The Calmodulin-like Calcium Binding Protein EhCaBP3 of Entamoeba histolytica Regulates Phagocytosis and Is Involved in Actin Dynamics

Saima Aslam, Sudha Bhattacharya, Alok Bhattacharya

PLoS Pathog (2012) 8(12): e1003055

Speaker: Jian-Ming Huang (黃建銘)                                  Time: 15:00~16:00, May. 28, 2014

Commentator: Dr. Jenn-Wei Chen (陳振暐 老師)             Place: Room 601

Abstract:

        Entamoeba histolytica is an anaerobic parasitic protozoan with an estimated 50 million people infected each year. E. histolytica, a parasite that colonizes the human gut and causes dysentery, is endemic in many developing countries and causes a high level of morbidity and mortality.¹ Phagocytosis is considered to be significant in E. histolytica pathogenesis when infecting sites such as liver, brain and lungs through the bloodstream and inducing lots of serious disease.² Hence, the authors inferred whether the Calmodulin-like Calcium Binding Protein of E. histolytica, EhCaBP3, regulates phagocytosis and is concerned with actin dynamics. By using imaging techniques, the authors have observed localization of EhCaBP3 and role of Ca²⁺ during phagocytosis of RBCs. First of all, EhCaBP3 was found in phagocytic cups and freshly formed phagosomes along with actin and myosin IB. In the second place, the authors demonstrated that EhCaBP3 directly binds actin to influence its polymerization and bundling activity by co-sedimentation assay; furthermore, it also welds myosin 1B in the presence of Ca²⁺. In consequently, Ca²⁺ plays a principal role in the process of phagocytosis. To comprehend whether EhCaBP3 is necessitated phagocytosis to occur, the authors hypothesized that the expressional level of EhCaBP3 was down regulated by antisense RNA in cells. Interestingly, the level of RBC uptake was reduced; on the other hand, myosin IB was found to be absent at the site of pseudopod cup closure. Therefore, the authors suggested that EhCaBP3 along with myosin 1B mediates the closure of phagocytic cups. In conclusion, EhCaBP3 is likely to participate in phagocytosis and actin mobilization by the presence of Ca²⁺. The authors could successfully solve the pathway of pathogenesis induced by phagocytosis fundamental to the growth and survival of this parasite; finally, developing newer drugs will be aimed accurately at the unique molecules.

References:

1.         Stanley SL, Jr. (2003) Amoebiasis. Lancet 361: 1025–1034.

2.         Orozco E, Guarneros G, Martinez-Palomo A, Sanchez T (1983) Entamoeba histolytica. Phagocytosis as a virulence factor. J Exp Med 158: 1511–1521.