Kren B T, Trembley J H, Steer C J
Department of Medicine, University of Minesota Medical School, Minneapolis 55455, USA.
Am J Physiol. 1996 May;270(5 Pt 1):G763-77. doi: 10.1152/ajpgi.1996.270.5.G763.
We examined the in vivo transcriptional and posttranscriptional regulation of various genes involved in hepatocyte growth and replication that exhibited changes in steady-state mRNA levels after 70% partial hepatectomy (PH). Of the 19 genes examined by nuclear run-on assay, 17 demonstrated no change in transcriptional activity through the first 96 h of regeneration. However, results from in vivo half-life determinations indicated that changes in mRNA stability played a critical role in regulating transcript levels during liver regeneration. For many of the genes, alterations in transcript abundance correlated with similar changes in mRNA half-lives. Inhibition of protein synthesis by cycloheximide was generally associated with increased levels of mRNA expression, but no detectable changes in transcriptional rates in both control and regenerating rat liver. Finally, genomic methylation status was investigated by Southern analysis for several genes that displayed changes in mRNA stability. Interestingly, increases in mRNA half-lives for the genes p53, c-myc, H-ras, and ornithine decarboxylase were associated with decreased genomic methylation. In conclusion, regulation of gene expression beyond the immediate early phase of te cell cycle during rat liver regeneration after PH occurs predominantly at the posttranscriptional level. mRNA stability appears to be a significant factor in this control, and may itself be modulated by the methylation status of the corresponding genomic DNA.
我们研究了部分肝切除（PH）70%后，参与肝细胞生长和复制的各种基因在体内的转录和转录后调控，这些基因在稳态mRNA水平上出现了变化。通过核转录分析检测的19个基因中，有17个在再生的前96小时内转录活性没有变化。然而，体内半衰期测定结果表明，mRNA稳定性的变化在肝脏再生过程中调节转录本水平方面起着关键作用。对于许多基因来说，转录本丰度的改变与mRNA半衰期的类似变化相关。用环己酰亚胺抑制蛋白质合成通常与mRNA表达水平的增加有关，但在对照和再生大鼠肝脏中，转录速率均未检测到变化。最后，通过Southern分析研究了几个在mRNA稳定性方面表现出变化的基因的基因组甲基化状态。有趣的是，p53、c-myc、H-ras和鸟氨酸脱羧酶基因的mRNA半衰期增加与基因组甲基化减少有关。总之，PH后大鼠肝脏再生过程中，在细胞周期的即时早期阶段之后的基因表达调控主要发生在转录后水平。mRNA稳定性似乎是这种调控中的一个重要因素，并且其本身可能受到相应基因组DNA甲基化状态的调节。
