A polymorphism in IRF4 affects human pigmentation through a tyrosinase-dependent MITF/TFAP2A pathway.

Sequence polymorphisms linked to human diseases and phenotypes in genome-wide association studies often affect noncoding regions. A SNP within an intron of the gene encoding Interferon Regulatory Factor 4 (IRF4), a transcription factor with no known role in melanocyte biology, is strongly associated with sensitivity of skin to sun exposure, freckles, blue eyes, and brown hair color. Here, we demonstrate that this SNP lies within an enhancer of IRF4 transcription in melanocytes. The allele associated with this pigmentation phenotype impairs binding of the TFAP2A transcription factor that, together with the melanocyte master regulator MITF, regulates activity of the enhancer. Assays in zebrafish and mice reveal that IRF4 cooperates with MITF to activate expression of Tyrosinase (TYR), an essential enzyme in melanin synthesis. Our findings provide a clear example of a noncoding polymorphism that affects a phenotype by modulating a developmental gene regulatory network.

POT1 and multiple primary melanomas: the dermatological phenotype.

POT1 is the second most frequently reported gene (after CDKN2A) in familial melanoma. Pathogenic variants are associated with earlier onset and/or multiple primary melanomas (MPMs). To date, POT1 phenotypical reports have been largely restricted to associated malignancies, and description of the dermatological landscape has been limited. We identified 10 variants in n=18 of 384 (4.7%) unrelated individuals (n=13 MPMs; n=5 single primary melanomas) of European ancestry. Five variants were rare (minor allele frequency <0.001) or novel (two loss-of-function (LOF), one splice acceptor and two missense) and were predicted to be functionally significant, in five unrelated probands with MPMs (≥3 melanomas). We performed three-dimensional total body photography on both individuals with confirmed pathogenic LOF variants to characterise the dermatological phenotype. Total body naevus counts (≥2 mm diameter) were significantly higher (p=7.72×10-12) in carriers compared with a control population. Majority of naevi were on the probands' back and lower limb regions, where only mild to moderate ultraviolet (UV) damage was observed. Conversely, the head/neck region, where both probands exhibited severe UV damage, had comparably fewer naevi. We hypothesise that carriage of functionally significant POT1 variants is associated with increased naevus counts generally, and naevi >5 mm in diameter specifically and the location of these are independent of UV damage.

Assessing the genetic risk of nodular melanoma using a candidate gene approach.

BACKGROUND: Nodular melanoma (NM) is a challenge to diagnose early due to its rapid growth and more atypical clinical presentation, making it the largest contributor to melanoma mortality. OBJECTIVES: Our study aim was to perform a rare-variant allele (RVA) analysis of whole-exome sequencing of patients with NM and non-NM (minor allele frequency ≤ 1% non-Finnish European) for a set of 500 candidate genes potentially implicated in melanoma. METHODS: This study recruited 131 participants with NM and 194 with non-NM from South-east Queensland and patients with NM from Victoria to perform a comparative analysis of possible genetic differences or similarities between the two melanoma cohorts. RESULTS: Phenotypic analysis revealed that a majority of patients diagnosed with NM were older males with a higher frequency of fair skin and red hair than is seen in the general population. The distribution of common melanoma polygenic risk scores was similar in patients with NM and non-NM, with over 28% in the highest quantile of scores. There was also a similar frequency of carriage of familial/high-penetrant melanoma gene and loss-of-function variants. We identified 39 genes by filtering 500 candidate genes based on the greatest frequency in NM compared with non-NM cases. The genes with RVAs of greatest frequency in NM included PTCH1, ARID2 and GHR. Rare variants in the SMO gene, which interacts with PTCH1 as ligand and receptor, were also identified, providing evidence that the Hedgehog pathway may contribute to NM risk. There was a cumulative effect in carrying multiple rare variants in the NM-associated genes. A 14.8-fold increased ratio for NM compared with non-NM was seen when two RVAs of the 39 genes were carried by a patient. CONCLUSIONS: This study highlights the importance of considering frequency of RVA to identify those at risk of NM in addition to known high penetrance genes.

