Clinical and biological significance of forkhead class box O 3a expression in glioma: mediation of glioma malignancy by transcriptional regulation of p27kip1

Abstract

Forkhead box class O 3a (FOXO3a) is an important direct target of the phosphatidylinositol 3-kinase (PI3K)/protein B(Akt) pathway, mediating signal transduction in regulating cell survival and cell-cycle progression. Recent reports have shown that FOXO3a inhibits cell-cycle progression at the G1/S transition by controlling transcription of the cyclin-dependent kinase inhibitor p27(kip1), which is frequently down-regulated in human cancers, including human glioma. In this study we investigated the status of FOXO3a expression and related signaling in human glioma in order to test its potential value as a therapeutic target for this disease. Immunohistochemistry, western blot, RT-PCR, and immunofluorescence staining analysis were performed on specimens from 70 cases of human glioma and on U87MG and T98G glioma cells. Our data showed FOXO3a expression is directly correlated with the malignant grade of glioma. More importantly, low expression of FOXO3a was associated with poor patient outcome. In vitro, FOXO3a modulated the cell cycle by transcriptional regulation of p27(kip1). Administration of the PI3K pharmacological inhibitor LY294002 abrogated this effect by regulating FOXO3a expression and subcellular localization. Our results suggested that FOXO3a may be a favorable independent prognostic indicator of glioma. Gene therapeutic approaches aimed at PI3K or at pharmacological inhibitors of PI3K to down-regulate P-FOXO3a expression could be developed for management of glioma.