SARM: a novel Toll-like receptor adaptor, is functionally conserved from arthropod to human.
Sterile-alpha and Armadillo motif containing protein (SARM) was recently identified as the fifth member of the Toll-like receptor (TLR) adaptor family. Whilst the Caenorhabditis elegans SARM homologue, TIR-1, is crucial for efficient immune responses against bacterial infections, human SARM was demonstrated to function as a specific inhibitor of TRIF-dependent TLR signaling. The opposing role of SARM in C. elegans and human is intriguing, prompting us to seek clarification on the enigmatic function of SARM in an ancient species which relies solely on innate immunity for survival. Here, we report the discovery of a primitive but functional SARM (CrSARM) in the immune defense of a "living fossil", the horseshoe crab, Carcinoscorpius rotundicauda. CrSARM shares numerous signature motifs and displays significant homology with vertebrate and invertebrate SARM homologues. CrSARM downregulates TRIF-dependent TLR signaling suggesting the conservation of SARM function from horseshoe crab to human. During infection by Pseudomonas aeruginosa, CrSARM is rapidly upregulated within 3h and strongly repressed at 6h, coinciding with the timing of bacterial clearance, thus demonstrating its dynamic role in innate immunity. Furthermore, yeast-two-hybrid screening revealed several potential interaction partners of CrSARM implying the role of SARM in downregulating TLR signaling events. Altogether, our study shows that, although C. elegans SARM upregulates immune signaling, its disparate role as a suppressor of TLR signaling, specifically via TRIF and not MyD88, is well-conserved from horseshoe crab to human.
Belinda
Loh Wei-Ching
LW
Department of Biological Sciences, National University of Singapore, 14 Science Drive 4, Singapore 117543, Singapore.
Wei
Wang Xiao
WX
Hanh
Bui Thi Hong
BT
Lei
Luan Xiao
LX
Bow
Ho
H
Ling
Ding Jeak
DJ
D000595:Amino Acid Sequence; D000818:Animals; D051186:Armadillo Domain Proteins / Q000235:genetics* / Q000502:physiology; D017124:Conserved Sequence; D003598:Cytoskeletal Proteins / Q000235:genetics* / Q000502:physiology; D006737:Horseshoe Crabs / Q000378:metabolism* / Q000382:microbiology; D006801:Humans; D008969:Molecular Sequence Data; D010802:Phylogeny; D011550:Pseudomonas aeruginosa / Q000502:physiology; D015398:Signal Transduction; D051193:Toll-Like Receptors / Q000502:physiology*
D051186:Armadillo Domain Proteins; D003598:Cytoskeletal Proteins; C435689:SARM1 protein, human; D051193:Toll-Like Receptors