Nakajima Wataru, Sharma Kanika, Lee June Young, Maxim Nicolas T, Hicks Mark A, Vu Thien-Trang, Luu Angela, Yeudall W Andrew, Tanaka Nobuyuki, Harada Hisashi
Phillips Institute for Oral Health Research, School of Dentistry, Massey Cancer Center, Virginia Commonwealth University, Richmond, Virginia, USA.
Department of Molecular Oncology, Institute for Advanced Medical Sciences, Nippon Medical School, Kawasaki, Japan.
Oncotarget. 2016 Jun 14;7(24):36353-36365. doi: 10.18632/oncotarget.9217.
Noxa, a BH3-only pro-apoptotic BCL-2 family protein, causes apoptosis by specifically interacting with the anti-apoptotic protein MCL-1 to induce its proteasome-mediated degradation. We show here that the DNA damaging agents cisplatin and etoposide upregulate Noxa expression, which is required for the phosphorylation of MCL-1 at Ser64/Thr70 sites, proteasome-dependent degradation, and apoptosis. Noxa-induced MCL-1 phosphorylation at these sites occurs at the mitochondria and is primarily regulated by CDK2. MCL-1 and CDK2 form a stable complex and Noxa binds to this complex to facilitate the phosphorylation of MCL-1. When Ser64 and Thr70 of MCL-1 are substituted with alanine, the mutated MCL-1 is neither phosphorylated nor ubiquitinated, and becomes more stable than the wild-type protein. As a consequence, this mutant can inhibit apoptosis induced by Noxa overexpression or cisplatin treatment. These results indicate that Noxa-mediated MCL-1 phosphorylation followed by MCL-1 degradation is critical for apoptosis induced by DNA damaging agents through regulation of the Noxa/MCL-1/CDK2 complex.
Noxa是一种仅含BH3结构域的促凋亡BCL-2家族蛋白，它通过与抗凋亡蛋白MCL-1特异性相互作用，诱导其经蛋白酶体介导的降解，从而引发细胞凋亡。我们在此表明，DNA损伤剂顺铂和依托泊苷上调Noxa表达，这是MCL-1在Ser64/Thr70位点磷酸化、蛋白酶体依赖性降解及细胞凋亡所必需的。Noxa诱导的MCL-1在这些位点的磷酸化发生在线粒体，且主要受CDK2调控。MCL-1与CDK2形成稳定复合物，Noxa与该复合物结合以促进MCL-1的磷酸化。当MCL-1的Ser64和Thr70被丙氨酸取代时，突变的MCL-1既不发生磷酸化也不发生泛素化，且比野生型蛋白更稳定。因此，该突变体可抑制Noxa过表达或顺铂处理诱导的细胞凋亡。这些结果表明，Noxa介导的MCL-1磷酸化继而MCL-1降解，通过调控Noxa/MCL-1/CDK2复合物，对DNA损伤剂诱导的细胞凋亡至关重要。
