Single-Cell Identification of Melanoma Biomarkers in Circulating Tumor Cells.

The current standard for investigating tumors is surgical biopsy, which is costly, invasive, and difficult to perform serially. As an adjunct, circulating tumor cells (CTCs)-cells that have broken away from the primary tumor or metastatic sites-can be obtained from a blood draw and offer the potential for obtaining serial genetic information and serving as biomarkers. Here, we detail the potential for melanoma CTCs to serve as biomarkers and discuss a clinically viable methodology for single-cell CTC isolation and analysis that overcomes previous limitations. We explore the use of melanoma CTC biomarkers by isolating and performing single-cell RNA sequencing on CTCs from melanoma patients. We then compared transcriptional profiles of single melanoma CTCs against A375 cells and peripheral blood mononuclear cells to identify unique genes differentially regulated in circulating melanoma tumor cells. The information that can be obtained via analysis of these CTCs has significant potential in disease tracking.

MITF Is Regulated by Redox Signals Controlled by the Selenoprotein Thioredoxin Reductase 1.

TR1 and other selenoproteins have paradoxical effects in melanocytes and melanomas. Increasing selenoprotein activity with supplemental selenium in a mouse model of UV-induced melanoma prevents oxidative damage to melanocytes and delays melanoma tumor formation. However, TR1 itself is positively associated with progression in human melanomas and facilitates metastasis in melanoma xenografts. Here, we report that melanocytes expressing a microRNA directed against TR1 (TR1low) grow more slowly than control cell lines and contain significantly less melanin. This phenotype is associated with lower tyrosinase (TYR) activity and reduced transcription of tyrosinase-like protein-1 (TYRP1). Melanoma cells in which the TR1 gene (TXNRD1) was disrupted using Crispr/Cas9 showed more dramatic effects including the complete loss of the melanocyte-specific isoform of MITF; other MITF isoforms were unaffected. We provide evidence that TR1 depletion results in oxidation of MITF itself. This newly discovered mechanism for redox modification of MITF has profound implications for controlling both pigmentation and tumorigenesis in cells of the melanocyte lineage.