Non-canonical phosphoglycerate dehydrogenase activity promotes liver cancer growth via mitochondrial translation and respiratory metabolism

Amino acids in cancer: Understanding metabolic plasticity and divergence for better therapeutic approaches

Metabolic reprogramming is a hallmark of malignant transformation. While initial studies in the field of cancer metabolism focused on central carbon metabolism, the field has expanded to metabolism beyond glucose and glutamine and uncovered the important role of amino acids in tumorigenesis and tumor immunity as energy sources, signaling molecules, and precursors for (epi)genetic modification. As a result of the development and application of new technologies, a multifaceted picture has emerged, showing that context-dependent heterogeneity in amino acid metabolism exists between tumors and even within distinct regions of solid tumors. Understanding the complexity and flexibility of amino acid metabolism in cancer is critical because it can influence therapeutic responses and predict clinical outcomes. This overview discusses the current findings on the heterogeneity in amino acid metabolism in cancer and how understanding the metabolic diversity of amino acids can be translated into more clinically relevant therapeutic interventions.

Acetylation: a new target for protein degradation in cancer

Acetylation is an increasing area of focus for cancer research as it is closely related to a variety of cellular processes through modulation of histone and non-histone proteins. However, broadly targeting acetylation threatens to yield nonselective toxic effects owing to the vital role of acetylation in cellular function. There is thus a pressing need to elucidate and characterize the specific cancer-relevant roles of acetylation for future therapeutic design. Acetylation-mediated protein homeostasis is an example of selective acetylation that affects a myriad of proteins as well as their correlated functions. We review recent examples of acetylation-mediated protein homeostasis that have emerged as key contributors to tumorigenesis, tumor proliferation, metastasis, and/or drug resistance, and we discuss their implications for future exploration of this intriguing phenomenon.

Acidosis overrides molecular heterogeneity to shape therapeutically targetable metabolic phenotypes in colon cancers

Colorectal cancer (CRC) represents a prototypical example of a cancer type for which inter- and intra-tumor heterogeneities remain major challenges for the clinical management of patients. Besides genotype-mediated phenotypic alterations, tumor microenvironment (TME) conditions are increasingly recognized to promote intrinsic diversity and phenotypic plasticity and sustain disease progression. In particular, acidosis is a common hallmark of solid tumors, including CRC, and it is known to induce aggressive cancer cell phenotypes. In this study, we report that long-term adaptation to acidic pH conditions is associated with common metabolic alterations, including a glycolysis-to-respiration switch and a higher reliance on the activity of phosphoglycerate dehydrogenase (PHGDH), in CRC cells initially displaying molecularly heterogeneous backgrounds. Pharmacological inhibition of PHGDH activity or mitochondrial respiration induces greater growth-inhibitory effects in acidosis-exposed CRC cells in 2D and 3D culture conditions, and in patient-derived CRC organoids. These data pave the way for drugs targeting the acidic tumor compartment as a "one-size-fits-all" therapeutic approach to delay CRC progression.

PRDX6 Prevents NNMT Ubiquitination and Degradation as a Nonenzymatic Mechanism to Promote Ovarian Cancer Progression

Cancer cells cope with oxidative stress for their proliferation and metastasis by equipping antioxidant systems, among which the antioxidant enzymes peroxiredoxins (PRDXs) play crucial roles. However, whether PRDXs exhibit nonenzymatic functions remains unclear. Here, it is shown that the 1-cysteine PRDX (PRDX6) upregulates nicotinamide N-methyltransferase (NNMT) to promote the growth and metastasis of ovarian cancer cells, independently of PRDX6's enzymatic activities. Mechanistically, PRDX6 interacts with NNMT to prevent its binding to the E3 ubiquitin ligase tripartite-motif protein 56 (TRIM56), leading to the inhibition of NNMT ubiquitination at lysine 23 and 210 and suppression of subsequent proteasomal degradation. In addition, PRDX6-mediated NNMT upregulation activates mitogen-activated protein kinase (MAPK) signaling, thereby promoting the growth and metastasis of ovarian cancer cells. Notably, PRDX6 overexpression is associated with higher NNMT protein levels in human ovarian cancer tissues and is predictive of poor prognosis of ovarian cancer patients. Overall, the findings illustrate a critical oncogenic mechanism of the antioxidant enzyme PRDX6 in promoting ovarian cancer progression beyond its enzymatic mechanisms.

