There is a world beyond protein mutations: the role of non-coding RNAs in melanomagenesis

MicroRNA heterogeneity in melanoma progression

The altered expression of miRNAs has been linked with neocarcinogenesis or the development of human malignancies including melanoma. Of significance, multiple clinical studies have documented that distinct sets of microRNAs (miRNAs) could be utilized as prognostic biomarkers for cancer development or predict the outcomes of treatment responses. To that end, an in-depth validation of such differentially expressed miRNAs is necessary in diverse settings of cancer patients in order to devise novel approaches to control tumor growth and/or enhance the efficacy of clinically-relevant therapeutic options. Moreover, considering the heterogeneity and sophisticated regulation of miRNAs, the precise delineation of their cellular targets could also be explored to design personalized medicine. Given the significance of miRNAs in regulating several key cellular processes of tumor cells including cell cycle progression and apoptosis, we review the findings of such miRNAs implicated in melanoma tumorigenesis. Understanding the novel mechanistic insights of such miRNAs will be useful for developing diagnostic or prognostic biomarkers or devising future therapeutic intervention for malignant melanoma.

Context-dependent miR-204 and miR-211 affect the biological properties of amelanotic and melanotic melanoma cells

Despite increasing amounts of experimental evidence depicting the involvement of non-coding RNAs in cancer, the study of BRAFV600E-regulated genes has thus far focused mainly on protein-coding ones. Here, we identify and study the microRNAs that BRAFV600E regulates through the ERK pathway.

By performing small RNA sequencing on A375 melanoma cells and a vemurafenib-resistant clone that was taken as negative control, we discover miR-204 and miR-211 as the miRNAs most induced by vemurafenib. We also demonstrate that, although belonging to the same family, these two miRNAs have distinctive features. miR-204 is under the control of STAT3 and its expression is induced in amelanotic melanoma cells, where it acts as an effector of vemurafenib's anti-motility activity by targeting AP1S2. Conversely, miR-211, a known transcriptional target of MITF, is induced in melanotic melanoma cells, where it targets EDEM1 and consequently impairs the degradation of TYROSINASE (TYR) through the ER-associated degradation (ERAD) pathway. In doing so, miR-211 serves as an effector of vemurafenib's pro-pigmentation activity. We also show that such an increase in pigmentation in turn represents an adaptive response that needs to be overcome using appropriate inhibitors in order to increase the efficacy of vemurafenib.

In summary, we unveil the distinct and context-dependent activities exerted by miR-204 family members in melanoma cells. Our work challenges the widely accepted “same miRNA family = same function” rule and provides a rationale for a novel treatment strategy for melanotic melanomas that is based on the combination of ERK pathway inhibitors with pigmentation inhibitors.

Pseudogenes in Human Cancer

Recent advances in the analysis of RNA sequencing data have shown that pseudogenes are highly specific markers of cell identity and can be used as diagnostic and prognostic markers. Furthermore, genetically engineered mouse models have recently provided compelling support for a causal link between altered pseudogene expression and cancer. In this review, we discuss the most recent milestones reached in the pseudogene field and the use of pseudogenes as cancer classifiers.