Melanocortin-1 receptor gene variants determine the risk of nonmelanoma skin cancer independently of fair skin and red hair

Melanocortin-1 receptor (MC1R): a review for dermatologists

Melanocortin-1 receptor (MC1R) and its variants have a pivotal role in melanin synthesis. However, MC1R has been associated to non-pigmentary pathways related to DNA-repair activities and inflammation. The aim of this review is to provide an up-to-date overview about the role of MC1R in the skin. Specifically, after summarizing the current knowledge about MC1R structure and polymorphisms, we report data concerning the correlation between MC1R, phenotypic traits, skin aging, other diseases and skin cancers and their risk assessment through genetic testing.

Melanoma-associated melanocortin 1 receptor variants confer redox signaling-dependent protection against oxidative DNA damage

Cutaneous melanoma, a lethal skin cancer, arises from malignant transformation of melanocytes. Solar ultraviolet radiation (UVR) is a major environmental risk factor for melanoma since its interaction with the skin generates DNA damage, either directly or indirectly via oxidative stress. Pheomelanin pigments exacerbate oxidative stress in melanocytes by UVR-dependent and independent mechanisms. Thus, oxidative stress is considered to contribute to melanomagenesis, particularly in people with pheomelanic pigmentation. The melanocortin 1 receptor gene (MC1R) is a major melanoma susceptibility gene. Frequent MC1R variants (varMC1R) associated with fair skin and red or yellow hair color display hypomorphic signaling to the cAMP pathway and are associated with higher melanoma risk. This association is thought to be due to production of photosensitizing pheomelanins as well as deficient induction of DNA damage repair downstream of varMC1R. However, the data on modulation of oxidative DNA damage repair by MC1R remain scarce. We recently demonstrated that varMC1R accelerates clearance of reactive oxygen species (ROS)-induced DNA strand breaks in an AKT-dependent manner. Here we show that varMC1R also protects against ROS-dependent formation of 8-oxodG, the most frequent oxidative DNA lesion. Since the base excision repair (BER) pathway mediates clearance of these DNA lesions, we analyzed induction of BER enzymes in human melanoma cells of varMC1R genotype. Agonist-mediated activation of both wildtype (wtMC1R) and varMC1R significantly induced OGG and APE-1/Ref1, the rate-limiting BER enzymes responsible for repair of 8-oxodG. Moreover, we found that NADPH oxidase (NOX)-dependent generation of ROS was responsible for AKT activation and oxidative DNA damage repair downstream of varMC1R. These observations provide a better understanding of the functional properties of melanoma-associated MC1R alleles and may be useful for the rational development of strategies to correct defective varMC1R responses for efficient photoprotection and melanoma prevention in fair-skinned individuals.

Adenosine and Its Receptors in the Pathogenesis and Treatment of Inflammatory Skin Diseases

Inflammatory skin diseases highlight inflammation as a central driver of skin pathologies, involving a multiplicity of mediators and cell types, including immune and non-immune cells. Adenosine, a ubiquitous endogenous immune modulator, generated from adenosine triphosphate (ATP), acts via four G protein-coupled receptors (A1, A2A, A2B, and A3). Given the widespread expression of those receptors and their regulatory effects on multiple immune signaling pathways, targeting adenosine receptors emerges as a compelling strategy for anti-inflammatory intervention. Animal models of psoriasis, contact hypersensitivity (CHS), and other dermatitis have elucidated the involvement of adenosine receptors in the pathogenesis of these conditions. Targeting adenosine receptors is effective in attenuating inflammation and remodeling the epidermal structure, potentially showing synergistic effects with fewer adverse effects when combined with conventional therapies. What is noteworthy are the promising outcomes observed with A2A agonists in animal models and ongoing clinical trials investigating A3 agonists, underscoring a potential therapeutic approach for the management of inflammatory skin disorders.

Afamelanotide in protoporphyria and other skin diseases: a review

Afamelanotide is a synthetic alpha melanocyte stimulating hormone presenting a higher activity than natural hormones. Its main properties are related to the enhanced production of eumelanin by agonistically binding to the melanocortin-1 receptor. Since 2016 afamelanotide has been especially applied to treat cases of erythropoietic porphyria (EPP), where painful photosensitivity has been observed since early childhood. The positive effect of afamelanotide in EPP administered subcutaneously improved tolerance to artificial white light and increased pain-free time spent in direct sunlight. In this review we summarize the possible use of afamelanotide in dermatology, with special emphasis on EPP and encourage including afamelanotide as a treatment option in patient care.

The Keratinocyte in the Picture Cutaneous Melanoma Microenvironment

Melanoma progression is a multistep evolution from a common melanocytic nevus through a radial superficial growth phase, the invasive vertical growth phase finally leading to metastatic dissemination into distant organs. Melanoma aggressiveness largely depends on the propensity to metastasize, which means the capacity to escape from the physiological microenvironment since tissue damage due to primary melanoma lesions is generally modest. Physiologically, epidermal melanocytes are attached to the basement membrane, and their adhesion/migration is under the control of surrounding keratinocytes. Thus, the epidermal compartment represents the first microenvironment responsible for melanoma spread. This complex process involves cell-cell contact and a broad range of secreted bioactive molecules. Invasion, or at the beginning of the microinvasion, implies the breakdown of the dermo-epidermal basement membrane followed by the migration of neoplastic melanocytic cells in the superficial papillary dermis. Correspondingly, several experimental evidences documented the structural and functional rearrangement of the entire tissue surrounding neoplasm that in some way reflects the atypia of tumor cells. Lastly, the microenvironment must support the proliferation and survival of melanocytes outside the normal epidermal-melanin units. This task presumably is mostly delegated to fibroblasts and ultimately to the self-autonomous capacity of melanoma cells. This review will discuss remodeling that occurs in the epidermis during melanoma formation as well as skin changes that occur independently of melanocytic hyperproliferation having possible pro-tumoral features.