Non-canonical function of PHGDH promotes HCC metastasis by interacting with METTL3

PURPOSE

Phosphoglycerate dehydrogenase (PHGDH), a pivotal enzyme in serine synthesis, plays a key role in the malignant progression of tumors through both its metabolic activity and moonlight functions. This study aims to elucidate the non-canonical function of PHGDH in promoting hepatocellular carcinoma (HCC) metastasis through its interaction with methyltransferase-like 3 (METTL3), potentially uncovering a novel therapeutic target.

METHODS

Western blot was used to study PHGDH expression changes under anoikis and cellular functional assays were employed to assess its role in HCC metastasis. PHGDH-METTL3 interactions were explored using GST pull-down, Co-immunoprecipitation and immunofluorescence assays. Protein stability and ubiquitination assays were performed to understand PHGDH's impact on METTL3. Flow cytometry, cellular assays and nude mice model were used to confirm PHGDH's effects on anoikis resistance and HCC metastasis in vitro and in vivo.

RESULTS

PHGDH is upregulated under anoikis conditions, thereby enhancing the metastatic potential of HCC cells. By interacting with METTL3, PHGDH prevents its ubiquitin-dependent degradation, resulting in higher METTL3 protein levels. This interaction upregulates epithelial-mesenchymal transition related genes, contributing to anoikis resistance and HCC metastasis. Nude mice model confirms that PHGDH's interaction with METTL3 is crucial for driving HCC metastasis.

CONCLUSION

Our research presents the first evidence that PHGDH promotes HCC metastasis by interacting with METTL3. The PHGDH-METTL3 axis may serve as a potential clinical therapeutic target, offering new insights into the multifaceted roles of PHGDH in HCC metastasis.

Mitochondria-localized MBD2c facilitates mtDNA transcription and drug resistance

Mitochondria contain a 16-kb double stranded DNA genome encoding 13 proteins essential for respiration, but the mechanisms regulating transcription and their potential role in cancer remain elusive. Although methyl-CpG-binding domain (MBD) proteins are essential for nuclear transcription, their role in mitochondrial DNA (mtDNA) transcription is unknown. Here we report that the MBD2c splicing variant translocates into mitochondria to mediate mtDNA transcription and increase mitochondrial respiration in triple-negative breast cancer (TNBC) cells. In particular, MBD2c binds the noncoding region in mtDNA and interacts with SIRT3, which in turn deacetylates and activates TFAM, a primary mitochondrial transcription factor, leading to enhanced mtDNA transcription. Furthermore, MBD2c recovered the decreased mitochondrial gene expression caused by the DNA synthesis inhibitor cisplatin, preserving mitochondrial respiration and consequently enhancing drug resistance and proliferation in TNBC cells. These data collectively demonstrate that MBD2c positively regulates mtDNA transcription, thus connecting epigenetic regulation by deacetylation with cancer cell metabolism, suggesting druggable targets to overcome resistance.

Elucidation of the Role of SHMT2 in L-Serine Homeostasis in Hypoxic Hepa1-6 Cells

Hypoxia is a characteristic feature of malignancy; however, its effect on metabolism remains unclear. In this study, Hepa1-6 cells were cultured under hypoxic conditions and their metabolites were analyzed. Elevated levels of L-serine along with increased glycolytic activity are prominent features of hypoxia. Transcriptome sequencing revealed the downregulation of genes involved in L-serine synthesis and metabolism, which was confirmed by PCR analysis and comparison with public databases. Further experimental evidence indicates that the accumulation of L-serine under hypoxic conditions is attributable not only to enhanced glycolysis but also to a reduction in the catabolism of L-serine mediated by serine hydroxymethyltransferase 2 (SHMT2).

cirSIRT5 induces ferroptosis in bladder cancer by forming a ternary complex with SYVN1/PHGDH

Bladder cancer (BC) represents a prevalent and formidable malignancy necessitating innovative diagnostic and therapeutic strategies. Circular RNAs (circRNAs) have emerged as crucial regulators in cancer biology. In this study, we comprehensively evaluated ferroptosis levels in BC cells utilizing techniques encompassing lipid peroxidation assessment, transmission electron microscopy, and malondialdehyde (MDA) measurement. Additionally, we probed into the mechanistic intricacies by which circRNAs govern BC, employing RNA pull-down, RNA immunoprecipitation (RIP), and immunoprecipitation (IP) assays. Our investigation unveiled circSIRT5, which displayed significant downregulation in BC. Notably, circSIRT5 emerged as a promising prognostic marker, with diminished expression correlating with unfavorable clinical outcomes. Functionally, circSIRT5 was identified as an inhibitor of BC progression both in vitro and in vivo. Mechanistically, circSIRT5 exerted its tumor-suppressive activities through the formation of a ternary complex involving circSIRT5, SYVN1, and PHGDH. This complex enhanced the ubiquitination and subsequent degradation of PHGDH, ultimately promoting ferroptosis in BC cells. This ferroptotic process contributed significantly to the inhibition of tumor growth and metastasis in BC. In addition, FUS was found to accelerate the biogenesis of circSIRT5 in BC. These findings provide valuable insights into the pivotal role of circSIRT5 in BC pathogenesis, underscoring its potential as a diagnostic biomarker and therapeutic target for this malignancy.