Uncovering molecular mechanisms for amelanotic/hypopigmented primary cutaneous melanoma.

BACKGROUND: A portion of approximately 2-20% of cutaneous melanoma (CM) are diagnosed as amelanotic/hypopigmented melanoma (AHM) and represent a challenge for early diagnosis. OBJECTIVES: Since the degree to which somatic mutations and copy number aberrations (CNA) in genes associated with skin-lightening or albinism may contribute to the loss of tumour pigmentation in AHM samples has not yet been addressed, we have investigated loss of function mutations of key pigmentation genes in matched germline and AHM as well as pigmented melanoma (PM) tumour DNA samples. METHODS: An analysis of clinical and histopathological characteristics together with whole exome sequencing data of 34 fresh frozen primary CM, graded according to the amount of pigmentation present was performed. Together with germline and somatic variant analysis, 30 samples were previously analysed for CNA changes. This study focussed on germline and somatic variants in the coding region of 16 genes known to be associated with albinism/hypopigmentation or variation in human pigmentation in all samples. Chromosomal regions encompassing these 16 genes were examined for DNA copy loss or gain. RESULTS: The finding that red hair related MC1R and TYR R402Q loss of activity gene variant alleles and genotypes are associated with AHM was validated in this study. Germline AHM-related gene variants were enriched in 70% (n=7 of 10) of AHM patients vs 8.3% (n=2 of 24) of PM patients. This surprisingly high frequency of rare germline variants in AHM patients constitutes the "first hit" and confirms that AHM patients are more likely to be albinism allele carriers than patients with PM. Next, in CNA analysis of each tumour sample, 50% (n=4 of 8) AHM samples with a pigmentation gene variant had LOH in the region containing the corresponding gene, and 25% (=2 of 8) had loss-of-heterozygosity (LOH) in chromosomal regions of two AHM-related genes. CONCLUSIONS: This study proposes that the likely molecular mechanism for development of amelanogenesis in AHM is carriage of an albinism/hypopigmentation allele followed by LOH of the corresponding gene in the tumour.

H3K4me3 remodeling induced acquired resistance through O-GlcNAc transferase.

AIMS: Drivers of the drug tolerant proliferative persister (DTPP) state have not been well investigated. Histone H3 lysine-4 trimethylation (H3K4me3), an active histone mark, might enable slow cycling drug tolerant persisters (DTP) to regain proliferative capacity. This study aimed to determine H3K4me3 transcriptionally active sites identifying a key regulator of DTPPs. METHODS: Deploying a model of adaptive cancer drug tolerance, H3K4me3 ChIP-Seq data of DTPPs guided identification of top transcription factor binding motifs. These suggested involvement of O-linked N-acetylglucosamine transferase (OGT), which was confirmed by metabolomics analysis and biochemical assays. OGT impact on DTPPs and adaptive resistance was explored in vitro and in vivo. RESULTS: H3K4me3 remodeling was widespread in CPG island regions and DNA binding motifs associated with O-GlcNAc marked chromatin. Accordingly, we observed an upregulation of OGT, O-GlcNAc and its binding partner TET1 in chronically treated cancer cells. Inhibition of OGT led to loss of H3K4me3 and downregulation of genes contributing to drug resistance. Genetic ablation of OGT prevented acquired drug resistance in in vivo models. Upstream of OGT, we identified AMPK as an actionable target. AMPK activation by acetyl salicylic acid downregulated OGT with similar effects on delaying acquired resistance. CONCLUSION: Our findings uncover a fundamental mechanism of adaptive drug resistance that governs cancer cell reprogramming towards acquired drug resistance, a process that can be exploited to improve response duration and patient outcomes.

The ATM Ser49Cys Variant Effects ATM Function as a Regulator of Oncogene-Induced Senescence.

