Lateral distribution of phosphatidylinositol 4,5-bisphosphate in membranes regulates formin- and ARP2/3-mediated actin nucleation

Abstract

Edited by Alex TokerSpatial and temporal control of actin polymerization is fundamental for many cellular processes, including cell migration, division, vesicle trafficking, and response to agonists. Many actin-regulatory proteins interact with phosphatidylinositol 4,5-bisphosphate (PI(4,5)P 2 ) and are either activated or inactivated by local PI(4,5)P 2 concentrations that form transiently at the cytoplasmic face of cell membranes. The molecular mechanisms of these interactions and how the dozens of PI(4,5)P 2sensitive actin-binding proteins are selectively recruited to membrane PI(4,5)P 2 pools remains undefined. Using a combination of biochemical, imaging, and cell biologic studies, combined with molecular dynamics and analytical theory, we test the hypothesis that the lateral distribution of PI(4,5)P 2 within lipid membranes and native plasma membranes alters the capacity of PI(4,5)P 2 to nucleate actin assembly in brain and neutrophil extracts and show that activities of formins and the Arp2/3 complex respond to PI(4,5)P 2 lateral distribution. Simulations and analytical theory show that cholesterol promotes the cooperative interaction of formins with multiple PI(4,5)P 2 headgroups in the membrane to initiate actin nucleation. Masking PI(4,5)P 2 with neomycin or disrupting PI(4,5)P 2 domains in the plasma membrane by removing cholesterol decreases the ability of these membranes to nucleate actin assembly in cytoplasmic extracts.

Defects in G-Actin Incorporation into Filaments in Myoblasts Derived from Dysferlinopathy Patients Are Restored by Dysferlin C2 Domains

“…Synaptotagmin-1, another protein with tandem C2 domains, also promotes actin remodeling by binding phosphatidylinositol 4,5-bisphosphate (PI(4,5)P 2 ) via a polybasic region [55]. Reportedly, PI(4,5)P 2 promotes actin remodeling by recruiting actin binding proteins, such as formins [56,57], a family of proteins involved in actin nucleation and assembly [58]. Dysferlin also binds and recruits PI(4,5)P 2 to membranes and promotes membrane remodeling and T-tubule biogenesis in a PI(4,5)P 2 -dependent manner [59].…”

Caveolae set levels of epithelial monolayer tension to eliminate tumor cells

“…Therefore, the increased levels of PtdIns(4,5)P 2 appeared to be responsible for increasing monolayer tension when caveolae were depleted. PtdIns(4,5)P 2 has been observed to concentrate in caveolae (Bucki et al, 2019;Fujita et al, 2009;Parton and Collins, 2016) and cavins can bind PtdIns(4,5)P 2 directly . Thus, caveolar downregulation may have released this pool of PtdIns(4,5)P 2 into the bulk membrane for signaling.…”

Phosphoinositides in Retinal Function and Disease

“…For example, PI(4,5)P 2 -binding proteins, ezrin and moesin, were reported to colocalize with Rac1 and Rab8 on rhodopsin transport carrier vesicles at the site of their fusion with the plasma membrane. A recent report suggesting the involvement of actin-nucleating proteins Arp2/Arp3 in basal disc extension [54] potentially implicates local pools or PI(4,5)P 2 , which are known to be critical for their function [55,56].…”