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

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 Ca 2+ 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.

Proteomic analysis of Atg8-dependent recruitment of phagosomal proteins in the enteric protozoan parasite Entamoeba histolytica

“…It may be possible that CAP is cooperatively involved in the closure/pinch-off of the phago/trogosomes. It is worth mentioning that by gene survey, E. histolytica lacks typical membrane-associated adenylyl cyclase and has soluble adenylyl cyclase ( Agarwal et al., 2020 ). Agarwal and colleagues have shown an adenylyl cyclase activator or inhibitor respectively increases or decreases erythrophagocytosis in E. histolytica ( Agarwal et al., 2020 ).…”

“…It is worth mentioning that by gene survey, E. histolytica lacks typical membrane-associated adenylyl cyclase and has soluble adenylyl cyclase ( Agarwal et al., 2020 ). Agarwal and colleagues have shown an adenylyl cyclase activator or inhibitor respectively increases or decreases erythrophagocytosis in E. histolytica ( Agarwal et al., 2020 ). The role of cAMP signaling and CAP in actin regulation during phagocytosis/trogocytosis needs to be elucidated in E. histolytica in future.…”

Signals and signal transduction pathways in Entamoeba histolytica during the life cycle and when interacting with bacteria or human cells

“…The β1‐adrenergic receptor is a surface G protein‐coupled receptor (GPCR) (Hall, 2004) that recognizes ligands, such as catecholamines through its extracellular N‐terminal domain. In humans, there are over 800 GPCRs (Sutkeviciute & Vilardaga, 2020), but no GPCR receptor implicated in amoebic encystation has been described so far, although other GPCRs have been found in E. histolytica (Agarwal et al, 2020; Brewer et al, 2013; Ehrenkaufer et al, 2007; Picazarri et al, 2005).…”

“…The presence of epinephrine in extracts of E. histolytica and the fact that encystation of E. invadens is activated by forskolin, a compound stimulating adenylyl cyclase (AC) to promotes cAMP synthesis, reinforce the hypothesis that GPCR/GTPase signaling supports amoebic encystation (Bosch & Siderovski, 2013). There are some evidences indicating the presence of a G‐protein‐regulated cAMP pathway in Entamoeba (Agarwal et al, 2020). cAMP is an activator of protein kinase A (Gilchrist, 2007; Patra et al, 2020; Sutkeviciute & Vilardaga, 2020), which in the nucleus, turns on the transcription factor CREB (cAMP response element‐binding protein (Bourtchuladze et al, 1994), which acts as a transcriptional gene regulator.…”