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The tumor-suppressor activity of PTEN is regulated by its carboxyl-terminal region
M M Georgescu1, K H Kirsch, T Akagi
1Laboratory of Molecular Oncology, The Rockefeller University, New York, NY 10021, USA. georgem@rockvax.rockefeller.edu
Abstract:
PTEN is a recently identified tumor suppressor inactivated in a variety of cancers such as glioblastoma and endometrial and prostate carcinoma. It contains an amino-terminal phosphatase domain and acts as a phosphatidylinositol 3,4,5-trisphosphate phosphatase antagonizing the activity of the phosphatidylinositol 3-OH kinase. PTEN also contains a carboxyl-terminal domain, and we addressed the role of this region that, analogous to the amino-terminal phosphatase domain, is the target of many mutations identified in tumors. Expression of carboxyl-terminal mutants in PTEN-deficient glioblastoma cells permitted the anchorage-independent growth of the cells that otherwise was suppressed by wild-type PTEN. The stability of these mutants in cells was reduced because of rapid degradation. Although the carboxyl-terminal region contains regulatory PEST sequences and a PDZ-binding motif, these specific elements were dispensable for the tumor-suppressor function. The study of carboxyl-terminal point mutations affecting the stability of PTEN revealed that these were located in strongly predicted beta-strands. Surprisingly, the phosphatase activity of these mutants was affected in correlation with the degree of disruption of these structural elements. We conclude that the carboxyl-terminal region is essential for regulating PTEN stability and enzymatic activity and that mutations in this region are responsible for the reversion of the tumor-suppressor phenotype. We also propose that the molecular conformational changes induced by these mutations constitute the mechanism for PTEN inactivation.
Insights
Mutations in the PTEN tumor suppressor's carboxyl-terminal region disrupt its stability and phosphatase activity, leading to cancer cell growth. This region is crucial for PTEN's tumor-suppressing function.
Area of Science:
- Oncology
- Molecular Biology
- Biochemistry
Background:
- PTEN is a critical tumor suppressor gene frequently inactivated in various cancers, including glioblastoma, endometrial, and prostate carcinoma.
- PTEN functions as a phosphatase, antagonizing the phosphatidylinositol 3-OH kinase pathway, and possesses both amino-terminal and carboxyl-terminal domains.
- The carboxyl-terminal domain of PTEN is often targeted by mutations in tumors, suggesting a significant role in its tumor-suppressive function.
Purpose of the Study:
- To investigate the role of the carboxyl-terminal region of PTEN in its tumor-suppressor activity.
- To determine how mutations in the carboxyl-terminal domain affect PTEN stability, enzymatic activity, and cellular phenotype.
- To elucidate the structural and functional consequences of PTEN carboxyl-terminal mutations in cancer.
Main Methods:
- Expression of wild-type and mutant PTEN in PTEN-deficient glioblastoma cells.
- Assessment of anchorage-independent cell growth as a measure of tumor-suppressive function.
- Analysis of protein stability, degradation pathways, and phosphatase activity of PTEN mutants.
- Bioinformatic prediction of structural elements (beta-strands) and analysis of mutation impact.
Main Results:
- Expression of carboxyl-terminal PTEN mutants in PTEN-deficient cells promoted anchorage-independent growth, reversing the wild-type PTEN-mediated suppression.
- PTEN mutants exhibited reduced stability and underwent rapid degradation within cells.
- Specific motifs (PEST sequences, PDZ-binding motif) in the carboxyl-terminal region were dispensable for tumor suppression.
- Mutations affecting PTEN stability were located in predicted beta-strands, and their disruption correlated with reduced phosphatase activity.
Conclusions:
- The carboxyl-terminal region of PTEN is essential for maintaining its stability and enzymatic activity.
- Mutations within this region are responsible for the loss of PTEN's tumor-suppressor phenotype by inducing conformational changes and inactivation.
- Understanding these mechanisms provides insights into PTEN-driven tumorigenesis and potential therapeutic strategies.