Natural hair color and skin cancers: A two-sample Mendelian randomization study

Previous observational studies have indicated an association between hair color and the risk of melanoma and keratinocyte skin cancer (KSC); however, different hair colors show inconsistent effects on skin cancers. Here, we conducted a two-sample Mendelian randomization (MR) study to evaluate the causal relationship between natural hair color and skin cancers by using 211 single nucleotide polymorphisms as genetic instruments from a genome-wide meta-analysis of 360,270 individuals of European ancestry. Light hair colors (red, blonde, and light brown) were associated with high levels of cutaneous melanoma (CM) and KSC (CM-inverse variance weighted [IVW] odds ratio [OR]-red: 1.034, 95% confidence interval [CI]: 1.025-1.044, P < 0.001; OR-blonde: 1.008, 95% CI: 1.003-1.014, P = 0.003; OR-light brown: 1.006, 95% CI: 1.002-1.011, P = 0.009; KSC-IVW OR-red: 1.078, 95% CI: 1.053-1.103, P < 0.001; OR-blonde: 1.024, 95% CI: 1.009-1.040, P = 0.002; OR-light brown: 1.018, 95% CI: 1.004-1.033, P = 0.01). However, dark brown hair showed an inverse causal relationship with skin cancers (CM IVW OR: 0.987, 95% CI: 0.984-0.990, P < 0.001; KSC IVW OR: 0.979, 95% CI: 0.970-0.988, P < 0.001). Black hair was associated with a decreased risk of KSC (IVW OR: 0.954, 95% CI: 0.913-0.997, P = 0.036) but showed no causal relationship with CM. The present study provides strong MR evidence of a causal association between hair color and skin cancer. Secondary MR analyses enhances result robustness by replicating findings, exploring gender-specific effects, and providing a more comprehensive understanding of the complex relationship between hair color and skin cancers. More large-scale MR studies or randomized controlled trials are required to further investigate the mechanisms of the association between hair color and skin cancers.

Cumulative UV Exposure or a Modified SCINEXA™-Skin Aging Score Do Not Play a Substantial Role in Predicting the Risk of Developing Keratinocyte Cancers after Solid Organ Transplantation-A Case Control Study

The risk of keratinocyte cancer is determined by intrinsic and extrinsic factors, which also influence skin aging. Few studies have linked skin aging and UV exposure with the incidence of non-melanoma skin cancer (NMSC). We evaluated signs of actinic skin damage and aging, individual UV burden, and melanocortin-1 receptor (MC1R) variants. A total of 194 organ transplant recipients (OTR) who suffered from NMSC were compared to 194 tumor-free controls matched for gender, age, type of transplanted organ, post-transplantation (TX) period, and immunosuppressive therapy. Compared with the cases, the controls scored higher in all skin aging scores and there were no differences in UV burden except for intentional whole-body UV exposure for specific UV scenarios and periods of life in favor of cases. The number of NMSCs correlated with all types of skin aging scores, the extent of intentional sun exposure, older age, longer post-TX period, shorter interval from TX to first NMSC, and specific MC1R risk groups. Multivariable models revealed a 7.5-fold risk of developing NMSC in individuals with actinic keratosis; 4.1- or 3.6-fold in those with green or blue eyes, respectively; and a 1.9-fold increased risk in the MC1R medium- + high-risk group. In the absence of skin aging contributing to NMSC development, certain MC1R risk types may identify OTR at risk for high tumor burden.

Melanocortin 1 receptor variants and their association with phenotypic characteristics and sporadic multiple primary melanomas in a cohort of 402 Spanish subjects

The melanocortin 1 receptor (MC1R) gene is considered to be a major determinant of the risk of melanoma. The role of MC1R polymorphisms as predisposing factors for the development of a second primary melanoma is not well established. The present study analyses the characteristics from subjects with certain MC1R variants without any other genetic predisposition, as well as the risk of second primary melanoma associated with these variants. We performed a prospective longitudinal single-centre study based on follow-up information of 402 patients diagnosed with cutaneous melanoma. MC1R gene was sequenced in all subjects. High-risk variants were defined as those previously associated with melanoma (V60L, V92M, I155T, R160W, R163Q and D294H). 253 (63%) patients had at least one predisposing variant. These individuals had higher proportion of red/blonde hair, multiple primary melanomas and first melanoma diagnosis under the age of 60. Second primary melanomas were detected in 28 (3.8%) subjects. Having more than 25 melanocytic nevi was associated significantly to the development of second primary melanomas. A higher proportion of individuals carrying at least one predisposing MC1R variant develop a second melanoma, although statistical significance was not reached. Therefore, some MC1R polymorphisms might determine clinical and histological differences between patients with cutaneous melanoma and may represent a risk factor for second primary melanoma, although more studies are needed.

Molecular Mechanisms and Targeted Therapies of Advanced Basal Cell Carcinoma

Among human cutaneous malignancies, basal cell carcinoma is the most common. Solid advances in unveiling the molecular mechanisms of basal cell carcinoma have emerged in recent years. In Gorlin syndrome, which shows basal cell carcinoma predisposition, identification of the patched 1 gene (PTCH1) mutation was a dramatic breakthrough in understanding the carcinogenesis of basal cell carcinoma. PTCH1 plays a role in the hedgehog pathway, and dysregulations of this pathway are known to be crucial for the carcinogenesis of many types of cancers including sporadic as well as hereditary basal cell carcinoma. In this review, we summarize the clinical features, pathological features and hedgehog pathway as applied in basal cell carcinoma. Other crucial molecules, such as p53 and melanocortin-1 receptor are also discussed. Due to recent advances, therapeutic strategies based on the precise molecular mechanisms of basal cell carcinoma are emerging. Target therapies and biomarkers are also discussed.

Melanocortin-1 receptor mutations and pigmentation: Insights from large animals

The melanocortin-1 receptor (MC1R) is a G protein-coupled receptor expressed in cutaneous and hair follicle melanocytes, and plays a central role in coat color determination in vertebrates. Numerous MC1R variants have been identified in diverse species. Some of these variants have been associated with specific hair and skin color phenotypes in humans as well as coat color in animals. Gain-of-function mutations of the MC1R gene cause dominant or partially dominant black/dark coat color, and loss-of-function mutations of the MC1R gene cause recessive or partially recessive red/yellow/pale coat color phenotypes. These have been well documented in a large number of mammals, including human, dog, cattle, horse, sheep, pig, and fox. Higher similarities between large mammals and humans makes them better models to understand pathogenesis of human diseases caused by MC1R mutations. High identities in MC1Rs and similar variants identified in both humans and large mammals also provide an opportunity for receptor structure and function study. In this review, we aim to summarize the naturally occurring mutations of MC1R in humans and large animals.

Functional divergence of the pigmentation gene melanocortin-1 receptor (MC1R) in six endemic Macaca species on Sulawesi Island

Coat color is often highly variable within and between animal taxa. Among hundreds of pigmentation-related genes, melanocortin-1 receptor (MC1R) plays key roles in regulating the synthesis of the dark eumelanin and the red-yellow pheomelanin. The six species of macaques that inhabit Sulawesi Island diverged rapidly from their common ancestor, M. nemestrina. Unlike most macaques, Sulawesi macaques commonly have a dark coat color, with divergence in shade and color pattern. To clarify the genetic and evolutionary basis for coat color in Sulawesi macaques, we investigated the MC1R sequences and functional properties, including basal cAMP production and α-MSH-induced activity in vitro. We found fixed non-synonymous substitutions in MC1R in each species. Furthermore, we found that six species-specific variants corresponded with variation in agonist-induced and basal activity of MC1R. Inconsistent with the dark coat color, four substitutions independently caused decreases in the basal activity of MC1R in M. hecki, M. nigra, M. tonkeana, and M. ochreata. Selective analysis suggested MC1R of M. nigra and M. nigrescens underwent purifying selection. Overall, our results suggest that fixed differences in MC1R resulted in different functional characteristics and might contribute to divergence in color among the six Sulawesi macaque species.

