Métayé Thierry, Menet Emmanuelle, Guilhot Joëlle, Kraimps Jean-Louis
Biophysics Laboratory, Department of Pathology, Jean Bernard Hospital, BP 577, 86021 Poitiers Cedex, France.
J Clin Endocrinol Metab. 2002 Jul;87(7):3279-86. doi: 10.1210/jcem.87.7.8618.
Most of the TSH effects on the proliferation and differentiation of thyroid cells are mediated by cAMP via an adenylyl cyclase-activating Gs protein. TSH receptor responsiveness in cell cultures, is regulated by G protein-coupled receptor kinase (GRK) 2 and 5. To determine whether an alteration in activity and expression of GRKs might be associated with variable levels of TSH receptor desensitization in vivo, we studied human thyroid tissues including 21 normal tissues and 18 differentiated carcinomas. GRK activity was assayed by rhodopsin phosphorylation, and GRK protein and mRNA expressions assessed by immunoblotting and real-time quantitative RT-PCR, respectively. GRK2 and GRK5 were found as the predominant isoforms in the human thyroid. GRK5 protein expression was significantly decreased in differentiated thyroid carcinoma (P < 0.02) and paralleled a decrease in GRK mRNA expression (P < 0.02). In contrast, no difference in protein and mRNA levels of GRK2 were observed between normal and cancerous thyroid tissues. Although GRK2 protein levels correlated with GRK activities, we demonstrated a significant increase in GRK activity in differentiated thyroid carcinoma (P < 0.02). Less TSH receptor desensitization occurred in differentiated carcinoma than in normal thyroid tissue, as judged by TSH-stimulated cAMP response in human thyroid cells in primary culture. In conclusion, this study indicates that GRK2 activity and GRK5 expression have opposite regulations in cancer cells. Furthermore, the decrease in GRK5 expression may underlie the reduction in homologous desensitization of the TSH receptor in differentiated thyroid carcinoma, contributing to explain the increased cAMP levels in these tumors.
促甲状腺激素（TSH）对甲状腺细胞增殖和分化的大多数作用是通过腺苷酸环化酶激活的Gs蛋白经环磷酸腺苷（cAMP）介导的。细胞培养中的TSH受体反应性受G蛋白偶联受体激酶（GRK）2和5调节。为了确定GRKs活性和表达的改变是否可能与体内TSH受体脱敏的不同水平相关，我们研究了包括21个正常组织和18个分化癌的人类甲状腺组织。通过视紫红质磷酸化测定GRK活性，分别通过免疫印迹和实时定量逆转录聚合酶链反应评估GRK蛋白和mRNA表达。发现GRK2和GRK5是人类甲状腺中的主要亚型。GRK5蛋白表达在分化型甲状腺癌中显著降低（P<0.02），且与GRK mRNA表达的降低平行（P<0.02）。相比之下，正常和癌性甲状腺组织之间未观察到GRK2蛋白和mRNA水平的差异。虽然GRK2蛋白水平与GRK活性相关，但我们证明分化型甲状腺癌中GRK活性显著增加（P<0.02）。根据原代培养的人甲状腺细胞中TSH刺激的cAMP反应判断，分化癌中TSH受体脱敏比正常甲状腺组织少。总之，本研究表明GRK2活性和GRK5表达在癌细胞中有相反的调节。此外，GRK5表达的降低可能是分化型甲状腺癌中TSH受体同源脱敏减少的基础，有助于解释这些肿瘤中环磷酸腺苷水平的升高。
