p53 codon 72 Pro homozygosity increases the risk of cutaneous melanoma in individuals with dark skin complexion and among noncarriers of melanocortin 1 receptor red hair variants

BACKGROUND: p53 has a common polymorphism at amino acid 72, encoding either arginine or proline. p53Arg and p53Pro exhibit differences in various biological activities, such as cell-cycle arrest and induction of apoptosis. Numerous epidemiological studies have examined the role of this polymorphism in several human malignancies, including cutaneous cancers, with contradictory results. OBJECTIVES: To investigate the germline frequency of p53 codon 72 polymorphism in malignant melanoma in a Mediterranean population, and to examine possible associations with various clinicopathological factors. METHODS: In this hospital-based case-control study we used allele-specific polymerase chain reaction for p53 codon 72 genotyping in blood specimens from 107 Greek patients with sporadic cutaneous melanoma and 145 healthy controls. RESULTS: After adjustment for age, sex and phototype the Pro/Pro genotype was associated with increased risk for cutaneous melanoma compared with the Arg/Arg genotype (adjusted odds ratio, OR 3.17, 95% confidence interval, CI 1.03-9.78). This correlation was more pronounced in subjects with phototypes III or IV (adjusted OR 9.56, 95% CI 1.56-58.46), dark skin (adjusted OR 10.96, 95% CI 1.64-73.28), dark eyes (adjusted OR 8.86, 95% CI 1.69-46.52) and dark hair (adjusted OR 3.17, 95% CI 1.01-9.95), and among noncarriers of melanocortin 1 receptor gene (MC1R) red hair polymorphisms (adjusted OR 2.99, 95% CI 1.02-8.78). CONCLUSIONS: p53 codon 72 Pro/Pro genotype could be a risk factor for the development of melanoma in the Greek population, especially in subgroups with darker skin pigmentation, as well as among noncarriers of the MC1R red hair polymorphic variants.     

Nevi, family history, and fair skin increase the risk of second primary melanoma

Although risk factors for primary cutaneous melanoma are well defined, relatively little is known about predictors for second primary melanoma. Given the rising incidence of this cancer, coupled with improvements in survival, there is a prevalent and growing pool of patients at risk of second primary melanomas. To identify the predictors of second primary melanoma, we followed a cohort of 1,083 Queensland patients diagnosed with incident melanoma between 1982 and 1990 and who completed a baseline questionnaire. During a median follow-up of 16.5 years, 221 patients were diagnosed with at least one additional primary melanoma. In multivariate analyses, second primary melanomas were associated with high nevus count (hazard ratio (HR), 2.91; 95% confidence interval (CI) 1.94-4.35), high familial melanoma risk (HR, 2.12; 95% CI 1.34-3.36), fair skin (HR, 1.51; 95% CI 1.06-2.16), inability to tan (HR, 1.66; 95% CI 1.13-2.43), an in situ first primary melanoma (HR, 1.36; 95% CI 0.99-1.87), and male sex (HR, 1.49; 95% CI 1.12-2.00). Patients whose first primary was lentigo maligna melanoma (HR, 1.80; 95% CI 1.05-3.07) or nodular melanoma (HR, 2.13; 95% CI 1.21-3.74) had higher risks of subsequent primaries than patients whose first primary tumor was superficial spreading melanoma. These characteristics could be assessed in patients presenting with first primary melanoma to evaluate risk of developing a second primary.     

Expression of melanocortin-1 receptor in normal, malformed and neoplastic skin glands and hair follicles

Melanocortin receptors (MC-Rs) are G-protein coupled receptors that mediate pleiotropic actions of melanocyte-stimulating hormones and adrenocorticotropin. There is increasing evidence that one of the five so far identified melanocortin receptors, i.e. melanocortin-1 receptor (MC-1R), has a more ubiquitous distribution in the skin than originally expected. In the present study, the expression of MC-1R in normal skin glands and hair follicles, various malformations and neoplasms with adnexal differentiation is described. Using an anti-MC-1R antibody directed against the amino acids 2-18 of the human MC-1R, specimens of normal healthy skin (n = 10) as well as hamartomas, cysts, hyperplasias, and benign or malignant neoplasms with eccrine, apocrine, sebaceous gland, and hair follicle differentiation (n = 98) were immunostained. MC-1R expression was widely preserved in various adnexal malformations and neoplasms as compared with normal skin and did not show major differences with regard to maturation of the neoplasms. The majority of adnexal epithelia showed an intracytoplasmically granular staining and, to a lesser extent, an intercellular staining pattern. Immunoelectron microscopical investigations revealed expression of MC-1R both along the cell surface and intracytoplasmically within tubular endosomes, the latter suggesting internalisation of the receptor. In conclusion, preserved MC-1R expression in adnexal epithelia suggests a functional role of proopiomelanocortin (POMC) in various malformations and neoplasms of the skin.     

