Toxoplasma gondii infection inhibits the mitochondrial apoptosis through induction of Bcl-2 and HSP70.
Heat-shock protein 70 (HSP70) is highly expressed in Toxoplasma gondii-infected cells. However, the role of this protein is not well understood, especially during apoptosis. This study addresses the mechanism behind the antiapoptotic chaperone activity of HSP70 in Toxoplasma-infected host cells using a human macrophage cell line, THP-1 by Western blot, DNA fragmentation assay, immunoprecipitation, and a caspase-3/7 activity assay based on cleavage of the colorimetric substrate DEVD-pNA. Apoptosis induced by arsenic trioxide (As(2)O(3)) was inhibited in T. gondii-infected THP-1 cells, but not in uninfected cells. Without As(2)O(3) induction of apoptosis, T. gondii infection caused increased expression of Bcl-2 and HSP70, but not caspase-3. However, active form caspase-3 levels were lower in As(2)O(3)-treated infected cells as compared with As(2)O(3)-treated uninfected cells. Bcl-2 expression in As(2)O(3)-treated infected cells was similar to that in cells infected with T. gondii. Translocation of apoptosis-inducing factor (AIF) and release of cytochrome c from mitochondria were inhibited in As(2)O(3)-treated infected cells as compared with As(2)O(3)-treated uninfected cells. Increased parasite loads in Toxoplasma-infected macrophages caused higher HSP70 and Bcl-2 expression in whole-cell extracts and fractionated components, respectively. However, expression of AIF and cytochrome c was unaffected. Toxoplasma dose-dependently inhibited caspase-3 activation, thus revealing an anti-apoptotic parasite activity on cytochrome c-mediated caspase activation in subcellular components. In addition, immunoprecipitation analysis suggested that HSP70 is capable of binding to the pro-apoptotic factors AIF and Apaf-1, but not to cytochrome c or procaspase-9. Taken together, these data demonstrate that T. gondii infection inhibits mitochondrial apoptosis through overproduction of anti-apoptotic Bcl-2 as well as HSP70, which are increased parasite loads dependently.
Hwang
Il-Young
IY
Department of Infection Biology, Research Institute for Medical Science, Chungnam National University School of Medicine, 6 Munhwa-dong, Jung-gu, Daejeon, 301-131, South Korea.
Quan
Juan Hua
JH
Ahn
Myoung-Hee
MH
Ahmed
Hassan Ahmed Hassan
HA
Cha
Guang-Ho
GH
Shin
Dae-Whan
DW
Lee
Young-Ha
YH
D017209:Apoptosis; D000077237:Arsenic Trioxide; D001152:Arsenicals; D015153:Blotting, Western; D053148:Caspase 3 / Q000378:metabolism; D053179:Caspase 7 / Q000378:metabolism; D002460:Cell Line; D053938:DNA Fragmentation; D018840:HSP70 Heat-Shock Proteins / Q000096:biosynthesis*; D006801:Humans; D047468:Immunoprecipitation; D008264:Macrophages / Q000469:parasitology*; D010087:Oxides / Q000633:toxicity; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000096:biosynthesis*; D014122:Toxoplasma / Q000472:pathogenicity*
D001152:Arsenicals; D018840:HSP70 Heat-Shock Proteins; D010087:Oxides; D019253:Proto-Oncogene Proteins c-bcl-2; D053148:Caspase 3; D053179:Caspase 7; D000077237:Arsenic Trioxide