ROCK I-mediated activation of NF-κB by RhoB

RhoB is a short-lived protein whose expression is increased by a variety of extra-cellular stimuli including UV irradiation, epidermal growth factor (EGF) and transforming growth factor β (TGF-β). Whereas most Rho proteins are modified by the covalent attachment of a geranylgeranyl group, RhoB is unique in that it can exist in either a geranylgeranylated (RhoB-GG) or a farnesylated (RhoB-F) form. Although each form is proposed to have different cellular functions, the signaling events that underlie these differences are poorly understood. Here we show that RhoB can activate NF-κB signaling in multiple cell types. Whereas RhoB-F is a potent activator of NF-κB, much weaker activation is observed for RhoB-GG, RhoA, and RhoC. NF-κB activation by RhoB is not associated with increased nuclear translocation of RelA/p65, but rather, by modification of the RelA/p65 transactivation domain. Activation of NF-κB by RhoB is dependent upon ROCK I but not PRK I. Thus, ROCK I cooperates with RhoB to activate NF-κB, and suppression of ROCK I activity by genetic or pharmacological inhibitors blocks NF-κB activation. Suppression of RhoB activity by dominant-inhibitory mutants, or siRNA, blocks NF-κB activation by Bcr, and TSG101, but not by TNFα or oncogenic Ras. Collectively, these observations suggest the existence of an endosome-associated pathway for NF-κB activation that is preferentially regulated by the farnesylated form of RhoB.