An apical component of the cell cycle checkpoint and DNA damage repair response is the ataxia-telangiectasia mutated (ATM) Ser/Thr protein kinase. A variant of ATM, Ser49Cys (rs1800054; minor allele frequency = 0.011), has been associated with an elevated risk of melanoma development; however, the functional consequence of this variant is not defined. ATM-dependent signalling in response to DNA damage has been assessed in a panel of patient-derived lymphoblastoid lines and primary human melanocytic cell strains heterozygous for the ATM Ser49Cys variant allele. The ATM Ser49Cys allele appears functional for acute p53-dependent signalling in response to DNA damage. Expression of the variant allele did reduce the efficacy of oncogene expression in inducing senescence. These findings demonstrate that the ATM 146C>G Ser49Cys allele has little discernible effect on the acute response to DNA damage but has reduced function observed in the chronic response to oncogene over-expression. Analysis of melanoma, naevus and skin colour genomics and GWAS analyses have demonstrated no association of this variant with any of these outcomes. The modest loss of function detected suggest that the variant may act as a modifier of other variants of ATM/p53-dependent signalling.

The MC1R r allele does not increase melanoma risk in MITF E318K carriers.

BACKGROUND: Population-wide screening for melanoma is not cost-effective, but genetic characterization could facilitate risk stratification and targeted screening. Common Melanocortin-1 receptor (MC1R) red hair colour (RHC) variants and Microphthalmia-associated transcription factor (MITF) E318K separately confer moderate melanoma susceptibility, but their interactive effects are relatively unexplored. OBJECTIVES: To evaluate whether MC1R genotypes differentially affect melanoma risk in MITF E318K+ vs. E318K- individuals. MATERIALS AND METHODS: Melanoma status (affected or unaffected) and genotype data (MC1R and MITF E318K) were collated from research cohorts (five Australian and two European). In addition, RHC genotypes from E318K+ individuals with and without melanoma were extracted from databases (The Cancer Genome Atlas and Medical Genome Research Bank, respectively). χ2 and logistic regression were used to evaluate RHC allele and genotype frequencies within E318K+/- cohorts depending on melanoma status. Replication analysis was conducted on 200 000 general-population exomes (UK Biobank). RESULTS: The cohort comprised 1165 MITF E318K- and 322 E318K+ individuals. In E318K- cases MC1R R and r alleles increased melanoma risk relative to wild type (wt), P < 0.001 for both. Similarly, each MC1R RHC genotype (R/R, R/r, R/wt, r/r and r/wt) increased melanoma risk relative to wt/wt (P < 0.001 for all). In E318K+ cases, R alleles increased melanoma risk relative to the wt allele [odds ratio (OR) 2.04 (95% confidence interval 1.67-2.49); P = 0.01], while the r allele risk was comparable with the wt allele [OR 0.78 (0.54-1.14) vs. 1.00, respectively]. E318K+ cases with the r/r genotype had a lower but not significant melanoma risk relative to wt/wt [OR 0.52 (0.20-1.38)]. Within the E318K+ cohort, R genotypes (R/R, R/r and R/wt) conferred a significantly higher risk compared with non-R genotypes (r/r, r/wt and wt/wt) (P < 0.001). UK Biobank data supported our findings that r did not increase melanoma risk in E318K+ individuals. CONCLUSIONS: RHC alleles/genotypes modify melanoma risk differently in MITF E318K- and E318K+ individuals. Specifically, although all RHC alleles increase risk relative to wt in E318K- individuals, only MC1R R increases melanoma risk in E318K+ individuals. Importantly, in the E318K+ cohort the MC1R r allele risk is comparable with wt. These findings could inform counselling and management for MITF E318K+ individuals.

The Genetics of Human Skin and Hair Pigmentation.

Human skin and hair color are visible traits that can vary dramatically within and across ethnic populations. The genetic makeup of these traits-including polymorphisms in the enzymes and signaling proteins involved in melanogenesis, and the vital role of ion transport mechanisms operating during the maturation and distribution of the melanosome-has provided new insights into the regulation of pigmentation. A large number of novel loci involved in the process have been recently discovered through four large-scale genome-wide association studies in Europeans, two large genetic studies of skin color in Africans, one study in Latin Americans, and functional testing in animal models. The responsible polymorphisms within these pigmentation genes appear at different population frequencies, can be used as ancestry-informative markers, and provide insight into the evolutionary selective forces that have acted to create this human diversity.

