Serine hydroxymethyltransferase 2 expression promotes tumorigenesis in rhabdomyosarcoma with 12q13-q14 amplification

Inducing disulfidptosis in tumors:potential pathways and significance

Regulated cell death (RCD) is crucial for the elimination of abnormal cells. In recent years, strategies aimed at inducing RCD, particularly apoptosis, have become increasingly important in cancer therapy. However, the ability of tumor cells to evade apoptosis has led to treatment resistance and relapse, prompting extensive research into alternative death processes in cancer cells. A recent study identified a novel form of RCD known as disulfidptosis, which is linked to disulfide stress. Cancer cells import cystine from the extracellular environment via solute carrier family 7 member 11 (SLC7A11) and convert it to cysteine using nicotinamide adenine dinucleotide phosphate (NADPH). When NADPH is deficient or its utilization is impaired, cystine accumulates, leading to the formation of disulfide bonds in the actin cytoskeleton, triggering disulfidptosis. Disulfidptosis reveals a metabolic vulnerability in tumors, offering new insights into cancer therapy strategies. This review provides a detailed overview of the mechanisms underlying disulfidptosis, the current research progress, and limitations. It also highlights innovative strategies for inducing disulfidptosis and explores the potential of combining these approaches with traditional cancer therapies, particularly immunotherapy, to expedite clinical translation.

Endoplasmic reticulum stress-dependent regulation of the expression of serine hydroxymethyltransferase 2 in glioblastoma cells

Objective. Serine hydroxymethyltransferase (SHMT2) plays a multifunctional role in mitochondria (folate-dependent tRNA methylation, translation, and thymidylate synthesis). The endoplasmic reticulum stress, hypoxia, and glucose and glutamine supply are significant factors of malignant tumor growth including glioblastoma. Previous studies have shown that the knockdown of the endoplasmic reticulum to nucleus signaling 1 (ERN1) pathway of endoplasmic reticulum stress strongly suppressed glioblastoma cell proliferation and modified the sensitivity of these cells to hypoxia and glucose or glutamine deprivations. The present study aimed to investigate the regulation of the SHMT2 gene in U87MG glioblastoma cells by ERN1 knockdown, hypoxia, and glucose or glutamine deprivations with the intent to reveal the role of ERN1 signaling in sensitivity of this gene expression to hypoxia and nutrient supply. Methods. The control U87MG glioblastoma cells (transfected by an empty vector) and ERN1 knockdown cells with inhibited ERN1 endoribonuclease and protein kinase (dnERN1) or only ERN1 endoribonuclease (dnrERN1) were used. Hypoxia was introduced by dimethyloxalylglycine (500 ng/ml for 4 h). For glucose and glutamine deprivations, cells were exposed in DMEM without glucose and glutamine, respectively for 16 h. RNA was extracted from cells and reverse transcribed. The expression level of the SHMT2 gene was studied by real-time qPCR and normalized to ACTB. Results. It was found that inhibition of ERN1 endoribonuclease and protein kinase in glioblastoma cells led to a down-regulation of SHMT2 gene expression in U87MG cells. At the same time, the expression of this gene did not significantly change in cells with inhibited ERN1 endoribonuclease, but tunicamycin strongly increased its expression. Moreover, the expression of the SHMT2 gene was not affected in U87MG cells after silencing of XBP1. Hypoxia up-regulated the expression level of the SHMT2 gene in both control and ERN1 knockdown U87MG cells. The expression of this gene was significantly up-regulated in glioblastoma cells under glucose and glutamine deprivations and ERN1 knockdown significantly increased the sensitivity of the SHMT2 gene to these nutrient deprivation conditions. Conclusion. The results of the present study demonstrate that the expression of the SHMT2 gene responsible for serine metabolism and formation of folate one-carbon is controlled by ERN1 protein kinase and induced by hypoxia as well as glutamine and glucose deprivation conditions in glioblastoma cells and reflects the ERN1-mediated reprogramming of sensitivity this gene expression to nutrient deprivation.

