Downregulating serine hydroxymethyltransferase 2 (SHMT2) suppresses tumorigenesis in human hepatocellular carcinoma

MiR-383-5p inhibits the proliferation and migration of lung adenocarcinoma cells by targeting SHMT2

Purpose: To explore the effects of miR-383-5p and serine hydroxymethyltransferase 2 (SHMT2) on the proliferation and migration of lung adenocarcinoma cells. Methods: SHMT2 expression in lung adenocarcinoma and normal tissues was investigated using The Cancer Genome Atlas database. Immunohistochemical analysis was performed to confirm SHMT2 expression in lung adenocarcinoma and adjacent normal lung tissues. Bioinformatics analysis and luciferase reporter assays were used to analyze the relationship between miR-383-5p and SHMT2 expression. The protein expression levels of SHMT2, vimentin, N-cadherin, E-cadherin, Bcl-2, and cyclinD1 were analyzed using western blotting. The reverse transcription-quantitative polymerase chain reaction was used to detect SHMT2 knockdown efficiency, miR-383-5p overexpression, and inhibition efficiency. The proliferative ability of cells was detected using the Cell Counting Kit-8 assay. The Transwell assay was used to detect the migration ability of cells. Results: SHMT2 expression was significantly increased in patients with lung adenocarcinoma compared to that in control patients; the higher the SHMT2 expression the worse the outcomes were in patients with lung adenocarcinoma. SHMT2 knockdown inhibited the proliferation, migration, and epithelial-mesenchymal transition of lung adenocarcinoma A549 and H1299 cells. MiR-383-5p directly targeted and downregulated SHMT2 in A549 and H1299 cells. The effects of miRNA-383-5p on the proliferation and migration of these cells differed from those of SHMT2. Exogenous overexpression of SHMT2 reversed the miR-383-5p-induced proliferation and migration inhibition in A549 and H1299 cells. Conclusion: MiR-383-5p inhibits the proliferation and migration of lung adenocarcinoma cells by targeting and downregulating SHMT2.

Targeting serine/glycine metabolism improves radiotherapy response in non-small cell lung cancer

BACKGROUND

Lung cancer is the most lethal cancer, and 85% of cases are classified as non-small cell lung cancer (NSCLC). Metabolic rewiring is a cancer hallmark that causes treatment resistance, and lacks insights into serine/glycine pathway adaptations upon radiotherapy.

METHODS

We analyzed radiotherapy responses using mass-spectrometry-based metabolomics in NSCLC patient's plasma and cell lines. Efficacy of serine/glycine conversion inhibitor sertraline with radiotherapy was investigated by proliferation, clonogenic and spheroid assays, and in vivo using a serine/glycine dependent NSCLC mouse model by assessment of tumor growth, metabolite and cytokine levels, and immune signatures.

RESULTS

Serine/glycine pathway metabolites were significantly consumed in response to radiotherapy in NSCLC patients and cell models. Combining sertraline with radiotherapy impaired NSCLC proliferation, clonogenicity and stem cell self-renewal capacity. In vivo, NSCLC tumor growth was reduced solely in the sertraline plus radiotherapy combination treatment group. Tumor weights linked to systemic serine/glycine pathway metabolite levels, and were inhibited in the combination therapy group. Interestingly, combination therapy reshaped the tumor microenvironment via cytokines associated with natural killer cells, supported by eradication of immune checkpoint galectin-1 and elevated granzyme B levels.

CONCLUSION

Our findings highlight that targeting serine/glycine metabolism using sertraline restricts cancer cell recovery from radiotherapy and provides tumor control through immunomodulation in NSCLC.

Hypoxia-induced SHMT2 protein lactylation facilitates glycolysis and stemness of esophageal cancer cells

Esophageal cancer (EC) is a familiar digestive tract tumor with highly lethal. The hypoxic environment has been demonstrated to be a significant factor in modulating malignant tumor progression and is strongly associated with the abnormal energy metabolism of tumor cells. Serine hydroxymethyl transferase 2 (SHMT2) is one of the most frequently expressed metabolic enzymes in human malignancies. The study was designed to investigate the biological functions and regulation mechanisms of SHMT2 in EC under hypoxia. We conducted RT-qPCR to assess SHMT2 levels in EC tissues and cells (TE-1 and EC109). EC cells were incubated under normoxia and hypoxia, respectively, and altered SHMT2 expression was evaluated through RT-qPCR, western blot, and immunofluorescence. The biological functions of SHMT2 on EC cells were monitored by performing CCK-8, EdU, transwell, sphere formation, glucose uptake, and lactate production assays. The SHMT2 protein lactylation was measured by immunoprecipitation and western blot. In addition, SHMT2-interacting proteins were analyzed by bioinformatics and validated by rescue experiments. SHMT2 was notably upregulated in EC tissues and cells. Hypoxia elevated SHMT2 protein expression, augmenting EC cell proliferation, migration, invasion, stemness, and glycolysis. In addition, hypoxia triggered lactylation of the SHMT2 protein and enhanced its stability. SHMT2 knockdown impeded the malignant phenotype of EC cells. Further mechanistic studies disclosed that SHMT2 is involved in EC progression by interacting with MTHFD1L. Hypoxia-induced SHMT2 protein lactylation and upregulated its protein level, which in turn enhanced MTHFD1L expression and accelerated the malignant progression of EC cells.

Identification of potential molecular targets for the treatment of cluster 1 human pheochromocytoma and paraganglioma via comprehensive proteomic characterization

BACKGROUND

Pheochromocytomas and paragangliomas (PPGLs) are rare neuroendocrine tumors. New drug targets and proteins that would assist sensitive PPGL imagining could improve therapy and quality of life of patients with PPGL, namely those with recurrent or metastatic disease. Using a combined proteomic strategy, we looked for such clinically relevant targets among integral membrane proteins (IMPs) upregulated on the surface of tumor cells and non-membrane druggable enzymes in PPGL.

METHODS

We conducted a detailed proteomic analysis of 22 well-characterized human PPGL samples and normal chromaffin tissue from adrenal medulla. A standard quantitative proteomic analysis of tumor lysate, which provides information largely on non-membrane proteins, was accompanied by specific membrane proteome-aimed methods, namely glycopeptide enrichment using lectin-affinity, glycopeptide capture by hydrazide chemistry, and enrichment of membrane-embedded hydrophobic transmembrane segments.

RESULTS

The study identified 67 cell surface integral membrane proteins strongly upregulated in PPGL compared to control chromaffin tissue. We prioritized the proteins based on their already documented direct role in cancer cell growth or progression. Increased expression of the seven most promising drug targets (CD146, CD171, ANO1, CD39, ATP8A1, ACE and SLC7A1) were confirmed using specific antibodies. Our experimental strategy also provided expression data for soluble proteins. Among the druggable non-membrane enzymes upregulated in PPGL, we identified three potential drug targets (SHMT2, ARG2 and autotaxin) and verified their upregulated expression.

CONCLUSIONS

Application of a combined proteomic strategy recently presented as "Pitchfork" enabled quantitative analysis of both, membrane and non-membrane proteome, and resulted in identification of 10 potential drug targets in human PPGL. Seven membrane proteins localized on the cell surface and three non-membrane druggable enzymes proteins were identified and verified as significantly upregulated in PPGL. All the proteins have been previously shown to be upregulated in several human cancers, and play direct role in cancer progression. Marked upregulation of these proteins along with their localization and established direct roles in tumor progression make these molecules promising candidates as drug targets or proteins for sensitive PPGL imaging.

