Growth suppression of glioma cells by PTEN requires a functional phosphatase catalytic domain

Deletions of all or part of chromosome 10 are the most common genetic alterations in high-grade gliomas. The PTEN gene (also called MMAC1 and TEP1) maps to chromosome region 10q23 and has been implicated as a target of alteration in gliomas and also in other cancers such as those of the breast, prostate, and kidney. Here we sought to provide a functional test of its candidacy as a growth suppressor in glioma cells. We used a combination of Northern blot analysis, protein truncation assays, and sequence analysis to determine the types and frequency of PTEN mutations in glioma cell lines so that we could define appropriate recipients to assess the growth suppressive function of PTEN by gene transfer. Introduction of wild-type PTEN into glioma cells containing endogenous mutant alleles caused growth suppression, but was without effect in cells containing endogenous wild-type PTEN. The ectopic expression of PTEN alleles, which carried mutations found in primary tumors and have been shown or are expected to inactivate its phosphatase activity, caused little growth suppression. These data strongly suggest that PTEN is a protein phosphatase that exhibits functional and specific growth-suppressing activity.