Methylation of a CpG island (CGI; a dense cluster of CpGs) located in the 5' region of a gene suppresses that gene's transcription.,The expression of G0/G1 switch gene 2 (G0S2) is potentially associated with tumorigenesis.,The aim of this study is to elucidate the methylation status of the CGI located in the 5' region of G0S2 (hereinafter called 5' G0S2 CGI) in cutaneous squamous cell carcinoma (SCC).,Quantitative real-time methylation-specific PCR (RT-MSP) and bisulfite sequencing were performed to evaluate the methylation statuses of cutaneous SCC and normal epithelial cell samples.,Quantitative real-time reverse transcription-PCR was performed to evaluate RNA expression levels.,Immunohistochemical analysis was performed to detect protein expression.,G0S2 was suppressed in the five SCC cell lines with 5' G0S2 CGI methylation levels of nearly 100.0% and was expressed in the two normal cultured keratinocytes with methylation levels of almost 0.0%.,G0S2 was re-expressed in SCC cell lines treated with a demethylating agent.,The in vivo methylation levels of 5' G0S2 CGI as determined by RT-MSP varied widely (0.0% to 77.7%) in 17 cutaneous SCC samples and narrowly (0.1% to 7.3%) in 6 normal epidermis samples.,Nine cutaneous SCC samples exhibited higher methylation levels than the highest methylation level (7.3%) of the 6 normal epidermis samples.,Bisulfite sequencing showed dense methylated CpG sites within 5' G0S2 CGI in these highly methylated cutaneous SCC samples.,The methylation levels of the cutaneous SCC samples did not correlate with any clinical parameters investigated or with histopathological grading.,G0S2 is silenced by aberrant DNA methylation in a subset of cutaneous SCCs.
Cutaneous squamous cell carcinoma (cSCC) is the second most common skin cancer and frequently progresses from an actinic keratosis (AK), a sun-induced keratinocyte intraepithelial neoplasia (KIN).,Epigenetic mechanisms involved in the phenomenon of progression from AK to cSCC remain to be elicited.,Expression of microRNAs in sun-exposed skin, AK and cSCC was analysed by Agilent microarrays.,DNA methylation of miR-204 promoter was determined by bisulphite treatment and pyrosequencing.,Identification of miR-204 targets and pathways was accomplished in HaCat cells.,Immunofluorescence and immunohistochemistry were used to analyze STAT3 activation and PTPN11 expression in human biopsies.,cSCCs display a marked downregulation of miR-204 expression when compared to AK.,DNA methylation of miR-204 promoter was identified as one of the repressive mechanisms that accounts for miR-204 silencing in cSCC.,In HaCaT cells miR-204 inhibits STAT3 and favours the MAPK signaling pathway, likely acting through PTPN11, a nuclear tyrosine phosphatase that is a direct miR-204 target.,In non-peritumoral AK lesions, activated STAT3, as detected by pY705-STAT3 immunofluorescence, is retained in the membrane and cytoplasm compartments, whereas AK lesions adjacent to cSCCs display activated STAT3 in the nuclei.,Our data suggest that miR-204 may act as a “rheostat” that controls the signalling towards the MAPK pathway or the STAT3 pathway in the progression from AK to cSCC.,The online version of this article (doi:10.1186/s12943-016-0537-z) contains supplementary material, which is available to authorized users.