Ras-related protein Rab18 from hydatid cyst of Echinococcus granulosus induces apoptosis and autophagy in AML12 cells by inhibiting the PI3K/AKT/mTOR signaling pathway.

Cystic echinococcosis (CE) is a global zoonotic parasitic disease caused by the larval stage of Echinococcus granulosus (Eg). The hydatid cysts of CE mainly develop in the liver, causing serious liver damage and even endangering the life of the host. Ras-related protein Rab18, which is involved in liver injury, represents a crucial protein in these disease and a potential therapeutic target. However, the regulation mechanism by which Rab18 from hydatid cyst on host hepatocytes has not been fully elucidated. Therefore, we expressed Rab18 recombinant protein (rRab18) in prokaryotic expression system and analysed its secretion characteristics and localisation. Then, the effects of rRab18 on the proliferation, apoptosis, and autophagy of AML12 cells were detected. In addition, the involvement of phosphoinositide 3-kinase/protein kinase B/mammalian target of rapamycin (PI3K/ AKT/mTOR) pathway was identified by western blot. The results showed that rRab18 was mainly expressed in the protoscoleces and could be secreted into the host liver tissue. rRab18 inhibited proliferation of AML12 cells. Moreover, rRab18 induced AML12 cells apoptosis, as evidenced by the increase in the number of cells with damaged cell membranes, and increased apoptosis rate, Bax/Bcl-2 ratio, and activated cleaved caspase-3 levels. Furthermore, rRab18 induced autophagy in AML12 cells by enhancing the expression of LC3-II and decreasing the p62. rRab18 inhibited the PI3K/AKT/mTOR pathway in AML12 cells, as shown by decreased p-PI3K, p-AKT and p-mTOR expression, and the PI3K inhibitor LY294002 promoted these changes and enhanced rRab18 induced apoptosis and autophagy, whereas the PI3K agonist 740Y-P reversed these effects. These results indicated that rRab18 may induce apoptosis and autophagy through PI3K/Akt/mTOR pathway, which provided a preliminary basis for further studying the interaction between hydatid cyst and the liver of host.