Time course of ultraviolet B-induced erythema in people with red hair harbouring homozygous melanocortin 1 receptor mutations

It has previously been reported that the time course of erythema may be delayed in those with sun-sensitive skin types and those with skin cancer. One molecular explanation for this putative phenotype would be that it is caused by mutations of the melanocortin 1 receptor (MC1R). In the present study of 20 persons, 10 of whom were MC1R homozygous, we measured erythema over a 21-day period in response to a range of ultraviolet B doses using methods that improved on previous studies. We could detect no consistent differences in ultraviolet radiation-induced erythema between the groups studied. The pharmacological mechanisms underpinning such prolonged inflammatory responses merit further investigation.     

Pharmacological characterization of loss of function mutations of the human melanocortin 1 receptor that are associated with red hair

Variation in skin color is the major host risk factor for melanoma and other forms of skin cancer. Individuals with red hair show an increased ratio of phaeomelanin to eumelanin in both hair and skin. This ratio is regulated by the melanocortin (MC) 1 receptor. There are several common point mutations in the human MC1 receptor that are overrepresented in North European red-heads, and in individuals with pale skin. In order to determine the functional significance of these mutations, we expressed the Asp84Glu, Val92Met, Arg163Gln, and Asp294His variants of the human MC1 receptors in eukaryotic cells and determined their ability to bind alpha-melanocyte stimulating hormone (MSH) peptides and increase intracellular cAMP. The mutants Asp84Glu and Asp294His showed a much lower response to alpha-MSH in cAMP and a slightly impaired ability to bind alpha-MSH, and the Val92Met mutant bound alpha-MSH with 100-fold lower affinity as compared with the wild-type. The Arg163Gln variant, widely found in some Asian populations, reached normal level of cAMP response but had just slightly lower potency for alpha-MSH in binding and second messenger studies. The results provide important pharmacological characterization of common MC1 receptor variants in various world populations.     

Functional melanocortin 1 receptor Mc1r is not necessary for an inflammatory response to UV radiation in adult mouse skin

The G‐protein‐coupled receptor, Mc1r, plays a major role in pigment production and has been reported to be important in the inflammatory response. We have investigated the effect of deficiency in Mc1r on UV‐induced inflammation. Mice on the same genetic background were used – C57BL/6‐c (albino), C57BL/6 (black), C57BL/6‐Mc1r^e/e deficient (yellow). FACS analysis of disaggregated skin showed a similar dose‐dependent increase in Ly6G⁺ and CD11b⁺ cells in response to UV radiation in all groups. No differences in UV‐induced edema or in DNA damage were detected between groups. The contact hypersensitivity response, neonatal immune tolerance and UV immunosuppression were all similar in C57BL/6 and C57BL/6‐Mc1r^e/e mice. We conclude that the absence of Mc1r does not impair the inflammatory response to UV radiation or the generation of immunosuppression.     

Melanocortin 1 receptor (MC1R) gene variants are associated with an increased risk for cutaneous melanoma which is largely independent of skin type and hair color

