration in revising the classical "ideal protein" concept and formulating balanced diets to improve protein accretion, food efficiency, and health in animals and humans.

On programmed ribosomal frameshifting: the alternative proteomes

Frameshifting results from two main mechanisms: genomic insertions or deletions (indels) or programmed ribosomal frameshifting. Whereas indels can disrupt normal protein function, programmed ribosomal frameshifting can result in dual-coding genes, each of which can produce multiple functional products. Here, I summarize technical advances that have made it possible to identify programmed ribosomal frameshifting events in a systematic way. The results of these studies suggest that such frameshifting occurs in all genomes, and I will discuss methods that could help characterize the resulting alternative proteomes.