Exploring the mechanism for cancer associated fibroblasts recruitment and the potential therapeutic value of the CAF-derived proteins in esophageal squamous cell carcinoma

Abstract

Esophageal squamous cell carcinoma (ESCC), the major histological subtype of esophageal cancer, is the eighth most common diagnosed cancer worldwide. Current therapeutic strategies lack reliable clinical predictors and sometimes with morbidities. Therefore, advanced diagnosis methods and treatment strategies are in urgent need to achieve better results. Tumor microenvironment plays an important role in tumor development and progression, thus components in the tumor microenvironment should be considered as valuable targets for new therapeutic strategies.

Caner Associated Fibroblast, short for CAF, as a major component in ESCC stroma, plays important roles in ESCC initiation and progression. Fibroblast Growth Factor Receptor 2 (FGFR2) IIIc was identified as specific marker for ESCC CAFs in our lab’s previous work. To clarify the activation and recruitment mechanism of CAFs in ESCC, our group used FGFR2 IIIc as marker to trace the origin of CAFs. Changes in percentage of FGFR2(+) cells in bone marrow and peripheral blood suggested CAFs might originate from bone marrow. The FGFR2(+) cells were identified as blood circulating fibrocyte using various CD markers and could be recruited by ESCC cells both in vitro and in vivo. Then our group confirmed that human fibrocytes could be induced into CAFs by direct contact with ESCC cells. The induced CAFs expressed specific markers for CAFs and showed similar effect on ESCC cells as established human CAFs from ESCC tumor. FGF2 was selected and verified as one activation factor that tumor released to trigger bone marrow FGFR2(+) cells expansion. To investigate the process that fibrocyte differentiated into CAF, RNA-seq was performed to elucidate the distinct expression profile between these two cells. Genes dysregulated in CAFs were shown to relate with extracellular matrix (ECM) remodeling, Cancer Stem Cell (CSC) niche maintenance and immune reprogramming and several transcription factors regulating those dysregulated genes were analyzed. Investigations related to the differentiation process will be conducted in the future. MFG-E8, as a highly expressed secreted protein in CAFs, was selected as a potential therapeutic target from the RNA-seq data. Cell migration assay, cell invasion assay and flow cytometry were performed to study the effect of MFG-E8 on ESCC cells. MFG-E8 promoted ESCC cell migration and invasion by triggering EMT, and stimulated drug resistance of ESCC cell via an altered Akt & STAT3 signaling pathway. Anti-MFG-E8 antibody was effective in reducing tumor volume, especially when combined with cis-platin, which may serve as potential targets for development of effective therapeutic strategies. In summary, this thesis elucidated the process from FGFR2(+) cells expansion, recruitment to differentiation into CAFs and secreted MFG-E8 to facilitate ESCC development. Several potential therapeutic targets in this process showed promising translational applications for ESCC treatment.