Tuberin, the tuberous sclerosis complex 2 tumor suppressor gene product, regulates Rho activation, cell adhesion and migration

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.

Mechanism of Akt1 inhibition of breast cancer cell invasion reveals a protumorigenic role for TSC2

“…In many systems, Akt1 has been shown to phosphorylate TSC2, triggering 14-3-3-dependent proteolytic degradation (16,19). Moreover, elevated TSC2 and TSC1 have been shown to increase Rho activity in epithelial Madin-Darby canine kidney cells (15) and in fibroblasts (47), respectively. Accordingly, we hypothesized that Akt1-mediated inhibition of Rho activity was the consequence of phosphorylation and downmodulation of TSC2.…”

“…Although it has been best characterized as a controller of cell size through its regulation of ribosomal synthesis proteins including ribosomal S6 kinase (17,18), TSC2 has been implicated in a number of related signaling pathways in a variety of cell types (19). Investigations of Madin-Darby canine kidney epithelial cells demonstrated that overexpression of TSC2 results in activation of Rho and increased cellular motility (15), and analysis of TSC2-deficient cells has shown reduced Rho activity (16), although these effects may depend on the cell type investigated (20). Although mutational inactivation of TSC2 contributes to tuberous sclerosis complex, regulation of intact TSC2 occurs principally through the action of the serine͞threonine kinase Akt1͞protein kinase B (21,22).…”

“…Inhibition of Rho or its effector Rho-kinase (ROCK) significantly compromises cellular migration and invasiveness (5)(6)(7)(8)(9)(10), and increased expression͞activation of Rho and its isoforms has been found in many types of cancers (11)(12)(13)(14). A recently discovered mechanism for activating Rho in epithelial cells involves the tuberous sclerosis complex 2 gene product, TSC2 (15).…”

Tuberous sclerosis complex: linking growth and energy signaling pathways with human disease

“…Both hamartin and tuberin activate members of the Rho GTPase superfamily, which regulate the actin cytoskeleton, cell morphology and migration, and induce focal adhesions (Lamb et al, 2000;Astrinidis et al, 2002;Goncharova et al, 2004). Tuberin-deficient smooth muscle cells exhibit increased migration in vitro, compared to cells with reintroduction of wild-type tuberin, and decreased RhoA-GTP (Astrinidis et al, 2002). Tuberin expression increases the in vitro attachment of cells on plastic, consistent with decreased expression of focal adhesion kinase (FAK) and increase in the fraction of phospho-FAK (Astrinidis et al, 2002).…”

mTOR Activation, Lymphangiogenesis, and Estrogen-Mediated Cell Survival: The “Perfect Storm” of Pro-Metastatic Factors in LAM Pathogenesis

“…16 We found that cells lacking Tsc2 have lower levels of Rho activity, enhanced chemotactic cell migration, and decreased cell adhesion. 17 Goncharova et al 18,19 found that TSC2 regulates cell migration and impacts the activity of both Rac and Rho. Interestingly, they found that the N-terminus of TSC2 was sufficient to inhibit cell migration and activate Rac1, suggesting that this is independent of the GTPase-activiating protein (GAP) activity of tuberin and independent of Rheb.…”