GJB5 association with BRAF mutation and survival in cutaneous malignant melanoma.

BACKGROUND: Gap-junctional intercellular communication is crucial for epidermal cellular homeostasis. Inability to establish melanocyte-keratinocyte contact and loss of the 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. OBJECTIVES: The aim of this study was to investigate connexin 31·1 (GJB5) expression and identify any association with BRAF mutational status, prognosis of patients with melanoma and mitogen-activated protein kinase (MAPK) inhibitor (MAPKi) treatment. METHODS: 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 (MEKi), as well as in cell lines which developed MAPKi resistance. Findings were further validated and confirmed by analysis of independent datasets. RESULTS: Our analysis reveals significant downregulation of GJB5 expression in metastatic melanoma lesions compared with primary ones and in BRAF-mutated vs. BRAF-wildtype (BRAFWT ) melanomas. Likewise, GJB5 expression is significantly lower in BRAFV600E compared with BRAFWT cell lines and increases on MAPKi treatment. MAPKi-resistant melanoma cells display a similar expression pattern compared with BRAFWT cells, with increased GJB5 expression associated with morphological changes. Enhancement of BRAFV600E expression in BRAFWT melanoma cells significantly upregulates miR-335-5p expression with consequent downregulation of GJB5, one of its targets. Furthermore, overexpression of miR-335-5p in two BRAFWT cell lines confirms specific GJB5 protein downregulation. Reverse transcriptase quantitative polymerase chain reaction analysis also revealed upregulation of miR-335 in BRAFV600E melanoma cells, which is significantly downregulated in cells resistant to MEKi. Our data were further validated using the TCGA_SKCM dataset, where BRAF mutations associate with increased miR-335 expression and inversely correlate with GJB5 expression. In clinical samples, GJB5 underexpression is also associated with patient overall worse survival, especially at early stages. CONCLUSIONS: We identified a significant association between metastases/BRAF mutation and low GJB5 expression in melanoma. Our results identify a novel mechanism of gap-junctional protein regulation, suggesting a prognostic role for GJB5 in cutaneous melanoma.

RNA-based drugs: from RNA interference to short interfering RNAs.

RNA interference consists of a sequence specific post-transcriptional gene silencing phenomenon triggered by a double strand RNA molecule homologous to the silenced gene. The dsRNA is cleaved by DICER enzyme in small dsRNA pieces, named short interfering RNAs (siRNAs). These fragments are thereafter associated to RISC complex where the cleavage of target RNA occurs. The observation that siRNAs can trigger the RNA interference mechanism in mammalian cells represents a fundamental discovery that discloses new horizons in genetic researches in that theoretically each gene can be silenced. The relative simplicity by which active short interfering RNAs can be designed and synthesized explains their widespread use in basic and applied researches, even if appropriate controls that exclude off-target effects are strictly required. The findings that siRNAs are active even when expressed in viral vectors open the possibility that they can be very soon used for gene therapy of several human diseases.

Efficacy of an amphipathic oligopeptide to shuttle and release a cis-acting DNA decoy into human cells.

We investigated the ability of an amphipathic oligopeptide to carry a synthetic dsDNA oligonucleotide inside human cells. The oligonucleotide was designed as a decoy binding site for the transcriptional activator of the methylguanine-DNA methyltransferase (MGMT) gene. The complex oligopeptide and decoy were administered to MCF10A exponentially growing cells, and the uptake was monitored by flow cytometry. After a 1-h exposure, almost all of the MCF10A cells were fluorescent, indicating that all of the cells had been transfected. By increasing the time, the fluorescence intensity per cell rapidly increased to a plateau at the 8-h time point. RT-PCR analysis of the MGMT gene was used as the molecular readout of the intracellular activity of the DNA decoy. MCF10A cells transfected with the oligopeptide/decoy complex showed a strong reduction in MGMT mRNA. Here, we discuss the advantages of using amphipathic oligopeptides as carriers of short DNA sequences.