Glycosylphosphatidylinositol-specific phospholipase C regulates transferrin endocytosis in the African trypanosome.

Abstract

GPI-PLC (glycosylphosphatidylinositol-specific phospholipase C) is expressed in bloodstream-form Trypanosoma brucei, a protozoan that causes human African trypanosomiasis. Loss of genes encoding GPI-PLC reduces the virulence of a pleomorphic strain of the parasite, for reasons that are not clear. In the present paper, we report that GPI-PLC stimulates endocytosis of transferrin by 300-500%. Surprisingly, GPI-PLC is not detected at endosomes, suggesting that the enzyme does not interact directly with the endosomal machinery. We therefore hypothesized that a diffusible product of the GPI-PLC enzyme reaction [possibly DAG (diacylglycerol)] mediated the biological effects of the protein. Two sets of data support this assertion. First, a catalytically inactive Q81L mutant of GPI-PLC, expressed in a GPI-PLC-null background, had no effect on endocytosis, indicating that enzyme activity is essential for the protein to stimulate endocytosis. Secondly, the exogenous DAGs OAG (1-oleyl-2-acetyl-sn-glycerol) and DMG (dimyristoylglycerol) independently stimulated endocytosis of transferrin. Furthermore, the DAG mimic PMA, a phorbol ester, also activated endocytosis in T. brucei. DAG-stimulated endocytosis is a novel pathway in the trypanosome. We surmise that (i) GPI-PLC regulates transferrin endocytosis in T. brucei, (ii) GPI-PLC is a signalling enzyme, and (iii) DAG is a second messenger for GPI-PLC. We propose that regulation of endocytosis is a physiological function of GPI-PLC in bloodstream T. brucei.

• Authors: Sandesh Subramanya, C Frank Hardin, Dietmar Steverding, Kojo Mensa-Wilmot
• Journal: The Biochemical journal (Biochem J) Vol. 417 Issue 3 Pg. 685-94 (Feb 01 2009) ISSN: 1470-8728 [Electronic] England
• PMID: 18785878 (Publication Type: Journal Article, Research Support, N.I.H., Extramural)

Chemical References

• Diglycerides
• Phorbol Esters
• Protozoan Proteins
• Transferrin
• Glycosylphosphatidylinositol Diacylglycerol-Lyase

Topics

• Animals
• Diglycerides (metabolism)
• Endocytosis (physiology)
• Glycosylphosphatidylinositol Diacylglycerol-Lyase (genetics, metabolism)
• Microscopy, Fluorescence
• Phorbol Esters (metabolism)
• Protozoan Proteins (genetics, metabolism)
• Transferrin (metabolism)
• Trypanosoma brucei brucei (enzymology, metabolism)