The melanocyte stimulating hormone receptor polymorphism: association of the V92M and A294H alleles with basal cell carcinoma

Comparative oncology: what dogs and other species can teach us about humans with cancer

Over 1.66 million humans (approx. 500/100,000 population rate) and over 4.2 million dogs (approx. 5300/100,000 population rate) are diagnosed with cancer annually in the USA. The interdisciplinary field of comparative oncology offers a unique and strong opportunity to learn more about universal cancer risk and development through epidemiology, genetic and genomic investigations. Working across species, researchers from human and veterinary medicine can combine scientific findings to understand more quickly the origins of cancer and translate these findings to novel therapies to benefit both human and animals. This review begins with the genetic origins of canines and their advantage in cancer research. We next focus on recent findings in comparative oncology related to inherited, or genetic, risk for tumour development. We then detail the somatic, or genomic, changes within tumours and the similarities between species. The shared cancers between humans and dogs that we discuss include sarcoma (osteosarcoma, soft tissue sarcoma, histiocytic sarcoma, hemangiosarcoma), haematological malignancies (lymphoma, leukaemia), bladder cancer, intracranial neoplasms (meningioma, glioma) and melanoma. Tumour risk in other animal species is also briefly discussed. As the field of genomics advances, we predict that comparative oncology will continue to benefit both humans and the animals that live among us.

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.

Melanocortin-1 receptor, skin cancer and phenotypic characteristics (M-SKIP) project: study design and methods for pooling results of genetic epidemiological studies

Background

For complex diseases like cancer, pooled-analysis of individual data represents a powerful tool to investigate the joint contribution of genetic, phenotypic and environmental factors to the development of a disease. Pooled-analysis of epidemiological studies has many advantages over meta-analysis, and preliminary results may be obtained faster and with lower costs than with prospective consortia.

Design and methods

Based on our experience with the study design of the Melanocortin-1 receptor (MC1R) gene, SKin cancer and Phenotypic characteristics (M-SKIP) project, we describe the most important steps in planning and conducting a pooled-analysis of genetic epidemiological studies. We then present the statistical analysis plan that we are going to apply, giving particular attention to methods of analysis recently proposed to account for between-study heterogeneity and to explore the joint contribution of genetic, phenotypic and environmental factors in the development of a disease. Within the M-SKIP project, data on 10,959 skin cancer cases and 14,785 controls from 31 international investigators were checked for quality and recoded for standardization. We first proposed to fit the aggregated data with random-effects logistic regression models. However, for the M-SKIP project, a two-stage analysis will be preferred to overcome the problem regarding the availability of different study covariates. The joint contribution of MC1R variants and phenotypic characteristics to skin cancer development will be studied via logic regression modeling.

Discussion

Methodological guidelines to correctly design and conduct pooled-analyses are needed to facilitate application of such methods, thus providing a better summary of the actual findings on specific fields.

MC1R and PTCH Gene Polymorphism in French Patients with Basal Cell Carcinomas

In this study, we assessed the role of melanocortin 1 receptor (MC1R) variants and of two patched (PTCH) polymorphisms (c.3944C>T (P1315L), insertion 18 bp IVS1-83) as risk factors for basal cell carcinoma (BCC) in the French population. The population investigated comprised 126 BCC patients who were enrolled on the basis of specific criteria (multiple and/or familial BCC and/or onset before the age of 40 years and/or association with another tumor)--and 151 controls matched for ethnicity, age, and sex. MC1R variants appeared as a moderate risk factor for BCC (odds ratio (OR) for one and two variants, 2.17 [1.28-3.68] and 7.72 [3.42-17.38], respectively), independently of pigmentation characteristics (OR = 2.53 [1.34-4.8]). Interestingly, in addition to the predictable red hair color (RHC) alleles, two non-RHC alleles (V60L and V92M) were also closely associated with BCC risk (OR 3.21 [1.91-5.38] and 2.87 [1.5-5.48], respectively), which differs from the situation in the Celtic population. In addition, the PTCH c.3944C/C genotype was also associated with BCC risk (OR 1.94 [1.2-3.1]), especially in the subgroup of patients with multiple tumors (OR 2.16 [1.3-3.6]). Thus, our data show that MC1R and PTCH variants are associated with BCC risk in the French population. We further suggest that assessing MC1R and PTCH status could be useful, combined with the assessment of clinical risk factors, in identifying high-risk patients to be targeted for prevention or more rigorous surveillance.

