Down-regulation of adipose tissue lipoprotein lipase during fasting requires that a gene, separate from the lipase gene, is switched on
Down-regulation of adipose tissue lipoprotein lipase during fasting requires that a gene, separate from the lipase gene, is switched on
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DOI：
10.1074/jbc.m200325200
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发表时间：
2002-04-05
影响因子：
4.8
通讯作者：
Olivecrona, T
中科院分区：
文献类型：
--
作者：
Bergö, M;Wu, GS;Olivecrona, T
在短期禁食期间，大鼠脂肪组织中的脂蛋白脂酶（LPL）活性迅速下调。这种下调发生在翻译后水平;它不伴随LPL mRNA或蛋白水平的变化。LPL活性可在4 h内恢复。以前，我们表明，在禁食期间，脂肪酶蛋白的分布向低肝素亲和力的非活性形式转移。为了研究调节机制的性质，我们测定了大鼠脂肪组织中LPL活性、蛋白质质量和mRNA的体内周转率。当蛋白质合成被抑制放线菌酮，LPL活性和蛋白质质量迅速下降，并在平行的半衰期约2小时，再喂养的效果被阻断。这表明维持高水平的LPL活性需要不断合成新的酶蛋白。当转录被抑制放线菌素，LPL mRNA减少与半衰期为13.3和16.8小时，分别在进食和禁食状态，表明缓慢营业额的LPL转录。令人惊讶的是，当给予喂食大鼠放线菌素时，LPL活性在禁食期间没有下调，表明放线菌素干扰了阻断新合成LPL蛋白激活的基因的转录。当放线菌素给予禁食大鼠，LPL活性增加4倍，6小时内，即使在没有再喂养。另一种转录抑制剂α-鹅膏蕈碱也有同样的效果。对放线菌素的反应在肥胖和胰岛素抵抗的老龄大鼠中不太明显。这些数据表明LPL蛋白在相对稳定的mRNA上合成并加工成其活性形式的默认状态。在禁食期间，一个基因被打开，其产物阻止酶变得活跃，即使LPL蛋白的合成继续有增无减。
During short term fasting, lipoprotein lipase (LPL) activity in rat adipose tissue is rapidly down-regulated. This down-regulation occurs on a posttranslational level; it is not accompanied by changes in LPL mRNA or protein levels. The LPL activity can be restored within 4 h by refeeding. Previously, we showed that during fasting there is a shift in the distribution of lipase protein toward an inactive form with low heparin affinity. To study the nature of the regulatory mechanism, we determined the in vivo turnover of LPL activity, protein mass, and mRNA in rat adipose tissue. When protein synthesis was inhibited with cycloheximide, LPL activity and protein mass decreased rapidly and in parallel with half-lives of around 2 h, and the effect of refeeding was blocked. This indicates that maintaining high levels of LPL activity requires continuous synthesis of new enzyme protein. When transcription was inhibited by actinomycin, LPL mRNA decreased with half-lives of 13.3 and 16.8 h in the fed and fasted states, respectively, demonstrating slow turnover of the LPL transcript. Surprisingly, when actinomycin was given to fed rats, LPL activity was not down-regulated during fasting, indicating that actinomycin interferes with the transcription of a gene that blocks the activation of newly synthesized LPL protein. When actinomycin was given to fasted rats, LPL activity increased 4-fold within 6 h, even in the absence of refeeding. The same effect was seen with a-amanitin, another inhibitor of transcription. The response to actinomycin was much less pronounced in aging rats, which are obese and insulin-resistant. These data suggest a default state where LPL protein is synthesized on a relatively stable mRNA and is processed into its active form. During fasting, a gene is switched on whose product prevents the enzyme from becoming active even though synthesis of LPL protein continues unabated.