Cassoni P, Papotti M, Ghè C, Catapano F, Sapino A, Graziani A, Deghenghi R, Reissmann T, Ghigo E, Muccioli G
Department of Biomedical Sciences and Oncology, University of Turin, 10126 Turin, Italy.
J Clin Endocrinol Metab. 2001 Apr;86(4):1738-45. doi: 10.1210/jcem.86.4.7402.
The family of GH secretagogues (GHS) includes synthetic peptidyl (hexarelin) and nonpeptidyl (MK-0677) molecules possessing specific receptors in the pituitary and central nervous system as well as in peripheral tissues, including the heart and some endocrine organs. A gastric-derived peptide, named ghrelin, has recently been proposed as the natural ligand of the GHS receptors (GHS-Rs). The presence of specific GHS-Rs has now been investigated in nontumoral and neoplastic human breast tissue using a radioiodinated peptidyl GHS ([(125)I]-Tyr-Ala-hexarelin) as ligand. Specific binding sites for GHS were detected in membranes from several types of breast carcinomas, whereas a negligible binding was found in fibroadenomas and mammary parenchyma. The highest binding activity was found in well-differentiated (G1) invasive breast carcinomas and was progressively reduced in moderately (G2) to poorly (G3) differentiated tumors. [(125)I]-Tyr-Ala-hexarelin bound to tumor membranes was displaced by different unlabeled GHS such as hexarelin, Tyr-Ala-hexarelin, human ghrelin, and MK-0677 as well as by desoctanoyl-ghrelin and hexarelin derivative EP-80317, which are devoid of GH-releasing properties in vivo. In contrast, no competition was seen between radiolabeled Tyr-Ala-hexarelin and some peptides (CRF and insulin-like growth factor I) structurally and functionally unrelated to hexarelin or when GHRH and SRIF were tested in the displacement studies. The presence of specific GHS binding sites was also demonstrated in three different human breast carcinoma cell lines (MCF7, T47D, and MDA-MB231), in which, surprisingly, no messenger RNA for GHS-R1a was demonstrated by RT-PCR. In these cell lines, ghrelin (as well as hexarelin, MK-0677, EP-80317, and even desoctanoyl ghrelin) caused a significant inhibition of cell proliferation at concentrations close to their binding affinity. In conclusion, this study provides the first demonstration of specific GHS binding sites, other than GHS-R1, in breast cancer. These receptors probably mediate growth inhibitory effects on breast carcinoma cells in vitro.
生长激素促分泌素（GHS）家族包括在垂体、中枢神经系统以及外周组织（包括心脏和一些内分泌器官）中具有特定受体的合成肽基（六肽生长激素释放肽）和非肽基（MK-0677）分子。一种源自胃的肽，即ghrelin，最近被认为是GHS受体（GHS-Rs）的天然配体。现在，使用放射性碘化肽基GHS（[(125)I]-酪氨酸-丙氨酸-六肽生长激素释放肽）作为配体，对非肿瘤性和肿瘤性人类乳腺组织中的特异性GHS-Rs进行了研究。在几种类型的乳腺癌细胞膜中检测到了GHS的特异性结合位点，而在纤维腺瘤和乳腺实质中发现的结合可以忽略不计。在高分化（G1）浸润性乳腺癌中发现了最高的结合活性，在中分化（G2）至低分化（G3）肿瘤中逐渐降低。与肿瘤细胞膜结合的[(125)I]-酪氨酸-丙氨酸-六肽生长激素释放肽可被不同的未标记GHS取代，如六肽生长激素释放肽、酪氨酸-丙氨酸-六肽生长激素释放肽、人ghrelin和MK-0677，以及去辛酰基ghrelin和六肽生长激素释放肽衍生物EP-80317，这些在体内均不具有生长激素释放特性。相反，在置换研究中测试促肾上腺皮质激素释放因子（CRF）和胰岛素样生长因子I等与六肽生长激素释放肽在结构和功能上无关的一些肽，或生长激素释放激素（GHRH）和生长抑素（SRIF）时，未观察到放射性标记的酪氨酸-丙氨酸-六肽生长激素释放肽之间的竞争。在三种不同的人乳腺癌细胞系（MCF7、T47D和MDA-MB231）中也证实了特异性GHS结合位点的存在，令人惊讶的是，通过逆转录聚合酶链反应（RT-PCR）未检测到GHS-R1a的信使核糖核酸（mRNA）。在这些细胞系中，ghrelin（以及六肽生长激素释放肽、MK-0677、EP-80317，甚至去辛酰基ghrelin）在接近其结合亲和力的浓度下可显著抑制细胞增殖。总之，本研究首次证明了乳腺癌中除GHS-R1外的特异性GHS结合位点。这些受体可能在体外介导对乳腺癌细胞的生长抑制作用。
