An integrated genomic approach identifies follistatin as a target of the p63-epidermal growth factor receptor oncogenic network in head and neck squamous cell carcinoma

Abstract

Although numerous putative oncogenes have been associated with the etiology of head and neck squamous cell carcinoma (HNSCC), the mechanisms by which these oncogenes and their downstream targets mediate tumor progression have not been fully elucidated. We performed an integrative analysis to identify a crucial set of targets of the oncogenic transcription factor p63 that are common across multiple transcriptomic datasets obtained from HNSCC patients, and representative cell line models. Notably, our analysis revealed FST which encodes follistatin, a secreted glycoprotein that inhibits the transforming growth factor TGFβ/activin signaling pathways, to be a direct transcriptional target of p63. In addition, we found that FST expression is also driven by epidermal growth factor receptor EGFR signaling, thus mediating a functional link between the TGF-β and EGFR pathways. We show through loss- and gain-of-function studies that FST predominantly imparts a tumor-growth and migratory phenotype in HNSCC cells. Furthermore, analysis of single-cell RNA sequencing data from HNSCC patients unveiled cancer cells as the dominant source of FST within the tumor microenvironment and exposed a correlation between the expression of FST and its regulators with immune infiltrates. We propose FST as a prognostic biomarker for patient survival and a compelling candidate mediating the broad effects of p63 on the tumor and its associated microenvironment.

The Reign of Follistatin in Tumors and Their Microenvironment: Implications for Drug Resistance

“…Intriguingly, YAP1 also functions as a coregulator in an immune evasion program orchestrated by TEAD/p63 within airway basal epithelial cells, where FST serves as a target gene [146]. These findings, along with the positive association between increased FST expression in HNSCC and tumor-infiltrating immunosuppressive cells as reported by our group [126], further support the role of transcriptional cross-talk that acts upstream of FST in fostering an immune-evasive TME (Figures 3B and 6). Together, these discoveries provide novel insights into FST regulation, particularly by oncogenes, and offer a potential mechanism for its dysregulation in squamous cancers, which intersects with its positive regulation by TGF-β [139,147].…”

“…Given its molecular complexity and frequently delayed diagnosis, extensive efforts have been devoted to molecular classifications and unraveling the intricate signaling dynamics within the TME. We and others have proposed FST as a potential biomarker in HNSCC, underscoring its significance in the malignant transformation of the oral epithelium [83,126].…”

“…Considering that FST expression is regulated by TGF-β signaling and the likelihood that cancer cells often become unresponsive to TGF-β as oncogenesis progresses, it becomes apparent that additional mechanisms must come into play to sustain high levels of FST expression in cancer. To explore this, our group recently harnessed scRNA-seq data from HNSCC primary tumors to examine the origin of FST expression within the TME [126,128]. We found a notable enrichment of FST within TP63-expressing tumor epithelial cells driven by the activation of the MAPK signaling pathway (Figure 6B).…”

“…Patients of various cancer types demonstrate increased levels of FST in their serum, making FST a potential biomarker [63,68,153,154]. Furthermore, the source of this increased FST is believed to originate from solid tumors, with transcriptomic studies revealing elevated expression of FST in tumor tissues [38,86,126]. Functional studies in preclinical model systems and patient data analyses support a regulatory role of FST in various oncogenic processes; cell proliferation, stem cell renewal, metastasis, and angiogenesis are prominent among them.…”

“…It is becoming clear that epithelial cells are one major source of FST dysregulation in tumors [126]. However, whether this arises from a TGF-β-stimulated immune onslaught or whether CAFs play a role warrants further investigation.…”