Vital role of SHMT2 in diverse disease

One-carbon metabolism is essential for our human cells to carry out nucleotide synthesis, methylation, and reductive metabolism through one-carbon units, and these pathways ensure the high proliferation rate of cancer cells. Serine hydroxymethyltransferase 2 (SHMT2) is a key enzyme in one-carbon metabolism. This enzyme can convert serine into a one-carbon unit bound to tetrahydrofolate and glycine, ultimately supporting the synthesis of thymidine and purines and promoting the growth of cancer cells. Due to SHMT2's crucial role in the one-carbon cycle, it is ubiquitous in human cells and even in all organisms and highly conserved. Here, we summarize the impact of SHMT2 on the progression of various cancers to highlight its potential use in the development of cancer treatments.

Targeting Oncometabolites in Peritoneal Cancers: Preclinical Insights and Therapeutic Strategies

Peritoneal cancers present significant clinical challenges with poor prognosis. Understanding the role of cancer cell metabolism and cancer-promoting metabolites in peritoneal cancers can provide new insights into the mechanisms that drive tumor progression and can identify novel therapeutic targets and biomarkers for early detection, prognosis, and treatment response. Cancer cells dynamically reprogram their metabolism to facilitate tumor growth and overcome metabolic stress, with cancer-promoting metabolites such as kynurenines, lactate, and sphingosine-1-phosphate promoting cell proliferation, angiogenesis, and immune evasion. Targeting cancer-promoting metabolites could also lead to the development of effective combinatorial and adjuvant therapies involving metabolic inhibitors for the treatment of peritoneal cancers. With the observed metabolomic heterogeneity in cancer patients, defining peritoneal cancer metabolome and cancer-promoting metabolites holds great promise for improving outcomes for patients with peritoneal tumors and advancing the field of precision cancer medicine. This review provides an overview of the metabolic signatures of peritoneal cancer cells, explores the role of cancer-promoting metabolites as potential therapeutic targets, and discusses the implications for advancing precision cancer medicine in peritoneal cancers.

Serine hydroxymethyltransferase 2 knockdown induces apoptosis in ccRCC by causing lysosomal membrane permeabilization via metabolic reprogramming

Serine hydroxymethyltransferase 2 (SHMT2) plays an important role in converting serine to glycine and supplying carbon to one-carbon metabolism to sustain cancer cell proliferation. However, the expression, function, and underlying mechanisms of SHMT2 in clear cell renal cell carcinoma (ccRCC) remain largely unknown. In this study, we demonstrated that SHMT2 was upregulated in ccRCC tissues compared with controls and associated with patient survival. SHMT2 knockdown inhibited proliferation, migration, and invasion in ccRCC cells. Overexpression of SHMT2 promoted tumor progression. Mechanistically, SHMT2 depletion disrupted one-carbon metabolism, increased reactive oxygen species (ROS) levels, and decreased ATP levels via metabolic reprogramming, which destroyed cell homeostasis. The SHMT2 knockdown-induced stress activated autophagy. A mass of autophagosomes fused with lysosomes, resulting in lysosomal membrane permeabilization (LMP) and leakage of lysosomal contents into the cytoplasm, which eventually led to apoptosis. Our work reveals that SHMT2 functions as an oncogenic gene to promote ccRCC progression. SHMT2 depletion induces apoptosis by causing LMP through excessive activation of the autophagy-lysosome pathway via metabolic reprogramming.

Schisantherin A inhibits cell proliferation by regulating glucose metabolism pathway in hepatocellular carcinoma

Schisantherin A (STA) is a traditional Chinese medicine extracted from the plant Schisandra chinensis, which has a wide range of anti-inflammatory, antioxidant, and other pharmacological effects. This study investigates the anti-hepatocellular carcinoma effects of STA and the underlying mechanisms. STA significantly inhibits the proliferation and migration of Hep3B and HCCLM3 cells in vitro in a concentration-dependent manner. RNA-sequencing showed that 77 genes are upregulated and 136 genes are downregulated in STA-treated cells compared with untreated cells. KEGG pathway analysis showed significant enrichment in galactose metabolism as well as in fructose and mannose metabolism. Further gas chromatography-mass spectrometric analysis (GC-MS) confirmed this, indicating that STA significantly inhibits the glucose metabolism pathway of Hep3B cells. Tumor xenograft in nude mice showed that STA has a significant inhibitory effect on tumor growth in vivo. In conclusion, our results indicate that STA can inhibit cell proliferation by regulating glucose metabolism, with subsequent anti-tumor effects, and has the potential to be a candidate drug for the treatment of liver cancer.

SHMT2 promotes cell viability and inhibits ROS-dependent, mitochondrial-mediated apoptosis via the intrinsic signaling pathway in bladder cancer cells

Mitochondrial serine hydroxymethyltransferase (SHMT2) catalyzes the conversion of serine to glycine and concomitantly produces one-carbon units to support cell growth and is upregulated in various cancer cells. SHMT2 knockdown triggers cell apoptosis; however, the detailed mechanism of apoptosis induced by SHMT2 inactivation remains unknown. Here, we demonstrate that SHMT2 supports the proliferation of bladder cancer (BC) cells by maintaining redox homeostasis. SHMT2 knockout decreased the pools of purine and one-carbon units and delayed cell cycle progression in a manner that was rescued by formate, demonstrating that SHMT2-mediated one-carbon units are essential for BC cell proliferation. SHMT2 deficiency promoted the accumulation of intracellular reactive oxygen species (ROS) by decreasing the NADH/NAD+, NADPH/NADP+, and GSH/GSSG ratios, leading to a loss in mitochondrial membrane potential, release of cytochrome c, translocation of Bcl-2 family protein and activation of caspase-3. Notably, blocking ROS production with the one-carbon donor formate and the ROS scavenger N-acetyl-cysteine (NAC) effectively rescued SHMT2 deficiency-induced cell apoptosis via the intrinsic signaling pathway. Treatment with the SHMT inhibitor SHIN1 resulted in a significant inhibitory effect on cell proliferation and induced cell apoptosis. Formate and NAC rescued SHIN1-induced cell apoptosis. Our findings reveal an important mechanism by which the loss of SHMT2 triggers ROS-dependent, mitochondrial-mediated apoptosis, which gives insight into the link between serine metabolism and cell apoptosis and provides a promising target for BC treatment and drug discovery.

DeepHisCoM: deep learning pathway analysis using hierarchical structural component models

Many statistical methods for pathway analysis have been used to identify pathways associated with the disease along with biological factors such as genes and proteins. However, most pathway analysis methods neglect the complex nonlinear relationship between biological factors and pathways. In this study, we propose a Deep-learning pathway analysis using Hierarchical structured CoMponent models (DeepHisCoM) that utilize deep learning to consider a nonlinear complex contribution of biological factors to pathways by constructing a multilayered model which accounts for hierarchical biological structure. Through simulation studies, DeepHisCoM was shown to have a higher power in the nonlinear pathway effect and comparable power for the linear pathway effect when compared to the conventional pathway methods. Application to hepatocellular carcinoma (HCC) omics datasets, including metabolomic, transcriptomic and metagenomic datasets, demonstrated that DeepHisCoM successfully identified three well-known pathways that are highly associated with HCC, such as lysine degradation, valine, leucine and isoleucine biosynthesis and phenylalanine, tyrosine and tryptophan. Application to the coronavirus disease-2019 (COVID-19) single-nucleotide polymorphism (SNP) dataset also showed that DeepHisCoM identified four pathways that are highly associated with the severity of COVID-19, such as mitogen-activated protein kinase (MAPK) signaling pathway, gonadotropin-releasing hormone (GnRH) signaling pathway, hypertrophic cardiomyopathy and dilated cardiomyopathy. Codes are available at https://github.com/chanwoo-park-official/DeepHisCoM.

