Neuromedin U stimulates contraction of human long saphenous vein and gastrointestinal smooth muscle in vitro

Oncogenic features of neuromedin U in breast cancer are associated with NMUR2 expression involving crosstalk with members of the WNT signaling pathway

Neuromedin U (NMU) has been shown driving the progression of various tumor entities, including breast cancer. However, the expression pattern of NMU and its receptors in breast cancer tissues as well as systematic insight into mechanisms and downstream targets of the NMU-driven signaling pathways are still elusive. Here, NMU expression was found up-regulated in all breast cancer subtypes when compared to healthy breast tissue. Using an in silico dataset comprising 1,195 samples, high NMU expression was identified as an indicator of poor outcome in breast tumors showing strong NMUR2 expression. Next, the biological impact of NMU on breast cancer cells in relation to NMUR2 expression was analyzed. Ectopic NMU expression reduced colony growth while promoting a motile phenotype in NMUR2-positive SKBR3 but not NMUR2-negative Hs578T cells. To uncover signaling pathways and key molecules affected by NMU in SKBR3 cells, Affymetrix microarray analysis was applied. Forced NMU expression affected molecules involved in WNT receptor signaling among others. As such we demonstrated enhanced activation of the WNT/planar cell polarity (PCP) effector RAC1 and down-regulation of canonical WNT targets such as MYC. In summary, NMU might contribute to progression of NMUR2-positive breast cancer representing a potential druggable target for future personalized strategies.

Neuromedin: An insight into its types, receptors and therapeutic opportunities

Neuropeptides are small protein used by neurons in signal communications. Neuromedin U was the first neuropeptide discovered from the porcine spinal and showed its potent constricting activities on uterus hence was entitled with neuromedin U. Following neuromedin U another of its isoform was discovered neuromedin S which was observed in suprachiasmatic nucleus hence was entitled neuromedin S. Neuromedin K and neuromedin L are of kanassin class which belong to tachykinin family. Bombesin family consists of neuromedin B and neuromedin C. All these different neuromedins have various physiological roles like constrictive effects on the smooth muscles, control of blood pressure, pain sensations, hunger, bone metastasis and release and regulation of hormones. Over the years various newer physiological roles have been observed thus opening ways for various novel therapeutic treatments. This review aims to provide an overview of important different types of neuromedin, their receptors, signal transduction mechanism and implications for various diseases.

Neuromedin U: a multifunctional neuropeptide with pleiotropic roles

BACKGROUND

Neuromedin U (NmU) belongs to the neuromedin family, comprising a series of neuropeptides involved in the gut-brain axis and including neuromedins B and C (bombesin-like), K (neurokinin B), L (neurokinin A or neurotensin), N, S, and U.

CONTENT

Although initially isolated from porcine spinal cord on the basis of their ability to induce uterine smooth muscle contraction, these peptides have now been found to be expressed in several different tissues and have been ascribed numerous functions, from appetite regulation and energy balance control to muscle contraction and tumor progression. NmU has been detected in several species to date, particularly in mammals (pig, rat, rabbit, dog, guinea pig, human), but also in amphibian, avian, and fish species. The NmU sequence is highly conserved across different species, indicating that this peptide is ancient and plays an important biological role. Here, we summarize the main structural and functional characteristics of NmU and describe its many roles, highlighting the jack-of-all-trades nature of this neuropeptide.

SUMMARY

NmU involvement in key processes has outlined the possibility that this neuropeptide could be a novel target for the treatment of obesity and cancer, among other disorders. Although the potential for NmU as a therapeutic target is obvious, the multiple functions of this molecule should be taken into account when designing an approach to targeting NmU and/or its receptors.

