Structure and expression of the murine muscle adenylosuccinate synthetase gene

Targeting nucleotide metabolism: a promising approach to enhance cancer immunotherapy

Targeting nucleotide metabolism can not only inhibit tumor initiation and progression but also exert serious side effects. With in-depth studies of nucleotide metabolism, our understanding of nucleotide metabolism in tumors has revealed their non-proliferative effects on immune escape, indicating the potential effectiveness of nucleotide antimetabolites for enhancing immunotherapy. A growing body of evidence now supports the concept that targeting nucleotide metabolism can increase the antitumor immune response by (1) activating host immune systems via maintaining the concentrations of several important metabolites, such as adenosine and ATP, (2) promoting immunogenicity caused by increased mutability and genomic instability by disrupting the purine and pyrimidine pool, and (3) releasing nucleoside analogs via microbes to regulate immunity. Therapeutic approaches targeting nucleotide metabolism combined with immunotherapy have achieved exciting success in preclinical animal models. Here, we review how dysregulated nucleotide metabolism can promote tumor growth and interact with the host immune system, and we provide future insights into targeting nucleotide metabolism for immunotherapeutic treatment of various malignancies.

An association study of ADSS gene polymorphisms with schizophrenia

Background

Adenylosuccinate synthase (ADSS) catalyzes the first committed step of AMP synthesis. It was suggested that the blood-derived RNA of ADSS was down-regulated in schizophrenia (SZ) and one of the eight putative biomarker genes to discriminate SZ from normal controls. However, it remains unclear whether the reduction of ADSS RNA is due to the polymorphisms of the gene or not.

Methods

We attempted to examine the association of ADSS gene with schizophrenia in a Chinese population of 480 schizophrenics and 502 normal controls. Genotyping was performed by the Sequenom platform.

Results

The 6 marker SNPs (rs3102460, rs3127459, rs3127460, rs3127465, rs3006001, and rs3003211) were genotyped. The frequencies of alleles, genotypes, and haplotypes were tested between cases and controls. There was no significant difference of genotypic, allelic, or haplotypic distributions of the 6 SNPs between the two groups.

Conclusion

Our data did not support ADSS gene as a susceptibility gene for SZ in Chinese Han population. Large sample size study is needed to validate or replicate our association study, especially from other ethnic populations.

Comparative molecular characterization of ADSS1 and ADSS2 genes in pig (Sus scrofa)

Adenylosuccinate synthetase (ADSS) catalyzes the key step of AMP synthesis. Vertebrates have two isozymes of ADSS, which are named ADSS1 and ADSS2, respectively. In this study, we cloned porcine ADSS1 and ADSS2 genes and comparatively analyzed their sequence, chromosome mapping, mRNA distribution and subcellular localization. According to our results, the ADSS1 gene was predominantly expressed in the striated muscle tissues, while ADSS2 gene distributed widely in all the tissues detected. Additionally, ADSS1 gene was up-regulated significantly along with porcine muscle growth, and ADSS2 gene expression was more constant during the muscle development. Porcine ADSS1 gene was assigned to SSC7q and the linked marker was SSC12B09, ADSS2 gene was mapped on SSC10p and the linked marker was SW497, and porcine ADSS2 protein was subcellular localized in mitochondria. Moreover, we found that one single nucleotide polymorphism (SNP, T/C(70)) in the ninth intron of ADSS2 gene was significantly associated with average daily gain trait (ADG, P<0.05) and loin muscle area trait (P<0.05).

