The tumor-suppressor activity of PTEN is regulated by its carboxyl-terminal region.
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.
Georgescu
M M
MM
Laboratory of Molecular Oncology, The Rockefeller University, New York, NY 10021, USA. georgem@rockvax.rockefeller.edu
Kirsch
K H
KH
Akagi
T
T
Shishido
T
T
Hanafusa
H
H
D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D005260:Female; D016147:Genes, Tumor Suppressor; D005909:Glioblastoma; D006801:Humans; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D051059:PTEN Phosphohydrolase; D010744:Phosphoric Monoester Hydrolases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D010920:Placenta / Q000378:metabolism; D017354:Point Mutation; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D014162:Transfection; D014407:Tumor Cells, Cultured; D025521:Tumor Suppressor Proteins
D011994:Recombinant Proteins; D025521:Tumor Suppressor Proteins; D010744:Phosphoric Monoester Hydrolases; D051059:PTEN Phosphohydrolase; C494929:PTEN protein, human