Analysis of human leukocyte antigen associations in human papillomavirus-positive and -negative head and neck cancer: Comparison with cervical cancer.

BACKGROUND: Although the majority of human papillomavirus (HPV) infections are cleared by the immune system, a small percentage of them progress to develop HPV-driven cancers. Cervical cancer studies highlight that HPV persistence and cancer risk are associated with genetic factors, especially at the human leukocyte antigen (HLA) genes. This study was conducted to investigate such associations in head and neck cancer (HNC). METHODS: In all, 192 patients with HNC and 384 controls were genotyped with the Infinium Global Screening Array (Illumina, Inc). HLA variants were imputed with SNP2HLA, and an association analysis was performed by logistic regression. RESULTS: HPV-positive HNCs were significantly associated with single-nucleotide polymorphisms (SNPs) at DRB1_32660090 (P = 1.728 × 10-6 ) and DRB1_32660116 (P = 1.728 × 10-6 ) and with the amino acid variant DRB1_11_32660115 (P = 1.728 × 10-6 ). None of these associations were observed in the HPV-negative cohort, and this suggested their specificity to convey risk for HPV-associated HNCs. In general, associations observed for HPV-negative HNC were relatively weak, and variants in the HLA-DPA1 region were the strongest among them (P = 4.531 × 10-4 ). Several lead signals reported by previous HNC genome-wide association studies, including SNPs rs3135001 (P = .012), rs1049055 (P = .012), and rs34518860 (P = .029) and allele HLA-DQB1*06 (P = .009), were replicated in the current study. However, these associations were limited to the HPV-positive HNC group. Several cervical cancer-associated HLA variants, including SNPs rs9272143 (P = .002) and rs9271858 (P = .002) and alleles HLA-B-1501 (P = .009) and HLA-B-15 (P = .015), were also exclusively associated with HPV-positive HNC. CONCLUSIONS: HPV-positive HNC risk is associated with distinct HLA variants, and some of them are shared by both cervical cancer and HPV-positive HNC. Human papillomavirus (HPV)-positive head and neck cancer (HNC) risk is associated with distinct human leukocyte antigen variants, and some of them are shared by both cervical cancer and HPV-positive HNC. LAY SUMMARY: Cervical cancer studies highlight that human papillomavirus (HPV)-driven cancer risk is linked with human leukocyte antigen (HLA) polymorphism. Hence, the current study was designed to investigate the HLA associations in HPV-positive and HPV-negative head and neck cancer (HNC) and compare these associations with cervical cancer. Several lead signals reported by previous HNC and cervical genome-wide association studies were replicated in the current study. However, these associations were limited to the HPV-positive HNC group, and this suggests that HPV-positive HNC risk is associated with distinct HLA variants, and some of them are shared by both cervical cancer and HPV-positive HNC.

Melanoma mutations modify melanocyte dynamics in co-culture with keratinocytes or fibroblasts.

Melanocytic cell interactions are integral to skin homeostasis, and affect the outcome of multiple diseases, including cutaneous pigmentation disorders and melanoma. By using automated-microscopy and machine-learning-assisted morphology analysis of primary human melanocytes in co-culture, we performed combinatorial interrogation of melanocyte genotypic variants and functional assessment of lentivirus-introduced mutations. Keratinocyte-induced melanocyte dendricity, an indicator of melanocyte differentiation, was reduced in the melanocortin 1 receptor (MC1R) R/R variant strain and by NRAS.Q61K and BRAF.V600E expression, while expression of CDK4.R24C and RAC1.P29S had no detectable effect. Time-lapse tracking of melanocytes in co-culture revealed dynamic interaction phenotypes and hyper-motile cell states that indicated that, in addition to the known role in activating mitogenic signalling, MEK-pathway-activating mutations may also allow melanocytes to escape keratinocyte control and increase their invasive potential. Expanding this combinatorial platform will identify other therapeutic target mutations and melanocyte genetic variants, as well as increase understanding of skin cell interactions.

