Related Experiment Videos
PTEN induces cell cycle arrest by decreasing the level and nuclear localization of cyclin D1
Aurelian Radu1, Valerie Neubauer, Tsuyoshi Akagi
1Carl C. Icahn Institute for Gene Therapy and Molecular Medicine, Mount Sinai School of Medicine, New York, New York,USA.
Abstract:
PTEN is a tumor suppressor frequently inactivated in brain, prostate, and uterine cancers that acts as a phosphatase on phosphatidylinositol-3,4,5-trisphosphate, antagonizing the activity of the phosphatidylinositol 3'-OH kinase. PTEN manifests its tumor suppressor function in most tumor cells by inducing G(1)-phase cell cycle arrest. To study the mechanism of cell cycle arrest, we established a tetracycline-inducible expression system for PTEN in cell lines lacking this gene. Expression of wild-type PTEN but not of mutant forms unable to dephosphorylate phosphoinositides reduced the expression of cyclin D1. Cyclin D1 reduction was accompanied by a marked decrease in endogenous retinoblastoma (Rb) protein phosphorylation on cyclin D/CDK4-specific sites, showing an early negative effect of PTEN on Rb inactivation. PTEN expression also prevented cyclin D1 from localizing to the nucleus during the G(1)- to S-phase cell cycle transition. The PTEN-induced localization defect and the cell growth arrest could be rescued by the expression of a nucleus-persistent mutant form of cyclin D1, indicating that an important effect of PTEN is at the level of nuclear availability of cyclin D1. Constitutively active Akt/PKB kinase counteracted the effect of PTEN on cyclin D1 translocation. The data are consistent with an oncogenesis model in which a lack of PTEN fuels the cell cycle by increasing the nuclear availability of cyclin D1 through the Akt/PKB pathway.
Insights
The tumor suppressor PTEN halts cell cycle progression by reducing cyclin D1 levels and nuclear localization. This mechanism, crucial in cancers, involves the Akt/PKB pathway.
Area of Science:
- Oncology
- Molecular Biology
- Cell Cycle Regulation
Background:
- PTEN is a critical tumor suppressor gene frequently lost in various cancers.
- PTEN functions as a phosphatase, antagonizing the PI3K/Akt pathway.
- Loss of PTEN function contributes to uncontrolled cell proliferation in cancer.
Purpose of the Study:
- To elucidate the molecular mechanisms by which PTEN induces G1 cell cycle arrest.
- To investigate the role of PTEN in regulating cyclin D1 expression and localization.
- To explore the interplay between PTEN, cyclin D1, and the Akt/PKB pathway in cell cycle control.
Main Methods:
- Utilized a tetracycline-inducible PTEN expression system in PTEN-deficient cell lines.
- Assessed cyclin D1 expression and retinoblastoma (Rb) protein phosphorylation.
- Examined the subcellular localization of cyclin D1 using microscopy.
- Investigated the effect of constitutively active Akt/PKB on PTEN-induced effects.
Main Results:
- Wild-type PTEN expression, but not catalytically inactive mutants, reduced cyclin D1 levels.
- PTEN expression decreased Rb phosphorylation at cyclin D/CDK4 sites, indicating impaired Rb inactivation.
- PTEN inhibited cyclin D1 nuclear translocation, a defect rescued by a nuclear-localized cyclin D1 mutant.
- Activated Akt/PKB counteracted PTEN's effects on cyclin D1 localization and cell cycle arrest.
Conclusions:
- PTEN enforces cell cycle arrest primarily by limiting nuclear cyclin D1 availability.
- The Akt/PKB pathway mediates PTEN's regulation of cyclin D1 nuclear import.
- PTEN inactivation promotes oncogenesis by enhancing nuclear cyclin D1 levels via the Akt/PKB pathway.