The GOLD domain-containing protein TMED7 inhibits TLR4 signalling from the endosome upon LPS stimulation

Abstract

Toll-like receptor 4 is an innate immune receptor responsible for the recognition of the Gram-negative cell wall component lipopolysaccharide. Here we show that transmembrane emp24 domain-containing protein 7 (TmED7) inhibits myD88-independent toll-like receptor 4 signalling. TmED7 overexpression inhibits the ability of TRAm, an adaptor utilized by tolllike receptor 4, or lipopolysaccharide to activate the interferon regulatory factor 3-signalling pathway, whereas TmED7 knockdown enhances production of the cytokine, RAnTEs, following lipopolysaccharide stimulation. upon lipopolysaccharide stimulation, TmED7 co-localizes with TRAm and toll-like receptor 4 in late endosomes where it encounters the negative regulator of TRAm, TAG. The TmED7 sequence is found in TAG because of a read-through from the tmed7 gene into the ticam2 gene. TmED7 is essential for TAG-mediated disruption of the TRAm/ TRIF complex and the degradation of toll-like receptor 4. A TmED homologue, logjam, has a negative role in the Toll and ImD pathways in Drosophila melanogaster; therefore, TmEDs may have a conserved role in the regulation of innate immunity.

UBE2O negatively regulates TRAF6-mediated NF-κB activation by inhibiting TRAF6 polyubiquitination

“…Flag-IRAK1, Flag-IRAK4 and MyD88-Myc were kindly given by Professor Thomas Miethke (Technische Universität München, Germany) [28]. TRIF-HA was provided by Dr Luke AJ O'Neill (Trinity College Dublin, Ireland) [29] and Flag-TLR3 (Addgene plasmid 32712) was a gift of Saumen Sarkar (University of Pittsburgh Cancer Institute, USA) [30].…”

The GOLD Domain-containing Protein TMED1 Is Involved in Interleukin-33 Signaling*

“…In mammals, TMED10 can bind to the MHC class I heavy chain and may protect free MHC class I heavy chains from destruction by ER-associated degradation (26). TAG and TMED7, which contain GOLD domains, have been demonstrated to negatively regulate MyD88-independent TLR4 signaling by displacing the adaptor TRIF from TRAM in the TLR4 signaling complex (20,21). Given that TMED7 regulates TLR4 signaling and that TMED1 has been shown to potentially interact with ST2L, we sought to determine whether TMED1 is involved in the ST2L signaling pathway.…”

“…TMED proteins are membrane-spanning proteins that were thought to have their N terminus and GOLD domain located in the ER/Golgi lumen and their C terminus on the cytosolic side of the membrane. However, recent data regarding TMED7 have demonstrated that it possesses an N-terminal transmembrane domain that is responsible for its ability to traverse the membrane and that its GOLD domain is actually located in the cytosolic compartment (20). Transmembrane prediction programs used to analyze the TMED1 sequence suggest that it does not possess a second transmembrane domain located at the N terminus, which corresponds to the region in which the transmembrane domain in TMED7 is found.…”

“…co-localize with TMED10 (16,28). TMED1 may also localize to endocytic compartments, such as early endosomes, as the related family member TMED7 has been shown to do so (20). Although the internalization of ST2L ultimately results in the degradation of the receptor, acting as a mechanism to limit signal activation (14), it is possible that signal activation can occur from intracellular endocytic compartments as well as from the plasma membrane while ST2L is being internalized.…”

“…In addition, the GOLD domain-containing proteins TAG (TRAM adaptor with GOLD domain) and the TMED family member TMED7 have been shown to limit TLR4 signaling to the transcription factor IRF3 (interferon regulatory factor 3). They act by displacing the adaptor TRIF (TIR domain-containing adaptor-inducing interferon-␤) from TRAM (TRIF-related adaptor molecule) in the endosomal TLR4 signaling complex (20,21).…”