title: Characterization of the autophagy marker protein Atg8 reveals atypical features of autophagy in Plasmodium falciparum.
abstract: Conventional autophagy is a lysosome-dependent degradation process that has crucial homeostatic and regulatory functions in eukaryotic organisms. As malaria parasites must dispose a number of self and host cellular contents, we investigated if autophagy in malaria parasites is similar to the conventional autophagy. Genome wide analysis revealed a partial autophagy repertoire in Plasmodium, as homologs for only 15 of the 33 yeast autophagy proteins could be identified, including the autophagy marker Atg8. To gain insights into autophagy in malaria parasites, we investigated Plasmodium falciparum Atg8 (PfAtg8) employing techniques and conditions that are routinely used to study autophagy. Atg8 was similarly expressed and showed punctate localization throughout the parasite in both asexual and sexual stages; it was exclusively found in the pellet fraction as an integral membrane protein, which is in contrast to the yeast or mammalian Atg8 that is distributed among cytosolic and membrane fractions, and suggests for a constitutive autophagy. Starvation, the best known autophagy inducer, decreased PfAtg8 level by almost 3-fold compared to the normally growing parasites. Neither the Atg8-associated puncta nor the Atg8 expression level was significantly altered by treatment of parasites with routinely used autophagy inhibitors (cysteine (E64) and aspartic (pepstatin) protease inhibitors, the kinase inhibitor 3-methyladenine, and the lysosomotropic agent chloroquine), indicating an atypical feature of autophagy. Furthermore, prolonged inhibition of the major food vacuole protease activity by E64 and pepstatin did not cause accumulation of the Atg8-associated puncta in the food vacuole, suggesting that autophagy is primarily not meant for degradative function in malaria parasites. Atg8 showed partial colocalization with the apicoplast; doxycycline treatment, which disrupts apicoplast, did not affect Atg8 localization, suggesting a role, but not exclusive, in apicoplast biogenesis. Collectively, our results reveal several atypical features of autophagy in malaria parasites, which may be largely associated with non-degradative processes.
authors.affiliation: Council of Scientific & Industrial Research (CSIR)-Centre for Cellular and Molecular Biology, Hyderabad, AP, India.
authors.forename: Rahul
authors.initials: R
authors.lastname: Navale
authors.affiliation: Council of Scientific & Industrial Research (CSIR)-Centre for Cellular and Molecular Biology, Hyderabad, AP, India.
authors.lastname: Atul
authors.affiliation: Council of Scientific & Industrial Research (CSIR)-Centre for Cellular and Molecular Biology, Hyderabad, AP, India.
authors.forename: Aparna Devi
authors.initials: AD
authors.lastname: Allanki
authors.affiliation: Council of Scientific & Industrial Research (CSIR)-Centre for Cellular and Molecular Biology, Hyderabad, AP, India.
authors.forename: Puran Singh
authors.initials: PS
authors.lastname: Sijwali
mesh_terms: D000225:Adenine / Q000031:analogs & derivatives / Q000494:pharmacology; D000595:Amino Acid Sequence; D000962:Antimalarials / Q000494:pharmacology; D063546:Apicoplasts / Q000187:drug effects / Q000502:physiology*; D001343:Autophagy / Q000187:drug effects / Q000235:genetics*; D000071190:Autophagy-Related Protein 8 Family; D002738:Chloroquine / Q000494:pharmacology; D004318:Doxycycline / Q000494:pharmacology; D004912:Erythrocytes / Q000187:drug effects / Q000469:parasitology; D005786:Gene Expression Regulation; D018503:Genome, Protozoan; D006801:Humans; D007930:Leucine / Q000031:analogs & derivatives / Q000494:pharmacology; D008018:Life Cycle Stages / Q000187:drug effects / Q000235:genetics; D008840:Microfilament Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D010436:Pepstatins / Q000494:pharmacology; D010963:Plasmodium falciparum / Q000187:drug effects / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D011480:Protease Inhibitors / Q000494:pharmacology; D015800:Protozoan Proteins / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
chemical_list: C000593619:ATG8 protein, Plasmodium falciparum; D000962:Antimalarials; D000071190:Autophagy-Related Protein 8 Family; D008840:Microfilament Proteins; D010436:Pepstatins; D011480:Protease Inhibitors; D015800:Protozoan Proteins; D029701:Saccharomyces cerevisiae Proteins; C025946:3-methyladenine; D002738:Chloroquine; D007930:Leucine; D000225:Adenine; D004318:Doxycycline; C024974:E 64; C031375:pepstatin