FAM120A couples SREBP-dependent transcription and splicing of lipogenesis enzymes downstream of mTORC1

Quantification of the inputs and outputs of serine and glycine metabolism in cancer cells

BACKGROUND

The significance of serine and glycine metabolism in cancer cells is increasingly acknowledged, yet the quantification of their metabolic flux remains incomplete, impeding a comprehensive understanding. This study aimed to quantify the metabolic flux of serine and glycine in cancer cells, focusing on their inputs and outputs, by means of Combinations of C-13 Isotopes Tracing and mathematical delineation, alongside Isotopically Nonstationary Metabolic Flux Analysis.

RESULTS

In HeLa cells, serine uptake, the serine synthesis pathway (SSP), and other sources (e.g., protein degradation) contribute 71.2 %, 24.0 %, and 5.7 %, respectively, to serine inputs. Conversely, glycine inputs stem from uptake (45.6 %), conversion from serine (45.1 %), and other sources (9.4 %). Serine input flux surpasses glycine by 7.3-fold. Serine predominantly directs a major fraction (94.7 %) to phospholipid, sphingolipid, and protein synthesis, with only a minor fraction (5.3 %) directing towards one-carbon unit and glycine production. Glycine mainly supports protein and nucleotide synthesis (100 %), without conversion back to serine. Serine output rate exceeds glycine output rate by 7.3-fold. Serine deprivation mainly impairs output to synthesis of phospholipid and sphingolipid, crucial for cell growth, while other outputs unaffected. AGS cells exhibit comparable serine and glycine flux to HeLa cells, albeit lacking SSP activity. Serine deprivation in AGS cells halts output flux to phospholipid, sphingolipid, protein synthesis, completely inhibiting cell growth.

CONCLUSIONS

By providing quantitative insights into serine and glycine metabolism, this study delineates the association of serine flux to different metabolic pathway with cancer cell growth and offers potential targets for therapeutic intervention, highlighting the importance of serine flux to pathway for the synthesis of phospholipids and sphingolipids in cancer cells growth.

Targeting lipid metabolism via nanomedicine: A prospective strategy for cancer therapy

Lipid metabolism has been increasingly recognized to play an influencing role in tumor initiation, progression, metastasis, and therapeutic drug resistance. Targeting lipid metabolic reprogramming represents a promising therapeutic strategy. Despite their structural complexity and poor targeting efficacy, lipid-metabolizing drugs, either used alone or in combination with chemotherapeutic agents, have been employed in clinical practice. The advent of nanotechnology offers new approaches to enhancing therapeutic effects, includingthe targeted delivery and integration of lipid metabolic reprogramming with chemotherapy, photodynamic therapy (PDT), and immunotherapy. The integrated nanoformulation, nanomedicine, could significantly advance the field of lipid metabolism therapy. In this review, we will briefly introduce the concept of cancer lipid metabolism reprogramming, then elaborate the latest advances in engineered nanomedicine for targeting lipid metabolism during cancer treatment, and finally provide our insights into future perspectives of nanomedicine for interference with lipid metabolism in the tumor microenvironment.

The splicing factor SRRM2 modulates two S6K kinases to promote colorectal cancer growth

The mechanistic target of rapamycin (mTOR) pathway plays a critical role in cell growth and metabolic homeostasis. The ribosomal protein S6 kinases S6K1 and S6K2 are the major effectors of the mTOR pathway key to translation efficiency, but the underlying regulatory mechanisms remain largely unclear. In this study, we searched for mTOR regulators and found that the splicing factor SRRM2 modulates the levels of S6K1 and S6K2, thereby activating the mTOR-S6K pathway. Interestingly, SRRM2 facilitates the expression of S6K2 by modulating alternative splicing, and enhances the stability of the S6K1 protein by regulating the E3 ubiquitin ligase WWP2. Moreover, SRRM2 is highly expressed in colorectal cancer (CRC) tissues and is associated with a poor prognosis. SRRM2 promotes CRC growth in vitro and in vivo. Combined, these data reveal an oncogenic role of SRRM2 in CRC through activating the mTOR-S6K pathway by two different approaches, further suggesting SRRM2 as a potential therapeutic target for CRC.

