a Department of Biochemistry and Molecular Biology , College of Basic Medical Sciences, Third Military Medical University , Chongqing, China.
b Battalion 17 of Students , College of Preventive Medicine, Third Military Medical University , Chongqing, China.
Autophagy. 2018;14(4):685-701. doi: 10.1080/15548627.2017.1407887. Epub 2018 Jan 29.
Phosphorylation is a major type of post-translational modification, which can influence the cellular physiological function. ATG4B, a key macroautophagy/autophagy-related protein, has a potential effect on the survival of tumor cells. However, the role of ATG4B phosphorylation in cancers is still unknown. In this study, we identified a novel phosphorylation site at Ser34 of ATG4B induced by AKT in HCC cells. The phosphorylation of ATG4B at Ser34 had little effect on autophagic flux, but promoted the Warburg effect including the increase of L-lactate production and glucose consumption, and the decrease of oxygen consumption in HCC cells. The Ser34 phosphorylation of ATG4B also contributed to the impairment of mitochondrial activity including the inhibition of FFo-ATP synthase activity and the elevation of mitochondrial ROS in HCC cells. Moreover, the phosphorylation of ATG4B at Ser34 enhanced its mitochondrial location and the subsequent colocalization with FFo-ATP synthase in HCC cells. Furthermore, recombinant human ATG4B protein suppressed the activity of FFo-ATP synthase in MgATP submitochondrial particles from patient-derived HCC tissues in vitro. In brief, our results demonstrate for the first time that the phosphorylation of ATG4B at Ser34 participates in the metabolic reprogramming of HCC cells via repressing mitochondrial function, which possibly results from the Ser34 phosphorylation-induced mitochondrial enrichment of ATG4B and the subsequent inhibition of FFo-ATP synthase activity. Our findings reveal a noncanonical working pattern of ATG4B under pathological conditions, which may provide a scientific basis for developing novel strategies for HCC treatment by targeting ATG4B and its Ser34 phosphorylation.
磷酸化是一种主要的翻译后修饰类型，可影响细胞的生理功能。ATG4B 是一种关键的巨自噬/自噬相关蛋白，对肿瘤细胞的存活有潜在影响。然而，ATG4B 磷酸化在癌症中的作用尚不清楚。在这项研究中，我们在 HCC 细胞中鉴定出一种由 AKT 诱导的 ATG4B 丝氨酸 34 位的新磷酸化位点。ATG4B 丝氨酸 34 位的磷酸化对自噬通量影响不大，但能促进沃伯格效应，包括 L-乳酸生成和葡萄糖消耗增加，以及 HCC 细胞耗氧量降低。ATG4B 的 Ser34 磷酸化也有助于损害线粒体活性，包括抑制 FFo-ATP 合酶活性和增加 HCC 细胞中线粒体 ROS。此外，ATG4B 的 Ser34 磷酸化增强了其在线粒体中的定位，并随后与 HCC 细胞中的 FFo-ATP 合酶发生共定位。此外，重组人 ATG4B 蛋白在体外抑制了来自患者源性 HCC 组织的线粒体亚颗粒中 FFo-ATP 合酶的活性。总之，我们的研究结果首次证明，ATG4B 的 Ser34 磷酸化通过抑制线粒体功能参与 HCC 细胞的代谢重编程，这可能是由于 Ser34 磷酸化诱导的 ATG4B 在线粒体中的富集以及随后抑制 FFo-ATP 合酶活性所致。我们的研究结果揭示了病理条件下 ATG4B 的非典型作用模式，这可能为通过靶向 ATG4B 及其 Ser34 磷酸化来开发治疗 HCC 的新策略提供科学依据。
