Rao G N, Church R L
Department of Ophthalmology, Emory University School of Medicine, Emory Eye Center, Atlanta, Georgia 30322.
Exp Cell Res. 1988 Oct;178(2):449-56. doi: 10.1016/0014-4827(88)90413-2.
We have analyzed the steady-state levels of CAD mRNA and ATCase activity in BALB/c 3T3 mouse fibroblasts at quiescence and at various time points following the initiation of serum stimulation. Steady-state levels of CAD mRNA in 3T3 cells following 12 h of serum stimulation increased 10-fold over levels measured at quiescence. In contrast to the observed increase in steady-state levels of CAD mRNA, its rate of transcription increased only 3-fold, suggesting that the expression of CAD gene in these cells is regulated at both the transcriptional and post-transcriptional levels, to a major extent by the latter. These increases in CAD mRNA in serum-stimulated cells were followed by parallel increases in ATCase activity as well. When comparing DNA synthesis [( 3H]thymidine uptake) to the accumulation of CAD mRNA and ATCase activity, it was observed that this accumulation occurred during the mid- to late-G1 phase of the cell cycle. These results suggest that the expression of CAD gene is cell growth dependent and may be a prerequisite to DNA synthesis.
我们分析了静止状态下以及血清刺激开始后不同时间点BALB/c 3T3小鼠成纤维细胞中CAD mRNA的稳态水平和天冬氨酸转氨甲酰酶（ATCase）活性。血清刺激12小时后，3T3细胞中CAD mRNA的稳态水平比静止状态下测得的水平增加了10倍。与观察到的CAD mRNA稳态水平增加相反，其转录速率仅增加了3倍，这表明这些细胞中CAD基因的表达在转录和转录后水平均受到调控，且在很大程度上受后者调控。血清刺激细胞中CAD mRNA的这些增加之后，ATCase活性也随之平行增加。当将DNA合成[（3H）胸腺嘧啶核苷摄取]与CAD mRNA和ATCase活性的积累进行比较时，发现这种积累发生在细胞周期的G1期中期至后期。这些结果表明，CAD基因的表达依赖于细胞生长，并且可能是DNA合成的先决条件。