A polymorphism in the agouti signalling protein (ASIP) is associated with decreased levels of mRNA

To date, a role for agouti signalling protein (ASIP) in human pigmentation has not been well characterized. It is known that agouti plays a pivotal role in the pigment switch from the dark eumelanin to the light pheomelanin in the mouse. However, because humans do not have an agouti banded hair pattern, its role in human pigmentation has been questioned. We previously identified a single polymorphism in the 3'-untranslated region (UTR) of ASIP that was found at a higher frequency in African-Americans compared with other population groups. To compare allele frequencies between European-Australians and indigenous Australians, the g.8818A --> G polymorphism was genotyped. Significant differences were seen in allele frequencies between these groups (P < 0.0001) with carriage of the G allele highest in Australian Aborigines. In the Caucasian sample set a strong association was observed between the G allele and dark hair colour (P = 0.004) (odds ratio 4.6; 95% CI 1.4-15.27). The functional consequences of this polymorphism are not known but it was postulated that it might result in message instability and premature degradation of the transcript. To test this hypothesis, ASIP mRNA levels were quantified in melanocytes carrying the variant and non-variant alleles. Using quantitative real-time polymerase chain reaction the mean ASIP mRNA ratio of the AA genotype to the AG genotype was 12 (P < 0.05). This study suggests that the 3'-UTR polymorphism results in decreased levels of ASIP and therefore less pheomelanin production.

Gene polymorphisms and their effects in the melanocortin system

In addition to its role in human pigmentation, components of the melanocortin system regulate appetite, energy homeostasis and hormone production. Recent studies have suggested possible roles of this system in immunity, transmission of pain signals, and reproductive potential. A number of polymorphisms have been identified in genes of the melanocortin system and are associated with pigmentation in humans, as well as being causative of disorders of adrenal hormone production and obesity. This review gives an outline of these polymorphisms, their functional significance and possible application to or impact on diagnosis and pharmacotherapy based on melanocortin pathways.

The relation between melanocortin 1 receptor (MC1R) variation and the generation of phenotypic diversity in the cutaneous response to ultraviolet radiation

The melanocortin 1 receptor (MC1R) is known to play an important role in determining physiological variation in human pigmentation, and consequently human susceptibility to ultraviolet radiation. A reason for wider interest is that the considerable phenotypic diversity has been in part generated by the effects of gene dosage, and the presence of a large number of mutations at this G-protein coupled receptor that are not functionally equivalent. Thus, a range of mutations at a single receptor locus can lead to a complex range of graded phenotypes.

Genetics of hair and skin color

Differences in skin and hair color are principally genetically determined and are due to variation in the amount, type, and packaging of melanin polymers produced by melanocytes secreted into keratinocytes. Pigmentary phenotype is genetically complex and at a physiological level complicated. Genes determining a number of rare Mendelian disorders of pigmentation such as albinism have been identified, but only one gene, the melanocortin 1 receptor (MCR1), has so far been identified to explain variation in the normal population such as that leading to red hair, freckling, and sun-sensitivity. Genotype-phenotype relations of the MC1R are reviewed, as well as methods to improve the phenotypic assessment of human pigmentary status. It is argued that given advances in model systems, increases in technical facility, and the lower cost of genotype assessment, the lack of standardized phenotype assessment is now a major limit on advance.

