Design of a retroviral-mediated ecdysone-inducible system and its application to the expression profiling of the PTEN tumor suppressor

We have engineered the ecdysone-inducible mammalian expression system for g eneral retroviral delivery to cultured mammalian cells. We inducibly expres sed PTEN in the glioblastoma cell line, U87MG, lacking this gene. Because n early all cells are recruited on induction, we find both up- and down-regul ated genes by cDNA microarray analysis. The changes we see are similar to t hose observed after treatment with LY294002, an inhibitor of phosphatidylin ositol 3-OH kinase, fully consistent with the model that PTEN antagonizes p hosphatidylinositol 3-OH kinase. Both treatments result in suppressed expre ssion of the transforming growth factor (TGF)-beta gene and the genes of th e cholesterol biosynthesis pathway. Our results illustrate the power of usi ng a fully inducible expression system in conjunction with cDNA microarray analysis for exploring gene function.