Chong-Shan Shi and John H. Kehrl

Chong-Shan Shi

B Cell Molecular Immunology Section; Laboratory of Immunoregulation; National Institute of Allergy and Infectious Diseases; National Institutes of Health; Bethesda, MD USA

John H. Kehrl

National Institutes of Health; Bethesda, MD

Toll-like receptor 4 (TLR4) signaling triggers autophagy, which has been linked to both adaptive and innate immunity. Engagement of TLR4 recruits to the receptor complex Beclin 1, a key component of a class III phosphatidylinositol 3-kinase complex (PI3KC3) that initiates autophagosome formation. Recently, we found that tumor necrosis factor receptor (TNFR)-associated factor 6 (TRAF6)-mediates Lys⁶³ (K63)-linked ubiquitination of Beclin 1 is crucial for TLR4-triggered autophagy in macrophages. We identified two TRAF6-binding motifs in Beclin 1 that facilitate the binding of TRAF6 and the ubiquitination of Beclin 1. A lysine located in the Bcl-2 homology 3 (BH3) domain of Beclin 1 serves as a major site for K63-linked ubiquitination. Opposing TRAF6, the deubiquitinating enzyme A20 reduces the extent of K63-linked ubiquitination of Beclin 1 and limits the induction of autophagy in response to TLR4 signaling. Furthermore, treatment of macrophages with either interferon- or interleukin-1 triggers the K63-linked ubiquitination of Beclin 1 and the formation of autophagosomes. These results indicate that the status of K63-linked ubiquitination of Beclin 1 plays a key role in regulating autophagy during inflammatory responses.

Punctum to: Shi CS, Kehrl JH. TRAF6 and A20 regulate lysine 63-linked ubiquitination of Beclin-1 to control TLR4-induced autophagy. Sci Signal 2010; 3:ra42; PMID: 20501938; DOI: 10.1126/scisignal.2000751.
PMID: 20501938 DOI: 10.1126/scisignal.20