Molecular cloning and characterization of a novel muscle adenylosuccinate synthetase, AdSSL1, from human bone marrow stromal cells

Vertebrates have muscle and non-muscle isozymes of adenylosuccinate synthetase (AdSS, EC 6.3.4.4), which catalyzes the first committed step in AMP synthesis. A novel muscle isozyme of adenylosuccinate synthetase, human AdSSL1, is identified from human bone marrow stromal cells. AdSSL1 is 98% identical to mouse muscle type AdSS1 and contains conserved sequence and structural features of adenylosuccinate synthetase. Human AdSSL1 gene is mapped to chromosome 14p32.33. After stimulation, leukemia cells express AdSSL1 in a time-dependent manner different from that of non-muscle adenylosuccinate synthetase. The human AdSSL1 is predominantly expressed in skeletal muscle and cardiac tissue consistent with the potential role for the enzyme in muscle metabolism. Overexpressed AdSSL1 protein in COS-7 cells locates in cytoplasm. Recombinant AdSSL1 protein possesses typical enzymatic activity to catalyze adenylosuccinate formation. The identification of human AdSSL1 with predominant expression in muscle tissue will facilitate future genetic and biochemical analysis of the enzyme in muscle physiology.

Mammalian target of rapamycin and protein kinase A signaling mediate the cardiac transcriptional response to glutamine

The addition of glutamine as a major nutrient to cultured neonatal rat cardiomyocytes produced an increase in myocyte size and the organization of actin into myofibrillar arrays. The cellular response was associated with increased abundance of the mRNAs encoding the contractile proteins, alpha-myosin heavy chain and cardiac alpha-actin, and the metabolic enzymes, muscle carnitine palmitoyl transferase I and muscle adenylosuccinate synthetase (ADSS1). Adss1 gene expression was induced approximately 5-fold in glutamine-treated rat neonatal cardiac myocytes. The induction was mediated through the protein kinase A and mammalian target of rapamycin signaling pathways and required a cyclic AMP response element associated with the promoter region of the Adss1 gene. These results highlight glutamine as a major nutrient regulator of cardiac gene expression and identify protein kinase A and mammalian target of rapamycin signaling pathways as mediators of the cardiomyocyte transcriptional response.

The adenylosuccinate synthetase-1 gene is activated in the hypertrophied heart

Adenylosuccinate synthetase 1 (ADSS1) functions as an important component in adenine nucleotide biosynthesis and is abundant in the heart. Here we report that the Adss1 gene is up-regulated in two in vivo rodent models of surgically induced cardiac hypertrophy. In addition, we examined an in vitro hypertrophy system of rat neonatal cardiomyocytes treated with angiotensin II to study Adss1 gene regulation. We show that this stimulus triggers a signaling cascade that results in the activation of the Adss1 gene. The induction of Adss1 gene expression was blocked by cyclosporin A in vitro, suggesting that calcineurin, a calmodulin activated phosphatase, is involved in this signaling pathway. Consistent with this view we provide evidence that the induction of Adss1 by angiotension II requires the presence of an NFAT binding site located 556 base pairs upstream of the Adss1 transcription start site. We propose that ADSS1 plays a role in the development of cardiac hypertrophy through its function in adenine nucleotide biosynthesis.

Electrical stimulation of neonatal cardiac myocytes activates the NFAT3 and GATA4 pathways and up-regulates the adenylosuccinate synthetase 1 gene

Electrically stimulated pacing of cultured cardiomyocytes serves as an experimentally convenient and physiologically relevant in vitro model of cardiac hypertrophy. Electrical pacing triggers a signaling cascade that results in the activation of the muscle-specific Adss1 gene and the repression of the nonmuscle Adss2 isoform. Activation of the Adss1 gene involves the calcineurin-mediated dephosphorylation of NFAT3, allowing its translocation to the nucleus, where it can directly participate in Adss1 gene activation. Mutational studies show that an NFAT binding site located in the Adss1 5'-flanking region is essential for this activation. Electrical pacing also results in the increased synthesis of GATA4, another critical cardiac transcription factor required for Adss1 gene expression. MEF2C also produces transactivation of the Adss1 gene reporter in control and paced cardiac myocytes. Using the Adss1 gene as a model, these studies are the first to demonstrate that electrical pacing activates the calcineurin/NFAT3 and GATA4 pathways as a means of regulating cardiac gene expression.

