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Phosphatidylinositol 3-kinase but not tuberin is required for PDGF-induced cell migration
Carla Irani1, Elena A Goncharova, Deborah S Hunter
1Pulmonary, Allergy, and Critical Care Division, Department of Medicine, University of Pennsylvania, 421 Curie Blvd., Philadelphia, PA 19104, USA.
Abstract:
The loss of function of the tumor suppressor gene TSC2 and its protein product tuberin promotes the development of benign lesions by stimulating cell growth, although the role of tuberin in regulating cell migration and metastasis has not been characterized. In addition, the role of phosphatidylinositol 3-kinase (PI 3-kinase), an important signaling event regulating cell migration, in modulating tuberin-deficient cell motility remains unknown. Using a tuberin-deficient rat smooth muscle cell line, ELT3, we demonstrate that platelet-derived growth factor (PDGF) stimulates cell migration by 3.2-fold, whereas vascular endothelial growth factor (VEGF), transforming growth factor (TGF)-alpha, and basic fibroblast growth factor (bFGF) increase migration by 2.1-, 2.1-, and 2.6-fold, respectively. Basal and PDGF-induced migration in tuberin-deficient ELT3, ELT4, and ERC15 cells was not significantly different from that of tuberin-positive transformed rat kidney epithelial 2, airway smooth muscle, and pulmonary arterial vascular smooth muscle cells. Expression of tuberin in tuberin-deficient ELT3 cells also had little effect on cell migration. In parallel experiments, the role of PI 3-kinase activation in ELT3 cell migration was investigated. LY-294002, a PI 3-kinase inhibitor, decreased PDGF-induced migration in a concentration-dependent manner with an IC(50) of approximately 5 microM. LY-294002 also abrogated ELT3 cell migration stimulated by bFGF and TGF-alpha but not by VEGF and phorbol 12-myristate 13-acetate. Furthermore, transient expression of constitutively active PI 3-kinase (p110*) was sufficient to induce ELT3 cell migration. However, the migration induced by p110* was less than that induced by growth factors, suggesting other signaling pathways are also critically important in modulating growth factor-induced cell migration. These data suggest that PI 3-kinase is required for growth factor-induced cell migration and loss of tuberin appears to have little effect on cell migration.
Insights
Loss of tuberin, a tumor suppressor, does not affect cell migration. Phosphatidylinositol 3-kinase (PI 3-kinase) is essential for growth factor-induced cell motility in tuberin-deficient cells.
Area of Science:
- Oncology
- Cell Biology
- Biochemistry
Background:
- The tumor suppressor gene TSC2, encoding tuberin, is linked to benign lesion development via cell growth stimulation.
- The specific roles of tuberin in cell migration and metastasis remain largely uncharacterized.
- The involvement of phosphatidylinositol 3-kinase (PI 3-kinase) signaling in tuberin-deficient cell motility is unknown.
Purpose of the Study:
- To investigate the role of tuberin in regulating cell migration.
- To determine the involvement of PI 3-kinase in the motility of tuberin-deficient cells.
Main Methods:
- Utilized a tuberin-deficient rat smooth muscle cell line (ELT3) and various growth factors (PDGF, VEGF, TGF-alpha, bFGF).
- Assessed cell migration using a PI 3-kinase inhibitor (LY-294002) and a constitutively active PI 3-kinase (p110*).
- Compared migration in tuberin-deficient cells with tuberin-positive cell lines.
Main Results:
- Growth factors significantly stimulated migration in tuberin-deficient cells, with no significant difference compared to tuberin-positive cells.
- PI 3-kinase inhibition (LY-294002) reduced migration induced by PDGF, bFGF, and TGF-alpha, but not VEGF.
- Expression of active PI 3-kinase (p110*) induced migration, but to a lesser extent than growth factors, indicating involvement of other pathways.
Conclusions:
- Loss of tuberin function has minimal impact on cell migration.
- PI 3-kinase signaling is crucial for mediating growth factor-induced cell migration.
- Other signaling pathways are also important for growth factor-stimulated cell motility.