# Ovulation-Derived Fibronectin Promotes Peritoneal Seeding of High-Grade Serous Carcinoma Precursor Cells via Integrin β1 Signaling

## TL;DR

Ovulation releases fibronectin, which helps spread early ovarian cancer cells through integrin β1 signaling, suggesting a new way to prevent the disease.

## Contribution

Identifies fibronectin in follicular fluid as a key driver of peritoneal seeding in high-grade serous ovarian carcinoma.

## Key findings

- Fibronectin in follicular fluid promotes migration, invasion, and peritoneal seeding of fallopian tube epithelial cells.
- Depletion of fibronectin reduces peritoneal tumor seeding by 82% in vivo and impairs these effects in vitro.
- Fibronectin activates ITGB1/FAK-SRC signaling to enhance tumor cell motility and colonization.

## Abstract

High-grade serous ovarian carcinoma (HGSC) is predominantly diagnosed at advanced stages with extensive peritoneal metastasis. A pivotal early event in HGSC development is the peritoneal seeding of tumor cells originating from the fallopian tube epithelial (FTE) precursor lesions. Ovulation releases follicular fluid (FF), which is known to contain oncogenic factors that promote FTE cell transformation. However, the specific mechanisms and factors within FF that drive the early metastatic seeding of precancerous FTE cells remain poorly defined. We investigated the role of FF in the peritoneal dissemination of FTE-derived cells, and the abundance of fibronectin (FN) as a potential key mediator. Functional assays were performed using FN-depleted FF to assess its impact on migration, invasion, anchorage-independent growth, and peritoneal attachment. The role of the fibronectin receptor, integrin β1 (ITGB1), and the signaling pathways were evaluated via knockdown studies. In vivo xenograft models were used to quantify peritoneal seeding, and mechanistic studies elucidated the involved signaling pathways. We identified FN as a critical component of FF, present at high concentrations (~210 µg/mL), that potently drives FTE cell migration, invasion, and peritoneal seeding. Depletion of FN from FF abrogated the majority of these pro-metastatic activities in vitro and led to a dramatic 82% reduction in peritoneal tumor seeding in vivo. Knockdown of ITGB1 similarly impaired seeding. Mechanistically, FF-derived FN activates the ITGB1/FAK-SRC signaling pathway to promote tumor cell motility and colonization. Our study establishes FF-fibronectin as an important regulator of the early peritoneal seeding of HGSC precursor cells. These findings reveal a direct link between ovulation and HGSC development, suggesting that targeting the FN-ITGB1 signaling axis may offer a novel preventive strategy for high-risk individuals.