IRAK3 modulates NFkB through its GC activity

LA Freihat, DT Manallack, JI Wheeler and HR Irving

Monash Institute of Pharmaceutical Sciences - Monash University

Interleukin-1 receptor associated kinase 3 (IRAK3) acts as a negative regulator of inflammation by inhibiting inflammatory downstream signaling and is involved in a number of inflammatory related diseases. IRAK3 is proposed to be useful as a diagnostic and prognostic marker in inflammation, and possibly a target for intervention. In cancer, IRAK3 is a critical mediator involved in the cross talk between tumor cells and macrophages. The exact mechanism of action and the selectivity of IRAK3 is however still largely unclear and further evaluation is needed. Our prior studies using bioinformatic search tools identified IRAK3 as a potentially novel guanylate cyclase (GC) catalyzing cyclic guanosine monophosphate (cGMP) synthesis, IRAK3 was shown to contain a GC centre within its kinase domain. We demonstrate that wild type IRAK3 is capable of producing cGMP, and that point mutations in the GC centre reduced cGMP production. cGMP alone affects downstream signaling through NFkB modulation in the presence of lipopolysaccharides. Wildtype IRAK3 functions to reduce lipopolysaccharide stimulated NFkB in cells and we have confirmed this role, however unlike wild type IRAK3, the mutant did not reduce NFkB activity. We believe that the cGMP produced may be involved in IRAK3s regulatory function where cGMP may affect selectivity in downstream signaling pathway(s) by modulating the binding and/or activity of nearby interacting proteins involved in the cascade. Our findings may provide insight into the selectivity and functionality of IRAK3 in the inflammatory signaling cascade.