Abstract
The CATERPILLER (CLR, also NOD and NLR) proteins share structural similarities with the nucleotide binding domain (NBD)-leucine-rich repeat (LRR) superfamily of plant disease-resistance (R) proteins and are emerging as important immune regulators in animals. CLR proteins contain NBD-LRR motifs and are linked to a limited number of distinct N-terminal domains including transactivation, CARD (caspase activation and recruitment), and pyrin domains (PyD). The CLR gene, Monarch-1/Pypaf7, is expressed by resting primary myeloid/monocytic cells, and its expression in these cells is reduced by Toll-like receptor (TLR) agonists tumor necrosis factor (TNF) alpha and Mycobacterium tuberculosis. Monarch-1 reduces NFkappaB activation by TLR-signaling molecules MyD88, IRAK-1 (type I interleukin-1 receptor-associated protein kinase), and TRAF6 (TNF receptor (TNFR)-associated factor) as well as TNFR signaling molecules TRAF2 and RIP1 but not the downstream NFkappaB subunit p65. This indicates that Monarch-1 is a negative regulator of both TLR and TNFR pathways. Reducing Monarch-1 expression with small interference RNA in myeloid/monocytic cells caused a dramatic increase in NFkappaB activation and cytokine expression in response to TLR2/TLR4 agonists, TNFalpha, or M. tuberculosis infection, suggesting that Monarch-1 is a negative regulator of inflammation. Because Monarch-1 is the first CLR protein that interferes with both TLR2 and TLR4 activation, the mechanism of this interference is significant. We find that Monarch-1 associates with IRAK-1 but not MyD88, resulting in the blockage of IRAK-1 hyperphosphorylation. Mutants containing the NBD-LRR or PyD-NBD also blocked IRAK-1 activation. This is the first example of a CLR protein that antagonizes inflammatory responses initiated by TLR agonists via interference with IRAK-1 activation.
Publication types
-
Research Support, N.I.H., Extramural
-
Research Support, Non-U.S. Gov't
MeSH terms
-
Adaptor Proteins, Signal Transducing / metabolism
-
Amino Acid Motifs
-
Antigens, Differentiation / metabolism
-
Caspases / chemistry
-
Cell Line
-
Cytokines / metabolism
-
Cytoskeletal Proteins / chemistry
-
Enzyme-Linked Immunosorbent Assay
-
Genes, Reporter
-
Humans
-
Immunoprecipitation
-
Inflammation
-
Interleukin-1 Receptor-Associated Kinases
-
Intracellular Signaling Peptides and Proteins / metabolism
-
Intracellular Signaling Peptides and Proteins / physiology*
-
Luciferases / metabolism
-
Monocytes / metabolism
-
Mycobacterium tuberculosis / metabolism*
-
Myeloid Differentiation Factor 88
-
NF-kappa B / metabolism
-
Nuclear Pore Complex Proteins / metabolism
-
Phosphorylation
-
Plasmids / metabolism
-
Promoter Regions, Genetic
-
Protein Kinases / metabolism
-
Protein Structure, Tertiary
-
Pyrin
-
RNA / metabolism
-
RNA, Small Interfering / metabolism
-
RNA-Binding Proteins / metabolism
-
Receptors, Immunologic / metabolism
-
Retroviridae / genetics
-
Reverse Transcriptase Polymerase Chain Reaction
-
Signal Transduction
-
TNF Receptor-Associated Factor 2 / metabolism
-
TNF Receptor-Associated Factor 6 / metabolism
-
Toll-Like Receptors / metabolism*
-
Transcription Factor RelA / metabolism
-
Transcriptional Activation
-
Transfection
-
Tumor Necrosis Factor-alpha / metabolism*
Substances
-
AGFG1 protein, human
-
Adaptor Proteins, Signal Transducing
-
Antigens, Differentiation
-
Cytokines
-
Cytoskeletal Proteins
-
Intracellular Signaling Peptides and Proteins
-
MEFV protein, human
-
MYD88 protein, human
-
Myeloid Differentiation Factor 88
-
NF-kappa B
-
NLRP12 protein, human
-
Nuclear Pore Complex Proteins
-
Pyrin
-
RELA protein, human
-
RNA, Small Interfering
-
RNA-Binding Proteins
-
Receptors, Immunologic
-
TNF Receptor-Associated Factor 2
-
TNF Receptor-Associated Factor 6
-
Toll-Like Receptors
-
Transcription Factor RelA
-
Tumor Necrosis Factor-alpha
-
RNA
-
Luciferases
-
Protein Kinases
-
Interleukin-1 Receptor-Associated Kinases
-
Caspases