Agouti signal protein regulation in human melanoma cells

Production of the pigment eumelanin is controlled by alpha-melanocyte stimulating hormone (alpha-MSH) stimulation of melanocortin 1 receptor (Mc1r), whereas production of pheomelanin results from agouti antagonism of alpha-MSH signalling through Mc1r. The role of agouti in mouse pigmentation has been extensively investigated but a role for agouti signalling protein (ASIP) in human pigmentation has not been determined. To determine whether ASIP regulates known melanogenic genes in humans, ASIP was over-expressed in a human melanoma cell line. Levels of mRNA and protein were measured in genes known to be up or down-regulated by agouti in the mouse, namely microphthalmia (Mitf), tyrosinase (Tyr), tyrosinase-related protein 1 (Tyrp1), dopachrome tautomerase (Dct), Mc1r, silver, initiation transcription factor 2 (Itf2) and mini chromosome maintenance protein 6 (Mcm6). These melanogenic genes were not found to be significantly up or down-regulated by ASIP at the transcriptional level in human melanoma cells. However, ASIP down-regulation of tyrp1 was observed at the translational level. To identify novel genes that may be regulated by ASIP in melanoma cells, microarrays were used to determine differences in gene expression between the control and ASIP transfected melanoma cells. The expression level of human RNAs were determined by microarray analysis using a 19,200 cDNA and a 19,200 oligonucleotide array representing 13,000 and 18,864 individual genes, respectively. Genes observed to be modulated by ASIP were confirmed by quantitative real-time polymerase chain reaction. Results identify five genes, namely PPARbeta, eIF-4B, RRM2, MINOR and EVI2B that are down-regulated by ASIP, indicating a likely role for ASIP in human melanogenesis.

Agouti: from mouse to man, from skin to fat

The agouti protein regulates pigmentation in the mouse hair follicle producing a black hair with a subapical yellow band. Its effect on pigmentation is achieved by antagonizing the binding of alpha-melanocyte stimulating hormone (alpha-MSH) to melanocortin 1 receptor (Mc1r), switching melanin synthesis from eumelanin (black/brown) to phaeomelanin (red/yellow). Dominant mutations in the non-coding region of mouse agouti cause yellow coat colour and ectopic expression also results in obesity, type 11 diabetes, increased somatic growth and tumourigenesis. At least some of these pleiotropic effects can be explained by antagonism of other members of the melanocortin receptor family by agouti protein. The yellow coat colour is the result of agouti chronically antagonizing the binding of alpha-MSH to Mc1r and the obese phenotype results from agouti protein antagonizing the binding of alpha-MSH to Mc3r and/or Mc4r. Despite the existence of a highly homologous agouti protein in humans, agouti signal protein (ASIP), its role has yet to be defined. However it is known that human ASIP is expressed at highest levels in adipose tissue where it may antagonize one of the melanocortin receptors. The conserved nature of the agouti protein combined with the diverse phenotypic effects of agouti mutations in mouse and the different expression patterns of human and mouse agouti, suggest ASIP may play a role in human energy homeostasis and possibly human pigmentation.

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

Melanocortin-1 receptor (MC1R) gene variants are associated with fair skin and red hair and, independently of these, with cutaneous malignant melanoma. The association of MC1R gene variants with nonmelanoma skin cancer is largely unknown. A total of 838 subjects were included in the present study: 453 patients with nonmelanoma skin cancer and 385 subjects with no skin cancer. The coding sequence of the human MC1R gene was tested using single-stranded conformation polymorphism analysis followed by sequencing of unknown variants. Risk of skin cancer dependent on the various MC1R gene variants was estimated using the exposure odds ratio. We investigated whether subjects with MC1R variant alleles were at increased risk of developing nonmelanoma skin cancer and, if so, whether this increased risk was mediated by fair skin and red hair. A total of 27 MC1R gene variants were found. The number of carriers of one, two, or three MC1R gene variants was 379 (45.2%), 208 (24.8%), and 7 (0.9%), respectively. A strong association between MC1R gene variants and fair skin and red hair was established, especially the variants Arg151Cys and Arg160Trp (P < .0001). Carriers of two variant alleles were at increased risk for developing cutaneous squamous cell carcinoma (odds ratio 3.77; 95% confidence interval [CI] 2.11-6.78), nodular basal cell carcinoma (odds ratio 2.26; 95% CI 1.45-3.52), and superficial multifocal basal cell carcinoma (odds ratio 3.43; 95% CI 1.92-6.15), compared with carriers of two wild-type alleles. Carriers of one variant allele had half the risk. The highest relative risks of nonmelanoma skin cancer were found in carriers of the Asp84Glu, His260Pro, and Asp294His variant alleles, and the risk was only slightly lower for carriers of the Val60Leu, Val92Met, Arg142His, Arg151Cys, and Arg160Trp variant alleles. When subjects were stratified by skin type and hair color, analysis showed that these factors did not materially change the relative risks. These findings indicate that MC1R gene variants are important independent risk factors for nonmelanoma skin cancer.

