自噬相关蛋白Atg4B通过偶联Bcl-2蛋白家族促进膀胱癌细胞线粒体凋亡的机制研究

Autophagy and apoptosis constitute important determinants of cell fate and engage in a complex interplay in both physiological and pathological settings. The molecular basis of this crosstalk is poorly understood. Here, we identify the essential autophagy protein Atg4B as a positive mediator of mitochondrial apoptosis and show that Atg4B directly regulates the apoptotic pathway by binding and inactivating prosurvival Bcl-2 family members, including Bcl-2 and Mcl-1. In apoptotic cells, knockdown of Atg4B inhibited Bax activation and cytochrome c release, while ectopic expression of Atg4B antagonized the antiapoptotic activity of Mcl-1. This study suggests that while the free Atg4B coupled Bcl-2 protein family which induced mitochondrial apoptosis, structure of Atg4B would also change, which weaken Atg4B enzyme activity and inhibited the progress of autophagy. The interaction between Atg4B and Bcl-2 family members may thus constitute an important point of convergence between autophagy and apoptosis.

细胞自噬和凋亡的交叉串扰作用对肿瘤发展产生复杂影响，但其调控机制远未明确。本项目组首次发现自噬的核心蛋白Atg4B可激活膀胱癌细胞线粒体凋亡。但是，目前已有的Atg4B通过保护性自噬促细胞生存的理论，无法解释该现象。而进一步的蛋白质构象预测及免疫共沉淀联合质谱分析，均表明Atg4B可通过竞争性偶联Bcl-2蛋白家族Bcl-2及Mcl-1，释放促凋亡蛋白，从而诱发了线粒体凋亡途径。据此本项目提出“游离型Atg4B偶联Bcl-2蛋白家族后，在启动线粒体凋亡的同时，Atg4B的空间结构也将发生改变，削弱了Atg4B的酶切活性，阻碍自噬过程的进展”的科学设想，以明确①Atg4B-Bcl-2蛋白家族复合体理论模型是否可行；②该蛋白复合体与游离型Atg4B的动态平衡关系是否为决定细胞自噬-凋亡交互作用的关键。这为后续拓展自噬-凋亡交互作用的新机制奠定基础。