ADSL-Generated Fumarate Binds and Inhibits STING to Promote Tumour Immune Evasion

Immunology Cell Biology Oncology Life Sciences Medicine
tumour immune evasion STING inhibition ADSL fumarate breast cancer

Research Background

In the tumor microenvironment, highly aggressive tumors evade immune system attacks by suppressing the cGAS-STING signaling pathway. The cGAS-STING pathway is a critical mechanism for cells to sense cytoplasmic double-stranded DNA and initiate immune responses. cGAS (cyclic GMP-AMP synthase) catalyzes the production of cGAMP upon binding to DNA, which then binds to STING (stimulator of interferon genes), activating downstream TBK1 and IRF3, ultimately inducing the expression of type I interferons (IFNs) and triggering anti-tumor immune responses. However, the mechanisms by which tumor cells inhibit STING activation remain unclear. This study aims to reveal how tumor cells suppress the STING pathway through fumarate generated by ADSL (adenylosuccinate lyase) under hypoxic conditions, thereby promoting tumor immune evasion.

Research Source

This study was conducted by Yuran Duan, Zhiqiang Hu, and their team from Zhejiang University and other institutions. The paper was published in April 2025 in the journal Nature Cell Biology, titled “ADSL-generated fumarate binds and inhibits STING to promote tumour immune evasion.”

Research Process and Results

1. ADSL Inhibits STING Activation Under Hypoxia

The study first found that hypoxia significantly activates the STING pathway in normal mammary epithelial cells, but this phenomenon was not observed in breast cancer cells. Through mass spectrometry analysis and co-immunoprecipitation experiments, researchers discovered that ADSL is highly expressed in breast cancer cells and binds to STING under hypoxic conditions. Further experiments demonstrated that ADSL inhibits the binding of cGAMP to STING through the fumarate it generates, thereby suppressing STING activation.

2. Phosphorylation of ADSL and Its Interaction with STING

The study revealed that under hypoxic conditions, IKKβ (IκB kinase β) phosphorylates the threonine at position 350 (T350) of ADSL, promoting its translocation to the endoplasmic reticulum (ER) and its binding to STING. In vitro kinase assays and mass spectrometry analysis confirmed IKKβ-mediated phosphorylation of ADSL T350. Additionally, the phosphorylation of ADSL T350 depends on its C-terminal ER translocation signal sequence and its interaction with KDELR3 (KDEL endoplasmic reticulum protein retention receptor 3).

3. Binding of Fumarate to STING and Its Inhibitory Effect

Through protein thermal shift assays and molecular dynamics simulations, researchers found that fumarate can bind to STING and competitively inhibit the binding of cGAMP to STING. Further experiments demonstrated that fumarate generated by ADSL inhibits STING activation by binding to the T263 site of STING. This discovery reveals the novel function of fumarate as a natural ligand of STING.

4. ADSL-Mediated STING Inhibition Promotes Tumor Immune Evasion

In in vivo experiments, researchers found that the phosphorylation level of ADSL T350 is inversely correlated with STING activation levels and is associated with poor prognosis in breast cancer patients. By constructing breast cancer cell models with ADSL mutants (T350A, E481/L482A, and A291V), researchers observed that these mutants enhanced STING activation, suppressed tumor growth, and increased the infiltration and activity of immune cells in the tumor microenvironment.

5. Development of ADSL ER-Blocking Peptide and Its Anti-Tumor Effects

To block ADSL-mediated STING inhibition, researchers designed an ADSL ER-blocking peptide that prevents ADSL translocation to the ER, thereby restoring STING activation. In vivo experiments demonstrated that the ADSL ER-blocking peptide significantly inhibits tumor growth and enhances the therapeutic effect of anti-PD-1 antibodies. Additionally, the ADSL ER-blocking peptide enhances the anti-tumor activity of CD8+ T cells, an effect dependent on the presence of CDC1 cells and Ly6Ehi neutrophils.

Research Conclusions and Significance

This study reveals a novel mechanism by which ADSL inhibits STING activation through the generation of fumarate, elucidating the molecular basis of tumor immune evasion under hypoxic conditions. The study not only uncovers the new function of fumarate as a natural ligand of STING but also develops the ADSL ER-blocking peptide as a potential strategy for tumor immunotherapy. This research provides new insights into improving the efficacy of immune checkpoint therapy and has significant scientific and clinical implications.

Research Highlights

  1. Discovery of a Novel Mechanism: For the first time, the study reveals the mechanism by which ADSL inhibits STING activation through fumarate generation, uncovering a new pathway for tumor immune evasion.
  2. New Function of Fumarate: The study identifies fumarate as a natural ligand of STING, expanding its role in tumor metabolism and immune regulation.
  3. Innovative Therapeutic Strategy: The development of the ADSL ER-blocking peptide effectively restores STING activation and enhances the therapeutic effect of anti-PD-1 antibodies.
  4. Clinical Relevance: The phosphorylation level of ADSL T350 is associated with poor prognosis in breast cancer patients, providing a new biomarker for breast cancer prognosis.

Other Valuable Information

The study also found that ADSL-mediated STING inhibition depends on its interaction with KDELR3, providing a theoretical basis for developing new ADSL-targeting drugs. Additionally, the application of the ADSL ER-blocking peptide is not limited to breast cancer and may have broad therapeutic potential for other types of tumors.