Suppression of nuclear GSK3 signaling promotes serine/one-carbon metabolism and confers metabolic vulnerability in lung cancer cells

Serine/one-carbon metabolism provides critical resources for nucleotide biosynthesis and epigenetic maintenance and is thus necessary in cancer cell growth, although the detailed regulatory mechanisms remain unclear. We uncover a critical role of glycogen synthase kinase 3 (GSK3) in regulating the expression of serine/one-carbon metabolic enzymes. Nuclear enrichment of GSK3 significantly suppresses genes that mediate de novo serine synthesis, including PHGDH, PSAT1, PSPH, and one-carbon metabolism, including SHMT2 and MTHFD2. FRAT1 promotes nuclear exclusion of GSK3, enhances serine/one-carbon metabolism, and, as a result, confers cell vulnerability to inhibitors that target this metabolic process such as SHIN1, a specific SHMT1/2 inhibitor. Furthermore, pharmacological or genetic suppression of GSK3 promotes serine/one-carbon metabolism and exhibits a significant synergistic effect in combination with SHIN1 in suppressing cancer cell proliferation in cultured cells and in vivo. Our observations indicate that inhibition of nuclear GSK3 signaling creates a vulnerability, which results in enhanced efficacy of serine/one-carbon metabolism inhibitors for the treatment of cancer.

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.

The role of SHMT2 in modulating lipid metabolism in hepatocytes via glycine-mediated mTOR activation

Serine hydroxymethyltransferase 2 (SHMT2) converts serine into glycine in the mitochondrial matrix, transferring a methyl group to tetrahydrofolate. SHMT2 plays an important role in the maintenance of one-carbon metabolism. Previously, we found a negative correlation between the serine concentration and the progression of fatty liver disease (FLD). However, little is known about the role of SHMT2 in hepatic lipid metabolism. We established SHMT2 knockdown (KD) mouse primary hepatocytes using RNA interference to investigate the role of SHMT2 in lipid metabolism. SHMT2 KD hepatocytes showed decreased lipid accumulation with reduced glycine levels compared to the scramble cells, which was restored upon reintroducing SHMT2. SHMT2 KD hepatocytes showed downregulation of the mTOR/PPARɣ pathway with decreased gene expression related to lipogenesis and fatty acid uptake. Pharmacological activation of mTOR or PPARɣ overexpression blocked the inhibitory effect of SHMT2 KD on lipid accumulation. We also showed that glycine activated mTOR/PPARɣ signaling and identified glycine as a mediator of SHMT2-responsive lipid accumulation in hepatocytes. In conclusion, silencing SHMT2 in hepatocytes ameliorates lipid accumulation via the glycine-mediated mTOR/PPARɣ pathway. Our findings underscore the possibility of SHMT2 as a therapeutic target of FLD.

Folate Metabolism in Hepatocellular Carcinoma. What Do We Know So Far?

Cancer cells are characterized by accelerated proliferation and an outstanding adaptation of their metabolic pathways to meet energy demands. The folate cycle, also known as folate metabolism or one-carbon metabolism, through enzymatic interconversions, provides metabolites necessary for nucleotide synthesis, methylation, and reduction power, helping to maintain the high rate of proliferation; therefore, the study of this metabolic pathway is of great importance in the study of cancer. Moreover, multiple enzymes involved in this cycle have been implicated in different types of cancer, corroborating the cell's adaptations under this pathology. During the last decade, nonalcoholic fatty liver disease has emerged as the leading etiology related to the rise in the incidence and deaths of hepatocellular carcinoma. Specifically, cholesterol accumulation has been a determinant promoter of tumor formation, with solid evidence that an enriched-cholesterol diet plays a crucial role in accelerating the development of an aggressive subtype of hepatocellular carcinoma compared to other models. In this review, we will discuss the most recent findings to understand the contribution of folate metabolism to cancer cells and tumor microenvironment while creating a link between the dynamics given by cholesterol and methylenetetrahydrofolate dehydrogenase 1-like, a key enzyme of the cycle located in the mitochondrial compartment.

Serine and one-carbon metabolisms bring new therapeutic venues in prostate cancer

Serine and one-carbon unit metabolisms are essential biochemical pathways implicated in fundamental cellular functions such as proliferation, biosynthesis of important anabolic precursors and in general for the availability of methyl groups. These two distinct but interacting pathways are now becoming crucial in cancer, the de novo cytosolic serine pathway and the mitochondrial one-carbon metabolism. Apart from their role in physiological conditions, such as epithelial proliferation, the serine metabolism alterations are associated to several highly neoplastic proliferative pathologies. Accordingly, prostate cancer shows a deep rearrangement of its metabolism, driven by the dependency from the androgenic stimulus. Several new experimental evidence describes the role of a few of the enzymes involved in the serine metabolism in prostate cancer pathogenesis. The aim of this study is to analyze gene and protein expression data publicly available from large cancer specimens dataset, in order to further dissect the potential role of the abovementioned metabolism in the complex reshaping of the anabolic environment in this kind of neoplasm. The data suggest a potential role as biomarkers as well as in cancer therapy for the genes (and enzymes) belonging to the one-carbon metabolism in the context of prostatic cancer.

Roles of Mitochondrial Serine Hydroxymethyltransferase 2 (SHMT2) in Human Carcinogenesis

In the last few years, cellular metabolic reprogramming has been acknowledged as a hallmark of human cancer and evaluated for its crucial role in supporting the proliferation and survival of human cancer cells. In a variety of human tumours, including hepatocellular carcinoma (HCC), breast cancer and non-small-cell lung cancer (NSCLC), a large amount of carbon is reused in serine/glycine biosynthesis, accompanied by higher expression of the key glycine synthetic enzyme mitochondrial serine hydroxymethyltransferase 2 (SHMT2). This enzyme can convert serine into glycine and a tetrahydrofolate-bound one-carbon unit, ultimately supporting thymidine synthesis and purine synthesis and promoting tumour growth. In tumour samples, elevated expression of SHMT2 was found to be associated with poor prognosis. In this review, the pivotal roles of SHMT2 in human carcinogenesis are described, highlighting the underlying regulatory mechanisms through promotion of tumour progression. In conclusion, SHMT2 may serve as a prognostic marker and a target for anticancer therapies.

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

The 12q13-q14 chromosomal region is recurrently amplified in 25% of fusion-positive (FP) rhabdomyosarcoma (RMS) cases and is associated with a poor prognosis. To identify amplified oncogenes in FP RMS, we compared the size, gene composition, and expression of 12q13-q14 amplicons in FP RMS with those of other cancer categories (glioblastoma multiforme, lung adenocarcinoma, and liposarcoma) in which 12q13-q14 amplification frequently occurs. We uncovered a 0.2 Mb region that is commonly amplified across these cancers and includes CDK4 and 6 other genes that are overexpressed in amplicon-positive samples. Additionally, we identified a 0.5 Mb segment that is only recurrently amplified in FP RMS and includes 4 genes that are overexpressed in amplicon-positive RMS. Among these genes, only serine hydroxymethyltransferase 2 (SHMT2) was overexpressed at the protein level in an amplicon-positive RMS cell line. SHMT2 knockdown in amplicon-positive RMS cells suppressed growth, transformation, and tumorigenesis, whereas overexpression in amplicon-negative RMS cells promoted these phenotypes. High SHMT2 expression reduced sensitivity of FP RMS cells to SHIN1, a direct SHMT2 inhibitor, but sensitized cells to pemetrexed, an inhibitor of the folate cycle. In conclusion, our study demonstrates that SHMT2 contributes to tumorigenesis in FP RMS and that SHMT2 amplification predicts differential response to drugs targeting this metabolic pathway.

