PhD Scientific Days 2021

MO_III_L: Molecular Sciences III. Lectures

The Systems Biological Analysis of PP2A-ULK1-mTOR Regulatory Triangle

Text of the abstract

Introduction: The autophagy is tightly regulated by kinases and phosphatases. mTOR inhibits autophagy by phosphorylating ULK1, the key inducer of autophagosome formation, meanwhile PP2A removes this phosphate group from ULK1 and promotes its activation. However, the active ULK1 can inhibit mTOR and mTOR is able to down-regulate PP2A. These double-negative feedback loops are essential for the proper working of the regulatory system.
Aims: We claim that there is a positive feedback loop between ULK1 and PP2A, namely not only PP2A activates ULK1 but ULK1 is able to activate PP2A, too. Besides the double-negative feedback loops of the PP2A-ULK1-mTOR system this connection is also necessary for the robust, irreversible decision making process between the autophagy and non-autophagy states.
Method: We approach our scientific analysis from a systems biological perspective by using both theoretical and molecular biological techniques. For molecular biological experiments, HEK293T cell line is used, meanwhile the dynamical characteristic of the regulatory network is described by mathematical modelling.
Results: In our study, we suppose that the positive feedback loop between ULK1 and PP2A is essential to manage a robust cellular answer upon various cellular stress (such as mTOR inhibition or starvation). We explore the dynamical role of PP2A in the regulatory network both experimentally and theoretically claiming that the presence of a regulated phosphatase makes the system even more robust with response to cellular stress. We confirm that the active ULK1 can up-regulate PP2A when mTOR is inactivated by rapamycin treatment or starvation. We identify one or more ULK1-dependent phosphorylation sites on both regulatory and catalytic subunit of PP2A using GPS 5.0. Thus, we suggest that ULK1 can activate PP2A by phosphorylation but it needs further investigation.
Conclusion: Understanding how the regulation of the cell survival occurs with the precise molecular balance of ULK1-mTOR-AMPK 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.
Funding: Supported by the ÚNKP-20-4-I-SE-32 New National Excellence Program of the Ministry for Innovation and Technology from the source of the National Research, Development and Innovation Fund.

University and Doctoral School

Semmelweis University, Doctoral School of Molecular Medicine