Novel role for carbamoyl phosphate synthetase 2 in cranial sensory circuit formation

Exploring Aspartate Transcarbamoylase: A Promising Broad-Spectrum Target for Drug Development

Pyrimidine nucleotides are essential for a wide variety of cellular processes and are synthesized either via a salvage pathway or through de novo biosynthesis. The latter is particularly important in proliferating cells, such as infectious diseases and cancer cells. Aspartate transcarbamoylase (ATCase) catalyzes the first committed and rate-limiting step in the de novo pyrimidine biosynthesis pathway, making it an attractive therapeutic target for various diseases. This review summarizes the development of a series of allosteric ATCase inhibitors, advancing them as potential candidates for malarial, tuberculosis and cancer therapies. Furthermore, it explores the potential for these compounds to be expanded into drugs targeting neglected tropical diseases, antimicrobial-resistant infections caused by the ESKAPE pathogens, and their possible application as herbicides. We identify the likely equivalent allosteric pocket in these systems and perform a structure and sequence-based analysis of the residues comprising it, providing a rationale for continued exploration of this compound series as both specific and broad-range inhibitors. The review concludes by emphasizing the importance of continued research into ATCase inhibitors, given their potential broad applicability in treating diverse diseases to enhance both human health and agricultural practices.

CHIP promotes CAD ubiquitination and degradation to suppress the proliferation and colony formation of glioblastoma cells

PURPOSE

Cancer cells are characterized as the uncontrolled proliferation, which demands high levels of nucleotides that are building blocks for DNA synthesis and replication. CAD (carbamoyl-phosphate synthetase 2, aspartate transcarbamylase and dihydroorotase) is a trifunctional enzyme that initiates the de novo pyrimidine synthesis, which is normally enhanced in cancer cells to preserve the pyrimidine pool for cell division. Glioma, representing most brain cancer, is highly addicted to nucleotides like pyrimidine to sustain the abnormal growth and proliferation of cells. CAD is previously reported to be dysregulated in glioma, but the underlying mechanism remains unclear.

METHODS

The expression of CAD and CHIP (carboxyl terminus of Hsc70-interacting protein) protein in normal brain cells and three glioblastoma (GBM) cell lines were measured by immunoblots. Lentiviruses-mediated expression of target proteins or shRNAs were used to specifically overexpress or knock down CAD and CHIP. Cell counting, colony formation, apoptosis and cell cycle assays were used to assess the roles of CAD and CHIP in GBM cell proliferation and survival. Co-immunoprecipitation and ubiquitination assays were used to examine the interaction of CHIP with CAD and the ubiquitination of CAD. The correlation of CAD and CHIP expression with GBM patients' survival was obtained by analyzing the GlioVis database.

RESULTS

In this study, we showed that the expression of CAD was upregulated in glioma, which was positively correlated with the tumor grade and survival of glioma patients. Knockdown of CAD robustly inhibited the cell proliferation and colony formation of GBM cells, indicating the essential role of CAD in the pathogenesis of GBM. Mechanistically, we firstly identified that CAD was modified by the K29-linked polyubiquitination, which was mediated by the E3 ubiquitin ligase CHIP. By interacting with and ubiquitinating CAD, CHIP enhanced its proteasomal and lysosomal degradation, which accounted for the anti-proliferative role of CHIP in GBM cells. To sustain the expression of CAD, CHIP is significantly downregulated, which is correlated with the poor prognosis and survival of GBM patients. Notably, the low level of CHIP and high level of CAD overall predict the short survival of GBM patients.

CONCLUSION

Altogether, these results illustrated the essential role of CAD in GBM and revealed a novel therapeutic strategy for CAD-positive and CHIP-negative cancer.

Zebrafish as a model for study of disorders in pyrimidine nucleotide metabolism

Pyrimidine nucleotides are not only the building blocks of DNA and RNA but also participate in multiple cellular metabolic processes, including protein, lipid and polysaccharide biosynthesis. Pyrimidine nucleotides are synthesized by two distinct pathways-the de novo and salvage pathways. Disorders in pyrimidine nucleotide metabolism cause severe neurodegenerative disorders in human. For example, deficiency in thymidylate kinase, an essential enzyme in dTTP synthesis, causes severe microcephaly in human patients. Zebrafish mutants selected by insertion mutagenesis that results in inactive enzymes in pyrimidine metabolism showed also neurological and developmental disorders. In this work I have summarized current data on neurological and developmental disorders caused by defects in enzymes in pyrimidine nucleotide metabolism in zebrafish and compared to human. All these data suggest that zebrafish is a useful animal model to study pathogenic mechanism of neurological disorders due to defect in pyrimidine nucleotide metabolism.