Serine hydroxymethyltransferase 2: a novel target for human cancer therapy

Serine and glycine are the primary sources of one-carbon units that are vital for cell proliferation. Their abnormal metabolism is known to be associated with cancer progression. As the key enzyme of serine metabolism, Serine Hydroxymethyltransferase 2 (SHMT2) has been a research hotspot in recent years. SHMT2 is a PLP-dependent tetrameric enzyme that catalyzes the reversible transition from serine to glycine, thus promoting the production of one-carbon units that are indispensable for cell growth and regulation of the redox and epigenetic states of cells. Under a hypoxic environment, SHMT2 can be upregulated and could promote the generation of nicotinamide adenine dinucleotide phosphate (NADPH) and glutathione for maintaining the redox balance. Accumulating evidence confirmed that SHMT2 facilitates cell proliferation and tumor growth and is tightly associated with poor prognosis. In this review, we present insights into the function and research development of SHMT2 and summarize the possible molecular mechanisms of SHMT2 in promoting tumor growth, in the hope that it could provide clues to more effective clinical treatment of cancer.

SHMT2 expression as a diagnostic and prognostic marker for thyroid cancer

BACKGROUND

Catabolism of serine via serine hydroxymethyltransferase2 (SHMT2) through the mitochondrial one-carbon unit pathway is important in tumorigenesis. Therefore, SHMT2 may play a role in thyroid cancer.

METHODS

Thyroid tissue samples and The Cancer Genome Atlas (TCGA) database were used to evaluate SHMT2 expression in thyroid tissues and the association with clinical outcomes.

RESULTS

SHMT2 protein expression was evaluated in thyroid tissues consisting of 52 benign nodules, 129 papillary thyroid carcinomas (PTC) and matched normal samples, and 20 anaplastic thyroid carcinomas (ATC). ATCs presented the highest (95.0%) positivity of SMHT2 protein expression. PTCs showed the second highest (73.6%) positivity of SHMT2 expression, which was significantly higher than that of benign nodules (19.2%, P = 0.016) and normal thyroid tissues (0%, P < 0.001). Analysis of TCGA data showed that SHMT2 messenger RNA (mRNA) expression was significantly higher in tumors than in normal tissues (P < 0.001). When we classified thyroid cancer into high and low groups according to SHMT2 mRNA expression levels, the thyroid differentiation score for the high SHMT2 group was significantly lower than that of the low SHMT2 group (P < 0.001). There was also a significant correlation between SHMT2 mRNA expression and the stemness index (r = 0.41, P < 0.001). The high SHMT2 group had more advanced TNM stages and shorter progression-free survival rates than the low SHMT2 group (P < 0.01 and P = 0.007, respectively).

CONCLUSION

SHMT2 expression is higher in thyroid cancers than normal or benign tissues and is associated with de-differentiation and poor clinical outcomes. Thus, SHMT2 might be useful as a diagnostic and prognostic marker for thyroid cancer.

Overexpression of SHMT2 Predicts a Poor Prognosis and Promotes Tumor Cell Growth in Bladder Cancer

SHMT2 was overexpressed in many tumors, however, the role of SHMT2 in bladder cancer (BLCA) remains unclear. We first analyzed the expression pattern of SHMT2 in BLCA using the TNMplot, Oncomine, the Cancer Genome Atlas (TCGA), and the Gene Expression Omnibus (GEO) databases. Next, the association between SHMT2 expression and overall survival (OS)/disease-free survival (DFS) in BLCA patients were analyzed using TCGA and PrognoScan database. The correlation between SHMT2 expression and clinicopathology was determined using TCGA database. Furthermore, the genes co-expressed with SHMT2 and their underlying molecular function in BLCA were explored based on the Oncomine database, Metascape and gene set enrichment analysis (GSEA). Finally, the effects of SHMT2 on cell proliferation, cell cycle, and apoptosis were assessed using in vitro experiments. As a results, SHMT2 was significantly overexpressed in BLCA tissues and cells compared to normal bladder tissues and cells. A high SHMT2 expression predicts a poor OS of BLCA patients. In addition, SHMT2 expression was higher in patients with a high tumor grade and in those who were older than 60 years. However, the expression of SHMT2 was not correlated with gender, tumor stage, lymph node stage, and distant metastasis stage. Finally, overexpression of SHMT2 promoted BLCA cell proliferation and suppressed apoptosis, the silencing of SHMT2 significantly inhibited BLCA cell proliferation by impairing the cell cycle, and promoting apoptosis. SHMT2 mediates BLCA cells growth by regulating STAT3 signaling. In summary, SHMT2 regulates the proliferation, cell cycle and apoptosis of BLCA cells, and may act as a candidate therapeutic target for BLCA.

One carbon metabolism in human lung cancer

Background

Lung cancer remains the major cause of cancer related death worldwide. The discovery of targeted therapies against activating mutations in genes like EGFR considerably improved the prognosis for a subgroup of patients but still leaves a large part without a targeted therapy. One carbon metabolism (1CM) has been investigated in several cancer entities and its increased activity has been linked to higher tumor aggressiveness and reduced prognosis. In spite of 1CM enzymes role and correlation to cancer cells progression, comprehensive analysis for the diagnostic and functional role of the complete 1CM enzymes in lung cancer has not been conducted so far.

Methods

We investigated the prognostic and functional relevance of five major 1CM factors (MTHFD2, PGDH3, SHMT2, MTHFD1 and TYMS) in the three major subclasses of lung cancer [pulmonary adenocarcinoma (AC), squamous cell lung cancer (SQCLC) and small cell lung cancer (SCLC)]. We analyzed 1CM enzymes expression and clinicopathological correlation in patient derived tissue samples of 103 AC, 183 SQCLC and 37 SCLC patients by immunohistochemistry. Furthermore, the effect of 1CM enzymes expression on lung cancer cell proliferation and the response to chemotherapy was investigated in 15 representative AC, SQCLC and SCLC cell lines.

Results

Expression of MTHFD2 and PGDH3 was significantly correlated to a worse overall survival only in AC patients. Cell proliferation assays resolved that all 1CM enzymes have a significant impact on cell growth in AC cell lines and are partially involved in cell proliferation in SQCLC and SCLC cell lines. In addition, expression of MTHFD2 correlated significantly with an increased pemetrexed chemoresistance.

Conclusions

Expression of MTHFD2 significantly reduces the prognosis of AC patients. Furthermore, MTHFD2 expression is crucial for survival of AC cell lines and its expression correlates with resistance against Pemetrexed. As MTHFD2 is almost not expressed in healthy adult tissue, we therefore suggest that the inhibition of MTHFD2 might be a potential therapeutic strategy to surround pemetrexed resistance in AC.

The loss of SHMT2 mediates 5-fluorouracil chemoresistance in colorectal cancer by upregulating autophagy

5-Fluorouracil (5-FU)-based chemotherapy is the first-line treatment for colorectal cancer (CRC) but is hampered by chemoresistance. Despite its impact on patient survival, the mechanism underlying chemoresistance against 5-FU remains poorly understood. Here, we identified serine hydroxymethyltransferase-2 (SHMT2) as a critical regulator of 5-FU chemoresistance in CRC. SHMT2 inhibits autophagy by binding cytosolic p53 instead of metabolism. SHMT2 prevents cytosolic p53 degradation by inhibiting the binding of p53 and HDM2. Under 5-FU treatment, SHMT2 depletion promotes autophagy and inhibits apoptosis. Autophagy inhibitors decrease low SHMT2-induced 5-FU resistance in vitro and in vivo. Finally, the lethality of 5-FU treatment to CRC cells was enhanced by treatment with the autophagy inhibitor chloroquine in patient-derived and CRC cell xenograft models. Taken together, our findings indicate that autophagy induced by low SHMT2 levels mediates 5-FU resistance in CRC. These results reveal the SHMT2-p53 interaction as a novel therapeutic target and provide a potential opportunity to reduce chemoresistance.

