Entamoeba histolytica stimulates the unstable transcription of c-fos and tumour necrosis factor-alpha mRNA by protein kinase C signal transduction in macrophages.
Macrophages play an important role in the control of and resistance to Entamoeba histolytica (E. histolytica). However, E. histolytica infections are characterized by suppression of cell-mediated immunity. To elucidate the molecular mechanisms whereby amoebae modulate host defences, we investigated whether the parasite elicits the 'immediate early' gene c-fos and cytokine tumour necrosis factor-alpha (TNF)-alpha mRNA and determined the signal transduction pathways involved in naive bone marrow-derived macrophages (BMM). E. histolytica stimulated a rapid and transient expression of c-fos and low levels of TNF-alpha mRNA, whereas the non-pathogenic Entamoeba moshkovshii (E. moshkovskii) did not. Inhibition of the protein kinase C (PKC) pathway with the pharmacological inhibitor H7 and by PKC depletion with phorbol myristate acetate showed that E. histolytica modulates TNF-alpha and c-fos gene expression through a PKC-dependent stimulus-response coupling event. E. histolytica activated and translocated PKC to the membrane fraction in BMM demonstrating a rapid and direct effect on PKC enzyme activity. Unlike lipopolysaccharide (LPS), BMM stimulated with E. histolytica had reduced stability of both c-fos and TNF-alpha mRNA transcripts (> 50%) and failed to secrete TNF-alpha protein. BMM treated with amoebic proteins and stimulated with LPS, or interferon-gamma (IFN-gamma)+LPS, resulted in a 33% and 50% reduction in TNF-alpha mRNA levels, respectively. These data argue that although E. histolytica stimulates c-fos and TNF-alpha gene expression through PKC signal transduction, the rapid degradation of the mRNAs, the lack of secreted TNF-alpha protein and the observed decreased responsiveness to a stimulatory signal may be a novel mechanism whereby the parasite modulates host defence mechanisms.
Seguin
R
R
Institute of Parasitology of McGill University, Ste-Anne-de-Bellevue, Québec, Canada.
Keller
K
K
Chadee
K
K
D000818:Animals; D015152:Blotting, Northern; D002478:Cells, Cultured; D004748:Entamoeba histolytica / Q000276:immunology*; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D007111:Immunity, Cellular; D008262:Macrophage Activation / Q000276:immunology*; D008264:Macrophages / Q000276:immunology* / Q000378:metabolism; D011493:Protein Kinase C / Q000032:analysis / Q000378:metabolism*; D016760:Proto-Oncogene Proteins c-fos / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D015398:Signal Transduction; D014158:Transcription, Genetic; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics / Q000378:metabolism*
D016760:Proto-Oncogene Proteins c-fos; D012333:RNA, Messenger; D014409:Tumor Necrosis Factor-alpha; D011493:Protein Kinase C