Tuberous sclerosis complex 2 loss-of-function mutation regulates reactive oxygen species production through Rac1
Tsukasa Suzuki1, Swadesh K Das, Hirohumi Inoue
1Department of Applied Biology and Chemistry, Tokyo University of Agriculture, 1-1-1 Sakuragaoka, Setagaya-ku, Tokyo 156-8502, Japan.
Abstract:
The products of the TSC1 (hamartin) and TCS2 (tuberin) tumor suppressor genes negatively regulate cell growth by inhibiting mTOR signaling. Recent research has led to the postulation that tuberin and/or hamartin are involved in tumor migration, presumably through Rho activation. Here we show that LEF-8 cells, which contain a Y1571 missense mutation in tuberin, express higher Rac1 activity than tuberin negative and positive cells. We also provide evidence of obvious lamellipodia formation in LEF-8 cells. Since the production of TSC2(Y1571H) cannot form a hetero-complex with hamartin, we further analyzed another mutant, TSC2(R611Q), which also lacks the ability to form a complex with hamartin. Introducing both forms of mutated TSC2 into COS-1 cells increased Rac1 activity as well as cell motility. We also found these two mutants interacted with Rac1. We further demonstrated that the introduction of mutated TSC2 into COS-1 cells can generate higher reactive oxygen species (ROS). These results indicate that loss-of-function mutated tuberin can activate Rac1 and thereby increase ROS production.
Insights
Loss-of-function mutations in tuberin (TSC2) activate Rac1, a protein involved in cell migration. This activation also leads to increased reactive oxygen species (ROS) production, suggesting a novel role for tuberin in tumor progression.
Area of Science:
- Cell Biology
- Oncology
- Molecular Genetics
Background:
- The TSC1 (hamartin) and TSC2 (tuberin) tumor suppressor genes normally inhibit cell growth by suppressing mTOR signaling.
- Emerging evidence suggests tuberin and/or hamartin play roles in tumor cell migration, potentially via Rho GTPase activation.
Purpose of the Study:
- To investigate the role of tuberin mutations in cell migration and Rac1 activity.
- To explore the impact of non-complex-forming tuberin mutants on Rac1 activation and reactive oxygen species (ROS) production.
Main Methods:
- Analysis of Rac1 activity in LEF-8 cells with a tuberin Y1571 missense mutation.
- Introduction of TSC2 mutants (Y1571H and R611Q), unable to form hamartin complexes, into COS-1 cells.
- Assessment of cell motility, Rac1 interaction, and ROS generation in transfected cells.
Main Results:
- LEF-8 cells with mutated tuberin exhibited elevated Rac1 activity and lamellipodia formation.
- Introduction of TSC2 mutants (Y1571H, R611Q) into COS-1 cells increased Rac1 activity, cell motility, and interaction with Rac1.
- Mutated TSC2 expression led to increased reactive oxygen species (ROS) production.
Conclusions:
- Loss-of-function mutations in tuberin can lead to constitutive Rac1 activation.
- Activated Rac1, downstream of mutated tuberin, contributes to increased cell motility and ROS production.
- These findings suggest a mechanism by which tuberin dysfunction promotes tumor cell migration and potentially other oncogenic processes.
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