Inefficient maturation of the rat luteinizing hormone receptor -: A putative way to regulate receptor numbers at the cell surface
Inefficient maturation of the rat luteinizing hormone receptor -: A putative way to regulate receptor numbers at the cell surface
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DOI：
10.1074/jbc.m413815200
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发表时间：
2005-07-15
影响因子：
4.8
通讯作者：
Petäjä-Repo, UE
中科院分区：
文献类型：
--
作者：
Pietila, EM;Tuusa, JT;Petäjä-Repo, UE
越来越多的证据表明，折叠和成熟的单体蛋白质和装配的多聚体蛋白质复合物在内质网（ER）可能是低效的，不仅是突变体，携带的一级结构的变化，而且野生型蛋白质。在本研究中，我们证明，大鼠促黄体激素受体，G蛋白偶联受体，是这些蛋白质的成熟效率低下，似乎是非常容易过早降解。在稳定转染的人胚肾293细胞中，相当一部分受体以M-r 73，000的未成熟形式存在，含有高甘露糖型N-连接聚糖。在代谢脉冲追踪研究中，发现这些受体前体中只有约20%获得激素结合能力，并成熟为Mr 90，000的形式，含有双触角和多触角唾液酸化N-连接聚糖。其余的倾向于与ER膜中的Mr 120，000蛋白形成二硫键结合的复合物，并最终在蛋白酶体中降解。当蛋白酶体降解被抑制时，膜结合受体前体的数量增加，并且没有检测到胞质受体形式，这表明错误折叠/不完全折叠的受体的逆易位与蛋白酶体功能紧密耦合。此外，发现蛋白酶体阻断增加能够与激素结合的受体的数量。因此，这些结果提出了一个有趣的可能性，即促黄体激素受体在细胞表面的表达可以通过调节新合成的蛋白质的数量来控制在ER水平，这些蛋白质将成熟并逃避ER质量控制和过早降解。
Increasing evidence suggests that the folding and maturation of monomeric proteins and assembly of multimeric protein complexes in the endoplasmic reticulum ( ER) may be inefficient not only for mutants that carry changes in the primary structure but also for wild type proteins. In the present study, we demonstrate that the rat luteinizing hormone receptor, a G protein-coupled receptor, is one of these proteins that matures inefficiently and appears to be very prone to premature degradation. A substantial portion of the receptors in stably transfected human embryonic kidney 293 cells existed in immature form of M-r 73,000, containing high man-nose-type N-linked glycans. In metabolic pulse-chase studies, only similar to 20% of these receptor precursors were found to gain hormone binding ability and matured to a form of Mr 90,000, containing bi- and multiantennary sialylated N-linked glycans. The rest had a propensity to form disulfide-bonded complexes with a Mr 120,000 protein in the ER membrane and were eventually targeted for degradation in proteasomes. The number of membrane-bound receptor precursors increased when proteasomal degradation was inhibited, and no cytosolic receptor forms were detected, suggesting that retro-translocation of the misfolded/incompletely folded receptors is tightly coupled to proteasomal function. Furthermore, a proteasomal blockade was found to increase the number of receptors that were capable of hormone binding. Thus, these results raise the interesting possibility that luteinizing hormone receptor expression at the cell surface may be controlled at the ER level by regulating the number of newly synthesized proteins that will mature and escape the ER quality control and premature degradation.