GART Functions as a Novel Methyltransferase in the RUVBL1/ß-Catenin Signaling Pathway to Promote Tumor Stemness in Colorectal Cancer.

Tumor stemness is associated with the recurrence and incurability of colorectal cancer (CRC), which lacks effective therapeutic targets and drugs. Glycinamide ribonucleotide transformylase (GART) fulfills an important role in numerous types of malignancies. The present study aims to identify the underlying mechanism through which GART may promote CRC stemness, as to developing novel therapeutic methods. An elevated level of GART is associated with poor outcomes in CRC patients and promotes the proliferation and migration of CRC cells. CD133+ cells with increased GART expression possess higher tumorigenic and proliferative capabilities both in vitro and in vivo. GART is identified to have a novel methyltransferase function, whose enzymatic activity center is located at the E948 site. GART also enhances the stability of RuvB-like AAA ATPase 1 (RUVBL1) through methylating its K7 site, which consequently aberrantly activates the Wnt/ß-catenin signaling pathway to induce tumor stemness. Pemetrexed (PEM), a compound targeting GART, combined with other chemotherapy drugs greatly suppresses tumor growth both in a PDX model and in CRC patients. The present study demonstrates a novel methyltransferase function of GART and the role of the GART/RUVBL1/ß-catenin signaling axis in promoting CRC stemness. PEM may be a promising therapeutic agent for the treatment of CRC.

A functional genetic screen for metabolic proteins unveils GART and the de novo purine biosynthetic pathway as novel targets for the treatment of luminal A ERα expressing primary and metastatic invasive ductal carcinoma.

Targeting tumor cell metabolism is a new frontier in cancer management. Thus, metabolic pathway inhibitors could be used as anti-estrogen receptor α (ERα) breast cancer (BC) drugs. Here, the interplay among metabolic enzyme(s), the ERα levels and cell proliferation was studied. siRNA-based screen directed against different metabolic proteins in MCF10a, MCF-7 and MCF-7 cells genetically resistant to endocrine therapy (ET) drugs and metabolomic analyses in numerous BC cell lines unveil that the inhibition of GART, a key enzyme in the purine de novo biosynthetic pathway, induces ERα degradation and prevent BC cell proliferation. We report here that a reduced GART expression correlates with a longer relapse-free-survival (RFS) in women with ERα-positive BCs. ERα-expressing luminal A invasive ductal carcinomas (IDCs) are sensitive to GART inhibition and GART expression is increased in receptor-positive IDCs of high grade and stage and plays a role in the development of ET resistance. Accordingly, GART inhibition reduces ERα stability and cell proliferation in IDC luminal A cells where it deregulates 17ß-estradiol (E2):ERα signaling to cell proliferation. Moreover, the GART inhibitor lometrexol (LMX) and drugs approved for clinical treatment of primary and metastatic BC (4OH-tamoxifen and the CDK4/CDK6 inhibitors) exert synergic antiproliferative effects in BC cells. In conclusion, GART inhibition by LMX or other inhibitors of the de novo purine biosynthetic pathway could be a novel effective strategy for the treatment of primary and metastatic BCs.

Stereoselective Synthesis of ß-Glycinamide Ribonucleotide.

A diastereoselective synthesis of the ß-anomer of glycinamide ribonucleotide (ß-GAR) has been developed. The synthesis was accomplished in nine steps from D-ribose and occurred in 5% overall yield. The route provided material on the multi-milligram scale. The synthetic ß-GAR formed was remarkably resistant to anomerization both in solution and as a solid.

VGLL3 increases the dependency of cancer cells on de novo nucleotide synthesis through GART expression.

