Polycomb group proteins--epigenetic repressors with emerging roles in melanocytes and melanoma

BMI1 is required for melanocyte stem cell maintenance and hair pigmentation

The epigenetic repressor BMI1 plays an integral role in promoting the self-renewal and proliferation of many adult stem cell populations, and also tumor types, primarily through silencing the Cdkn2a locus, which encodes the tumor suppressors p16Ink4a and p19Arf . However, in cutaneous melanoma, BMI1 drives epithelial-mesenchymal transition programs, and thus metastasis, while having little impact on proliferation or primary tumor growth. This raised questions about the requirement and role for BMI1 in melanocyte stem cell (McSC) biology. Here, we demonstrate that murine melanocyte-specific Bmi1 deletion causes premature hair greying and gradual loss of melanocyte lineage cells. Depilation enhances this hair greying defect, accelerating depletion of McSCs in early hair cycles, suggesting that BMI1 acts to protect McSCs against stress. RNA-seq of McSCs, harvested before onset of detectable phenotypic defects, revealed that Bmi1 deletion derepresses p16Ink4a and p19Arf , as observed in many other stem cell contexts. Additionally, BMI1 loss downregulated the glutathione S-transferase enzymes, Gsta1 and Gsta2, which can suppress oxidative stress. Accordingly, treatment with the antioxidant N-acetyl cysteine (NAC) partially rescued melanocyte expansion. Together, our data establish a critical function for BMI1 in McSC maintenance that reflects a partial role for suppression of oxidative stress, and likely transcriptional repression of Cdkn2a.

Redundancy analysis, genome-wide association studies and the pigmentation of brown trout (Salmo trutta L.)

The association of molecular variants with phenotypic variation is a main issue in biology, often tackled with genome-wide association studies (GWAS). GWAS are challenging, with increasing, but still limited, use in evolutionary biology. We used redundancy analysis (RDA) as a complimentary ordination approach to single- and multitrait GWAS to explore the molecular basis of pigmentation variation in brown trout (Salmo trutta) belonging to wild populations impacted by hatchery fish. Based on 75,684 single nucleotide polymorphic (SNP) markers, RDA, single- and multitrait GWAS allowed the extraction of 337 independent colour patterning loci (CPLs) associated with trout pigmentation traits, such as the number of red and black spots on flanks. Collectively, these CPLs (i) mapped onto 35 out of 40 brown trout linkage groups indicating a polygenic genomic architecture of pigmentation, (ii) were found to be associated with 218 candidate genes, including 197 genes formerly mentioned in the literature associated to skin pigmentation, skin patterning, differentiation or structure notably in a close relative, the rainbow trout (Onchorhynchus mykiss), and (iii) related to functions relevant to pigmentation variation (e.g., calcium- and ion-binding, cell adhesion). Annotated CPLs include genes with well-known pigmentation effects (e.g., PMEL, SLC45A2, SOX10), but also markers associated with genes formerly found expressed in rainbow or brown trout skins. RDA was also shown to be useful to investigate management issues, especially the dynamics of trout pigmentation submitted to several generations of hatchery introgression.

Current understanding of epigenetics role in melanoma treatment and resistance

Melanoma is the most aggressive form of skin cancer resulting from genetic mutations in melanocytes. Several factors have been considered to be involved in melanoma progression, including genetic alteration, processes of damaged DNA repair, and changes in mechanisms of cell growth and proliferation. Epigenetics is the other factor with a crucial role in melanoma development. Epigenetic changes have become novel targets for treating patients suffering from melanoma. These changes can alter the expression of microRNAs and their interaction with target genes, which involves cell growth, differentiation, or even death. Given these circumstances, we conducted the present review to discuss the melanoma risk factors and represent the current knowledge about the factors related to its etiopathogenesis. Moreover, various epigenetic pathways, which are involved in melanoma progression, treatment, and chemo-resistance, as well as employed epigenetic factors as a solution to the problems, will be discussed in detail.

