Pattern recognition receptor mediated innate immune response requires a Rif-dependent pathway

Small GTPases play critical roles in cell morphology, movement, and adhesion by dynamic regulation of actin cytoskeleton. The small Rho GTPase Rif/RhoF (Rho in filopodia) regulates the formation of filopodia and stress fibers in cells. Rif is highly expressed in a number of cell types in the immune system; however, it's role in immune system function is unclear. In this research, we found that Rif expression is necessary for NF-κB activation in primary immune cells, and mature dendritic cell (mature DCs) induced from Bone Marrow-Derived Dendritic Cells (BMDCs) isolated from Rif knock out (Rif KO) mice displayed impaired degradation of I-κBα, as well as reduced TNF-α secretion and p38 MAPK phosphorylation under LPS stimulation. Interestingly, we revealed that TLR agonists, such as LPS and poly (I:C), as well as bacterial virulence factor SopE could induce a transient increase in Rif activation in monocytes THP-1 cells. Furthermore, Rif was found to be an integral part of the TLR4, TLR3 and nodosome signaling complex. We further identified Src tyrosine kinases as upstream activator of Rif in both bacterial and viral induced immune responses. Moreover, activated Rif induces activation of transcription factors, such as NF-κB, AP-1 and IRF-3, and mediates inflammation through secretion of IL-6, IL-8 or TNFα. Rif activation by PRRs contributes in a variety of ways to protective host responses against invading microbes. Taken together, this study reveals that Rif is indispensable for both extracellular and intracellular pattern-recognition receptor-mediated innate immune responses. Rif possess broad anti-pathogenic effect and understanding of the molecular mechanisms by which this small Rho GTPase interferes with innate immune system will be beneficial to develop therapies against infectious agents.