Polunovsky V A, Ingbar D H, Peterson M, Bitterman P B
Department of Medicine, Pulmonary and Critical Care Division, University of Minnesota Medical School, Minneapolis, USA.
Am J Pathol. 1996 Jul;149(1):115-28.
Studies examining the regulation of nuclear rearrangements during apoptosis have led to conflicting results. Cytoplasmic control of nuclear events has been strongly suggested by cell-free experimental systems. In contrast, strict cytoplasmic control cannot account for the results of fibroblast-thymocyte fusion experiments in which dexamethasone induction of polykaryons led only to thymocyte nuclear apoptosis. Unresolved by these fusion studies was whether fibroblast nuclei were indifferent to heterologous cytoplasmic signals. Our objective was to resolve this discrepancy using cell fusion in a homologous system. Our strategy was to fuse endothelial cells with high levels of susceptibility to the induction of apoptosis (log phase cells arrested in G1 for 48 hours by isoleucine deprivation) with those manifesting low levels of susceptibility (serum-deprived, G0). Resultant fused and unfused cells were induced to undergo apoptosis by incubation with tumor necrosis factor-alpha and cycloheximide. Depending on the parental cell of origin, between 14 and 30% of dikaryons contained one apoptotic and one intact nucleus, indicating that strict cytoplasmic control was not occurring. In accord with this, the total frequency of nuclear apoptosis was unchanged after fusion. However, the distribution of apoptotic nuclei revealed a pronounced cytoplasmic influence, with a two- to fivefold increase in coordinate nuclear behavior. This pattern of nuclear apoptosis was consistent with a model of control in which both the state of nuclear susceptibility to apoptosis and expression of cytoplasmic pro-apoptotic regulators determined whether nuclear apoptosis would eventuate.
研究细胞凋亡过程中核重排的调控机制，结果却相互矛盾。无细胞实验系统强烈表明存在对核事件的细胞质控制。相比之下，严格的细胞质控制无法解释成纤维细胞 - 胸腺细胞融合实验的结果，在该实验中，地塞米松诱导多核体仅导致胸腺细胞核凋亡。这些融合研究未解决的问题是，成纤维细胞核是否对异源细胞质信号无动于衷。我们的目标是利用同源系统中的细胞融合来解决这一差异。我们的策略是将对凋亡诱导高度敏感的内皮细胞（通过异亮氨酸剥夺在G1期停滞48小时的对数期细胞）与敏感性较低的细胞（血清剥夺的G0期细胞）融合。将融合和未融合的细胞与肿瘤坏死因子 -α 和环己酰亚胺一起孵育，诱导其发生凋亡。根据亲本细胞的来源，14%至30%的双核体包含一个凋亡细胞核和一个完整细胞核，这表明不存在严格的细胞质控制。与此一致的是，融合后核凋亡的总频率没有变化。然而，凋亡细胞核的分布显示出明显的细胞质影响，协同核行为增加了两到五倍。这种核凋亡模式与一种控制模型一致，在该模型中，细胞核对凋亡的敏感性状态和细胞质促凋亡调节因子的表达共同决定了核凋亡是否会发生。
