PTEN modulates cell cycle progression and cell survival by regulating phosphatidylinositol 3,4,5,-trisphosphate and Akt/protein kinase B signaling pathway

Abstract

To investigate the molecular basis of PTENmediated tumor suppression, we introduced a null mutation into the mouse Pten gene by homologous recombination in embryonic stem (ES) cells. Pten ؊/؊ ES cells exhibited an increased growth rate and proliferated even in the absence of serum. ES cells lacking PTEN function also displayed advanced entry into S phase. This accelerated G 1 ͞S transition was accompanied by down-regulation of p27 KIP1 , a major inhibitor for G 1 cyclindependent kinases. Inactivation of PTEN in ES cells and in embryonic fibroblasts resulted in elevated levels of phosphatidylinositol 3,4,5,-trisphosphate, a product of phosphatidylinositol 3 kinase. Consequently, PTEN deficiency led to dosagedependent increases in phosphorylation and activation of Akt͞ protein kinase B, a well-characterized target of the phosphatidylinositol 3 kinase signaling pathway. Akt activation increased Bad phosphorylation and promoted Pten ؊/؊ cell survival. Our studies suggest that PTEN regulates the phosphatidylinositol 3,4,5,-trisphosphate and Akt signaling pathway and consequently modulates two critical cellular processes: cell cycle progression and cell survival.The tumor susceptibility gene encoding PTEN͞MMAC1͞TEP1 (1-3) is mutated at high frequency in many primary human cancers and several familial cancer predisposition disorders (4). PTEN contains the sequence motif that is highly conserved in the members of the protein tyrosine phosphatase family. PTEN has been shown in vitro to possess phosphatase activity on phosphotyrosyl, phosphothreonyl-containing substrates (3, 5) and more recently, on phosphatidylinositol 3,4,5-trisphosphate (PIP3), a product of phosphatidylinositol 3 (PI3) kinase (6). Many cancerrelated mutations have been mapped within the conserved catalytic domain of PTEN, suggesting that the phosphatase activity of PTEN is required for tumor suppressor function. In addition, wild-type PTEN, but not mutant derivatives lacking phosphatase activity, suppresses the growth of glioblastoma cells and their tumorigenecity in nude mice (7-9), confirming the functional relevance of the PTEN phosphatase domain for tumor suppression. Very recently, inactivation of PTEN in a mouse model has confirmed the role of PTEN as a bona fide tumor suppressor (10). However, the exact function of PTEN in regulation of cell growth and tumorigenesis remains unclear.In this study, we have investigated the molecular basis underlying the tumor suppression function of PTEN by using a combination of molecular genetic, cell biological, and biochemical approaches. We have identified PIP3, a product of PI3 kinase, as an intracellular target of PTEN. Our studies suggest that PTEN acts as a negative regulator for the PI3-kinase͞Akt signaling pathway, which controls and coordinates two major cellular processes: cell cycle progression and cell death.

The PTEN/MMAC1/TEP tumor suppressor gene decreases cell growth and induces apoptosis and anoikis in breast cancer cells

“…Considerable controversy exists as to the e ects of PTEN on cell proliferation, viability and anoikis (Cheney et al, 1998(Cheney et al, , 1999Davies et al, 1998Davies et al, , 1999Furnari et al, 1997Furnari et al, , 1998Li and Sun, 1998;Stambolic et al, 1998;Podsypanina et al, 1999;Ramaswamy et al, 1999;Sun et al, 1999;Tian et al, 1999). In the current study, induced expression of PTEN in PTEN de®cient breast cancer cells, was associated with a marked decrease in the basal phosphorylation of AKT, p70S6 kinase, BAD, and GSK3a, alterations indicative of decreased activity and signaling through the PI3K pathway.…”

“…Enforced expression of PTEN has been reported to result in decreased cell proliferation and decreased tumorigenicity (Cheney et al, 1998(Cheney et al, , 1999Furnari et al, 1998;Li and Sun, 1998;Tamura et al, 1999;Tian et al, 1999), an observation attributed to the ability of PTEN to induce cell cycle arrest, apoptosis or anoikis, a form of apoptosis that occurs when cells are dissociated from their extracellular matrix (Davies et al, 1998(Davies et al, , 1999Frisch and Ruoslahti, 1997;Furnari et al, 1998;Li and Sun, 1998;Sun et al, 1999;Ramaswamy et al, 1999;Stambolic et al, 1998). However, a consensus has not been reached on whether the capacity of PTEN to modulate these processes is determined by cell lineage or culture conditions.…”

“…Similarly, the biochemical mechanisms whereby PTEN in¯uences cell behavior are not well understood. However, enforced expression of PTEN has been linked to the decreased phosphorylation or activity of AKT, BAD and 4E-BP1 proteins, which act downstream of PI3K in various signaling cascades (Datta et al, 1997;Davies et al, 1998Davies et al, , 1999Delcommenne et al, 1998;Haas-Kogan et al, 1998;Pap and Cooper, 1998;Wu et al, 1998;Tian et al, 1999;Ramaswamy et al, 1999) and increased expression of p27, which is also downstream of PI3K (Cheney et al, 1999;Sun et al, 1999).…”

E-cadherin inhibits tumor cell growth by suppressing PI3K/Akt signaling via β-catenin-Egr1-mediated PTEN expression

“…As shown in Figure 4E, the luciferase activities of different 5 0 -truncated PTEN promoter constructs that contain the Egr1-binding site were reduced by E-cadherin loss, whereas the luciferase activity of a full-length construct with a mutated Egr1-binding site, pGL3-PTEN2526/427(mutEgr1), was low in both control and shEcad-transfected SKOV-3 cells. As E-cadherin regulates PTEN, which has previously been implicated in the suppression of cell growth (Ramaswamy et al, 1999;Sun et al, 1999), we investigated whether the overexpression of PTEN regulates cyclin D1 and p27 Kip1 protein levels. Transient transfection of SKOV-3 cells with PTEN decreased cyclin D1 and increased p27 Kip1 protein levels ( Figure 4F).…”

Loss of Expression of the PTEN Gene Protein Product Is Associated with Poor Outcome in Breast Cancer

“…Specifically, in breast cancer, cell line analyses have shown that PTEN appears to suppress breast cancer growth by down-regulation of PI3K, with resultant G1 arrest and cell death (6,7). Studies of embryonic stem cells have shown that cells featuring mutations of the PTEN gene exhibited an increased growth rate and displayed an advanced entry into S-phase (8). The accelerated G 1 /S transition was accompanied by down-regulation of p27, a major inhibitor of G 1 cyclin-dependent kinases.…”