Vestigial-like family member 3 (VGLL3) is a member of the VGLL family that serves as cofactors for TEA-domain transcription factors. Although VGLL3 is involved in the proliferation of cancer cells, the molecular mechanisms underlying VGLL3-mediated cell proliferation remain largely unknown. In this study, we found that stable expression of VGLL3 in human lung cancer A549 cells affects glutamine metabolism and increases their dependency on de novo nucleotide synthesis for proliferation. Mechanistically, VGLL3 was found to induce the expression of GART, which encodes a trifunctional enzyme that catalyzes de novo purine synthesis from glutamine. GART knockdown and the glycinamide ribonucleotide synthase, aminoimidazole ribonucleotide synthase, and glycinamide ribonucleotide formyltransferase trifunctional protein (GART) inhibitor lometrexol repressed the proliferation and survival of A549 cells stably expressing VGLL3. Mesenchymal breast cancer BT549 cells and MDA-MB-231 cells showed high expression of VGLL3, and VGLL3 knockdown was found to reduce GART expression. Lometrexol also repressed the proliferation of these breast cancer cells, whereas addition of inosine monophosphate, an important metabolite downstream of GART, rescued this repression. Taken together, these results suggest that VGLL3 induces GART expression and thereby confers de novo nucleotide-dependent cell proliferation in cancer cells.

pH Effects and Cooperativity among Key Titratable Residues for Escherichia coli Glycinamide Ribonucleotide Transformylase.

Human glycinamide ribonucleotide transformylase (GAR Tfase) is a regulatory enzyme in the de novo purine biosynthesis pathway that has been extensively studied as an anticancer target. To some extent, inhibition of GAR Tfase selectively targets cancer cells over normal cells and inhibits purine formation and DNA replication. In this study, we investigated E. coli GAR Tfase, which shares high sequence similarity with the human GAR Tfase, and most functional residues are conserved. Herein, we aim to predict the pH-activity curve through a computational approach. We carried out pH-replica exchange molecular dynamics (pH-REMD) simulations to investigate pH-dependent functions such as structural changes, ligand binding, and catalytic activity. To compute the pH-activity curve, we identified the catalytic residues in specific protonation states, referred to as the catalytic competent protonation states (CCPS), which maintain the structure, keep ligands bound, and facilitate catalysis. Our computed population of CCPS with respect to pH matches well with the experimental pH-activity curve. To compute the microscopic pKa values in the catalytically active conformation, we devised a thermodynamic model that considers the coupling between protonation states of CCPS residues and conformational states. These results allow us to correctly identify the general acid and base catalysts and interpret the pH-activity curve at an atomistic level.

The transcriptome profile of human trisomy 21 blood cells.

BACKGROUND: Trisomy 21 (T21) is a genetic alteration characterised by the presence of an extra full or partial human chromosome 21 (Hsa21) leading to Down syndrome (DS), the most common form of intellectual disability (ID). It is broadly agreed that the presence of extra genetic material in T21 gives origin to an altered expression of genes located on Hsa21 leading to DS phenotype. The aim of this study was to analyse T21 and normal control blood cell gene expression profiles obtained by total RNA sequencing (RNA-Seq). RESULTS: The results were elaborated by the TRAM (Transcriptome Mapper) software which generated a differential transcriptome map between human T21 and normal control blood cells providing the gene expression ratios for 17,867 loci. The obtained gene expression profiles were validated through real-time reverse transcription polymerase chain reaction (RT-PCR) assay and compared with previously published data. A post-analysis through transcriptome mapping allowed the identification of the segmental (regional) variation of the expression level across the whole genome (segment-based analysis of expression). Interestingly, the most over-expressed genes encode for interferon-induced proteins, two of them (MX1 and MX2 genes) mapping on Hsa21 (21q22.3). The altered expression of genes involved in mitochondrial translation and energy production also emerged, followed by the altered expression of genes encoding for the folate cycle enzyme, GART, and the folate transporter, SLC19A1. CONCLUSIONS: The alteration of these pathways might be linked and involved in the manifestation of ID in DS.

