Regulation of RhoA GTPase and novel target proteins for ROCK.

Rho GTPases play significant roles in cellular function and their activity is regulated by guanine nucleotide exchange factors (GEFs) and GTPase activating proteins (GAPs), providing activation and inactivation of these GTPases, respectively. Active GTP-bound form of RhoA activates its effector proteins while the inactive GDP-bound form of RhoA exists in a RhoA-RhoGDI (guanine nucleotide dissociation inhibitor) complex in the cytosol. In particular, IκB kinase γ IKKγ/NF-κB essential modulator (NEMO) plays a role as a GDI displacement factor (GDF) for RhoA activation through binding to RhoA-RhoGDI complex. Meanwhile, prion protein inactivates RhoA despite RhoA/RhoGDI association. Novel target proteins for Rho-associated kinase (ROCK) such as glycogen synthase kinase (GSK)-3β and IKKβ are recently discovered. Here, we elaborate on a post-translationally modified version of RhoA, phosphorylated at Tyr42 and oxidized at Cys16/20. This form of RhoA dissociates from RhoA-RhoGDI complex and activates IKKβ on IKKγ/NEMO, thus providing possibly a critical role for tumourigenesis.