Jaken S, Feldman H, Blumberg P M, Tashjian A H
Cancer Res. 1983 Dec;43(12 Pt 1):5795-800.
Sustained exposure of GH4C1 rat pituitary cells to phorbol esters or the hypothalamic tripeptide thyrotropin-releasing hormone decreases the number of phorbol ester binding sites without changing affinity (down modulation; Jaken, S., Tashjian, A. H., Jr., and Blumberg, P. M. Cancer Res., 41: 2175-2181, 1981). In untreated control cultures, the concentration of receptors in lysates was not significantly different from the concentration in intact cells. In contrast, in down-modulated cultures, the concentration of receptors in lysates was greater than the concentration in the corresponding intact cells and instead was equal to the concentration in lysates of control cultures. Therefore, the processes of both homologous (phorbol ester-induced) and heterologous (thyrotropin-releasing hormone-induced) phorbol ester receptor down modulation involves the generation of a cryptic receptor state that is revealed upon cell lysis. Furthermore, comparison of receptor properties in cells and lysates revealed that the affinity of the receptor for phorbol dibutyrate was decreased from a Kd of 11.1 +/- 0.6 nM (S.D.) in intact cells to 40 +/- 10 nM in cell lysates. Binding of the receptor for the structurally related diterpene, mezerein, fit a one-component model in intact cells, but was better fit to a two-component model in cell lysates. That is, the apparently homogeneous phorbol 12,13-dibutyrate receptor population in cell lysates appeared heterologous with respect to mezerein binding. This is not due to a preferential recovery of a subset of receptors in the lysates, because no substantial loss of receptor number was associated with cell lysis. Instead, these results suggest that the affinity and ligand specificity of the phorbol ester receptor may depend on its cellular environment.
将GH4C1大鼠垂体细胞持续暴露于佛波酯或下丘脑三肽促甲状腺激素释放激素会减少佛波酯结合位点的数量，而不改变亲和力（下调；杰克恩，S.，塔什吉安，A.H.，Jr.，和布卢姆伯格，P.M.《癌症研究》，41: 2175 - 2181，1981）。在未处理的对照培养物中，裂解物中受体的浓度与完整细胞中的浓度无显著差异。相反，在下调的培养物中，裂解物中受体的浓度大于相应完整细胞中的浓度，而是与对照培养物裂解物中的浓度相等。因此，同源（佛波酯诱导）和异源（促甲状腺激素释放激素诱导）佛波酯受体下调过程都涉及一种隐匿受体状态的产生，这种状态在细胞裂解时被揭示出来。此外，对细胞和裂解物中受体特性的比较表明，受体对佛波二丁酸酯的亲和力从完整细胞中的解离常数Kd为11.1±0.6 nM（标准差）降至细胞裂解物中的40±10 nM。受体与结构相关的二萜米泽瑞因的结合在完整细胞中符合单一组分模型，但在细胞裂解物中更符合双组分模型。也就是说，细胞裂解物中明显均匀的佛波12,13 - 二丁酸酯受体群体在米泽瑞因结合方面表现为异源。这不是由于裂解物中一部分受体的优先回收，因为细胞裂解并未导致受体数量的大量损失。相反，这些结果表明佛波酯受体的亲和力和配体特异性可能取决于其细胞环境。