Epigenetic regulation during melanocyte development and homeostasis

Melanocytes originate in the neural crest as precursor cells which then migrate and proliferate to reach their destination where they differentiate into pigment-producing cells. Melanocytes not only determine the colour of hair, skin and eyes but also protect against the harmful effects of UV irradiation. The establishment of the melanocyte lineage is regulated by a defined set of transcription factors and signalling pathways that direct the specific gene expression programmes underpinning melanoblast specification, survival, migration, proliferation and differentiation. In addition, epigenetic modifiers and replacement histones play key roles in regulating gene expression and its timing during the different steps of this process. Here, we discuss the evidence for the role of epigenetic regulators in melanocyte development and function and how they interact with transcription factors and signalling pathways to establish and maintain this important cell lineage.

Gene Expression Signature of BRAF Inhibitor Resistant Melanoma Spheroids

In vitro cell cultures are frequently used to define the molecular background of drug resistance. The majority of currently available data have been obtained from 2D in vitro cultures, however, 3D cell culture systems (spheroids) are more likely to behave similarly to in vivo conditions. Our major aim was to compare the gene expression signature of 2D and 3D cultured BRAFV600E mutant melanoma cell lines. We successfully developed BRAF-drug resistant cell lines from paired primary/metastatic melanoma cell lines in both 2D and 3D in vitro cultures. Using Affymetrix Human Gene 1.0 ST arrays, we determined the gene expression pattern of all cell lines. Our analysis revealed 1049 genes (562 upregulated and 487 downregulated) that were differentially expressed between drug-sensitive cells grown under different cell cultures. Pathway analysis showed that the differently expressed genes were mainly associated with the cell cycle, p53, and other cancer-related pathways. The number of upregulated genes (72 genes) was remarkably fewer when comparing the resistant adherent cells to cells that grow in 3D, and were associated with cell adhesion molecules and IGF1R signalling. Only 1% of the upregulated and 5.6% of the downregulated genes were commonly altered between the sensitive and the resistant spheroids. Interestingly, we found several genes (BNIP3, RING1 and ABHD4) with inverse expression signature between sensitive and resistant spheroids, which are involved in anoikis resistance and cell cycle regulation. In summary, our study highlights gene expression alterations that might help to understand the development of acquired resistance in melanoma cells in tumour tissue.

Role of epigenetic regulation on the induction of apoptosis in Jurkat leukemia cells by white grape pomace rich in phenolic compounds

Grape pomace is a rich source of phenolic compounds commonly employed for elaboration of dietary supplements.

Melanocytic Nevi and the Genetic and Epigenetic Control of Oncogene-Induced Senescence

Melanocytic nevi represent benign clonal proliferations of the melanocytes in the skin that usually remain stable in size and behavior or disappear during life. Infrequently, melanocytic nevi undergo malignant transformation to melanoma. Understanding molecular and cellular mechanisms underlying oncogene-induced senescence should help identify pathways underlying melanoma development, leading to the development of new strategies for melanoma prevention and early detection.

The Ezh2 polycomb group protein drives an aggressive phenotype in melanoma cancer stem cells and is a target of diet derived sulforaphane

Melanoma is a metastatic cancer associated with poor survival. Here, we study a subpopulation of melanoma cancer cells displaying melanoma cancer stem cell (MCS cells) properties including elevated expression of stem cell markers, increased ability to survive as spheroids, and enhanced cell migration and invasion. We show that the Ezh2 stem cell survival protein is enriched in MCS cells and that Ezh2 knockdown or treatment with small molecule Ezh2 inhibitors, GSK126 or EPZ-6438, reduces Ezh2 activity. This reduction is associated with a reduced MCS cell spheroid formation, migration, and invasion. Moreover, the diet-derived cancer prevention agent, sulforaphane (SFN), suppresses MCS cell survival and this is associated with loss of Ezh2. Forced expression of Ezh2 partially reverses SFN suppression of MCS cell spheroid formation, migration, and invasion. A375 melanoma cell-derived MCS cells form rapidly growing tumors in immune-compromised mice and SFN treatment of these tumors reduces tumor growth and this is associated with reduced Ezh2 level and H3K27me3 formation, reduced matrix metalloproteinase expression, increased TIMP3 expression and increased apoptosis. These studies identify Ezh2 as a MCS cell marker and cancer stem cell prevention target, and suggest that SFN acts to reduce melanoma tumor formation via a mechanism that includes suppression of Ezh2 function. © 2015 Wiley Periodicals, Inc.