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Tuberin, the tuberous sclerosis complex 2 tumor suppressor gene product, regulates Rho activation, cell adhesion and
Aristotelis Astrinidis1, Timothy P Cash, Deborah S Hunter
1Fox Chase Cancer Center, 7701 Burholme Avenue, Philadelphia, Pennsylvania, PA 19111, USA.
Abstract:
Tuberous sclerosis complex (TSC) is a tumor suppressor gene syndrome characterized by seizures, mental retardation, autism, and tumors of the brain, kidney, heart, retina, and skin. TSC is caused by mutations in either TSC1 or TSC2, both of which are tumor suppressor genes. Hamartin, the protein product of TSC1, was found to interact with the ezrin-radixin-moesin family of cytoskeletal proteins and to activate the small GTPase Rho. To determine whether tuberin, the TSC2 product, can also activate Rho, we stably expressed full-length human tuberin in two cell types: MDCK cells and ELT3 cells. ELT3 cells lack endogenous tuberin expression. We found that expression of human tuberin in both MDCK and ELT3 cells was associated with an increase in the amount of Rho-GTP, but not in Rac1-GTP or cdc42-GTP. Tuberin expression increased cell adhesion in both cell types, and decreased chemotactic cell migration in ELT3 cells. In MDCK cells, there was a decrease in the amount of total Focal Adhesion Kinase (FAK) and an increase in the fraction of phosphorylated FAK. These findings demonstrate for the first time that tuberin activates Rho and regulates cell adhesion and migration. Pathways involving Rho activation may have relevance to the clinical manifestations of TSC, including pulmonary lymphangioleiomyomatosis.
Insights
Tuberous sclerosis complex (TSC) is linked to mutations in TSC1 or TSC2. This study shows tuberin, the TSC2 protein, activates Rho, influencing cell adhesion and migration, potentially explaining TSC
Area of Science:
- Cell Biology
- Genetics
- Biochemistry
Background:
- Tuberous sclerosis complex (TSC) is a genetic disorder caused by mutations in tumor suppressor genes TSC1 or TSC2.
- The TSC1 protein, hamartin, interacts with cytoskeletal proteins and activates the small GTPase Rho.
- The function of the TSC2 protein, tuberin, in Rho activation was previously unknown.
Purpose of the Study:
- To investigate whether tuberin (TSC2 product) can activate Rho.
- To determine the effects of tuberin expression on cell adhesion and migration.
- To explore the role of tuberin in cellular signaling pathways relevant to TSC.
Main Methods:
- Stable expression of full-length human tuberin in MDCK and ELT3 cells (lacking endogenous tuberin).
- Analysis of Rho, Rac1, and cdc42 GTP-bound forms using GTPase assays.
- Assessment of cell adhesion and chemotactic migration.
- Measurement of Focal Adhesion Kinase (FAK) total and phosphorylated levels.
Main Results:
- Tuberin expression increased Rho-GTP levels in both cell types, without affecting Rac1 or cdc42.
- Tuberin expression enhanced cell adhesion in MDCK and ELT3 cells.
- Tuberin expression reduced chemotactic cell migration in ELT3 cells.
- In MDCK cells, tuberin expression altered Focal Adhesion Kinase (FAK) phosphorylation and total levels.
Conclusions:
- Tuberin activates the small GTPase Rho.
- Tuberin regulates cell adhesion and migration.
- Rho signaling pathways may be implicated in the clinical features of tuberous sclerosis complex, such as pulmonary lymphangioleiomyomatosis.