Transferrin regulates mRNA levels of a gene involved in iron utilization in Entamoeba histolytica

Abstract

Entamoeba histolytica is a human pathogen, which can survive using haemoglobin (Hb) as only iron supply. Two probable haemophores (Ehhmbp26 and Ehhmbp45) are involved in iron acquisition in this parasite. However, mechanisms related to their transcriptional regulation have not been studied yet. In the present work, transcriptional profiles of both genes were evaluated in trophozoites cultures grown with different iron sources. ehhmbp26 gene was repressed totally by free iron, whereas ehhmbp45 gene showed clearly detectable mRNA levels. Expression profiles for both genes were significantly increased under iron privation condition. Interestingly, ehhmbp26 transcript was highly expressed by Holo-transferrin presence. This induction appears to be independent of direct contact between these proteins, because, in vitro assays evidenced that Ehhmbp26 protein was unable to bind this metalloprotein. Besides, in silico analysis of promoter nucleotide sequences of ehhmbp26 and ehhmbp45 genes revealed some distinctive core promoter elements described in E. histolytica and T-rich regions. Taking altogether these data suggest in E. histolytica dissimilar transcriptional mechanisms involved on iron acquisition control the expression of these genes, and they are unlike to those previously described for instance: in bacteria. Our findings evidenced this pathogen regulates the expression of ehhmbp26 and ehhmbp45 genes depending on the available iron supply, always ensuring the success of its infective process.

Stem–Loop Structures in Iron-Regulated mRNAs of Giardia duodenalis

“…In all three groups, the viability of the amebae was higher than 80% after 72 h of culture. It is possible that iron differentially modulates virulence in G. duodenalis , as has been reported in E. histolytica [ 18 , 21 , 24 , 25 , 26 ] and T. vaginalis [ 17 , 19 , 20 , 22 , 23 ]. In this study, a marked decrease in parasite viability was observed over long periods of time in media under IR conditions, reflecting the parasite’s need for iron to survive.…”

“…All three genes were negatively regulated by iron, showing overexpression under IR conditions ( Figure 2 A–F). The expression of these three genes was similar to that of the E. histolytica Ehhmbp26 gene [ 24 ], whose RNA sequence formed two IRE-like hairpins at both UTRs. However, the IRE-like structure at the 3′ UTR appeared to be more stable [ 26 ].…”

“…However, the acquisition of iron is regulated to avoid the toxicity induced by the formation of free radicals. For example, in E. histolytica and T. vaginalis, iron regulates many of the proteins involved in cytoadherence and cytotoxicity, other virulence factors, and the molecules involved in growth and the basal metabolism [ 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 ]. The recent observation of therapies against protozoan pathogens based on the combination of compounds is currently a very promising direction in the drug discovery field, and iron chelation is under study [ 47 ].…”

“…This mechanism consists of cytoplasmic iron regulatory proteins (IRPs) that interact with iron-responsive elements (IREs), which are conserved stem–loop structures found in untranslated regions (UTRs) of the mRNA-encoding proteins related to iron homeostasis [ 13 , 14 , 15 , 16 ]. In protozoans such as T. vaginalis and E. histolytica , iron affects growth and pathogenicity mechanisms [ 17 , 18 , 19 , 20 , 21 ], as well as the expression of some mRNA-encoding virulence proteins [ 18 , 22 , 23 , 24 , 25 , 26 ]. In T. vaginalis, the presence of IRE-like structures in tvcp4 and tvcp12 mRNAs that are differentially regulated by iron at the post-transcriptional level [ 23 , 27 , 28 ], as well as the presence of a 135 kDa α-actinin that behaves similarly to an RNA-binding protein under iron-restricted conditions and binds to these structures, have been reported [ 29 ].…”

RNA-Binding Proteins in Trichomonas vaginalis: Atypical Multifunctional Proteins

“…Entamoeba histolytica , an enteric protozoan parasite capable of invading the intestinal mucosa and spreading to other organs uses iron as an important factor for growth, adherence, and virulence induction. The iron-dependent differential expression of mRNA encoding a 26 kDa hemoglobin-binding protein ( ehhmbp26 ), a protein involved in iron acquisition, was also reported [ 79 ]. The existence of mRNAs with IRE-like hairpins in this organism is being experimentally analyzed.…”