In chronic injury, aberrant activation of PI3K/Akt signaling can lead to uncontrolled cell growth, proliferation, metabolism, and transition of human pleural mesothelial cells (HPMCs) transition into myofibroblasts, thus, directly contributing to the progression of pleural fibrosis. Downstream of PI3K/Akt signaling is mTORC1 which activates the translational regulators; S6 Kinase (S6K1/2) and eIF4F. We have shown that inhibiting mTORC1 paradoxically enhanced Akt activation (Thr308 and Ser473) and this may lead to sustained activation of PI3K/Akt/mTOR signaling and myofibroblast abundance. More so, reports show that therapeutically targeting mTORC1 in diverse diseases with rapamycin and its derivatives may have cell-specific adverse effects, which could complicate their use. To investigate the role of mTORC1 and effectors, such as S6K, in regulating TGF-β-induced PI3K/Akt signaling, we utilized inhibitors targeting mTORC1/S6K and siRNA targeting S6K to access cellular processes by qPCR, western blotting, confocal microscopy, and M7 pulldown assays in HPMCs. Our data indicates that mTOR regulates TGF-β-induced PI3K/Akt signaling via S6K. Also, we find that S6K’s function as a kinase is important in the negative regulation of TGFβ signaling in HPMCs. S6K2 may play other roles independent of its kinase activity. S6K inhibition enhanced cap-dependent translation and activated the profibrotic mTORC2 pathway in HPMCs. These results may explain the decreased efficacy associated with PI3K/mTOR signal-targeted therapeutics.

Date of publication

Spring 5-2024

Document Type

Thesis (Local Only Access)



Persistent identifier


Committee members

Dr. Vijay Rao, Dr. Guoqing Qian, Dr. Osamu Sato, Dr. Amy Tvinnereim


Master of Science, Biotechnology