Expression of the FGFR2 mesenchymal splicing variant in epithelial cells drives epithelial-mesenchymal transition

Abstract

The FGFRs are receptor tyrosine kinases expressed by tissue-specific alternative splicing in epithelial IIIb or mesenchymal IIIc isoforms. Deregulation of FGF/FGFR signaling unbalances the epithelial-stromal homeostasis and may lead to cancer development. In the epithelial-context, while FGFR2b/KGFR acts as tumor suppressor, FGFR2c appears to play an oncogenic role. Based on our recent observation that the switching of FGFR2b versus FGFR2c induces EMT, here we investigated the biological outcome of the ectopic expression of FGFR2c in normal human keratinocytes. Morphological analysis showed that, differently from FGFR2b overexpression, the forced expression and activation of FGFR2c drive the epithelial cells to acquire a mesenchymal-like shape and actin reorganization. Moreover, the appearance of invasiveness and anchorage-independent growth ability in FGFR2c transfected keratinocytes was consistent with the potential tumorigenic role proposed for this receptor variant. Biochemical and molecular approaches revealed that the observed phenotypic changes were accompanied by modulation of EMT biomarkers and indicated the involvement of EMT transcription factors and miRs. Finally, the analysis of the expression pattern of discriminating markers strongly suggested that activation of FGFR2c triggers a process corresponding to the initiation of the pathological type III EMT, but not to the more physiological type II EMT occurring during FGFR2b-mediated wound healing.

Expression of the FGFR2c mesenchymal splicing variant in human keratinocytes inhibits differentiation and promotes invasion

“…As a consequence of the initiation of a pathological cancer‐associated type III EMT process driven by the ectopic expression of FGFR2c in normal human keratinocytes, we have also recently described that the mesenchymal‐like morphology, actin reorganization, and modulation of EMT markers led to invasiveness and anchorage‐independent growth of the cells . These interesting observations prompted us to further investigate the behaviour of our cell model of keratinocytes, ectopically expressing the mesenchymal FGFR2c variant, during in vitro differentiation and stratification and in comparison with cells endogenously expressing or overexpressing by transfection the epithelial FGFR2b isoform.…”

“…All assays included a negative control and were replicated three times. The thermal cycling program was performed as described . Real‐time quantitation was performed with the help of the iCycler IQ optical system software version 3.0a (Bio‐Rad), according to the manufacturer's manual.…”

“…Consistent with this role, studies from our group have demonstrated that FGFR2b expression and signaling promote keratinocyte early differentiation, triggering the shift from the basal to the suprabasal layers of the epidermis. On the other hand, altered FGFR2 isoform switching and aberrant expression of the mesenchymal FGFR2c isoform in epithelial cells induces epithelial‐mesenchymal transition (EMT) and is involved in cancer progression …”

Single-Cell Transcriptomic Analysis of Primary and Metastatic Tumor Ecosystems in Head and Neck Cancer

“…Conversely, when we considered “incoming” signals to malignant cells, we found that CAFs expressed notably higher numbers of ligands that correspond to receptors expressed by the malignant cells of the corresponding tumor (hypergeometric test, p<0.05; Figures 4E and S5L). These included interactions that may promote EMT, such as TGFB3-TGFBR2, FGF7-FGFR2 and CXCL12-CXCR7 (Figure 4F) (Moustakas and Heldin, 2016; Ranieri et al, 2016; Yao et al, 2016). Accordingly, when we stained tumors for CAF markers (FAP, PDPN), we found that CAFs were present near p-EMT cells at the leading edge (Figures 4C and S5M).…”

Analyses of publicly available genomics resources define FGF-2-expressing bladder carcinomas as EMT-prone, proliferative tumors with low mutation rates and high expression of CTLA-4, PD-1 and PD-L1

“…The exon 9-containing isoform, which is known as the IIIc isoform, recognizes FGF-2 and is expressed in mesenchymal cells. Moreover, the expression of the IIIc isoform in various types of human cancer has been linked to epithelial to mesenchymal transition (EMT) and increased invasiveness, metastatic potential and cancer stem cell self-renewal 9, 10 . Our studies have shown that Akt3, and secondarily Akt1, transduce signals that shift the alternative splicing of FGFR-2 toward the IIIc isoform, which is recognized by FGF-2.…”