Plasmodium falciparum Atg18 localization to the food vacuole is phosphatidylinositol 3-phosphate-dependent and quinoline-sensitive

Malaria parasites exhibit atypical, but essential, autophagy process, which is also associated with resistance to chloroquine and artemisinin. To better understand the autophagy process and its association with drug resistance, we investigated P. falciparum Atg18 (PfAtg18), a PROPPIN family protein, whose members like S. cerevisiae Atg18 and human WIPI2 are essential for autophagy. PfAtg18 and its mutants were expressed in P. falciparum and assessed for localization and co-localization, the effect of various inhibitors and antimalarials on PfAtg18 localization, and to identify PfAtg18-interacting proteins. PfAtg18 is expressed in asexual erythrocytic stages and localized to the food vacuole, which was also observed with other Plasmodium Atg18 proteins, indicating that food vacuole localization is a conserved feature. Interaction of PfAtg18 with the food vacuole-associated phosphatidylinositol 3-phosphate (PI3P) is essential for localization, as PfAtg18 mutants of PI3P-binding motifs neither bound PI3P nor localized to the food vacuole. PfAtg18 also interacted with the food vacuole multi-drug resistance protein 1, which, in addition to PI3P, could play a major role in localization of PfAtg18. PfAtg18 interacted and co-localized with P. falciparum Atg8 at a peri-food vacuole site, which may be a site for generation of PfAtg8 puncta. PfAtg18 localization was greatly affected upon treatment with chloroquine and amodiaquine, suggesting that these quinolines target PfAtg18 or the proteins that might be involved in its localization. Food vacuole localization, altered localization upon treatment with chloroquine and amodiaquine, and interaction with the multi-drug resistance protein 1 present PfAtg18 as a potential link between autophagy and the associated drug resistance.