Expression of Melanocortin-1 Receptor and Serum Melanin in Canities at Young Male students

BACKGROUND: Molecular genetics suggest that hair pigmentation is related to the melanocortin-1 receptor gene. It is a G protein-coupled receptor, which is activated by a number of peptides to stimulate melanogenesis. Melanocortin-1 receptor gene mutation tends to produce functional variability in premature hair graying (PHG) or canities. AIM: Therefore, the objective of this study was to determine melanocortin-1 receptor expression and asses serum melanin in college students canities at Universitas Sumatera Utara. METHODS: This study was a cross-sectional design. We recruited 80 subjects equally divided into normal (control) and premature hair graying groups. The sample included males, aged 25 years who had gray hair and had no history of pigmentary disorders of the skin. Expression of melanocortin-1 receptor was detected with conventional PCR and serum melanin was measured with Elisa using Elisa kit melanin for human. RESULTS: The results showed that the Mean ± SD graying age was 20.28 ± 1.99 years with an age range of 19–24 years and the average age in the control group was 21.25 ± 2.02 years with an age range of 18–24 years. Melanocortin-1 receptor gene expression was shown in the control and PHG groups. Serum melanin levels were decreased significantly (p = 0.0001) in the gray-haired group was 9.27 ± 1.62 μg/dl and the control group was 10.72 ± 1.78 μg/dl. CONCLUSION: Melanocortin-1 receptor gene plays a role in hair graying at young age and there serum melanin levels were low significantly.

Melanogenic effect of dersimelagon (MT-7117), a novel oral melanocortin 1 receptor agonist

Background

The activation of melanocortin 1 receptor (MC1R) on melanocytes stimulates the production of eumelanin. A tridecapeptide α melanocyte‐stimulating hormone (αMSH) is known to induce skin pigmentation.

Objectives

We characterised the properties of a novel oral MC1R agonist dersimelagon (MT‐7117) with respect to its specific binding to MC1R, downstream signalling and eumelanin production in experimental models.

Methods

The competitive binding and production of intracellular cyclic adenosine 3′, 5′‐monophosphate in cells expressing recombinant melanocortin receptors were examined. A mouse melanoma cell line B16F1 was used for the evaluation of in vitro melanin production. The in vitro activity of MT‐7117 was determined with αMSH and [Nle⁴, D‐Phe⁷]‐αMSH (NDP‐αMSH) as reference comparators. The change of coat colour and skin pigmentation were evaluated after repeat administration of MT‐7117 by oral gavage to C57BL/6J‐A^y/+ mice and cynomolgus monkeys, respectively.

Results

MT‐7117 showed the highest affinity for human MC1R compared to the other melanocortin receptors evaluated and agonistic activity for human, cynomolgus monkey and mouse MC1R, with EC₅₀ values in the nanomolar range. In B16F1 cells, MT‐7117 increased melanin production in a concentration‐dependent manner. In vivo, MT‐7117 (≥0.3 mg/kg/day p.o.) significantly induced coat colour darkening in mice. MT‐7117 (≥1 mg/kg/day p.o.) induced significant skin pigmentation in monkeys and complete reversibility was observed after cessation of its administration.

Conclusions

MT‐7117 is a novel oral MC1R agonist that induces melanogenesis in vitro and in vivo, suggesting its potential application for the prevention of phototoxic reactions in patients with photodermatoses, such as erythropoietic protoporphyria and X‐linked protoporphyria.

Behind the Scene: Exploiting MC1R in Skin Cancer Risk and Prevention

Melanoma and non-melanoma skin cancers (NMSCs) are the most frequent cancers of the skin in white populations. An increased risk in the development of skin cancers has been associated with the combination of several environmental factors (i.e., ultraviolet exposure) and genetic background, including melanocortin-1 receptor (MC1R) status. In the last few years, advances in the diagnosis of skin cancers provided a great impact on clinical practice. Despite these advances, NMSCs are still the most common malignancy in humans and melanoma still shows a rising incidence and a poor prognosis when diagnosed at an advanced stage. Efforts are required to underlie the genetic and clinical heterogeneity of melanoma and NMSCs, leading to an optimization of the management of affected patients. The clinical implications of the impact of germline MC1R variants in melanoma and NMSCs' risk, together with the additional risk conferred by somatic mutations in other peculiar genes, as well as the role of MC1R screening in skin cancers' prevention will be addressed in the current review.

The α-melanocyte-stimulating hormone/melanocortin-1 receptor interaction: A driver of pleiotropic effects beyond pigmentation

Melanocortin-1 Receptor (MC1R), when stimulated by alpha-melanocyte-stimulating hormone (α-MSH), is a driver of eumelanogenesis. Brown/black eumelanin is an effective filter against ultraviolet radiation (UVR) and is a scavenger of free radicals. Several polymorphic variants of MC1R are frequent in red-head people. These polymorphisms reduce the ability of MC1R to promote eumelanogenesis after its activation and spontaneous pheomelanogenesis take place. Since pheomelanin can act as an endogenous photosensitizer, people carrying MC1R polymorphisms are more susceptible to skin cancer. Here, we summarize current knowledge on the biology of MC1R beyond its ability to drive eumelanogenesis. We analyze its capacity to cope with oxidative insult and consequent DNA damage. We describe its ability to transduce through different pathways. We start from the canonical pathway, the cAMP/protein kinase A (PKA) pathway mainly involved in promoting eumelanogenesis, and protection from oxidative damage, and we then move on to describe more recent knowledge concerning ERK pathways, phosphoinositide 3-kinase (PI3K) pathway/AKT, and α-MSH/Peroxisome proliferators activated receptor-γ (PPAR-γ) connection. We describe MC1R polymorphic variants associated with melanoma risk which represent an open window of clinical relevance.

Neuropeptides and neurohormones in immune, inflammatory and cellular responses to ultraviolet radiation

Humans are exposed to varying amounts of ultraviolet radiation (UVR) through sunlight. UVR penetrates into human skin leading to release of neuropeptides, neurotransmitters and neuroendocrine hormones. These messengers released from local sensory nerves, keratinocytes, Langerhans cells (LCs), mast cells, melanocytes and endothelial cells (ECs) modulate local and systemic immune responses, mediate inflammation and promote differing cell biologic effects. In this review, we will focus on both animal and human studies that elucidate the roles of calcitonin gene-related peptide (CGRP), substance P (SP), nerve growth factor (NGF), nitric oxide and proopiomelanocortin (POMC) derivatives in mediating immune and inflammatory effects of exposure to UVR as well as other cell biologic effects of UVR exposure.

