FGFR2c Upregulation Contributes to Cancer-Associated Fibroblast Program Activation and to Enhanced Autophagy in Actinic Keratosis-Derived Dermal Fibroblasts: A Possible Role in Precancerous Cell/Stromal Cell Crosstalk

Simple Summary In this work, we checked the possible tumor-promoting role of the mesenchymal FGFR2c isoform when overexpressed in AK stromal fibroblasts. We found that already starting from the early AK lesions, the dermal expression of FGFR2c is upregulated and accompanied by: (i) the repression of the CAF transcription repressor CSL, (ii) the upregulation of the CAF activator ULK3, and (iii) the induction of CAF genes. Immunofluorescence and molecular analysis coupled with silencing approaches suggested that, in primary cultures of KIN I-derived fibroblasts, the upregulation of FGFR2c contribute to the CAF signature and the increased autophagy in response to FGF2. Magnetic bead-based multiplex assay combined with FGFR tyrosine kinase inhibitors suggested that the enhanced secretion of IL-6, especially in response to FGF2, could be attributable to FGFR2c increased expression and signaling, possibly via the establishment of FGFR2c-mediated secretory autophagy. Overall, our results suggest that FGFR2c could be a signaling molecule contributing to precancerous/stromal cell oncogenic crosstalk, indicating it as a possible early molecular marker predictive for AK malignant progression. Actinic keratosis (AK) is a preneoplastic skin disorder which can rapidly progress to cutaneous squamous cell carcinomas (SCCs). In light of our previous findings, indicating a possible oncogenic role of the mesenchymal isoform of FGFR2 (FGFR2c) aberrantly expressed in AK keratinocytes, we analyzed the possible tumor-promoting role of this receptor in the stromal AK counterpart in this work. Molecular analysis showed that, particularly in early AK lesions, FGFR2c dermal upregulation is accompanied by the downregulation of the cancer-associated fibroblasts (CAF) transcription repressor CSL, the upregulation of the CAF activator ULK3, and the consequent CAF gene induction. Immunofluorescence and molecular analysis, coupled with silencing approaches by siRNA, applied on primary cultures of KIN I-derived fibroblasts, indicated that FGFR2c upregulation contribute to CAF signature and the increased autophagy in response to FGF2. Magnetic bead-based multiplex assay, combined with FGFR2 signaling shut-off approaches, indicated that, especially in response to FGF2, IL-6 secretion could depend on FGFR2c high expression and signaling, suggesting the possible establishment of FGFR2c-dependent secretory autophagy, contributing to tumor-promoting factor release. Overall, our results identified FGFR2c as a signaling molecule involved in controlling precancerous/stromal cell oncogenic crosstalk, pointing to this receptor as a possible early molecular marker predictive for AK's rapid malignant progression.