Wilhelm S, Wagner H, Häcker G
Institut für Medizinische Mikrobiologie, Immunologie und Hygiene, Technische Universität München, Germany.
Eur J Immunol. 1998 Mar;28(3):891-900. doi: 10.1002/(SICI)1521-4141(199803)28:03<891::AID-IMMU891>3.0.CO;2-X.
The activation of the caspase family of cysteine proteases is a key step in the implementation of apoptotic cell death leading to further downstream effects such as DNA fragmentation. In cultured tumor cells, caspase activity appears only when cells are undergoing apoptosis. Here we show that human and murine T lymphocytes acquire high intracellular activities of cell death-specific caspases upon activation by mitogens and IL-2 without evidence that apoptosis is proceeding. The highest activity is seen when cells are mitogen activated for 3 days. On a per cell basis, caspase activity in activated T cells is much higher than in tumor cells induced to undergo apoptosis. In the presence of exogenously added IL-2 cells stay alive and maintain a high level of caspase activity while IL-2 withdrawal results in cell death and decline of caspase activity. Caspase activity can also be measured in extracts from spleen and lymph nodes from mice injected with superantigen. While in tumor cell lines caspase activity correlates with cleavage of poly(ADP)-ribose polymerase (PARP) and DNA fragmentation, in activated T cells cleavage products of cellular PARP can be detected whereas DNA fragmenting activity appears only upon IL-2 withdrawal which coincides with cell death. These data show that caspase activation in intact cells does not necessarily lead to cell death and argue for a checkpoint in the apoptotic pathway downstream of caspases. Furthermore, they provide a molecular correlate for the high susceptibility of activated T cells for apoptosis.
半胱氨酸蛋白酶家族的激活是凋亡性细胞死亡过程中的关键步骤，会导致进一步的下游效应，如DNA片段化。在培养的肿瘤细胞中，半胱天冬酶活性仅在细胞发生凋亡时出现。在此我们表明，人类和小鼠T淋巴细胞在被丝裂原和白细胞介素-2激活后，细胞内会出现高活性的细胞死亡特异性半胱天冬酶，但没有证据表明细胞正在进行凋亡。当细胞被丝裂原激活3天时，半胱天冬酶活性最高。以单个细胞计算，激活的T细胞中的半胱天冬酶活性远高于诱导凋亡的肿瘤细胞。在外源添加白细胞介素-2的情况下，细胞存活并维持高水平的半胱天冬酶活性，而撤除白细胞介素-2则导致细胞死亡和半胱天冬酶活性下降。半胱天冬酶活性也可以在注射超抗原的小鼠的脾脏和淋巴结提取物中检测到。在肿瘤细胞系中，半胱天冬酶活性与聚（ADP）-核糖聚合酶（PARP）的裂解和DNA片段化相关，而在激活的T细胞中可以检测到细胞PARP的裂解产物，而DNA片段化活性仅在撤除白细胞介素-2时出现，这与细胞死亡同时发生。这些数据表明，完整细胞中的半胱天冬酶激活不一定导致细胞死亡，并支持在半胱天冬酶下游的凋亡途径中存在一个检查点。此外，它们为激活的T细胞对凋亡的高度敏感性提供了分子关联。
