This study reveals a novel mechanism by which the bacterial signaling molecule c-di-GMP suppresses cancer metastasis through direct binding to PSMD3, thereby inhibiting the NF-κB pathway independently of the STING pathway, providing a potential target for developing new anti-metastatic therapies.
Literature Overview
The article titled 'Cyclic di-GMP suppresses cancer metastasis by targeting proteasome 26S subunit non-ATPase 3 independently of STING,' published in the journal Signal Transduction and Targeted Therapy, reviews and summarizes the newly discovered function and molecular mechanism of the bacterial second messenger c-di-GMP in suppressing cancer metastasis. The study finds that c-di-GMP significantly inhibits migration and in vivo metastasis of various cancer cells even at low doses, and this effect is independent of the well-known STING pathway. Instead, c-di-GMP directly binds to the protein PSMD3, blocking its interaction with TBK1 and subsequently suppressing activation of the NF-κB signaling pathway. Furthermore, PSMD3 is highly expressed in aggressive tumors such as triple-negative breast cancer (TNBC) and correlates with poor prognosis, suggesting its potential as a therapeutic target. These findings expand the biological functions of c-di-GMP and offer new strategies for anti-metastasis therapy.Background Knowledge
Cancer metastasis is the leading cause of cancer-related deaths. In particular, triple-negative breast cancer (TNBC) lacks defined therapeutic targets, limiting treatment options primarily to chemotherapy, which is often associated with drug resistance and recurrence. Therefore, identifying new drivers of metastasis and therapeutic targets is crucial. The NF-κB signaling pathway plays a key role in tumor progression and metastasis by promoting the expression of inflammatory and chemotactic factors, thereby enhancing cancer cell invasiveness and migratory capacity. The STING pathway, a key sensor in innate immunity, can be activated by cyclic dinucleotides such as c-di-GMP and is widely explored in cancer immunotherapy. However, whether c-di-GMP possesses anti-tumor functions independent of STING remains unclear. PSMD3 is a regulatory subunit of the 19S proteasome, traditionally involved in ubiquitin-proteasome degradation. Its non-canonical roles in cancer have not been fully elucidated. This study is based on the hypothesis that c-di-GMP may exert direct anti-metastatic effects independent of immune modulation, systematically exploring its direct intracellular targets and signaling mechanisms to provide a theoretical foundation for developing novel anti-metastatic drugs.
Research Methods and Experiments
Researchers first evaluated the effects of c-di-GMP on cell viability and migration in multiple human cancer cell lines, finding that it significantly inhibited cell migration even at low concentrations. Subsequently, a mouse lung metastasis model via tail vein injection was used to confirm the anti-metastatic effect of c-di-GMP in vivo and to assess its toxicity. To investigate whether this effect depends on STING, STING expression levels in different cancer cells were measured, and migration assays were performed using STING-knockout cells. RNA-seq analysis of transcriptomic changes after c-di-GMP treatment revealed significant downregulation of the NF-κB pathway. Further, biotin-labeled c-di-GMP was used in pull-down assays coupled with mass spectrometry to identify PSMD3 as a high-affinity binding protein. Direct binding between c-di-GMP and PSMD3 was confirmed using CETSA, SPR, and ITC assays. Co-IP and truncation experiments were employed to map the interaction domain between PSMD3 and TBK1. Finally, siRNA-mediated knockdown of PSMD3 was used to validate its functional role in the TBK1-NF-κB pathway, and clinical database analyses were conducted to examine the expression and prognostic relevance of PSMD3 in breast cancer.Key Conclusions and Perspectives
Research Significance and Prospects
This study unveils a previously unknown mechanism by which c-di-GMP suppresses cancer metastasis through targeting the PSMD3-TBK1-NF-κB axis, expanding the biological functions of c-di-GMP and suggesting its potential not only as an immune modulator but also as a direct anti-metastatic agent. PSMD3, identified as a novel positive regulator of the NF-κB pathway, presents a new therapeutic target through its non-proteasomal function. Given that systemic inhibition of the NF-κB pathway often causes severe side effects, targeting upstream specific regulators such as PSMD3 may allow for more precise intervention with reduced toxicity.
Future studies could further explore the role of PSMD3 in other cancer types and develop high-affinity small-molecule inhibitors targeting the PSMD3-TBK1 interaction. Additionally, the stability, delivery efficiency, and efficacy of c-di-GMP in other metastasis models require further optimization and validation. Evaluating the synergistic anti-tumor effects of c-di-GMP in combination with immunotherapy or chemotherapy will also be important translational directions. This work lays a solid foundation for developing anti-metastatic therapies based on c-di-GMP or PSMD3 targeting.
Conclusion
This study systematically elucidates a novel mechanism by which the bacterial signaling molecule c-di-GMP inhibits cancer metastasis—through direct binding to the protein PSMD3, disrupting its interaction with TBK1, thereby suppressing activation of the NF-κB signaling pathway and ultimately inhibiting cancer cell migration and in vivo metastasis. This process is independent of the canonical STING pathway, revealing a non-immune-dependent anti-tumor function of c-di-GMP. PSMD3 is identified as a novel positive regulator of the NF-κB pathway, highly expressed in aggressive cancers such as triple-negative breast cancer and associated with poor prognosis, underscoring its value as a therapeutic target. c-di-GMP demonstrates potent and low-toxicity anti-metastatic activity in mouse models, supporting its development as a potential therapeutic agent. This research not only expands our understanding of the non-canonical functions of PSMD3 but also provides new strategies for precision targeting of the NF-κB pathway, holding significant translational medical implications. Future efforts may focus on developing novel anti-metastatic drugs based on this pathway or optimizing c-di-GMP delivery systems to enhance clinical potential.
