The thyroid-stimulating hormone receptor (TSHR) is a heterotrimeric guanine nucleotide–binding protein (G protein)–coupled receptor (GPCR). Autoimmune hyperthyroidism, commonly known as Graves’ disease (GD), is caused by stimulating autoantibodies to the TSHR. We previously described TSHR-specific antibodies (TSHR-Abs) in GD that recognize linear epitopes in the cleavage region of the TSHR ectodomain (C-TSHR-Abs) and induce thyroid cell apoptosis instead of stimulating the TSHR. We found that C-TSHR-Abs entered the cell through clathrin-mediated endocytosis but did not trigger endosomal maturation and failed to undergo normal vesicular sorting and trafficking. We found that stimulating TSHR-Abs (S-TSHR-Abs) activated Gα_s and, to a lesser extent, Gα_q but that C-TSHR-Abs failed to activate any of the G proteins normally activated in response to TSH. Furthermore, specific inhibition of G proteins in the presence of S-TSHR-mAbs or TSH resulted in a similar failure of endosomal maturation as that caused by C-TSHR-mAbs. Hence, whereas S-TSHR-mAbs and TSH contributed to normal vesicular trafficking of TSHR through the activation of major G proteins, the C-TSHR-Abs resulted in GRK2- and β-arrestin-1–dependent biased signaling, which is interpreted as a danger signal by the cell. Our observations suggest that the binding of antibodies to different TSHR epitopes may decrease cell survival. Antibody-induced cell injury and the response to cell death amplify the loss of self-tolerance, which most likely helps to perpetuate GPCR-mediated autoimmunity.

促甲状腺激素受体（TSHR）是异三聚体鸟嘌呤核苷酸结合蛋白（G蛋白）偶联受体（GPCR）。自身免疫性甲状腺功能亢进症，通常称为Graves病（GD），是由刺激TSHR的自身抗体引起的。我们先前在GD中描述了TSHR特异性抗体（TSHR-Abs），该抗体识别TSHR胞外域（C-TSHR-Abs）裂解区域中的线性表位，并诱导甲状腺细胞凋亡而不是刺激TSHR。我们发现C-TSHR-Abs通过网格蛋白介导的内吞作用进入细胞，但未触发内体成熟，并且未进行正常的囊泡分选和运输。我们发现，刺激TSHR-ABS（S-TSHR-ABS）活化Gα_小号和，在较小程度上，Gα _q但是C-TSHR-Abs未能激活任何正常响应TSH激活的G蛋白。此外，在S-TSHR-mAbs或TSH存在下对G蛋白的特异性抑制导致内体成熟的失败与C-TSHR-mAbs引起的相似。因此，尽管S-TSHR-mAbs和TSH通过激活主要G蛋白促进了正常TSHR的囊泡运输，但C-TSHR-Abs导致了GRK2和β-arrestin-1依赖性偏向信号传导，这被解释为牢房发出危险信号。我们的观察结果表明抗体与不同TSHR表位的结合可能会降低细胞存活率。抗体诱导的细胞损伤和对细胞死亡的反应会加剧自我耐受性的丧失，这很可能有助于使GPCR介导的自身免疫永存。