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.

MGRN1 depletion promotes intercellular adhesion in melanoma by upregulation of E-cadherin and inhibition of CDC42

Mahogunin Ring Finger 1 is an E3-ubiquitin ligase encoded by the color gene MGRN1. Our previous in vitro and in vivo studies demonstrated that Mgrn1 deletion in mouse melanoma cells induced cell differentiation and adhesion, and decreased cell motility and invasion on collagen I, and lung colonization in an in vivo model. Here, we investigated the role of MGRN1 on human melanoma cell morphology, adhesion and expression of genes/proteins involved in an EMT-like transition. We demonstrated that wild-type BRAF human melanoma cells adopted a clustering-like morphology on collagen I, with permanent MGRN1 abrogation resulting in bigger cell clusters. Enhanced intercellular adhesion was mostly mediated by induction of E-cadherin and higher co-localization with β-catenin. Transcriptional upregulation of E-cadherin likely occurred through downregulation of the ZEB1 repressor. Finally, pulldown assays showed reduced activation of CDC42 in the absence of MGRN1, which was reverted after E-cadherin silencing. Overall, these findings highlight a new MGRN1-dependent pathway regulating melanoma cell shape, motility, and invasion potential.

A Side-by-Side Comparison of Wildtype and Variant Melanocortin 1 Receptor Signaling with Emphasis on Protection against Oxidative Damage to DNA

Common variants of the MC1R gene coding the α-melanocyte stimulating hormone receptor are associated with light skin, poor tanning, blond or red hair, and increased melanoma risk, due to pigment-dependent and -independent effects. This complex phenotype is usually attributed to impaired activation of cAMP signaling. However, several MC1R variants show significant residual coupling to cAMP and efficiently activate mitogenic extracellular signal-regulated kinase 1 and 2 (ERK1/2) signaling. Yet, residual signaling and the key actions of wildtype and variant MC1R have never been assessed under strictly comparable conditions in melanocytic cells of identical genetic background. We devised a strategy based on CRISPR-Cas9 knockout of endogenous MC1R in a human melanoma cell line wildtype for BRAF, NRAS and NF1, followed by reconstitution with epitope-labeled MC1R constructs, and functional analysis of clones expressing comparable levels of wildtype, R151C or D294H MC1R. The proliferation rate, shape, adhesion, motility and sensitivity to oxidative DNA damage were compared. The R151C and D294H RHC variants displayed impaired cAMP signaling, intracellular stability similar to the wildtype, triggered ERK1/2 activation as effectively as the wildtype, and afforded partial protection against oxidative DNA damage, although less efficiently than the wildtype. Therefore, common melanoma-associated MC1R variants display biased signaling and significant genoprotective activity.

MGRN1 as a Phenotypic Determinant of Human Melanoma Cells and a Potential Biomarker

Mahogunin Ring Finger 1 (MGRN1), a ubiquitin ligase expressed in melanocytes, interacts with the α melanocyte-stimulating hormone receptor, a well-known melanoma susceptibility gene. Previous studies showed that MGRN1 modulates the phenotype of mouse melanocytes and melanoma cells, with effects on pigmentation, shape, and motility. Moreover, MGRN1 knockdown augmented the burden of DNA breaks in mouse cells, indicating that loss of MGRN1 promoted genomic instability. However, data concerning the roles of MGRN1 in human melanoma cells remain scarce. We analyzed MGRN1 knockdown in human melanoma cells. Transient MGRN1 depletion with siRNA or permanent knockdown in human melanoma cells by CRISPR/Cas9 caused an apparently MITF-independent switch to a more dendritic phenotype. Lack of MGRN1 also increased the fraction of human cells in the S phase of the cell cycle and the burden of DNA breaks but did not significantly impair proliferation. Moreover, in silico analysis of publicly available melanoma datasets and estimation of MGRN1 in a cohort of clinical specimens provided preliminary evidence that MGRN1 expression is higher in human melanomas than in normal skin or nevi and pointed to an inverse correlation of MGRN1 expression in human melanoma with patient survival, thus suggesting potential use of MGRN1 as a melanoma biomarker.

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.

