PIP4Ks Suppress Insulin Signaling Through a Catalytic-Independent Mechanism

Abstract

Insulin stimulates conversion of phosphatidylinositol-4,5-bisphosphate (PI(4,5)P2) to 4,4,5)P3), which mediates downstream cellular responses. PI(4,5)P2 is produced by phosphatidylinositol-4-phosphate 5kinases (PIP5Ks) and byphosphatidylinositol-5-phosphate 4-kinases (PIP4Ks). Here we show that deletion of the three genes that encode PIP4Ks (PIP4K2A, PIP4K2B and PIP4K2C) in vitro results in a paradoxical increase in PI(4,5)P2 and a subsequent increase in insulin-stimulated production of PI(3,4,5)P3. Surprisingly, reintroduction of either wild-type or kinase-dead forms of the PIP4Ks restored cellular PI(4,5)P2 levels and insulin stimulation of the PI3K pathway. These effects are explained by an increase in PIP5K activity upon deletion of PIP4Ks, which we demonstrate can suppress PIP5K activity in vitro through a direct binding interaction. Collectively, our work reveals an important non-catalytic function of PIP4Ks in suppressing PIP5K-mediated PI(4,5)P2 synthesis and insulin-dependent conversion to PI(3,4,5)P3 by PI3K enzymes and suggests that pharmacological depletion of PIP4K enzymes using emerging degrader technologies could represent a novel strategy for stimulating insulin signaling.

Phosphatidylinositol 5 Phosphate 4-Kinase Regulates Plasma-Membrane PIP3 Turnover and Insulin Signaling

“…However, a link between the levels of the two lipids cannot be ruled out completely. Interestingly, a recent study has reported that cells depleted of PIP4K show elevated levels of PIP2 and PIP3; evidence is presented that the interaction of PIP5K, the enzyme that synthesizes the majority of PIP2 cells, is inhibited by its interaction with PIP4K (Wang et al, 2019).…”

Integrated regulation of the phosphatidylinositol cycle and phosphoinositide‐driven lipid transport at ER‐PM contact sites

“…However, while interactions between the type I PIP5K and type II PIP4K isoforms have been documented previously, more recent studies now define an important kinase‐independent role for PIP4Ks in the indirect regulation of PtdIns(4,5)P 2 levels within the PM . This unique mechanism involves the allosteric inhibition of PIP5Ks through a conserved N‐terminal motif . These studies stress the continued importance of exploring the non‐catalytic functions of PPIn‐modifying enzymes as well as the potential impact of targeting these types of allosteric interactions in drug discovery efforts.…”

“…It has also been postulated that the true function of the PIP4Ks might actually be related to the maintenance of PtdIns5P levels, rather than for contributing to local PtdIns(4,5)P 2 production . However, while interactions between the type I PIP5K and type II PIP4K isoforms have been documented previously, more recent studies now define an important kinase‐independent role for PIP4Ks in the indirect regulation of PtdIns(4,5)P 2 levels within the PM . This unique mechanism involves the allosteric inhibition of PIP5Ks through a conserved N‐terminal motif .…”

Distribution and localization of phosphatidylinositol 5‐phosphate, 4‐kinase alpha and beta in the brain

“…The type 2 phosphatidylinositol-5-phosphate 4-kinases (PI5P4Ks), composed of a family of 3 isoforms (α, β and γ), catalyze the formation of phosphatidylinositol 4,5-bisphosphate (PI-4,5-P 2 ) by phosphorylating phosphatidylinositol 5-phosphate (PI-5-P) at the 4 position of the inositol ring. These kinases play a role in a variety of disease states, including cancer, insulin signaling, and oxidative stress (Carricaburu et al, 2003;Emerling et al, 2013;Jones et al, 2006;Jones, Foulger, Keune, Bultsma, & Divecha, 2013;Jude et al, 2015;Keune et al, 2012;Sharma, Mathre, Ramya, Shinde, & Raghu, 2019;Wang et al, 2019).…”

“…Furthermore, they regulate early endosomal homeostasis during clathrin-mediated endocytosis, a key step in synaptic vesicle trafficking (Kamalesh et al, 2017). Of particular interest, these enzymes also play a major role in suppressing the activity of the type 1 phosphatidylinositol-4-phosphate 5-kinases through direct binding to these enzymes (Wang et al, 2019). Although the expression and function of these kinases have been explored in oncogenic signaling pathways and in settings of nutrient stress, few studies have examined their role in the brain.…”