Differential expression of melanocortin 2 receptor accessory protein in cancers of the breast.

Breast cancer affects women at relatively high frequency (1). We mined published microarray datasets (2, 3) to determine in an unbiased fashion and at the systems level genes most differentially expressed in the primary tumors of patients with breast cancer. We report here significant differential expression of the gene encoding melanocortin 2 receptor accessory protein, MRAP, when comparing primary tumors of the breast to the tissue of origin, the normal breast. MRAP was also differentially expressed in the brain metastases of patients with metastatic breast cancer. MRAP mRNA was present at significantly lower quantities in tumors of the breast as compared to normal breast tissue. Analysis of human survival data revealed that expression of MRAP in primary tumors of the breast was correlated with overall survival in patients with luminal A subtype cancer, demonstrating a relationship between primary tumor expression of a differentially expressed gene and patient survival outcomes influenced by PAM50 molecular subtype. MRAP may be of relevance to initiation, maintenance or progression of cancers of the female breast.

Topmouth culter melanocortin-3 receptor: regulation by two isoforms of melanocortin-2 receptor accessory protein 2

Melanocortin-3 receptor (MC3R) is a regulator of energy homeostasis, and interaction of MC3R and melanocortin-2 receptor accessory protein 2 (MRAP2) plays a critical role in MC3R signaling of mammals. However, the physiological roles of MC3R in teleosts are not well understood. In this study, qRT-PCR was used to measure gene expression. Radioligand binding assay was used to study the binding properties of topmouth culter MC3R (caMC3R). Intracellular cAMP generation was determined by radioimmunoassay and caMC3R expression was quantified with flow cytometry. We showed that culter mc3r had higher expression in the central nervous system. All agonists could bind and stimulate caMC3R to increase dose-dependently intracellular cAMP accumulation. Compared to hMC3R, culter MC3R showed higher constitutive activity, higher efficacies and Rmax to α-MSH, des-α-MSH, and ACTH. Both caMRAP2a and caMRAP2b markedly decreased caMC3R basal cAMP production. However, only caMRAP2a significantly decreased cell surface expression, Bmax and Rmax of caMC3R. Expression analysis suggested that MRAP2a and MRAP2b might be more important in regulating MC3R/MC4R signaling during larval period, and reduced mc3r, mc4r, and pomc expression might be primarily involved in modulation of MC3R/MC4R in adults. These data indicated that the cloned caMC3R was a functional receptor. MRAP2a and MRAP2a had different effects on expression and signaling of caMC3R. In addition, expression analysis suggested that MRAP2s, receptors, and hormone might play different roles in regulating culter development and growth.

Non-Coding Genetic Analysis Implicates Interleukin 18 Receptor Accessory Protein 3′UTR in Amyotrophic Lateral Sclerosis

The non-coding genome is substantially larger than the protein-coding genome, but the lack of appropriate methodologies for identifying functional variants limits genetic association studies. Here, we developed analytical tools to identify rare variants in pre-miRNAs, miRNA recognition elements in 3′UTRs, and miRNA-target networks. Region-based burden analysis of >23,000 variants in 6,139 amyotrophic lateral sclerosis (ALS) whole-genomes and 70,403 non-ALS controls identified Interleukin-18 Receptor Accessory Protein (IL18RAP) 3′UTR variants significantly enriched in non-ALS genomes, replicate in an independent cohort and associate with a five-fold reduced risk of developing ALS. IL18RAP 3′UTR variants modify NF-κB signaling, provide survival advantage for cultured ALS motor neurons and ALS patients, and reveal direct genetic evidence and therapeutic targets for neuro-inflammation. This systematic analysis of the non-coding genome and specifically miRNA-networks will increase the power of genetic association studies and uncover mechanisms of neurodegeneration.

Therapeutic Opportunities of Interleukin-33 in the Central Nervous System

Interleukin-33 (IL-33), a member of the IL-1 cytokine family, is involved in various diseases. IL-33 exerts its effects via its heterodimeric receptor complex, which comprises suppression of tumorigenicity 2 (ST2) and the IL-1 receptor accessory protein (IL-1RAP). Increasing evidence has demonstrated that IL-33/ST2 signaling plays diverse but crucial roles in the homeostasis of the central nervous system (CNS) and the pathogenesis of CNS diseases, including neurodegenerative diseases, cerebrovascular diseases, infection, trauma, and ischemic stroke. In the current review, we focus on the functional roles and cellular signaling mechanisms of IL-33 in the CNS and evaluate the potential for diagnostic and therapeutic applications.

