Cupidin influences Cdc42V12-induced changes in HeLa cell morphology. (A) Human fibroblast HeLa cells were transfected with vector alone (mock), CPD, CPDΔ191–230 (= Δ191–230), Cdc42V12 (dominant active form), Cdc42V12 + CPD, and Cdc42V12 + CPDΔ191–230. Actin cytoskeletons of transfected cells were stained by Texas Red-conjugated phalloidin. In mock-, CPD- and CPDΔ191–230-transfected cells, F-actin is concentrated in the cell periphery and in fine stress fibers that traverse in the cytoplasm. On the other hand, cells transfected with dominant-active Cdc42V12 show many filopodia-like protrusions and thin actin bundles around the cell periphery and lack cytoplasmic stress fibers. Co-expression of CPD suppresses Cdc42V12-induced filopodia formation, whereas that of CPDΔ191–230 does not. (B) Filopodia formation in (A) was statistically quantified as described in the methods. *, p < 0.01; **, p < 0.001.