RRP22 is a farnesylated, nucleolar, ras-related protein with tumor suppressor potential

Ras proteins are members of a superfamily of related small GTPases. Some members, such as Ras, are oncogenic. However, other members seem to serve as tumor suppressors, such as Rig and Noey2. We now identify and characterize a novel member of the Ras superfamily, RRP22. Like Ras, RRP22 can be posttranslationally modified by farnesyl. Unlike Ras, RRP22 inhibits cell growth and promotes caspase-independent cell death. Examination of human tumor cells shows that RRP22 is frequently down-regulated due to promoter methylation. Moreover, reexpression of RRP22 in an RRP22-negative neural tumor cell line impairs its growth in soft agar. Unusually for a Ras-related protein, RRP22 localizes to the nucleolus in a GTP-dependent manner, suggesting a novel mechanism of action. Thus, we identify a new member of the Ras superfamily that can serve as a potential tumor suppressor.