Exploring the multifaceted role of adenosine nucleotide translocase 2 in cellular and disease processes: A comprehensive review

Adenosine nucleotide translocases (ANTs) are a family of proteins abundant in the inner mitochondrial membrane, primarily responsible for shuttling ADP and ATP across the mitochondrial membrane. Additionally, ANTs are key players in balancing mitochondrial energy metabolism and regulating cell death. ANT2 isoform, highly expressed in undifferentiated and proliferating cells, is implicated in the development and drug resistance of various tumors. We conduct a detailed analysis of the potential mechanisms by which ANT2 may influence tumorigenesis and drug resistance. Notably, the significance of ANT2 extends beyond oncology, with roles in non-tumor cell processes including blood cell development, gastrointestinal motility, airway hydration, nonalcoholic fatty liver disease, obesity, chronic kidney disease, and myocardial development, making it a promising therapeutic target for multiple pathologies. To better understand the molecular mechanisms of ANT2, this review summarizes the structural properties, expression patterns, and basic functions of the ANT2 protein. In particular, we review and analyze the controversy surrounding ANT2, focusing on its role in transporting ADP/ATP across the inner mitochondrial membrane, its involvement in the composition of the mitochondrial permeability transition pore, and its participation in apoptosis.

CBX4 plays a bidirectional role in transcriptional regulation and lung adenocarcinoma progression

Lung adenocarcinoma (LUAD) remains a leading cause of cancer-related mortality worldwide. Understanding the dysregulated epigenetics governing LUAD progression is pivotal for identifying therapeutic targets. CBX4, a chromobox protein, is reported to be upregulated in LUAD. This study highlights the dual impact of CBX4 on LUAD proliferation and metastasis through a series of rigorous in vitro and in vivo experiments. Further investigation into the underlying mechanism through high-throughput ChIP-seq and RNA-seq reveals that CBX4 functions in promoting LUAD proliferation via upregulating PHGDH expression and subsequent serine biosynthesis, while concurrently suppressing LUAD metastasis by inhibiting ZEB2 transcription. CBX4 facilitates PHGDH transcription through the interaction with GCN5, inducing heightened histone acetylation on the PHGDH promoter. Simultaneously, the inhibition of ZEB2 transcription involves CBX4-mediated recruitment of canonical PRC1 (cPRC1), establishing H2K119ub on the ZEB2 promoter. These findings underscore CBX4's pivotal role as a regulator of LUAD progression, emphasizing its diverse transcriptional regulatory functions contingent upon interactions with specific epigenetic partners. Understanding the nuanced interplay between CBX4 and epigenetic factors sheds light on potential therapeutic avenues in LUAD.

PHGDH is Key to a Prognostic Multigene Signature and a Potential Therapeutic Target in Acute Myeloid Leukemia

As a rate-limiting enzyme for the serine biosynthesis pathway (SSP) in the initial step, phosphoglycerate dehydrogenase (PHGDH) is overexpressed in many different tumors, and pharmacological or genetic inhibition of PHGDH promotes antitumor effects. In the present research, by analyzing several acute myeloid leukemia (AML) datasets in the Gene Expression Omnibus (GEO), we identified prognosis-related genes and constructed a multigene signature by univariate, multivariate Cox regression and LASSO regression. Subsequently, the multigene signature was confirmed through Cox, Kaplan-Meier, and ROC analyses in the validation cohort. Moreover, PHGDH acted as a risk factor and was correlated with inferior overall survival. We further analysed other datasets and found that PHGDH was overexpressed in AML. Importantly, the expression of PHGDH was higher in drug-resistant AML compared to drug-sensitive ones. In vitro experiments showed that inhibition of PHGDH induced apoptosis and reduced proliferation in AML cells, and these antitumor effects could be related to the Bcl-2/Bax signaling pathway by the noncanonical or nonmetabolic functions of PHGDH. In summary, we constructed a twenty-gene signature that could predicate prognosis of AML patients and found that PHGDH may be a potential target for AML treatment.

