A High Avidity Biosensor Reveals PI(3,4)P2is Predominantly a Class I PI3K Signaling Product

Class I PI 3-kinase (PI3K) signaling is central to animal growth and metabolism, and disruption of this pathway occurs frequently in cancer and diabetes. However, the specific spatial/temporal dynamics and signaling roles of its minor lipid messenger, phosphatidylinositol (3,4)-bisphosphate [PI(3,4)P 2 ], are not well understood. This owes principally to a lack of tools to study this scarce lipid. Here, we developed a high sensitivity genetically encoded biosensor for PI(3,4)P 2 , demonstrating high selectivity and specificity of the sensor for the lipid. We show that despite clear evidence for class II PI3K in PI(3,4)P 2 -driven function, the overwhelming majority of the lipid accumulates through degradation of class I PI3K-produced PIP 3 . However, we show that PI(3,4)P 2 is also subject to hydrolysis by the tumor suppressor lipid phosphatase PTEN. Collectively, our results show that PI(3,4)P 2 is potentially an important driver of class I PI3K-driven signaling, and provides powerful new tools to begin to resolve the biological functions of this lipid downstream of class I and II PI3K.