Role of PKCε in the epithelial-mesenchymal transition induced by FGFR2 isoform switch

Abstract

Background: The epithelial isoform of the fibroblast growth factor receptor 2 (FGFR2b) controls the entire program of keratinocyte differentiation via the sequential involvement of protein kinase C (PKC) δ and PKCα. In contrast, the FGFR2 isoform switch and the aberrant expression of the mesenchymal FGFR2c isoform leads to impairment of differentiation, epithelial-mesenchymal transition (EMT) and tumorigenic features. Aim of our present study was to contribute in clarifying the complex network of signaling pathways involved in the FGFR2c-mediated oncogenic outcomes focusing on PKCε, which appears to be involved in the induction of EMT and tumorigenesis in several epithelial contexts. Methods: Biochemical and molecular analysis, as well as in vitro invasion assays, combined with the use of specific small interfering RNA (siRNA), were performed in human keratinocytes stably expressing FGFR2c or FGFR2b isoforms. Results: Our results showed that aberrant expression and signaling of FGFR2c, but not those of FGFR2b, in human keratinocytes induced a strong phosphorylation/activation of PKCε. The use of siRNA approach showed that PKCε is the hub signaling downstream FGFR2c responsible for the modulation of EMT markers and for the induction of the EMT-related transcription factors STAT3, Snail1 and FRA1, as well as for the acquisition of the invasive behavior. Moreover, experiments of depletion of ESRP1, responsible for FGFR2 splicing in epithelial cells, indicated that the activation of PKCε is the key molecular event triggered by FGFR2 isoform switch and underlying EMT induction. Conclusions: Overall, our results point to the identification of the downstream PKC isoform responsible for the FGFR signaling deregulation occurring in epithelial tissues from the physiological oncosoppressive to the pathological oncogenic profile.

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

“…Despite these supporting studies, our current results seem apparently in contrast with the recent findings reported by Basu, which indicate a key role of PKCε in promoting autophagic process in metastatic breast cancer cells 17 . This discrepancy would be explained considering the hypothesis that FGFR2c plays its oncogenic role in the early steps of tumour development, 4‐6 further confirming the dual and opposite contribution of autophagy in different (early and advanced‐metastatic) steps of carcinogenesis 8 . In fact, it has been proposed that autophagy can play a ‘double‐edged sword’ role on EMT, repressing the process in early, but inducing it in late, stages of tumorigenesis 8 …”

“…The fibroblast growth factor receptors (FGFR1‐4) are receptor tyrosine kinases regulating key processes, such as cell proliferation, differentiation, migration and survival 1 . The epithelial isoform of fibroblast growth factor receptor 2 (FGFR2b) isoform controls the entire program of keratinocytes differentiation, 2,3 while the FGFR2 isoform switch and the consequent aberrant expression of the mesenchymal FGFR2c isoform in epithelial context induces the impairment of differentiation, EMT and tumorigenic features, 4,5 mainly involving PKCε signalling 6 …”

Expression Profile of Fibroblast Growth Factor Receptors, Keratinocyte Differentiation Markers, and Epithelial Mesenchymal Transition-Related Genes in Actinic Keratosis: A Possible Predictive Factor for Malignant Progression?

“…Although the role of FGFR2c expression in the epithelial context begins to be clarified, the specific signaling network activated downstream this receptor and underlying its oncogenic outcome still remain to a large extent to be identified. Concerning this topic, we recently identified Protein Kinase Cε (PKCε)-mediated signaling as being mainly responsible for FGFR2c-mediated EMT and tumorigenic features in human keratinocytes [ 35 , 36 ]. Among the various transcription factors involved in the malignant progression and that can be therapeutically targeted [ 37 ], we found that PKCε acts downstream FGFR2c regulating Snail1, Fos-Related Antigen-1 (FRA1), and Signal Transducer and Activator of Transcription 3 (STAT3), which are induced in cascade [ 35 ].…”

“…Concerning this topic, we recently identified Protein Kinase Cε (PKCε)-mediated signaling as being mainly responsible for FGFR2c-mediated EMT and tumorigenic features in human keratinocytes [ 35 , 36 ]. Among the various transcription factors involved in the malignant progression and that can be therapeutically targeted [ 37 ], we found that PKCε acts downstream FGFR2c regulating Snail1, Fos-Related Antigen-1 (FRA1), and Signal Transducer and Activator of Transcription 3 (STAT3), which are induced in cascade [ 35 ]. Actually, the activation of PKCε-mediated signaling in consequence of FGFR2 isoform switch and the involvement of this pathway in FGFR2c-mediated epidermal carcinogenesis could explain the higher occurrence of SCC in AK lesions treated with ingenol mebutate, the most common topical therapy used in the last few years for AK treatment.…”

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

“…PKC-mediated signaling has been described as one of the main RAS-independent pathways activated by several receptor tyrosine kinases (RTKs), including fibroblast growth factor receptors (FGFRs) [ 6 ], whose dysregulation significantly contributes to cancer development [ 7 ]. Concerning this topic, we have recently demonstrated a central contribution for the PKCε isoform in the oncogenic outcomes established by the signaling of the mesenchymal isoform of FGFR2 (FGFR2c) when expressed in the epithelial context [ 8 , 9 ]. Even if the aberrant expressions of FGFR2c or FGFR2 altered splicing have been previously proposed as events contributing to pancreatic carcinogenesis [ 10 , 11 , 12 ], their relevance in the establishment of cell invasion, even if extensively investigated [ 10 , 11 , 12 ], remains controversial and still to be clarified.…”