Targeting one-carbon metabolism for cancer immunotherapy

BACKGROUND

One-carbon (1C) metabolism is a metabolic network that plays essential roles in biological reactions. In 1C metabolism, a series of nutrients are used to fuel metabolic pathways, including nucleotide metabolism, amino acid metabolism, cellular redox defence and epigenetic maintenance. At present, 1C metabolism is considered the hallmark of cancer. The 1C units obtained from the metabolic pathways increase the proliferation rate of cancer cells. In addition, anticancer drugs, such as methotrexate, which target 1C metabolism, have long been used in the clinic. In terms of immunotherapy, 1C metabolism has been used to explore biomarkers connected with immunotherapy response and immune-related adverse events in patients.

METHODS

We collected numerous literatures to explain the roles of one-carbon metabolism in cancer immunotherapy.

RESULTS

In this review, we focus on the important pathways in 1C metabolism and the function of 1C metabolism enzymes in cancer immunotherapy. Then, we summarise the inhibitors acting on 1C metabolism and their potential application on cancer immunotherapy. Finally, we provide a viewpoint and conclusion regarding the opportunities and challenges of targeting 1C metabolism for cancer immunotherapy in clinical practicability in the future.

CONCLUSION

Targeting one-carbon metabolism is useful for cancer immunotherapy.

Regulatory mechanisms of one-carbon metabolism enzymes

One-carbon metabolism is a central metabolic pathway critical for the biosynthesis of several amino acids, methyl group donors, and nucleotides. The pathway mostly relies on the transfer of a carbon unit from the amino acid serine, through the cofactor folate (in its several forms), and to the ultimate carbon acceptors that include nucleotides and methyl groups used for methylation of proteins, RNA, and DNA. Nucleotides are required for DNA replication, DNA repair, gene expression, and protein translation, through ribosomal RNA. Therefore, the one-carbon metabolism pathway is essential for cell growth and function in all cells, but is specifically important for rapidly proliferating cells. The regulation of one-carbon metabolism is a critical aspect of the normal and pathological function of the pathway, such as in cancer, where hijacking these regulatory mechanisms feeds an increased need for nucleotides. One-carbon metabolism is regulated at several levels: via gene expression, posttranslational modification, subcellular compartmentalization, allosteric inhibition, and feedback regulation. In this review, we aim to inform the readers of relevant one-carbon metabolism regulation mechanisms and to bring forward the need to further study this aspect of one-carbon metabolism. The review aims to integrate two major aspects of cancer metabolism-signaling downstream of nutrient sensing and one-carbon metabolism, because while each of these is critical for the proliferation of cancerous cells, their integration is critical for comprehensive understating of cellular metabolism in transformed cells and can lead to clinically relevant insights.

NFYB increases chemosensitivity in glioblastoma by promoting HDAC5-mediated transcriptional inhibition of SHMT2

Temozolomide (TMZ) is a commonly used chemotherapeutic agent for glioblastoma (GBM), but acquired drug resistance prevents its therapeutic efficacy. We investigated potential mechanisms underlying TMZ resistance and glycolysis in GBM cells through regulation by nuclear transcription factor Y subunit β (NFYB) of the oncogene serine hydroxymethyltransferase 2 (SHMT2). GBM U251 cells were transfected with NFYB-, SHMT2-, and the potential NFYB target histone deacetylase 5 (HDAC5)-related vectors. Glucose uptake and lactate production were measured with detection kits. CCK-8/colony formation, scratch, Transwell, and flow cytometry assays were performed to detect cell proliferation, migration, invasion, and apoptosis, respectively. The binding of NFYB to the HDAC5 promoter and the regulation of NFYB on HDAC5 promoter activity were detected with chromatin immunoprecipitation and dual-luciferase reporter assays, respectively. NFYB and HDAC5 were poorly expressed and SHMT2 was expressed at high levels in GBM U251 cells. NFYB overexpression or SHMT2 knockdown decreased glucose uptake, lactate production, proliferation, migration, and invasion and increased apoptosis and TMZ sensitivity of the cells. NFYB activated HDAC5 to inhibit SHMT2 expression. SHMT2 overexpression nullified the inhibitory effects of NFYB overexpression on glycolysis and TMZ resistance. Thus, NFYB may reduce tumorigenicity and TMZ resistance of GBM through effects on the HDAC5/SHMT2 axis.

