Latif Rauf, Mezei Mihaly, Davies Terry F
Department of Medicine, Thyroid Research Unit, Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA.
James J. Peters VA Medical Center, New York, NY 10468, USA.
Endocrinology. 2025 Jan 6;166(2). doi: 10.1210/endocr/bqaf009.
The pathogenesis of thyroid eye disease (TED) has been suggested as due to signal enhancement in orbital fibroblasts as a result of autoantibody-induced, synergistic interaction between the TSH receptor (TSHR) and the IGF-1 receptor (IGF-1R). This interaction has been explained by a "receptor cross-talk," mediated via β-arrestin binding. Here we have examined if this interaction can be mediated via direct receptor contact using modeling and experimental approaches. First, we docked a model of the leucine-rich domain of the TSHR ectodomain (ECD) to an available cryo-electron microscopy-based structure of the active-state IGF-1R dimer and demonstrated the stability of the complex using molecular dynamics simulations. We then extended the complex with the full-length TSHR and the transmembrane helices of the IGF1R and a 3000 ns simulation also showed stability of this complex. We then performed coimmunoprecipitation studies with anti-TSHR and anti-IGF-1R antibodies using cells expressing the IGF-1R and the full-length TSHR and also cells that expressed the IGF-1R and only the TSHR-ECD and, therefore, unable to bind β-arrestin. These studies showed a 360 kD complex protein in the immunoprecipitation, which was present in both the full-length TSHR and the TSHR-ECD-only expressing cells, evidencing a direct interaction of receptors via their ectodomains in the absence of arrestin. Colocalized staining of TSHR and IGF-1R in the TSHR-ECD cells further supported this direct interaction. These data showed that the TSHR and IGF-1R can interact directly and in the absence of β-arrestin binding. Understanding these interactions is important in the pathogenesis of TED and its therapeutic intervention.
甲状腺眼病（TED）的发病机制被认为是由于自身抗体诱导的促甲状腺激素受体（TSHR）和胰岛素样生长因子-1受体（IGF-1R）之间的协同相互作用，导致眼眶成纤维细胞中的信号增强。这种相互作用已通过由β-抑制蛋白结合介导的“受体串扰”来解释。在这里，我们使用建模和实验方法研究了这种相互作用是否可以通过直接受体接触来介导。首先，我们将TSHR胞外域（ECD）富含亮氨酸结构域的模型对接至基于低温电子显微镜的活性状态IGF-1R二聚体的可用结构，并使用分子动力学模拟证明了该复合物的稳定性。然后，我们用全长TSHR、IGF1R的跨膜螺旋扩展了该复合物，3000 ns的模拟也显示了该复合物的稳定性。然后，我们使用表达IGF-1R和全长TSHR的细胞，以及表达IGF-1R且仅表达TSHR-ECD（因此无法结合β-抑制蛋白）的细胞，用抗TSHR和抗IGF-1R抗体进行了免疫共沉淀研究。这些研究在免疫沉淀中显示出一种360 kD的复合蛋白，其存在于全长TSHR和仅表达TSHR-ECD的细胞中，证明了在没有抑制蛋白的情况下受体通过其胞外域的直接相互作用。TSHR-ECD细胞中TSHR和IGF-1R的共定位染色进一步支持了这种直接相互作用。这些数据表明，TSHR和IGF-1R可以直接相互作用，且无需β-抑制蛋白结合。了解这些相互作用对于TED的发病机制及其治疗干预很重要。
