Regulation of antimicrobial peptide genes by a new transcription factor, LPS-induced TNF-α factor (LITAF)

In virtually all organisms, the innate immune system is responsible for the primary defense against pathogens. Insects only have the innate immune system and they can synthesize a battery of antimicrobial peptides (AMPs)against microbial infections.In the fruit fly Drosophila melanogaster,expression of AMP genes is regulated by NF-κB factors such as Dorsal, Dif and Relish. In vertebrates, tumor necrosis factor-alpha (TNF-α) is an important mediator of immune reactions and is involved in apoptotic cell death, inflammation, regulation of immune genes via NF-κB, and cellular proliferation/differentiation. Bacterial endotoxin lipopolysaccharide (LPS) can induce TNF-αand other cytokines in vertebrates.LITAF (LPS-induced TNF-α factor) is a transcription factor that can bind to the TNF-α promoter in response to LPS stimulation.Although insects don’t have TNF-α like factor, insect LITAF like factors have been identified,and LITAF-like 3 (LL3) in the mosquitoAnopheles gambiae has been shown to modulate expression ofSRPN6, a serpin gene with anti-Plasmodiumfunction.We have identified anLITAF from the tobacco hornwormManducasexta.This study is to investigate the roleof MsLITAFin regulation of insect AMP genes. MsLITAF transcript was detected in several tissues of naïve M. sextalarvae with a higher expression levelin the midgut, and MsLITAF protein was detected in larval hemocytes as dimers. Drosophila S2 cell lines expressing recombinant MsLITAF-V5 (predominantlyas monomers) and MsLITAF (predominantly as dimers) have been established.Dual-luciferase reporter assays showed thatoverexpression of MsLITAF-V5 (monomer) and MsLITAF (dimers) could both regulateseveralDrosophilaand M. sexta AMP gene reporters, but activate AMP genes differently. Our results suggest that LITAF is a new transcription factor in addition to NF-αB factors in insects that can regulation expression of AMP genes.