Individuals carrying melanocortin 1 receptor gene variants have an increased risk for the development of cutaneous melanoma. Melanocortin 1 receptor gene variants are also associated with other risk factors for melanoma such as fair skin and red hair. We evaluated the relationship of melanocortin 1 receptor gene variants, fair skin, red hair and the development of melanoma in 123 patients with cutaneous melanoma and 385 control subjects. To analyze the association between melanocortin 1 receptor gene variants and skin type or hair color we also made use of 453 patients with nonmelanoma skin cancer. We analyzed the coding sequence of the melanocortin 1 receptor gene region by single-stranded conformation polymorphism analysis, followed by DNA sequence analysis. Risk of melanoma dependent on the various melanocortin 1 receptor variant alleles was estimated by exposure odds ratios. The analyses of all different melanocortin 1 receptor gene variants combined, showed that the presence of melanocortin 1 receptor gene variants amounted to a higher melanoma risk, which, in stratified analyses, was independent of skin type and hair color. The odds ratios after adjusting for skin type were 3.6 (95% CI 1.7-7.2) for two variants and 2.7 (95% CI 1.5-5.1) for one variant, respectively. Compound heterozygotes and homozygotes for the Val60Leu, Val92Met, Arg142His, Arg151Cys, Arg160Trp, Arg163Gln, and His260Pro variants had odds ratios of about 4 to develop melanoma, whereas heterozygotes for these variants had half the risk. The presence of the melanocortin 1 receptor gene variant Asp84Glu appeared to impose the highest risk for cutaneous melanoma with odds ratios of 16.1 (95% CI 2.3-139.0) and 8.1 (95% CI 1.2-55.9) in compound heterozygotes and heterozygotes, respectively. The broad confidence intervals, when the different variants were analyzed separately, however, do not allow drawing definite conclusions about the magnitude of these risks. Of the more frequently occurring melanocortin 1 receptor variant alleles the Asp84Glu, Arg142His, Arg151Cys, Arg160Trp, His260Pro, and Asp294His variants were strongly associated with both fair skin and red hair. The Val60Leu, Val92Met, and Arg163Gln variant alleles, however, were only weakly or not associated with fair skin type and/or red hair, which further illustrates the finding that skin type, hair color, and melanoma are independent outcomes of the presence of melanocortin 1 receptor gene variants. We conclude that numerous melanocortin 1 receptor variants predispose to cutaneous melanoma and that possibly the Asp84Glu variant confers the highest risk. This predisposition is largely independent of skin type and hair color.     

Oligonucleotide treatment increases eumelanogenesis, hair pigmentation and melanocortin-1 receptor expression in the hair follicle

It was previously reported that telomere homologue oligonucleotides (T-oligos) can induce a variety of cellular responses in skin including increased melanogenesis. To assess the effects of T-oligos on hair pigmentation, we administered thymidine dinucleotide (pTT), one-third of the TTAGGG telomere repeat sequence, intradermally at distinct time points of the depilation-induced hair cycle in C3H/HeJ mice. Penetration of T-oligos into the hair follicle (HF) was monitored by using FITC-labelled pTT and confocal microscopy. pTT treatment on days 1-5 after depilation, during early anagen, did not significantly alter the number and proliferation of melanocytes (Trp-2-positive cells), compared with vehicle-treated controls. However, pTT treatment on days 5-12 after depilation, during mid- to late anagen, resulted in the formation of darker hairs, that showed a significantly increased eumelanin/total melanin ratio in their sub-apical agouti band region, compared with vehicle-treated controls (P < 0.05). By RT-PCR and western blot, full thickness skin of pTT-treated mice showed increases in Trp-1, Trp-2 and tyrosinase mRNA and protein levels, compared with control mice. Western blot analyses of two receptors that positively regulate eumelanogenesis, melanocortin type 1 receptor (MC-1R) and kit, showed increased expression of MC-1R protein in pTT-treated versus control skin, while the levels of c-kit receptor remained unchanged. These data demonstrate that pTT treatment increases eumelanogenesis in HFs, associated with increased tyrosinase, TRP-1 and MC-1R expression. These data also raise the possibility of using T-oligos to modulate hair pigmentation.     

A ''hot'' new twist to hair biology – involvement of vanilloid receptor-1 signaling in human hair growth control

The melanocortin hormones act on epidermal melanocytes to increase eumelanogenesis, melanocyte dendricity and likely melanosome transfer to keratinocytes. These actions are mediated by the melanocortin 1 receptor (MC1R), positively coupled to adenylyl cyclase. Gain-of-function Mc1r alleles are associated with dark, eumelanic skin. Conversely, loss-of-function variants or overexpression of agouti, the natural antagonist, yield yellow, pheomelanic furs. In humans, loss-of-function MC1R variants are associated with fair skin, poor tanning and increased skin cancer risk. Therefore, MC1R is a key regulator of mammalian pigmentation. An induction of constitutive pigmentation in amelanotic mouse melanoma cells following the expression of MC1R has been reported, suggesting that this receptor might display agonist-independent activity, although this aspect has not yet been comparatively studied for MC1R and Mc1r. We show that the expression of MC1R in heterologous systems leads to high agonist-independent increases in intracellular cAMP. This basal signalling is a function of the quantity of receptor expressed, is considerably higher for MC1R than Mc1r and is also observed in human melanoma cells overexpressing MC1R. Moreover, MC1R basal signalling is abolished or reduced by point mutations impairing the response to agonists. Lastly, the expression of wild-type MC1R, but not of loss-of-function mutants potently stimulates forskolin activation of adenylyl cyclase, a feature characteristic of constitutively active G-coupled receptors. Therefore, we conclude that MC1R displays a strong agonist-independent constitutive activity.     

