Melanocyte phenotype and melanoma behaviour strictly depend on dual TRPM1 activity, with loss of TRPM1 protein promoting melanoma aggressiveness and miR-211 expression supporting tumour suppressor.
Here, we generated miR-211 loss-of-function cell lines using CRISPR/Cas9 technology and show that miR-211 loss slowed growth and invasion in vitro, inhibited phosphoinositol-3-kinase signaling, and inhibited melanoma growth in vivo. miR-211 deficiency rendered melanoma cells metabolically vulnerable by attenuating mitochondrial respiration and tricarboxylic acid cycling. miR-211 was up-regulated by the BRAF inhibitor vemurafenib and in vemurafenib-resistant melanoma cells, with miR-211 loss rendering them more drug sensitive. miR-211 loss represents a "two-pronged" anticancer strategy by inhibiting both critical growth-promoting cell signaling pathways and rendering cells metabolically vulnerable, making it an extremely attractive and specific candidate combinatorial therapeutic target in melanoma.
Here we study the impact of the tumour suppressive melanoma miRNA miR-211 on transcriptome stability and phenotype in the non-pigmented melanoma cell line, A375.
Overall, our findings show how upregulation of miR-204-5p and miR-211-5p following vemurafenib treatment enables the emergence of resistance, with potential implications for mechanism-based strategies to improve vemurafenib responses.<b>Significance:</b> Identification of miRNAs that enable resistance to BRAF inhibitors in melanoma suggests a mechanism-based strategy to limit resistance and improve clinical outcomes.<i></i>.
Increase of miR-21 and miR-142, and decrease of miR-125b, miR-211, miR-101 and miR-513c in the melanomas were verified in both cohorts using qPCR, whereas the decrease of miR-205 observed with array analysis could not be confirmed using qPCR.
These results support miR-211 as a leading miRNA candidate for melanoma diagnosis and miRNA in situ hybridization as a uniquely uncomplicated ancillary test.
In summary, the present study firstly demonstrated that DNMT1 mediated promoter methylation is a mechanism of miRNA suppression in melanoma and revealed a new tumor suppressor role of the miR-211 by targeting RAB22A in melanoma.
Compared to normal human melanocytes, miR-211 expression is significantly reduced or absent in nonpigmented melanoma cells and lost during human melanoma progression.
Inhibition of miR-211 increases NUAK1 expression and decreases melanoma adhesion, whereas upregulation of miR-211 restores adhesion through NUAK1 repression.
By transcriptionally up-regulating TRPM1, MITF, which is critical for both melanocyte differentiation and survival and for melanoma progression, indirectly drives the expression of miR-211.
We have identified a series of differentially expressed miRNAs that could be useful as diagnostic or prognostic markers for melanoma and have shown that three miRNAs (namely miR-200c, miR-205 and miR-211) act as tumour suppressors.
Because TRPM1 gene codes two transcripts: TRPM1 channel protein in its exons and miR-211 in one of its introns, we propose a dual role for TRPM1 gene where the loss of TRPM1 channel protein is an excellent marker of melanoma aggressiveness, while the expression of miR-211 is linked to the tumor suppressor function of TRPM1.
Given previous reports of high KCNMA1 levels in metastasizing melanoma, prostate cancer and glioma, our findings that miR-211 is a direct posttranscriptional regulator of KCNMA1 expression as well as the dependence of this miRNA's expression on MITF activity, establishes miR-211 as an important regulatory agent in human melanoma.
These data implicate miR-211 as a suppressor of melanoma invasion whose expression is silenced or selected against via suppression of the entire melastatin locus during human melanoma progression.