Jones K E, Chin W W
Department of Medicine, Brigham and Women's Hospital, Boston, Massachusetts 02115.
Endocrinology. 1991 Apr;128(4):1763-8. doi: 10.1210/endo-128-4-1763.
In addition to its well known actions in stimulating TSH and PRL synthesis and secretion, TRH has been shown to decrease the concentration of thyroid hormone receptors (TRs) in GH4C1 cells as measured by nuclear thyroid hormone (T3) binding. In the present study we have investigated the effects of TRH on the levels of mRNA encoding the different forms of TR, TR beta-1, TR beta-2, and TR alpha-1 as well as that of the non-T3-binding variant, c-erbA alpha-2. GH3 cells were incubated with 100 nM TRH in the presence or absence of 1 nM T3 for 48 h, and mRNA levels were determined by Northern blot analysis. Results revealed that there is differential regulation of the individual TRs by TRH at the pretranslational level. The mRNA for the pituitary-specific form of TR, TR beta-2, was down-regulated by 60% by TRH in GH3 cells, while that of its alternative splice product, TR beta-1, was unchanged. A modest change was observed in TR alpha-1 mRNA levels, which were down-regulated by 20%; there was no change in c-erbA alpha-2 mRNA levels. Levels of nuclear T3 binding were assessed under the same conditions, and 100 nM TRH was found to decrease binding by 40% from 0.78 to 0.46 fmol/micrograms DNA. A similar change in nuclear T3 binding was seen after incubation with 1 nM T3. The effect of TRH on the GH mRNA response to T3 was investigated. In the absence of TRH there was a 4-fold induction of GH mRNA after incubation with 1 nM T3. In the presence of 100 nM TRH, no significant induction in GH mRNA by T3 was seen, indicating that T3 responsiveness as well as receptor concentration are diminished by TRH under these conditions.
除了其在刺激促甲状腺激素（TSH）和催乳素（PRL）合成与分泌方面的知名作用外，促甲状腺激素释放激素（TRH）已被证明可降低生长激素4C1（GH4C1）细胞中甲状腺激素受体（TRs）的浓度，这是通过核甲状腺激素（T3）结合来测定的。在本研究中，我们研究了TRH对编码不同形式TR（TRβ-1、TRβ-2和TRα-1）以及非T3结合变体c-erbAα-2的mRNA水平的影响。将GH3细胞在存在或不存在1 nM T3的情况下与100 nM TRH孵育48小时，并通过Northern印迹分析测定mRNA水平。结果显示，TRH在翻译前水平对各个TRs有不同的调节作用。在GH3细胞中，TR的垂体特异性形式TRβ-2的mRNA被TRH下调了60%，而其可变剪接产物TRβ-1的mRNA则没有变化。观察到TRα-1 mRNA水平有适度变化，下调了20%；c-erbAα-2 mRNA水平没有变化。在相同条件下评估核T3结合水平，发现100 nM TRH可使结合从0.78 fmol/μg DNA降低40%至0.46 fmol/μg DNA。与1 nM T3孵育后也观察到核T3结合有类似变化。研究了TRH对GH mRNA对T3反应的影响。在不存在TRH的情况下，与1 nM T3孵育后GH mRNA有4倍的诱导。在存在100 nM TRH的情况下，未观察到T3对GH mRNA有明显诱导，这表明在这些条件下TRH降低了T3反应性以及受体浓度。
