Parasitol Res. 2010 Aug 3. [Epub ahead of print]
Toxoplasma gondii infection inhibits the mitochondrial apoptosis through induction of Bcl-2 and HSP70
Hwang IY, Quan JH, Ahn MH, Hassan Ahmed HA, Cha GH, Shin DW, Lee YH.
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.
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.
PMID: 20680337 [PubMed - as supplied by publisher]