Melanocortin-1 Receptor Signaling Markedly Induces the Expression of the NR4A Nuclear Receptor Subgroup in Melanocytic Cells

Abstract

The melanocortin-1 receptor (MCIR) is a G-protein-coupled receptor expressed primarily in melanocytes and is known to play a pivotal role in the regulation of pigmentation in mammals. In humans MC1R has been found to be highly polymorphic with several functional variants associated with the phenotype of red hair color and fair skin, cutaneous UV sensitivity, and increased risk of developing melanoma and non-melanoma skin cancer. Recent evidence suggests that MC1R plays a photo-protective role in melanocytes in response to UV irradiation. Relatively few genetic targets of MC1R signaling have been identified independent of the pigmentation pathway. Here we show that MC1R signaling in B16 mouse melanoma cells and primary human melanocytes rapidly, and transiently, induces the transcription of the NR4A subfamily of orphan nuclear receptors. Furthermore, primary human melanocytes harboring homozygous RHC variant MC1R alleles exhibited an impaired induction of NR4A genes in response to the potent MC1R agonist (Nle4,D-Phe7)-␣-melanocyte-stimulating hormone. Using small interference RNA-mediated attenuation of NR4A1 and NR4A2 expression in melanocytes, the ability to remove cyclobutane pyrimidine dimers following UV irradiation appeared to be impaired in the context of MC1R signaling. These data identify the NR4A receptor family as potential mediators of an MC1R-coordinated DNA damage response to UV exposure in melanocytic cells.It has long been recognized that individuals with fair skin and poor tanning ability have an increased incidence of melanoma and non-melanoma skin cancer (1-3). Cutaneous pigmentation in humans is the result of melanin synthesis by epidermal melanocytes within specialized organelles termed melanosomes, which are transferred to surrounding keratinocytes (4).Human pigmentation is a polygenic trait with Ͼ60 genetic loci identified so far (5, 6). Efforts over the last decade to understand the genetic basis of human pigmentary traits have revealed the melanocortin-1 receptor (MC1R) 5 as a key determinant of the wide phenotypic diversity in mammals (7-9). MC1R is a seven-transmembrane G-protein-coupled receptor that has been found to be highly polymorphic in Caucasian individuals, with a number of functional variants strongly associating with a phenotype of red hair, fair skin, and poor tanning ability often referred to as the Red Hair Color (RHC) phenotype (7). MC1R preferentially binds the pro-opiomelanocortin-derived peptides ␣-melanocyte-stimulating hormone (␣-MSH) and adrenocorticotropic hormone, which leads to an elevation in intracellular cAMP levels (10). RHC variant MC1Rs have been demonstrated to elicit weak cAMP responses as a result of reduced receptor coupling (2, 11-13) or abnormal receptor localization (2, 12-15). Molecular analysis has revealed that MC1R signaling modulates the expression and function of the microphthalmia-associated transcription factor, a key regulator of pigmentation genes, suggesting that this pathway underlies MC1R coordination of melanogenesis (16). Accumulating ...

Genome-wide gene expression profiling of the Angelman syndrome mice with Ube3a mutation

“…Among them, both melanocortin 1 receptor (Mc1r), which is shown to have a neuroprotective effect in the brain, and nuclear receptor subfamily 4, group A, member 2 (Nr4a2), which is critical for survival of dopamine neurons and whose expression can be induced by Mc1r, are downregulated. [15][16][17] We have confirmed that the decline of Mc1r and Nr4a2 at transcriptional level is reflected at the protein level in the Ube3a mÀ/p+ mouse. Using RNA interfering approach, we have further shown that shRNA-mediated knockdown of Ube3a in P19 cells leads to downregulation of Mc1r and Nr4a2.…”

“…A recent report shows that Mc1r signaling induces the expression of Nr4a2. 17 Because both mRNAs are downregulated in the AS mice, we extended our differential expression analysis to the protein level for these two genes. To determine if downregulation of Mc1r and Nr4a2 can be reflected at the protein levels, we performed Western blot comparing cerebellum total protein extract from wild-type and Ube3a mÀ/p+ mice.…”

Involvement of Nurr-1/Nur77 in corticotropin-releasing factor/urocortin1-induced tyrosinase-related protein 1 gene transcription in human melanoma HMV-II cells

“…It is therefore possible that Nurr-1/Nur77 is also involved in -MSH-induced activation of TRP1 gene transcription. In fact, MC1R signaling was previously shown to rapidly stimulate transcription of the NR4A subfamily in mouse melanoma cells and primary human melanocytes (Smith et al, 2008). In addition to the standard MITF pathway, -MSH therefore seems to stimulate TRP1 gene expression at least partially through Nurr-1/Nur77 binding to NBREs.…”

“…Nurr-1/Nur77 has been shown to be involved in MC1R signaling in mouse melanoma cells and primary human melanocytes (Smith et al, 2008). We therefore determined whether both Nurr-1 and Nur77 were the target of MC1R signaling in HMV-II cells.…”

“…They also have characteristics of immediate early genes and are induced by a variety of extracellular signals. Indeed, it has been reported that interleukin-1 stimulates Nur77 expression in melanoma cells (Rangnekar et al, 1992), while MC1R signaling immediately induces expression in melanocytic cells (Smith et al, 2008). Both Nurr-1 and Nur77 are known to act via a NGFI-B response element (NBRE) on the TRP1 promoter.…”