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p27Kip1 is required for PTEN-induced G1 growth arrest
A R Gottschalk1, D Basila, M Wong
1Department of Radiation Oncology, University of California at San Francisco, 94143, USA.
Abstract:
The tumor suppressor PTEN is one of the most commonly inactivated genes in human cancer. Glioblastoma multiforme cells harboring mutant PTEN have abnormally high levels of 3' phosphoinositides and elevated protein kinase B activity. Expression of wild-type PTEN in glioma cells, containing endogenous mutant PTEN, reduces 3' phosphoinositides levels, inhibits PKB activity, and induces G1 cell cycle arrest. We investigated the mechanism of the PTEN-induced growth arrest in glioma cell lines. Expression of PTEN is associated with increased expression of p27Kip1, decreased expression of cyclins A and D3, inhibition of cdk2 activity, and dephosphorylation of pRb. Inactivation of p53, by the human papilloma virus E6 oncoprotein, does not prevent PTEN-induced G1 arrest, implying that p53 is not required for G1 arrest. In contrast, p27Kip1 antisense oligonucleotides abrogated the growth arrest induced by PTEN. Furthermore, blocking p27Kip1 expression prevented the PTEN-induced reduction of cyclin-dependent kinase 2 activity, indicating that p27Kip1 functions upstream of cyclin-dependent kinase 2 in the PTEN regulatory cascade. These results implicate p27Kip1 as a critical mediator of PTEN-induced G1 arrest.
Insights
The tumor suppressor PTEN halts glioma cell growth by regulating cell cycle proteins. This study reveals p27Kip1 is essential for PTEN
Area of Science:
- Oncology
- Molecular Biology
- Cell Cycle Regulation
Background:
- The PTEN gene is frequently inactivated in human cancers, particularly glioblastoma.
- Mutant PTEN in glioblastoma cells leads to increased 3' phosphoinositides and elevated protein kinase B (PKB) activity.
- Restoring wild-type PTEN function in glioma cells reduces phosphoinositides, inhibits PKB, and triggers G1 cell cycle arrest.
Purpose of the Study:
- To elucidate the molecular mechanisms underlying PTEN-mediated G1 cell cycle arrest in glioma cells.
- To identify key mediators in the PTEN regulatory pathway responsible for growth inhibition.
Main Methods:
- Expression of wild-type PTEN in glioma cell lines harboring mutant PTEN.
- Analysis of cell cycle regulatory proteins, including p27Kip1, cyclins A and D3, cdk2 activity, and pRb phosphorylation.
- Investigation of the role of p53 and p27Kip1 using human papilloma virus E6 oncoprotein and antisense oligonucleotides, respectively.
Main Results:
- PTEN expression correlated with increased p27Kip1, decreased cyclins A and D3, inhibited cdk2 activity, and dephosphorylated pRb.
- PTEN-induced G1 arrest was independent of p53 status.
- Antisense oligonucleotides targeting p27Kip1 abolished PTEN-induced growth arrest and prevented the reduction in cdk2 activity.
- p27Kip1 acts upstream of cdk2 in the PTEN signaling pathway.
Conclusions:
- p27Kip1 is a critical mediator of PTEN-induced G1 cell cycle arrest in glioma cells.
- The PTEN/p27Kip1 axis represents a significant regulatory cascade controlling glioma cell proliferation.
- Understanding this pathway offers potential therapeutic targets for glioblastoma treatment.