Skin carcinogenesis is known to be a multi-step process with several stages along its malignant evolution. We hypothesized that transformation of normal epidermis to cutaneous squamous cell carcinoma (cSCC) is causally linked to alterations in microRNAs (miRNA) expression. For this end we decided to evaluate their alterations in the pathologic states ending in cSCC. Total RNA was extracted from formalin fixed paraffin embedded biopsies of five stages along the malignant evolution of keratinocytes towards cSCC: Normal epidermis, solar elastosis, actinic keratosis KIN1-2, advanced actinic keratosis KIN3 and well-differentiated cSCC. Next-generation small RNA sequencing was performed. We found that 18 miRNAs are overexpressed and 28 miRNAs are underexpressed in cSCC compared to normal epidermis. miR-424, miR-320, miR-222 and miR-15a showed the highest fold change among the overexpressed miRNAs. And miR-100, miR-101 and miR-497 showed the highest fold change among the underexpressed miRNAs. Heat map of hierarchical clustering analysis of significantly changed miRNAs and principle component analysis disclosed that the most prominent change in miRNAs expression occurred in the switch from 'early' stages; normal epidermis, solar elastosis and early actinic keratosis to the 'late' stages of epidermal carcinogenesis; late actinic keratosis and cSCC. We found several miRNAs with 'stage specific' alterations while others display a clear 'gradual', either progressive increase or decrease in expression along the malignant evolution of keratinocytes. The observed alterations focused in miRNAs involved in the regulation of AKT/mTOR or in those involved in epithelial to mesenchymal transition. We chose to concentrate on the evaluation of the molecular role of miR-497. We found that it induces reversion of epithelial to mesenchymal transition. We proved that SERPINE-1 is its biochemical target. The present study allows us to further study the pathways that are regulated by miRNAs along the malignant evolution of keratinocytes towards cSCC.

The present review describes in detail the existent data regarding feedback loops between miRNAs and cytokines or growth factors in the psoriatic inflammation. We have chosen to describe the roles of miR-31, miR-21, miR-146a, miR-155, miR-197 and miR-99a in this process. This choice derives from the fact that among around 250 miRNAs being altered in the psoriatic lesion, the comprehensive functional role was described only in those detailed above. In addition, considering the molecular targets and the pathways, which may possibly be regulated by those miRNAs, it seems that they may be chosen as preferred targets for the therapy of psoriasis.

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Psoriasis is a chronic inflammatory skin disorder which results from pathological interactions between activated immunocytes and keratinocytes. Recent studies implicated the role of IL-17 and IL-22, secreted from Th17 and Th22 in the generation and propagation of the psoriatic plaque. Previously, we and others have shown that the expression of miR-197 is significantly decreased in psoriatic lesions. We further showed that miR-197 targets IL-22RA1 and that ectopic expression of miR-197 prevent IL-22 induced proliferation and migration of keratinocytes.Since the 3'UTR of the IL17RA subunit mRNA contains a putative binding site for miR-197, our aim was to expand our understanding of the miRNA-mediated crosstalk between immunocytes and keratinocytes by studying the effect of miR-197 expression on IL-17A signaling pathway. Luciferase reporter assays along with Western blot analysis revealed that miR-197 directly targets the 3'UTR of IL17RA. Furthermore, ectopic expression of miR-197 led to a significant decrease in IL-17A-induced expression of CCL20, a known downstream effector of IL-17A. Interestingly, the addition of IL-17A to keratinocytes led to a rapid and transient increase in the expression of miR-197. Chromatin immuno-precipitation assays showed that keratinocytes' treatment with IL-17 leads to C/EBP binding to the promoter region of miR-197, and that the expression level of miR-197 is directly proportional to the extent of C/EBP binding to the promoter. Moreover, following treatment with IL-17A, the histone acetylation pattern at the miR-197 promoter turns to become characteristic of transcribed chromatin.Taken together, our results suggest that a positive-negative feedback loop exists between IL-17A and miR-197 in keratinocytes; the cytokine induces the binding of C/EBPα to miR-197 promoter sequences, enhances miR-197 expression that negatively attenuates IL-17 receptor and decreases the input along the IL-17A pathway. Our work suggests that in psoriasis, decreased expression of miR-197 may prevent the miR-197-induced attenuation of the IL-17 cascade, leading to its over-activity.

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Psoriasis is one of the most common chronic inflammatory skin disorders, with cutaneous and systemic manifestations and substantial negative effects on affected patients' quality of life. [1] MicroRNAs (miRNAs) are post-transcriptional regulators of gene expression. [2] Recent studies have revealed that interactions between miRNAs and their targets play critical roles in regulating distinct signalling pathways during skin differentiation. [3,4] Evidence is rapidly accumulating for the roles of miRNAs in the pathogenesis of inflammatory skin disorders. [5][6][7] In previous studies, others and we have shown that miR-197-3p (hereafter named miR-197) expression is downregulated in the psoriatic lesions compared to normal or uninvolved psoriatic skin. [6,8] Moreover, we showed that miR-197 modulates IL-22 and IL-17 signalling in normal keratinocytes (KC). Specifically, we found that both IL-22 and IL-17 activated the transcription of miR-197, and miR-197 targets and inhibits the expression of both the IL22RA1 subunit of

Cutaneous squamous cell carcinoma (CSCC) is an epidermal skin cancer that evolves from normal epidermis along several pre-malignant stages. Previously we found specific miRNAs alterations in each step along these stages. miR-199a-3p expression decreases at the transition to later stages. A crucial step for epithelial carcinoma cells to acquire invasive capacity is the disruption of cell–cell contacts and the gain of mesenchymal motile phenotype, a process known as epithelial-to-mesenchymal transition (EMT). This study aims to study the role of decreased expression of miR-199a-3p in keratinocytes’ EMT towards carcinogenesis. First, we measured miR-199a-3p in different stages of epidermal carcinogenesis. Then, we applied Photoactivatable Ribonucleoside-Enhanced Crosslinking and Immunoprecipitation (PAR-CLIP) assay to search for possible biochemical targets of miR-199a-3p and verified that Ras-associated protein B2 (RAP2B) is a bona-fide target of miR-199a-3p. Next, we analyzed RAP2B expression, in CSCC biopsies. Last, we evaluated possible mechanisms leading to decreased miR-199a-3p expression. miR-199a-3p induces a mesenchymal to epithelial transition (MET) in CSSC cells. Many of the under-expressed genes in CSCC overexpressing miR-199a-3p, are possible targets of miR-199a-3p and play roles in EMT. RAP2B is a biochemical target of miR-199a-3p. Overexpression of miR-199a-3p in CSCC results in decreased phosphorylated focal adhesion kinase (FAK). In addition, inhibiting FAK phosphorylation inhibits EMT marker genes’ expression. In addition, we proved that DNA methylation is part of the mechanism by which miR-199a-3p expression is inhibited. However, it is not by the methylation of miR-199a putative promoter. These findings suggest that miR-199a-3p inhibits the EMT process by targeting RAP2B. Inhibitors of RAP2B or FAK may be effective therapeutic agents for CSCC.