As Crk failed to elicit Rac1 activation probably because of masking of the subcellular activation of Rac1 (Supplementary information, Figure S2B) as evaluated by pull-down assay using whole cell lysates of cancer cells, we thus carefully examined the localization of active Rac1 by immunofluorescence using its target PAK1, and found significant increases in ruffling-specific activation of Rac1 observed in Crk-expressing cell lines (Figure 1E and Supplementary information, Figure S2C). Here, CRK is linked to cancer.