Cytochrome c-mediated caspase-9 activation triggers apoptosis in Streptococcus pyogenes-infected epithelial cells.
Epithelial cells are the initial sites of host invasion by group A Streptococcus pyogenes (GAS), and their infection of epithelial cells has been suggested to induce apoptosis. However, the mechanism responsible for bacteria-host interaction and the induction of apoptosis has not been clearly understood. We demonstrate here that human pharyngeal epithelial HEp-2 cells became apoptotic with DNA fragmentation by invasion of GAS strains JRS4 (M6+, F1+) and JRS145 (M6-, F1+ mutant of JRS4), whereas apoptotic cellular changes were not observed in SAM1 (M6+, F1- mutant) or SAM2 (M6-, F1- mutant) infected HEp-2 cells. Confocal microscopy revealed that Bax translocation to mitochondria and cytochrome c release occurred after 4 h of infection. Western blot analyses showed that the amounts of Bcl-2 and Bcl-xL were decreased in the mitochondria of infected cells. In addition, we demonstrated that the release of nuclear histone from infected cells was prevented by the addition of caspase-9 inhibitor (Ac-LEHD-CHO). We conclude that the internalization of GAS in epithelial cells is necessary and sufficient for the induction of apoptosis, which is initiated by mitochondrial dysfunction, and the mechanism of GAS-induced apoptosis is clearly different from that induced by other intracellular invasive bacteria, e.g. Shigella and Salmonella species.
Nakagawa
I
I
Department of Oral Microbiology, Osaka University Faculty of Dentistry, 1-8 Yamadaoka, Suita-Osaka, 565-0871 Japan. ichiro@dent.osaka-u.ac.jp
Nakata
M
M
Kawabata
S
S
Hamada
S
S
D017209:Apoptosis; D053453:Caspase 9; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism*; D003574:Cytochrome c Group / Q000378:metabolism*; D004789:Enzyme Activation; D004847:Epithelial Cells / Q000382:microbiology*; D006801:Humans; D010610:Pharyngeal Neoplasms; D013297:Streptococcus pyogenes / Q000472:pathogenicity*; D014407:Tumor Cells, Cultured
D061945:Caspase Inhibitors; D003574:Cytochrome c Group; C506433:CASP9 protein, human; D053453:Caspase 9; D020169:Caspases