Elevated Interleukin-18 Receptor Accessory Protein Mediates Enhancement in Reactive Oxygen Species Production in Neutrophils of Systemic Lupus Erythematosus Patients

Interleukin-18 receptor accessory protein (IL18RAP) is an indispensable subunit for the IL-18 receptor (IL-18R) complex’s ability to mediate high-affinity IL-18 binding and signalling transduction. Interest in IL-18 in systemic lupus erythematosus (SLE) has been mostly focused on its role as a type 1 T helper cell-driving cytokine. The functional significance of IL18RAP in mediating the IL-18-driven response in myeloid cells in SLE remains largely unexplored. This study aimed to investigate the expression and function significance of IL18RAP in neutrophils of SLE patients. By qRT-PCR and Western blot analyses, elevated expressions of IL18RAP mRNA and protein were observed in neutrophils from SLE patients—particularly those with a history of nephritis. IL18RAP expression correlated negatively with complement 3 level and positively with disease activity, with higher expression in patients exhibiting renal and immunological manifestations. The increased IL18RAP expression in SLE neutrophils could be attributed to elevated type I interferon level in sera. Functionally, neutrophils from SLE patients showed higher IL-18-mediated enhancement in reactive oxygen species (ROS) generation, which showed positive correlation with IL18RAP expression and could be neutralized by anti-IL18RAP blocking antibodies. Taken together, our findings suggest that IL-18 could contribute to SLE pathogenesis through mediation of neutrophil dysfunction via the upregulation of IL18RAP expression.

Du nouveau dans la génétique des formes monogéniques d’obésité et son impact pour mieux en comprendre la physiopathologie

L’obésité est une maladie complexe multifactorielle. Chez environ 5 % des individus obèses, il existe des formes monogéniques d’obésité pour laquelle une seule mutation est suffisante pour entraîner la maladie. Jusqu’à présent, les gènes mutés identifiés dans ces formes monogéniques sont impliqués dans la voie leptine/mélanocortine, principalement active au niveau de l’hypothalamus et régissant la satiété. Récemment, notre laboratoire a décrit une nouvelle forme monogénique d’obésité. Elle est due à une déficience du gène MRAP2 (melanocortin-2 receptor accessory protein 2) pour laquelle, contrairement aux formes précédemment décrites, on retrouve chez les porteurs une hyperglycémie et une hypertension, suggérant que MRAP2 joue un rôle biologique général dans les tissus métaboliques en plus de son rôle dans l’hypothalamus.

Melanocortin Receptor 4 (MC4R) Signaling System in Nile Tilapia

The melanocortin receptor 4 (MC4R) signaling system consists of MC4R, MC4R ligands [melanocyte-stimulating hormone (MSH), adrenocorticotropin (ACTH), agouti-related protein (AgRP)], and melanocortin-2 receptor accessory protein 2 (MRAP2), and it has been proposed to play important roles in feeding and growth in vertebrates. However, the expression and functionality of this system have not been fully characterized in teleosts. Here, we cloned tilapia MC4R, MRAP2b, AgRPs (AgRP, AgRP2), and POMCs (POMCa1, POMCb) genes and characterized the interaction of tilapia MC4R with MRAP2b, AgRP, α-MSH, and ACTH in vitro. The results indicate the following. (1) Tilapia MC4R, MRAP2b, AgRPs, and POMCs share high amino acid identity with their mammalian counterparts. (2) Tilapia MRAP2b could interact with MC4R expressed in CHO cells, as demonstrated by Co-IP assay, and thus decrease MC4R constitutive activity and enhance its sensitivity to ACTH1-40. (3) As in mammals, AgRP can function as an inverse agonist and antagonist of MC4R, either in the presence or absence of MRAP2b. These data, together with the co-expression of MC4R, MRAP2b, AgRPs, and POMCs in tilapia hypothalamus, suggest that as in mammals, ACTH/α-MSH, AgRP, and MRAP2 can interact with MC4R to control energy balance and thus play conserved roles in the feeding and growth of teleosts.

Membrane orientation and oligomerization of the melanocortin receptor accessory protein 2

The melanocortin receptor accessory protein 2 (MRAP2) plays a pivotal role in the regulation of several G protein–coupled receptors that are essential for energy balance and food intake. MRAP2 loss-of-function results in obesity in mammals. MRAP2 and its homolog MRAP1 have an unusual membrane topology and are the only known eukaryotic proteins that thread into the membrane in both orientations. In this study, we demonstrate that the conserved polybasic motif that dictates the membrane topology and dimerization of MRAP1 does not control the membrane orientation and dimerization of MRAP2. We also show that MRAP2 dimerizes through its transmembrane domain and can form higher-order oligomers that arrange MRAP2 monomers in a parallel orientation. Investigating the molecular details of MRAP2 structure is essential for understanding the mechanism by which it regulates G protein–coupled receptors and will aid in elucidating the pathways involved in metabolic dysfunction.