Afamelanotide for prevention of phototoxicity in erythropoietic protoporphyria

Introduction: In erythropoietic protoporphyria (EPP), an inherited disorder of heme biosynthesis, accumulation of protoporphyrin IX results in acute phototoxicity. EPP patients experience severe burning pain after light exposure, which results in a markedly reduced quality of life. Afamelanotide is the first effective approved medical treatment for EPP, acting on melanocortin-1 receptors. This article aims to review afamelanotide.Areas covered: This review summarizes the chemical properties, pharmacokinetics, safety, preclinical and clinical data on afamelanotide in EPP, and post-marketing surveillance. PubMed search, manufacturers' websites, and relevant articles used for approval by authorities were used for the literature search.Expert opinion: Afamelanotide is an α-melanocyte-stimulating hormone analog. It can activate eumelanogenesis without exposure to UV radiation. Clinical studies in EPP showed that afamelanotide treatment significantly increased exposure to sunlight and QoL. In our clinical experience afamelanotide treatment is much more effective in clinical practice than demonstrated in clinical trials and should be made available for all EPP patients meeting inclusion criteria. The 60-day interval period was not based on effectiveness studies, and therefore for some of the patients the maximum of four implants per year with the 60-day interval is insufficient. Afamelanotide is well tolerated; common adverse events were headache, fatigue, and nausea.

Incidence and survival of cutaneous melanoma in Belgium and the Netherlands from 2004 to 2016: striking differences and similarities of two neighbouring countries

BACKGROUND

Cutaneous melanoma (CM) is a multifactorial disease, with both environmental and genetic factors involved. The incidence of CM has risen rapidly during the last decades, making it a growing public health problem.

OBJECTIVES

The purpose of this retrospective study was to compare incidence and survival data of CM between two neighbouring countries, Belgium (BE) and the Netherlands (NL).

METHODS

Data were collected by the Belgian Cancer Registry (BCR) and the Netherlands Cancer Registry (NCR) from 1 January 2004 until 31 December 2016. Mucosal melanoma, in situ CM and melanoma in children from 0 to 14 years were excluded. Age-standardized incidence rates were calculated using the World Standard Population (WSR) per 100 000 persons. Five-year relative survival ratios were calculated using the Ederer II methodology.

RESULTS

Total number of CM was higher in NL (63 789) compared with BE (27 679). The WSR was 1.5 times higher in NL compared with BE (27.7 vs. 18.6/100 000/year). The WSR of stage IV tumours was higher in BE than in NL (0.3 vs. 0.2/100 000/year). Five-year relative survival of stage IV tumours was higher in BE compared with NL (27.2% vs. 13.7%).

CONCLUSIONS

Incidence of CM was higher in NL, indicating a higher risk of CM diagnosis. Stage IV tumours were relatively more frequent in BE for both sexes, while relative survival of stage IV tumours was higher in BE. As geographical location and latitude of both neighbouring countries are almost identical, other factors like differences in behaviour, follow-up and/or treatment may explain these differences.

Loss-of-Function Variants in the Tumor-Suppressor Gene PTPN14 Confer Increased Cancer Risk

The success of genome-wide association studies (GWAS) in identifying common, low-penetrance variant-cancer associations for the past decade is undisputed. However, discovering additional high-penetrance cancer mutations in unknown cancer predisposing genes requires detection of variant-cancer association of ultra-rare coding variants. Consequently, large-scale next-generation sequence data with associated phenotype information are needed. Here, we used genotype data on 166,281 Icelanders, of which, 49,708 were whole-genome sequenced and 408,595 individuals from the UK Biobank, of which, 41,147 were whole-exome sequenced, to test for association between loss-of-function burden in autosomal genes and basal cell carcinoma (BCC), the most common cancer in Caucasians. A total of 25,205 BCC cases and 683,058 controls were tested. Rare germline loss-of-function variants in PTPN14 conferred substantial risks of BCC (OR, 8.0; P = 1.9 × 10^-12), with a quarter of carriers getting BCC before age 70 and over half in their lifetime. Furthermore, common variants at the PTPN14 locus were associated with BCC, suggesting PTPN14 as a new, high-impact BCC predisposition gene. A follow-up investigation of 24 cancers and three benign tumor types showed that PTPN14 loss-of-function variants are associated with high risk of cervical cancer (OR, 12.7, P = 1.6 × 10^-4) and low age at diagnosis. Our findings, using power-increasing methods with high-quality rare variant genotypes, highlight future prospects for new discoveries on carcinogenesis. SIGNIFICANCE: This study identifies the tumor-suppressor gene PTPN14 as a high-impact BCC predisposition gene and indicates that inactivation of PTPN14 by germline sequence variants may also lead to increased risk of cervical cancer.

Cyclic adenosine monophosphate (cAMP) signaling in melanocyte pigmentation and melanomagenesis

The second messenger cyclic adenosine monophosphate (cAMP) regulates numerous functions in both benign melanocytes and melanoma cells. cAMP is generated from two distinct sources, transmembrane and soluble adenylyl cyclases (tmAC and sAC, respectively), and is degraded by a family of proteins called phosphodiesterases (PDEs). cAMP signaling can be regulated in many different ways and can lead to varied effects in melanocytes. It was recently revealed that distinct cAMP signaling pathways regulate pigmentation by either altering pigment gene expression or the pH of melanosomes. In the context of melanoma, many studies report seemingly contradictory roles for cAMP in tumorigenesis. For example, cAMP signaling has been implicated in both cancer promotion and suppression, as well as both therapy resistance and sensitization. This conundrum in the field may be explained by the fact that cAMP signals in discrete microdomains and each microdomain can mediate differential cellular functions. Here, we review the role of cAMP signaling microdomains in benign melanocyte biology, focusing on pigmentation, and in melanomagenesis.

Oxidative Stress and Genotoxicity in Melanoma Induction: Impact on Repair Rather Than Formation of DNA Damage?

