Hintermann E, Tanner H, Talke-Messerer C, Schlumberger S, Zumsteg U, Eberle A N
Laboratory of Endocrinology, Department of Research (ZLF), University Hospital and University Children's Hospital, CH-4031 Basel, Switzerland.
J Recept Signal Transduct Res. 2001 Feb;21(1):93-116. doi: 10.1081/rrs-100107145.
Melanin-concentrating hormone (MCH) and alpha-melanocyte-stimulating hormone (alpha-MSH) are known to exhibit mostly functionally antagonistic, but in some cases agonistic activities, e.g., in pigment cells and in the brain. Neuropeptide E-I (NEI) displays functional MCH-antagonist and MSH-agonist activity in different behavioral paradigms; the role of neuropeptide G-E (NGE) is not known. This study addressed the question of possible molecular interactions between alpha-MSH, MCH and the MCH-precursor-derived peptides NEI and NGE at the level of the pigment cell MCH receptor subtype (MCH-Rpc) and the different melanocortin (MC) receptors. Radioreceptor assays using [125I]MCH, [125l]alpha-MSH and [125I]NEI as radioligands and bioassays were performed with MCI-R-positive and MC1-R-negative mouse B16 melanoma cells and with COS cells expressing the different MC receptors. The IC50s of alpha-MSH and NEI or NGE for [125I]MCH displacement from mouse MCH-Rpc were 80-fold and, respectively, >300-fold higher than that of MCH, and the IC50s for MCH and NEI or NGE for [125I]alpha-MSH displacement from mouse MC1-R were 50,000-fold and >200,000-fold higher than that of alpha-MSH. No high-affinity binding sites for NEI were detected on B16 melanoma cells and there was no significant displacement of [1251]alpha-MSH by MCH, NEI or NGE with MC3-R, MC4-R and MC5-R expressed in COS cells. At concentrations of 100 nM to 10 microM, however, MCH, NEI and NGE induced cAMP formation and melanin synthesis which could be blocked by agouti protein or inhibitors of adenylate cyclase or protein kinase A. This shows that mammalian MCH-precursor-derived peptides may mimic MSH signalling via MC1-R activation at relatively high, but physiologically still relevant concentrations, as e.g. found in autocrine/paracrine signalling mechanisms.
已知黑色素浓缩激素（MCH）和α-促黑素细胞激素（α-MSH）大多表现出功能拮抗作用，但在某些情况下也有激动活性，例如在色素细胞和大脑中。神经肽E-I（NEI）在不同行为范式中表现出功能性MCH拮抗和MSH激动活性；神经肽G-E（NGE）的作用尚不清楚。本研究探讨了α-MSH、MCH以及MCH前体衍生肽NEI和NGE在色素细胞MCH受体亚型（MCH-Rpc）和不同黑素皮质素（MC）受体水平上可能的分子相互作用。使用[125I]MCH、[125I]α-MSH和[125I]NEI作为放射性配体进行放射受体分析，并对MCI-R阳性和MC1-R阴性小鼠B16黑色素瘤细胞以及表达不同MC受体的COS细胞进行生物测定。α-MSH和NEI或NGE从小鼠MCH-Rpc置换[125I]MCH的IC50分别比MCH高80倍和>300倍，MCH和NEI或NGE从小鼠MC1-R置换[125I]α-MSH的IC50分别比α-MSH高50,000倍和>200,000倍。在B16黑色素瘤细胞上未检测到NEI的高亲和力结合位点，在COS细胞中表达的MC3-R、MC4-R和MC5-R上，MCH、NEI或NGE对[125I]α-MSH没有明显的置换作用。然而，在100 nM至10 μM的浓度下，MCH、NEI和NGE诱导cAMP形成和黑色素合成，这可被刺鼠蛋白或腺苷酸环化酶或蛋白激酶A抑制剂阻断。这表明哺乳动物MCH前体衍生肽可能在相对较高但在生理上仍相关的浓度下，例如在自分泌/旁分泌信号机制中发现的浓度，通过MC1-R激活模拟MSH信号传导。
