Georgescu M M, Kirsch K H, Akagi T, Shishido T, Hanafusa H
Laboratory of Molecular Oncology, The Rockefeller University, New York, NY 10021, USA.
Proc Natl Acad Sci U S A. 1999 Aug 31;96(18):10182-7. doi: 10.1073/pnas.96.18.10182.
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.
PTEN是一种最近发现的肿瘤抑制因子，在多种癌症中失活，如胶质母细胞瘤、子宫内膜癌和前列腺癌。它含有一个氨基末端磷酸酶结构域，作为磷脂酰肌醇3,4,5-三磷酸磷酸酶，拮抗磷脂酰肌醇3-羟基激酶的活性。PTEN还含有一个羧基末端结构域，我们研究了该区域的作用，该区域类似于氨基末端磷酸酶结构域，是肿瘤中鉴定出的许多突变的靶点。在PTEN缺陷的胶质母细胞瘤细胞中表达羧基末端突变体，可使细胞实现不依赖贴壁生长，而野生型PTEN原本会抑制这种生长。由于快速降解，这些突变体在细胞中的稳定性降低。尽管羧基末端区域包含调节性的PEST序列和一个PDZ结合基序，但这些特定元件对于肿瘤抑制功能是可有可无的。对影响PTEN稳定性的羧基末端点突变的研究表明，这些突变位于预测的强β链中。令人惊讶的是，这些突变体的磷酸酶活性与这些结构元件的破坏程度相关。我们得出结论，羧基末端区域对于调节PTEN稳定性和酶活性至关重要，该区域的突变导致肿瘤抑制表型的逆转。我们还提出，这些突变引起的分子构象变化构成了PTEN失活的机制。