Keratinocytes and melanocytes, two cutaneous cell types located within the epidermis, are the origin of most skin cancers, namely carcinomas and melanomas. These two types of tumors differ in many ways. First, carcinomas are almost 10 times more frequent than melanomas. In addition, the affected cellular pathways, the mutated genes and the metastatic properties of the tumors are not the same. This review addresses another specificity of melanomas: the role of photo-oxidative stress. UVA efficiently produces reactive oxygen species in melanocytes, which results in more frequent oxidatively generated DNA lesions than in other cell types. The question of the respective contribution of UVB-induced pyrimidine dimers and UVA-mediated oxidatively generated lesions to mutagenesis in melanoma remains open. Recent results based on next-generation sequencing techniques strongly suggest that the mutational signature associated with pyrimidine dimers is overwhelming in melanomas like in skin carcinomas. UVA-induced oxidative stress may yet be indirectly linked to the genotoxic pathways involved in melanoma through its ability to hamper DNA repair activities.

The current status of anti-GPCR drugs against different cancers

G protein coupled receptors (GPCRs) have emerged as the most potential target for a number of drug discovery programs ranging from control of blood pressure, diabetes, cure for genetic diseases to treatment of cancer. A panel of different ligands including hormones, peptides, ions and small molecules is responsible for activation of these receptors. Molecular genetics has identified key GPCRs, whose mutations or altered expressions are linked with tumorgenicity. In this review, we discussed recent advances regarding the involvement of GPCRs in the development of cancers and approaches to manipulating the mechanism behind GPCRs involved tumor growth and metastasis to treat different types of human cancer. This review provides an insight into the current scenario of GPCR-targeted therapy, progress to date and the challenges in the development of anticancer drugs.

Hierarchical modeling of melanocortin 1 receptor variants with skin cancer risk

The human MC1R gene is highly polymorphic among lightly pigmented populations, and several variants in the MC1R gene have been associated with increased risk of both melanoma and nonmelanoma skin cancers. The functional consequences of MC1R gene variants have been studied in vitro and in vivo in postulated causal pathways, such as G-protein-coupled signaling transduction, pigmentation, immune response, inflammatory response, cell proliferation, and extracellular matrix adhesion. In a case-control study nested within the Nurses' Health Study, we utilized hierarchical modeling approaches, incorporating quantitative information from these functional studies, to examine the association between particular MC1R alleles and the risk of skin cancers. Different prior matrices were constructed according to the phenotypic associations in controls, cell surface expression, and enzymatic kinetics. Our results showed the parameter variance estimates of each single nucleotide polymorphism (SNP) were smaller when using a hierarchical modeling approach compared to standard multivariable regression. Estimates of second-level parameters gave information about the relative importance of MC1R effects on different pathways, and odds ratio estimates changed depending on prior models (e.g., the change ranged from -21% to 7% for melanoma risk assessment). In addition, the estimates of prior model hyperparameters in the hierarchical modeling approach allow us to determine the relevance of individual pathways on the risk of each of the skin cancer types. In conclusion, hierarchical modeling provides a useful analytic approach in addition to the widely used conventional models in genetic association studies that can incorporate measures of allelic function.

cAMP-independent non-pigmentary actions of variant melanocortin 1 receptor: AKT-mediated activation of protective responses to oxidative DNA damage

The melanocortin 1 receptor gene (MC1R), a well-established melanoma susceptibility gene, regulates the amount and type of melanin pigments formed within epidermal melanocytes. MC1R variants associated with increased melanoma risk promote the production of photosensitizing pheomelanins as opposed to photoprotective eumelanins. Wild-type (WT) MC1R activates DNA repair and antioxidant defenses in a cAMP-dependent fashion. Since melanoma-associated MC1R variants are hypomorphic in cAMP signaling, these non-pigmentary actions are thought to be defective in MC1R-variant human melanoma cells and epidermal melanocytes, consistent with a higher mutation load in MC1R-variant melanomas. We compared induction of antioxidant enzymes and DNA damage responses in melanocytic cells of defined MC1R genotype. Increased expression of catalase (CAT) and superoxide dismutase (SOD) genes following MC1R activation was cAMP-dependent and required a WT MC1R genotype. Conversely, pretreatment of melanocytic cells with an MC1R agonist before an oxidative challenge with Luperox decreased (i) accumulation of 8-oxo-7,8-dihydro-2'-deoxyguanine, a major product of oxidative DNA damage, (ii) phosphorylation of histone H2AX, a marker of DNA double-strand breaks, and (iii) formation of DNA breaks. These responses were comparable in cells WT for MC1R or harboring hypomorphic MC1R variants without detectable cAMP signaling. In MC1R-variant melanocytic cells, the DNA-protective responses were mediated by AKT. Conversely, in MC1R-WT melanocytic cells, high cAMP production downstream of MC1R blocked AKT activation and was responsible for inducing DNA repair. Accordingly, MC1R activation could promote repair of oxidative DNA damage by a cAMP-dependent pathway downstream of WT receptor, or via AKT in cells of variant MC1R genotype.

A Common Variant in the MC1R Gene (p.V92M) is associated with Alzheimer's Disease Risk

Despite the recent identification of some novel risk genes for Alzheimer's disease (AD), the genetic etiology of late-onset Alzheimer's disease (LOAD) remains largely unknown. The inclusion of these novel risk genes to the risk attributable to the APOE gene accounts for roughly half of the total genetic variance in LOAD. The evidence indicates that undiscovered genetic factors may contribute to AD susceptibility. In the present study, we sequenced the MC1R gene in 525 Spanish LOAD patients and in 160 controls. We observed that a common MC1R variant p.V92M (rs2228479), not related to pigmentation traits, was present in 72 (14%) patients and 15 (9%) controls and confers increased risk of developing LOAD (OR: 1.99, 95% CI: 1.08-3.64, p = 0.026), especially in those patients whose genetic risk could not be explained by APOE genotype. This association remains and even increased in the subset of 69 patients with typical AD cerebrospinal fluid profile (OR: 3.40 95% CI: 1.40-8.27, p = 0.007). We did not find an association between p.V92M and age of onset of AD. Further studies are necessary to elucidate the role of MC1R in brain cells through the different MC1R pathways.

Key amino acid residue in Melanocortin-1 receptor (melanocyte α-MSH receptor) for ligand selectivity

The melanocortin-1 receptor (MC1R) is a subtype of the melanocortin receptor family and NDP-α-MSH is a non-selective agonist for MC1R. The core sequence of NDP-α-MSH, His-Phe-Arg-Trp, is important for ligand binding and biological activities at the melanocortin receptor subtypes (MCRs). A recent study indicates that Trp⁹ in NDP-α-MSH plays an important role in ligand selectivity. Deletion of Trp⁹ in NDP-α-MSH (des-Trp⁹-NDP-α-MSH) resulted in loss of agonist activity at MC4R, although remains agonist activity at MC1R. The molecular basis for this receptor ligand selectivity is unknown. In this study we examined what region of the MC1R is responsible for des-NDP-α-MSH selectivity. Our results indicate that (1) substitution of TM3 of MC4R with the corresponding region of MC1R switches des-Trp⁹-NDP-α-MSH from no activity to agonist; (2) des-Trp⁹-NDP-α-MSH exhibits agonistic activity at the L133M mutation of the MC4R; and (3) substitution of non-conserved amino acid residue M128 in TM3 of MC1R significantly reduced des-Trp⁹-NDP-α-MSH agonist activity. Our results demonstrate that amino acid residue 128 in TM3 of MC1R, or amino acid residue L133 in TM3 of the MC4R, play crucial roles in ligand des-Trp⁹-NDP-α-MSH selectivity at MC1R or MC4R.

