Tang D, Kidd V J
Department of Tumor Cell Biology, St. Jude Children's Research Hospital, Memphis, Tennessee 38101, USA.
J Biol Chem. 1998 Oct 30;273(44):28549-52. doi: 10.1074/jbc.273.44.28549.
Apoptosis involves the proteolysis of specific cellular proteins by a group of cysteine proteases known as caspases. Many of these cellular targets are either functionally inactivated (e.g. poly(ADP-ribose) polymerase) or activated (e.g. other caspases, gelsolin) by such processing, thereby facilitating the cell death process. Caspase 3 is involved in the processing of many of these proteins. Recently, however, it was reported that caspase 3 is dispensable for the cleavage of a large number of cellular caspase substrates during apoptosis. Among these substrates is DFF-45/ICAD, a subunit of the heterodimeric DNA fragmentation factor (DFF), otherwise known as caspase-activated DNase (CAD), that mediates genomic DNA degradation during apoptosis. Conversely, others have reported that caspase 3 is essential for the cleavage and activation of DFF-45/ICAD. To resolve this controversy we examined DFF-45/ICAD processing during apoptosis in MCF-7 breast carcinoma cells that lack functional caspase 3 and in MCF-7 cells expressing caspase 3. We found that DFF-45/ICAD is cleaved by two distinct caspases, one of which is caspase 3. Furthermore, cleavage of the carboxyl-terminal region of DFF-45/ICAD, which is necessary for activation of the enzyme, requires functional caspase 3. In the absence of caspase 3 cleavage of the amino-terminal region of DFF-45/ICAD by another caspase occurs, but the DFF-45 enzyme remains inactive.
细胞凋亡涉及一组被称为半胱天冬酶的半胱氨酸蛋白酶对特定细胞蛋白的蛋白水解作用。这些细胞靶点中的许多通过这种加工过程要么功能失活（如聚（ADP - 核糖）聚合酶），要么被激活（如其他半胱天冬酶、凝溶胶蛋白），从而促进细胞死亡过程。半胱天冬酶3参与了许多这些蛋白的加工过程。然而，最近有报道称，在细胞凋亡过程中，半胱天冬酶3对于大量细胞半胱天冬酶底物的切割并非必需。这些底物中包括DFF - 45/ICAD，它是异二聚体DNA片段化因子（DFF）的一个亚基，也被称为半胱天冬酶激活的脱氧核糖核酸酶（CAD），在细胞凋亡过程中介导基因组DNA的降解。相反，其他人报道半胱天冬酶3对于DFF - 45/ICAD的切割和激活至关重要。为了解决这一争议，我们研究了在缺乏功能性半胱天冬酶3的MCF - 乳腺癌细胞以及表达半胱天冬酶3的MCF - 细胞凋亡过程中DFF - 45/ICAD的加工情况。我们发现DFF - 45/ICAD被两种不同的半胱天冬酶切割，其中一种是半胱天冬酶3。此外，DFF - 45/ICAD羧基末端区域的切割是该酶激活所必需的，这需要功能性的半胱天冬酶3。在没有半胱天冬酶3的情况下，另一种半胱天冬酶会对DFF - 45/ICAD的氨基末端区域进行切割，但DFF - 45酶仍保持无活性。