Therapeutic targeting of the mitochondrial one-carbon pathway: perspectives, pitfalls, and potential

Most of the drugs currently prescribed for cancer treatment are riddled with substantial side effects. In order to develop more effective and specific strategies to treat cancer, it is of importance to understand the biology of drug targets, particularly the newly emerging ones. A comprehensive evaluation of these targets will benefit drug development with increased likelihood for success in clinical trials. The folate-mediated one-carbon (1C) metabolism pathway has drawn renewed attention as it is often hyperactivated in cancer and inhibition of this pathway displays promise in developing anticancer treatment with fewer side effects. Here, we systematically review individual enzymes in the 1C pathway and their compartmentalization to mitochondria and cytosol. Based on these insight, we conclude that (1) except the known 1C targets (DHFR, GART, and TYMS), MTHFD2 emerges as good drug target, especially for treating hematopoietic cancers such as CLL, AML, and T-cell lymphoma; (2) SHMT2 and MTHFD1L are potential drug targets; and (3) MTHFD2L and ALDH1L2 should not be considered as drug targets. We highlight MTHFD2 as an excellent therapeutic target and SHMT2 as a complementary target based on structural/biochemical considerations and up-to-date inhibitor development, which underscores the perspectives of their therapeutic potential.

The expanding world of tRNA modifications and their disease relevance

Transfer RNA (tRNA) is an adapter molecule that links a specific codon in mRNA with its corresponding amino acid during protein synthesis. tRNAs are enzymatically modified post-transcriptionally. A wide variety of tRNA modifications are found in the tRNA anticodon, which are crucial for precise codon recognition and reading frame maintenance, thereby ensuring accurate and efficient protein synthesis. In addition, tRNA-body regions are also frequently modified and thus stabilized in the cell. Over the past two decades, 16 novel tRNA modifications were discovered in various organisms, and the chemical space of tRNA modification continues to expand. Recent studies have revealed that tRNA modifications can be dynamically altered in response to levels of cellular metabolites and environmental stresses. Importantly, we now understand that deficiencies in tRNA modification can have pathological consequences, which are termed 'RNA modopathies'. Dysregulation of tRNA modification is involved in mitochondrial diseases, neurological disorders and cancer.

Structural basis for selective inhibition of human serine hydroxymethyltransferase by secondary bile acid conjugate

Bile acids are metabolites of cholesterol that facilitate lipid digestion and absorption in the small bowel. Bile acids work as agonists of receptors to regulate their own metabolism. Bile acids also regulate other biological systems such as sugar metabolism, intestinal multidrug resistance, and adaptive immunity. However, numerous physiological roles of bile acids remain undetermined. In this study, we solved the crystal structure of human serine hydroxymethyltransferase (hSHMT) in complex with an endogenous secondary bile acid glycine conjugate. The specific interaction between hSHMT and the ligand was demonstrated using mutational analyses, biophysical measurements, and structure-activity relationship studies, suggesting that secondary bile acid conjugates may act as modulators of SHMT activity.

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The crystal structures of hSHMT in complex with secondary bile acid glycine conjugate

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Specific interactions between hSHMT and secondary bile acid conjugate were validated

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Biological role of bile acids as modulators for one-carbon metabolism is suggested

Metabolism of Amino Acids in Cancer

Metabolic reprogramming has been widely recognized as a hallmark of malignancy. The uptake and metabolism of amino acids are aberrantly upregulated in many cancers that display addiction to particular amino acids. Amino acids facilitate the survival and proliferation of cancer cells under genotoxic, oxidative, and nutritional stress. Thus, targeting amino acid metabolism is becoming a potential therapeutic strategy for cancer patients. In this review, we will systematically summarize the recent progress of amino acid metabolism in malignancy and discuss their interconnection with mammalian target of rapamycin complex 1 (mTORC1) signaling, epigenetic modification, tumor growth and immunity, and ferroptosis. Finally, we will highlight the potential therapeutic applications.

A cell-nonautonomous mechanism of yeast chronological aging regulated by caloric restriction and one-carbon metabolism

Caloric restriction (CR) improves health span and life span of organisms ranging from yeast to mammals. Understanding the mechanisms involved will uncover future interventions for aging-associated diseases. In budding yeast, Saccharomyces cerevisiae, CR is commonly defined by reduced glucose in the growth medium, which extends both replicative and chronological life span (CLS). We found that conditioned media collected from stationary-phase CR cultures extended CLS when supplemented into nonrestricted (NR) cultures, suggesting a potential cell-nonautonomous mechanism of CR-induced life span regulation. Chromatography and untargeted metabolomics of the conditioned media, as well as transcriptional responses associated with the longevity effect, pointed to specific amino acids enriched in the CR conditioned media (CRCM) as functional molecules, with L-serine being a particularly strong candidate. Indeed, supplementing L-serine into NR cultures extended CLS through a mechanism dependent on the one-carbon metabolism pathway, thus implicating this conserved and central metabolic hub in life span regulation.

Implementing Curcumin in Translational Oncology Research

Most data published on curcumin and curcumin-based formulations are very promising. In cancer research, the majority of data has been obtained in vitro. Less frequently, researchers used experimental animals. The results of several clinical studies are conclusive, and these studies have established a good foundation for further research focusing on implementing curcumin in clinical oncology. However, the issues regarding timely data reporting and lack of disclosure of the exact curcumin formulations used in these studies should not be neglected. This article is a snapshot of the current status of publicly available data on curcumin clinical trials and a detailed presentation of results obtained so far with some curcumin formulations. Phenomena related to the observed effects of curcumin shown in clinical trials are presented, and its modifying effect on gut microbiota and metabolic reprogramming is discussed. Based on available data, there is a strong indication that curcumin and its metabolites present molecules that do not necessarily need to be abundant in order to act locally and benefit systemically. Future clinical studies should be designed in a way that will take that fact into consideration.

Increased Expression of SHMT2 Is Associated With Poor Prognosis and Advanced Pathological Grade in Oral Squamous Cell Carcinoma

This study focused on the expression of mitochondrial serine hydroxymethyltransferase (SHMT2) in oral squamous cell carcinoma (OSCC) and its correlation with clinical traits and the prognosis of OSCC patients. Immunochemical staining and Western blotting were used to quantify the expression of SHMT2 and related immune markers in OSCC. Using OSCC microarrays and The Cancer Genome Atlas (TCGA) database, we evaluated the association between SHMT2 and various clinical traits. We found that increased expression of SHMT2 was detected in OSCC and correlated with advanced pathological grade and recurrence of OSCC. By a multivariate Cox proportional hazard model, high expression of SHMT2 was shown to indicate a negative prognosis. In addition, in the OSCC microenvironment, increasing the expression of SHMT2 was associated with high expression levels of programmed cell death-ligand 1 (PD-L1), CKLF-like MARVEL transmembrane domain containing 6 (CMTM6), V-type immunoglobulin domain-containing suppressor (VISTA), B7-H4, Slug, and CD317. In the future, more effort will be required to investigate the role of SHMT2 in the OSCC microenvironment.