Discovery of 6-substituted thieno[2,3-d]pyrimidine analogs as dual inhibitors of glycinamide ribonucleotide formyltransferase and 5-aminoimidazole-4-carboxamide ribonucleotide formyltransferase in de novo purine nucleotide biosynthesis in folate receptor expressing human tumors.

We discovered 6-substituted thieno[2,3-d]pyrimidine compounds (3-9) with 3-4 bridge carbons and side-chain thiophene or furan rings for dual targeting one-carbon (C1) metabolism in folate receptor- (FR) expressing cancers. Synthesis involved nine steps starting from the bromo-aryl carboxylate. From patterns of growth inhibition toward Chinese hamster ovary cells expressing FRα or FRß, the proton-coupled folate transporter or reduced folate carrier, specificity for uptake by FRs was confirmed. Anti-proliferative activities were demonstrated toward FRα-expressing KB tumor cells and NCI-IGROV1 ovarian cancer cells. Inhibition of de novo purine biosynthesis at both 5-aminoimidazole-4-carboxamide ribonucleotide formyltransferase and glycinamide ribonucleotide formyltransferase (GARFTase) was confirmed by metabolite rescue, metabolomics and enzyme assays. X-ray crystallographic structures were obtained with compounds 3-5 and human GARFTase. Our studies identify first-in-class C1 inhibitors with selective uptake by FRs and dual inhibition of enzyme targets in de novo purine biosynthesis, resulting in anti-tumor activity. This series affords an exciting new platform for selective multi-targeted anti-tumor agents.

Design, synthesis and biological evaluation of novel pyrrolo[2,3-d]pyrimidine as tumor-targeting agents with selectivity for tumor uptake by high affinity folate receptors over the reduced folate carrier.

Tumor-targeted 6-substituted pyrrolo[2,3-d]pyrimidine benzoyl compounds based on 2 were isosterically modified at the 4-carbon bridge by replacing the vicinal (C11) carbon by heteroatoms N (4), O (5) or S (6), or with an N-substituted formyl (7), trifluoroacetyl (8) or acetyl (9). Replacement with sulfur (6) afforded the most potent KB tumor cell inhibitor, ~6-fold better than the parent 2. In addition, 6 retained tumor transport selectivity via folate receptor (FR) α and -ß over the ubiquitous reduced folate carrier (RFC). FRα-mediated cell inhibition for 6 was generally equivalent to 2, while the FRß-mediated activity was improved by 16-fold over 2. N (4) and O (5) substitutions afforded similar tumor cell inhibitions as 2, with selectivity for FRα and -ß over RFC. The N-substituted analogs 7-9 also preserved transport selectivity for FRα and -ß over RFC. For FRα-expressing CHO cells, potencies were in the order of 8 > 7 > 9. Whereas 8 and 9 showed similar results with FRß-expressing CHO cells, 7 was ~16-fold more active than 2. By nucleoside rescue experiments, all the compounds inhibited de novo purine biosynthesis, likely at the step catalyzed by glycinamide ribonucleotide formyltransferase. Thus, heteroatom replacements of the CH2 in the bridge of 2 afford analogs with increased tumor cell inhibition that could provide advantages over 2, as well as tumor transport selectivity over clinically used antifolates including methotrexate and pemetrexed.

Co-expression analysis provides important module and pathways of human dilated cardiomyopathy.