Combinatorial interactions regulate cardiac expression of the murine adenylosuccinate synthetase 1 gene

The mammalian heart begins contracting at the linear tube stage during embryogenesis and continuously pumps, nonstop, throughout the entire lifetime of the animal. Therefore, the cardiac energy metabolizing pathways must be properly established and efficiently functioning. While the biochemistry of these pathways is well defined, limited information regarding the regulation of cardiac metabolic genes is available. Previously, we reported that 1.9 kilobase pairs of murine adenylosuccinate synthetase 1 gene (Adss1) 5'-flanking DNA directs high levels of reporter expression to the adult transgenic heart. In this report, we define the 1.9-kilobase pair fragment as a cardiac-specific enhancer that controls correct spatiotemporal expression of a reporter similar to the endogenous Adss1 gene. A 700-base pair fragment within this region activates a heterologous promoter specifically in adult transgenic hearts. Proteins present in a cardiac nuclear extract interact with potential transcription factor binding sites of this region and these cis-acting sites play important regulatory roles in the cardiac expression of this reporter. Finally, we report that several different cardiac transcription factors trans-activate the 1.9HSCAT construct through these sites and that combinations result in enhanced reporter expression. Adss1 appears to be one of the first target genes identified for the bHLH factors Hand1 and Hand2.

Adenylosuccinate synthetase genes: molecular cloning and phylogenetic analysis of a highly conserved archaeal gene

Adenylosuccinate synthetase (PurA) catalyzes the first step in the de novo AMP synthesis and has been extensively studied in both Bacteria and Eukarya. We cloned the purA gene from the hyperthermophilic archaeon, Pyrococcus furiosus. The gene appears to be individually transcribed and encodes a protein of 339 amino acids. The amino acid sequence comparison with other archael PurAs found from recent genome analyses indicated that two deletions, one central and the other C-terminal, are a common feature of archaeal PurAs. None of the 21 PurA homologues analyzed from Eukarya and Bacteria exhibited this feature. Amino acid sequences of PurAs in Archaea showed 64% average identities which were significantly higher than the 50% and 55% calculated for Bacteria and Eukarya, respectively. Several residues conserved in PurAs of both Eukarya and Bacteria and shown to be of catalytic importance are missing in the archaeal PurAs. Phylogenetic analysis using PurA as the marker grouped life into 3 domains, hence it was consistent with results derived from 16-18S ribosomal RNA sequences. The topology within the three domains, in general, portrayed the hitherto accepted evolutionary relationship among the organisms utilized. PurA can, thus, serve as an additional marker to evaluate phylogenetic inferences drawn from sequence data from rRNA and other conserved genes. The presence of two unique deletions in both euryarchaeal and crenarchaeal PurAs, but not in those of Bacteria and Eukarya, is a strong evidence confirming the common lineage of these two subdomains of Archaea.

Role of NRF-1 in bidirectional transcription of the human GPAT-AIRC purine biosynthesis locus

GPAT and AIRC encode enzymes for steps one and six plus seven respectively in the pathway for de novo purine nucleotide synthesis in vertebrates. The human GPAT and AIRC genes are divergently transcribed from a 558 bp intergenic promoter region. Cis-acting sites and transcription factors important for bidirectional expression were identified. A cluster of sites between nt 215 and 260 are essential, although not sufficient, for expression of both genes. Two proteins from HepG2 cell nuclear extract, identified as NRF-1 and Sp1, bound to the promoter at sites within the 215-260 region. NRF-1 was required for stable binding of Sp1. Deletion of a 5'promoter region including nt 215-260 resulted in decreased expression of GPAT and AIRC in transfected HepG2 cells. The decreased expression was accounted for by point mutations in an NRF-1 site and either of two flanking sites for Sp1. These transcription factors account in part for the coordinated expression of human GPAT and AIRC.