Cyclin G2 interacts with actin filaments, and the interaction is required for the motility of glioblastoma cells. (A) Endogenous cyclin G2 (green) localizes at the leading edge of migrating U87MG cells merging with F-actin (red). In hypoxia-stimulated U87MG cells, endogenous cyclin G2 accumulated at membrane ruffles. (B and C) Exogenously expressed cyclin G2-EGFP (B) and cyclin G2-V5 (C) also localize at the ruffles. (D) Immunoelectron microscopy of U87MG cells transfected with cyclin G2-EGFP. Arrowheads indicate the immunogold labeling of EGFP. (E) Cyclin G2 interacts with both filamentous actin and microtubules. (F) Cyclin G2 has a putative WH2 motif. (G–I) The K219Q mutant impairs the interaction with actin filaments (G), the potentiation of ruffle formation (H), and the consequent migration (I). Cortactin (blue) served as a marker of membrane ruffles (H). The scale bars represent 50 µm (A, H), 10 µm (B, C), 200 nm (D), or 200 µm (I).