Two chicken neuromedin U receptors: characterization of primary structure, biological activity and tissue distribution

Neuromedin U (NMU) is a bioactive peptide that is involved in a variety of physiological functions. Two of its receptors, NMUR1 and NMUR2, have been identified and characterized in mammals. In this study, we performed cDNA cloning of chicken NMUR1 and NMUR2, and characterized their primary structure, biological activity, and expression patterns in chicken tissues. The chicken NMUR1 and NMUR2 cDNAs encoded 438 and 395 amino acid sequences, respectively. Chicken NMUR1 showed 54.8%-56.5% sequence identity with human, rat, and mouse NMUR1, and NMUR2 shared 67.3%-70.1% sequence identity with mammalian orthologs. Both chicken receptors have typical characteristics of G-protein-coupled receptors with seven transmembrane domains and the D/ERY motif. An increase in intracellular Ca(2+) mobilization was observed in HEK293 cells transfected with chicken NMUR1 or NMUR2 cDNA and treated with chicken or rat NMU. Real-time PCR analysis revealed that NMUR1 mRNA was preferentially expressed in the intestinal tissues such as the duodenum, jejunum, ileum, cecum, and colon/rectum, and brain regions such as the midbrain and optic lobe, and the ovary in adult hens. NMUR2 mRNA was exclusively expressed in the brain regions such as the cerebrum and midbrain. These results indicate that NMUR1 and NMUR2 mRNAs, which encode functional receptor proteins, are expressed in chicken tissues with different distribution patterns.

Neuromedin U: physiology, pharmacology and therapeutic potential

Neuromedin U (NmU), a multifunctional neuropeptide, belongs to a family of neuropeptides, the neuromedins. It is ubiquitously distributed with highest levels found in the gastrointestinal tract and pituitary. The conservation of structural elements of NmU across species, the widespread distribution of NmU and its receptors throughout the body point to a fundamental role in key physiological processes. Two G protein coupled receptors for NmU have been cloned NmU R1 and NmU R2. NmU R1 is expressed pre-dominantly in the periphery especially the gastrointestinal tract whereas NmU R2 is expressed pre-dominantly in the central nervous system. Current evidence suggests a role of NmU in pain, in regulation of feeding and energy homeostasis, stress, cancer, immune mediated inflammatory diseases like asthma, inflammatory diseases, maintaining the biological clock, in the regulation of smooth muscle contraction in the gastrointestinal and genitourinary tract, and in the control of blood flow and blood pressure. With the development of drugs selectively acting on receptors and knockout animal models, exact pathophysiological roles of NmU will become clearer.

Emerging pharmacology and physiology of neuromedin U and the structurally related peptide neuromedin S

Neuromedin U (NMU) has been paired with the G-protein-coupled receptors (GPRs) NMU(1) (formerly designated as the orphan GPR66 or FM-3) and NMU(2) (FM-4 or hTGR-1). Recently, a structurally related peptide, neuromedin S (NMS), which shares an amidated C-terminal heptapeptide motif, has been identified in both rat and human, and has been proposed as a second ligand for these receptors. Messenger RNA encoding NMU receptor subtypes shows differential expression: NMU(1) is predominantly expressed in peripheral tissues, particularly the gastrointestinal tract, whereas NMU(2) is abundant within the brain and spinal cord. NMU peptide parallels receptor distribution with highest expression in the gastrointestinal tract and specific structures within the brain, reflecting its major role in the regulation of energy balance. The NMU knockout mouse has an obese phenotype and, in agreement, the Arg165Trp amino acid variant of NMU-25 in humans, which is functionally inactive, co-segregated with childhood-onset obesity. Emerging physiological roles for NMU include vasoconstriction mediated predominantly via NMU(1) with nociception and bone remodelling via NMU(2). The NMU system has also been implicated in the pathogenesis of septic shock and cancers including bladder carcinoma and acute myeloid leukaemia. Intriguingly, NMS is more potent at NMU(2) receptors in vivo where it has similar central actions in suppression of feeding and regulation of circadian rhythms to NMU. Taken together with its vascular actions, NMU may be a functional link between energy balance and the cardiovascular system and may provide a future target for therapies directed against the disorders that comprise metabolic syndrome.

Expression and vasoconstrictor function of anorexigenic peptides neuromedin U-25 and S in the human cardiovascular system

AIMS

Neuromedin U-25 (NMU-25), a brain-gut peptide with anorexigenic actions, was paired with the G-protein-coupled receptors NMU1 and NMU2 in 2000. NMU-25 elicited a potent hypertensive effect in rats but little is known about its cardiovascular effects in humans. We examined the hypothesis that NMU fulfils the criteria for controlling vascular reactivity within the human cardiovascular system.

