Tumor suppressor and anti-inflammatory actions of PPARγ agonists are mediated via upregulation of PTEN

The PTEN tumor suppressor gene modulates several cellular functions, including cell migration, survival, and proliferation [1] by antagonizing phosphatidylinositol 3-kinase (PI 3-kinase)mediated signaling cascades. Mechanisms by which the expression of PTEN is regulated are, however, unclear. The ligand-activated nuclear receptor peroxisome proliferator-activated receptor gamma (PPAR gamma) [2] has been shown to regulate differentiation and/or cell growth in a number of cell types [3, 4, 5], which has led to the suggestion that PPAR gamma, like PTEN [1, 6], could act as a tumor suppressor, PPAR gamma has also been implicated in antiinflammatory responses [7, 8], although downstream mediators of these effects are not well defined. Here, we show that the activation of PPAR gamma by its selective ligand, rosiglitazone, upregulates PTEN expression in human macrophages, Caco2 colorectal cancer cells, and MCF7 breast cancer cells, This upregulation correlated with decreased PI 3-kinase activity as measured by reduced phosphorylation of protein kinase B. One consequence of this was that rosiglitazone treatment reduced the proliferation rate of Caco2 and MCF7 cells, Antisense-mediated disruption of PPAR gamma expression prevented the upregulation of PTEN that normally accompanies monocyte differentiation and reduced the proportion of macrophages undergoing apoptosis, while electrophoretic mobility shift assays showed that PPAR gamma is able to bind two response elements in the genomic sequence upstream of PTEN, Our results demonstrate a role for PPAR gamma in regulating PI 3-kinase signaling by modulating PTEN expression in inflammatory and tumor-derived cells.