Derived immune and ancestral pigmentation alleles in a 7,000-year-old Mesolithic European.

Ancient genomic sequences have started to reveal the origin and the demographic impact of farmers from the Neolithic period spreading into Europe. The adoption of farming, stock breeding and sedentary societies during the Neolithic may have resulted in adaptive changes in genes associated with immunity and diet. However, the limited data available from earlier hunter-gatherers preclude an understanding of the selective processes associated with this crucial transition to agriculture in recent human evolution. Here we sequence an approximately 7,000-year-old Mesolithic skeleton discovered at the La Braña-Arintero site in León, Spain, to retrieve a complete pre-agricultural European human genome. Analysis of this genome in the context of other ancient samples suggests the existence of a common ancient genomic signature across western and central Eurasia from the Upper Paleolithic to the Mesolithic. The La Braña individual carries ancestral alleles in several skin pigmentation genes, suggesting that the light skin of modern Europeans was not yet ubiquitous in Mesolithic times. Moreover, we provide evidence that a significant number of derived, putatively adaptive variants associated with pathogen resistance in modern Europeans were already present in this hunter-gatherer.

Skin Pigmentation Genetics for the Clinic.

Human pigmentation characteristics play an important role in the effects of sun exposure, skin cancer induction and disease outcomes. Several of the genes most important for this diversity are involved in the regulation and distribution of melanin pigmentation or enzymes involved in melanogenesis itself within the melanocyte cell present in the skin, hair and eyes. The single nucleotide polymorphisms and extended haplotypes within or surrounding these genes have been identified as risk factors for skin cancer, in particular, melanoma. These same polymorphisms have been under selective pressure leading towards lighter pigmentation in Europeans in the last 5,000-20,000 years that have driven the increase in frequency in modern populations. Although pigmentation is a polygenic trait, due to interactive and quantitative gene effects, strong phenotypic associations are readily apparent for these major genes. However, predictive value and utility are increased when considering gene polymorphism interactions. In melanoma, an increased penetrance is found in cases when pigmentation gene risk alleles such as MC1R variants are coincident with mutation of higher-risk melanoma genes including CDKN2A, CDK4 and MITF E318K, demonstrating an interface between the pathways for pigmentation, naevogenesis and melanoma. The clinical phenotypes associated with germline changes in pigmentation and naevogenic genes must be understood by clinicians, and will be of increasing relevance to dermatologists, as genomics is incorporated into the delivery of personalised medicine.

The Microphthalmia-Associated Transcription Factor p.E318K Mutation Does Not Play a Major Role in Sporadic Renal Cell Tumors from Caucasian Patients.

OBJECTIVE: The transcription factor MITF (microphthalmia-associated transcription factor) is known to induce expression of hypoxia-inducible factor (HIF1-α), which is involved in renal carcinogenesis. The MITF p.E318K mutation leads to deficient SUMOylation of MITF, resulting in enhanced activation of its target genes. A case-control study on melanoma patients who coincidentally were affected by renal cell carcinoma (RCC) has revealed an elevated risk for mutation carriers to be affected by one or both of these malignancies, suggesting a possible role for MITF p.E318K in renal carcinogenesis. The same study described an MITF mutation frequency of 1.5% in a small cohort of sporadic RCC, but comprehensive data on sporadic renal cell tumors are missing. We therefore tested a large cohort of sporadic renal tumors for MITF p.E318K mutation status. METHODS: Genomic DNA was extracted from 426 formalin-fixed, paraffin-embedded sporadic renal tumors that had been graded according to the 2004 WHO classification of renal tumors and staged according to the 2002 TNM classification. The tumor cohort was enriched with papillary and chromophobe RCC, and also contained benign oncocytomas. DNA was tested for MITF p.E318K by pyrosequencing. RESULTS: Of 403 analyzable tumors, 402 renal tumors were wild-type ones, and only 1 case showed the MITF p.E318K mutation. This tumor was a clear-cell RCC (pT3b N0 M0 G3 according to the TNM classification 2002). The affected patient was male, 61 years old, and had no known coexisting malignancies. CONCLUSION: The MITF p.E318K mutation does not appear to play a major role in sporadic RCC carcinogenesis, but is possibly restricted to a rare subpopulation of inherited RCC.

