Brumatti G, Yon M, Castro F A, Bueno-da-Silva A E B, Jacysyn J F, Brunner T, Amarante-Mendes G P
Departamento de Imunologia, Instituto de Ciências Biomédicas, Universidade de São Paulo, Brazil; Instituto de Investigação em Imunologia, Institutos do Milênio, Brazil.
Exp Cell Res. 2008 Feb 1;314(3):554-63. doi: 10.1016/j.yexcr.2007.11.003. Epub 2007 Nov 17.
CD95 (Fas/Apo-1)-mediated apoptosis was shown to occur through two distinct pathways. One involves a direct activation of caspase-3 by large amounts of caspase-8 generated at the DISC (Type I cells). The other is related to the cleavage of Bid by low concentration of caspase-8, leading to the release of cytochrome c from mitochondria and the activation of caspase-3 by the cytochrome c/APAF-1/caspase-9 apoptosome (Type II cells). It is also known that the protein synthesis inhibitor cycloheximide (CHX) sensitizes Type I cells to CD95-mediated apoptosis, but it remains contradictory whether this effect also occurs in Type II cells. Here, we show that sub-lethal doses of CHX render both Type I and Type II cells sensitive to the apoptogenic effect of anti-CD95 antibodies but not to chemotherapeutic drugs. Moreover, Bcl-2-positive Type II cells become strongly sensitive to CD95-mediated apoptosis by the addition of CHX to the cell culture. This is not the result of a restraint of the anti-apoptotic effect of Bcl-2 at the mitochondrial level since CHX-treated Type II cells still retain their resistance to chemotherapeutic drugs. Therefore, CHX treatment is granting the CD95-mediated pathway the ability to bypass the mitochondria requirement to apoptosis, much alike to what is observed in Type I cells.
CD95（Fas/Apo-1）介导的细胞凋亡通过两条不同途径发生。一条途径涉及在死亡诱导信号复合物（DISC，I型细胞）处大量生成的半胱天冬酶-8直接激活半胱天冬酶-3。另一条途径与低浓度半胱天冬酶-8切割Bid有关，导致细胞色素c从线粒体释放，并通过细胞色素c/凋亡蛋白酶激活因子-1/半胱天冬酶-9凋亡小体激活半胱天冬酶-3（II型细胞）。还已知蛋白质合成抑制剂放线菌酮（CHX）使I型细胞对CD95介导的细胞凋亡敏感，但这种效应在II型细胞中是否也会发生仍存在矛盾。在此，我们表明亚致死剂量的CHX使I型和II型细胞对抗CD95抗体的凋亡诱导作用敏感，但对化疗药物不敏感。此外，通过在细胞培养中添加CHX，Bcl-2阳性的II型细胞对CD95介导的细胞凋亡变得高度敏感。这不是Bcl-2在线粒体水平的抗凋亡作用受到抑制的结果，因为用CHX处理的II型细胞仍保留对化疗药物的抗性。因此，CHX处理赋予CD95介导的途径绕过细胞凋亡对线粒体需求的能力，这与在I型细胞中观察到的情况非常相似。