Survival strategies of cancer cells: the role of macropinocytosis in nutrient acquisition, metabolic reprogramming, and therapeutic targeting

Macropinocytosis is a nonselective form of endocytosis that allows cancer cells to largely take up the extracellular fluid and its contents, including nutrients, growth factors, etc. We first elaborate meticulously on the process of macropinocytosis. Only by thoroughly understanding this entire process can we devise targeted strategies against it. We then focus on the central role of the MTOR (mechanistic target of rapamycin kinase) complex 1 (MTORC1) in regulating macropinocytosis, highlighting its significance as a key signaling hub where various pathways converge to control nutrient uptake and metabolic processes. The article covers a comprehensive analysis of the literature on the molecular mechanisms governing macropinocytosis, including the initiation, maturation, and recycling of macropinosomes, with an emphasis on how these processes are hijacked by cancer cells to sustain their growth. Key discussions include the potential therapeutic strategies targeting macropinocytosis, such as enhancing drug delivery via this pathway, inhibiting macropinocytosis to starve cancer cells, blocking the degradation and recycling of macropinosomes, and inducing methuosis - a form of cell death triggered by excessive macropinocytosis. Targeting macropinocytosis represents a novel and innovative approach that could significantly advance the treatment of cancers that rely on this pathway for survival. Through continuous research and innovation, we look forward to developing more effective and safer anti-cancer therapies that will bring new hope to patients.Abbreviation: AMPK: AMP-activated protein kinase; ASOs: antisense oligonucleotides; CAD: carbamoyl-phosphate synthetase 2, aspartate transcarbamylase, and dihydroorotase; DC: dendritic cell; EGF: epidermal growth factor; EGFR: epidermal growth factor receptor; ERBB2: erb-b2 receptor tyrosine kinase 2; ESCRT: endosomal sorting complex required for transport; GAP: GTPase-activating protein; GEF: guanine nucleotide exchange factor; GRB2: growth factor receptor bound protein 2; LPP: lipopolyplex; MTOR: mechanistic target of rapamycin kinase; MTORC1: mechanistic target of rapamycin kinase complex 1; MTORC2: mechanistic target of rapamycin kinase complex 2; NSCLC: non-small cell lung cancer; PADC: pancreatic ductal adenocarcinoma; PDPK1: 3-phosphoinositide dependent protein kinase 1; PI3K: phosphoinositide 3-kinase; PIK3C3: phosphatidylinositol 3-kinase catalytic subunit type 3; PtdIns(3,4,5)P3: phosphatidylinositol-(3,4,5)-trisphosphate; PtdIns(4,5)P2: phosphatidylinositol-(4,5)-bisphosphate; PTT: photothermal therapies; RAC1: Rac family small GTPase 1; RPS6: ribosomal protein S6; RPS6KB1: ribosomal protein S6 kinase B1; RTKs: receptor tyrosine kinases; SREBF: sterol regulatory element binding transcription factor; TFEB: transcription factor EB; TNBC: triple-negative breast cancer; TSC2: TSC complex subunit 2; ULK1: unc-51 like autophagy activating kinase 1; UPS: ubiquitin-proteasome system.

The Central FacilitaTOR: Coordinating Transcription and Translation in Eukaryotes

One of the biggest challenges to eukaryotic gene expression is coordinating transcription in the nucleus and protein synthesis in the cytoplasm. However, little is known about how these major steps in gene expression are connected. The Target of Rapamycin (TOR) signaling pathway is crucial in connecting these critical phases of gene expression. Highly conserved among eukaryotic cells, TOR regulates growth, metabolism, and cellular equilibrium in response to changes in nutrients, energy levels, and stress conditions. This review examines the extensive role of TOR in gene expression regulation. We highlight how TOR is involved in phosphorylation, remodeling chromatin structure, and managing the factors that facilitate transcription and translation. Furthermore, the critical functions of TOR extend to processing RNA, assembling RNA-protein complexes, and managing their export from the nucleus, demonstrating its wide-reaching impact throughout the cell. Our discussion emphasizes the integral roles of TOR in bridging the processes of transcription and translation and explores how it orchestrates these complex cellular processes.

Splice age: mTORC1-mediated RNA splicing in metabolism and ageing

The target of rapamycin complex mTORC1 has key roles in cell growth and metabolism and its inhibition delays ageing. Recent work by Ogawa et al. in Caenorhabditis elegans argues that modulation of pre-mRNA splicing factors and alternative splicing are key mediators of mTORC1 signalling and can enhance longevity.

Defined Diets Link Iron and α-Linolenic Acid to Cyp1b1 Regulation of Neonatal Liver Development Through Srebp Forms and LncRNA H19

