Clathrin-dependent targeting of receptors to the flagellar pocket of procyclic-form Trypanosoma brucei.
In trypanosomatids, endocytosis and exocytosis occur exclusively at the flagellar pocket, which represents about 0.43% of the pellicle membrane and is a deep invagination of the plasma membrane where the flagellum extends from the cell. Receptor molecules are selectively retained at the flagellar pocket. We studied the function of clathrin heavy chain (TbCLH) in the trafficking of the flagellar pocket receptors in Trypanosoma brucei by using the double-stranded RNA interference approach. It appears that TbCLH is essential for the survival of both the procyclic form and the bloodstream form of T. brucei, even though structures resembling large coated endocytic vesicles are absent in procyclic-form trypanosomes. Down-regulation of TbCLH by RNA interference (RNAi) for 24 h rapidly and drastically reduced the uptake of macromolecules via receptor-mediated endocytosis in procyclic-form trypanosomes. This result suggested the importance of TbCLH in receptor-mediated endocytosis of the procyclic-form trypanosome, in which the formation of large coated endocytic vesicles may not be required. Surprisingly, induction of TbCLH RNAi in the procyclic T. brucei for a period of 48 h prohibited the export of the flagellar pocket-associated transmembrane receptor CRAM from the endoplasmic reticulum to the flagellar pocket, while trafficking of the glycosylphosphatidylinositol-anchored procyclin coat was not significantly affected. After 72 h of induction of TbCLH RNAi, procyclics exhibited morphological changes to an apolar round shape without a distinct structure of the flagellar pocket and flagellum. Although trypanosomes, like other eukaryotes, use similar organelles and machinery for protein sorting and transport, our studies reveal a novel role for clathrin in the secretory pathway of trypanosomes. We speculate that the clathrin-dependent trafficking of proteins to the flagellar pocket may be essential for the biogenesis and maintenance of the flagellar pocket in trypanosomes.
Hung
Chien-Hui
CH
Department of Pathology, New York University School of Medicine, 550 First Avenue, New York, NY 10016, USA.
Qiao
Xugang
X
Lee
Pei-Tseng
PT
Lee
Mary Gwo-Shu
MG
D000818:Animals; D002462:Cell Membrane / Q000378:metabolism* / Q000648:ultrastructure; D048430:Cell Shape; D033922:Clathrin Heavy Chains / Q000235:genetics / Q000378:metabolism*; D004705:Endocytosis / Q000502:physiology; D005407:Flagella / Q000378:metabolism* / Q000648:ultrastructure; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D015800:Protozoan Proteins / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D011956:Receptors, Cell Surface / Q000378:metabolism*; D014346:Trypanosoma brucei brucei / Q000166:cytology* / Q000502:physiology*
D008565:Membrane Proteins; D015800:Protozoan Proteins; D011956:Receptors, Cell Surface; C065453:cysteine-rich, acidic integral membrane protein, Trypanosoma brucei; D033922:Clathrin Heavy Chains