Aloj S M, Grieco D, Kohn A D, Nikodem V M, Kohn L D
Clinical Endocrinology Branch, National Institute of Diabetes, Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892.
Mol Endocrinol. 1990 Apr;4(4):611-22. doi: 10.1210/mend-4-4-611.
TSH-induced increases in malic enzyme mRNA levels in FRTL-5 rat thyroid cells are paralleled by increases in malic enzyme activity and are mimicked by 8-bromo-cAMP. Apparent approximately 4 h after TSH challenge and maximal after 16 h, they decline by 24 h and are at basal levels by 48 h. The increase occurs in the absence of a measurable effect of TSH on DNA synthesis related to cell growth, since [3H] thymidine incorporation into DNA is still at basal levels 24 h after TSH challenge and is maximal only at 48 h. A protein(s) whose formation is inhibited by cycloheximide appears to be critical to the ability of TSH to increase malic enzyme mRNA levels. Thus, cycloheximide given 30 min before TSH prevents the hormone-induced increase in malic enzyme mRNA; also, when given 24 h after TSH, cycloheximide accelerates the loss of the TSH-induced increase in malic enzyme mRNA. In neither case does cycloheximide affect beta-actin mRNA levels. A second factor(s) whose formation is prevented by actinomycin-D appears to be important for the decrease in malic enzyme mRNA levels seen 24 and 48 h after TSH challenge. Thus, in experiments in which it is given 24 h after TSH, actinomycin-D preserves the hormone-induced increase in malic enzyme mRNA levels rather than accelerating the decrease, as does cycloheximide. In the same experiment, beta-actin mRNA levels decrease to less than 10-20% of control values over the same period; this factor also, therefore, appears to exhibit some degree of specificity.(ABSTRACT TRUNCATED AT 250 WORDS)
促甲状腺激素（TSH）诱导FRTL-5大鼠甲状腺细胞中苹果酸酶mRNA水平升高，同时苹果酸酶活性也升高，且8-溴-环磷酸腺苷（8-bromo-cAMP）可模拟这种作用。TSH刺激后约4小时明显出现，16小时达到最大值，24小时下降，48小时恢复到基础水平。这种增加在TSH对与细胞生长相关的DNA合成没有可测量影响的情况下发生，因为在TSH刺激后24小时，[3H]胸苷掺入DNA仍处于基础水平，仅在48小时达到最大值。一种其形成受环己酰亚胺抑制的蛋白质似乎对TSH增加苹果酸酶mRNA水平的能力至关重要。因此，在TSH给药前30分钟给予环己酰亚胺可阻止激素诱导的苹果酸酶mRNA增加；此外，在TSH给药后24小时给予环己酰亚胺，可加速TSH诱导的苹果酸酶mRNA增加的丧失。在这两种情况下，环己酰亚胺均不影响β-肌动蛋白mRNA水平。另一种其形成受放线菌素-D阻止的因子似乎对TSH刺激后24小时和48小时观察到的苹果酸酶mRNA水平下降很重要。因此，在TSH给药后24小时进行的实验中，放线菌素-D可维持激素诱导的苹果酸酶mRNA水平升高，而不是像环己酰亚胺那样加速下降。在同一实验中，β-肌动蛋白mRNA水平在同一时期下降至对照值的不到10%-20%；因此，这个因子似乎也表现出一定程度的特异性。（摘要截短至250字）
