Cassoni P, Papotti M, Catapano F, Ghè C, Deghenghi R, Ghigo E, Muccioli G
Department of Biomedical Sciences and Human Oncology, University of Turin, Turin, Italy.
J Endocrinol. 2000 Apr;165(1):139-46. doi: 10.1677/joe.0.1650139.
The presence of specific receptors for synthetic growth hormone secretagogues (GHSs) has been investigated in non-tumoral and neoplastic human thyroid tissue using a radio-iodinated peptidyl GHS ((125)I-labelled Tyr-Ala-hexarelin) as ligand. Specific binding sites for Tyr-Ala-hexarelin were detected in membranes from non-tumoral and follicular-derived neoplastic thyroid tissue, but not in thyroid tumours (medullary carcinomas) of parafollicular (C cell) origin. The binding activity was greatest in well differentiated neoplasms (papillary and follicular carcinomas), followed by poorly differentiated carcinomas, non-tumoral thyroid parenchyma, follicular adenomas and anaplastic carcinomas. Both peptidyl (Tyr-Ala-hexarelin, hexarelin, growth hormone releasing peptide (GHRP6) and non-peptidyl (MK 0677) GHSs completely displaced the radioligand from binding sites of non-tumoral thyroid gland, but MK 0677 was significantly less potent. The IC(50) values were (1. 9+/-0.3)x10(-8) mol/l for Tyr-Ala-hexarelin, (2.1+/-0.2)x10(-8) mol/l for hexarelin, (2.4+/- 0.3)x10(-8) mol/l for GHRP6 and only (1. 5+/-0.4)x 10(-7) mol/l for MK 0677. Similar IC(50) values were found in neoplastic thyroid tissue. Scatchard analysis of the binding revealed a finite number of binding sites in non-tumoral (B(max): 1232+/-32 fmol/mg protein, n=3) and neoplastic (papillary carcinomas) thyroid tissue (B(max): 2483+/-380 fmol/mg protein, n=5), with dissociation constants (K(d)) of (3.8+/-0.3)x10(-9) and (4. 4+/-0.6)x 10(-9) mol/l, respectively. On the basis of this evidence, we investigated the effects of some GHS on the proliferation of three different human follicular thyroid carcinoma cell lines (NPA, WRO and ARO) in which the presence of specific GHS receptors was also demonstrated. Tyr-Ala-hexarelin, GHRP6 and MK 0677 were able to inhibit serum-stimulated [(3)H]thymidine incorporation in NPA cells at concentrations close to their binding affinity. These substances also caused a significant inhibition of cell proliferation, which was evident at the earliest time of treatment (24 h) in all the cell lines, and at the latest time (96 h) in NPA cells only. In conclusion, this paper confirms the existence of specific binding sites for GHS in normal thyroid tissue and demonstrates, for the first time, that these binding sites are present in papillary and follicular carcinomas, low in anaplastic carcinomas and absent in medullary carcinomas of the thyroid. This work also provides evidence of a growth-inhibitory effect of GHS on cell lines derived from follicular thyroid cancers.
利用放射性碘化肽基生长激素促分泌素（(125)I标记的Tyr-Ala-六肽瑞林）作为配体，在非肿瘤性和肿瘤性人类甲状腺组织中研究了合成生长激素促分泌素（GHSs）特异性受体的存在情况。在非肿瘤性和滤泡源性肿瘤性甲状腺组织的膜中检测到了Tyr-Ala-六肽瑞林的特异性结合位点，但在滤泡旁（C细胞）起源的甲状腺肿瘤（髓样癌）中未检测到。结合活性在高分化肿瘤（乳头状癌和滤泡状癌）中最高，其次是低分化癌、非肿瘤性甲状腺实质、滤泡性腺瘤和未分化癌。肽基（Tyr-Ala-六肽瑞林、六肽瑞林、生长激素释放肽（GHRP6））和非肽基（MK 0677）GHSs均能使放射性配体从非肿瘤性甲状腺的结合位点上完全解离，但MK 0677的效力明显较低。Tyr-Ala-六肽瑞林的IC(50)值为(1.9±0.3)×10(-8)mol/L，六肽瑞林为(2.1±0.2)×10(-8)mol/L，GHRP6为(2.4±0.3)×10(-8)mol/L，而MK 0677仅为(1.5±0.4)×10(-7)mol/L。在肿瘤性甲状腺组织中也发现了类似的IC(50)值。对结合情况的Scatchard分析显示，非肿瘤性（B(max)：1232±32 fmol/mg蛋白，n = 3）和肿瘤性（乳头状癌）甲状腺组织（B(max)：2483±380 fmol/mg蛋白，n = 5）中存在有限数量的结合位点，解离常数（K(d)）分别为(3.8±0.3)×10(-9)和(4.4±0.6)×10(-9)mol/L。基于这些证据，我们研究了一些GHS对三种不同的人类滤泡性甲状腺癌细胞系（NPA、WRO和ARO）增殖的影响，这些细胞系中也证实存在特异性GHS受体。Tyr-Ala-六肽瑞林、GHRP6和MK 0677在接近其结合亲和力的浓度下能够抑制NPA细胞中血清刺激的[(3)H]胸腺嘧啶核苷掺入。这些物质也显著抑制细胞增殖，在所有细胞系中最早在处理后24小时就很明显，而在NPA细胞中最晚在96小时才明显。总之，本文证实了正常甲状腺组织中存在GHS的特异性结合位点，并首次证明这些结合位点存在于乳头状癌和滤泡状癌中，在未分化癌中含量较低，在甲状腺髓样癌中不存在。这项工作还提供了GHS对滤泡性甲状腺癌细胞系具有生长抑制作用的证据。
