Investigation of breast cancer-associated mutations in RND1 gene

We identified the Rho family GTPase Rnd1 as a candidate breast tumor suppressor by using bioinformatics analysis in conjunction with iRNA silencing. Upon silencing of Rnd1, normal mammary epithelial cells underwent a complete EMT but eventually became senescent, suggesting that they had experienced an oncogenic insult. Expression of c-Myc rescued the Rnd1-depleted cells from senescence by suppressing p27Kip and it enabled their neoplastic conversion. The resulting cells were able to grow in soft agar and to form invasive, multi-acinar structures in 3D Matrigel. Silencing of Rnd1 promoted disruption of epithelial adhesion and polarity in xenograft models. In contrast, expression of Rnd1 inhibited tumor development. Mechanistic studies revealed that Rnd1 suppresses Ras signaling and prevents the EMT by activating the Ras-GAP domain of Plexin B1. Finally, analysis of clinical samples and cancer cell lines provided evidence that gene deletion, epigenetic silencing, and missense mutations contribute to inactivate RND1 in a subset of human breast cancers. These results indicate that Rnd1 promotes epithelial adhesion and polarity and suppresses oncogenesis by restraining unscheduled activation of Ras.