Functional characterization of a C-terminal splice variant of the human melanocortin 1 receptor

The melanocortin 1 receptor (MC1R) is a major determinant of skin pigmentation and sensitivity to ultraviolet radiation. When stimulated by its natural agonists, it promotes the switch from synthesis of poorly photoprotective and lightly colored pheomelanins to production of photoprotective and darker eumelanins. In addition to an unusually high number of single nucleotide polymorphisms, the MC1R is expressed as 3 protein-coding splice variants. Two transcripts display different 5' untranslated sequences but yield the same open reading frame corresponding to the canonical 317 aminoacids protein (termed MC1R). An alternative transcript named MC1R-203 encodes for a 382 amino acids protein of poorly characterized functional properties containing an additional 65 aminoacids C-terminal extension. Given the known roles of the MC1R C-terminal extension in forward trafficking, coupling to intracellular effectors and desensitization, the different structure of this domain in MC1R and MC1R-203 may lead to significant functional alteration(s). We have assessed the functional properties of MC1R-203, as compared with the canonical MC1R form. We show that unstimulated HBL human melanoma cells express the MC1R-203 spliceoform, although at much lower levels than canonical MC1R. When expressed in heterologous HEK293 cells, the presence of the 65 aminoacid-long cytosolic extension immediately after Cys316 in MC1R-203 did not impair the intracellular stability of the protein, but it interfered with functional coupling to the cAMP cascade and with the ubiquitylation of ARRB2 associated with MC1R desensitization. Conversely, MC1R-203 retained full capacity to activate ERK1/2 signaling. Accordingly, MC1R-203 displays biased signaling when expressed in HEK293 cells.

Regional Activation of Myosin II in Cancer Cells Drives Tumor Progression via a Secretory Cross-Talk with the Immune Microenvironment

ROCK-Myosin II drives fast rounded-amoeboid migration in cancer cells during metastatic dissemination. Analysis of human melanoma biopsies revealed that amoeboid melanoma cells with high Myosin II activity are predominant in the invasive fronts of primary tumors in proximity to CD206+CD163+ tumor-associated macrophages and vessels. Proteomic analysis shows that ROCK-Myosin II activity in amoeboid cancer cells controls an immunomodulatory secretome, enabling the recruitment of monocytes and their differentiation into tumor-promoting macrophages. Both amoeboid cancer cells and their associated macrophages support an abnormal vasculature, which ultimately facilitates tumor progression. Mechanistically, amoeboid cancer cells perpetuate their behavior via ROCK-Myosin II-driven IL-1α secretion and NF-κB activation. Using an array of tumor models, we show that high Myosin II activity in tumor cells reprograms the innate immune microenvironment to support tumor growth. We describe an unexpected role for Myosin II dynamics in cancer cells controlling myeloid function via secreted factors.

Functional interplay between secreted ligands and receptors in melanoma

Melanoma, the most aggressive form of skin cancer, results from the malignant transformation of melanocytes located in the basement membrane separating the epidermal and dermal skin compartments. Cutaneous melanoma is often initiated by solar ultraviolet radiation (UVR)-induced mutations. Melanocytes intimately interact with keratinocytes, which provide growth factors and melanocortin peptides acting as paracrine regulators of proliferation and differentiation. Keratinocyte-derived melanocortins activate melanocortin-1 receptor (MC1R) to protect melanocytes from the carcinogenic effect of UVR. Accordingly, MC1R is a major determinant of susceptibility to melanoma. Despite extensive phenotypic heterogeneity and high mutation loads, the molecular basis of melanomagenesis and the molecules mediating the crosstalk between melanoma and stromal cells are relatively well understood. Mutations of intracellular effectors of receptor tyrosine kinase (RTK) signalling, notably NRAS and BRAF, are major driver events more frequent than mutations in RTKs. Nevertheless, melanomas often display aberrant signalling from RTKs such as KIT, ERRB1-4, FGFR, MET and PDGFR, which contribute to disease progression and resistance to targeted therapies. Progress has also been made to unravel the role of the tumour secretome in preparing the metastatic niche. However, key aspects of the melanoma-stroma interplay, such as the molecular determinants of dormancy, remain poorly understood.

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.

The NADPH oxidase NOX4 represses epithelial to amoeboid transition and efficient tumour dissemination