Cyp1b1 substantially affects hepatic vascular and stellate cells (HSC) with linkage to liver fibrosis. Despite minimal hepatocyte expression, Cyp1b1 deletion substantially impacts liver gene expression at birth and weaning. The appreciable Cyp1b1 expression in surrounding embryo mesenchyme, during early organogenesis, provides a likely source for Cyp1b1. Here defined breeder diets established major interconnected effects on neonatal liver of α-linolenic acid (ALA), vitamin A deficiency (VAD) and suboptimal iron fed mice. At birth Cyp1b1 deletion and VAD each activated perinatal HSC, while suppressing iron control by hepcidin. Cyp1b1 deletion also advanced the expression of diverse genes linked to iron regulation. Postnatal stimulations of Srebp-regulated genes in the fatty acid and cholesterol biosynthesis pathways were suppressed by Cyp1b1-deficiency. LncRNA H19 and the neutrophil alarmin S100a9 expression increased due to slower postnatal decline with Cyp1b1 deficiency. VAD reversed each of Cyp1b1 effect, probably due to enhanced HSC release of Apo-Rbp4. At birth, Cyp1b1 deletion enhanced H19 participation. Notably, a suppressor (Cnot3) decreased while an activity partner (Ezh2/H3K methylation) increased H19 expression. ALA elevated hepcidin mRNA and countered the inhibitory effects of Cyp1b1 deletion on hepcidin expression. Oxylipin metabolites of ALA from highly expressed hepatic Cyps are potential mediators. Cyp expression patterns demonstrated female dimorphism for neonatal liver. Mothers followed one of three fetal growth support programs probably linked to maturity at conception.

mTOR-related linc-PMB promotes mitochondrial biogenesis via stabilizing SIRT1 mRNA through binding to the HuR protein

Mitochondrial dysfunction is implicated in numerous disorders, including type 2 diabetes, Alzheimer's disease and cancer. Long non-coding RNAs (lncRNAs) are emerging as pivotal regulators of cellular energy metabolism, yet their roles remain largely unclear. In this study, we identify an lncRNA named linc-PMB, which is associated with mTOR and promotes mitochondrial biogenesis, through microarray analysis. We demonstrate that the knockdown of linc-PMB results in significantly impaired mitochondrial respiration and biogenesis, along with altered expressions of related genes. Conversely, overexpression of linc-PMB markedly increases mitochondrial function. We further reveal that linc-PMB interacts with the RNA-binding protein HuR, promoting the stabilization of SIRT1 mRNA and a substantial increase in SIRT1 expression, which in turn activates the PGC-1α/mtTFA pathway and mitochondrial biogenesis. Collectively, our findings reveal a novel regulatory pathway in which linc-PMB, through its interaction with HuR, modulates the SIRT1/PGC-1α/mtTFA axis to maintain mitochondrial biogenesis and function.

mTORC1, the maestro of cell metabolism and growth

The mechanistic target of rapamycin (mTOR) pathway senses and integrates various environmental and intracellular cues to regulate cell growth and proliferation. As a key conductor of the balance between anabolic and catabolic processes, mTOR complex 1 (mTORC1) orchestrates the symphonic regulation of glycolysis, nucleic acid and lipid metabolism, protein translation and degradation, and gene expression. Dysregulation of the mTOR pathway is linked to numerous human diseases, including cancer, neurodegenerative disorders, obesity, diabetes, and aging. This review provides an in-depth understanding of how nutrients and growth signals are coordinated to influence mTOR signaling and the extensive metabolic rewiring under its command. Additionally, we discuss the use of mTORC1 inhibitors in various aging-associated metabolic diseases and the current and future potential for targeting mTOR in clinical settings. By deciphering the complex landscape of mTORC1 signaling, this review aims to inform novel therapeutic strategies and provide a road map for future research endeavors in this dynamic and rapidly evolving field.

Nutrient control of growth and metabolism through mTORC1 regulation of mRNA splicing

Cellular growth and organismal development are remarkably complex processes that require the nutrient-responsive kinase mechanistic target of rapamycin complex 1 (mTORC1). Anticipating that important mTORC1 functions remained to be identified, we employed genetic and bioinformatic screening in C. elegans to uncover mechanisms of mTORC1 action. Here, we show that during larval growth, nutrients induce an extensive reprogramming of gene expression and alternative mRNA splicing by acting through mTORC1. mTORC1 regulates mRNA splicing and the production of protein-coding mRNA isoforms largely independently of its target p70 S6 kinase (S6K) by increasing the activity of the serine/arginine-rich (SR) protein RSP-6 (SRSF3/7) and other splicing factors. mTORC1-mediated mRNA splicing regulation is critical for growth; mediates nutrient control of mechanisms that include energy, nucleotide, amino acid, and other metabolic pathways; and may be conserved in humans. Although mTORC1 inhibition delays aging, mTORC1-induced mRNA splicing promotes longevity, suggesting that when mTORC1 is inhibited, enhancement of this splicing might provide additional anti-aging benefits.