Transcriptional Activation of Chac1 and Other Atf4-Target Genes Induced by Extracellular l-Serine Depletion is negated with Glycine Consumption in Hepa1-6 Hepatocarcinoma Cells

Mouse embryonic fibroblasts lacking D-3-phosphoglycerate dehydrogenase (Phgdh), which catalyzes the first step of de novo synthesis of l-serine, are particularly sensitive to depletion of extracellular L-serine. In these cells, depletion of l-serine leads to a rapid reduction of intracellular L-serine, cell growth arrest, and altered expression of a wide variety of genes. However, it remains unclear whether reduced availability of extracellular l-serine elicits such responses in other cell types expressing Phgdh. Here, we show in the mouse hepatoma cell line Hepa1-6 that extracellular l-serine depletion transiently induced transcriptional activation of Atf4-target genes, including cation transport regulator-like protein 1 (Chac1). Expression levels of these genes returned to normal 24 h after l-serine depletion, and were suppressed by the addition of l-serine or glycine in the medium. Extracellular l-serine depletion caused a reduction of extracellular and intracellular glycine levels but maintained intracellular l-serine levels in the cells. Further, Phgdh and serine hydroxymethyltransferase 2 (Shmt2) were upregulated after l-serine depletion. These results led us to conclude that the Atf4-mediated gene expression program is activated by extracellular l-serine depletion in Hepa1-6 cells expressing Phgdh, but is antagonized by the subsequent upregulation of l-serine synthesis, mainly from autonomous glycine consumption.

Pathway-Based Integrative Analysis of Metabolome and Microbiome Data from Hepatocellular Carcinoma and Liver Cirrhosis Patients

Aberrations of the human microbiome are associated with diverse liver diseases, including hepatocellular carcinoma (HCC). Even if we can associate specific microbes with particular diseases, it is difficult to know mechanistically how the microbe contributes to the pathophysiology. Here, we sought to reveal the functional potential of the HCC-associated microbiome with the human metabolome which is known to play a role in connecting host phenotype to microbiome function. To utilize both microbiome and metabolomic data sets, we propose an innovative, pathway-based analysis, Hierarchical structural Component Model for pathway analysis of Microbiome and Metabolome (HisCoM-MnM), for integrating microbiome and metabolomic data. In particular, we used pathway information to integrate these two omics data sets, thus providing insight into biological interactions between different biological layers, with regard to the host's phenotype. The application of HisCoM-MnM to data sets from 103 and 97 patients with HCC and liver cirrhosis (LC), respectively, showed that this approach could identify HCC-related pathways related to cancer metabolic reprogramming, in addition to the significant metabolome and metagenome that make up those pathways.

Identification of three new compounds that directly target human serine hydroxymethyltransferase 2

Mitochondrial serine hydroxymethyltransferase 2 (SHMT2) is an important drug target in the one-carbon metabolic pathway, since its activity is critical for purine and pyrimidine biosynthesis. Additionally, it plays a prominent role during metabolic reprogramming of cancer cells, and SHMT2 inhibitors have proven useful as anticancer drugs. Compared to drugs targeting one-carbon metabolic enzymes (mainly dihydrofolate reductase and thymidylate synthase) that have been used for clinical treatment of cancer, efficient SHMT2-specific inhibitors are lacking. Therefore, we established a direct system for virtual screening, protein expression, and identification of inhibitors targeting SHMT2. First, 27 compounds qualifying as potential SHMT2 inhibitors were selected for biological activity verification through virtual screening of the 210 thousand compounds registered in the Specs database. Second, these 27 hits were subjected to quick screening by an in vitro non-competitive kinetic assay of SHMT2 single-enzyme catalysis. This allowed us to identify three compounds featuring medium-strength and non-competitive inhibition of SHMT2: AM-807/42004511 (IC₅₀  = 14.52 ± 4.1665 μM), AM-807/40675298 (IC₅₀  = 12.74 ± 5.8991 μM), and AM-807/42004633 (IC₅₀  = 9.43 ± 0.5646 μM). We describe a quick screening method for the identification of inhibitors targeting SHMT2, providing a basis for subsequent identification and screening of new inhibitors.

[Protective effect of serine methyltransferase against hepatic ischemia-reperfusion injury in mice]

OBJECTIVE

To investigate the protective effect of serine hydroxymethyl transferase 2 (SHMT2) against hepatic ischemia-reperfusion injury in mice.

METHODS

Sixty C57BL/6 mice were divided equally into sham-operated group, saline adeno-associated virus group (AVV-GFP), and adeno-associated virus silencing group (AAV-SHMT2). The adeno-associated virus and normal saline were injected into the tail vein of the mice 2 weeks before establishment of a 70% ischemia-reperfusion model in the liver. qPCR, Western blotting, immunofluorescence and immunohistochemistry were used to detect the changes of AST/ALT concentration, SHMT2, JNK, NF-κB, caspase-3 and downstream inflammatory factors in the mice, and HE staining was used to observe the pathological damage of the liver tissue in each group; the cell apoptosis in the liver was detected using TUNEL assay.

RESULTS

The expression of SHMT2 increased with time after hepatic ischemia-reperfusion and reached the highest level at 24 h (the relative expression was 1.5, P &lt; 0.05). At 24 h after hepatic ischemia-reperfusion, the levels of AST/ALT in AAV-SHMT2 group (588/416 U/L) were significantly higher than those in the control group (416/345 U/L) and the empty vector group (387/321 U/L) (P &lt; 0.05). Compared with those in the control group and the empty vector group, the level of SHMT2 was significantly decreased in AAV-SHMT2 group (with a relative expression of 0.24, P &lt; 0.05), the levels of p-JNK and p-p65 were significantly increased (relative expression of 0.80 and 0.97, respectively, P &lt; 0.05), and the levels TNF-α and IL-1β were consistently elevated (relative expression levels of 1.6 and 1.2, respectively, P &lt; 0.05). No significant differences were found in these parameters between the empty vector group and the control group (P&gt;0.05).

CONCLUSIONS

SHMT2 may alleviate liver cell apoptosis in mice with hepatic ischemia-reperfusion injury by inhibiting the activation of JNK pathway and excessive activation of NF-κB pathway to reduce hepatic damage.

SHMT2 Promotes Liver Regeneration Through Glycine-activated Akt/mTOR Pathway

BACKGROUND

The development of liver transplantation (LT) is increasingly being limited by the unavailability of liver grafts. Unique regenerative capacity of liver in response to injuries makes living-donor liver transplantation (LDLT) a feasible strategy to meet clinical demands. Serine hydroxymethyl-transferase 2 (SHMT2) serves as the key enzyme in the biosynthesis of glycine. Glycine affects the activity of mammalian target of rapamycin (mTOR), which is important for cellular growth and proliferation. In this study, the effects of SHMT2 on mouse liver regeneration were investigated using a classical partial hepatectomy (PH) model.

METHODS

In vivo, PH was performed on mice with or without knockdown of SHMT2. In vitro, SHMT2 was overexpressed in primary hepatocytes, which were cultured in customized Dulbecco's modified eagle media and LY294002 (an Akt inhibitor). Relevant indexes of liver regeneration, cell proliferation, and Akt/mTOR signal pathways were analyzed.

RESULTS

After PH, the expression levels of SHMT2 fluctuated with time and knockdown of SHMT2 in vivo lowered the regenerative ability of liver, with reduced glycine levels compared to the scramble group. In addition, overexpression of SHMT2 in hepatocytes boosted glycine production while enhancing Akt/mTOR pathway activity. These results were validated by the application of LY294002 in vitro.

CONCLUSIONS

SHMT2 can contribute to liver regeneration after PH, and this is likely related to the activation of Akt/mTOR signaling pathway by its metabolic product, glycine, in hepatocytes. These results might have therapeutic implications for the prognosis of patients undergoing hepatic resection or transplantation.

