Studies on the recycling of the transferrin receptor in Trypanosoma brucei using an inducible gene expression system.

Uptake of host transferrin in bloodstream forms of Trypanosoma brucei is mediated by a heterodimeric, glycosylphosphatidylinositol-anchored receptor. After endocytosis, transferrin is delivered to lysosomes where it is proteolytically degraded. Whether the heterodimeric transferrin receptor is returned to mediate several cycles in ligand uptake is undefined. By using an inducible gene expression system we provide evidence for recycling of the transferrin receptor in bloodstream forms of T. brucei. The metabolic half-life of the transferrin receptor in bloodstream-form trypanosomes is determined to be 7 h which is comparable to the half-lives of recycling receptors in mammalian cells. The cycling time of the trypanosomal transferrin receptor is calculated to be 11 min. By means of the half-life and the cycling time, we calculated that each receptor is recycled 60 times before being degraded on average.