Toll-like receptor (TLR) 3 signaling requires the TLR4 interactor with leucine-rich repeats (TRIL).

Abstract

Toll-like (TLRs) receptors are a family of proteins that act as the primary sensors of microbial products. Many TLRs require accessory molecules in order to recognize these microbial products and initiate signal transduction cascades. We have identified TLR4 interactor with leucine rich repeats (TRIL) as a novel modulator of TLR4 signaling showing high expression in the brain. We now show that TRIL also plays a role in TLR3 signaling. TRIL is expressed intracellularly in the astrocytoma cell line U373 and in the monocytic cell line THP1. TRIL co-localizes with the endosomal compartment. These data are consistent with a role for TRIL in TLR3 signaling and endosomal TLR4 signaling. TRIL was induced by the TLR3 ligand Poly:IC. Over-expression of TRIL enhanced cytokine production and ISRE-luciferase activity following PolyI:C stimulation in U373. TRIL interacted with TLR3 and this interaction was enhanced following PolyI:C stimulation. Transient knock down of TRIL with siRNA or stable knockdown using shRNA in U373 cells inhibited TLR3 signaling, reducing ISRE-Lucifersae, RANTES, and Type I Interferon production. Knockdown of TRIL did not affect TLR2 signaling. Most accessory molecules identified to date such as CD14, gp96, PRAT4a and Unc93B all play roles in multiple TLR signaling pathways, and we now show that this is also the case for TRIL.