Reprogramming of serine, glycine and one-carbon metabolism in cancer

Metabolic pathways leading to the synthesis, uptake, and usage of the nonessential amino acid serine are frequently amplified in cancer. Serine encounters diverse fates in cancer cells, including being charged onto tRNAs for protein synthesis, providing head groups for sphingolipid and phospholipid synthesis, and serving as a precursor for cellular glycine and one-carbon units, which are necessary for nucleotide synthesis and methionine cycle reloading. This review will focus on the participation of serine and glycine in the mitochondrial one-carbon (SGOC) pathway during cancer progression, with an emphasis on the genetic and epigenetic determinants that drive SGOC gene expression. We will discuss recently elucidated roles for SGOC metabolism in nucleotide synthesis, redox balance, mitochondrial function, and epigenetic modifications. Finally, therapeutic considerations for targeting SGOC metabolism in the clinic will be discussed.

Mitochondrial Redox Hubs as Promising Targets for Anticancer Therapy

Mitochondria play multifaceted roles in malignant tumor progression. Beyond their bioenergetic role, mitochondria are essential for providing malignant cells a higher plasticity to face the harsh environmental conditions. Cell-autonomous metabolic deregulation of cancer cells, or metabolic adaptation to microenvironmental cues (lack of nutrients, stromal supply, hypoxia, etc.), represent the triggering event of mitochondria overexploitation to orchestrate nutrient sensing and upload, signaling, and redox circuits. As readout of their higher function, mitochondria produce high amounts of reactive oxygen species (ROS) that are functional for multiple signaling networks underlying tumor proliferation, survival, and metastatic process. To compensate for the higher rate of mitochondrial ROS production, cancer cells have evolved adaptive mechanisms to increase their antioxidant systems and to address ROS activating pathways useful for the tumor cell adaptation to environmental changes. As these properties are critical for cancer progression, mitochondrial ROS have recently become an attractive target for anti-cancer therapies. We discuss how understanding of mitochondrial function in the tumor-specific generation of ROS will impact on the development of novel redox-based targeted therapeutic strategies.

NAD- and NADPH-Contributing Enzymes as Therapeutic Targets in Cancer: An Overview

Actively proliferating cancer cells require sufficient amount of NADH and NADPH for biogenesis and to protect cells from the detrimental effect of reactive oxygen species. As both normal and cancer cells share the same NAD biosynthetic and metabolic pathways, selectively lowering levels of NAD(H) and NADPH would be a promising strategy for cancer treatment. Targeting nicotinamide phosphoribosyltransferase (NAMPT), a rate limiting enzyme of the NAD salvage pathway, affects the NAD and NADPH pool. Similarly, lowering NADPH by mutant isocitrate dehydrogenase 1/2 (IDH1/2) which produces D-2-hydroxyglutarate (D-2HG), an oncometabolite that downregulates nicotinate phosphoribosyltransferase (NAPRT) via hypermethylation on the promoter region, results in epigenetic regulation. NADPH is used to generate D-2HG, and is also needed to protect dihydrofolate reductase, the target for methotrexate, from degradation. NAD and NADPH pools in various cancer types are regulated by several metabolic enzymes, including methylenetetrahydrofolate dehydrogenase, serine hydroxymethyltransferase, and aldehyde dehydrogenase. Thus, targeting NAD and NADPH synthesis under special circumstances is a novel approach to treat some cancers. This article provides the rationale for targeting the key enzymes that maintain the NAD/NADPH pool, and reviews preclinical studies of targeting these enzymes in cancers.

Architecture of The Human Ape1 Interactome Defines Novel Cancers Signatures

APE1 is essential in cancer cells due to its central role in the Base Excision Repair pathway of DNA lesions and in the transcriptional regulation of genes involved in tumor progression/chemoresistance. Indeed, APE1 overexpression correlates with chemoresistance in more aggressive cancers, and APE1 protein-protein interactions (PPIs) specifically modulate different protein functions in cancer cells. Although important, a detailed investigation on the nature and function of protein interactors regulating APE1 role in tumor progression and chemoresistance is still lacking. The present work was aimed at analyzing the APE1-PPI network with the goal of defining bad prognosis signatures through systematic bioinformatics analysis. By using a well-characterized HeLa cell model stably expressing a flagged APE1 form, which was subjected to extensive proteomics analyses for immunocaptured complexes from different subcellular compartments, we here demonstrate that APE1 is a central hub connecting different subnetworks largely composed of proteins belonging to cancer-associated communities and/or involved in RNA- and DNA-metabolism. When we performed survival analysis in real cancer datasets, we observed that more than 80% of these APE1-PPI network elements is associated with bad prognosis. Our findings, which are hypothesis generating, strongly support the possibility to infer APE1-interactomic signatures associated with bad prognosis of different cancers; they will be of general interest for the future definition of novel predictive disease biomarkers. Future studies will be needed to assess the function of APE1 in the protein complexes we discovered. Data are available via ProteomeXchange with identifier PXD013368.

PLCε knockdown prevents serine/glycine metabolism and proliferation of prostate cancer by suppressing YAP

The metabolic reprogramming is an important basis for the development of many tumors, including prostate cancer (PCa). Metabolic changes in many amino acids consist of serine and glycine affect the biological behavior of them. Phospholipase C epsilon (PLCε) plays an important role as an oncogene. However, its role in regulating amino acid metabolism remains unclear. In this study, results found significantly positive correlation between PLCε and Yes-associated protein (YAP) in PCa tissues. LC-MS/MS and GC-MS results further displayed abnormally elevated levels of serine, glycine and its some downstream metabolites in the blood of PCa patients. Secondly, PLCε knockdown can inhibit serine/glycine producing and proliferation of PCa both in vivo and in vitro. Mechanistically, PLCε may affect the serine/glycine metabolism by regulating dephosphorylation and nuclear translocation of YAP. More interestingly, verteporfin (VP, a specific inhibitor of YAP) could effectively enhance the PLCε-depletion induced inhibition of serine/glycine secretion and growth. Overall, this research revealed the possibility of anomalous serine/glycine levels in the blood for the diagnosis of PCa, identified the important role of the PLCε/YAP axis in regulating serine/glycine metabolism, cell proliferation and tumor growth, and suggested the combination of VP with PLCε-depletion may provide a new idea for the treatment of PCa.

Circulatory miRNA-484, 524, 615 and 628 expression profiling in HCV mediated HCC among Egyptian patients; implications for diagnosis and staging of hepatic cirrhosis and fibrosis

Circulatory microRNAs have recently emerged as non-invasive and effective biomarkers for diagnosis of various diseases. Currently there is no reliable biomarker for diagnosis, prognosis or even staging of fibrotic and cirrhotic complications arising from HCV infection. This study aimed at investigating plasma miR-484, miR-524, miR-615-5p and miR-628-3p expression signatures in Egyptian patients with HCV mediated cirrhosis, fibrosis and HCC. Plasma miRNAs expressions in 168 samples [(40 healthy controls, 47 with HCV liver fibrosis, 40 with HCV-cirrhosis and 41 with HCV-hepatocellular carcinoma (HCC)] were quantified using RT-PCR. The studied miRNAs were differentially expressed among all participating groups. Plasma miR-484 levels exhibited significant downregulation in advanced fibrosis as compared to mild fibrosis and HCC. Moreover, miR-484 showed significant upregulation in HCC versus cirrhosis. Both miR-524-5p and miR-615-5p were upregulated in cirrhotic group as compared to controls. Differential expression between HCC and controls was noticeable in miR-524-5p. Receiver operator characteristic curve analysis revealed promising diagnostic performance for miR-484 in discriminating late fibrosis from both mild fibrosis and HCC and also for miR-524 in distinguishing between cirrhosis and fibrosis. In conclusion, investigated miRNAs could serve as potential and sensitive biomarkers for staging, prognosis and early diagnosis of various HCV mediated hepatic disease progression.