Serine synthesis pathway enzyme PHGDH is critical for muscle cell biomass, anabolic metabolism, and mTORC1 signaling

Cells use glycolytic intermediates for anabolism, e.g., via the serine synthesis and pentose phosphate pathways. However, we still understand poorly how these metabolic pathways contribute to skeletal muscle cell biomass generation. The first aim of this study was therefore to identify enzymes that limit protein synthesis, myotube size, and proliferation in skeletal muscle cells. We inhibited key enzymes of glycolysis, the pentose phosphate pathway, and the serine synthesis pathway to evaluate their importance in C2C12 myotube protein synthesis. Based on the results of this first screen, we then focused on the serine synthesis pathway enzyme phosphoglycerate dehydrogenase (PHGDH). We used two different PHGDH inhibitors and mouse C2C12 and human primary muscle cells to study the importance and function of PHGDH. Both myoblasts and myotubes incorporated glucose-derived carbon into proteins, RNA, and lipids, and we showed that PHGDH is essential in these processes. PHGDH inhibition decreased protein synthesis, myotube size, and myoblast proliferation without cytotoxic effects. The decreased protein synthesis in response to PHGDH inhibition appears to occur mainly mechanistic target of rapamycin complex 1 (mTORC1)-dependently, as was evident from experiments with insulin-like growth factor 1 and rapamycin. Further metabolomics analyses revealed that PHGDH inhibition accelerated glycolysis and altered amino acid, nucleotide, and lipid metabolism. Finally, we found that supplementing an antioxidant and redox modulator, N-acetylcysteine, partially rescued the decreased protein synthesis and mTORC1 signaling during PHGDH inhibition. The data suggest that PHGDH activity is critical for skeletal muscle cell biomass generation from glucose and that it regulates protein synthesis and mTORC1 signaling.NEW & NOTEWORTHY The use of glycolytic intermediates for anabolism was demonstrated in both myoblasts and myotubes, which incorporate glucose-derived carbon into proteins, RNA, and lipids. We identify phosphoglycerate dehydrogenase (PHGDH) as a critical enzyme in those processes and also for muscle cell hypertrophy, proliferation, protein synthesis, and mTORC1 signaling. Our results thus suggest that PHGDH in skeletal muscle is more than just a serine-synthesizing enzyme.

Low glucose metabolite 3-phosphoglycerate switches PHGDH from serine synthesis to p53 activation to control cell fate

Glycolytic intermediary metabolites such as fructose-1,6-bisphosphate can serve as signals, controlling metabolic states beyond energy metabolism. However, whether glycolytic metabolites also play a role in controlling cell fate remains unexplored. Here, we find that low levels of glycolytic metabolite 3-phosphoglycerate (3-PGA) can switch phosphoglycerate dehydrogenase (PHGDH) from cataplerosis serine synthesis to pro-apoptotic activation of p53. PHGDH is a p53-binding protein, and when unoccupied by 3-PGA interacts with the scaffold protein AXIN in complex with the kinase HIPK2, both of which are also p53-binding proteins. This leads to the formation of a multivalent p53-binding complex that allows HIPK2 to specifically phosphorylate p53-Ser46 and thereby promote apoptosis. Furthermore, we show that PHGDH mutants (R135W and V261M) that are constitutively bound to 3-PGA abolish p53 activation even under low glucose conditions, while the mutants (T57A and T78A) unable to bind 3-PGA cause constitutive p53 activation and apoptosis in hepatocellular carcinoma (HCC) cells, even in the presence of high glucose. In vivo, PHGDH-T57A induces apoptosis and inhibits the growth of diethylnitrosamine-induced mouse HCC, whereas PHGDH-R135W prevents apoptosis and promotes HCC growth, and knockout of Trp53 abolishes these effects above. Importantly, caloric restriction that lowers whole-body glucose levels can impede HCC growth dependent on PHGDH. Together, these results unveil a mechanism by which glucose availability autonomously controls p53 activity, providing a new paradigm of cell fate control by metabolic substrate availability.

PHGDH and cancer: new job for an old enzyme!

How do cancer cells bolster their energy metabolism under conditions of stress? Recent work by Shu et al (2022) unveils a novel, non-canonical function of the de novo serine synthesis pathway enzyme phosphoglycerate dehydrogenase (PHGDH) as a regulator of mitochondrial translation and tumor progression in liver cancer.