Gavin L A, Moller M, McMahon F, Gulli R, Cavalieri R R
Division of Endocrinology-Metabolism, Veterans Administration Medical Center, San Francisco, California 94121.
Endocrinology. 1989 Feb;124(2):635-41. doi: 10.1210/endo-124-2-635.
The T3 concentration in brain predominantly reflects local production from T4 rather than T3 uptake from the circulating pool. We recently demonstrated that rat brain T3 content is increased by glucose feeding compared to chow feeding. One possible mechanism for this effect is an increase in brain T4 5'-deiodinase (5'-D) activity. Our recent preliminary studies of neuroblastoma (NB) cells demonstrate that renewal of RPMI-1640 medium stimulates T4 5'-D type II (NB T4 5'-D II) activity in these cells. The present studies were performed to determine the mechanism of this response. Studies were performed on NB cells supported in thyroid hormone-depleted (deficient) medium. This approach increased NB T4 5'-DII activity 4-fold compared to that in thyroid hormone-replete medium. Medium renewal further stimulated enzyme activity (7- to 9-fold; maximum at 6 h) in each group. The difference between the hypothyroid group and control was sustained over a 24-h period. Subsequent studies demonstrated that glucose (11 mM) was the specific medium ingredient mediating the medium renewal response. A progressive increase in NB T4 5'-DII activity was noted over 8 h during RPMI-1640 salt plus glucose (11 mM) incubation. This was equivalent to the effect of complete medium containing glucose (11 mM). Coincubation with insulin (10(-7)-10(-9) M) did not modify the enzyme response to glucose. In addition, fructose (10 mM) had a similar effect on enzyme activity. Glycerol and essential and nonessential amino acids also modestly increased NB T4 5'-DII activity compared to that in the control group (P less than 0.01). Actinomycin-D (1 microM), cycloheximide (100 microM), and puromycin (100 microM) significantly (P less than 0.001) decreased the glucose effect on T4 5'-DII by 5-, 9-, and 17-fold, respectively, after 6 h of incubation. In addition, puromycin (10-200 microM) inhibited both NB T4 5'-DII activity and [3H]amino acid incorporation during incubation in glucose. There was a significant correlation between these parameters (r = 0.8; P less than 0.001). The enzyme activity decay curves in the glucose-activated and control groups subsequent to puromycin (100 microM) addition at 8 h were parallel. The fractional turnover rate was 13%/h in the controls and 11%/h in the glucose groups. The calculated enzyme production rate was significantly higher (P less than 0.005) in the glucose group compared to that in the control group (17.4 vs. 6.8 fmol/mg protein.h).(ABSTRACT TRUNCATED AT 400 WORDS)
大脑中的T3浓度主要反映T4的局部生成，而非来自循环池的T3摄取。我们最近发现，与喂食普通食物相比，喂食葡萄糖会使大鼠脑内T3含量增加。这种效应的一种可能机制是脑内T4 5'-脱碘酶（5'-D）活性增加。我们最近对神经母细胞瘤（NB）细胞的初步研究表明，更换RPMI-1640培养基可刺激这些细胞中的T4 5'-D II型（NB T4 5'-D II）活性。进行本研究以确定这种反应的机制。研究在甲状腺激素缺乏的培养基中培养的NB细胞上进行。与甲状腺激素充足的培养基相比，这种方法使NB T4 5'-DII活性增加了4倍。更换培养基进一步刺激了每组中的酶活性（7至9倍；6小时时达到最大值）。甲状腺功能减退组与对照组之间的差异在24小时内持续存在。随后的研究表明，葡萄糖（11 mM）是介导培养基更换反应的特定培养基成分。在RPMI-1640盐加葡萄糖（11 mM）孵育期间，NB T4 5'-DII活性在8小时内逐渐增加。这与含有葡萄糖（11 mM）的完全培养基的效果相当。与胰岛素（10(-7)-10(-9) M）共同孵育并未改变酶对葡萄糖的反应。此外，果糖（10 mM）对酶活性有类似影响。与对照组相比，甘油以及必需和非必需氨基酸也适度增加了NB T4 5'-DII活性（P小于0.01）。放线菌素-D（1 microM）、环己酰亚胺（100 microM）和嘌呤霉素（100 microM）在孵育6小时后，分别使葡萄糖对T4 5'-DII的作用显著降低（P小于0.001）5倍、9倍和17倍。此外，嘌呤霉素（10 - 200 microM）在葡萄糖孵育期间抑制了NB T4 5'-DII活性和[3H]氨基酸掺入。这些参数之间存在显著相关性（r = 0.8；P小于0.001）。在8小时添加嘌呤霉素（100 microM）后，葡萄糖激活组和对照组中的酶活性衰减曲线是平行的。对照组的分数周转率为13%/小时，葡萄糖组为11%/小时。计算得出的葡萄糖组酶产生率显著高于对照组（P小于0.005）（17.4对6.8 fmol/mg蛋白质·小时）。（摘要截短至400字）