Downregulating Serine Hydroxymethyltransferase 2 Deteriorates Hepatic Ischemia-Reperfusion Injury through ROS/JNK/P53 Signaling in Mice

Background

Serine hydroxymethyltransferase 2 (SHMT2) activity ensures that cells have a survival advantage in ischemic conditions and regulates redox homeostasis. In this study, we aimed to investigate the role of SHMT2 after hepatic ischemia-reperfusion (IR), which involves hypoxia, ischemic conditions, and cell apoptosis.

Methods

A 70% IR model was established in C57BL/6J mice with or without SHMT2 knockdown. H&E staining, liver weight/body weight, serum alanine aminotransferase (ALT), and aspartate aminotransferase (AST) levels and cell apoptosis were tested to analyze liver damage and function. Then, the related cellular signals were probed.

Results

The level of SHMT2 protein was significantly increased at 24 h and 48 h after IR (p < 0.001). Mice in the shSHMT2 group showed more necrotic areas and histological damage at 24 h (p < 0.01) after IR and higher levels of serum ALT and AST (p < 0.05) compared with those of mice in the scramble group. After IR for 24 h, the expression of TUNEL in the shSHMT2 group was significantly higher than that in the scramble group, as shown by histological analysis (p < 0.01). Mechanistically, the JNK/P53 signaling pathway was activated by IR, and knockdown of SHMT2 exacerbated hepatocyte apoptosis.

Conclusions

Knockdown of SHMT2 worsens IR injury through the ROS/JNK/P53 signaling pathway. Our discovery expands the understanding of both molecular and metabolic mechanisms involved in IR. SHMT2 is a possible therapeutic target to improve the prognosis of liver transplantation (LT) and subtotal hepatectomy.

Mitochondrial Dysfunction in the Transition from NASH to HCC

The liver constantly adapts to meet energy requirements of the whole body. Despite its remarkable adaptative capacity, prolonged exposure of liver cells to harmful environmental cues (such as diets rich in fat, sugar, and cholesterol) results in the development of chronic liver diseases (including non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH)) that can progress to hepatocellular carcinoma (HCC). The pathogenesis of these diseases is extremely complex, multifactorial, and poorly understood. Emerging evidence suggests that mitochondrial dysfunction or maladaptation contributes to detrimental effects on hepatocyte bioenergetics, reactive oxygen species (ROS) homeostasis, endoplasmic reticulum (ER) stress, inflammation, and cell death leading to NASH and HCC. The present review highlights the potential contribution of altered mitochondria function to NASH-related HCC and discusses how agents targeting this organelle could provide interesting treatment strategies for these diseases.

Study of SHMT2 Inhibitors and Their Binding Mechanism by Computational Alanine Scanning

Mitochondrial serine hydroxymethyl transferase isoform 2 (SHMT2) has attracted increasing attention as a pivotal catalyzing regulator of the serine/glycine pathway in the one-carbon metabolism of cancer cells. However, few inhibitors that target this potential anticancer target have been discovered. Quantitative characterization of the interactions between SHMT2 and its known inhibitors should benefit future discovery of novel inhibitors. In this study, we employed a recently developed alanine-scanning-interaction-entropy method to quantitatively calculate the residue-specific binding free energy of 28 different SHMT2 inhibitors that originate from the same skeleton. Major contributing residues from SHMT2 and chemical groups from the inhibitors were identified, and the binding energy of each residue was quantitatively determined, revealing essential features of the protein-inhibitor interaction. The most important contributing residue is Y105 of the B chain followed by L166 of the A chain. The calculated protein-ligand binding free energies are in good agreement with the experimental results and showed better correlation and smaller errors compared with those obtained using the conventional MM/GBSA with the normal mode method. These results may aid the rational design of more effective SHMT2 inhibitors.

Increased Expression of Serine Hydroxymethyltransferase 2 (SHMT2) is a Negative Prognostic Marker in Patients with Hepatocellular Carcinoma and is Associated with Proliferation of HepG2 Cells

Background

Serine hydroxymethyltransferase 2 (SHMT2) is a key enzyme in one-carbon cell metabolism, including in liver cancer. However, the associations between SHMT2 expression at the gene and protein level and prognosis in patients with hepatocellular carcinoma (HCC) remains unknown. This study aimed to investigate the expression levels of SHMT2 in tumor tissue samples from patients with HCC and clinical outcome and the effects of silencing the expression of the SHMT2 gene in HepG2 cells.

Material/Methods

Expression levels of SHMT2 were evaluated in 144 cases of HCC using immunohistochemistry and correlated with clinicopathological factors using the chi-squared (χ²) test. The prognostic significance of SHMT2 expression was analyzed by univariate analysis and multivariate analysis. Twenty pairs of HCC tissue and adjacent normal liver tissue were compared for SHMT2 expression levels using quantitative reverse transcription polymerase chain reaction (qRT-PCR). HepG2 cells underwent SHMT2 gene silencing and MTT and transwell assays investigated cell proliferation and migration. Western blot was used to detect the expression of markers of epithelial-mesenchymal transition (EMT).

Results

Expression levels of SHMT2 in HCC tissues were significantly correlated with tumor grade and hepatitis B virus (HBV) infection, and increased expression was an independent negative prognostic factor in patients with HCC (P=0.003). Increased expression of the SHMT2 gene promoted the proliferation and migration of the HepG2 HCC cell line.

Conclusions

Increased expression of SHMT2 was a negative prognostic biomarker in patients with HCC. Expression of the SHMT2 gene promoted the proliferation and migration of HepG2 HCC cells.

Metabolic and chemical regulation of tRNA modification associated with taurine deficiency and human disease

Modified uridine containing taurine, 5-taurinomethyluridine (τm5U), is found at the anticodon first position of mitochondrial (mt-)transfer RNAs (tRNAs). Previously, we reported that τm5U is absent in mt-tRNAs with pathogenic mutations associated with mitochondrial diseases. However, biogenesis and physiological role of τm5U remained elusive. Here, we elucidated τm5U biogenesis by confirming that 5,10-methylene-tetrahydrofolate and taurine are metabolic substrates for τm5U formation catalyzed by MTO1 and GTPBP3. GTPBP3-knockout cells exhibited respiratory defects and reduced mitochondrial translation. Very little τm5U34 was detected in patient's cells with the GTPBP3 mutation, demonstrating that lack of τm5U results in pathological consequences. Taurine starvation resulted in downregulation of τm5U frequency in cultured cells and animal tissues (cat liver and flatfish). Strikingly, 5-carboxymethylaminomethyluridine (cmnm5U), in which the taurine moiety of τm5U is replaced with glycine, was detected in mt-tRNAs from taurine-depleted cells. These results indicate that tRNA modifications are dynamically regulated via sensing of intracellular metabolites under physiological condition.

Metabolic Intermediates in Tumorigenesis and Progression

Traditional antitumor drugs inhibit the proliferation and metastasis of tumour cells by restraining the replication and expression of DNA. These drugs are usually highly cytotoxic. They kill tumour cells while also cause damage to normal cells at the same time, especially the hematopoietic cells that divide vigorously. Patients are exposed to other serious situations such as a severe infection caused by a decrease in the number of white blood cells. Energy metabolism is an essential process for the survival of all cells, but differs greatly between normal cells and tumour cells in metabolic pathways and metabolic intermediates. Whether this difference could be used as new therapeutic target while reducing damage to normal tissues is the topic of this paper. In this paper, we introduce five major metabolic intermediates in detail, including acetyl-CoA, SAM, FAD, NAD⁺ and THF. Their contents and functions in tumour cells and normal cells are significantly different. And the possible regulatory mechanisms that lead to these differences are proposed carefully. It is hoped that the key enzymes in these regulatory pathways could be used as new targets for tumour therapy.