FOXC1-Mediated Serine Metabolism Reprogramming Enhances Colorectal Cancer Growth and 5-FU Resistance

Background

Colorectal cancer (CRC) is the third most common cancer globally and the second leading cause of cancer-related deaths. Although surgical resection and adjuvant chemotherapy are the primary treatments for CRC, tumor development and chemotherapy resistance remain significant challenges in clinical management. 5-Fluorouracil (5-FU) is the main chemotherapeutic drug for CRC, and its mechanism of action involves inhibiting thymidylate synthase (TS) to disrupt nucleotide biosynthesis, thereby suppressing DNA replication and repair. However, the resistance rate of CRC to 5-FU remains high, making the exploration of resistance mechanisms a critical research focus.

Metabolic reprogramming plays a key role in tumor growth and chemotherapy resistance, with serine metabolism being a prominent feature of tumor metabolism. Serine, a non-essential amino acid, is primarily obtained through exogenous uptake and the de novo synthesis pathway (Serine Synthesis Pathway, SSP). Studies have shown that exogenous serine deprivation can inhibit tumor growth and reduce 5-FU resistance, but the clinical efficacy of dietary serine restriction alone is suboptimal, as external deprivation triggers compensatory activation of endogenous serine synthesis. Therefore, understanding how CRC modulates serine metabolism reprogramming under serine-deprived conditions is crucial for addressing 5-FU resistance.

Source of the Paper

This paper was co-authored by researchers from the Endoscopy Center of Shanghai East Hospital, including Zhukai Chen, Jiacheng Xu, Kang Fang, and others, with corresponding authors Lechi Ye, Meidong Xu, Lingnan He, and Tao Chen. The paper was published in 2025 in the journal Cell Communication and Signaling under the title “FOXC1-mediated serine metabolism reprogramming enhances colorectal cancer growth and 5-FU resistance under serine restriction.”

Research Process and Results

1. Upregulation of Serine Metabolic Enzymes Under Serine Deprivation

The study began by analyzing gene expression changes in CRC cells (SW1116) under serine-deprived conditions using RNA sequencing. The results showed that serine deprivation significantly upregulated the expression of serine synthesis pathway (SSP)-related genes, including PHGDH, PSAT1, and PSPH. The expression of these genes peaked at 24 hours post-deprivation, with protein levels reaching their maximum at 48 hours. Further experiments revealed that serine deprivation activated the ERK1/2-p-ELK1 signaling axis, upregulating the expression of the transcription factor FOXC1. Elevated FOXC1 promoted the transcription of serine metabolic enzymes PHGDH, PSAT1, and PSPH, thereby enhancing serine synthesis and supporting CRC cell growth.

2. Impact of SSP Genes on CRC Cell Growth and 5-FU Resistance

To investigate the role of SSP genes in CRC cell growth and 5-FU resistance under serine-deprived conditions, researchers used small interfering RNA (siRNA) to knock down the expression of PHGDH, PSAT1, and PSPH. The results showed that knocking down these genes significantly reduced intracellular serine levels and inhibited cell proliferation. Additionally, silencing SSP genes markedly decreased CRC cell resistance to 5-FU, indicating that serine metabolism plays a crucial role in 5-FU resistance.

3. Mechanism of FOXC1 Under Serine Deprivation

The researchers further discovered that serine deprivation upregulated FOXC1 expression by activating the ERK1/2-p-ELK1 signaling axis. Elevated FOXC1 promoted the transcription of SSP genes, enhancing serine synthesis. Moreover, FOXC1 modulated one-carbon metabolism and DNA damage repair, thereby increasing CRC cell resistance to 5-FU. Experiments demonstrated that knocking down FOXC1 significantly reduced intracellular serine levels and increased the expression of the DNA damage marker γH2AX, indicating FOXC1’s critical role in DNA damage repair.

4. Validation in Animal Models

To validate the role of FOXC1 in vivo, researchers conducted xenograft experiments using NSG mice. The results showed that under serine-deprived conditions, knocking down FOXC1 or using the ERK1/2 inhibitor U0126 significantly inhibited tumor growth and enhanced the efficacy of 5-FU. Additionally, serine deprivation significantly reduced serine levels in tumor tissues, further supporting FOXC1’s key role in serine metabolism.

Conclusions and Significance

This study reveals that serine deprivation activates the ERK1/2-p-ELK1 signaling axis, upregulating FOXC1 expression, which in turn promotes the transcription of serine metabolic enzymes PHGDH, PSAT1, and PSPH, enhancing serine synthesis and supporting CRC growth and 5-FU resistance. The findings suggest that combining dietary serine restriction with targeted therapy against the ERK1/2-p-ELK1-FOXC1 axis could be an effective strategy for treating CRC, significantly improving the efficacy of 5-FU.

Research Highlights

1. Novel Mechanistic Discovery: The study is the first to reveal that FOXC1, under serine-deprived conditions, enhances CRC growth and 5-FU resistance by regulating the expression of serine metabolic enzymes.
2. Multi-Level Experimental Validation: The research comprehensively validated FOXC1’s critical role in serine metabolism and 5-FU resistance through cell experiments, animal models, and clinical data analysis.
3. Potential Clinical Applications: The study proposes a strategy combining dietary restriction and targeted therapy, offering new insights for CRC treatment.

Additional Valuable Information

The study also found that serine deprivation increases intracellular reactive oxygen species (ROS) levels, activating the ERK1/2 signaling pathway and further supporting FOXC1 upregulation. This discovery provides new perspectives on the relationship between serine metabolism and oxidative stress.

This research not only elucidates the metabolic adaptation mechanisms of CRC under serine-deprived conditions but also provides a theoretical foundation for developing new therapeutic strategies.