Homburger V, Pantaloni C, Lucas M, Gozlan H, Bockaert J
J Cell Physiol. 1984 Dec;121(3):589-97. doi: 10.1002/jcp.1041210318.
C6 glioma cells possess beta adrenergic receptors coupled with adenylate cyclase which can be irreversibly blocked by bromoacetylaminomethylpindolol (Br-AAM-pindolol), a beta adrenergic antagonist. With 1 microM Br-AAM-pindolol, more than 80% of beta adrenergic receptors, labeled by (3H)-dihydroalprenolol [3H)-DHA), were blocked. After this blockade, new beta adrenergic receptors were synthesized only during cell division. However, at cell confluency when the cell number was constant, turnover of beta adrenergic receptors was barely detectable. Cycloheximide (1 microgram/ml) inhibited cell growth as well as reappearance of beta adrenergic receptors. A 90% loss of beta adrenergic receptors in C6 glioma cells was obtained after down-regulation for 15 h with 10 microM isoproterenol, a beta adrenergic agonist. After removal of the agonist, recovery of beta-adrenergic-sensitive adenylate cyclase was complete within 2 to 3 days, whereas beta adrenergic receptors reached 90% of control value within 6 days. The half-life of the receptor recovery was 2 to 3 days. Pretreatment of C6 glioma cells by Br-AAM-pindolol and subsequent cell exposure to isoproterenol indicated that down regulation and recovery of unblocked beta adrenergic receptors did occur; however isoproterenol did not accelerate the biosynthesis of beta adrenergic receptors. The recovery of both biological response and beta adrenergic receptor occupancy was restored both in the presence or absence of cycloheximide (1 microgram/ml), a concentration which blocked 90% of protein synthesis. Our results suggest that reappearance of beta adrenergic receptors in C6 glioma cells, following isoproterenol-induced down regulation, was not due to synthesis of new receptors but to recycling of the beta adrenergic receptors.
C6胶质瘤细胞具有与腺苷酸环化酶偶联的β肾上腺素能受体，该受体可被β肾上腺素能拮抗剂溴乙酰氨基甲基吲哚洛尔（Br-AAM-吲哚洛尔）不可逆地阻断。使用1微摩尔的Br-AAM-吲哚洛尔时，超过80%由（3H）-二氢烯丙洛尔[（3H）-DHA]标记的β肾上腺素能受体被阻断。在这种阻断之后，仅在细胞分裂期间合成新的β肾上腺素能受体。然而，在细胞汇合时细胞数量恒定，β肾上腺素能受体的周转几乎检测不到。放线菌酮（1微克/毫升）抑制细胞生长以及β肾上腺素能受体的重新出现。用10微摩尔的β肾上腺素能激动剂异丙肾上腺素下调15小时后，C6胶质瘤细胞中90%的β肾上腺素能受体丧失。去除激动剂后，β肾上腺素能敏感的腺苷酸环化酶在2至3天内完全恢复，而β肾上腺素能受体在6天内达到对照值的90%。受体恢复的半衰期为2至3天。用Br-AAM-吲哚洛尔预处理C6胶质瘤细胞，随后使细胞暴露于异丙肾上腺素，表明未被阻断的β肾上腺素能受体确实发生了下调和恢复；然而异丙肾上腺素并未加速β肾上腺素能受体的生物合成。无论是否存在放线菌酮（1微克/毫升），生物反应和β肾上腺素能受体占有率的恢复均得以恢复，该浓度可阻断90%的蛋白质合成。我们的结果表明，异丙肾上腺素诱导下调后，C6胶质瘤细胞中β肾上腺素能受体的重新出现不是由于新受体的合成，而是由于β肾上腺素能受体的再循环。