Dilated cardiomyopathy (DCM) is a heart disease that injured greatly to the people wordwide. Systemic co-expression analysis for this cancer is still limited, although massive clinic experiments and gene profiling analyses had been well performed previously. Here, using the public RNA-Seq data "GSE116250" and gene annotation of Ensembl database, we built the co-expression modules for DCM by Weighted Gene Co-Expression Network Analysis, and investigated the function enrichment and protein-protein interaction (PPI) network of co-expression genes of each module by Database for Annotation, Visualization, and Integrated Discovery and Search Tool for the Retrieval of Interacting Genes/Proteins database, respectively. First, 5,000 genes in the 37 samples were screened and 11 co-expression modules were conducted. The number of genes for each module ranged from 77 to 936, with a mean of 455. Second, interaction relationships of hub-genes between pairwise modules showed great differences, suggesting relatively high-scale independence of the modules. Third, functional enrichments of the co-expression modules exhibited great differences. We found that genes in module 3 were significantly enriched in the pathways of focal adhesion and ubiquitin-mediated proteolysis. This module was inferred as the key module involved in DCM. In addition, PPI analysis revealed that the genes HSP90AA1, CTNNB1, MAPK1, GART, and PPP2CA owned the largest number of adjacency genes, unveiling that they may function importantly during the occurrence of DCM. Focal adhesion and ubiquitin-mediated proteolysis play important roles in human DCM.

Mapping Post-Translational Modifications of de Novo Purine Biosynthetic Enzymes: Implications for Pathway Regulation.

Purines represent a class of essential metabolites produced by the cell to maintain cellular homeostasis and facilitate cell proliferation. In times of high purine demand, the de novo purine biosynthetic pathway is activated; however, the mechanisms that facilitate this process are largely unknown. One plausible mechanism is through intracellular signaling, which results in enzymes within the pathway becoming post-translationally modified to enhance their individual enzyme activities and the overall pathway metabolic flux. Here, we employ a proteomic strategy to investigate the extent to which de novo purine biosynthetic pathway enzymes are post-translationally modified in 293T cells. We identified 7 post-translational modifications on 135 residues across the 6 human pathway enzymes. We further asked whether there were differences in the post-translational modification state of each pathway enzyme isolated from cells cultured in the presence or absence of purines. Of the 174 assigned modifications, 67% of them were only detected in one experimental growth condition in which a significant number of serine and threonine phosphorylations were noted. A survey of the most-probable kinases responsible for these phosphorylation events uncovered a likely AKT phosphorylation site at residue Thr397 of PPAT, which was only detected in cells under purine-supplemented growth conditions. These data suggest that this modification might alter enzyme activity or modulate its interaction(s) with downstream pathway enzymes. Together, these findings propose a role for post-translational modifications in pathway regulation and activation to meet intracellular purine demand.

Detecting Purinosome Metabolon Formation with Fluorescence Microscopy.

A long-standing hypothesis in the de novo purine biosynthetic pathway is that there must be highly coordinated processes to allow for enhanced metabolic flux when a cell demands purines. One mechanism by which the pathway meets its cellular demand is through the spatial organization of pathway enzymes into multienzyme complexes called purinosomes. Cellular conditions known to impact the activity of enzymes in the pathway or overall pathway flux have been reflected in a change in the number of purinosome-positive cells or the density of purinosomes in a given cell. The following general protocols outline the steps needed for purinosome detection through transient expression of fluorescent protein chimeras or through immunofluorescence in purine-depleted HeLa cells using confocal laser scanning microscopy. These protocols define a purinosome as a colocalization of FGAMS with one additional pathway enzyme, such as PPAT or GART, and provide insights into the proper identification of a purinosome from other reported cellular bodies.

The mTORC1 Signaling Network Senses Changes in Cellular Purine Nucleotide Levels.

Mechanistic (or mammalian) target of rapamycin complex 1 (mTORC1) integrates signals from growth factors and nutrients to control biosynthetic processes, including protein, lipid, and nucleic acid synthesis. We find that the mTORC1 pathway is responsive to changes in purine nucleotides in a manner analogous to its sensing of amino acids. Depletion of cellular purines, but not pyrimidines, inhibits mTORC1, and restoration of intracellular adenine nucleotides via addition of exogenous purine nucleobases or nucleosides acutely reactivates mTORC1. Adenylate sensing by mTORC1 is dependent on the tuberous sclerosis complex (TSC) protein complex and its regulation of Rheb upstream of mTORC1, but independent of energy stress and AMP-activated protein kinase (AMPK). Even though mTORC1 signaling is not acutely sensitive to changes in intracellular guanylates, long-term depletion of guanylates decreases Rheb protein levels. Our findings suggest that nucleotide sensing, like amino acid sensing, enables mTORC1 to tightly coordinate nutrient availability with the synthesis of macromolecules, such as protein and nucleic acids, produced from those nutrients.

