Demarcq C, Bunch R T, Creswell D, Eastman A
Department of Pharmacology and Toxicology, Dartmouth Medical School, Hanover, New Hampshire 03755.
Cell Growth Differ. 1994 Sep;5(9):983-93.
Many anticancer drugs arrest cells in G2 of the cell cycle and subsequently induce cell death by apoptosis. The current experiments establish a detailed sequence of events that occur in Chinese hamster ovary CHO/UV41 cells following incubation with cisplatin. Synchronized CHO/UV41 cells were damaged with cisplatin in early S. The cells progressed at a normal rate through S but arrested in G2. The arrested cells exhibited normal levels of the mitosis-promoting kinase p34cdc2 in its fully phosphorylated, inactive form. After a protracted arrest, the cells dephosphorylated p34cdc2 and underwent an aberrant mitosis and cytokinesis in which the chromosomes segregated unequally due to the formation of multipolar mitotic spindles. These cells subsequently lost contact with the extracellular matrix, and only then digested their DNA in a manner characteristic of apoptosis. This sequence of events could be dramatically accelerated by the addition of caffeine to G2-arrested cells, which induced dephosphorylation of p34cdc2 and passage through an aberrant mitosis. It has previously been suggested that protein synthesis is required for both caffeine-induced premature mitosis and apoptosis. However, when added in G2, cycloheximide could inhibit neither the caffeine-induced mitosis nor apoptosis. Inhibition was only seen if cycloheximide was added during S before complete synthesis of the proteins required for mitosis. These results demonstrate that, in this model, the proteins thought to be involved in apoptosis are those required for normal cell cycle progression. It is hypothesized that the DNA digestion results from loss of signal transduction originating from the extracellular matrix but that earlier events leading to loss of cell adhesion are critical for the induction of apoptosis.
许多抗癌药物可使细胞停滞于细胞周期的G2期，随后通过凋亡诱导细胞死亡。当前实验确定了中国仓鼠卵巢CHO/UV41细胞在用顺铂孵育后发生的一系列详细事件。同步化的CHO/UV41细胞在S期早期受到顺铂损伤。细胞以正常速率通过S期，但停滞于G2期。停滞的细胞以完全磷酸化的无活性形式表现出正常水平的有丝分裂促进激酶p34cdc2。经过长时间的停滞，细胞使p34cdc2去磷酸化，并经历异常的有丝分裂和胞质分裂，其中由于多极有丝分裂纺锤体的形成，染色体不等分离。这些细胞随后失去与细胞外基质的接触，然后才以凋亡特征性的方式消化其DNA。向停滞于G2期的细胞中添加咖啡因可显著加速这一系列事件，咖啡因诱导p34cdc2去磷酸化并通过异常有丝分裂。此前有人提出，蛋白质合成是咖啡因诱导的过早有丝分裂和凋亡所必需的。然而，当在G2期添加时，环己酰亚胺既不能抑制咖啡因诱导的有丝分裂，也不能抑制凋亡。只有在S期添加环己酰亚胺，在有丝分裂所需蛋白质完全合成之前，才会出现抑制作用。这些结果表明，在这个模型中，被认为参与凋亡的蛋白质是正常细胞周期进程所需的蛋白质。据推测，DNA消化是由于源自细胞外基质的信号转导丧失所致，但导致细胞黏附丧失的早期事件对于凋亡的诱导至关重要。
