the original source The original premise of this

The original premise of this study was that the melanoma-enriched miRNAs identified in our previous study (Stark et al., 2015) would be translated directly to the expression observed in melanoma patient-derived serum. Evidence for this notion is apparent in the serially collected stage IV melanoma patients, when, at progression (or recurrence), the MELmiR-7 panel increases, which is reflective of increased tumour burden (i.e., the detectable miRNA expression was from the presence of tumour the original source and/or tumour derived extracellular vesicles (e.g., exosomes) in the circulation). These data strongly suggest that the expression is tumour derived and as such this panel could be considered melanoma-related. However, as we have noted, we observe a paradoxical decrease in the expression of the significantly expressed (miR-509-5p, miR-509-3p, miR-4731-5p, miR-4487, miR-4706) miRNAs when melanoma serum cohorts were compared with control cohorts. These data thus provide evidence that the assessed miRNAs (detectable in serum) are not restricted to the melanocytic lineage as initially thought. The source of this miRNA expression is currently unknown but could include cells of the haematopoietic lineage including T-cells, B-cells and NK cells. This loss of expression from a ‘non-tumour’ source has not been elucidated but warrants further investigation. An observed loss of expression of serum-derived miRNAs has been noted previously by Friedman et al. (2012) in post-operative specimens as compared to specimens collected at disease relapse. A plausible reason for a loss of expression observed in the serum may be due to a cytokine-driven systemic response. For example, pro-inflammatory cytokines have been shown to down-regulate miRNAs present in the circulation (Noren Hooten et al., 2013). Specifically, in a study by Noren Hooten et al. (2013) the serum expression of miR-181a was found to be negatively correlated with pro-inflammatory cytokines IL-6 and TNFα and positively correlated with the anti-inflammatory cytokines TGFβ and IL-10 (Noren Hooten et al., 2013). Recently, it has been confirmed that IL-6 expression is induced in melanoma cells with mutant BRAF (V600E). Therefore a possible explanation for what we have observed is that the miRNAs of interest could be expressed by non-melanocyte derived cells where expression is down-regulated in patients with melanoma due to melanoma-related cytokines (e.g. IL-6) (Whipple and Brinckerhoff, 2014). In conclusion, we envisage that as a growing number of miRNA-panels have been identified as potential prognostic indicators for melanoma (Fleming et al., 2015; Friedman et al., 2012; Tembe et al., 2015), it will eminently feasible to quantify circulating cell-free miRNAs directly (Ono et al., 2015), paving the way for rapid measurements to occur in a diagnostic laboratory. Given these advances, combined with the data presented herein, future melanoma treatment regimens should consider the utility of miRNAs as a prognostic aid in the clinical setting. Our sensitive and specific miRNA panel, in combination with newly identified panels, may enable more precise measurement of disease progression, and in conjunction with current therapy options, may herald an increase in overall survival.
Conflict of Interest
Authors\' Contributions
Acknowledgements The authors would like to thank the participants, and are grateful for the support of their colleagues: in particular Jessica Hayman, Dr. James Wilmott, and Valerie Jakrot. GJM, RAS and JFT are grateful for financial support from the National Health and Medical Research Council (NHMRC) of Australia (633004) and the Cancer Institute New South Wales (10TPG/1/02); MSS received scholarships from the NHMRC and the Queensland Government Smart Futures Fund. PMP is supported by a CDF2 fellowship from the NHMRC. NKH holds a fellowship from the NHMRC. The funders had no role in the study design, data collection, data analysis, interpretation, or writing of the report.