Novel 6-substituted benzoyl and non-benzoyl straight chain pyrrolo[2,3-d]pyrimidines as potential antitumor agents with multitargeted inhibition of TS, GARFTase and AICARFTase.

A novel series of 6-substituted benzoyl and non-benzoyl straight chain pyrrolo[2,3-d]pyrimidines were designed and synthesized as potential antitumor agents targeting both thymidylate and purine nucleotide biosynthesis. Starting from the key intermediate 2-amino-4-oxo-pyrrolo[2,3-d]pyrimidin-6-yl-acetic acid, target compounds 1-6 were successfully obtained through two sequential condensation and saponification reactions in decent yield. The newly synthesized compounds showed antiproliferative potencies against a panel of tumor cell lines including KB, SW620 and MCF7. In particular, most compounds of this series exhibited nanomolar to subnanomolar inhibitory activities toward KB tumor cells, significantly more potent than the positive control methotrexate (MTX) and pemetrexed (PMX). Along with the results of nucleoside protection assays, molecular modeling studies suggested that the antitumor activity of compound 6 could be attributed to multitargeted inhibition of folate-dependent enzymes thymidylate synthase (TS), glycinamide ribonucleotide formyltransferase (GARFTase) and 5-aminoimidazole-4-carboxamide ribonucleotide formyltransferase (AICARFTase). Growth inhibition by compound 6 also induced distinct early apoptosis and cell cycle arrest at S-phase, which resulted in cell death.

Association of genetic polymorphisms of de novo nucleotide biosynthesis with increased CHD susceptibility in the northern Chinese population.

Congenital heart disease (CHD) is one of most prevalent birth defects in the world. However, the underlying molecular mechanism(s) have not been fully understood. Here we report that increased CHD susceptibility is associated with genetic polymorphisms for de novo nucleotide biosynthesis in northern Chinese population, which has been reported with lower plasma folate levels. Nine tagSNPs of four genes (GART, ATIC, MTHFD1 and SHMT1) in de novo nucleotide biosynthesis were sequenced in 802 sporadic CHD patients and 1093 controls from two Han Chinese populations, located in north China (Shandong) and South China (Shanghai), respectively. Six SNPs were found to be significantly associated with CHDs or septation defects only in the Shandong population dataset, but none displayed significant association with any CHDs in the Shanghai population dataset as well as in the combined dataset. We also showed that the minor A allele of rs7279549 in GART reduced transcriptional activity and displayed lower affinity for unknown transcription factor(s), demonstrating the allele is a functional risk factor for CHD in Shandong population. Our study indicates that dysregulation of de novo nucleotide biosynthesis pathway may conditionally contribute to CHD pathogenesis in northern Chinese.

Comparative Genomic Analysis of Haemophilus haemolyticus and Nontypeable Haemophilus influenzae and a New Testing Scheme for Their Discrimination.

Haemophilus haemolyticus has been recently discovered to have the potential to cause invasive disease. It is closely related to nontypeable Haemophilus influenzae (NT H. influenzae). NT H. influenzae and H. haemolyticus are often misidentified because none of the existing tests targeting the known phenotypes of H. haemolyticus are able to specifically identify H. haemolyticus Through comparative genomic analysis of H. haemolyticus and NT H. influenzae, we identified genes unique to H. haemolyticus that can be used as targets for the identification of H. haemolyticus A real-time PCR targeting purT (encoding phosphoribosylglycinamide formyltransferase 2 in the purine synthesis pathway) was developed and evaluated. The lower limit of detection was 40 genomes/PCR; the sensitivity and specificity in detecting H. haemolyticus were 98.9% and 97%, respectively. To improve the discrimination of H. haemolyticus and NT H. influenzae, a testing scheme combining two targets (H. haemolyticus purT and H. influenzae hpd, encoding protein D lipoprotein) was also evaluated and showed 96.7% sensitivity and 98.2% specificity for the identification of H. haemolyticus and 92.8% sensitivity and 100% specificity for the identification of H. influenzae, respectively. The dual-target testing scheme can be used for the diagnosis and surveillance of infection and disease caused by H. haemolyticus and NT H. influenzae.

