PIP4Ks Suppress Insulin Signaling through a Catalytic-Independent Mechanism.

Overview

Insulin stimulates the conversion of phosphatidylinositol-4,5-bisphosphate (PI(4,5)P₂) to phosphatidylinositol-3,4,5-trisphosphate (PI(3,4,5)P₃), which mediates downstream cellular responses. PI(4,5)P₂ is produced by phosphatidylinositol-4-phosphate 5-kinases (PIP5Ks) and by phosphatidylinositol-5-phosphate 4-kinases (PIP4Ks). Here, we show that the loss of PIP4Ks (PIP4K2A, PIP4K2B, and PIP4K2C) in vitro results in a paradoxical increase in PI(4,5)P₂ and a concomitant increase in insulin-stimulated production of PI(3,4,5)P₃. The reintroduction of either wild-type or kinase-dead mutants of the PIP4Ks restored cellular PI(4,5)P₂ levels and insulin stimulation of the PI3K pathway, suggesting a catalytic-independent role of PIP4Ks in regulating PI(4,5)P₂ levels. These effects are explained by an increase in PIP5K activity upon the deletion of PIP4Ks, which normally suppresses PIP5K activity through a direct binding interaction mediated by the N-terminal motif VMLΦPDD of PIP4K. Our work uncovers an allosteric function of PIP4Ks in suppressing PIP5K-mediated PI(4,5)P₂ synthesis and insulin-dependent conversion to PI(3,4,5)P₃ and suggests that the pharmacological depletion of PIP4K enzymes could represent a strategy for enhancing insulin signaling.