Kren B T, Trembley J H, Krajewski S, Behrens T W, Reed J C, Steer C J
Department of Medicine, University of Minnesota Medical School, Minneapolis 55455, USA.
Cell Growth Differ. 1996 Dec;7(12):1633-42.
Liver regeneration (LR) after 70% partial hepatectomy (PH) represents a unique in vivo model of cell cycle and gene regulation. This study was conducted to characterize apoptosis-associated gene expression during LR. The results indicated that transcripts for both bcl-x and bcl-2 exhibited similar patterns of expression during LR with peaks at 6 h post-PH. In contrast, the major 1.1-kb bax transcript exhibited peaks at 18 (P < 0.05) and 72 h (P < 0.001) post-PH. Nuclear run-on analyses for all three genes indicated no detectable transcription rate changes during LR. At 6 h post-PH, when bcl-x mRNA levels were increased by 25-fold (P < 0.001), bcl-x mRNA half-life was elevated 4-fold (P < 0.001). Similarly, bax transcript half-life increased from 2.8 h at 0 h to 4.3 h at 24 h (P < 0.001) and > 8 h at 40 h (P < 0.001) post-PH, coincident with increases in steady-state levels of mRNA. Western blot analyses of Bcl-2 and Bcl-x proteins showed no significant change through 96 h of LR, whereas Bax protein levels cycled in parallel with its mRNA. Interestingly, novel Bax- and Bcl-2-cross-reactive proteins of 31 and 32 kDa, respectively, were detected in nuclei isolated from quiescent liver. When liver growth was induced by the peroxisome proliferator clofibrate, transcript and protein levels were coupled for bcl-x but not for bax. In conclusion, the apoptosis-associated genes bcl-2, bcl-x and bax are modulated at the transcript and protein levels during LR, suggesting a role for these gene products in normal liver growth. The alterations in transcript levels occur posttranscriptionally and involve changes in mRNA stability. Furthermore, unlike bax, steady-state protein and transcript levels are uncoupled for both bcl-2 and bcl-x, suggesting a role for translational regulation during LR after PH.
70%肝部分切除术后的肝再生（LR）是细胞周期和基因调控的一种独特体内模型。本研究旨在描述肝再生过程中凋亡相关基因的表达特征。结果表明，bcl-x和bcl-2的转录本在肝再生过程中表现出相似的表达模式，在肝部分切除术后6小时达到峰值。相比之下，主要的1.1-kb bax转录本在肝部分切除术后18小时（P < 0.05）和72小时（P < 0.001）出现峰值。对这三个基因的核转录分析表明，在肝再生过程中未检测到转录速率的变化。在肝部分切除术后6小时，当bcl-x mRNA水平增加25倍（P < 0.001）时，bcl-x mRNA半衰期升高4倍（P < 0.001）。同样，bax转录本半衰期从肝部分切除术后0小时的2.8小时增加到24小时的4.3小时（P < 0.001），在40小时时> 8小时（P < 0.001），与mRNA稳态水平的增加一致。对Bcl-2和Bcl-x蛋白的蛋白质印迹分析表明，在肝再生的96小时内没有显著变化，而Bax蛋白水平与其mRNA平行循环。有趣的是，在从静止肝脏分离的细胞核中检测到分别为31 kDa和32 kDa的新型Bax和Bcl-2交叉反应蛋白。当用过氧化物酶体增殖剂氯贝丁酯诱导肝脏生长时，bcl-x的转录本和蛋白水平是相关的，但bax不是。总之，凋亡相关基因bcl-2、bcl-x和bax在肝再生过程中在转录本和蛋白水平上受到调节，表明这些基因产物在正常肝脏生长中起作用。转录本水平的改变发生在转录后，涉及mRNA稳定性的变化。此外，与bax不同，bcl-2和bcl-x的稳态蛋白和转录本水平是不相关的，这表明在肝部分切除术后的肝再生过程中存在翻译调控作用。
