Striking the balance between PTEN and PDK1: it all depends on the cell context.

The phosphatidyl-inosital-3 kinase (PI3K) signaling pathway is critical for normal brain development and function and is commonly hyperactivated in brain cancer. The PTEN (phosphatase and tensin homolog deleted on chromosome 10) tumor suppressor protein and phosphate-depended kinase 1 (PDK-1) are critical regulators of this pathway. In the July 15, 2009, issue of Genes & Development, Chalhoub and colleagues (pp. 1619-1624) demonstrate PDK1-dependent and PDK1-independent effects of conditional PTEN deletion in the brain, and they identify cell type-specific differences in feedback regulation of the PI3K pathway. These studies provide important insights as to how neurons and glia may differentially regulate PI3K signaling, yielding intriguing clues about targeting PTEN-deficient brain cancers.