A Reducing Milieu Renders Cofilin Insensitive to Phosphatidylinositol 4,5-Bisphosphate (PIP2) Inhibition

• Published in: The Journal of biological chemistry 2013-10, Vol.288 (41), p.29430-29439
• Main Authors: Schulte, Bianca, John, Isabel, Simon, Bernd, Brockmann, Christoph, Oelmeier, Stefan A., Jahraus, Beate, Kirchgessner, Henning, Riplinger, Selina, Carlomagno, Teresa, Wabnitz, Guido H., Samstag, Yvonne
• Format: Article
• Language: English
• Subjects: Actin Depolymerizing Factors - chemistry; Actin Depolymerizing Factors - genetics; Actin Depolymerizing Factors - metabolism; Actins - metabolism; Blotting, Western; Cell Line, Tumor; Cell Membrane - metabolism; Cells, Cultured; Cofilin; Cysteine - chemistry; Cysteine - genetics; Cysteine - metabolism; Humans; Magnetic Resonance Spectroscopy; Models, Molecular; Molecular Dynamics Simulation; Mutation; Oxidation-Reduction; Phosphatidylinositol 4,5-Diphosphate - chemistry; Phosphatidylinositol 4,5-Diphosphate - metabolism; Phosphatidylinositol Signaling; Phosphorylation; Polymerization; Protein Binding; Protein Conformation; Protein Structure and Folding; Protein Structure, Tertiary; Redox Regulation; T Cell; T-Lymphocytes - metabolism
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M113.479766

Oxidative stress can lead to T cell hyporesponsiveness. A reducing micromilieu (e.g. provided by dendritic cells) can rescue T cells from such oxidant-induced dysfunction. However, the reducing effects on proteins leading to restored T cell activation remained unknown. One key molecule of T cell activation is the actin-remodeling protein cofilin, which is dephosphorylated on serine 3 upon T cell costimulation and has an essential role in formation of mature immune synapses between T cells and antigen-presenting cells. Cofilin is spatiotemporally regulated; at the plasma membrane, it can be inhibited by phosphatidylinositol 4,5-bisphosphate (PIP2). Here, we show by NMR spectroscopy that a reducing milieu led to structural changes in the cofilin molecule predominantly located on the protein surface. They overlapped with the PIP2- but not actin-binding sites. Accordingly, reduction of cofilin had no effect on F-actin binding and depolymerization and did not influence the cofilin phosphorylation state. However, it did prevent inhibition of cofilin activity through PIP2. Therefore, a reducing milieu may generate an additional pool of active cofilin at the plasma membrane. Consistently, in-flow microscopy revealed increased actin dynamics in the immune synapse of untransformed human T cells under reducing conditions. Altogether, we introduce a novel mechanism of redox regulation: reduction of the actin-remodeling protein cofilin renders it insensitive to PIP2 inhibition, resulting in enhanced actin dynamics. Background: Cofilin is a key molecule for actin dynamics whose activity can be locally inhibited by PIP2. Results: Changes in the cofilin structure upon reduction render cofilin insensitive to PIP2 inhibition. Conclusion: Local effects of PIP2 on cofilin activity are determined by the redox microenvironment. Significance: We discovered a mechanism of spatio-microenvironmental control of actin dynamics by cofilin reduction at the plasma membrane.