SOX5 is involved in balanced MITF regulation in human melanoma cells

Abstract

BackgroundMelanoma is a cancer with rising incidence and new therapeutics are needed. For this, it is necessary to understand the molecular mechanisms of melanoma development and progression. Melanoma differs from other cancers by its ability to produce the pigment melanin via melanogenesis; this biosynthesis is essentially regulated by microphthalmia-associated transcription factor (MITF). MITF regulates various processes such as cell cycling and differentiation. MITF shows an ambivalent role, since high levels inhibit cell proliferation and low levels promote invasion. Hence, well-balanced MITF homeostasis is important for the progression and spread of melanoma. Therefore, it is difficult to use MITF itself for targeted therapy, but elucidating its complex regulation may lead to a promising melanoma-cell specific therapy.MethodWe systematically analyzed the regulation of MITF with a novel established transcription factor based gene regulatory network model. Starting from comparative transcriptomics analysis using data from cells originating from nine different tumors and a melanoma cell dataset, we predicted the transcriptional regulators of MITF employing ChIP binding information from a comprehensive set of databases. The most striking regulators were experimentally validated by functional assays and an MITF-promoter reporter assay. Finally, we analyzed the impact of the expression of the identified regulators on clinically relevant parameters of melanoma, i.e. the thickness of primary tumors and patient overall survival.ResultsOur model predictions identified SOX10 and SOX5 as regulators of MITF. We experimentally confirmed the role of the already well-known regulator SOX10. Additionally, we found that SOX5 knockdown led to MITF up-regulation in melanoma cells, while double knockdown with SOX10 showed a rescue effect; both effects were validated by reporter assays. Regarding clinical samples, SOX5 expression was distinctively up-regulated in metastatic compared to primary melanoma. In contrast, survival analysis of melanoma patients with predominantly metastatic disease revealed that low SOX5 levels were associated with a poor prognosis.ConclusionMITF regulation by SOX5 has been shown only in murine cells, but not yet in human melanoma cells. SOX5 has a strong inhibitory effect on MITF expression and seems to have a decisive clinical impact on melanoma during tumor progression.Electronic supplementary materialThe online version of this article (doi:10.1186/s12920-016-0170-0) contains supplementary material, which is available to authorized users.

NK-cell Editing Mediates Epithelial-to-Mesenchymal Transition via Phenotypic and Proteomic Changes in Melanoma Cell Lines

“…In search of EMT markers that could be more specifically modulated by NK cells, we reevaluated the proteomic data and noticed that MeDeBO cells exposed to either NK cells or cytokines showed upregulation of SOX5, a transcription factor involved in the negative regulation of MITF and in the induction of EMT (see Supplementary Table S1; refs. 38,39). We analyzed this molecule in the melanoma lesions and found a clear statistical correlation between the rich NK-cell infiltrate and the high expression of SOX5 ( Supplementary Fig.…”

Validation and Enhancement of the Clinicopathological Melanoma Nomogram via Incorporation of a Molecular Marker in the Primary Tumor

“…Recent reports investigating the molecular mechanisms of melanoma development documented that high levels of MITF expression exert an antiproliferative activity in melanoma cells (26), whereas low levels of MITF protein were found in invasive melanoma cells (27). However, the majority of melanoma cells tend to maintain a low basal expression of this protein (28). This ambivalent function of MITF made it difficult to use for targeted therapy.…”

A lentiviral vector‐based insertional mutagenesis screen identifies mechanisms of resistance to MAPK inhibitors in melanoma

“…Among the other BRAFi + MEKi resistance genes, SOX5 and SOX6 are transcription factors that regulate cellular differentiation. In particular, SOX5 inhibits MITF expression in melanoma (Kordass et al, 2016), which is associated with a transcriptional switch and drug resistance (Muller et al, 2014). RASGRP3 is a well-known RAS activator that contributes to melanoma transformation (Yang et al, 2011).…”