Phospholipase C–mediated hydrolysis of PIP2 releases ERM proteins from lymphocyte membrane

Abstract

Mechanisms controlling the disassembly of ezrin/radixin/moesin (ERM) proteins, which link the cytoskeleton to the plasma membrane, are incompletely understood. In lymphocytes, chemokine (e.g., SDF-1) stimulation inactivates ERM proteins, causing their release from the plasma membrane and dephosphorylation. SDF-1–mediated inactivation of ERM proteins is blocked by phospholipase C (PLC) inhibitors. Conversely, reduction of phosphatidylinositol 4,5-bisphosphate (PIP2) levels by activation of PLC, expression of active PLC mutants, or acute targeting of phosphoinositide 5-phosphatase to the plasma membrane promotes release and dephosphorylation of moesin and ezrin. Although expression of phosphomimetic moesin (T558D) or ezrin (T567D) mutants enhances membrane association, activation of PLC still relocalizes them to the cytosol. Similarly, in vitro binding of ERM proteins to the cytoplasmic tail of CD44 is also dependent on PIP2. These results demonstrate a new role of PLCs in rapid cytoskeletal remodeling and an additional key role of PIP2 in ERM protein biology, namely hydrolysis-mediated ERM inactivation.

Dynamic Regulation of CD45 Lateral Mobility by the Spectrin-Ankyrin Cytoskeleton of T Cells

“…␤⌱ versus ␤⌱⌱ spectrin (also known as fodrin) versus ␤⌱⌱⌱ spectrin) (12,13), as well as direct linkages of spectrin to the membrane that do not involve ankyrin, such as the interaction of the ␤-spectrin PH domain with phosphatidylinositol 4,5-bisphosphate (PIP2) (35) and PKC␤ (36,37) or the interaction of its associated ␣⌱⌱ spectrin subunit with G-protein-coupled receptors (38). Actinmembrane linkages mediated by the ERM family of proteins (39) or variable partitioning of the spectrin membrane complex into lipid raft domains (13) could also contribute to the observed heterogeneity. Interestingly, all of the latter interactions (PIP2 binding, ERM-mediated attachment, and lipid raft partitioning) are modulated during lymphocyte activation (39).…”

“…Actinmembrane linkages mediated by the ERM family of proteins (39) or variable partitioning of the spectrin membrane complex into lipid raft domains (13) could also contribute to the observed heterogeneity. Interestingly, all of the latter interactions (PIP2 binding, ERM-mediated attachment, and lipid raft partitioning) are modulated during lymphocyte activation (39). Disruption of the actin-spectrin-ankyrin complex by the N-5 FIGURE 6.…”

Regulation of cell shape and adhesion by CD34

“…The spherical shape of leukocytes is also maintained by phosphorylated ERM proteins and an actin cortex. 26 Furthermore, phosphorylated ERM proteins and actin filaments are localized at microvilli. 18,19 Antisense oligonucleotides against ERM expression perturb microvilli, 27 indicating that ERM proteins are essential for microvillus formation and/or maintenance.…”

“…It has been reported that the SDF-1-CXCR4 interaction is the major regulatory element for the trafficking, retention, and adhesion of HSCs and HPCs. 30,31 Taken together with the effect of SDF-1 on microvillus collapse of lymphocytes, 26,29 alterations of HPC/HSC morphology can be caused by the SDF-1-CXCR4 interaction. Thus, cell adhesion of HPCs and HSCs may be regulated by cell shape, and CD34 might play significant roles in the formation and/or maintenance of cell shape and adhesion.…”

Angiopoietin-1 blocks neurotoxic zinc entry into cortical cells via PIP2 hydrolysis-mediated ion channel inhibition

“…Integrin-mediated modulation of zinc-permeable ion channels, such as NMDA receptor channels (Juhász et al, 2008;Lin et al, 2003), AMPA receptor channels (Cingolani et al, 2008;Juhász et al, 2008) and Ltype Ca 2+ channels (Waitkus-Edwards, 2002;Wu et al, 2001), has been previously documented, but little is known about the details of these regulatory mechanisms beyond their FAK-activity dependence or modulation by Src. Notably, one study reported a role for FAK in promoting the activity of phospholipase C (PLC)-γ1 (Zhang et al, 1999), which is responsible for mediating the hydrolysis of membrane-bound PIP 2 into inositol 1,4,5-trisphosphate (IP 3 ) and diacylglycerol (Hao et al, 2009;van Rheenen et al, 2005). Importantly, PIP 2 has been shown to be a critical cofactor for the function of various ion channels (Brown et al, 2007;Gamper and Shapiro, 2007;Suh and Hille, 2008), including zinc-permeable TRPM7 (Runnels et al, 2002), voltage-gated calcium channels (Lechner et al, 2005), and NMDA channels (Mandal and Yan, 2009), such that depletion of PIP 2 through PLC-mediated hydrolysis results in channel inhibition.…”