Role of phosphatidylinositol 4-phosphate and its effector proteins in neurotransmitter release

Abstract

Phosphoinositides are minor components of cellular membrane, but serve crucial roles in cell physiology through the recruitment of effector proteins based on electrostatic interaction. Phosphatidylinositol 4-phosphate [PI4P], in recent, has emerged as an important regulator of diverse cellular process at the plasma membrane. However, in neuronal exocytosis, its own roles beyond being a synthetic precursor of phosphatidylinositol 4,5-bisphosphatate [PI(4,5)$P_2$] is unknown. Here, using structured illumination microscopy on the plasma membrane of PC12 cells from Rattus norvegicus, we show that PI4P is an inner-leaflet lipid that clusters in microdomains and that is involved in clustering of t-SNARE protein syntaxin 1, a protein essential for vesicle docking. Furthermore, we found that the syntaxin 1？associated exocytic proteins synaptotagmin 1 and synaptotagmin-like protein 4 interact with PI4P independently of $Ca^{2+}$ through their C2 domains at the plasma membrane. These electrostatic protein-lipid interaction is required for recruiting vesicles to the plasma membrane. Our results demonstrate that PI4P contribute to the anionic lipid pools that defines plasma membrane identify, directly regulate vesicle docking through electrostatic interaction with syntaxin 1 and C2 domain-contained exocytic proteins