Stress-Dependent Expression of a Polymorphic, Charged Antigen in the Protozoan Parasite Entamoeba histolytica

Abstract

We have identified a novel stress inducible gene, Ehssp1 in Entamoeba histolytica, the causative agent of amebiasis. Ehssp1 belongs to a polymorphic, multigene family and is present on multiple chromosomes. No homologue of this gene was found in the NCBI database. Sequence alignment of the multiple copies, and genomic PCR data restricted the polymorphism to the central region of the gene. This region contains a polypurine stretch that encodes a domain rich in acidic and basic amino acids. Under normal culture conditions only one copy of this multigene family is expressed, as observed by Northern blot and RT-PCR analysis. The size of this copy of the gene is 1,077 nucleotides, encoding a protein of 359 amino acids. The polymorphic domain in this copy is 64 nucleotides long. However, on exposure of cells to stress conditions such as heat shock or oxidative stress, multiple polymorphic copies of the gene are expressed, suggesting a possible role of this gene in adaptation of cells to stress conditions. The gene copy expressed under normal conditions, and the expression profile of cells under heat stress was identical in two different strains of E. histolytica tested. Interestingly, the extent of polymorphism in this gene was very less in E. dispar, a nonpathogenic sibling species of E. histolytica. Ehssp1 was found to be antigenic in invasive amebiasis patients.

The lysine- and glutamic acid-rich protein KERP1 plays a role in Entamoeba histolytica liver abscess pathogenesis

“…Genes encoding stress-related proteins were among the most highly expressed ones. Noteworthy findings included the ninefold overexpression of the ssp1 stress-inducible gene (Satish et al, 2003), peroxiredoxin (providing protection from oxidative stress) and, very close to scores, two isoforms of Hsp90 (an important chaperone in the stress response). Genes involved in the ubiquitin-dependent proteolysis pathway and those encoding 26S proteasome regulatory complex components were also upregulated in virulent parasites.…”

Identification of Differentially Expressed Genes in Virulent and NonvirulentEntamoebaSpecies: Potential Implications for Amebic Pathogenesis

“…The majority (ϳ80%) of genes in this category did not have highly conserved homologues in the E. dispar SAW760 database, and none of the genes had been identified in previous studies relating to amebic virulence. Interestingly, five of the identified genes (147.m00110, 543.m00021, 864.m00008, 296.m00047, and 460.m00024) showed homology to the open reading frame found in the SSE58 repeat region identified as encoding a stress-dependent polymorphic charged antigen (Ehssp1) (48). We confirmed a lack of expression in E. dispar SAW760 and E. histolytica Rahman for one gene family member (460.m00024) by Northern blot analysis (data not shown; P. Vanchinathan, personal communication).…”

Identification of putative transcriptional regulatory networks in Entamoeba histolytica using Bayesian inference

“…The majority of genes that contain ⩾2 of these motifs are annotated as hypothetical proteins by The Institute for Genomic Research, but a number of those have significant BLASTP matches to a polymorphic, charged antigen, E. histolytica stress-sensitive protein 1 (Ehssp1) (32). Three subfamilies of the Ehssp gene family were previously identified, varying in domain composition, primarily of the charged medial domain (32). We created an HMM of the C-terminal domain shared by all three subfamilies.…”

“…When the Ehssp gene family was first identified, it was shown that some members of this gene family were responsive to heat and oxidative stresses (32). However, the authors did not determine how many members of the Ehssp gene family were responsive to stress, or if there were other members of the Ehssp gene family that were not stress responsive.…”