TNFAIP8 variant 2 has an anti-inflammatory role in Toll like Receptor 4 signaling

Abstract

Abstract The cell response to pathogens involves complex signaling that affects expression of thousands of genes. Characterization of the regulation and function of these genes is critical since failure of this response can foster the development of chronic disorders. In a high-throughput microarray analysis of human macrophages stimulated with the TLR4 ligand LPS, we found high and rapid induction of Tumor Necrosis Factor-a-Inducible Protein-8 (TNFAIP8), a poorly defined gene proposed to regulate cell fate. While very little is known about TNFAIP8 expression and function, recent studies of murine Tnfaip8 suggest a role in antibacterial immunity and inflammation. Our analysis of human TNFAIP8 revealed two previously uncharacterized expression variants (v1 and v2) that possess distinct predicted functional domains. Primary human macrophages predominantly express v1, whereas a panel of human cancer cell lines displayed a marked v2 predominance. Interestingly, we found that v1 and v2 are both induced by LPS in macrophages, but with different kinetics, suggesting that they may have distinct functions in innate immunity. Selective depletion of v2 in A549 cells dramatically enhanced the baseline expression of several pro-inflammatory cytokines including IL-6, IL-8 and IL-1b. Furthermore, in response to LPS, v2-depleted cells had increased induction of IL-8, IL-1b, and TNFa. Together, these data suggest that TNFAIP8 v2 has an anti-inflammatory role in resting and TLR ligand-stimulated cells. Work is currently underway to determine 1) the molecular mechanisms of the anti-inflammatory role of TNFAIP8, for example, whether NF-kB activation is altered by v2 depletion; and 2) whether v1 has a distinct role in immune signaling.