Melanocortin 1 receptor variants, pigmentation, and skin cancer susceptibility

The melanocortin 1 receptor is a key regulator of variation in normal human pigmentation. Genetic variants of this receptor cause red hair and fair skin, and several case-control studies have demonstrated that these genetic variants increase the risk of skin cancer development in humans. The mechanism whereby the risks of skin cancer are increased is not entirely clear, and may be because of a combination of effects on pigmentation and non-pigmentary pathways.     

Bubble hair – a possible explanation for its distribution

A 23-year-old white woman presented with a circumscribed area of shortened hairs along the anterior hairline. Approximately 1 month previously, the involved hairs had broken abruptly following shampooing. She used a hot air blow dryer for hair styling, but did not use electric rollers or a curling iron. Nor did she bleach, dye, or permanently wave her hair. The patient's hair styling technique involved wrapping hairs of the frontal hairline over a round brush whilst blow drying. There was no personal or family history of alopecia or scalp infections.
On physical examination, an oval-shaped area of shortened hairs (5–6 cm in length) was noted along the anterior hairline (Fig. 1). The area of involvement measured 5×4 cm and was to the left of the midline. The texture of the affected hairs was coarser than that of the unaffected hairs, and these broken hairs were somewhat crinkled in appearance. There was no erythema, scale, or discrete areas of alopecia on the scalp. By light microscopy, the broken hairs demonstrated multiple bubbles within the hair shafts (Fig. 2). Some of the bubbles led to the distension of the hair shaft. There was no evidence of trichorrhexis nodosa.     

Dimerization of the human melanocortin 1 receptor: functional consequences and dominant-negative effects

The melanocortin 1 receptor (MC1R), a G(S)-protein-coupled receptor (GPCR), is a key regulator of proliferation and differentiation of epidermal melanocytes, and a determinant of human skin phototype and cancer risk. Homodimerization has been demonstrated for several GPCRs, but little information is available for MC1R. SDS-PAGE analysis of melanoma cells and heterologous cells expressing epitope-tagged MC1R revealed dimeric and oligomeric species in detergent-solubilized extracts, confirmed by co-immunoprecipitation of differentially tagged MC1R forms. Dimerization occurs early during MC1R biosynthesis, and is seen for mutants displaying intracellular retention. These mutants exerted dominant-negative effects on wild-type (WT) MC1R. Conversely, partial functional trans-complementation of selected loss-of-function mutants was observed. WT-MC1R lacks cooperativity in agonist binding, yet coexpression of WT and a C-terminal deletion mutant yielded a form of different pharmacological properties. The natural diminished function alleles R151C, R160W, and D294H, associated with red hair, displayed dimerization and heterodimerization with WT. Coexpression of WT and R151C or R160W reduced the density of binding sites on the plasma membrane of transfected cells, whereas D294H mediated a dominant-negative effect on functional coupling to adenylyl cyclase. Therefore, subtle changes of functional properties may be associated with different MC1R haplotypes, contributing to the complexity of skin phenotype.     

Human scalp skin and hair follicles express neurotrophin-3 and its high-affinity receptor tyrosine kinase C, and show hair cycle-dependent alterations in expression

BACKGROUND: Neurotrophin (NT)-3 and its high-affinity receptor tyrosine kinase C (Trk C) are essential for nervous system development. These members of the NT family are also involved in murine hair morphogenesis and cycling. However, their role in human hair follicle (HF) biology remains to be elucidated. OBJECTIVES: To explore the role of NTs in human skin and HF biology. METHODS: The immunoreactivity (IR) of NT-3 and Trk C was studied in human scalp skin and HFs by immunofluorescent and light microscopic immunohistology. Skin biopsies were obtained from normal human scalp containing mainly anagen VI HFs from women (age 53-57 years) undergoing elective plastic surgery. RESULTS: Both NT-3 and Trk C showed prominent, yet distinct, IR patterns in human scalp anagen HFs (anagen VI), whereas they were weakly expressed in catagen and increased again in telogen HFs. Within HF compartments, NT-3 IR was prominent in the outer root sheath, inner root sheath, dermal papilla and connective tissue sheath. Trk C IR was prominent in all HF epithelial and mesenchymal compartments. Outside the HF, both NT-3 and Trk C showed prominent IR in the epidermis, sebaceous glands and sweat glands. CONCLUSIONS: These observations provide the first indication that NT-3 and Trk C are expressed in human scalp skin and HFs, and suggest that Trk C-mediated signalling is involved not only in murine but also in human HF biology. They may be useful in determining therapeutic strategies for the treatment of hair cycle and skin-related disorders.