The ChaC1 active site: Defining the residues and determining the role of ChaC1-exclusive residues in the structural and functional stability

Glutathione-specific gamma-glutamylcyclotransferase 1 (CHAC1) increases kidney disease risk by modulating ferroptosis

Genome-wide association studies (GWASs) have identified more than 1000 loci where genetic variants correlate with kidney function. However, the specific genes, cell types, and mechanisms influenced by these genetic variants remain largely uncharted. Here, we identified glutathione-specific gamma-glutamylcyclotransferase 1 (CHAC1) on chromosome 15 as affected by GWAS variants by analyzing human kidney gene expression and methylation information. Both CHAC1 RNA and protein were expressed in the loop of Henle region in mouse and human kidneys, and CHAC1 expression was higher in patients carrying disease risk variants. Using CRISPR technology, we created mice with a single functional copy of the Chac1 gene (Chac1+/-) that displayed no baseline phenotypic alterations in kidney structure or function. These mice demonstrated resilience to kidney disease in multiple models, including folic acid-induced nephropathy, adenine-induced chronic kidney disease, and uninephrectomy-streptozotocin-induced diabetic nephropathy. We further showed that CHAC1 plays a critical role in degrading the cellular antioxidant glutathione. Tubule cells isolated from Chac1+/- mice showed increased glutathione, decreased lipid peroxidation, improved cell viability, and protection against ferroptosis. Expression of ferroptosis-associated genes was also lower in mice with only one copy of Chac1. Higher CHAC1 protein also correlated with ferroptosis-related protein abundance in kidney biopsies from patients with kidney disease. This study positions CHAC1 as an important mediator of kidney disease that influences glutathione concentrations and ferroptosis, suggesting potential avenues to explore for the treatment of kidney diseases.

CHAC1: a master regulator of oxidative stress and ferroptosis in human diseases and cancers

CHAC1, an essential regulator of oxidative stress and ferroptosis, is increasingly recognized for its significant roles in these cellular processes and its impact on various human diseases and cancers. This review aims to provide a comprehensive overview of CHAC1's molecular functions, regulatory mechanisms, and effects in different pathological contexts. Specifically, the study objectives are to elucidate the biochemical pathways involving CHAC1, explore its regulatory network, and discuss its implications in disease progression and potential therapeutic strategies. As a γ-glutamyl cyclotransferase, CHAC1 degrades glutathione, affecting calcium signaling and mitochondrial function. Its regulation involves transcription factors like ATF4 and ATF3, which control CHAC1 mRNA expression. CHAC1 is crucial for maintaining redox balance and regulating cell death pathways in cancer. Its elevated levels are associated with poor prognosis in many cancers, indicating its potential as a biomarker and therapeutic target. Additionally, CHAC1 influences non-cancerous diseases such as neurodegenerative and cardiovascular disorders. Therapeutically, targeting CHAC1 could increase cancer cell sensitivity to ferroptosis, aiding in overcoming resistance to standard treatments. This review compiles current knowledge and recent discoveries, emphasizing CHAC1's vital role in human diseases and its potential in diagnostic and therapeutic applications.

Identification of inhibitors of human ChaC1, a cytoplasmic glutathione degrading enzyme through high throughput screens in yeast

The cytosolic glutathione-degrading enzyme, ChaC1, is highly up-regulated in several cancers, with the up-regulation correlating to poor prognosis. The ability to inhibit ChaC1 is therefore important in different pathophysiological situations, but is challenging owing to the high substrate Km of the enzyme. As no inhibitors of ChaC1 are known, in this study we have focussed on this goal. We have initially taken a computational approach where a systemic structure-based virtual screening was performed. However, none of the predicted hits proved to be effective inhibitors. Synthetic substrate analogs were also not inhibitory. As both these approaches targeted the active site, we shifted to developing two high-throughput, robust, yeast-based assays that were active site independent. A small molecule compound library was screened using an automated liquid handling system using these screens. The hits were further analyzed using in vitro assays. Among them, juglone, a naturally occurring naphthoquinone, completely inhibited ChaC1 activity with an IC50 of 8.7 µM. It was also effective against the ChaC2 enzyme. Kinetic studies indicated that the inhibition was not competitive with the substrate. Juglone is known to form adducts with glutathione and is also known to selectively inhibit enzymes by covalently binding to active site cysteine residues. However, juglone continued to inhibit a cysteine-free ChaC1 variant, indicating that it was acting through a novel mechanism. We evaluated different inhibitory mechanisms, and also analogues of juglone, and found plumbagin effective as an inhibitor. These compounds are the first inhibitor leads against the ChaC enzymes using a robust yeast screen.

Glutathione‑degrading enzymes in the complex landscape of tumors (Review)

Glutathione (GSH)‑degrading enzymes are essential for starting the first stages of GSH degradation. These enzymes include extracellular γ‑glutamyl transpeptidase (GGT) and intracellular GSH‑specific γ‑glutamylcyclotransferase 1 (ChaC1) and 2. These enzymes are essential for cellular activities, such as immune response, differentiation, proliferation, homeostasis regulation and programmed cell death. Tumor tissue frequently exhibits abnormal expression of GSH‑degrading enzymes, which has a key impact on the development and spread of malignancies. The present review summarizes gene and protein structure, catalytic activity and regulation of GSH‑degrading enzymes, their vital roles in tumor development (including regulation of oxidative and endoplasmic reticulum stress, control of programmed cell death, promotion of inflammation and tumorigenesis and modulation of drug resistance in tumor cells) and potential role as diagnostic biomarkers and therapeutic targets.

ChaC1 upregulation reflects poor prognosis in a variety of cancers: analysis of the major missense SNPs of ChaC1 as an aid to refining prognosis

The ChaC1 enzyme that catalyzes cytosolic glutathione degradation is highly upregulated in several cancers. In a systematic review of gene signature panels for cancer prognosis based on oxidative stress and ferroptosis genes, we observed that ChaC1 was found in panels in a wide variety of different cancers, with the upregulation correlating with poor prognosis. Since SNPs can have an impact on functionality and prognosis, ChaC1 SNPs from various databases were also investigated. Six frequently observed missense SNPs were chosen for reconstruction, and their functionality was evaluated. Three out of six SNPs resulted in either a partial or complete loss of ChaC1 function, and these SNPs had the changes R72Q, A156V, and G173S in their proteins. This study highlights the importance of ChaC1 in cancer prognosis across a wide variety of cancers. Additionally, the information on the SNPs of ChaC1 with altered enzymatic activities would improve the prognostic ability of these panels and facilitate treatment regimens.