SPTLC2 Drives an EGFR-FAK-HBEGF Signaling Axis to Promote Ovarian Cancer Progression

Academic Background

Ovarian cancer (OC) is one of the most lethal cancers in the female reproductive system, with complex pathogenesis and limited treatment options. The epidermal growth factor receptor (EGFR) signaling pathway is widely dysregulated in various cancers, particularly in ovarian cancer, where EGFR overexpression is closely associated with poor patient prognosis. Although the EGFR signaling pathway plays a crucial role in ovarian cancer progression, monotherapy targeting EGFR has shown limited efficacy in ovarian cancer patients, indicating that the regulatory mechanisms of the EGFR signaling pathway are not fully understood. Therefore, in-depth research into the regulatory mechanisms of the EGFR signaling pathway, especially the identification of new regulatory factors, is of great significance for developing more effective ovarian cancer treatment strategies.

Serine palmitoyltransferase long chain base subunit 2 (SPTLC2) is the catalytic subunit of serine palmitoyltransferase (SPT), which is involved in the de novo synthesis of sphingolipids. SPTLC2 plays a critical role in embryonic development, but its role in cancer remains unclear. Previous studies have shown that SPTLC2 exhibits dual functions in different cell types, potentially promoting or inhibiting tumor growth. Therefore, the specific role and mechanisms of SPTLC2 in ovarian cancer warrant further investigation.

Source of the Paper

This paper was co-authored by Xingyue Zhai, Ning Shen, Tao Guo, Jianxin Wang, Chunrui Xie, Yukai Cao, Ling Liu, Yumei Yan, Songshu Meng, and Sha Du, from the Institute of Cancer Stem Cell at Dalian Medical University, the Clinical Nutrition Department of the Second Hospital of Dalian Medical University, the Department of Thoracic Surgery at the First Affiliated Hospital of Dalian Medical University, and the First Department of Ultrasound at the First Affiliated Hospital of Dalian Medical University. The paper was published in 2024 in the journal Oncogene, with the DOI: https://doi.org/10.1038/s41388-024-03249-0.

Research Process and Results

1. Expression of SPTLC2 in Ovarian Cancer and Its Clinical Significance

The study first analyzed data from The Cancer Genome Atlas (TCGA) and found that SPTLC2 mRNA levels were significantly higher in ovarian cancer tissues compared to normal tissues. Further Kaplan-Meier survival analysis indicated that high SPTLC2 expression was significantly associated with poor prognosis in ovarian cancer patients. Immunohistochemical (IHC) analysis of tumor samples from 88 ovarian cancer patients revealed that SPTLC2 protein expression was significantly elevated in ovarian cancer tissues compared to normal ovarian tissues, and high SPTLC2 expression was associated with high-grade serous ovarian cancer and distant metastasis.

2. Effects of SPTLC2 on Ovarian Cancer Cell Growth and Migration

To investigate the function of SPTLC2 in ovarian cancer, researchers used lentivirus-mediated shRNA to knock down SPTLC2 expression and found that SPTLC2 knockdown significantly inhibited the proliferation, migration, and clonogenic ability of ovarian cancer cells (HEY-A8 and OVCAR3). Additionally, SPTLC2 knockdown significantly suppressed tumor growth and angiogenesis in the chick embryo chorioallantoic membrane (CAM) model. In a mouse xenograft model, SPTLC2-knockdown OVCAR3 cells formed significantly smaller tumors with reduced weight and fewer pulmonary micrometastases.

Conversely, overexpression of SPTLC2 significantly enhanced the proliferation, migration, and clonogenic ability of ovarian cancer cells and promoted tumor growth in both the CAM model and the mouse xenograft model.

3. SPTLC2 Promotes Ovarian Cancer Cell Migration via the FAK Signaling Pathway

To further elucidate the mechanisms of SPTLC2 in ovarian cancer progression, researchers performed RNA sequencing (RNA-seq) on SPTLC2-knockdown OVCAR3 cells. Gene Ontology (GO) analysis revealed that differentially expressed genes were enriched in pathways related to cell adhesion, cell adhesion molecule binding, and focal adhesion. Further experiments showed that SPTLC2 knockdown significantly reduced the number of focal adhesions in ovarian cancer cells and decreased the phosphorylation levels of FAK (Y397) and paxillin (Y118). FAK inhibitors Defactinib and PF-573228 significantly reversed the enhanced migration induced by SPTLC2 overexpression, indicating that SPTLC2 promotes ovarian cancer cell migration by activating the FAK signaling pathway.