Epithelial to mesenchymal transition is a common event during tumour dissemination. However, direct epithelial to amoeboid transition has not been characterized to date. Here we provide evidence that cells from hepatocellular carcinoma (HCC), a highly metastatic cancer, undergo epithelial to amoeboid transition in physiological environments, such as organoids or three-dimensional complex matrices. Furthermore, the NADPH oxidase NOX4 inhibits this transition and therefore suppresses efficient amoeboid bleb-based invasion. Moreover, NOX4 expression is associated with E-cadherin levels and inversely correlated with invasive features. NOX4 is necessary to maintain parenchymal structures, increase cell-cell and cell-to-matrix adhesion, and impair actomyosin contractility and amoeboid invasion. Importantly, NOX4 gene deletions are frequent in HCC patients, correlating with higher tumour grade. Contrary to that observed in mesenchymal cell types, here NOX4 suppresses Rho and Cdc42 GTPase expression and downstream actomyosin contractility. In HCC patients, NOX4 expression inversely correlates with RhoC and Cdc42 levels. Moreover, low expression of NOX4 combined with high expression of either RhoC or Cdc42 is associated with worse prognosis. Therefore, loss of NOX4 increases actomyosin levels and favours an epithelial to amoeboid transition contributing to tumour aggressiveness.

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.

Anti-Folate Receptor-α IgE but not IgG Recruits Macrophages to Attack Tumors via TNFα/MCP-1 Signaling

IgE antibodies are key mediators of antiparasitic immune responses, but their potential for cancer treatment via antibody-dependent cell-mediated cytotoxicity (ADCC) has been little studied. Recently, tumor antigen-specific IgEs were reported to restrict cancer cell growth by engaging high-affinity Fc receptors on monocytes and macrophages; however, the underlying therapeutic mechanisms were undefined and in vivo proof of concept was limited. Here, an immunocompetent rat model was designed to recapitulate the human IgE-Fcε receptor system for cancer studies. We also generated rat IgE and IgG mAbs specific for the folate receptor (FRα), which is expressed widely on human ovarian tumors, along with a syngeneic rat tumor model expressing human FRα. Compared with IgG, anti-FRα IgE reduced lung metastases. This effect was associated with increased intratumoral infiltration by TNFα+ and CD80+ macrophages plus elevated TNFα and the macrophage chemoattractant MCP-1 in lung bronchoalveolar lavage fluid. Increased levels of TNFα and MCP-1 correlated with IgE-mediated tumor cytotoxicity by human monocytes and with longer patient survival in clinical specimens of ovarian cancer. Monocytes responded to IgE but not IgG exposure by upregulating TNFα, which in turn induced MCP-1 production by monocytes and tumor cells to promote a monocyte chemotactic response. Conversely, blocking TNFα receptor signaling abrogated induction of MCP-1, implicating it in the antitumor effects of IgE. Overall, these findings show how antitumor IgE reprograms monocytes and macrophages in the tumor microenvironment, encouraging the clinical use of IgE antibody technology to attack cancer beyond the present exclusive reliance on IgG. Cancer Res; 77(5); 1127-41. ©2017 AACR.

Reactive oxygen species and tumor dissemination: Allies no longer

For decades, reactive oxygen species (ROS) linked to oxidative stress have been suggested to promote carcinogenesis. However, we and others have demonstrated a protective role for ROS in metastatic dissemination. These recent studies partly explain the large failure observed in clinical trials using antioxidants for cancer prevention.

Reactivation of p53 by a Cytoskeletal Sensor to Control the Balance Between DNA Damage and Tumor Dissemination

BACKGROUND

Abnormal cell migration and invasion underlie metastasis, and actomyosin contractility is a key regulator of tumor invasion. The links between cancer migratory behavior and DNA damage are poorly understood.

METHODS

Using 3D collagen systems to recapitulate melanoma extracellular matrix, we analyzed the relationship between the actomyosin cytoskeleton of migrating cells and DNA damage. We used multiple melanoma cell lines and microarray analysis to study changes in gene expression and in vivo intravital imaging (n = 7 mice per condition) to understand how DNA damage impacts invasive behavior. We used Protein Tissue Microarrays (n = 164 melanomas) and patient databases (n = 354 melanoma samples) to investigate the associations between markers of DNA damage and actomyosin cytoskeletal features. Data were analyzed with Student's and multiple t tests, Mann-Whitney's test, one-way analysis of variance, and Pearson correlation. All statistical tests were two-sided.

RESULTS

Melanoma cells with low levels of Rho-ROCK-driven actomyosin are subjected to oxidative stress-dependent DNA damage and ATM-mediated p53 protein stabilization. This results in a specific transcriptional signature enriched in DNA damage/oxidative stress responsive genes, including Tumor Protein p53 Inducible Protein 3 (TP53I3 or PIG3). PIG3, which functions in DNA damage repair, uses an unexpected catalytic mechanism to suppress Rho-ROCK activity and impair tumor invasion in vivo. This regulation was suppressed by antioxidants. Furthermore, PIG3 levels decreased while ROCK1/2 levels increased in human metastatic melanomas (ROCK1 vs PIG3; r = -0.2261, P < .0001; ROCK2 vs PIG3: r = -0.1381, P = .0093).

