Lubrano-Berthelier Cecile, Cavazos Martha, Dubern Beatrice, Shapiro Astrid, Stunff Catherine L E, Zhang Sumei, Picart Franck, Govaerts Cedric, Froguel Philippe, Bougneres Pierre, Clement Karine, Vaisse Christian
Department of Medicine, University of California, San Francisco, California 94143, USA.
Ann N Y Acad Sci. 2003 Jun;994:49-57. doi: 10.1111/j.1749-6632.2003.tb03161.x.
Heterozygous coding mutations in the melanocortin 4 receptor (MC4R) are implicated in 1 to 6% of early onset or severe adult obesity cases. To better address the problem of the genotype:phenotype relationship within this specific form of obesity, we systematically studied the functional characteristics of 50 different obesity-associated MC4R mutations. Structure modeling of MC4R indicates that obesity-associated MC4R mutations are not localized in a single domain of the protein. We developed a flow cytometry-based assay to compare cell membrane expression of obesity-associated MC4R mutants. Using this assay, we demonstrate that over 54% of the obesity-associated MC4R mutations impair the membrane expression of MC4R. All other mutations impair the basal constitutive activity and/or the EC(50) for the physiological agonist alpha-MSH as measured in a cAMP- dependent luciferase assay. The extent of the alterations in receptor activity ranges from a total suppression of MC4R activation in response to alpha-MSH to a mild alteration of the basal constitutive activity of the receptor. Since most patients are heterozygous for MC4R mutations, these data indicate that a small decrease in overall MC4R activity can cause obesity, strongly supporting the hypothesis that the MC4R is a critical component of the adipostat in humans.
黑皮质素4受体（MC4R）的杂合编码突变与1%至6%的早发性或严重成人肥胖病例有关。为了更好地解决这种特定形式肥胖中基因型与表型关系的问题，我们系统地研究了50种不同的与肥胖相关的MC4R突变的功能特性。MC4R的结构建模表明，与肥胖相关的MC4R突变并不局限于该蛋白质的单个结构域。我们开发了一种基于流式细胞术的检测方法，以比较与肥胖相关的MC4R突变体的细胞膜表达。使用该检测方法，我们证明超过54%的与肥胖相关的MC4R突变会损害MC4R的膜表达。所有其他突变会损害基础组成性活性和/或在依赖cAMP的荧光素酶检测中测得的生理激动剂α-MSH的EC(50)。受体活性改变的程度范围从对α-MSH反应的MC4R激活的完全抑制到受体基础组成性活性的轻度改变。由于大多数患者是MC4R突变的杂合子，这些数据表明MC4R总体活性的小幅下降会导致肥胖，有力地支持了MC4R是人类脂肪稳态关键组成部分的假设。
