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Entamoeba histolytica phagocytosis of human erythrocytes involves PATMK, a member of the transmembrane kinase family.

ABSTRACT: Entamoeba histolytica is the cause of amebic colitis and liver abscess. This parasite induces apoptosis in host cells and utilizes exposed ligands such as phosphatidylserine to ingest the apoptotic corpses and invade deeper into host tissue. The purpose of this work was to identify amebic proteins involved in the recognition and ingestion of dead cells. A member of the transmembrane kinase family, phagosome-associated TMK96 (PATMK), was identified in a proteomic screen for early phagosomal proteins. Anti-peptide affinity-purified antibody produced against PATMK demonstrated that it was a type I integral membrane protein that was expressed on the trophozoite surface, and that co-localized with human erythrocytes at the site of contact. The role of PATMK in erythrophagocytosis in vitro was demonstrated by: (i) incubation of ameba with anti-PATMK antibodies; (ii) PATMK mRNA knock-down using a novel shRNA expression system; and (iii) expression of a carboxy-truncation of PATMK (PATMK(delta932)). Expression of the carboxy-truncation of PATMK(delta932) also caused a specific reduction in the ability of E. histolytica to establish infection in the intestinal model of amebiasis, however these amebae retained the ability to cause hepatic abscesses when directly injected in the liver. In conclusion, PATMK was identified as a member of the TMK family that participates in erythrophagocytosis and is uniquely required for intestinal infection.

SUBMITTER: Boettner DR

PROVIDER: S-EPMC2211552 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Entamoeba histolytica transmembrane kinases (EhTMKs) can be grouped into six distinct families on the basis of motifs and sequences. Analysis of the E. histolytica genome revealed the presence of 35 EhTMKB1 members on the basis of sequence identity (>or=95%). Only six homologs were full length containing an extracellular domain, a transmembrane segment and an intracellular kinase domain. Reverse transcription followed by polymerase chain reaction (RT-PCR) of the kinase domain was used to generate a library of expressed sequences. Sequencing of randomly picked clones from this library revealed that about 95% of the clones were identical with a single member, EhTMKB1-9, in proliferating cells. On serum starvation, the relative number of EhTMKB1-9 derived sequences decreased with concomitant increase in the sequences derived from another member, EhTMKB1-18. The change in their relative expression was quantified by real time PCR. Northern analysis and RNase protection assay were used to study the temporal nature of EhTMKB1-9 expression after serum replenishment of starved cells. The results showed that the expression of EhTMKB1-9 was sinusoidal. Specific transcriptional induction of EhTMKB1-9 upon serum replenishment was further confirmed by reporter gene (luciferase) expression and the upstream sequence responsible for serum responsiveness was identified. EhTMKB1-9 is one of the first examples of an inducible gene in Entamoeba. The protein encoded by this member was functionally characterized. The recombinant kinase domain of EhTMKB1-9 displayed protein kinase activity. It is likely to have dual specificity as judged from its sensitivity to different kinase inhibitors. Immuno-localization showed EhTMKB1-9 to be a surface protein which decreased on serum starvation and got relocalized on serum replenishment. Cell lines expressing either EhTMKB1-9 without kinase domain, or EhTMKB1-9 antisense RNA, showed decreased cellular proliferation and target cell killing. Our results suggest that E. histolytica TMKs of B1 family are functional kinases likely to be involved in serum response and cellular proliferation.

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Entamoeba histolytica phagocytosis of human erythrocytes involves PATMK, a member of the transmembrane kinase family.

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