Malonyl-CoA is a conserved endogenous ATP-competitive mTORC1 inhibitor

FASN regulates STING palmitoylation via malonyl-CoA in macrophages to alleviate sepsis-induced liver injury

STING (stimulator of interferon genes) is a critical immunoregulatory protein in sepsis and is regulated by various mechanisms, especially palmitoylation. FASN (fatty acid synthase) is the rate-limiting enzyme to generate cellular palmitic acid (PA) via acetyl-CoA and malonyl-CoA and participates in protein palmitoylation. However, the mechanisms underlying the interaction between STING and FASN have not been completely understood. In this study, STING-knockout mice were used to confirm the pivotal role of STING in sepsis-induced liver injury. Metabolomics confirmed the dyslipidemia in septic mice and patients. The compounds library was screened, revealing that FASN inhibitors exerted a significant inhibitory effect on the STING pathway. Mechanically, the regulatory effect of FASN on the STING pathway was dependent on palmitoylation. Further experiments indicated that the upstream of FASN, malonyl-CoA inhibited STING pathway possibly due to C91 (palmitoylated residue) of STING. Overall, this study reveals a novel paradigm of STING regulation and provides a new perspective on immunity and metabolism.

Emerging targets in lipid metabolism for cancer therapy

Cancer cells perturb lipid metabolic pathways for a variety of pro-tumorigenic functions, and deregulated cellular metabolism is a hallmark of cancer cells. Although alterations in lipid metabolism in cancer cells have been appreciated for over 20 years, there are no FDA-approved cancer treatments that target lipid-related pathways. Recent advances pertaining to cancer cell fatty acid synthesis (FAS), desaturation, and uptake, microenvironmental and dietary lipids, and lipid metabolism of tumor-infiltrating immune cells have illuminated promising clinical applications for targeting lipid metabolism. This review highlights emerging pathways and targets for tumor lipid metabolism that may soon impact clinical treatment.

Malate, a natural inhibitor of 6PGD, improves the efficacy of chemotherapy in lung cancer

OBJECTIVE

Metabolic reprogramming is an important coordinator of tumor development and resistance to therapy, such as the tendency of tumor cells to utilize glycolytic energy rather than oxidative phosphorylation, even under conditions of sufficient oxygen. Therefore, targeting metabolic enzymes is an effective strategy to overcome therapeutic resistance.

MATERIALS AND METHODS

We explored the differential expression and growth-promoting function of MDH2 by immunohistochemistry and immunoblotting experiments in lung cancer patients and lung cancer cells. Pentose phosphate pathway-related phenotypes (including ROS levels, NADPH levels, and DNA synthesis) were detected intracellularly, and the interaction of malate and proteinase 6PGD was detected in vitro. In vivo experiments using implanted xenograft mouse models to explore the growth inhibitory effect and pro-chemotherapeutic function of dimethyl malate (DMM) on lung cancer.

RESULTS

We found that the expression of malate dehydrogenase (MDH2) in the tricarboxylic acid cycle (TCA cycle) was increased in lung cancer. Biological function enrichment analysis revealed that MDH2 not only promoted oxidative phosphorylation, but also promoted the pentose phosphate pathway (PPP pathway). Mechanistically, it was found that malate, the substrate of MDH2, can bind to the PPP pathway metabolic enzyme 6PGD, inhibit its activity, reduce the generation of NADPH, and block DNA synthesis. More importantly, DMM can improve the sensitivity of lung cancer to the clinical drug cisplatin.

CONCLUSION

We have identified malate as a natural inhibitor of 6PGD, which will provide new leads for the development of 6PGD inhibitors. In addition, the metabolic enzyme MDH2 and the metabolite malate may provide a backup option for cells to inhibit their own carcinogenesis, as the accumulated malate targets 6PGD to block the PPP pathway and inhibit cell cycle progression.

A fast-acting lipid checkpoint in G1 prevents mitotic defects

Lipid synthesis increases during the cell cycle to ensure sufficient membrane mass, but how insufficient synthesis restricts cell-cycle entry is not understood. Here, we identify a lipid checkpoint in G1 phase of the mammalian cell cycle by using live single-cell imaging, lipidome, and transcriptome analysis of a non-transformed cell. We show that synthesis of fatty acids in G1 not only increases lipid mass but extensively shifts the lipid composition to unsaturated phospholipids and neutral lipids. Strikingly, acute lowering of lipid synthesis rapidly activates the PERK/ATF4 endoplasmic reticulum (ER) stress pathway that blocks cell-cycle entry by increasing p21 levels, decreasing Cyclin D levels, and suppressing Retinoblastoma protein phosphorylation. Together, our study identifies a rapid anticipatory ER lipid checkpoint in G1 that prevents cells from starting the cell cycle as long as lipid synthesis is low, thereby preventing mitotic defects, which are triggered by low lipid synthesis much later in mitosis.

Cytochrome c levels affect the TOR pathway to regulate growth and metabolism under energy-deficient conditions

Mitochondrial function is essential for plant growth, but the mechanisms involved in adjusting growth and metabolism to changes in mitochondrial energy production are not fully understood. We studied plants with reduced expression of CYTC-1, one of two genes encoding the respiratory chain component cytochrome c (CYTc) in Arabidopsis, to understand how mitochondria communicate their status to coordinate metabolism and growth. Plants with CYTc deficiency show decreased mitochondrial membrane potential and lower ATP content, even when carbon sources are present. They also exhibit higher free amino acid content, induced autophagy, and increased resistance to nutritional stress caused by prolonged darkness, similar to plants with triggered starvation signals. CYTc deficiency affects target of rapamycin (TOR)-pathway activation, reducing S6 kinase (S6K) and RPS6A phosphorylation, as well as total S6K protein levels due to increased protein degradation via proteasome and autophagy. TOR overexpression restores growth and other parameters affected in cytc-1 mutants, even if mitochondrial membrane potential and ATP levels remain low. We propose that CYTc-deficient plants coordinate their metabolism and energy availability by reducing TOR-pathway activation as a preventive signal to adjust growth in anticipation of energy exhaustion, thus providing a mechanism by which changes in mitochondrial activity are transduced to the rest of the cell.