Mattson M P, Spaziani E
Gen Comp Endocrinol. 1986 Sep;63(3):414-23. doi: 10.1016/0016-6480(86)90141-3.
The crustacean neuropeptide, molt-inhibiting hormone (MIH), directly inhibits Y-organ ecdysteroidogenesis, an effect mediated by cyclic AMP (cAMP) and antagonized by calcium-calmodulin. We investigated regulation of Y-organ protein. RNA, and DNA syntheses by MIH, cAMP, and calcium in relation to steroidogenesis in vitro. Ecdysteroid production and [3H]leucine incorporation into protein were inhibited 50-60 and 80-90%, respectively, by MIH activity in eyestalk extracts (4 eyestalk equivalents), 10(-6) M forskolin, or a combination of 10(-2) M dibutyryl cAMP and 10(-4) M 3-isobutyl-1-methylxanthine (dbcAMP-IBMX). Calcium ionophore A23187 (10(-4) M) stimulated ecdysteroidogenesis two-fold, did not affect the relatively high basal (control) rate of protein synthesis, and reduced the inhibitory effects of forskolin on steroidogenesis and protein synthesis. Incorporation of [3H]uridine into RNA was unaffected by MIH, forskolin, or A23187 but was reduced 50% by dbcAMP-IBMX. Basal rates of [3H]thymidine incorporation into DNA were low and were not affected by treatments. The effects of MIH were specific; extracts of brain or muscle did not alter Y-organ steroidogenesis or protein synthesis, while muscle extract increased precursor incorporation into RNA. Eyestalk extract did not affect [3H]leucine incorporation into protein of brain, muscle, or gill. Cycloheximide (5 micrograms/ml) depressed protein synthesis 90% and steroidogenesis 60%, enhanced the inhibition induced by MIH, and blocked the stimulation of steroidogenesis induced by A23187; effects on basal steroidogenesis were evident after 1 hr. Actinomycin D (1 microgram/ml) depressed RNA synthesis 86% but did not alter basal, MIH-inhibited, or A23187-stimulated ecdysteroidogenesis during incubations. These results indicate that MIH suppresses Y-organ steroidogenesis in part by inhibiting protein synthesis at the translational level; the effect is mediated by cAMP. The stimulation of steroidogenesis by calcium, mediated by lowering cAMP, also appears to depend in part upon protein synthesis.
甲壳类动物神经肽——蜕皮抑制激素（MIH）可直接抑制Y器官的蜕皮类固醇生成，该效应由环磷酸腺苷（cAMP）介导，并受到钙 - 钙调蛋白的拮抗。我们研究了MIH、cAMP和钙对Y器官蛋白质、RNA和DNA合成的调节作用及其与体外类固醇生成的关系。眼柄提取物（4个眼柄当量）中的MIH活性、10⁻⁶ M的福司可林，或10⁻² M的二丁酰cAMP与10⁻⁴ M的3 - 异丁基 - 1 - 甲基黄嘌呤（dbcAMP - IBMX）的组合，分别使蜕皮类固醇生成和[³H]亮氨酸掺入蛋白质的过程受到50 - 60%和80 - 90%的抑制。钙离子载体A23187（10⁻⁴ M）使蜕皮类固醇生成增加了两倍，对相对较高的基础（对照）蛋白质合成速率没有影响，并降低了福司可林对类固醇生成和蛋白质合成的抑制作用。[³H]尿苷掺入RNA的过程不受MIH、福司可林或A23187的影响，但被dbcAMP - IBMX降低了50%。[³H]胸苷掺入DNA的基础速率较低，且不受处理的影响。MIH的作用具有特异性；脑或肌肉提取物不会改变Y器官类固醇生成或蛋白质合成，而肌肉提取物会增加前体掺入RNA的过程。眼柄提取物不会影响[³H]亮氨酸掺入脑、肌肉或鳃的蛋白质。放线菌酮（5微克/毫升）使蛋白质合成降低90%，类固醇生成降低60%，增强了MIH诱导的抑制作用，并阻断了A23187诱导的类固醇生成刺激；对基础类固醇生成的影响在1小时后明显。放线菌素D（1微克/毫升）使RNA合成降低86%，但在孵育过程中不会改变基础、MIH抑制或A23187刺激的蜕皮类固醇生成。这些结果表明，MIH部分通过在翻译水平抑制蛋白质合成来抑制Y器官类固醇生成；该效应由cAMP介导。钙通过降低cAMP介导的对类固醇生成的刺激作用，似乎也部分依赖于蛋白质合成。
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