Unbalancing the Phosphatidylinositol-4,5-bisphosphate–Cofilin Interaction Impairs Cell Steering

Abstract

Cofilin is a key player in actin dynamics during cell migration. Its activity is regulated by (de)phosphorylation, pH, and binding to phosphatidylinositol-4,5-bisphosphate [PI(4,5)P 2 ]. Here, we here use a human cofilin-1 (D122K) mutant with increased binding affinity for PI(4,5)P 2 and slower release from the plasma membrane to study the role of the PI(4,5)P 2 -cofilin interaction in migrating cells. In fibroblasts in a background of endogenous cofilin, D122K cofilin expression negatively affects cell turning frequency. In carcinoma cells with down-regulated endogenous cofilin, D122K cofilin neither rescues the drastic morphological defects nor restores the effects in cell turning capacity, unlike what has been reported for wild-type cofilin. In cofilin knockdown cells, D122K cofilin expression promotes outgrowth of an existing lamellipod in response to epidermal growth factor (EGF) but does not result in initiation of new lamellipodia. This indicates that, next to phospho-and pH regulation, the normal release kinetics of cofilin from PI(4,5)P 2 is crucial as a local activation switch for lamellipodia initiation and as a signal for migrating cells to change direction in response to external stimuli. Our results demonstrate that the PI(4,5)P 2 regulatory mechanism, that is governed by EGF-dependent phospholipase C activation, is a determinant for the spatial and temporal control of cofilin activation required for lamellipodia initiation.

Functions of cofilin in cell locomotion and invasion

“…This follows a general mechanism whereby membrane lipids have been shown to bind various actin regulatory proteins such as profilin 33 and gelsolin 94 that also interact with PtdIns(4,5)P 2 to inhibit their function 95 . In migrating cells, the hydrolysis of PtdIns(4,5)P 2 by phospholipase C (PLC) to form inositol-1,4,5-triphosphate (IP 3 ) and diacylglycerol (DAG) can release cofilin from its inhibitory interaction with the lipid, resulting in the local activation of F-actin filament severing, protrusion and cell polarity 49,96 (FIG. 4).…”

Considering Protonation as a Posttranslational Modification Regulating Protein Structure and Function

“…Two recently reported alternative mechanisms include binding to PI(4,5)P 2 in the plasma membrane (34) and to cortactin in invadopodia – invasive plasma membrane protrusions of cancer cells (81). Binding to PI(4,5)P 2 maintains cofilin inactive at the plasma membrane but locally available for the rapid assembly of actin filaments (74; 141) (figure 3a). How cofilin is inactive when bound to PI(4,5)P 2 was resolved by an NMR study (42) showing that the PI(4,5)P 2 -binding site includes His133 and basic residues in the F site.…”

Activity of PLCε contributes to chemotaxis of fibroblasts towards PDGF

“…Further complexity of PLC signalling is due to the involvement of several downstream events linked either to changes in PtdIns(4,5)P2 concentrations or generation of second messengers, diacylglycerol and Ins(1,4,5)P 3 . Studies in cancer cells emphasised reduction of local PtdIns(4,5)P2 and linked this to the activity state of coffilin (Leyman et al, 2009;van Rheenen et al, 2007). In contrast, studies in fibroblasts focused on the role of Ins(1,4,5)P 3 production and subsequent, more complex and dynamic changes in calcium levels in protrusions of cells responding to PDGF gradient (Wei et al, 2009).…”