CONCLUSIONS

The results suggest using Rho-kinase inhibitors to reactivate the p53-PIG3 axis as a novel therapeutic strategy; we suggest that the use of antioxidants in melanoma should be very carefully evaluated.

Rho GTPases modulate malignant transformation of tumor cells

Rho GTPases are involved in the acquisition of all the hallmarks of cancer, which comprise 6 biological capabilities acquired during the development of human tumors. The hallmarks include proliferative signaling, evading growth suppressors, resisting cell death, enabling replicative immortality, inducing angiogenesis, and activating invasion and metastasis programs, as defined by Hanahan and Weinberg. (1) Controlling these hallmarks are genome instability and inflammation. Emerging hallmarks are reprogramming of energy metabolism and evading immune destruction. To give a different view to the readers, we will not be focusing on invasion, metastasis, or cytoskeletal remodeling, but we will review here how Rho GTPases contribute to other hallmarks of cancer with a special emphasis on malignant transformation.

Differential and competitive regulation of human melanocortin 1 receptor signaling by β-arrestin isoforms

The melanocortin 1 receptor (MC1R) is a G protein-coupled receptor (GPCR) crucial for the regulation of melanocyte proliferation and differentiation. MC1R activation by melanocortin hormones triggers the cAMP pathway and stimulates the extracellular signal-regulated protein kinases ERK1 and ERK2 to promote synthesis of photoprotective eumelanin pigments among other effects. Signaling from most GPCRs is regulated by the β-arrestin (ARRB) family of cytosolic multifunctional adaptor proteins which mediate signal termination and endocytosis of GPCR-agonist complexes. The ubiquitously expressed non-visual β-arrestin1 (ARRB1) and β-arrestin2 (ARRB2) are highly homologous but not functionally equivalent. Their role in the regulation of MC1R is unknown. Using a combination of co-immunoprecipitation, gel filtration chromatography, confocal microscopy, siRNA-mediated knockdown and functional assays, we demonstrated agonist-independent competitive interactions of ARRB1 and ARRB2 with MC1R, which might also be independent of phosphorylation of MC1R C-terminal Ser/Thr residues. The effects of ARRBs were isoform-specific. ARRB2 inhibited MC1R agonist-dependent cAMP production but not ERK activation, stimulated internalization and showed prolonged co-localization with the receptor in endocytic vesicles. Conversely, ARRB1 had no effect on internalization or functional coupling, but competed with ARRB2 for binding MC1R, which might increase signaling by displacement of inhibitory ARRB2. These data suggest a novel mechanism of MC1R functional regulation based on the relative expression of ARRB isoforms, with possible activatory ARRB1-dependent effects arising from partial relief of inhibitory ARRB2-MC1R interactions. Thus, competitive displacement of inhibitory ARRBs by functionally neutral ARRB isoforms might exert a paradigm-shifting signal-promoting effect to fine-tune signaling downstream of certain GPCRs.

Functional status and relationships of melanocortin 1 receptor signaling to the cAMP and extracellular signal-regulated protein kinases 1 and 2 pathways in human melanoma cells

Melanocortin 1 receptor (MC1R), a major determinant of skin phototype frequently mutated in melanoma, is a Gs protein-coupled receptor that regulates pigment production in melanocytes. MC1R stimulation activates cAMP synthesis and the extracellular signal-regulated (ERK) ERK1 and ERK2. In human melanocytes, ERK activation by MC1R relies on cAMP-independent transactivation of the c-KIT receptor. Thus MC1R functional coupling to the cAMP and ERK pathways may involve different structural requirements giving raise to biased effects of skin cancer-associated mutations. We evaluated the impact of MC1R mutations on ERK activation, cAMP production and agonist binding. We found that MC1R mutations impair cAMP production much more often than ERK activation, suggesting less stringent requirements for functional coupling to the ERK pathway. We examined the crosstalk of the cAMP and ERK pathways in HBL human melanoma cells (wild-type for MC1R, NRAS and BRAF). ERK activation by constitutively active upstream effectors or pharmacological inhibition had little effect on MC1R-stimulated cAMP synthesis. High cAMP levels were compatible with normal ERK activation but, surprisingly, the adenylyl cyclase activator forskolin abolished ERK activation by MC1R, most likely by a cAMP-independent mechanism. These results indicate little crosstalk of the cAMP and ERK pathways in HBL melanoma cells. Finally, we studied cAMP accumulation in a panel of 22 human melanoma cell lines stimulated with MC1R agonists or forskolin. cAMP synthesis was often inhibited, even in cells wild-type for MC1R and NRAS. Therefore, the cAMP pathway is more frequently impaired in melanoma than could be predicted by the MC1R or NRAS genotype.