The ataxia-telangiectasia disease protein ATM controls vesicular protein secretion via CHGA and microtubule dynamics via CRMP5

The autosomal recessive disease ataxia-telangiectasia (A-T) presents with cerebellar degeneration, immunodeficiency, radiosensitivity, capillary dilatations, and pulmonary infections. Most symptoms outside the nervous system can be explained by failures of the disease protein ATM as a Ser/Thr-kinase to coordinate DNA damage repair. However, ATM in adult neurons has cytoplasmic localization and vesicle association, where its roles remain unclear. Here, we defined novel ATM protein targets in human neuroblastoma cells, and filtered initial pathogenesis events in ATM-null mouse cerebellum. Profiles of global proteome and phosphoproteomics - both direct ATM/ATR substrates and overall phosphorylation changes - confirmed previous findings for NBN, MRE11, MDC1, CHEK1, EIF4EBP1, AP3B2, PPP2R5C, SYN1 and SLC2A1. Even stronger downregulation of ATM/ATR substrate phosphopeptides after ATM-depletion was documented for CHGA, EXPH5, NBEAL2 and CHMP6 as key factors of protein secretion and endosome dynamics, as well as for CRMP5, DISP2, PHACTR1, PLXNC1, INA and TPX2 as neurite extension factors. Prominent effects on semaphorin-CRMP5-microtubule signals and ATM association with CRMP5 were validated. As a functional consequence, microtubules were stabilized, and neurite retraction ensued. The impact of ATM on secretory granules confirms previous ATM-null cerebellar transcriptome findings. This study provides the first link of A-T neural atrophy to growth cone collapse and aberrant microtubule dynamics.

Metabolic regulation of mRNA splicing

Alternative mRNA splicing enables the diversification of the proteome from a static genome and confers plasticity and adaptiveness on cells. Although this is often explored in development, where hard-wired programs drive the differentiation and specialization, alternative mRNA splicing also offers a way for cells to react to sudden changes in outside stimuli such as small-molecule metabolites. Fluctuations in metabolite levels and availability in particular convey crucial information to which cells react and adapt. We summarize and highlight findings surrounding the metabolic regulation of mRNA splicing. We discuss the principles underlying the biochemistry and biophysical properties of mRNA splicing, and propose how these could intersect with metabolite levels. Further, we present examples in which metabolites directly influence RNA-binding proteins and splicing factors. We also discuss the interplay between alternative mRNA splicing and metabolite-responsive signaling pathways. We hope to inspire future research to obtain a holistic picture of alternative mRNA splicing in response to metabolic cues.

FAM120A deficiency improves resistance to cisplatin in gastric cancer by promoting ferroptosis

The occurrence of chemoresistance is an inescapable obstacle affecting the clinical efficacy of cisplatin in gastric cancer (GC). Exploring the regulatory mechanism of cisplatin resistance will help to provide potential effective targets for improving the prognosis of gastric cancer patients. Here, we find that FAM120A is upregulated in GC tissues and higher in cisplatin-resistant GC tissues, and its high expression is positively correlated with the poor outcome of GC patients. Functional studies indicate that FAM120A confers chemoresistance to GC cells by inhibiting ferroptosis. Mechanically, METTL3-induced m6A modification and YTHDC1-induced stability of FAM120A mRNA enhance FAM120A expression. FAM120A inhibits ferroptosis by binding SLC7A11 mRNA and enhancing its stability. FAM120A deficiency enhances cisplatin sensitivity by promoting ferroptosis in vivo. These results reveal the function of FAM120A in chemotherapy tolerance and targeting FAM120A is an effective strategy to alleviate cisplatin resistance in GC.

Chitosan-Based Sustained Expression of Sterol Regulatory Element-Binding Protein 1a Stimulates Hepatic Glucose Oxidation and Growth in Sparus aurata

The administration of a single dose of chitosan nanoparticles driving the expression of sterol regulatory element-binding protein 1a (SREBP1a) was recently associated with the enhanced conversion of carbohydrates into lipids. To address the effects of the long-lasting expression of SREBP1a on the growth and liver intermediary metabolism of carnivorous fish, chitosan-tripolyphosphate (TPP) nanoparticles complexed with a plasmid expressing the N terminal active domain of hamster SREBP1a (pSG5-SREBP1a) were injected intraperitoneally every 4 weeks (three doses in total) to gilthead sea bream (Sparus aurata) fed high-protein-low-carbohydrate and low-protein-high-carbohydrate diets. Following 70 days of treatment, chitosan-TPP-pSG5-SREBP1a nanoparticles led to the sustained upregulation of SREBP1a in the liver of S. aurata. Independently of the diet, SREBP1a overexpression significantly increased their weight gain, specific growth rate, and protein efficiency ratio but decreased their feed conversion ratio. In agreement with an improved conversion of dietary carbohydrates into lipids, SREBP1a expression increased serum triglycerides and cholesterol as well as hepatic glucose oxidation via glycolysis and the pentose phosphate pathway, while not affecting gluconeogenesis and transamination. Our findings support that the periodical administration of chitosan-TPP-DNA nanoparticles to overexpress SREBP1a in the liver enhanced the growth performance of S. aurata through a mechanism that enabled protein sparing by enhancing dietary carbohydrate metabolisation.