Department of Neurobiology, Gifu University Graduate School of Medicine, Yanagido, Gifu, Japan.
Department of Anatomy School of Medicine, University of Occupational and Environmental Health, Iseigaoka, Fukuoka, Japan.
PLoS One. 2019 Jul 22;14(7):e0219782. doi: 10.1371/journal.pone.0219782. eCollection 2019.
Apoptotic protease-activating factor 1 (Apaf-1) is a component of apoptosome, which regulates caspase-9 activity. In addition to apoptosis, Apaf-1 plays critical roles in the intra-S-phase checkpoint; therefore, impaired expression of Apaf-1 has been demonstrated in chemotherapy-resistant malignant melanoma and nuclear translocation of Apaf-1 has represented a favorable prognosis of patients with non-small cell lung cancer. In contrast, increased levels of Apaf-1 protein are observed in the brain in Huntington's disease. The regulation of Apaf-1 protein is not yet fully understood. In this study, we show that etoposide triggers the interaction of Apaf-1 with Cullin-4B, resulting in enhanced Apaf-1 ubiquitination. Ubiquitinated Apaf-1, which was degraded in healthy cells, binds p62 and forms aggregates in the cytosol. This complex of ubiquitinated Apaf-1 and p62 induces caspase-9 activation following MG132 treatment of HEK293T cells that stably express bcl-xl. These results show that ubiquitinated Apaf-1 may activate caspase-9 under conditions of proteasome impairment.
凋亡蛋白酶激活因子 1（Apaf-1）是凋亡体的一个组成部分，调节半胱氨酸蛋白酶-9 的活性。除了凋亡作用外，Apaf-1 在细胞内 S 期检查点中也起着关键作用；因此，在化疗耐药的恶性黑色素瘤中已证明 Apaf-1 的表达受损，而 Apaf-1 的核转位则代表非小细胞肺癌患者的预后良好。相反，在亨廷顿病的大脑中观察到 Apaf-1 蛋白水平增加。Apaf-1 蛋白的调节尚未完全了解。在这项研究中，我们表明依托泊苷触发 Apaf-1 与 Cullin-4B 的相互作用，导致 Apaf-1 泛素化增强。在健康细胞中被降解的泛素化 Apaf-1 与 p62 结合并在细胞质中形成聚集体。这种泛素化 Apaf-1 和 p62 的复合物在稳定表达 bcl-xl 的 HEK293T 细胞用 MG132 处理后诱导半胱氨酸蛋白酶-9 的激活。这些结果表明，在蛋白酶体受损的情况下，泛素化的 Apaf-1 可能激活半胱氨酸蛋白酶-9。
