Defining the Subcellular Distribution and Metabolic Channeling of Phosphatidylinositol

Abstract

1 Pemberton et al. characterize a molecular toolbox for the visualization and manipulation of 2 phosphatidylinositol (PtdIns) within intact cells. Results using these approaches define the steady-state 3 distribution of PtdIns across subcellular membrane compartments as well as provide new insights into the 4 relationship between PtdIns availability and polyphosphoinositide turnover. 5 6 7 Abstract 8Phosphatidylinositol (PtdIns) is an essential structural component of eukaryotic membranes that also 9 serves as the common precursor for polyphosphoinositide (PPIn) lipids. Despite the recognized importance 10 of PPIn species for signal transduction and membrane homeostasis, there is still a limited understanding of 11 how the dynamic regulation of PtdIns synthesis and transport contributes to the turnover of PPIn pools. To 12 address these shortcomings, we capitalized on the substrate selectivity of a bacterial enzyme, PtdIns-specific 13 PLC, to establish a molecular toolbox for investigations of PtdIns distribution and availability within intact cells. 14 In addition to its presence within the ER, our results reveal low steady-state levels of PtdIns within the plasma 15 membrane (PM) and endosomes as well as a relative enrichment of PtdIns within the cytosolic leaflets of the 16 Golgi complex, peroxisomes, and outer mitochondrial membranes. Kinetic studies also demonstrate the 17 requirement for sustained PtdIns supply from the ER for the maintenance of monophosphorylated PPIn 18 species within the PM, Golgi complex, and endosomal compartments. 19

Suppression of SARS‐CoV‐2 infection in ex‐vivo human lung tissues by targeting class III phosphoinositide 3‐kinase

“…It is noted that the Vps34‐IN1 has been well‐characterized not only in in vitro assays 25 but also in a subsequent in vivo animal study 26 . This potent and specific Vps34‐IN1 inhibitor has also been applied for specific inhibition of Vps34 in numerous studies 26–37 . Therefore, the potential off‐target effect of class III PI3‐K inhibitor, Vps34‐IN1, used in this study will be minimal.…”

Control of Neuronal Excitability by Cell Surface Receptor Density and Phosphoinositide Metabolism

“…It would be of great interest to expand the model to include such spatial information. Recent work by Zewe et al and Pemberton et al using newly developed fluorescent biosensors for the most prominent member of the phosphoinositide family, phosphatidylinositol (PI), revealed a very low presence of PI at the plasma membrane, but provided evidence for pools of PI in the endoplasmic reticulum, cytosolic leaflets of the Golgi complex, peroxisomes, and the outer mitochondrial membrane ( Pemberton et al, 2020 ; Zewe et al, 2020 ). These new fluorescent biosensors will allow us to not only acquire experimental data needed for the simulation of compartmental transport of PI, but also provide the possibility to determine kinetics of PI synthesis and breakdown, thereby significantly enhancing the mathematical description of phosphoinositide metabolism in our current model.…”

The Complex Dance of Organelles during Mitochondrial Division

“…Phosphoinositides are a family of phospholipids in cellular membranes that are involved in many cellular processes including recruitment of proteins, membrane remodelling, or lipid exchange. Although phosphoinositides are not major components of mitochondrial membranes, PI and PI(4,5)P 2 have been identified at mitochondria [44,45]. Nevertheless, even if mitochondrial PI4P pools have not yet been described, they can be induced by the artificial recruitment of the PI4KIIIα catalytic domain, confirming that mitochondrial PI can serve as precursor for PI4P synthesis at the OMM [44].…”

“…Although phosphoinositides are not major components of mitochondrial membranes, PI and PI(4,5)P 2 have been identified at mitochondria [44,45]. Nevertheless, even if mitochondrial PI4P pools have not yet been described, they can be induced by the artificial recruitment of the PI4KIIIα catalytic domain, confirming that mitochondrial PI can serve as precursor for PI4P synthesis at the OMM [44]. Although the exact mechanism by which PI reaches the mitochondria is unknown, it can be hypothesized that PI-transfer proteins (PITPs) could facilitate PI trafficking from the ER to the OMM, as described at ER-PM [93] and ER-TGN MCSs [94].…”

“…To date, stable PI4P pools have not been documented at mitochondria, although the presence of its precursor PI has been described [44,45]. Recent studies have identified different PI4K isoforms at mitochondrial membranes, suggesting that minor and fluctuating PI4P pools could be synthesized [12,46].…”