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Abstract
Autophagy delivers cytoplasmic constituents to autophagolysosomes and is linked to both innate and adaptive immunity. Toll-like receptor 4 (TLR4) signaling induces autophagy and recruits Beclin-1, the mammalian homolog of yeast Atg6, to the receptor complex. We found that tumor necrosis factor receptor (TNFR)–associated factor 6 (TRAF6)–mediated, Lys63 (K63)–linked ubiquitination of Beclin-1 is critical for TLR4-triggered autophagy in macrophages. Two TRAF6-binding motifs in Beclin-1 facilitated the binding of TRAF6 and the ubiquitination of Beclin-1. Lys117, which is strategically located in the Bcl-2 homology 3 (BH3) domain of Beclin-1, was a major site for K63-linked ubiquitination. The deubiquitinating enzyme A20 reduced the extent of K63-linked ubiquitination of Beclin-1 and limited the induction of autophagy in response to TLR signaling. Treatment of macrophages with either interferon-γ or interleukin-1 also triggered 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.
