PTEN is a tumor suppressor gene with homology to protein tyrosine phosphatases and the cytoskeletal protein tensin. Mutant PTEN (mPTEN) in mice leads to increased cell proliferation in embryos, while mPTEN-deficient immortalized mouse embryonic fibroblasts show decreased sensitivity to apoptosis and elevated PKB/Akt activity. Exogenous PTEN expression restores sensitivity to apoptosis and normal PKB/Akt phosphorylation. PTEN dephosphorylates phosphatidylinositol (3,4,5) trisphosphate (PI(3,4,5)P3), a key product of PI3K activity, thereby negatively regulating the PI3K/PKB/Akt signaling pathway. This regulation is crucial for tumor suppression, as PTEN loss leads to increased cell survival and proliferation, contributing to tumorigenesis. PTEN also interacts with focal adhesion kinase (FAK) and inhibits cell migration and integrin-mediated spreading. The study demonstrates that PTEN functions as a tumor suppressor by inhibiting the PI3K/PKB/Akt pathway, which is essential for cell survival. Loss of PTEN function is associated with various cancers, including glioblastomas, breast, ovarian, and prostate cancers. PTEN mutations are linked to Cowden disease, an autosomal-dominant hamartoma syndrome. The findings highlight PTEN's role in regulating cell survival, proliferation, and apoptosis, and its importance in preventing tumor development.PTEN is a tumor suppressor gene with homology to protein tyrosine phosphatases and the cytoskeletal protein tensin. Mutant PTEN (mPTEN) in mice leads to increased cell proliferation in embryos, while mPTEN-deficient immortalized mouse embryonic fibroblasts show decreased sensitivity to apoptosis and elevated PKB/Akt activity. Exogenous PTEN expression restores sensitivity to apoptosis and normal PKB/Akt phosphorylation. PTEN dephosphorylates phosphatidylinositol (3,4,5) trisphosphate (PI(3,4,5)P3), a key product of PI3K activity, thereby negatively regulating the PI3K/PKB/Akt signaling pathway. This regulation is crucial for tumor suppression, as PTEN loss leads to increased cell survival and proliferation, contributing to tumorigenesis. PTEN also interacts with focal adhesion kinase (FAK) and inhibits cell migration and integrin-mediated spreading. The study demonstrates that PTEN functions as a tumor suppressor by inhibiting the PI3K/PKB/Akt pathway, which is essential for cell survival. Loss of PTEN function is associated with various cancers, including glioblastomas, breast, ovarian, and prostate cancers. PTEN mutations are linked to Cowden disease, an autosomal-dominant hamartoma syndrome. The findings highlight PTEN's role in regulating cell survival, proliferation, and apoptosis, and its importance in preventing tumor development.