Tang H, Shirai H, Inagami T
Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, TN 37232, USA.
Circ Res. 1995 Aug;77(2):239-48. doi: 10.1161/01.res.77.2.239.
The type 1B angiotensin II (AT1B) receptor cloned from rat kidney was stably expressed in Chinese hamster ovary cells. The stably expressed receptor was characterized by radioligand binding studies and functional coupling to inositol 1,4,5-triphosphate (IP3) formation. Exposure of cells expressing the AT1B receptor to angiotensin II (Ang II) resulted in a rapid and dose-dependent homologous desensitization of receptor-mediated production of IP3, with an essentially complete desensitization at an agonist concentration > 10 nmol/L. Binding studies revealed no significant change in the number of AT1B receptors in transfected cells exposed to 1 nmol/L Ang II, whereas exposure to 100 nmol/L Ang II caused a rapid decrease of cell surface receptors, with a 75% loss of receptor number seen at 1 hour. Rapid desensitization occurred in the absence of receptor internalization. Blockade of receptor internalization with concanavalin A had at most only a slight effect on the agonist-induced desensitization. This indicates that factors other than internalization are chiefly responsible for the rapid agonist-induced desensitization. Phorbol 12-myristate 13-acetate (PMA), a protein kinase C (PKC) activator, caused rapid desensitization of the receptor-mediated IP3 response. Neither tyrosine kinase inhibitors nor a protein kinase A activator affected the receptor-mediated IP3 response. The specific PKC inhibitor GF109203X or PKC depletion by prolonged treatment with 1 mumol/L PMA completely blocked the PMA-dependent desensitization. Desensitization evoked by a low Ang II agonist concentration (1 nmol/L) was reversed by the PKC-specific inhibitor GF109203X or PKC depletion, whereas the desensitizing effect at a high agonist concentration (100 nmol/L) is only partially prevented by PKC inhibitory treatment. These results demonstrate that PKC plays a crucial role in the desensitization of the AT1B receptor. They also suggest that receptor internalization and an additional PKC-independent pathway also contribute to desensitization of the AT1B receptor in transfected cells.
从大鼠肾脏克隆的1B型血管紧张素II（AT1B）受体在中国仓鼠卵巢细胞中稳定表达。通过放射性配体结合研究以及与肌醇1,4,5 - 三磷酸（IP3）生成的功能偶联对稳定表达的受体进行了表征。将表达AT1B受体的细胞暴露于血管紧张素II（Ang II）会导致受体介导的IP3产生迅速且剂量依赖性的同源脱敏，在激动剂浓度> 10 nmol/L时基本完全脱敏。结合研究表明，暴露于1 nmol/L Ang II的转染细胞中AT1B受体数量无显著变化，而暴露于100 nmol/L Ang II会导致细胞表面受体迅速减少，1小时时受体数量减少75%。在没有受体内化的情况下发生了快速脱敏。用伴刀豆球蛋白A阻断受体内化对激动剂诱导的脱敏最多只有轻微影响。这表明除内化之外的因素主要负责激动剂诱导的快速脱敏。佛波醇12 - 肉豆蔻酸酯13 - 乙酸酯（PMA），一种蛋白激酶C（PKC）激活剂，导致受体介导的IP3反应迅速脱敏。酪氨酸激酶抑制剂和蛋白激酶A激活剂均不影响受体介导的IP3反应。特异性PKC抑制剂GF109203X或用1 μmol/L PMA长时间处理使PKC耗竭可完全阻断PMA依赖性脱敏。低浓度Ang II激动剂（1 nmol/L）引起的脱敏可被PKC特异性抑制剂GF109203X或PKC耗竭逆转，而高激动剂浓度（100 nmol/L）时的脱敏作用仅部分被PKC抑制处理所阻止。这些结果表明PKC在AT1B受体脱敏中起关键作用。它们还表明受体内化和另一条不依赖PKC的途径也有助于转染细胞中AT1B受体的脱敏。
