Linker scanning analysis of TBP promoter binding factor DNA binding, activation, and repression domains

Mechanism of cyst specific protein 21 mRNA induction during Acanthamoeba differentiation

The Acanthamoeba cyst specific protein 21 (CSP21) gene is tightly repressed in growing cells and highly induced early during differentiation into a dormant cyst. This increase is mediated by the rate of transcription of the CSP21 gene as determined by nuclear run-on assays. The promoter region of the CSP21 gene was analyzed by transcript start site mapping and in vitro transcription of wild-type or mutant templates, using extracts from growing cells. A sequence located 3' to a modified TATA box completely inhibits transcription and removal of this region permits robust transcription utilizing a start site approximately 35 base pairs downstream of the TATA box. Sequences 5' to the TATA box had no effect on transcription, suggesting that anti-repression is the only mechanism required for CSP21 induction. Fractionation of nuclear extracts yielded a fraction capable of transcription from the CSP21 promoter, and a fraction containing a promoter-specific repressing activity. Anti-repression may thus be a major mechanism regulating differentiation or maintenance of the proliferative cycle in Acanthamoeba.

In vivo interactions of the Acanthamoeba TBP gene promoter

Transcription of the TATA box binding protein (TBP) gene in Acanthamoeba castellanii is regulated by TATA box binding protein promoter binding factor (TPBF), which binds to an upstream TBP promoter element to stimulate transcription, and to a TATA proximal element, where it represses transcription. In order to extend these observations to the in vivo chromatin context, the TBP gene was examined by in situ footprinting and chromatin immunoprecipitation (ChIP). Acanthamoeba DNA is nucleosomal with a repeat of approximately 160 bp, and an intranucleosomal DNA periodicity of 10.5 bp. The TBP gene comprises a 220 bp micrococcal nuclease hypersensitive site corresponding to the promoter regulatory elements previously identified, flanked by protected regions of a size consistent with the presence of nucleosomes. ChIP data indicated that TPBF is associated with the TBP, TPBF and MIL gene promoters, but not to the CSP21, MIIHC, 5SrRNA or 39SrRNA promoters, or to the MIL gene C-terminal region. Binding by TPBF to the TPBF and MIL gene promoters was confirmed by in vitro assays. These results validate the in vitro model for TBP gene regulation and further suggest that TPBF may be autoregulated and may participate in the regulation of the MIL gene.

Acanthamoeba spp. as agents of disease in humans

Acanthamoeba spp. are free-living amebae that inhabit a variety of air, soil, and water environments. However, these amebae can also act as opportunistic as well as nonopportunistic pathogens. They are the causative agents of granulomatous amebic encephalitis and amebic keratitis and have been associated with cutaneous lesions and sinusitis. Immuno compromised individuals, including AIDS patients, are particularly susceptible to infections with Acanthamoeba. The immune defense mechanisms that operate against Acanthamoeba have not been well characterized, but it has been proposed that both innate and acquired immunity play a role. The ameba's life cycle includes an active feeding trophozoite stage and a dormant cyst stage. Trophozoites feed on bacteria, yeast, and algae. However, both trophozoites and cysts can retain viable bacteria and may serve as reservoirs for bacteria with human pathogenic potential. Diagnosis of infection includes direct microscopy of wet mounts of cerebrospinal fluid or stained smears of cerebrospinal fluid sediment, light or electron microscopy of tissues, in vitro cultivation of Acanthamoeba, and histological assessment of frozen or paraffin-embedded sections of brain or cutaneous lesion biopsy material. Immunocytochemistry, chemifluorescent dye staining, PCR, and analysis of DNA sequence variation also have been employed for laboratory diagnosis. Treatment of Acanthamoeba infections has met with mixed results. However, chlorhexidine gluconate, alone or in combination with propamidene isethionate, is effective in some patients. Furthermore, effective treatment is complicated since patients may present with underlying disease and Acanthamoeba infection may not be recognized. Since an increase in the number of cases of Acanthamoeba infections has occurred worldwide, these protozoa have become increasingly important as agents of human disease.