RhoB induces the production of proinflammatory cytokines in TLR-triggered macrophages

- TLR agonists (LPS, CpG, poly(I:C)) induce RhoB expression in macrophages.
- RhoB increases the production of proinflammatory mediators in macrophages upon TLR agonists stimulation.
- RhoB induces LPS-initiated signaling pathways, including phosphorylation of Btk, IκBα, JNK, Erk and p38 in macrophages.
- RhoB interacts with major histocompatibility complex class II (MHCII) α chain, but not β chain, in endosomes of macrophages.
- RhoB induces TLR-mediated signaling via interaction with MHCII.

Toll-like receptors (TLRs) are the primary sensors detecting conserved molecular patterns on microorganisms, thus acting as important components of innate immunity against invading pathogens. Many positive and negative regulators of TLR-triggered signaling have been identified. The Rho GTPase RhoB plays a key role in cell migration, division and polarity; however, the function and regulatory mechanisms of RhoB in TLR ligand-triggered innate immune responses remain to be investigated. Here, we report that the expression of RhoB is induced by TLR agonists (lipopolysaccharide (LPS), CpG, poly(I:C)) in macrophages. Knockdown of RhoB expression markedly decreased TLR ligand-induced activation of mitogen activated protein kinases and nuclear factor-κB (NF-κB), and the production of tumor necrosis factor α (TNFα), interleukin (IL)-6 and IL-1β in macrophages stimulated with TLR ligands. Furthermore, we demonstrated that RhoB interacts with major histocompatibility complex class II (MHCII) α chain, but not β chain, in endosomes of macrophages. Knockdown of MHCII expression greatly reduced the interaction of RhoB with Btk, and attenuated the induction of NF-κB and interferon β activity by RhoB upon LPS stimulation. These findings suggest that RhoB is a positive physiological regulator of TLRs signaling via binding to MHCII in macrophages, and therefore RhoB may be a potential therapeutic target in inflammatory diseases.