RAC1 and Familial prostate cancer: We found that a series of Plexin-B1 mutations in the hydrophobic interface, Trp1807GluPlex, Leu1815ProPlex (previously linked to prostate cancer [4]), and Leu1815GluPlex, completely abolished its interactions with Rac1* and Rnd1 (Figure 1d–e, Figure S6).