RECEPTOR-MEDIATED ENDOCYTOSIS IN Giardia lamblia.

MARÍA R. RIVERO; CECILIA V. VRANYCH; NAHUEL ZAMPONI; ANDREA S. RÓPOLO; MARÍA C. TOUZ

Rosario. Santa Fe.

Congreso; VIII Congreso Argentino de Protozoología y Enfermedades Parasitarias; 2008

Sociedad Argentina de Protozoología

Endocytosis mechanisms are poorly known in protozoa parasites.  Giardia lamblia possesses a simplified lysosomal protein trafficking system, where only two clathrin-adaptor protein complexes (AP1 and AP2) are involved. In this work, we characterize Giardia AP2 (gAP2), which shares high structural identity with the mammalian AP2 complex, which has a vital role in the accomplishment of the endocytosis process. Using a specific monoclonal antibody against the µ2 subunit of gAP2 complex, we observed its localization at the plasma membrane and in lysosome-like peripheral vacuoles, its interaction with associated proteins (e.g. receptors) and its association with clathrin. Production of µ2 double stranded RNA for protein knock-down shown that depletion of gAP2 causes a major decrease in endocytosis, being critical for the parasite growth and differentiation. In other eukaryotic cells, AP2 is not obligatory for all clathrin-mediated uptakes, and several alternate adaptors appear to perform similar sorting and assembly functions arguing against the simplified mechanism suggested for Giardia. The use of standard molecules and the discovery of a putative LDL-membrane receptor together with the employment of classical and cutting-edge technologies like confocal and total internal reflection fluorescence (TIRF) microscopy demonstrated that, indeed, gAP2 specifically participates in receptor-mediated endocytosis without the participation of clathrin-associated sorting proteins. Once more, our studies support a model whereby lysosomal sorting and transport in Giardia require minimal machinery and that it is significantly divergent from higher eukaryotes.