Tam S P, Deeley R G
Department of Biochemistry, Queen's University, Kingston, Ontario, Canada.
Atherosclerosis. 1994 Feb;105(2):235-43. doi: 10.1016/0021-9150(94)90054-x.
Apolipoprotein (apo) A-I is the major protein constituent of plasma high density lipoprotein (HDL), which has been suggested to play a protective role against the development of atherosclerosis. The effect of phenobarbital on apo A-I mRNA and protein levels was studied in the human hepatoma cell line, Hep3B. Exposure of Hep3B cells to the drug (200 micrograms/ml) for 16 h resulted in a 4-fold and 8-fold increase in apo A-I mRNA and secreted protein levels, respectively. The induction of apo A-I mRNA level caused by phenobarbital could be due to increased rates of transcription and/or alteration in mRNA stability. To test these possibilities, nuclear run-off transcription assays and pulse-chase deinduction experiments were performed. We have demonstrated that phenobarbital treatment is associated with a 2-fold induction in apo A-I transcriptional activity. The estimated half-lives for apo A-I mRNA are 2 h and 3.6 h in the absence or presence of phenobarbital, respectively. The combination of increase in apo A-I transcription rate and mRNA stabilization could explain the 4-fold induction in apo A-I mRNA levels caused by phenobarbital treatment. However, these events could not be solely responsible for the 8-fold increase in secreted apo A-I protein level observed. The results suggest that the mechanism(s) by which phenobarbital induces apo A-I production operate at both pre- and either co- or post-translational mechanisms. The induction of apo A-I is specific since no significant alteration in apo E mRNA and proteins was observed in drug-treated cells.
载脂蛋白（apo）A-I是血浆高密度脂蛋白（HDL）的主要蛋白质成分，有人认为它对动脉粥样硬化的发展具有保护作用。在人肝癌细胞系Hep3B中研究了苯巴比妥对apo A-I mRNA和蛋白质水平的影响。将Hep3B细胞暴露于该药物（200微克/毫升）16小时，导致apo A-I mRNA和分泌蛋白水平分别增加了4倍和8倍。苯巴比妥引起的apo A-I mRNA水平的诱导可能是由于转录速率增加和/或mRNA稳定性改变。为了测试这些可能性，进行了核转录分析和脉冲追踪去诱导实验。我们已经证明，苯巴比妥治疗与apo A-I转录活性的2倍诱导有关。在不存在或存在苯巴比妥的情况下，apo A-I mRNA的估计半衰期分别为2小时和3.6小时。apo A-I转录速率增加和mRNA稳定化的结合可以解释苯巴比妥治疗引起的apo A-I mRNA水平的4倍诱导。然而，这些事件不能完全解释所观察到的分泌的apo A-I蛋白水平增加8倍的原因。结果表明，苯巴比妥诱导apo A-I产生的机制在转录前以及转录和翻译后机制中起作用。apo A-I的诱导是特异性的，因为在药物处理的细胞中未观察到apo E mRNA和蛋白质有明显变化。