Melanocortin-1 receptor genotype is a risk factor for basal and squamous cell carcinoma

MC1R gene variants have previously been associated with red hair and fair skin color, moreover skin ultraviolet sensitivity and a strong association with melanoma has been demonstrated for three variant alleles that are active in influencing pigmentation: Arg151Cys, Arg160Trp, and Asp294His. This study has confirmed these pigmentary associations with MC1R genotype in a collection of 220 individuals drawn from the Nambour community in Queensland, Australia, 111 of whom were at high risk and 109 at low risk of basal cell carcinoma and squamous cell carcinoma. Comparative allele frequencies for nine MC1R variants that have been reported in the Caucasian population were determined for these two groups, and an association between prevalence of basal cell carcinoma, squamous cell carcinoma, solar keratosis and the same three active MC1R variant alleles was demonstrated [odds ratio = 3.15 95% CI (1.7, 5.82)]. Three other commonly occurring variant alleles: Val60Leu, Val92Met, and Arg163Gln were identified as having a minimal impact on pigmentation phenotype as well as basal cell carcinoma and squamous cell carcinoma risk. A significant heterozygote effect was demonstrated where individuals carrying a single MC1R variant allele were more likely to have fair and sun sensitive skin as well as carriage of a solar lesion when compared with those individuals with a consensus MC1R genotype. After adjusting for the effects of pigmentation on the association between MC1R variant alleles and basal cell carcinoma and squamous cell carcinoma risk, the association persisted, confirming that presence of at least one variant allele remains informative in terms of predicting risk for developing a solar-induced skin lesion beyond that information wained through observation of pigmentation phenotype.

Glutathione S-transferase GSTP1 and cyclin D1 genotypes: association with numbers of basal cell carcinomas in a patient subgroup at high-risk of multiple tumours

We previously described associations between basal cell carcinoma (BCC) numbers and allelic variants at loci that mediate host response to ultraviolet radiation (UV). These associations were largely exerted in cases with the multiple presentation phenotype (MPP). This phenotype describes patients who present at their first or a later presentation with a cluster of BCC (2-10 new BCC). Remaining BCC cases have the single presentation phenotype (SPP) and may develop more than one BCC but only have single new lesions at any presentation. We proposed that the MPP cases comprise a high-risk group as they suffer significantly more lesions than SPP cases. We are attempting to determine, in the total BCC case group and subgroups, how many genes influence BCC numbers and their relative importance. In this study, we assessed the influence of two further candidates, glutathione S-transferase GSTP1 and cyclin D1 (CCND1), on tumour numbers in a total group of 457 patients comprising MPP and SPP cases. The relative importance of these genes in comparison with occupational UV exposure and host response (skin type) was also considered. We found that the frequencies of GSTP1 genotypes based on the Ile105 and Val105-expressing alleles and CCND1 AA, AG, GG genotypes were similar in MPP and SPP cases and that there were no significant associations between GSTP1 or CCND1 genotypes and BCC numbers in the total or SPP groups. However, in the MPP cases, GSTP1 Val105/Val105 was associated with more tumours (P = 0.05, reference GSTP1 Ile105/Ile105). Inclusion of skin type and indoor/outdoor occupation in the negative binomial regression models did not alter the associations of these genotypes with tumour numbers. DNA from 258 cases was analysed to identify GSTP1*A (Ile105-Ala114), GSTP1*B (Val105-Ala114), GSTP1*C (Val105-Val114) and GSTP1*D (Ile105-Val114). In SPP cases, there was no association between BCC numbers and GSTP1 BB, though the association with GSTP1 BC approached significance (P = 0.09). In MPP cases, GSTP1 BC was associated with BCC numbers (P = 0.03). We also found that the interaction term, GSTP1 Val105/Val105 with CCND1 AA, was associated with BCC numbers in the total (P = 0.001) and MPP (P = 0.006) but not SPP (P = 0.68) groups. In a stepwise model including GSTP1 Val105/Val105, CCND1 AA and their interaction terms as well as GSTM1, GSTT1 and CYP2D6 genotypes, skin type 1 and gender, the combination of genotypes was the best predictor of BCC numbers. These data suggest that study of further genes involved in cell-cycle control and protection from oxidative stress will be useful, particularly in high-risk subgroups.