Cofilin mediates lamellipodium extension and polarized cell migration by accelerating actin filament dynamics at the leading edge of migrating cells. Cofilin is inactivated by LIM kinase (LIMK)–1-mediated phosphorylation and is reactivated by cofilin phosphatase Slingshot (SSH)-1L. In this study, we show that cofilin activity is temporally and spatially regulated by LIMK1 and SSH1L in chemokine-stimulated Jurkat T cells. The knockdown of LIMK1 suppressed chemokine-induced lamellipodium formation and cell migration, whereas SSH1L knockdown produced and retained multiple lamellipodial protrusions around the cell after cell stimulation and impaired directional cell migration. Our results indicate that LIMK1 is required for cell migration by stimulating lamellipodium formation in the initial stages of cell response and that SSH1L is crucially involved in directional cell migration by restricting the membrane protrusion to one direction and locally stimulating cofilin activity in the lamellipodium in the front of the migrating cell. We propose that LIMK1- and SSH1L-mediated spatiotemporal regulation of cofilin activity is critical for chemokine-induced polarized lamellipodium formation and directional cell movement.

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The transcription factor Foxp3 specifically expressed in regulatory T (Treg) cells controls Treg function by repressing some genes and activating others. We have shown here that the transcription factor Ikzf1 associates with Foxp3 via its exon 5 (called IkE5) and that conditional deletion of IkE5 up-regulated the genes, including Ifng, normally repressed by Foxp3 upon TCR stimulation. IkE5-deletion in Treg cells indeed incurred IFN-γ overproduction, which destabilized Foxp3 expression and impaired suppressive function, consequently producing fatal systemic autoimmune diseases and evoking strong anti-tumor immunity. In addition, pomalidomide, which degrades IKZF1 and IKZF3, induced IFN-γ overproduction in human Treg cells. Mechanistically, the Foxp3/Ikzf1/Ikzf3 complex exerted gene-repressing function by competing with epigenetic co-activators, such as p300 and NFAT1, for binding to the target gene loci via chromatin remodeling. Collectively, the association of Ikzf1 with Foxp3 is essential for repressive function of Foxp3, and can be targeted to control autoimmunity and tumor immunity.