Tank A W, Curella P, Ham L
Mol Pharmacol. 1986 Nov;30(5):497-503.
When rat pheochromocytoma PC18 cells are exposed to the cyclic AMP analog, 8-bromocyclic AMP, and/or the synthetic glucocorticoid, dexamethasone, there is a marked increase in the level of a single RNA species that hybridizes to the recombinant plasmid pTH.4, which contains sequences complementary to the RNA coding for tyrosine hydroxylase. This RNA species is 1800-1900 nucleotides in length and is presumably identical to an RNA species of similar size, isolated from rat pheochromocytoma PC8b cells and shown to code for tyrosine hydroxylase. Using RNA dot hybridization to quantitate the relative level of this tyrosine mRNA species, time course studies show that this mRNA increases relatively rapidly in PC18 cells treated with either 8-bromocyclic AMP or dexamethasone. A new steady state level of tyrosine hydroxylase mRNA is achieved after 6 hr or 12-24 hr of treatment with either 8-bromocyclic AMP or dexamethasone, respectively. The changes in the level of the mRNA slightly precede the changes in the rate of synthesis of tyrosine hydroxylase in cells treated with these inducing agents. After 24 hr of treatment with either 8-bromocyclic AMP or dexamethasone, the increases in the level of tyrosine hydroxylase mRNA are identical to the increases in the rate of synthesis of the enzyme in the cells. In cells treated simultaneously with both 8-bromocyclic AMP and dexamethasone, the increases in the enzyme level and rate of synthesis of tyrosine hydroxylase are approximately equal to the sum of the increases in these parameters observed in cells treated with either inducing agent alone. In contrast, there is not an additive increase in the level of tyrosine hydroxylase mRNA in cells treated with both inducing agents. This lack of an additive increase in mRNA for tyrosine hydroxylase is observed in total cellular RNA samples or in cytoplasmic RNA samples. Our results suggest that in cells exposed to elevated levels of either cyclic AMP or glucocorticoids, tyrosine hydroxylase is induced by a mechanism which increases the level of its mRNA, resulting in an increased rate of synthesis of the enzyme. However, in cells exposed to elevated levels of both cyclic AMP and dexamethasone, tyrosine hydroxylase enzyme levels are regulated by multiple mechanisms, one of which regulates the rate of synthesis of the enzyme without affecting the level of its mRNA.
当大鼠嗜铬细胞瘤PC18细胞暴露于环磷酸腺苷类似物8-溴环磷酸腺苷和/或合成糖皮质激素地塞米松时，与重组质粒pTH.4杂交的单一RNA种类的水平显著增加，该质粒含有与编码酪氨酸羟化酶的RNA互补的序列。这种RNA种类长度为1800 - 1900个核苷酸，可能与从大鼠嗜铬细胞瘤PC8b细胞中分离出的大小相似的RNA种类相同，且已证明该RNA种类编码酪氨酸羟化酶。使用RNA点杂交来定量这种酪氨酸mRNA种类的相对水平，时间进程研究表明，在用8-溴环磷酸腺苷或地塞米松处理的PC18细胞中，这种mRNA相对迅速增加。分别用8-溴环磷酸腺苷或地塞米松处理6小时或12 - 24小时后，酪氨酸羟化酶mRNA达到新的稳态水平。在用这些诱导剂处理的细胞中，mRNA水平的变化略先于酪氨酸羟化酶合成速率的变化。用8-溴环磷酸腺苷或地塞米松处理24小时后，酪氨酸羟化酶mRNA水平的增加与细胞中该酶合成速率的增加相同。在用8-溴环磷酸腺苷和地塞米松同时处理的细胞中，酪氨酸羟化酶水平和合成速率的增加大约等于在用任一诱导剂单独处理的细胞中观察到的这些参数增加的总和。相比之下，在用两种诱导剂处理的细胞中，酪氨酸羟化酶mRNA水平没有累加增加。在总细胞RNA样本或细胞质RNA样本中均观察到酪氨酸羟化酶mRNA缺乏累加增加。我们的结果表明，在暴露于高水平环磷酸腺苷或糖皮质激素的细胞中，酪氨酸羟化酶是通过增加其mRNA水平的机制被诱导的，从而导致该酶合成速率增加。然而，在暴露于高水平环磷酸腺苷和地塞米松的细胞中，酪氨酸羟化酶的酶水平受多种机制调节，其中一种机制调节该酶的合成速率而不影响其mRNA水平。
