Activity of the Bacillus anthracis 20 kDa protective antigen component.
BACKGROUND
Anthrax is caused by Bacillus anthracis that produce two exotoxins, lethal toxin and edema toxin. The lethal toxin is composed of the lethal factor (LF) complexed with the cell binding protective antigen (PA83, 83 kDa). Likewise, the edema factor (EF) binds to the PA83 to form the edema toxin. Once PA83 is bound to the host cell surface, a furin-like protease cleaves the full-length, inactive protein into 63 kDa and 20 kDa antigens (PA63 and PA20). PA63 forms a heptamer and is internalized via receptor mediated endocytosis forming a protease-stable pore, which allows EF and LF to enter the cell and exert their toxic effects.Both proteolytically cleaved protective antigens (PA63 and PA20 fragments) are found in the blood of infected animals. The 63 kDa protective antigen PA63 fragment has been thoroughly studied while little is known about the PA20.


METHODS
In this study we examined the role of PA20 using high throughput gene expression analysis of human peripheral blood mononuclear cells (PBMC) exposed to the PA20. We constructed a PA mutant in which a Factor Xa proteolytic recognition site was genetically engineered into the protective antigen PA83 to obtain PA20 using limited digestion of this recombinant PA83 with trypsin.


RESULTS
Global gene expression response studies indicated modulation of various immune functions and showed gene patterns indicative of apoptosis via the Fas pathway in a subset of the lymphoid cells. This finding was extended to include observations of increased Caspase-3 enzymatic activity and the identification of increases in the population of apoptotic, but not necrotic cells, based on differential staining methods. We identified a list of approximately 40 inflammatory mediators and heat-shock proteins that were altered similarly upon exposure of PBMC to either rPA20 or B. anthracis spores/vegetative cells.


CONCLUSIONS
This study shows that the PA20 has an effect on human peripheral blood leukocytes and can induce apoptosis in the absence of other PA components.
Hammamieh
Rasha
R
Walter Reed Army Institute of Research, Silver Spring, Maryland, USA. rasha.hammamieh1@us.army.mil
Ribot
Wilson J
WJ
Abshire
Terry G
TG
Jett
Marti
M
Ezzell
John
J
D051997:ADP-ribosyl Cyclase 1 / Q000276:immunology; D000881:Anthrax / Q000276:immunology* / Q000382:microbiology; D000942:Antigens, Bacterial / Q000276:immunology / Q000378:metabolism*; D017209:Apoptosis; D001408:Bacillus anthracis / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D001426:Bacterial Proteins / Q000276:immunology / Q000378:metabolism; D001427:Bacterial Toxins / Q000276:immunology / Q000378:metabolism*; D053148:Caspase 3 / Q000276:immunology; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D006801:Humans; D007963:Leukocytes, Mononuclear / Q000276:immunology* / Q000382:microbiology; D020411:Oligonucleotide Array Sequence Analysis; D011994:Recombinant Proteins / Q000276:immunology / Q000378:metabolism; D019014:fas Receptor / Q000276:immunology
D000942:Antigens, Bacterial; D001426:Bacterial Proteins; D001427:Bacterial Toxins; D011994:Recombinant Proteins; C030325:anthrax toxin; D019014:fas Receptor; D051997:ADP-ribosyl Cyclase 1; D053148:Caspase 3