Pasireotide and Octreotide Stimulate Distinct Patterns of sst2A Somatostatin Receptor Phosphorylation
Pasireotide and Octreotide Stimulate Distinct Patterns of sst2A Somatostatin Receptor Phosphorylation
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DOI：
10.1210/me.2009-0315
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发表时间：
2010-02-01
影响因子：
--
通讯作者：
Schulz, Stefan
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文献类型：
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作者：
Poell, Florian;Lehmann, Diana;Schulz, Stefan
帕瑞肽（SOM 230）目前正在临床评价中，作为奥曲肽的后继化合物，用于治疗肢端肥大症、库欣病和类癌肿瘤。奥曲肽主要通过sst（2A）生长抑素受体发挥作用，而帕瑞肽被设计为表现出奥曲肽样sst（2A）活性，并与其他生长抑素受体亚型结合增强。在本研究中，我们使用磷酸盐特异性抗体来检查激动剂诱导的大鼠sst（2A）受体磷酸化。我们表明，生长抑素和奥曲肽刺激细胞质（353）TTETQRT（359）基序内的一组四个苏氨酸残基的完全磷酸化，在各种培养的细胞系在体外，以及在完整的动物在体内。这种磷酸化是由G蛋白偶联受体激酶（GRK）2和3介导的，随后受体和β-抑制蛋白快速共内化到相同的内吞囊泡中。相比之下，帕瑞肽未能促进大鼠sst（2A）受体的实质性磷酸化和内化。在奥曲肽或SS-14的存在下，SOM 230显示部分激动剂行为，抑制磷酸化和sst的内化（2A）。在GRK 2或GRK 3过表达时，帕瑞肽刺激Thr 356和Thr 359的选择性磷酸化，但不刺激（353）TTETQRT（359）基序内的Thr 353或Thr 354。帕瑞肽介导的磷酸化导致相对不稳定的β-arrestin-sst（2A）复合物的形成，该复合物在质膜或质膜附近解离。因此，奥曲肽和帕瑞肽在通过sst（2A）生长抑素受体诱导经典的G蛋白依赖性信号传导中具有同等活性。然而，我们发现它们促进了显著不同的sst（2A）受体磷酸化模式，因此刺激了功能不同的β-抑制蛋白库。（分子内分泌学24：436-446，2010）
Pasireotide (SOM230) is currently under clinical evaluation as a successor compound to octreotide for the treatment of acromegaly, Cushing's disease, and carcinoid tumors. Whereas octreotide acts primarily via the sst(2A) somatostatin receptor, pasireotide was designed to exhibit octreotide-like sst(2A) activity combined with enhanced binding to other somatostatin receptor subtypes. In the present study, we used phophosite-specific antibodies to examine agonist-induced phosphorylation of the rat sst(2A) receptor. We show that somatostatin and octreotide stimulate the complete phosphorylation of a cluster of four threonine residues within the cytoplasmic (353)TTETQRT(359) motif in a variety of cultured cell lines in vitro as well as in intact animals in vivo. This phosphorylation was mediated by G protein-coupled receptor kinases (GRK) 2 and 3 and followed by rapid cointernalization of the receptor and beta-arrestin into the same endocytic vesicles. In contrast, pasireotide failed to promote substantial phosphorylation and internalization of the rat sst(2A) receptor. In the presence of octreotide or SS-14, SOM230 showed partial agonist behavior, inhibiting phosphorylation, and internalization of sst(2A). Upon overexpression of GRK2 or GRK3, pasireotide stimulated selective phosphorylation of Thr356 and Thr359 but not of Thr353 or Thr354 within the (353)TTETQRT(359) motif. Pasireotide-mediated phosphorylation led to the formation of relatively unstable beta-arrestin-sst(2A) complexes that dissociated at or near the plasma membrane. Thus, octreotide and pasireotide are equally active in inducing classical G protein-dependent signaling via the sst(2A) somatostatin receptor. Yet, we find that they promote strikingly different patterns of sst(2A) receptor phosphorylation and, hence, stimulate functionally distinct pools of beta-arrestin. (Molecular Endocrinology 24: 436-446, 2010)