N-glycosylation of the human melanocortin 1 receptor: occupancy of glycosylation sequons and functional role

The melanocortin 1 receptor (MC1R), a major determinant of skin pigmentation and phototype, mediates the actions of α-melanocyte-stimulating hormone on melanocytes and is critical for melanocyte proliferation and differentiation. MC1R has two putative N-glycosylation targets, Asn15 and Asn29. It has been shown that MC1R is a glycoprotein with an unusual sensitivity to endoglycosidase H digestion. However, the occupancy and functional importance of each specific glycosylation sequon remains unknown. We demonstrate that MC1R is N-glycosylated at Asn15 and Asn29, with structurally and functionally different glycan chains. N-glycosylation is not necessary for high affinity agonist binding or functional coupling but has a strong effect on the availability of MC1R molecules on the plasma membrane, most likely by a combination of improved forward trafficking and decreased internalization. Finally, we found that MC1R variants exhibit different degrees of glycosylation which do not show a simple correlation with their functional status or intracellular trafficking.

Signaling from the human melanocortin 1 receptor to ERK1 and ERK2 mitogen-activated protein kinases involves transactivation of cKIT

Melanocortin 1 receptor (MC1R), a Gs protein-coupled receptor expressed in melanocytes, is a major determinant of skin pigmentation, phototype and cancer risk. Upon stimulation by αMSH, MC1R triggers the cAMP and ERK1/ERK2 MAPK pathways. In mouse melanocytes, ERK activation by αMSH binding to Mc1r depends on cAMP, and melanocytes are considered a paradigm for cAMP-dependent ERK activation. However, human MC1R variants associated with red hair, fair skin [red hair color (RHC) phenotype], and increased skin cancer risk display reduced cAMP signaling but activate ERKs as efficiently as wild type in heterologous cells, suggesting independent signaling to ERKs and cAMP in human melanocytes. We show that MC1R signaling activated the ERK pathway in normal human melanocytes and melanoma cells expressing physiological levels of endogenous RHC variants. ERK activation was comparable for wild-type and mutant MC1R and was independent on cAMP because it was neither triggered by stimulation of cAMP synthesis with forskolin nor blocked by the adenylyl cyclase inhibitor 2',5'-dideoxyadenosine. Stimulation of MC1R with αMSH did not lead to protein kinase C activation and ERK activation was unaffected by protein kinase C inhibitors. Conversely, pharmacological interference, small interfering RNA studies, expression profiles, and functional reconstitution experiments showed that αMSH-induced ERK activation resulted from Src tyrosine kinase-mediated transactivation of the stem cell factor receptor, a receptor tyrosine kinase essential for proliferation, differentiation, and survival of melanocyte precursors, thus demonstrating a functional link between the stem cell factor receptor and MC1R. Moreover, this transactivation phenomenon is unique because it is unaffected by natural mutations impairing canonical MC1R signaling through the cAMP pathway.

Melanocortin 1 receptor mutations impact differentially on signalling to the cAMP and the ERK mitogen-activated protein kinase pathways

Melanocortin 1 receptor (MC1R), a Gs protein-coupled receptor expressed in melanocytes, is a major determinant of skin pigmentation, phototype and cancer risk. MC1R activates cAMP and mitogen-activated protein kinase ERK1/ERK2 signalling. When expressed in rat pheochromocytoma cell line cells, the R151C, R160W and D294H MC1R variants associated with melanoma and impaired cAMP signalling mediated ERK activation and ERK-dependent, agonist-induced neurite outgrowth comparable with wild-type. Dose-response curves for ERK activation and cAMP production indicated higher sensitivity of the ERK response. Thus, the melanoma-associated MC1R mutations impact differently on cAMP and ERK signalling, suggesting that cAMP is not responsible for functional coupling of MC1R to the ERK cascade.

