MyD88-induced downregulation of IRAK-4 and its structural requirements


  • Editor: Patrick Brennan

Correspondence: Ken-ichi Tanamoto, Division of Microbiology, National Institute of Health Sciences, 1-18-1 Kamiyoga, Setagaya, Tokyo 158-8501, Japan. Tel.: +81 3 3700 1141, ext. 272; fax: +81 3 3707 6950; e-mail:


IRAK-4 plays an essential role in Toll-like receptor (TLR)/IL-1 receptor signaling. However, its signaling and regulation mechanisms have remained elusive. We have reported previously that stimulation of TLR2, TLR4 or TLR9, but not TLR3, leads to downregulation of IRAK-4 protein. Here, we show that expression of MyD88 leads to downregulation of endogenous as well as exogenously expressed IRAK-4 protein in HEK293 cells. Expression of TRIF did not cause IRAK-4 downregulation although it induced NF-κB activation. Expression of either a deletion mutant of MyD88 lacking its death domain or MyD88s, neither of which induced NF-κB activation, did not lead to IRAK-4 downregulation. MyD88-induced downregulation was observed in an IRAK-4 mutant lacking the kinase domain, but not in another mutant lacking the death domain. These results demonstrate that downregulation of IRAK-4 requires activation of the MyD88-dependent pathway and that the death domains of both MyD88 and IRAK-4 are important for this downregulation.