Petronijevic T, Edwards A M
Department of Medical Biochemistry, School of Medicine, Flinders University of South Australia, Adelaide.
J Cell Physiol. 1993 Apr;155(1):44-53. doi: 10.1002/jcp.1041550107.
This study examines the effects of extracellular Ca2+ concentrations, [Ca2+]o, and of treatments known to modulate intracellular Ca2+ levels on the extent and timing of DNA synthesis in primary cultures of adult rat hepatocytes. In cultures exposed to insulin and EGF, the extent of DNA synthesis between 40 h and 70 h in culture was independent of [Ca2+]o in the range 25-1,800 microM, although the peak of DNA synthesis occurred 5-10 h earlier with 1.2 mM Ca2+ than with 25 microM Ca2+. Complete removal of extracellular Ca2+ using EGTA blocked DNA synthesis if Ca2+ was removed on the second day after EGF addition but not if Ca2+ was absent only on day 1. Treatment of cultures in 1.2 mM Ca(2+)-containing media with Ca(2+)-ionophore A23187 or with thapsigargin, agents expected to raise cytosolic [Ca2+], failed to augment the stimulation of DNA synthesis by EGF. These observations suggest that hepatocytes may have a permissive requirement for [Ca2+]o > 0 at least late in the sequence of events leading from growth factor stimulation to DNA synthesis. However, sustained elevation of cytosolic [Ca2+] does not appear to be important as an early signalling event either in mediating or augmenting EGF action in hepatocytes. The ability of liver tumor promoters alpha-hexachlorocyclohexane or DDT to stimulate DNA synthesis in combination with EGF was independent of [Ca2+]o. By contrast, the skin tumor-promoting phorbol ester, TPA, or liver tumor promoter, phenobarbital, were without effect or inhibitory at low [Ca2+]o but in combination with EGF, stimulated DNA synthesis at [Ca2+]o > 0.4 mM, suggesting that Ca2+ may have some role in mediating or modulating the stimulatory effects of these agents.
本研究考察了细胞外钙离子浓度（[Ca2+]o）以及已知可调节细胞内钙离子水平的处理方法对成年大鼠肝细胞原代培养物中DNA合成的程度和时间的影响。在暴露于胰岛素和表皮生长因子（EGF）的培养物中，培养40小时至70小时期间的DNA合成程度在25 - 1800微摩尔范围内与[Ca2+]o无关，尽管在1.2毫摩尔钙离子条件下DNA合成的峰值比在25微摩尔钙离子条件下提前5 - 10小时出现。如果在添加EGF后的第二天使用乙二醇双（2-氨基乙基醚）四乙酸（EGTA）完全去除细胞外钙离子，则会阻断DNA合成，但如果仅在第1天不存在钙离子则不会。用钙离子载体A23187或毒胡萝卜素处理含1.2毫摩尔钙离子的培养基中的培养物，预期这些试剂会升高胞质[Ca2+]，但未能增强EGF对DNA合成的刺激作用。这些观察结果表明，至少在从生长因子刺激到DNA合成的事件序列后期，肝细胞可能对[Ca2+]o > 0有允许性需求。然而，胞质[Ca2+]的持续升高似乎在介导或增强EGF在肝细胞中的作用方面，作为早期信号事件并不重要。肝脏肿瘤启动剂α-六氯环己烷或滴滴涕与EGF联合刺激DNA合成的能力与[Ca2+]o无关。相比之下，皮肤肿瘤促进剂佛波酯（TPA）或肝脏肿瘤启动剂苯巴比妥在低[Ca2+]o时无作用或有抑制作用，但与EGF联合时，在[Ca2+]o > 0.4毫摩尔时刺激DNA合成，这表明钙离子可能在介导或调节这些试剂的刺激作用中发挥一定作用。