Aberrant trafficking of human melanocortin 1 receptor variants associated with red hair and skin cancer: Steady-state retention of mutant forms in the proximal golgi

The melanocortin 1 receptor (MC1R), a Gs protein-coupled receptor (GPCR) expressed in melanocytes, is a major determinant of skin pigmentation and phototype. MC1R activation stimulates melanogenesis and increases the ratio of black, strongly photoprotective eumelanins to reddish, poorly photoprotective pheomelanins. Several MC1R alleles are associated with red hair, fair skin, increased sensitivity to ultraviolet radiation (the RHC phenotype) and increased skin cancer risk. Three highly penetrant RHC variants, R151C, R160W, and D294H are loss-of-function MC1R mutants with altered cell surface expression. In this study, we show that forward trafficking was normal for D294H. Conversely, export traffic was impaired for R151C, which accumulated in the endoplasmic reticulum (ER), and for R160W, which was enriched in the cis-Golgi. This is the first report of steady-state retention in a post-ER secretory compartment of a GPCR mutant found in the human population. Residues R151 and R160 are located in the MC1R second intracellular loop (il2). Two other mutations in il2, T157A preventing T157 phosphorylation and R162P disrupting a (160)RARR(163) motif, also caused intracellular retention. Moreover, T157 was phosphorylated in wild-type MC1R and a T157D mutation mimicking constitutive phosphorylation allowed normal traffic, and rescued the retention phenotype of R160W and R162P. Therefore, MC1R export is likely regulated by T157 phosphorylation and the (160)RARR(163) arginine-based motif functions as an ER retrieval signal. These elements are conserved in mammalian MC1Rs and in all five types of human melanocortin receptors. Thus, members of this GPCR subfamily might share common mechanisms for regulation of plasma membrane expression.

Mechanism of dimerization of the human melanocortin 1 receptor

The melanocortin 1 receptor (MC1R) is a dimeric G protein-coupled receptor expressed in melanocytes, where it regulates the amount and type of melanins produced and determines the tanning response to ultraviolet radiation. We have studied the mechanisms of MC1R dimerization. Normal dimerization of a deleted mutant lacking the seventh transmembrane fragment and the C-terminal cytosolic extension excluded coiled-coil interactions as the basis of dimerization. Conversely, the electrophoretic pattern of wild type receptor and several Cys-->Ala mutants showed that four disulfide bonds are established between the monomers. Disruption of any of these bonds abolished MC1R function, but only the one involving Cys35 was essential for traffic to the plasma membrane. A quadruple Cys35-267-273-275Ala mutant migrating as a monomer in SDS-PAGE in the absence of reducing agents was able to dimerize with WT, suggesting that in addition to disulfide bond formation, dimerization involves non-covalent interactions, likely of domain swap type.

Auditory discrimination therapy (ADT) for tinnitus management

Auditory discrimination training (ADT) designs a procedure to increase cortical areas responding to trained frequencies (damaged cochlear areas with cortical misrepresentation) and to shrink the neighboring over-represented ones (tinnitus pitch). In a prospective descriptive study of 27 patients with high frequency tinnitus, the severity of the tinnitus was measured using a visual analog scale (VAS) and the tinnitus handicap inventory (THI). Patients performed a 10-min auditory discrimination task twice a day during one month. Discontinuous 4 kHz pure tones were mixed randomly with short broadband noise sounds through an MP3 system. After the treatment mean VAS scores were reduced from 5.2 to 4.5 (p=0.000) and the THI decreased from 26.2% to 21.3% (p=0.000). Forty percent of the patients had improvement in tinnitus perception (RESP). Comparing the ADT group with a control group showed statistically significant improvement of their tinnitus as assessed by RESP, VAS, and THI.

Consensus for tinnitus patient assessment and treatment outcome measurement: Tinnitus Research Initiative meeting, Regensburg, July 2006

There is widespread recognition that consistency between research centres in the ways that patients with tinnitus are assessed and outcomes following interventions are measured would facilitate more effective co-operation and more meaningful evaluations and comparisons of outcomes. At the first Tinnitus Research Initiative meeting held in Regensburg in July 2006 an attempt was made through workshops to gain a consensus both for patient assessments and for outcome measurements. It is hoped that this will contribute towards better cooperation between research centres in finding and evaluating treatments for tinnitus by allowing better comparability between studies.

Auditory discrimination therapy (ADT) for tinnitus managment: preliminary results

CONCLUSION

This clinical assay has demonstrated the efficacy of auditory discrimination therapy (ADT) in tinnitus management compared with a waiting-list group. In all, 43% of the ADT patients improved their tinnitus, and its intensity together with its handicap were statistically decreased (EMB rating: B-2).

