A High Avidity Biosensor Reveals PI(3,4)P₂ is Predominantly a Class I PI3K Signaling Product

Abstract

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)P2], 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)P2, 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)P2-driven function, the overwhelming majority of the lipid accumulates through degradation of class I PI3K-produced PIP3. However, we show that PI(3,4)P2 is also subject to hydrolysis by the tumor suppressor lipid phosphatase PTEN.Collectively, our results show that PI(3,4)P2 is potentially an important driver of class I PI3Kdriven signaling, and provides powerful new tools to begin to resolve the biological functions of this lipid downstream of class I and II PI3K.

TGFβ receptor endocytosis and Smad signaling require synaptojanin1, PI3K–C2α-, and INPP4B-mediated phosphoinositide conversions

“…In contrast, KD of INPP4B, which converts PI(3,4)P 2 to PI(3)P, did not affect a TGFβ1-induced PI(3,4)P 2 increase. Because several previous studies (Bae et al, 2010;Goulden et al, 2019) suggested that PI(3,4)P 2 was produced through the 5′-dephosphorylation of PI(3,4,5)P 3 generated by class I PI3K in growth factor-stimulated cells, we tested the effect of the class I PI3K-specific inhibitor GDC-0941on GFβ1-induced PI(3,4)P 2 FIGURE 1: Synj1 and INPP4B as well as C2α are required for TGFβ1-induced phosphorylation and nuclear translocation of Smad2/3 in EC. (A) siRNA-mediated KD of the mRNAs of C2α and phosphatases.…”