Traf6 and A20 differentially regulate TLR4-induced autophagy by affecting the ubiquitination of Beclin 1.

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 Lys(63) (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 interferonγ 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.