3-Deazaadenosine, an S -adenosylhomocysteine hydrolase inhibitor, attenuates lipopolysaccharide-induced inflammatory responses via inhibition of AP-1 and NF-κB signaling

3-Deazadenosine (3-DA) is a general methylation inhibitor that depletes S-adenosylmethionine, a methyl donor, by blocking S-adenosylhomocysteine hydrolase (SAHH). In this study, we investigated the inhibitory activity and molecular mechanisms of 3-DA in inflammatory responses. 3-DA suppressed the secretion of inflammatory mediators such as nitric oxide (NO) and prostaglandin E-2 (PGE(2)) in lipopolysaccharide-treated RAW264.7 cells and phorbol 12-myristate 13-acetate (PMA)-differentiated U937 cells. It also reduced mRNA expression of inducible nitric oxide synthase, cyclooxygenase-2, tumor necrosis factor-alpha, interleukin-1 beta (IL-1 beta), and IL-6, indicating that 3-DA has anti-inflammatory properties in murine and human macrophages. Moreover, 3-DA strongly blocked AP-1 and NF-kappa B luciferase activity under PMA-, MyD88-, and TRIF-stimulated conditions and decreased the translocation of c-Jun, c-Fos, p65, and p50 into the nucleus. In addition, the p-ERK level in AP-1 signaling and the p-I kappa B alpha level in NF-kB signaling were diminished by 3-DA treatment. Interestingly, 3-DA did not alter the phosphorylation of MEK1/2, an ERK modulator, or IKK alpha/beta, an I kappa B alpha regulator. Instead, 3-DA prevented MEK1/2 and IKK alpha/beta from combining with ERK and I kappa B alpha, respectively, and directly suppressed MEK1/2 and IKK alpha/beta kinase activity. These results indicate that MEK1/2 and IKK alpha/beta are direct targets of 3-DA. In addition, suppression of SAHH by siRNA or treatment with adenosine dialdehyde, another SAHH inhibitor, showed inhibitory patterns against p-ERK and I kappa B alpha similar to those of 3-DA. Taken together, this study demonstrates that 3-DA inhibits AP-1 and NF-kappa B signaling by directly blocking MEK1/2 and IKK alpha/beta or indirectly mediating SAHH, resulting in antiinflammatory activity.