PI4P and PI(4,5)P ₂ Are Essential But Independent Lipid Determinants of Membrane Identity

Abstract

The quantitatively minor phospholipid phosphatidylinositol (4,5)-bisphosphate [PI(4,5)P2] fulfils many cellular functions in the plasma membrane (PM), whereas its major synthetic precursor, phosphatidylinositol 4-phosphate (PI4P), has no assigned PM roles apart from PI(4,5)P2 synthesis. We used a combination of pharmacological and chemical genetic approaches to probe the function of PM PI4P, which was not required for the synthesis or functions of PI(4,5)P2. However, depletion of both lipids was required to prevent PM targeting of proteins that interact with acidic lipids, or activation of the transient receptor potential vanilloid 1 cation channel. Therefore, PI4P contributes to the pool of polyanionic lipids that define plasma membrane identity, and to some functions previously attributed specifically to PI(4,5)P2 that may be fulfilled by a more general polyanionic lipid requirement.

Golgi and plasma membrane pools of PI(4)P contribute to plasma membrane PI(4,5)P 2 and maintenance of KCNQ2/3 ion channel current

“…We focused on the two membranes most likely to contribute to the maintenance of PM PI(4,5)P 2 , the plasma membrane (using the Lyn 11 anchor) and the Golgi [using the trans-Golgi network 38 (Tgn38) anchor]. The experiments used four lipid-phosphatase constructs related to pseudojanin (PJ) (29) (Fig. 1).…”

“…For example, following transient activation of voltage-sensitive 5-phosphatase (49,54), the recovery of PM PI(4,5)P 2 from its PM PI(4)P precursor is extremely fast (τ = ∼10 s), suggesting that these pools normally may be in a rapid, dynamic equilibrium. Nevertheless, recent studies monitoring phosphoinositide levels by isotope labeling, mass spectrometry, and antibody staining in fixed cells have advanced the idea that the participation of PM PI(4)P pools in maintaining resting PM PI(4,5)P 2 is truly minor (29)(30)(31). Our experimental methods differ from theirs in that we record from single, living cells, monitor enzyme recruitment by FRET, and use KCNQ2/3 currents as a real-time readout of PM PI(4,5)P 2 levels.…”

A phosphoinositide conversion mechanism for exit from endosomes

“…The plasma membrane PI(4)P pool is generated by PI4K3α (Bojjireddy, Botyanszki et al 2014) and serves as a substrate for local PI(4,5)P 2 synthesis by PI(4)P-5-kinases (PIP5Ks). Besides being a precursor for PI(4,5)P 2 , recent studies indicate that PI(4)P contributes to the polyanionic lipid pool that defines the PM, additionally to, but independent of PI(4,5)P 2 (Hammond, Fischer et al 2012). Clathrin coated pit (CCP) nucleation, although dependent on the general PM PI(4,5)P 2 content (Zoncu, Perera et al 2007), is driven by local synthesis of PI(4,5)P 2 by PIP5K type I.…”

Endocytic Accessory Factors and Regulation of Clathrin-Mediated Endocytosis

“…The PIP(3,4)P 2 concentrated at CCPs is produced locally from PI(4,5)P 2 by the concerted action of PI5 phosphatases and PI3K C2a and is required for recruitment of the BAR domain protein sorting nexin 9 (SNX9) (Posor et al 2013). It should be noted that PI4P may also contribute to the recruitment of EAPs because PI(4,5)P 2 and PI4P have some degree of overlap in defining the electrostatic properties of the inner leaflet of the plasma membrane (Hammond et al 2012). The phosphoinositide PI4P has been associated with clathrin-coated vesicle (CCV) uncoating, so precisely how PIP2, PI(3,4)P 2 , and PI4P are coordinated at CCPs remains an intriguing area of investigation (Nakatsu et al 2012;Posor et al 2013).…”