The Contribution of Neanderthals to Phenotypic Variation in Modern Humans

Assessing the genetic contribution of Neanderthals to non-disease phenotypes in modern humans has been difficult because of the absence of large cohorts for which common phenotype information is available. Using baseline phenotypes collected for 112,000 individuals by the UK Biobank, we can now elaborate on previous findings that identified associations between signatures of positive selection on Neanderthal DNA and various modern human traits but not any specific phenotypic consequences. Here, we show that Neanderthal DNA affects skin tone and hair color, height, sleeping patterns, mood, and smoking status in present-day Europeans. Interestingly, multiple Neanderthal alleles at different loci contribute to skin and hair color in present-day Europeans, and these Neanderthal alleles contribute to both lighter and darker skin tones and hair color, suggesting that Neanderthals themselves were most likely variable in these traits.

MC1R signaling. Intracellular partners and pathophysiological implications

The melanocortin-1 receptor (MC1R) preferentially expressed in melanocytes is best known as a key regulator of the synthesis of epidermal melanin pigments. Its paracrine stimulation by keratinocyte-derived melanocortins also activates DNA repair pathways and antioxidant defenses to build a complex, multifaceted photoprotective response. Many MC1R actions rely on cAMP-dependent activation of two transcription factors, MITF and PGC1α, but pleiotropic MC1R signaling also involves activation of mitogen-activated kinases and AKT. MC1R partners such as β-arrestins, PTEN and the E3 ubiquitin ligase MGRN1 differentially regulate these pathways. The MC1R gene is complex and polymorphic, with frequent variants associated with skin phenotypes and increased cancer risk. We review current knowledge of signaling from canonical MC1R, its splice isoforms and natural polymorphic variants. Recently discovered intracellular targets and partners are also discussed, to highlight the diversity of mechanisms that may contribute to normal and pathological variation of pigmentation and sensitivity to solar radiation-induced damage. This article is part of a Special Issue entitled: Melanocortin Receptors - edited by Ya-Xiong Tao.

PDE4D promotes FAK-mediated cell invasion in BRAF-mutated melanoma

The cyclic AMP (cAMP) signaling pathway is critical in melanocyte biology for regulating differentiation. It is downregulated by phosphodiesterase (PDE) enzymes, which degrade cAMP itself. In melanoma evidence suggests that inhibition of the cAMP pathway by PDE type 4 (PDE4) favors tumor progression. For example, in melanomas harboring RAS mutations, the overexpression of PDE4 is crucial for MAPK pathway activation and proliferation induced by oncogenic RAS. Here we showed that PDE4D is overexpressed in BRAF-mutated melanoma cell lines, constitutively disrupting the cAMP pathway activation. PDE4D promoted melanoma invasion by interacting with focal adhesion kinase (FAK) through the scaffolding protein RACK1. Inhibition of PDE4 activity or inhibition of PDE4D interaction with FAK reduced invasion. PDE4D expression is increased in patients with advanced melanoma and PDE4D-FAK interaction is detectable in situ in metastatic melanoma. Our study establishes the role of PDE4D in BRAF-mutated melanoma as regulator of cell invasion, and suggests its potential as a target for preventing metastatic dissemination.

Genetic analysis of melanocortin 1 receptor red hair color variants in a Russian population of Eastern Siberia

The melanocortin 1 receptor is a G_s protein-coupled receptor implicated in melanogenesis regulation. The receptor gene is highly polymorphic, which accounts for the association of several of its single-nucleotide polymorphisms (SNPs) with an increased risk of melanoma. The present study aimed to evaluate the distribution of melanocortin 1 receptor gene variants R151C, R160W, and D294H within the Russian population of Eastern Siberia and its association with melanoma development. Melanoma patients (n=95) admitted to Krasnoyarsk Territorial Oncological Center and healthy controls (n=334) were enrolled in the study. A clinical examination of patients was performed to evaluate the phenotypic features of melanoma patients. SNPs were analyzed by real-time PCR. Clinical examination indicated a more frequent occurrence of fair skin type, blue eyes, blonde and red hair, and more frequent localization of freckles on the neck, trunk, and extremities in the melanoma group of patients. The R151C melanocortin 1 receptor gene variant was found in 18% of melanoma patients and associated with an increased likelihood of melanoma development (odds ratio=6.4; 95% confidence interval: 2.8–14.3; P=0.0001). The two remaining variant alleles of the melanocortin 1 receptor gene occurred with low frequency both in controls and in the melanoma group. The R160W SNP was identified neither in controls nor in melanoma patients. The D294H heterozygous variant was observed in 0.3% of individuals in the control group and in 1.1% of the patients in the melanoma group. Such an asymmetric distribution of the melanocortin 1 receptor within red hair color genotypes in the population under study compared with other populations may be because of Russian genetic homogeneity. Carriers of the mutant R151C allele should exercise caution in terms of exposure to the sun to avoid the risk of melanoma development.

From Normal Skin to Squamous Cell Carcinoma: A Quest for Novel Biomarkers

Squamous cells carcinoma (SCC) is the second most frequent of the keratinocyte-derived malignancies after basal cell carcinoma and is associated with a significant psychosocial and economic burden for both the patient himself and society. Reported risk factors for the malignant transformation of keratinocytes and development of SCC include ultraviolet light exposure, followed by chronic scarring and inflammation, exposure to chemical compounds (arsenic, insecticides, and pesticides), and immune-suppression. Despite various available treatment methods and recent advances in noninvasive or minimal invasive diagnostic techniques, the risk recurrence and metastasis are far from being negligible, even in patients with negative histological margins and lymph nodes. Analyzing normal, dysplastic, and malignant keratinocyte proteome holds special promise for novel biomarker discovery in SCC that could be used in the future for early detection, risk assessment, tumor monitoring, and development of targeted therapeutic strategies.

