Farwell A P, DiBenedetto D J, Leonard J L
Molecular Endocrinology Laboratory, University of Massachusetts Medical School, Worcester 01655.
J Biol Chem. 1993 Mar 5;268(7):5055-62.
In the brain, thyroid hormone dynamically regulates levels of the short-lived plasma membrane protein, type II iodothyronine 5'-deiodinase. In cultured astrocytes, thyroxine modulates deiodinase levels by activating cytoskeletal-plasma membrane interactions that increase the rate of inactivation of the enzyme. Here we characterized the effects of these thyroxine-dependent cytoskeletal interactions upon the route of internalization of the deiodinase by following the intracellular transit of the affinity-labeled substrate-binding subunit of the deiodinase (p29). Thyroxine rapidly induced the inactivation of the deiodinase and initiated the binding of p29 to F-actin. By 40 min, > 75% of the p29 had been transported to an endosomal pool, which was followed by dissociation of the F-actin-p29 complex. There was no significant accumulation of p29 in the dense lysosomes seen in the presence of thyroxine. In the absence of thyroxine, p29 was internalized and transported to the dense lysosomes at a rate parallel to the inactivation rate of the deiodinase (t1/2 0.75 and 0.64 h, respectively) without involvement with the microfilaments. These data demonstrate that thyroxine targets type II iodothyronine 5'-deiodinase to an endosomal pool by activating specific protein-F-actin interactions involved in microfilament-mediated intracellular protein trafficking.
在大脑中，甲状腺激素动态调节短寿命质膜蛋白II型碘甲状腺原氨酸5'-脱碘酶的水平。在培养的星形胶质细胞中，甲状腺素通过激活细胞骨架-质膜相互作用来调节脱碘酶水平，这种相互作用会增加该酶的失活速率。在这里，我们通过追踪脱碘酶（p29）的亲和标记底物结合亚基的细胞内转运过程，来表征这些甲状腺素依赖性细胞骨架相互作用对脱碘酶内化途径的影响。甲状腺素迅速诱导脱碘酶失活，并引发p29与F-肌动蛋白的结合。到40分钟时，超过75%的p29已被转运至内体池，随后F-肌动蛋白-p29复合物解离。在甲状腺素存在的情况下，致密溶酶体中未观察到p29的显著积累。在没有甲状腺素的情况下，p29被内化并以与脱碘酶失活速率平行的速率转运至致密溶酶体（半衰期分别为0.75小时和0.64小时），且不涉及微丝。这些数据表明，甲状腺素通过激活参与微丝介导的细胞内蛋白质运输的特定蛋白质-F-肌动蛋白相互作用，将II型碘甲状腺原氨酸5'-脱碘酶靶向至内体池。