OBJECTIVE

To describe the effect of sound discrimination training on tinnitus. ADT designs a procedure to increase the cortical representation of trained frequencies (damaged cochlear areas with a secondary reduction of cortical stimulation) and to shrink the neighbouring over-represented ones (corresponding to tinnitus pitch).

STUDY DESIGN

This prospective descriptive study included 14 patients with high frequency matched tinnitus. Tinnitus severity was measured according to a visual analogue scale (VAS) and the Tinnitus Handicap Inventory (THI). Patients performed a 10-min auditory discrimination task twice a day for 1 month. Discontinuous 8 kHz pure tones were randomly mixed with 500 ms 'white noise' sounds through a MP3 system. ADT group results were compared with a waiting-list group (n=21).

RESULTS

In all, 43% of our patients had improvement in their tinnitus. A significant improvement in VAS (p=0.004) and THI mean scores was achieved (p=0.038). Statistical differences between ADT and the waiting-list group have been proved, considering patients' self-evaluations (p=0.043) and VAS scores (p=0.004). A non-significant reduction of THI was achieved (p=0.113).

Tinnitus and Ménière's disease: characteristics and prognosis in a tinnitus clinic sample

The aim of this study is to describe tinnitus epidemiological characteristics in Ménière's disease (MD), the prognosis and its interaction with other MD symptoms. It is a descriptive transversal study. One hundred two MD patients were referred to a tinnitus clinic. Tinnitus was evaluated according to psychoacoustical tinnitogram, visual analogue scale, and tinnitus handicap inventory (THI). All patients were diagnosed with definitive MD (following AAO-HNS' 95 criteria). Pitch was more commonly identified in low and medium frequencies. Psychoacoustical intensity was matched in 12.7 dB. The visual analogue scale showed a value of 7.1, while THI score reached an average of 49%. Compared with other aetiologies (acoustic trauma, otosclerosis), MD showed a statistical difference in tinnitus severity parameters (P<0.05). Tinnitus increased VAS and THI score as a function of duration and bilateral disease (P<0.01). We found a statistical association (P<0.05) between tinnitus intensity and worse hearing loss or hyperacusis, but it was not influenced by number of vertigo spells. Higher MD stage increased tinnitus intensity and handicap. Tinnitus in MD patients referred to our tinnitus clinic presents a high intensity and handicap levels and represents the most troublesome symptom. Severity is influenced by the longer duration of the disease, the bilateral affection, hearing impairment or hyperacusis and a higher MD stage.

Mecanismos fisiopatológicos en la génesis y cronificación del acúfeno

Progress in neuroscience research has given birth to new theories for tinnitus generation. From a point of view where cochlear dysfunctions would be considered as the origin and maintenance mechanisms, it has been introduced the important role of compensation systems from the central auditory pathways. They could act as the most relevant factor for chronic persistent tinnitus after a peripheral aggression. Unmasking of silent synapses or sprouting of new ones activate cortical reorganization for frecuencial areas nearby the non-stimulated ones through brain plasticity. Connections to associative cortex and limbic-amigdala area using the non-classical auditory system explain the presence of hyperacusis, anxiety or depression, factors that increase the severity of tinnitus. Implementation of these physiopathological theories reinforces the tinnitus neurophysiological model. The development of an aversive response through the survival reflex and the participation of negative emotional response are the responsible for signal persistence and vegetative reactions from the autonomous nervous system. Implications of this knowledge for tinnitus treatment involve the central auditory system approach through the combination of medical counselling for reduction of the aversive reaction and sound therapy to diminish its perception.

[Magnetic resonance: first choice test in the screening of internal auditory canal and cerebellopontine angle tumors]

Although internal auditory canal (IAC) and cerebellopontine angle (CPA) tumors are rare, their clinical suspicion is quite common in the otolaryngology office. MRI is the imaging modality of choice in diagnosing these tumors. Perceived high costs may prevent clinicians from using it as a screening tool. A protocol designed to improve cost-effectiveness in such diagnosis results in a more rationale clinical practice. Our aim was to evaluate the usefulness of MRI as screening tool in diagnosis of IAC and CPA tumors in our population. Between March 1998 and March 2000, a prospective series of 200 cases had a MRI screening requested. MRI were performed following Fast Spin Echo technique, providing T2-weighted images. Gadolinium enhanced MRI was reserved for selected cases. We report on 190 MRI done. We found 7 neuromas (3.5%), one CPA metastasis, one epidermoid cyst and 9 IAC vascular anomalies. Only 138 cases (69%) had normal MRI images. When used following a designed protocol, MRI is our procedure of choice while screening IAC and CPA tumors because it is a cost-effective tool.