Dermoscopy, reflectance confocal microscopy and histopathology of a melanoma in situ from an individual homozygous for GSTP1*105Val/MC1R*92Met.

Glutathione S-transferase 1 is an enzyme involved in the detoxification of reactive oxygen species, and the rs1695*Val polymorphism has been proposed as a melanoma-associated variant with significant effect. We report a case of malignant melanoma in an individual homozygous for the rs1695*Val variant and discuss the non-invasive and histopathological tools used in diagnosis.

Genetics of skin color variation in Europeans: genome-wide association studies with functional follow-up.

In the International Visible Trait Genetics (VisiGen) Consortium, we investigated the genetics of human skin color by combining a series of genome-wide association studies (GWAS) in a total of 17,262 Europeans with functional follow-up of discovered loci. Our GWAS provide the first genome-wide significant evidence for chromosome 20q11.22 harboring the ASIP gene being explicitly associated with skin color in Europeans. In addition, genomic loci at 5p13.2 (SLC45A2), 6p25.3 (IRF4), 15q13.1 (HERC2/OCA2), and 16q24.3 (MC1R) were confirmed to be involved in skin coloration in Europeans. In follow-up gene expression and regulation studies of 22 genes in 20q11.22, we highlighted two novel genes EIF2S2 and GSS, serving as competing functional candidates in this region and providing future research lines. A genetically inferred skin color score obtained from the 9 top-associated SNPs from 9 genes in 940 worldwide samples (HGDP-CEPH) showed a clear gradual pattern in Western Eurasians similar to the distribution of physical skin color, suggesting the used 9 SNPs as suitable markers for DNA prediction of skin color in Europeans and neighboring populations, relevant in future forensic and anthropological investigations.

TLR3 drives IRF6-dependent IL-23p19 expression and p19/EBI3 heterodimer formation in keratinocytes.

Interferon regulatory factor (IRF) family members impart cell-type specificity to toll-like receptor (TLR) signalling, and we recently identified a role for IRF6 in TLR2 signalling in epithelial cells. TLR3 has a well-characterized role in wound healing in the skin, and here, we examined TLR3-dependent IRF6 functions in human keratinocytes. Primary keratinocytes responded robustly to the TLR3 agonist poly(IC) with upregulation of mRNAs for interferon-ß (IFN-ß), the interleukin-12 (IL-12) family member IL-23p19 and the chemokines IL-8 and chemokine (C-C motif) ligand 5 (CCL5). Silencing of IRF6 expression enhanced poly(IC)-inducible IFN-ß mRNA levels and inhibited poly(IC)-inducible IL-23p19 mRNA expression in primary keratinocytes. Consistent with these data, co-transfection of IRF6 increased poly(IC)-inducible IL-23p19 promoter activity, but inhibited poly(IC)-inducible IFN-ß promoter activity in reporter assays. Surprisingly, poly(IC) did not regulate IL-12p40 expression in keratinocytes, suggesting that TLR3-inducible IL-23p19 may have an IL-23-independent function in these cells. The only other IL-12 family member that was strongly poly(IC) inducible was EBI3, which has not been shown to heterodimerize with IL-23p19. Both co-immunoprecipitation and proximity ligation assays revealed that IL-23p19 and EBI3 interact in cells. Co-expression of IL-23p19 and EBI3, as compared with IL-23p19 alone, resulted in increased levels of secreted IL-23p19, implying a functional role for this heterodimer. In summary, we report that IRF6 regulates a subset of TLR3 responses in human keratinocytes, including the production of a novel IL-12 family heterodimer (p19/EBI3). We propose that the TLR3-IRF6-p19/EBI3 axis may regulate keratinocyte and/or immune cell functions in the context of cell damage and wound healing in the skin.