Toxicological and pharmacokinetic properties of sucralose-6-acetate and its parent sucralose: in vitro screening assays

The purpose of this study was to determine the toxicological and pharmacokinetic properties of sucralose-6-acetate, a structural analog of the artificial sweetener sucralose. Sucralose-6-acetate is an intermediate and impurity in the manufacture of sucralose, and recent commercial sucralose samples were found to contain up to 0.67% sucralose-6-acetate. Studies in a rodent model found that sucralose-6-acetate is also present in fecal samples with levels up to 10% relative to sucralose which suggest that sucralose is also acetylated in the intestines. A MultiFlow® assay, a high-throughput genotoxicity screening tool, and a micronucleus (MN) test that detects cytogenetic damage both indicated that sucralose-6-acetate is genotoxic. The mechanism of action was classified as clastogenic (produces DNA strand breaks) using the MultiFlow® assay. The amount of sucralose-6-acetate in a single daily sucralose-sweetened drink might far exceed the threshold of toxicological concern for genotoxicity (TTCgenotox) of 0.15 µg/person/day. The RepliGut® System was employed to expose human intestinal epithelium to sucralose-6-acetate and sucralose, and an RNA-seq analysis was performed to determine gene expression induced by these exposures. Sucralose-6-acetate significantly increased the expression of genes associated with inflammation, oxidative stress, and cancer with greatest expression for the metallothionein 1 G gene (MT1G). Measurements of transepithelial electrical resistance (TEER) and permeability in human transverse colon epithelium indicated that sucralose-6-acetate and sucralose both impaired intestinal barrier integrity. Sucralose-6-acetate also inhibited two members of the cytochrome P450 family (CYP1A2 and CYP2C19). Overall, the toxicological and pharmacokinetic findings for sucralose-6-acetate raise significant health concerns regarding the safety and regulatory status of sucralose itself.

Anaplastic thyroid cancer cells upregulate mitochondrial one-carbon metabolism to meet purine demand, eliciting a critical targetable vulnerability

Anaplastic thyroid cancer (ATC) is one of the most aggressive and lethal tumor types, characterized by loss of differentiation, epithelial-to-mesenchymal transition, extremely high proliferation rate, and generalized resistance to therapy. To identify novel relevant, targetable molecular alterations, we analyzed gene expression profiles from a genetically engineered ATC mouse model and from human patient datasets, and found consistent upregulation of genes encoding enzymes involved in the one-carbon metabolic pathway, which uses serine and folates to generate both nucleotides and glycine. Genetic and pharmacological inhibition of SHMT2, a key enzyme of the mitochondrial arm of the one-carbon pathway, rendered ATC cells glycine auxotroph and led to significant inhibition of cell proliferation and colony forming ability, which was primarily caused by depletion of the purine pool. Notably, these growth-suppressive effects were significantly amplified when cells were grown in the presence of physiological types and levels of folates. Genetic depletion of SHMT2 dramatically impaired tumor growth in vivo, both in xenograft models and in an immunocompetent allograft model of ATC. Together, these data establish the upregulation of the one-carbon metabolic pathway as a novel and targetable vulnerability of ATC cells, which can be exploited for therapeutic purposes.

Anaplastic Thyroid Cancer Cells Upregulate Mitochondrial One-Carbon Metabolism To Meet Purine Demand, Eliciting A Critical Targetable Vulnerability

Anaplastic thyroid cancer (ATC) is one of the most aggressive and lethal tumor types, characterized by loss of differentiation, epithelial-to-mesenchymal transition, extremely high proliferation rate, and generalized resistance to therapy. To identify novel relevant, targetable molecular alterations, we analyzed gene expression profiles from a genetically engineered ATC mouse model and from human patient datasets, and found consistent upregulation of genes encoding enzymes involved in the one-carbon metabolic pathway, which uses serine and folates to generate both nucleotides and glycine. Genetic and pharmacological inhibition of SHMT2 , a key enzyme of the mitochondrial arm of the one-carbon pathway, rendered ATC cells glycine auxotroph and led to significant inhibition of cell proliferation and colony forming ability, which was primarily caused by depletion of the purine pool. Notably, these growth-suppressive effects were significantly amplified when cells were grown in the presence of physiological types and levels of folates. Genetic depletion of SHMT2 dramatically impaired tumor growth in vivo, both in xenograft models and in an immunocompetent allograft model of ATC. Together, these data establish the upregulation of the one-carbon metabolic pathway as a novel and targetable vulnerability of ATC cells, which can be exploited for therapeutic purposes.

