Acetate Reprograms Tumor Metabolism and Promotes Immune Evasion and PD-L1 Expression by Upregulating c-myc

Introduction

Reprogramming of tumor metabolism is of great significance in cancer research, and acetate plays a crucial role in this process. In tumor cells, acetate is an important precursor of acetyl-CoA, which is used for energy production, lipid synthesis, and protein acetylation. However, it remains unclear whether acetate can reprogram tumor metabolism and play a role in tumor immune evasion. Therefore, this study aims to explore the role of acetate in non-small cell lung cancer (NSCLC) and its potential mechanisms.

Source of the Paper

This study was co-authored by Juhong Wang, Yannan Yang, Fei Shao, Jie He from the Chinese Academy of Medical Sciences and Peking Union Medical College, and Ying Meng, Dong Guo, and Zhimin Lu from the Zhejiang University School of Medicine. The paper was published in the May 2024 issue of Nature Metabolism.

Research Process

Study Design

1. Initial Metabolomic Analysis: Metabolomic analysis of 14 human NSCLC specimens revealed that acetate was the most abundant short-chain fatty acid.
2. Isotopic Tracer Experiments: By injecting 13C or 3D-labeled acetate into mice, a significant increase in acetyl-CoA was observed in tumor tissues.
3. Gene Knockout Experiments: Using shRNA technology to knock out the acetate transporter gene MCT1, the levels of acetyl-CoA and newly synthesized fatty acids were significantly reduced, and tumor growth was inhibited.
4. Cell Experiments and Animal Models: Under low-glucose conditions, acetate significantly increased the proliferation of NSCLC cells, and dietary supplementation of acetate reversed the glucose deprivation-induced decrease in acetyl-CoA.
5. Protein Functional Analysis: The study revealed the crucial role of the dlat protein in the acetate-mediated acetylation of c-myc.

Data Analysis and Experimental Methods

• Metabolomics: Mass spectrometry was used to analyze the concentration of acetate in NSCLC.
• Isotopic Tracing: 13C or 3D-labeled acetate was used in combination with mass spectrometry and positron emission tomography (PET) imaging.
• Gene Expression and Protein Analysis: RT-qPCR, Western blotting, and immunofluorescence techniques were employed.
• Cell and Animal Model Experiments: The effects of acetate on tumor cell proliferation and glucose metabolism were observed through gene knockdown and cell culture experiments.
• Protein-Protein Interaction Studies: Immunoprecipitation and mass spectrometry were used to detect the interaction between dlat and c-myc.

Research Results

Experimental Findings

1. Metabolic Changes: In NSCLC tumors, the concentration of acetate was significantly higher than in normal tissues, and after injection of 13C or 3D-labeled acetate, the level of acetyl-CoA in tumor tissues increased significantly.
2. Gene Knockout Effects: Knocking out MCT1 significantly reduced the levels of acetyl-CoA and newly synthesized fatty acids in NSCLC cells, and significantly inhibited tumor growth.
3. Acetate Promotes Cell Proliferation: Under low-glucose conditions, supplementation of acetate significantly promoted the proliferation of NSCLC cells and significantly reversed the glucose deprivation-induced decrease in acetyl-CoA.
4. Protein Acetylation and Its Mechanism: Mass spectrometry analysis revealed that c-myc is a significantly acetylated target, and its acetylation at Lys148 can significantly increase the stability and expression of the c-myc protein.
5. Role of dlat: It was discovered that dlat acts as an acetyl transferase on the Lys148 position of c-myc, thereby inhibiting its ubiquitination and degradation, ultimately increasing the stability and expression of c-myc.

Main Results

• Role of MCT1 in Tumors: Mouse models with MCT1 gene knockout showed significantly reduced acetate uptake and acetyl-CoA levels, and tumor growth was markedly inhibited.
• Interaction between dlat and c-myc: Experiments demonstrated that dlat enhances the stability of c-myc through acetylation and prevents its degradation by inhibiting c-myc ubiquitination.
• Immune Evasion and PD-L1 Expression: Experiments showed that acetylation of c-myc significantly increased the expression of PD-L1, thereby inhibiting the activation of CD8+ T cells.

Conclusion

This study revealed the role of acetate in reprogramming NSCLC metabolism, particularly under low-glucose conditions. It was discovered that dlat can acetylate c-myc, thereby increasing the stability and expression of c-myc, further promoting the expression of PD-L1, leading to tumor immune evasion. Additionally, the research demonstrated that inhibiting the uptake and utilization of acetate can help suppress tumor growth and enhance the effectiveness of anti-PD-1 immunotherapy.

Research Highlights

• Crucial Role of Acetate: For the first time, this study systematically revealed the crucial role of acetate in tumor metabolism and immune evasion.
• New Function of dlat: The study uncovered the novel role of dlat as a protein acetyl transferase, a “multifunctional” role.
• Positive Feedback Mechanism: By regulating MCT1 expression, a positive feedback mechanism was formed for acetate uptake and metabolism.
• Clinical Significance: The research results suggest that modulating acetate metabolism could provide new directions for the treatment of NSCLC and enhance the effectiveness of immunotherapy.

Summary

This study, through detailed data and experiments, elucidated the role and mechanisms of acetate in NSCLC, providing new insights into the mechanisms of tumor metabolism and immune evasion. By inhibiting the uptake and utilization of acetate, not only can tumor growth be slowed, but the effectiveness of anti-PD-1 therapy can also be enhanced, offering important recommendations for future research and clinical applications in cancer treatment.