RAC1 and neoplasm: Indeed, among the most upregulated genes in FAT4 knockdown cells we found ARHGEF6, encoding for the guanine nucleotide exchange factor αPIX that activates Rac1 and Cdc42 GTPases [32–34] and ARHGDIB, a negative modulator of the RhoA tumor suppressor [35, 36] (Fig. 4b).