4. Central Role of EGFR in SPTLC2-Mediated Ovarian Cancer Cell Growth and Migration

Researchers further explored how SPTLC2 regulates ovarian cancer cell growth and migration through the EGFR signaling pathway. Experiments showed that SPTLC2 knockdown significantly reduced the phosphorylation levels of EGFR (Y1068), FAK (Y397), and their downstream signaling molecules ERK1/2 and AKT, while SPTLC2 overexpression had the opposite effect. The EGFR inhibitor Erlotinib significantly reversed the enhanced proliferation and migration induced by SPTLC2 overexpression, indicating that EGFR plays a central role in SPTLC2-mediated ovarian cancer progression.

5. Interaction Between SPTLC2 and EGFR and Its Regulation of the EGFR-FAK-HBEGF Signaling Axis

Through co-immunoprecipitation (Co-IP) experiments, researchers confirmed the interaction between SPTLC2 and EGFR in ovarian cancer cells. Further experiments demonstrated that SPTLC2 binds to EGFR via its C-terminal 338-562 amino acid residues and regulates the activation of the EGFR-FAK-HBEGF signaling axis. The serine palmitoyltransferase activity of SPTLC2 is crucial for its regulation of the EGFR-FAK-HBEGF signaling axis, as a catalytically inactive SPTLC2 mutant (K379T) failed to restore the decreased phosphorylation levels of EGFR and FAK caused by SPTLC2 knockdown.

6. SPTLC2 Regulates Ovarian Cancer Progression via HBEGF

RNA-seq analysis revealed that SPTLC2 knockdown significantly downregulated the expression of HBEGF (Heparin-Binding EGF-Like Growth Factor) and AMIGO2 (Adhesion Molecule with IgG-like Domain 2). HBEGF is a ligand of EGFR and plays an important role in ovarian cancer progression. Experiments showed that the addition of HBEGF significantly reversed the decreased phosphorylation levels of EGFR, FAK, AKT, and ERK1/2 caused by SPTLC2 knockdown and restored the proliferation and migration capabilities of ovarian cancer cells. Conversely, knockdown of HBEGF significantly inhibited the enhanced proliferation and migration induced by SPTLC2 overexpression.

Conclusions and Significance

This study found that SPTLC2 promotes the growth and migration of ovarian cancer cells by driving the EGFR-FAK-HBEGF signaling axis. High expression of SPTLC2 is significantly associated with high-grade serous ovarian cancer and distant metastasis, indicating that SPTLC2 plays an oncogenic role in ovarian cancer progression. The study also revealed the mechanism by which SPTLC2 regulates the EGFR-FAK-HBEGF signaling axis through its serine palmitoyltransferase activity, providing a new potential target for ovarian cancer treatment.

Research Highlights

1. Oncogenic Role of SPTLC2: This study is the first to reveal the oncogenic role of SPTLC2 in ovarian cancer, demonstrating that it promotes ovarian cancer progression by regulating the EGFR-FAK-HBEGF signaling axis.
2. Discovery of the EGFR-FAK-HBEGF Signaling Axis: The study identified a novel mechanism by which SPTLC2 regulates ovarian cancer cell growth and migration through the EGFR-FAK-HBEGF signaling axis.
3. Clinical Significance of SPTLC2: High expression of SPTLC2 is significantly associated with poor prognosis in ovarian cancer patients, suggesting that it may serve as a prognostic marker and therapeutic target for ovarian cancer.

Research Value

This study not only elucidates the oncogenic mechanisms of SPTLC2 in ovarian cancer but also provides a theoretical basis for developing new therapeutic strategies targeting the EGFR signaling pathway. In the future, inhibitors targeting SPTLC2 or combination therapies with EGFR inhibitors may offer better treatment outcomes for ovarian cancer patients.