Berry S A, Shah M C, Khan N, Roth B L
Department of Biochemistry Case Western Reserve University School of Medicine, Cleveland, Ohio 44106, USA.
Mol Pharmacol. 1996 Aug;50(2):306-13.
The mechanism by which agonists induce 5-hydroxytryptamine2A (5-HT2A) receptor internalization was investigated in a clonal cell line stably transfected with the 5-HT2A receptor cDNA. Confocal laser microscopy of immunolabeled 5-HT2A receptors in control (untreated) cells demonstrated that most of the immunoreactivity was associated with the cell surface. After quipazine administration, a significant increase in intracellular immunofluorescence was measured. Time course studies demonstrated rapid agonist-dependent internalization of 5-HT2A receptors, with significant internalization occurring as early as 5 min after agonist administration at 37 degrees. In GF-62 cells, agonist-induced internalization was blocked by preincubation with the 5-HT2A receptor antagonist ketanserin. Internalization was also temperature sensitive because agonist-induced internalization did not occur at 4 degrees. Dual-label experiments disclosed that 5-HT2A and transferrin receptors were internalized via the same endocytotic vesicles. These results suggest that 5-HT2A receptors and transferrin receptors are internalized via the endosomal pathway in GF-62 cells. Although 5-HT2A receptors were internalized, down-regulation, or loss of radioligand binding sites, did not occur. Our results demonstrate that agonists rapidly induce 5-HT2A receptor internalization via the endosomal pathway and that internalization can be dissociated from down-regulation.
在稳定转染了5-羟色胺2A（5-HT2A）受体cDNA的克隆细胞系中，研究了激动剂诱导5-HT2A受体内化的机制。对照（未处理）细胞中免疫标记的5-HT2A受体的共聚焦激光显微镜检查表明，大部分免疫反应性与细胞表面相关。给予喹哌嗪后，细胞内免疫荧光显著增加。时间进程研究表明，5-HT2A受体快速发生激动剂依赖性内化，在37℃给予激动剂后5分钟就出现显著内化。在GF-62细胞中，激动剂诱导的内化被5-HT2A受体拮抗剂酮色林预孵育所阻断。内化也对温度敏感，因为在4℃时激动剂诱导的内化不发生。双标记实验表明，5-HT2A和转铁蛋白受体通过相同的内吞小泡内化。这些结果表明，在GF-62细胞中，5-HT2A受体和转铁蛋白受体通过内体途径内化。尽管5-HT2A受体内化了，但放射性配体结合位点并未下调或丧失。我们的结果表明，激动剂通过内体途径快速诱导5-HT2A受体内化，并且内化可以与下调分离。
