Coordinated regulation of Rap1 and thyroid differentiation by cyclic AMP and protein kinase A.
Coordinated regulation of Rap1 and thyroid differentiation by cyclic AMP and protein kinase A.
复制标题
环 AMP 和蛋白激酶 A 协调调节 Rap1 和甲状腺分化。
DOI：
10.1128/mcb.21.6.1921-1929.2001
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发表时间：
2001
影响因子：
5.3
通讯作者：
Meinkoth,JL
中科院分区：
文献类型：
--
作者：
Tsygankova,OM;Saavedra,A;Rebhun,JF;Quilliam,LA;Meinkoth,JL
Rap1 最初被确定为 Ras 作用的拮抗剂，表现出许多与 Ras 无关的作用，包括在环 AMP (cAMP) 启动的信号通路中发挥作用。由于 cAMP 是促甲状腺素 (TSH) 对细胞增殖和分化影响的关键介质，因此我们在连续的大鼠甲状腺样细胞系中检测了 TSH 对 Rap1 的调节。 cAMP 和蛋白激酶 A (PKA) 都有助于调节 Rap1 活性和 TSH 信号传导。 TSH 通过 cAMP 介导且不依赖于 PKA 的机制激活 Rap1。 TSH 以 PKA 依赖性方式磷酸化 Rap1。干扰 PKA 活性会阻断磷酸化，但不会阻断 Rap1 的激活。相反，PKA 抑制剂延长了 Rap1 的激活时间，缺乏 PKA 磷酸化位点的 Rap1A 突变体的表达也是如此。这些结果表明 PKA 对某些细胞中 cAMP 刺激的 Rap1 活性引起负反馈调节。 cAMP 和 PKA 对 Rap1 的双重调节延伸至下游效应器。 TSH 刺激 Akt 磷酸化的能力因激活的 Rap1A 的表达而显着增强，并且在表达假定的显性失活 Rap1A 突变体的细胞中受到抑制。尽管激活的 Rap1A 的表达足以刺激渥曼青霉素敏感的 Akt 磷酸化，但 TSH 以磷脂酰肌醇 3 激酶和 PKA 依赖性方式进一步增加 Akt 磷酸化。在表达 Rap1A 突变体的细胞中，TSH 磷酸化 Akt 的能力受损，该突变体可以被激活但不能磷酸化。这些发现表明，Rap1 激活和磷酸化双重信号有助于 TSH 刺激的 Akt 磷酸化。 Rap1 在 cAMP 调节的分化中发挥重要作用。 TSH 对甲状腺特异性基因表达的影响，但对增殖的影响，在表达活化 Rap1A 的细胞中显着增强，而在表达显性失活 Rap1A 突变体的细胞中则受到抑制。这些发现揭示了 cAMP 对 Rap1 的复杂调节，包括 PKA 独立激活和 PKA 依赖性负反馈调节。这两个信号似乎都是 TSH 向 Akt 发出信号所必需的。
Originally identified as an antagonist of Ras action, Rap1 exhibits many Ras-independent effects, including a role in signaling pathways initiated by cyclic AMP (cAMP). Since cAMP is a critical mediator of the effects of thyrotropin (TSH) on cell proliferation and differentiation, we examined the regulation of Rap1 by TSH in a continuous line of rat thyroid-like cells. Both cAMP and protein kinase A (PKA) contribute to the regulation of Rap1 activity and signaling by TSH. TSH activates Rap1 through a cAMP-mediated and PKA-independent mechanism. TSH phosphorylates Rap1 in a PKA-dependent manner. Interference with PKA activity blocked phosphorylation but not the activation of Rap1. Rather, PKA inhibitors prolonged Rap1 activation, as did expression of a Rap1A mutant lacking a PKA phosphorylation site. These results indicate that PKA elicits negative feedback regulation on cAMP-stimulated Rap1 activity in some cells. The dual regulation of Rap1 by cAMP and PKA extends to downstream effectors. The ability of TSH to stimulate Akt phosphorylation was markedly enhanced by the expression of activated Rap1A and was repressed in cells expressing a putative dominant-negative Rap1A mutant. Although the expression of activated Rap1A was sufficient to stimulate wortmannin-sensitive Akt phosphorylation, TSH further increased Akt phosphorylation in a phosphatidylinositol 3-kinase- and PKA-dependent manner. The ability of TSH to phosphorylate Akt was impaired in cells expressing a Rap1A mutant that could be activated but not phosphorylated. These findings indicate that dual signals, Rap1 activation and phosphorylation, contribute to TSH-stimulated Akt phosphorylation. Rap1 plays an essential role in cAMP-regulated differentiation. TSH effects on thyroid-specific gene expression, but not its effects on proliferation, were markedly enhanced in cells expressing activated Rap1A and repressed in cells expressing a dominant-negative Rap1A mutant. These findings reveal complex regulation of Rap1 by cAMP including PKA-independent activation and PKA-dependent negative feedback regulation. Both signals appear to be required for TSH signaling to Akt.