Drosophila melanogaster NPC2 proteins bind bacterial cell wall components and may function in immune signal pathways

Abstract

ML (MD-2 (myeloid differentiation factor 2)-related Lipid-recognition) is a conserved domain identified in MD-2, MD-1, NPC2 (Niemann-Pick disease type C2), and mite major allergen protein from animals, plants, and fungi. Vertebrate members of the ML family proteins, such as NPC2 and MD-2, play important roles in lipid metabolism and immune signaling pathway. MD-2 is an essential co-receptor in the lipopolysaccharide (LPS)/Toll-like receptor 4 (TLR4) signaling pathway. Insects contain multiple ML genes, arbitrarily named md-2- or npc2-like genes. However, whether insect ML genes have functions similar to vertebrate md-2 is unknown. In Drosophila melanogaster, there are eight npc2 genes (npc2a-h), and they can be further divided into three subgroups based on the numbers of cysteine residues (6, 7 and 8 Cys) in the mature proteins. The purpose of this study is to investigate whether any Drosophila npc2 genes may have functions in immune signaling pathways. We chose npc2a, npc2e and npc2h genes representing the three subgroups for this study. We showed that recombinant NPC2a, NPC2e and NPC2h not only bound to LPS and lipid A, but also bound to peptidoglycan (PG) and lipoteichoic acid (LTA), a property that has not been reported previously for vertebrate NPC2 or MD-2. More importantly, we showed that over-expression of NPC2a and NPC2e activated diptericin promoter reporter in S2 cells stimulated by PG, suggesting that NPC2e and NPC2a may play a role in the immune deficiency (Imd) pathway. This is the first in vitro study about NPC2 proteins in innate immunity of D. melanogaster.

Aedes aegypti ML and Niemann-Pick type C family members are agonists of dengue virus infection

“…Activation of the Toll, Imd, and JAK/STAT pathways results in increased antimicrobial peptide (AMP) gene expression (Shi et al, 2012; Souza-Neto et al, 2009; Xi et al, 2008). We hypothesized that if AaegNPC1b and AaegML33 play a role in regulating these immune pathways (as potential negative regulators), silencing these genes would result in changes in the transcript abundance of AMPs and other effector genes.…”

“…MD2 is a secreted glycoprotein that mediates the activation of the vertebrate Toll-like receptor 4 (TLR4) upon exposure to bacterial lipopolysaccharide (LPS) (Shimazu et al, 1999). Drosophila MD2 homologs have been shown to mediate the activation of the immune deficiency (IMD) immune signaling pathway upon exposure to lipopolysaccharide (LPS) (Shi et al, 2012). The An.…”

Isolation of a novel LPS-induced component of the ML superfamily in Ciona intestinalis

“…In invertebrates, components of the NPC2 family have been identified in D. melanogaster (Shi et al, 2012), insect (Ishida et al, 2014) and shrimp (Liao et al, 2011). However, little is known letters (28e146 a.a.).…”

“…Bar indicate the number of amino acid residues substitutions for site. (Ishida et al, 2014) or binding LPS (Liao et al, 2011;Shi et al, 2012) suggesting that the specific role of this protein is still a matter of discussion in invertebrate.…”

“…Members of the ML domain play important role in lipid metabolism (sterol homeostasis and steroid biosynthesis) but also in innate immune signal pathways (LPS induced signalling). In invertebrates, a few ML genes have been identified in Drosophila melanogaster (Shi et al, 2012), in the shrimp Litopenaeus vannamei (Liao et al, 2011) and worker ant Camponotus japonicus (Ishida et al, 2014). These proteins may have multiple roles in binding bacterial cell wall components and working in chemical and immune signal pathways.…”