[Myringotomy under topical anesthesia with phenol]

Myringotomy is a common outpatient surgical procedure. It can be performed under general inhaled anesthesia, but it is usually carried out under local anesthesia by lidocaine infiltration or instillation of different anesthetic agents. We present our experience with myringotomy and tympanic tube placement using topical anesthesia with 88% phenol as an outpatient procedure. We report 55 patients in which we performed 81 treatments. In this series, only two ears (2.47%) did not tolerate the surgical procedure, tube insertion under general anesthesia being necessary in one case. Topical anesthesia with phenol facilitates the outpatient treatment of adult otitis media with effusion.

The migraine: benign paroxysmal vertigo of childhood complex

The migraine--a benign paroxysmal vertigo of childhood complex is the most frequent etiology of pediatric dizziness, with an incidence of 34.7%. We present a series of 34 children in whom this entity was diagnosed. We describe the most important characteristics and discuss the possible etiological factors. We review the theories about a common pathophysiological origin for migraine, benign paroxysmal vertigo of childhood, and paroxysmal torticollis. Evolution of these entities confirms the idea of a common origin and a different vestibular symptomatology, depending on the age of the child experiencing dizziness.

[Equilibrium disorders in childhood]

Dizziness and imbalance are uncommon in children, but often alarming for their families. A detailed interview and otoneurological examination are important for reaching a specific diagnosis and treatment. The purpose of our study was to obtain our own etiological, clinical and diagnostic statistics, and to review the major related pathologies. We report a series of 76 children with imbalance or dizziness as the presenting symptom. Paroxysmal benign vertigo of childhood was the most common pathology in our study, followed by vestibular neuronitis. Our findings were compared to those of other authors. Early diagnosis is emphasized as the most important factor for achieving an effective vestibular rehabilitation in children.

A novel locus for non-syndromic sensorineural deafness (DFN6) maps to chromosome Xp22

Non-syndromic X-linked deafness is highly heterogeneous. At least five different clinical forms have been described, but only two loci have been mapped. Here we report a Spanish family affected by a previously undescribed X-linked form of hearing impairment. Deafness is non-syndromic, sensorineural, and progressive. In affected males, the auditory impairment is first detected at school age, affecting mainly the high frequencies. Later it evolves to become severe to profound, involving all frequencies for adulthood. Carrier females manifest a moderate hearing impairment in the high frequencies, with the onset delayed to the fourth decade of life. Deafness was assumed to be X-linked dominant, with incomplete penetrance and variable expressivity in carrier females. The family was genotyped for a set of microsatellite markers evenly spaced at intervals of about 10 cM. We found evidence of linkage to markers in the Xp22 region (maximum lod score of 5.30 at theta = 0.000 for DXS8036 and for DXS8022). The position of the novel deafness locus (DFN6) was refined by haplotype analysis. Mapping of the breakpoints in two critical recombinants allowed us to define an interval for DFN6, delimited by DXS7108 on the distal side and by DXS7105 on the proximal side, and spanning a genetic distance of about 15 cM.

[Changes in the cerebrospinal fluid in patients with HIV infection]

Spinal fluid from 53 HIV infected patients has been reviewed. A diagnosis was made exclusively from the spinal fluid exam in 15 cases while in 15 others it contributed to diagnosis together with other exams. The exam did not contribute any positive data in 23 cases. AIDS diagnosis was obtained in 11 patients by the spinal fluid exam. The most frequently occurring disease was infectious meningitis (10 cases) being 3 of them HIV aseptic meningitis. In our experience, a spinal fluid exam in HIV infected patients and fever of unknown origin did contribute useful data for the diagnosis of AIDS in a large number of cases.

[Tuberculosis in patients with HIV infection]

28 cases of tuberculosis in patients infected with HIV, 22 of them having AIDS criteria (CDC 87), are presented. Tuberculosis was the first diagnosis criteria in 34% of the cases 68% were I.V.U., 25% homosexuals and 7% heterosexual. Half of the patients had disseminated tuberculosis and the other half had localised disease with a high frequency of pulmonary setting. The most frequent symptoms were fever and constitutional syndrome (92% and 91%). The patient's chest X-rays showed few cavitations and infiltrates and frequently had mediastinal and/or hilar (22%) lymphatic gland enlargement. The study of lymphocyte populations showed levels of CD4 lower than 400 in 79% of the cases. The response to treatment was favorable in 16 patients and only 3 died of tuberculosis.