The MC1R Gene and Youthful Looks

Looking young for one's age has been a desire since time immemorial. This desire is attributable to the belief that appearance reflects health and fecundity. Indeed, perceived age predicts survival [1] and associates with molecular markers of aging such as telomere length [2]. Understanding the underlying molecular biology of perceived age is vital for identifying new aging therapies among other purposes, but studies are lacking thus far. As a first attempt, we performed genome-wide association studies (GWASs) of perceived facial age and wrinkling estimated from digital facial images by analyzing over eight million SNPs in 2,693 elderly Dutch Europeans from the Rotterdam Study. The strongest genetic associations with perceived facial age were found for multiple SNPs in the MC1R gene (p < 1 × 10(-7)). This effect was enhanced for a compound heterozygosity marker constructed from four pre-selected functional MC1R SNPs (p = 2.69 × 10(-12)), which was replicated in 599 Dutch Europeans from the Leiden Longevity Study (p = 0.042) and in 1,173 Europeans of the TwinsUK Study (p = 3 × 10(-3)). Individuals carrying the homozygote MC1R risk haplotype looked on average up to 2 years older than non-carriers. This association was independent of age, sex, skin color, and sun damage (wrinkling, pigmented spots) and persisted through different sun-exposure levels. Hence, a role for MC1R in youthful looks independent of its known melanin synthesis function is suggested. Our study uncovers the first genetic evidence explaining why some people look older for their age and provides new leads for further investigating the biological basis of how old or young people look.

A Genome-Wide Association Study of Cutaneous Squamous Cell Carcinoma among European Descendants

BACKGROUND

No GWAS on the risk of cutaneous squamous cell carcinoma (SCC) has been published. We conducted a multistage genome-wide association study (GWAS) to identify novel genetic loci for SCC.

METHODS

The study included 745 SCC cases and 12,805 controls of European descent in the discovery stage and 531 SCC cases and 551 controls of European ancestry in the replication stage. We selected 64 independent loci that showed the most significant associations with SCC in the discovery stage (linkage disequilibrium r(2) < 0.4) for replication.

RESULTS

Rs8063761 in the DEF8 gene on chromosome 16 showed the strongest association with SCC (P = 1.7 × 10(-9) in the combined set; P = 1.0 × 10(-6) in the discovery set and P = 4.1 × 10(-4) in the replication set). The variant allele of rs8063761 (T allele) was associated with a decreased expression of DEF8 (P = 1.2 × 10(-6)). Besides, we validated four other SNPs associated with SCC in the replication set, including rs9689649 in PARK2 gene (P = 2.7 × 10(-6) in combined set; P = 3.2 × 10(-5) in the discovery; and P = 0.02 in the replication), rs754626 in the SRC gene (P = 1.1 × 10(-6) in combined set; P = 1.4 × 10(-5) in the discovery and P = 0.02 in the replication), rs9643297 in ST3GAL1 gene (P = 8.2 × 10(-6) in combined set; P = 3.3 × 10(-5) in the discovery; and P = 0.04 in the replication), and rs17247181 in ERBB2IP gene (P = 4.2 × 10(-6) in combined set; P = 3.1 × 10(-5) in the discovery; and P = 0.048 in the replication).

CONCLUSION

Several genetic variants were associated with risk of SCC in a multistage GWAS of subjects of European ancestry.

IMPACT

Further studies are warranted to validate our finding and elucidate the genetic function of these variants. Cancer Epidemiol Biomarkers Prev; 25(4); 714-20. ©2016 AACR.

Identification of Susceptibility Loci for Cutaneous Squamous Cell Carcinoma

We report a genome-wide association study of cutaneous squamous cell carcinoma conducted among non-Hispanic white members of the Kaiser Permanente Northern California health care system. The study includes a genome-wide screen of 61,457 members (6,891 cases and 54,566 controls) genotyped on the Affymetrix Axiom European array and a replication phase involving an independent set of 6,410 additional members (810 cases and 5,600 controls). Combined analysis of screening and replication phases identified 10 loci containing single-nucleotide polymorphisms (SNPs) with P-values < 5 × 10(-8). Six loci contain genes in the pigmentation pathway; SNPs at these loci appear to modulate squamous cell carcinoma risk independently of the pigmentation phenotypes. Another locus contains HLA class II genes studied in relation to elevated squamous cell carcinoma risk following immunosuppression. SNPs at the remaining three loci include an intronic SNP in FOXP1 at locus 3p13, an intergenic SNP at 3q28 near TP63, and an intergenic SNP at 9p22 near BNC2. These findings provide insights into the genetic factors accounting for inherited squamous cell carcinoma susceptibility.

Genetics and nonmelanoma skin cancer in kidney transplant recipients

Kidney transplant recipients (KTRs) have a 65- to 250-fold greater risk than the general population of developing nonmelanoma skin cancer. Immunosuppressive drugs combined with traditional risk factors such as UV radiation exposure are the main modifiable risk factors for skin cancer development in transplant recipients. Genetic variation affecting immunosuppressive drug pharmacokinetics and pharmacodynamics has been associated with other transplant complications and may contribute to differences in skin cancer rates between KTRs. Genetic polymorphisms in genes encoding the prednisolone receptor, GST enzyme, MC1R, MTHFR enzyme and COX-2 enzyme have been shown to increase the risk of nonmelanoma skin cancer in KTRs. Genetic association studies may improve our understanding of how genetic variation affects skin cancer risk and potentially guide immunosuppressive treatment and skin cancer screening in at risk individuals.

Risk factors for keratinocyte skin cancer in patients diagnosed with melanoma, a large retrospective study

BACKGROUND

Melanoma survivors are at an increased risk of developing other malignancies, including keratinocyte skin cancer (KSC). While it is known that many risk factors for melanoma also impact risk of KSC in the general population, no previous study has investigated risk factors for KSC development in melanoma patients.

OBJECTIVE

We assessed associations of personal and clinical characteristics, including skin phenotype and variations in the melanocortin 1 receptor (MC1R) gene, with KSC risk in melanoma patients.

PATIENTS AND METHODS

We used prospective follow-up information on 1200 patients treated for melanoma at the Instituto Valenciano de Oncología, Spain, between 2000 and 2011. We computed hazard ratios and 95% confidence intervals (CIs) for the association of clinical, personal and genetic characteristics with risk of KSC, squamous cell carcinoma (SCC), or basal cell carcinoma (BCC) from Cox proportional hazard models. Five-year cumulative incidence based on competing risk models of SCC, BCC or KSC overall was computed using multivariate subdistribution hazard models. To assess predictive performance of the models, we computed areas under the receiver-operating characteristic curves (AUCs, discriminatory power) using cross-validation.

RESULTS

Median follow-up was 57.2 months; a KSC was detected in 163 patients (13.6%). In multivariable Cox models, age, sex, sunburns, chronic sun exposure, past personal history of non-melanoma skin cancer or other non-cutaneous neoplasia, and the MC1R variants p.D294H and p.R163Q were significantly associated with KSC risk. A cumulative incidence model including age, sex, personal history of KSC, and of other non-cutaneous neoplasia had an AUC of 0.76 (95% CI: 0.71-0.80). When p.D294H and p.R163Q variants were added to the model, the AUC increased to 0.81 (95% CI: 0.77-0.84) (p-value for difference <0.0001).

