Fig. 8. Mechanism of formation of the inducible amphisome with anti-IAV activity.

After IAV infection, newly synthesized HA is transported to the apical surface of the plasma membrane via vesicular trafficking (i). PVF-tet can penetrate into the cells and directly bind to the newly synthesized HA in the trans-Golgi Network to form an HA-containing structure. This structure subsequently matures into the amphisome, resulting in the sequestration of HA in this structure to inhibit virus propagation. Autophagic machinery is essential for this maturation step, because gene knockout of PIK3C3 and ULK1, both of which are indispensable for the formation of an autophagosome from a pre-autophagosomal structure, abrogates the sequestration (ii). In general, ABCA3 has an essential role in the maturation of the multivesicular endosome into the lamellar body through fusion with the autophagosome (iii). After IAV infection, even in the absence of PVF-tet, the overproduction of lamellar bodies promoted by overexpression of ABCA3 can induce the formation of amphisomes with anti-IAV activity depending on the autophagic machinery (iv).