Translocation of interleukin-1β into a vesicle intermediate in autophagy-mediated secretion

Recent evidence suggests that autophagy facilitates the unconventional secretion of the pro-inflammatory cytokine interleukin 1 beta (IL-1 beta). Here, we reconstituted an autophagy-regulated secretion of mature IL-1 beta (m-IL-1 beta) in non-macrophage cells. We found that cytoplasmic IL-1 beta associates with the autophagosome and m-IL-1 beta enters into the lumen of a vesicle intermediate but not into the cytoplasmic interior formed by engulfment of the autophagic membrane. In advance of secretion, m-IL-1 beta appears to be translocated across a membrane in an event that may require m-IL-1 beta to be unfolded or remain conformationally flexible and is dependent on two KFERQ-like motifs essential for the association of IL-1 beta with HSP90. A vesicle, possibly a precursor of the phagophore, contains translocated m-IL-1 beta and later turns into an autophagosome in which m-IL-1 beta resides within the intermembrane space of the double-membrane structure. Completion of IL-1 beta secretion requires Golgi reassembly and stacking proteins (GRASPs) and multi-vesicular body (MVB) formation.