Gap junctional intercellular communication is crucial for epidermal cellular homeostasis. Inability to establish melanocyte-keratinocytes contacts and loss of intercellular junction’s integrity may contribute to melanoma development. Connexins, laminins and desmocollins have been implicated in the control of melanoma growth where their reduced expression has been reported in metastatic lesions. We have investigated Connexin 31.1 (GJB5) expression and looked for any association with BRAF mutational status, patient prognosis and MAPK inhibitors (MAPKi) treatment. GJB5 expression was measured at RNA and protein level in melanoma clinical samples and established cell lines treated or not with BRAF and MEK inhibitors as well as in cell lines which developed MAPKi resistance. Our analysis reveals significant downregulation of GJB5 expression in metastatic compared to primary melanoma lesions and in BRAF mutated versus wild-type melanomas. Likewise GJB5 expression is significantly lower in BRAFV600E compared with BRAFWT cell lines, and slightly increases upon MAPKi treatment. MAPKi-resistant melanoma cells display a similar expression pattern to BRAFWT cells with a significant increased GJB5 expression. Enhancement of BRAF signalling by transfection of BRAFV600E in CHL1 cells, significantly upregulates miR-335 expression with consequent down-regulation of one of its target, GJB5. This was further validated using the TCGA-SKCM dataset, where BRAF mutations significantly associate with increased miR-335 expression and inversely correlate with GJB5 expression. In clinical samples, GJB5 expression also correlates with patient overall survival. Our results identify a novel mechanism of Gap-junctional regulation, highlighting GJB5 as a potential prognostic marker in cutaneous melanoma.

GJB5 association with BRAF mutation and survival in cutaneous melanoma