Abstract 5231: Follistatin shapes the tumor microenvironment in head and neck squamous cell carcinoma through COL1A1-CD44-mediated tumor-stroma crosstalk

Abstract Head and Neck Squamous Cell Carcinoma (HNSCC) is a common malignancy with limited therapeutic options. The initiation and progression of HNSCC is closely tied to epithelial cell fate decisions influenced by the tumor microenvironment (TME). The Transforming Growth Factor-β (TGF-β) Superfamily of ligands are pleiotropic growth factors and key mediators of cell-cell communication within the TME. Although TGF-β has been extensively studied for its critical role in cancer progression, therapeutic strategies targeting TGF-β have been largely unsuccessful. Such efforts have often overlooked the potential contribution of myriad factors that influence TGF-β signaling such as follistatin (FST), a secreted glycoprotein and potent inhibitor of TGF-β. FST is frequently upregulated in solid tumors where it is associated with dismal survival outcomes and reduced therapeutic responses. However, the molecular mechanisms by which FST counterbalances TGF-β and potentially other signaling pathways to modulate the TME is not well understood. This underscores the critical need for a more nuanced and molecular understanding of the FST driven networks to develop more effective therapeutic approaches. Here we examined the tumor cell intrinsic and extrinsic roles of FST within the TME of HNSCC by leveraging single cell RNA-seq and spatial transcriptomics datasets from HNSCC patients and analyzing transcriptional changes following depletion of FST in human HNSCC cell lines. We find that while fibroblasts and epithelial cells both express FST, tumor epithelial cells are the primary source of heightened FST levels in HNSCC. Notably, we discover that FST expression is intrinsically linked to a transcriptional program promoting a basal stem-like state in cancer epithelial cells, suggesting a role for FST in tumor plasticity. Consistently, tumor cells that express FST exhibit increased signaling and molecular attributes of the epithelial-to-mesenchymal transition (EMT) program and reduced differentiation. Since cancer stem cells are enriched at the tumor leading edge, where they leverage EMT processes for dissemination, we investigated the spatial distribution of FST-enriched tumor cells and their interactions with the surrounding extracellular milieu. Our analyses show that FST is enriched within the tumor leading edge invasive niche, and further, that tumor-stroma crosstalk via COL1A1-CD44 interactions is spatially localized within FST-rich domains. Finally, we find CD44 positively correlates with FST expression in patient tumors and cancer cells at the transcriptional and protein level. Collectively, our findings define the functional role of FST within the HNSCC TME and supports a model in which FST counterbalances TGF-β signaling and facilitates distinct epithelial-stroma interactions at the dynamic leading edge to enhance tumor aggression. Citation Format: Jennifer Sosa, Satrajit Sinha. Follistatin shapes the tumor microenvironment in head and neck squamous cell carcinoma through COL1A1-CD44-mediated tumor-stroma crosstalk [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 5231.