GWAS findings for human iris patterns: associations with variants in genes that influence normal neuronal pattern development.

Human iris patterns are highly variable. The origins of this variation are of interest in the study of iris-related eye diseases and forensics, as well as from an embryological developmental perspective, with regard to their possible relationship to fundamental processes of neurodevelopment. We have performed genome-wide association scans on four iris characteristics (crypt frequency, furrow contractions, presence of peripupillary pigmented ring, and number of nevi) in three Australian samples of European descent. Both the discovery (n = 2121) and replication (n = 499 and 73) samples showed evidence for association between (1) crypt frequency and variants in the axonal guidance gene SEMA3A (p = 6.6 × 10(-11)), (2) furrow contractions and variants within the cytoskeleton gene TRAF3IP1 (p = 2.3 × 10(-12)), and (3) the pigmented ring and variants in the well-known pigmentation gene SLC24A4 (p = 7.6 × 10(-21)). These replicated findings individually accounted for around 1.5%-3% of the variance for these iris characteristics. Because both SEMA3A and TRAFIP1 are implicated in pathways that control neurogenesis, neural migration, and synaptogenesis, we also examined the evidence of enhancement among such genes, finding enrichment for crypts and furrows. These findings suggest that genes involved in normal neuronal pattern development may also influence tissue structures in the human iris.

MC1R and NR4A receptors in cellular stress and DNA repair: implications for UVR protection.

Ultraviolet radiation (UVR) is the most common mutagen that melanocytes are exposed to. UVR causes a diverse range of DNA photolesions contributing to genome instability and promotes melanoma and non-melanoma development. Melanocytes are pigment-producing cells that synthesise the photoprotective melanins when the melanocortin-1 receptor (MC1R) is activated. MC1R is a G-protein-coupled receptor expressed predominantly in melanocytes. Its signalling pathway has been directly linked to melanogenesis, enhanced cytoprotection against UV damage and augmented DNA repair response. Interestingly, previous studies have revealed that MC1R signalling induces the transcription of the NR4A subfamily of orphan nuclear receptors in response to UV. In line with this, studies have also observed that NR4A receptors are recruited to distinct nuclear foci in response to cellular stress, independent of their transcriptional roles. Here, we review the regulated expression of NR4A2 and its potential roles upon cellular stress conditions. Current work in developing synthetic NR4A2 agonists further provides exciting avenues for exploring the potential role of NR4A2 as an antiskin cancer drug target.

DCT protects human melanocytic cells from UVR and ROS damage and increases cell viability.

Dopachrome tautomerase (DCT) is involved in the formation of the photoprotective skin pigment eumelanin and has also been shown to have a role in response to apoptotic stimuli and oxidative stress. The effect of DCT on UVR DNA damage responses and survival pathways in human melanocytic cells was examined by knockdown experiments using melanoma cells, neonatal foreskin melanoblasts (MB) in monoculture and in co-culture with human keratinocytes. MB cell strains genotyped as either MC1R WT or MC1R RHC homozygotes, which are known to be deficient in DCT, were transduced with lentivirus vectors for either DCT knockdown or overexpression. We found melanoma cell survival was reduced by DCT depletion and by UVR over time. UVR-induced p53 and pp53-Ser15 levels were reduced with DCT depletion. Knockdown of DCT in MC1R WT and MC1R RHC MB cells reduced their survival after UVR exposure, whereas increased DCT protein levels enhanced survival. DCT depletion reduced p53 and pp53-Ser15 levels in WM266-4 melanoma and MC1R WT MB cells, while MC1R RHC MB cells displayed variable levels. Both MC1R WT and RHC genotypes of MB cells were responsive to UVR at 3 h with increases in both p53 and pp53-Ser15 proteins. MC1R WT MB cell strains in coculture with keratinocytes have an increased cell survival after UVR exposure when compared to those in monoculture, a protective effect which appears to be conferred by the keratinocytes.