The aberrant expression in epithelial cells of the mesenchymal isoform of FGFR2 controls the negative crosstalk between EMT and autophagy

Abstract

Signalling of the epithelial splicing variant of fibroblast growth factor receptor 2 (FGFR2b) triggers both differentiation and autophagy, while the aberrant expression of the mesenchymal FGFR2c isoform in epithelial cells induces impaired differentiation, inhibition of autophagy as well as the induction of the epithelial‐mesenchymal transition (EMT). In light of the widely proposed negative loop linking autophagy and EMT in the early steps of carcinogenesis, here we investigated the possible involvement of FGFR2c aberrant expression and signalling in orchestrating this crosstalk in human keratinocytes. Biochemical, molecular, quantitative immunofluorescence analysis and in vitro invasion assays, coupled to the use of specific substrate inhibitors and transient or stable silencing approaches, showed that AKT/MTOR and PKCε are the two hub signalling pathways, downstream FGFR2c, intersecting with each other in the control of both the inhibition of autophagy and the induction of EMT and invasive behaviour. These results indicate that the expression of FGFR2c, possibly resulting from FGFR2 isoform switch, could represent a key upstream event responsible for the establishment of a negative interplay between autophagy and EMT, which contributes to the assessment of a pathological oncogenic profile in epithelial cells.

Role of FGFR2c and Its PKCε Downstream Signaling in the Control of EMT and Autophagy in Pancreatic Ductal Adenocarcinoma Cells

“…Then, we shifted our attention to EMT-related gene profile expressed in PDAC cells expressing different levels of FGFR2c. We found that the expression levels of the transcription factors Snail1, FRA1 and STAT3, which we previously identified as involved in FGFR2c-mediated EMT [ 8 , 21 ], overlapped with those of FGFR2c, appearing significantly higher in PANC-1 cells, compared to MiaPaCa-2 cells ( Supplementary Figure S1A ). Consistent with what was observed for the EMT-related transcription factors, the modulation of epithelial/mesenchymal markers compatible with EMT also appeared to overlap FGFR2c expression, displaying a more pronounced downregulation of the epithelial markers E-cadherin and a higher expression of the mesenchymal marker vimentin in PANC-1 cells compared to Mia PaCa-2 cells ( Supplementary Figure S1B ).…”

“…We have recently proposed a role of PKCε-mediated signaling not only in FGFR2c-mediated induction of EMT, but also in FGFR2c-dependent inhibition of the autophagic process in human keratinocytes [ 21 ]. Therefore, we investigated here the possible contribution of PKCε on autophagy also in the specific context of pancreatic cancer.…”

“…We have also been interested in the signaling pathways and substrates of downstream FGFR2c possibly responsible for the establishment of an EMT-related phenotype, paying particular attention to PKCε, whose oncogenic role in epithelial cells has been widely described [ 7 ]. The choice of PKCε also stems from our recent findings indicating that the activation of this signaling substrate is the key event underlying FGFR2c-mediated EMT in the context of human keratinocytes [ 8 , 21 ]. The involvement of PKCε was investigated taking advantage of the use of specific shRNA approaches, which showed that PKCε depletion strongly impairs the increase of EMT signature, as well as the morphological changes triggered by FGF2 in PANC-1 cells.…”

“…Interestingly, we also found that PKCε silencing abolished the ability of FGF2 to repress autophagy, another important process contributing to PDAC development and progression [ 2 , 14 , 15 ]. Autophagy and EMT in cancer are linked in a complex crosstalk [ 13 ], which we have recently proposed to be regulated by FGFR2c and, to some extent, by its downstream PKCε-mediated signaling, at least during the early steps of human epidermal carcinogenesis [ 8 , 21 , 30 ]. In line with our previous data, here we highlighted a negative impact of PKCε downstream FGFR2c on autophagy at least in the PANC-1 cell model, which highly expresses the receptor.…”

PTBP1 promotes hepatocellular carcinoma progression by regulating the skipping of exon 9 in NUMB pre-mRNA

“…Alternative splicing is achieved by regulating the inclusion or exclusion of exons, which are then translated into protein sequences that perform different functions [ 32 ]. For example, alternative splicing of FGFR2 generates two transcripts, Ⅲb and Ⅲc, which promote or inhibit the EMT process, respectively [ 33 ]. In addition, alternative splicing of Bcl-x exon 2 produces two isoforms with opposing effects on cell survival: the anti-apoptotic long isoform (Bcl-xL) and the pro-apoptotic short isoform (Bcl-xS) [ 34 ].…”