Pyrimidine Biosynthetic Enzyme CAD: Its Function, Regulation, and Diagnostic Potential

CAD (Carbamoyl-phosphate synthetase 2, Aspartate transcarbamoylase, and Dihydroorotase) is a multifunctional protein that participates in the initial three speed-limiting steps of pyrimidine nucleotide synthesis. Over the past two decades, extensive investigations have been conducted to unmask CAD as a central player for the synthesis of nucleic acids, active intermediates, and cell membranes. Meanwhile, the important role of CAD in various physiopathological processes has also been emphasized. Deregulation of CAD-related pathways or CAD mutations cause cancer, neurological disorders, and inherited metabolic diseases. Here, we review the structure, function, and regulation of CAD in mammalian physiology as well as human diseases, and provide insights into the potential to target CAD in future clinical applications.

The Metalloproteinase adam19b Is Required for Sensory Axon Guidance in the Hindbrain

Little is known about the molecular and cellular mechanisms involved in the formation of the cranial peripheral sensory system in vertebrates. To identify genes involved in the formation of these circuits, we performed a forward genetic screen utilizing a transgenic zebrafish line (p2rx3.2:gfp^sl1) that expresses green fluorescent protein (gfp) in sensory neurons of the Vth, VIIth, IXth and Xth cranial ganglia. Here, we describe a novel zebrafish mutant in which a missense mutation in the adam19b gene selectively affects the epibranchial sensory circuits.

CDG Therapies: From Bench to Bedside

Congenital disorders of glycosylation (CDG) are a group of genetic disorders that affect protein and lipid glycosylation and glycosylphosphatidylinositol synthesis. More than 100 different disorders have been reported and the number is rapidly increasing. Since glycosylation is an essential post-translational process, patients present a large range of symptoms and variable phenotypes, from very mild to extremely severe. Only for few CDG, potentially curative therapies are being used, including dietary supplementation (e.g., galactose for PGM1-CDG, fucose for SLC35C1-CDG, Mn²⁺ for TMEM165-CDG or mannose for MPI-CDG) and organ transplantation (e.g., liver for MPI-CDG and heart for DOLK-CDG). However, for the majority of patients, only symptomatic and preventive treatments are in use. This constitutes a burden for patients, care-givers and ultimately the healthcare system. Innovative diagnostic approaches, in vitro and in vivo models and novel biomarkers have been developed that can lead to novel therapeutic avenues aiming to ameliorate the patients’ symptoms and lives. This review summarizes the advances in therapeutic approaches for CDG.

Biallelic mutations in CAD, impair de novo pyrimidine biosynthesis and decrease glycosylation precursors

In mitochondria, carbamoyl-phosphate synthetase 1 activity produces carbamoyl phosphate for urea synthesis, and deficiency results in hyperammonemia. Cytoplasmic carbamoyl-phosphate synthetase 2, however, is part of a tri-functional enzyme encoded by CAD; no human disease has been attributed to this gene. The tri-functional enzyme contains carbamoyl-phosphate synthetase 2 (CPS2), aspartate transcarbamylase (ATCase) and dihydroorotase (DHOase) activities, which comprise the first three of six reactions required for de novo pyrimidine biosynthesis. Here we characterize an individual who is compound heterozygous for mutations in different domains of CAD. One mutation, c.1843-1G>A, results in an in-frame deletion of exon 13. The other, c.6071G>A, causes a missense mutation (p.Arg2024Gln) in a highly conserved residue that is essential for carbamoyl-phosphate binding. Metabolic flux studies showed impaired aspartate incorporation into RNA and DNA through the de novo synthesis pathway. In addition, CTP, UTP and nearly all UDP-activated sugars that serve as donors for glycosylation were decreased. Uridine supplementation rescued these abnormalities, suggesting a potential therapy for this new glycosylation disorder.