Department of Molecular Biology, Institute of Biochemistry and Molecular Biology, Semmelweis University, 1083 Budapest, Hungary.
Faculty of Information Technology and Bionics, Pázmány Péter Catholic University, 1083 Budapest, Hungary.
Biomolecules. 2022 Oct 28;12(11):1587. doi: 10.3390/biom12111587.
Autophagy-dependent cellular survival is tightly regulated by both kinases and phosphatases. While mTORC1 inhibits autophagy by phosphorylating ULK1, PP2A is able to remove this phosphate group from ULK1 and promotes the key inducer of autophagosome formation. However, ULK1 inhibits mTORC1, mTORC1 is able to down-regulate PP2A. In addition, the active ULK1 promotes PP2A via phosphorylation. We claim that these double-negative (mTORC1 -| PP2A -| mTORC1, mTORC1 -| ULK1 -| mTORC1) and positive (ULK1 -> PP2A -> ULK1) feedback loops are all necessary for the robust, irreversible decision making process between the autophagy and non-autophagy states. We approach our scientific analysis from a systems biological perspective by applying both theoretical and molecular biological techniques. For molecular biological experiments, HEK293T cell line is used, meanwhile the dynamical features of the regulatory network are described by mathematical modelling. In our study, we explore the dynamical characteristic of mTORC1-ULK1-PP2A regulatory triangle in detail supposing that the positive feedback loops are essential to manage a robust cellular answer upon various cellular stress events (such as mTORC1 inhibition, starvation, PP2A inhibition or ULK1 silencing). We confirm that active ULK1 can up-regulate PP2A when mTORC1 is inactivated. By using theoretical analysis, we explain the importance of cellular PP2A level in stress response mechanism. We proved both experimentally and theoretically that PP2A down-regulation (via addition of okadaic acid) might generate a periodic repeat of autophagy induction. Understanding how the regulation of the cell survival occurs with the precise molecular balance of ULK1-mTORC1-PP2A in autophagy, is highly relevant in several cellular stress-related diseases (such as neurodegenerative diseases or diabetes) and might help to promote advanced therapies in the near future, too.
自噬依赖性细胞存活受到激酶和磷酸酶的严格调控。虽然 mTORC1 通过磷酸化 ULK1 来抑制自噬，但 PP2A 能够从 ULK1 上去除这个磷酸基团，并促进自噬体形成的关键诱导剂。然而，ULK1 抑制 mTORC1，mTORC1 能够下调 PP2A。此外，活性 ULK1 通过磷酸化促进 PP2A。我们声称，这些双阴性（mTORC1 -| PP2A -| mTORC1，mTORC1 -| ULK1 -| mTORC1）和阳性（ULK1 -> PP2A -> ULK1）反馈回路对于自噬和非自噬状态之间的强、不可逆决策过程都是必要的。我们从系统生物学的角度来进行科学分析，同时运用理论和分子生物学技术。对于分子生物学实验，我们使用 HEK293T 细胞系，同时用数学建模来描述调控网络的动态特征。在我们的研究中，我们详细探讨了 mTORC1-ULK1-PP2A 调控三角的动态特征，假设阳性反馈回路对于管理各种细胞应激事件（如 mTORC1 抑制、饥饿、PP2A 抑制或 ULK1 沉默）下的强大细胞反应是必要的。我们证实，当 mTORC1 失活时，活性 ULK1 可以上调 PP2A。通过理论分析，我们解释了细胞内 PP2A 水平在应激反应机制中的重要性。我们通过实验和理论证明，PP2A 的下调（通过添加 okadaic acid）可能会产生自噬诱导的周期性重复。了解细胞存活的调控如何通过 ULK1-mTORC1-PP2A 在自噬中的精确分子平衡来发生，对于几种与细胞应激相关的疾病（如神经退行性疾病或糖尿病）具有重要意义，并且可能有助于在不久的将来促进先进的治疗方法。