METHODS AND RESULTS

The radioligand [125I]-NMU-25 demonstrated specific, saturable, and high affinity (K(D) = 0.26 +/- 0.06 nM) binding in the human left ventricle and coronary artery, and quantitative reverse transcription-polymerase chain reaction revealed that mRNA encoding NMU1 predominated in these tissues. NMU-25-like immunoreactivity was detected in human plasma, left ventricle, coronary artery, saphenous vein, and epicardial adipose tissue, and both NMU-25 and a related peptide, neuromedin S (NMS), were identified by high-performance liquid chromatography in the left ventricle. NMU receptor and peptide were localized to endothelial cells, with the receptor also present on vascular smooth muscle cells. NMU-25 was a potent vasoconstrictor of isolated rings of human coronary and mammary artery and saphenous vein. Compared with NMU-25, NMS had a significantly reduced maximum response in saphenous vein, and the Arg165Trp variant of NMU-25, associated with childhood-onset obesity, was without effect. NMU-25 precursor mRNA was upregulated in the left ventricle from patients with dilated cardiomyopathy and ischaemic heart disease.

CONCLUSION

We have detected the expression of both NMU receptor and peptide in human cardiovascular tissues and have shown that NMU-25 and NMS act as potent vasoconstrictors in human vascular beds.

Distribution of neuromedin U binding sites in the rat CNS revealed by in vitro receptor autoradiography

Neuromedin U (NMU), a neuropeptide implicated in feeding, inflammation, pain control and anxiety-related behaviours, is widely distributed in peripheral organs and the CNS. These effects are thought to be mediated by its receptors NMU(1) and NMU(2). Since its precise sites of interaction in the CNS were to date unknown, we studied the distribution of in vitro binding sites for (125)I-NMU-23 in the rat CNS by receptor autoradiography. High-density specific binding was found in discrete areas of the brain and spinal cord, namely in the limbic system (hippocampal formation, septohippocampal nucleus, indusium griseum, hypothalamus, amygdaloid nuclei), superior colliculus, dorsal raphé, and substantia gelatinosa of the spinal cord. Our findings provide further supportive evidence for a multifunctional role for the peptide in the brain and spinal cord.

Paradoxical behavior of neuromedin U in isolated smooth muscle cells and intact tissue

Neuromedin U (NmU) is a neuropeptide showing high levels of structural conservation across different species. Since its discovery in 1985, NmU has been implicated in numerous physiological roles, including smooth muscle contraction, energy homeostasis, stress, intestinal ion transport, pronociception, and circadian rhythm. Two G-protein-coupled receptors have been identified for NmU and cloned from humans, rats, and mice. Recombinantly expressed NmU receptors couple to both Galpha(q/11) and Galpha(i) G-proteins, and NmU binds essentially irreversibly, preventing signaling to repetitive applications of NmU. However, it is unclear whether these properties reflect those of endogenously expressed NmU receptors or how these properties influence the functional consequences of NmU receptor signaling. Here, we have explored the signaling by rat NmU receptors expressed endogenously in cultured rat colonic smooth muscle cells and explore the functional consequence of this signaling by investigating the NmU-mediated contraction of ex vivo rat colonic smooth muscle preparations. We demonstrate that endogenous rat NmU receptors couple to both Galpha(q/11) and Galpha(i) G-proteins. Furthermore, we show complex patterns of Ca(2+) signaling, including oscillations, and provide evidence of essentially irreversible binding of NmU to smooth muscle cells. Challenge of either circular or longitudinal rat isolated colonic smooth muscle preparations with NmU resulted in robust contractions. Stimulation was direct, and paradoxically, repetitive applications of NmU mediated repetitive contractions with no evidence of desensitization, highlighting a major discrepancy in the behavior of NmU in single cells and in intact tissues. The reason for this discrepancy is presently unknown.