CONCLUSIONS

In addition to age, sex, skin characteristics, and sun exposure, p.R163Q and p.D294H MC1R variants significantly increased KSC risk among melanoma patients. Our findings may help identify patients who could benefit most from preventive measures.

Sex Differences in Kappa Opioid Receptor Function and Their Potential Impact on Addiction

Behavioral, biological, and social sequelae that lead to drug addiction differ between men and women. Our efforts to understand addiction on a mechanistic level must include studies in both males and females. Stress, anxiety, and depression are tightly linked to addiction, and whether they precede or result from compulsive drug use depends on many factors, including biological sex. The neuropeptide dynorphin (DYN), an endogenous ligand at kappa opioid receptors (KORs), is necessary for stress-induced aversive states and is upregulated in the brain after chronic exposure to drugs of abuse. KOR agonists produce signs of anxiety, fear, and depression in laboratory animals and humans, findings that have led to the hypothesis that drug withdrawal-induced DYN release is instrumental in negative reinforcement processes that drive addiction. However, these studies were almost exclusively conducted in males. Only recently is evidence available that there are sex differences in the effects of KOR activation on affective state. This review focuses on sex differences in DYN and KOR systems and how these might contribute to sex differences in addictive behavior. Much of what is known about how biological sex influences KOR systems is from research on pain systems. The basic molecular and genetic mechanisms that have been discovered to underlie sex differences in KOR function in pain systems may apply to sex differences in KOR function in reward systems. Our goals are to discuss the current state of knowledge on how biological sex contributes to KOR function in the context of pain, mood, and addiction and to explore potential mechanisms for sex differences in KOR function. We will highlight evidence that the function of DYN-KOR systems is influenced in a sex-dependent manner by: polymorphisms in the prodynorphin (pDYN) gene, genetic linkage with the melanocortin-1 receptor (MC1R), heterodimerization of KORs and mu opioid receptors (MORs), and gonadal hormones. Finally, we identify several gaps in our understanding of “if” and “how” DYN and KORs modulate addictive behavior in a sex-dependent manner. Future work may address these gaps by building on the mechanistic studies outlined in this review. Ultimately this will enable the development of novel and effective addiction treatments tailored to either males or females.

Family history of skin cancer is associated with early-onset basal cell carcinoma independent of MC1R genotype

BACKGROUND

As a marker of genetic susceptibility and shared lifestyle characteristics, family history of cancer is often used to evaluate an individual's risk for developing a particular malignancy. With comprehensive data on pigment characteristics, lifestyle factors, and melanocortin 1 receptor (MC1R) gene sequence, we sought to clarify the role of family history of skin cancer in early-onset basal cell carcinoma (BCC).

MATERIALS AND METHODS

Early onset BCC cases (n=376) and controls with benign skin conditions (n=383) under age 40 were identified through Yale dermatopathology. Self-report data on family history of skin cancer (melanoma and non-melanoma skin cancer), including age of onset in relatives, was available from a structured interview. Participants also provided saliva samples for sequencing of MC1R.

RESULTS

A family history of skin cancer was associated with an increased risk of early-onset BCC (OR 2.49, 95% CI 1.80-3.45). In multivariate models, family history remained a strong risk factor for early-onset BCC after adjustment for pigment characteristics, UV exposure, and MC1R genotype (OR 2.41, 95% CI 1.74-3.35).

CONCLUSIONS

Risk for BCC varied based upon the type and age of onset of skin cancer among affected relatives; individuals with a first-degree relative diagnosed with skin cancer prior to age 50 were at highest risk for BCC (OR 4.79, 95% CI 2.90-7.90). Even after taking into account potential confounding effects of MC1R genotype and various lifestyle factors that close relatives may share, family history of skin cancer remained strongly associated with early-onset BCC.

MC1R gene variants and non-melanoma skin cancer: a pooled-analysis from the M-SKIP project

BACKGROUND

The melanocortin-1-receptor (MC1R) gene regulates human pigmentation and is highly polymorphic in populations of European origins. The aims of this study were to evaluate the association between MC1R variants and the risk of non-melanoma skin cancer (NMSC), and to investigate whether risk estimates differed by phenotypic characteristics.

METHODS

Data on 3527 NMSC cases and 9391 controls were gathered through the M-SKIP Project, an international pooled-analysis on MC1R, skin cancer and phenotypic characteristics. We calculated summary odds ratios (SOR) with random-effect models, and performed stratified analyses.

RESULTS

Subjects carrying at least one MC1R variant had an increased risk of NMSC overall, basal cell carcinoma (BCC) and squamous cell carcinoma (SCC): SOR (95%CI) were 1.48 (1.24-1.76), 1.39 (1.15-1.69) and 1.61 (1.35-1.91), respectively. All of the investigated variants showed positive associations with NMSC, with consistent significant results obtained for V60L, D84E, V92M, R151C, R160W, R163Q and D294H: SOR (95%CI) ranged from 1.42 (1.19-1.70) for V60L to 2.66 (1.06-6.65) for D84E variant. In stratified analysis, there was no consistent pattern of association between MC1R and NMSC by skin type, but we consistently observed higher SORs for subjects without red hair.

CONCLUSIONS

Our pooled-analysis highlighted a role of MC1R variants in NMSC development and suggested an effect modification by red hair colour phenotype.

New basal cell carcinoma susceptibility loci

In an ongoing screen for DNA sequence variants that confer risk of cutaneous basal cell carcinoma (BCC), we conduct a genome-wide association study (GWAS) of 24,988,228 SNPs and small indels detected through whole-genome sequencing of 2,636 Icelanders and imputed into 4,572 BCC patients and 266,358 controls. Here we show the discovery of four new BCC susceptibility loci: 2p24 MYCN (rs57244888[C], OR=0.76, P=4.7 × 10(-12)), 2q33 CASP8-ALS2CR12 (rs13014235[C], OR=1.15, P=1.5 × 10(-9)), 8q21 ZFHX4 (rs28727938[G], OR=0.70, P=3.5 × 10(-12)) and 10p14 GATA3 (rs73635312[A], OR=0.74, P=2.4 × 10(-16)). Fine mapping reveals that two variants correlated with rs73635312[A] occur in conserved binding sites for the GATA3 transcription factor. In addition, expression microarrays and RNA-seq show that rs13014235[C] and a related SNP rs700635[C] are associated with expression of CASP8 splice variants in which sequences from intron 8 are retained.