Mechanism Study on 5-Hydroxytryptamine Regulating Histone Modifications to Drive Liver Metastasis

Academic Background

Cancer metastasis is one of the leading causes of cancer patient mortality, especially visceral organ metastases such as liver metastasis (liver metastasis). Neuroendocrine tumors (NETs) are a class of highly metastatic tumors, among which neuroendocrine prostate cancer (NEPC) and small cell lung cancer (SCLC) have high rates of liver metastasis and extremely poor prognosis. Despite significant progress in understanding cancer metastasis mechanisms, the role of neurotransmitters (neurotransmitter) in promoting metastasis through interactions with immune cells in neuroendocrine tumors remains unclear.

5-hydroxytryptamine (5-HT) is an important neurotransmitter, and recent studies have found it plays a crucial role in cancer progression. For example, 5-HT can promote tumor cell proliferation and invasion. However, whether 5-HT promotes cancer metastasis by regulating immune cells (such as neutrophils) in the tumor microenvironment remains an unsolved mystery. Neutrophil extracellular traps (NETs) are web-like structures composed of DNA and antimicrobial proteins released by neutrophils, originally used to kill pathogens. Recent studies have shown that NETs may promote metastasis in cancer by attracting circulating tumor cells or activating dormant cancer cells.

Therefore, this study aims to explore whether 5-HT induces NET formation by regulating histone modifications in neutrophils, thereby promoting liver metastasis in neuroendocrine tumors.

Paper Source

This paper was co-authored by Kaiyuan Liu, Yingchao Zhang, and multiple researchers from institutions including Shanghai Jiao Tong University School of Medicine, Renji Hospital, and Shanghai Cancer Institute. The paper was published in Journal of Clinical Investigation (JCI) in 2025, titled “5-ht orchestrates histone serotonylation and citrullination to drive neutrophil extracellular traps and liver metastasis”.

Research Process and Results

1. Role of Neutrophils and NETs in NEPC Liver Metastasis

The research team first analyzed the SU2C prostate cancer dataset using a multi-omics analysis tool called IOBR, discovering that the infiltration level of neutrophils in liver metastases was significantly higher than in other metastatic sites. Further experiments using a mouse model (NEPC liver metastasis model) confirmed through flow cytometry and immunofluorescence staining that there was substantial infiltration of neutrophils and NET formation in early-stage liver metastases.

Experiments showed that NET formation promoted migration and adhesion of NEPC cells, while treatment with DNase I (an enzyme that degrades NETs) significantly reduced the number of liver metastases and extended the survival of mice. These results suggest that neutrophils and NETs play a critical role in NEPC liver metastasis.

2. NEPC-Derived 5-HT Promotes NET Formation and Liver Metastasis

The research team found that NEPC cells highly express the 5-HT synthesis enzyme TPH1 and secrete large amounts of 5-HT. In vitro experiments demonstrated that 5-HT could significantly induce NET formation in both murine and human neutrophils. Further experiments revealed that NEPC cells with TPH1 gene knockdown were unable to effectively induce NET formation, but supplementation with 5-HT restored this function.

In mouse models, NEPC cells with TPH1 knockdown had significantly reduced liver metastasis capacity, which was reversed by 5-HT supplementation. These results indicate that 5-HT secreted by NEPC promotes liver metastasis by inducing NET formation.

3. TGM2-Mediated Histone Serotonylation (H3Q5ser) Promotes NET Formation

The research team further explored the molecular mechanism by which 5-HT induces NET formation. They found that after entering neutrophils via the serotonin transporter (serotonin transporter, SERT), 5-HT is catalyzed by transglutaminase 2 (TGM2) to cause serotonylation at the 5th glutamine residue of histone H3 (H3Q5ser), leading to chromatin decondensation and NET formation.

Experiments showed that TGM2 inhibitors or SERT inhibitors like fluoxetine (fluoxetine) significantly inhibited 5-HT-induced H3Q5ser and NET formation. Additionally, neutrophils from TGM2 knockout mice were unable to effectively form NETs. These results confirm that TGM2-mediated H3Q5ser plays a key role in NET formation.

4. TGM2 and PAD4 Collaboratively Regulate Histone Modifications

The research team also discovered a mutually reinforcing effect between H3Q5ser and histone citrullination (histone citrullination, H3cit). PAD4 is the key enzyme that catalyzes H3cit, and TGM2 and PAD4 can physically interact to jointly promote the deposition of H3Q5ser and H3cit. Experiments showed that inhibiting either TGM2 or PAD4 led to a decrease in these two histone modifications and inhibited NET formation.

Further in vitro experiments and genomic analyses (such as CUT&Tag sequencing) revealed significant co-localization of H3Q5ser and H3cit on the genome and their joint regulation of genes related to NET formation.

5. Potential Therapeutic Value of Targeting the 5-HT Signaling Pathway

The research team found that the SERT inhibitor fluoxetine (Zoloft) effectively inhibited liver metastasis in NEPC, SCLC, and medullary thyroid cancer (medullary thyroid cancer). In mouse models, fluoxetine significantly reduced the number of liver metastases and inhibited H3Q5ser and NET formation.

Conclusion and Significance

This study reveals the molecular mechanism by which 5-HT induces TGM2-mediated histone serotonylation and PAD4-mediated histone citrullination, promoting NET formation in neutrophils and driving liver metastasis in neuroendocrine tumors. This discovery not only expands our understanding of the role of neurotransmitters in cancer metastasis but also provides new insights for targeting the 5-HT signaling pathway in anti-metastatic therapies.

Highlights of the Study

1. Novel Discovery: First revelation of how 5-HT regulates histone modifications to induce NET formation and promote cancer metastasis.
2. Interdisciplinary Approach: Combines neuroscience, immunology, and epigenetics, providing a new perspective on cancer metastasis research.
3. Clinical Application Potential: FDA-approved antidepressant fluoxetine has been shown to inhibit NET formation and cancer metastasis, offering important evidence for drug repurposing.

Additional Valuable Information

This study also suggests that the synergy between TGM2 and PAD4 may play an important role in other diseases, such as Alzheimer’s disease, warranting further investigation. Moreover, the multi-omics analysis tools and CUT&Tag sequencing technology developed by the research team provide significant methodological support for epigenetic studies.

This study not only uncovers new mechanisms of liver metastasis in neuroendocrine tumors but also provides important evidence for developing new anti-metastatic therapeutic strategies.