GART mediates the renewal of intestinal epithelial barrier via p38/p53/PUMA cascade in colitis.

Glycinamide ribonucleotide formyltransferase (GART) has been established as a pivotal enzyme in de novo purine synthesis, and mediates cellular apoptosis in many diseases. We aimed to investigate the role of GART in the pathogenesis of Crohn's disease (CD). In our study, we demonstrated for the first time that GART expression is up-regulated in patients with active CD and in 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced acute colitis model. Moreover, the inhibition of GART induced cellular apoptosis and suppressed the migration of IECs through the activation of the MEKK3-MKK3-p38 mitogen-activated protein kinase (MAPK) pathway, following with the dys-regulation of p53 and p53 up-regulated modulator of apoptosis (PUMA). Taken together, GART plays a critical role in the protection of cellular apoptosis and migration of intestinal epithelial cells to maintain the integrity of the epithelial barrier, thus providing a new potential approach in designing a novel therapy for CD.

Structural and Enzymatic Analysis of Tumor-Targeted Antifolates That Inhibit Glycinamide Ribonucleotide Formyltransferase.

Pemetrexed and methotrexate are antifolates used for cancer chemotherapy and inflammatory diseases. These agents have toxic side effects resulting, in part, from nonspecific cellular transport by the reduced folate carrier (RFC), a ubiquitously expressed facilitative transporter. We previously described 2-amino-4-oxo-6-substituted pyrrolo[2,3-d]pyrimidine antifolates with modifications of the side chain linker and aromatic ring that are poor substrates for RFC but are efficiently transported via folate receptors (FRs) and the proton-coupled folate transporter (PCFT). These targeted antifolates are cytotoxic in vitro toward FR- and PCFT-expressing tumor cells and in vivo with human tumor xenografts in immune-compromised mice, reflecting selective cellular uptake. Antitumor efficacy is due to inhibition of glycinamide ribonucleotide (GAR) formyltransferase (GARFTase) activity in de novo synthesis of purine nucleotides. This study used purified human GARFTase (formyltransferase domain) to assess in vitro inhibition by eight novel thieno- and pyrrolo[2,3-d]pyrimidine antifolates. Seven analogues (AGF23, AGF71, AGF94, AGF117, AGF118, AGF145, and AGF147) inhibited GARFTase with Ki values in the low- to mid-nanomolar concentration range, whereas AGF50 inhibited GARFTase with micromolar potency similar to that of PMX. On the basis of crystal structures of ternary complexes with GARFTase, ß-GAR, and the monoglutamyl antifolates, differences in inhibitory potencies correlated well with antifolate binding and the positions of the terminal carboxylates. Our data provide a mechanistic basis for differences in inhibitory potencies between these novel antifolates and a framework for future structure-based drug design. These analogues could be more efficacious than clinically used antifolates, reflecting their selective cellular uptake by FRs and PCFT and potent GARFTase inhibition.

Tumor Targeting with Novel 6-Substituted Pyrrolo [2,3-d] Pyrimidine Antifolates with Heteroatom Bridge Substitutions via Cellular Uptake by Folate Receptor α and the Proton-Coupled Folate Transporter and Inhibition of de Novo Purine Nucleotide Biosynthesis.