Characterization of thermostable serine hydroxymethyltransferase for β-hydroxy amino acids synthesis

β-hydroxy amino acids, such as serine, threonine, and phenylserine, are important compounds for medical purposes. To date, there has been only limited exploration of thermostable serine hydroxylmethyltransferase (SHMT) for the synthesis of these amino acids, despite the great potential that thermostable enzymes may offer for commercial use due to their high stability and catalytic efficiencies. ITBSHMT_1 (ITB serine hydroxylmethyltransferase clone number 1) from thermophilic and methanol-tolerant bacteria Pseudoxanthomonas taiwanensis AL17 was successfully cloned. Biocomputational analysis revealed that ITBSHMT_1 contains Pyridoxal-3'-phosphate and tetrahydrofolatebinding residues. Structural comparisons show that ITBSHMT_1 has 5 additional residues VSRQG on loop near PLP-binding site as novel structural feature which distinguish this enzyme with other characterized SHMTs. In silico mutation revealed that the fragment might have very essential role in maintaining of PLP binding on structure of ITBSHMT_1. Recombinant protein was produced in Escherichia coli Rosetta 2(DE3) in soluble form and purified using NiNTA affinity chromatography. The purified protein demonstrated the best activity at 80 °C and pH 7.5 based on the retro aldol cleavage of phenylserine. Activity decreased significantly in the presence of 3 mM transition metal ions but increased in the presence of 30 mM β-mercaptoethanol. ITBSHMT_1 demonstrated Vmax, Km, Kcat, and Kcat/Km at 242 U/mg, 23.26 mM, 186/s, and 8/(mM.s), respectively. The aldol condensation reaction showed the enzyme's best activity at 80 °C for serine, threonine, or phenylserine, with serine synthesis showing the highest specific activity. Biocomputational analysis revealed that high intramolecular interaction within the 3D structure of ITBSHMT_1 might be correlated with the enzyme's high thermal stability. The above data suggest that ITBSHMT_1 is a potential and novel enzyme for the production of various β-hydroxy amino acids.

Inhibition of SHMT2 mRNA translation increases embryonic mortality in sheep

The one-carbon metabolism (OCM) pathway provides purines and thymidine for synthesis of nucleic acids required for cell division, and S-adenosyl methionine for polyamine and creatine syntheses and the epigenetic regulation of gene expression. This study aimed to determine if serine hydroxymethyltransferase 2 (SHMT2), a key enzyme in the OCM pathway, is critical for ovine trophectoderm (oTr) cell function and conceptus development by inhibiting translation of SHMT2 mRNA using a morpholino antisense oligonucleotide (MAO). In vitro treatment of oTr cells with MAO-SHMT2 decreased expression of SHMT2 protein, which was accompanied by reduced proliferation (P = 0.053) and migration (P < 0.05) of those cells. Intrauterine injection of MAO-SHMT2 in ewes on Day 11 post-breeding tended to decrease the overall pregnancy rate (on Days 16 and 18) compared to MAO-control (3/10 vs 7/10, P = 0.07). The three viable conceptuses (n = 2 on Day 16 and n = 1 on Day 18) recovered from MAO-SHMT2 ewes had only partial inhibition of SHMT2 mRNA translation. Conceptuses from the three pregnant MAO-SHMT2 ewes had similar levels of expression of mRNAs and proteins involved in OCM as compared to conceptuses from MAO-control ewes. These results indicate that knockdown of SHMT2 protein reduces proliferation and migration of oTr cells (in vitro) to decrease elongation of blastocysts from spherical to elongated forms. These in vitro effects suggest that increased embryonic deaths in ewes treated with MAO-SHMT2 are the result of decreased SHMT2-mediated trophectoderm cell proliferation and migration supporting a role for the OCM pathway in survival and development of ovine conceptuses.

