START-GAP/DLC Family Proteins: Molecular Mechanisms for Anti-Tumor Activities

The Rho family of GTPases belongs to the superfamily named “Ras-like” proteins, which consists of over 150 varieties in mammals [1]. Significant progress has recently been made in understanding the biological functions mediated by this family of small (~21 kDa) G proteins (guanine nucleotide-binding proteins). Rho GTPases affect crucial biological processes such as transcriptional regulation, cell cycle progression, apoptosis and membrane trafficking [2, 3]. Thus far, a total of 23 Rho proteins have been identified [4], among which RhoA, Rac1 and Cdc42 are characterized in detail. Rho GTPases are also involved in the cytoskeleton formation of the cell via the regulation of actin dynamics [5, 6]. RhoA induces stress fiber formation and focal adhesion assembly, thereby regulating cell shape, attachment and motility, whereas Rac1 promotes extension of lamellipodia and membrane ruffling [7]. Cdc42 has been shown to play a role in the formation of filopodia [8].