Targeted antifolates with heteroatom replacements of the carbon vicinal to the phenyl ring in 1 by N (4), O (8), or S (9), or with N-substituted formyl (5), acetyl (6), or trifluoroacetyl (7) moieties, were synthesized and tested for selective cellular uptake by folate receptor (FR) α and ß or the proton-coupled folate transporter. Results show increased in vitro antiproliferative activity toward engineered Chinese hamster ovary cells expressing FRs by 4-9 over the CH2 analogue 1. Compounds 4-9 inhibited de novo purine biosynthesis and glycinamide ribonucleotide formyltransferase (GARFTase). X-ray crystal structures for 4 with FRα and GARFTase showed that the bound conformations of 4 required flexibility for attachment to both FRα and GARFTase. In mice bearing IGROV1 ovarian tumor xenografts, 4 was highly efficacious. Our results establish that heteroatom substitutions in the 3-atom bridge region of 6-substituted pyrrolo[2,3-d]pyrimidines related to 1 provide targeted antifolates that warrant further evaluation as anticancer agents.

Folate-Dependent Purine Nucleotide Biosynthesis in Humans.

Purine nucleotide biosynthesis de novo (PNB) requires 2 folate-dependent transformylases-5'-phosphoribosyl-glycinamide (GAR) and 5'-phosphoribosyl-5-aminoimidazole-4-carboxamide (AICAR) transformylases-to introduce carbon 8 (C8) and carbon 2 (C2) into the purine ring. Both transformylases utilize 10-formyltetrahydrofolate (10-formyl-H4folate), where the formyl-carbon sources include ring-2-C of histidine, 3-C of serine, 2-C of glycine, and formate. Our findings in human studies indicate that glycine provides the carbon for GAR transformylase (exclusively C8), whereas histidine and formate are the predominant carbon sources for AICAR transformylase (C2). Contrary to the previous notion, these carbon sources may not supply a general 10-formyl-H4folate pool, which was believed to equally provide carbons to C8 and C2. To explain these phenomena, we postulate that GAR transformylase is in a complex with the trifunctional folate-metabolizing enzyme (TFM) and serine hydroxymethyltransferase to channel carbons of glycine and serine to C8. There is no evidence for channeling carbons of histidine and formate to AICAR transformylase (C2). GAR transformylase may require the TFM to furnish 10-formyl-H4folate immediately after its production from serine to protect its oxidation to 10-formyldihydrofolate (10-formyl-H2folate), whereas AICAR transformylase can utilize both 10-formyl-H2folate and 10-formyl-H4folate. Human liver may supply AICAR to AICAR transformylase in erythrocytes/erythroblasts. Incorporation of ring-2-C of histidine and formate into C2 of urinary uric acid presented a circadian rhythm with a peak in the morning, which corresponds to the maximum DNA synthesis in the bone marrow, and it may be useful in the timing of the administration of drugs that block PNB for the treatment of cancer and autoimmune disease.

Disruption of host antiviral resistances by gammaherpesvirus tegument proteins with homology to the FGARAT purine biosynthesis enzyme.

All known gammaherpesviruses encode at least one conserved tegument protein that contains sequence homology to the cellular purine biosynthesis enzyme: phosphoribosylformylglycineamide amidotransferase (FGARAT, or PFAS). While no enzymatic activity have been found on these viral FGARAT-homology proteins (vFGARAT), they are important for disarming host intrinsic antiviral machinery. Most vFGARAT proteins disrupt the intrinsic antiviral response-associated cellular subnuclear structure: ProMyelocytic Leukemia (PML) associated nuclear body (PML-NB). vFGARATs from different viruses target different components of PML-NB to prevent cellular repression of viral infection. In addition, vFGARATs of rhadinoviruses were recently found to oligomerize with the cellular FGARAT to deamidate RIG-I and repress inflammatory cytokine production. In this review we discuss the diverse mechanisms of antiviral response disruption by gammaherpesvirus vFGARATs and the significance of the enzyme homology domain.