SHMT2 promotes tumor growth through VEGF and MAPK signaling pathway in breast cancer

Cancer cells modulate their metabolic activities to adapt to their growth and proliferation. Despite advances in breast cancer biology having led to the widespread use of molecular targeted therapy and hormonal drugs, the molecular mechanisms in metabolism related to the regulation of breast cancer cell proliferation are still poorly understood. Here, we investigate the possible role of SHMT2, a key enzyme in serine metabolism, in breast cancer. Firstly, SHMT2 is found highly expressed in both breast cancer cells and tissues, and patients with high expression of SHMT2 have a worse prognosis. Moreover, the intervention of SHMT2 by either knockdown or over-expression in vitro induces the effect on breast cancer proliferation. Mechanistically, RNA-seq shows that over-expression of SHMT2 affect multiple signaling pathways and biological process in breast cancer cells. Furthermore, we confirm that SHMT2 promotes breast cancer cell growth through MAPK and VEGF signaling pathways. Finally, we verify the role of SHMT2 in promoting breast cancer growth in the xenograft tumor model. Our results indicate that SHMT2 plays a critical role in regulating breast cancer growth through MAPK, and VEGF signaling pathways, and maybe serve as a therapeutic target for breast cancer therapy.

Glycyrrhetinic acid restricts mitochondrial energy metabolism by targeting SHMT2

Glycyrrhetinic acid (GA) is a natural product of licorice with mitochondria targeting properties and shows broad anticancer activities, but its targets and underlying mechanisms remain elusive. Here, we identified the mitochondrial enzyme serine hydroxymethyltransferase 2 (SHMT2) as a target of GA by using chemical proteomics. Binding to and inhibiting the activity of SHMT2 by GA were validated in vitro and in vivo. Knockout of SHMT2 or inhibiting SHMT2 with GA restricts mitochondrial energy supplies by downregulating mitochondrial oxidative phosphorylation (OXPHOS) and fatty acid β-oxidation, and consequently suppresses cancer cell proliferation and tumor growth. Crystal structures of GA derivatives indicate that GA occupies SHMT2 folate-binding pocket and regulates SHMT2 activity. Modifications at GA carboxylic group with diamines significantly improved its anticancer potency, demonstrating GA as a decent structural template for SHMT2 inhibitor development.

Serine hydroxymethyltransferase 2 (SHMT2) potentiates the aggressive process of oral squamous cell carcinoma by binding to interleukin enhancer-binding factor 2 (ILF2)

Oral squamous cell carcinoma (OSCC) is a frequent threatening head and neck malignancy. Serine hydroxymethyltransferase 2 (SHMT2) was identified to be upregulated in OSCC and its high expression was associated with poor patient prognosis. This paper set out to assess the influence of SHMT2 on OSCC progression and the potential mechanisms related to interleukin enhancer-binding factor 2 (ILF2). First of all, reverse transcription-quantitative PCR (RT-qPCR) and western blot examined the expression of SHMT2 and ILF2 in OSCC cells. Cell Counting Kit-8 (CCK-8) and colony formation assays appraised cell proliferation. Terminal-deoxynucleotidyl Transferase Mediated Nick End Labeling (TUNEL) staining was to estimate the apoptotic rate of cells. Further, wound healing and transwell assays verified the migration and invasion of cells. Western blot was adopted to detect the expression of factors related to apoptosis, migration, and epithelial–mesenchymal transition (EMT). The possible interaction of SHMT2 and ILF2 was predicted by a Molecular INTeraction (MINT) and BioGRID databases and determined using co-immunoprecipitation (IP) assay. Subsequently, ILF2 was overexpressed to investigate whether SHMT2 regulated OSCC progression by binding to ILF2. Results implied that SHMT2 possessed increased expression in OSCC cells, and OSCC cell viability, migration, invasion, EMT were inhibited and apoptosis was potentiated after its silencing. ILF2 bound to SHMT2 and ILF2 expression was downregulated after SHMT2 silencing in OSCC cells. Importantly, ILF2 overexpression abolished the suppressive role of SHMT2 interference in the progression of OSCC. Collectively, SHMT2 could promote the progression of OSCC by binding to ILF2.