Feeding and insulin increase leptin translation - Importance of the leptin mRNA untranslated regions
Feeding and insulin increase leptin translation - Importance of the leptin mRNA untranslated regions
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DOI：
10.1074/jbc.m609518200
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发表时间：
2007-01-05
影响因子：
4.8
通讯作者：
Fried, Susan K.
中科院分区：
文献类型：
--
作者：
Lee, Mi-Jeong;Yang, Rong-Ze;Fried, Susan K.
喂养和胰岛素促进瘦素产生的转录后机制还知之甚少。6~7周龄大鼠饥饿14h后，瘦素mRNA水平仅下降22%，但血浆瘦素水平、脂肪组织瘦素含量和释放水平均下降75%以上。通过代谢标记和免疫沉淀法测量瘦素生物合成的相对速率降低85%，可以解释饥饿时瘦素的减少。体外胰岛素处理喂养或饥饿大鼠的脂肪组织2小时，可使瘦素生物合成的相对速率增加2-3倍，这种作用可被磷脂酰肌醇3-激酶或哺乳动物靶标雷帕霉素所阻断。与喂食/胰岛素促进瘦素翻译的假设一致，喂食的大鼠脂肪组织中与多聚体相关的瘦素mRNA比饥饿大鼠多，体外胰岛素孵育饥饿大鼠的脂肪组织将瘦素mRNA转移到多聚体中。为了研究瘦素翻译的调控机制，将人瘦素非翻译区(UTR)嵌合报告结构瞬时导入分化的3T3-L1脂肪细胞。Leptin mRNA的5‘-UTR使荧光素酶报告活性增加2-3倍，而全长3’-UTR(核苷酸1-2804)对荧光素酶报告活性有抑制作用(-65%)。瘦素3‘-非编码区核苷酸462和1130之间的序列提供了大部分的抑制作用。胰岛素刺激包括全长5‘-非编码区和抑制性3’-非编码区的构建体的表达，这种作用可被磷脂酰肌醇3-激酶或雷帕霉素的哺乳动物靶标阻断。我们的数据表明，胰岛素通过同时需要5‘-非编码区和3’-非编码区的机制来降低瘦素的翻译，并可能有助于随着进食而增加瘦素的产生。
The post-transcriptional mechanisms by which feeding and insulin increase leptin production are poorly understood. Starvation of 6-7-week-old rats for 14 h decreased leptin mRNA level by only 22% but decreased plasma levels, adipose tissue leptin content, and release by over 75%. The decreased leptin with starvation was explained by > 85% decrease in relative rates of leptin biosynthesis measured by metabolic labeling and immunoprecipitation. In vitro insulin treatment of adipose tissue from fed or starved rats for 2 h increased relative rates of leptin biosynthesis by 2-3-fold, and the effect was blocked by inhibition of phosphatidylinositol 3-kinase or mammalian target of rapamycin. Consistent with the hypothesis that feeding/insulin increases leptin translation, more leptin mRNA was associated with polysomes in adipose tissue of fed than starved rats and in vitro incubation of adipose tissue of starved rats with insulin shifted leptin mRNA into polysomes. To assess the mechanisms regulating leptin translation, chimeric human leptin untranslated region (UTR) reporter constructs were transiently transfected into differentiated 3T3-L1 adipocytes. The 5'-UTR of leptin mRNA increased luciferase reporter activity 2-3-fold, whereas the full-length 3'-UTR (nucleotides 1-2804) was inhibitory (-65%). Sequences between nucleotides 462 and 1130 of the leptin 3'-UTR conferred most of the inhibitory effect. Insulin stimulated the expression of constructs that included both the full-length 5'-UTR and the inhibitory 3'-UTR, and the effect was blocked by inhibition of phosphatidylinositol 3-kinase or mammalian target of rapamycin. Our data suggest that insulin derepresses leptin translation by a mechanism that requires both the 5'-UTR and the 3'-UTR and may contribute to the increase in leptin production with feeding.