Uncovering the Cyclic AMP Signaling Pathway of the Protozoan Parasite Entamoeba histolytica and Understanding Its Role in Phagocytosis.

Shalini Agarwal,Pragyan Parimita Rath,Gaurav Anand,Samudrala Gourinath

doi:10.3389/fcimb.2020.566726

Abstract

Second messenger signaling controls a surprisingly diverse range of processes in several eukaryotic pathogens. Molecular machinery and pathways involving these messengers thus hold tremendous opportunities for therapeutic interventions. Relative to Ca2+ signaling, the knowledge of a crucial second messenger cyclic AMP (cAMP) and its signaling pathway is very scant in the intestinal parasite Entamoeba histolytica. In the current study, mining the available genomic resources, we have for the first time identified the cAMP signal transduction pathway of E. histolytica. Three heptahelical proteins with variable G-protein-coupled receptor domains, heterotrimeric G-proteins (Gα, Gβ, and Gγ subunits), soluble adenylyl cyclase, cyclase-associated protein, and enzyme carbonic anhydrase were identified in its genome. We could also identify several putative candidate genes for cAMP downstream effectors such as protein kinase A, A-kinase anchoring proteins, and exchange protein directly activated by the cAMP pathway. Using specific inhibitors against key identified targets, we could observe changes in the intracellular cAMP levels as well as defect in the rate of phagocytosis of red blood cells by the parasite E. histolytica. We thus strongly believe that characterization of some of these unexplored crucial signaling determinants will provide a paradigm shift in understanding the pathogenicity of this organism.

Highlights

Entamoeba histolytica is a major causative organism of water-borne diarrheal disease globally (Walsh, 1986; WHO, 1998)
Since the cyclic AMP (cAMP) signaling system has not yet been determined in E. histolytica, through a thorough in silico analysis we have in this study unraveled its cAMP signal transduction pathway (Figure 4)
Our in silico analysis predicted the presence of three heptahelical proteins with a variable GPCR domain, none of which have been functionally characterized to date

Summary

Introduction

Entamoeba histolytica is a major causative organism of water-borne diarrheal disease globally (Walsh, 1986; WHO, 1998). The disease accounts for nearly 50 million clinical cases and up to 100,000 deaths due to parasitic infections every year (Li and Stanley, 1996; Petri et al, 2000; Stauffer and Ravdin, 2003). E. histolytica displays a simple life cycle existing in two different stages, the infective cysts and vegetative trophozoites. Infection occurs when the human host ingests the infective and dormant cyst stage of the parasite through contaminated food and water. The cysts are converted into invasive trophozoites in the human intestine. Trophozoites multiply and encyst, and the cysts generated pass on with the stool to infect new hosts (Haque et al, 2003; Stanley, 2003; Aguilar-Diaz et al, 2011)

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Conclusion