title: The LAMP-like protein p67 plays an essential role in the lysosome of African trypanosomes.
abstract: RNAi knockdown was employed to study the function of p67, a lysosome-associated membrane protein (LAMP)-like type I transmembrane lysosomal glycoprotein in African trypanosomes. Conditional induction of p67 dsRNA resulted in specific approximately 90% reductions in de novo p67 synthesis in both mammalian bloodstream and procyclic insect-stage parasites. Bloodstream cell growth was severely retarded with extensive death after > 24 h of induction. Biosynthetic trafficking of residual p67, and of the soluble lysosomal protease trypanopain, were unimpaired. Endocytosis of tomato lectin, a surrogate receptor-mediated cargo, was only mildly impaired (approximately 20%), but proper lysosomal targeting was unaffected. p67 ablation had dramatic effects on lysosomal morphology with gross enlargement (four- to fivefold) and internal membrane profiles reminiscent of autophagic vacuoles. Ablation of p67 expression rendered bloodstream trypanosomes refractory to lysis by human trypanolytic factor (TLF), a lysosomally activated host innate immune mediator. Similar effects on lysosomal morphology and TLF sensitivity were also obtained by two pharmacological agents that neutralize lysosomal pH--chloroquine and bafilomycin A1. Surprisingly, however, lysosomal pH was not affected in ablated cells suggesting that other physiological alterations must account for increased resistance to TLF. These results indicate p67 plays an essential role in maintenance of normal lysosomal structure and physiology in bloodstream-stage African trypanosomes.
authors.affiliation: Department of Medical Microbiology & Immunology, University of Wisconsin School of Medicine and Public Health, Madison, WI 53706, USA.
authors.forename: Ronald F
authors.initials: RF
authors.lastname: Peck
authors.forename: April M
authors.initials: AM
authors.lastname: Shiflett
authors.forename: Kevin J
authors.initials: KJ
authors.lastname: Schwartz
authors.forename: Amanda
authors.initials: A
authors.lastname: McCann
authors.forename: Stephen L
authors.initials: SL
authors.lastname: Hajduk
authors.forename: James D
authors.initials: JD
authors.lastname: Bangs
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D004705:Endocytosis; D023061:Gene Order; D018503:Genome, Protozoan; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008075:Lipoproteins, HDL / Q000276:immunology; D051907:Lysosomal Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008247:Lysosomes / Q000378:metabolism* / Q000648:ultrastructure; D008969:Molecular Sequence Data; D010447:Peptide Hydrolases / Q000378:metabolism; D015800:Protozoan Proteins / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D014346:Trypanosoma brucei brucei / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D014353:Trypanosomiasis, African / Q000469:parasitology*
chemical_list: D008075:Lipoproteins, HDL; D051907:Lysosomal Membrane Proteins; D015800:Protozoan Proteins; C434063:TLF1 protein, human; D010447:Peptide Hydrolases