In this study, we investigated the activity of
transcription factor NF-kappaB in macrophages infected with Yersinia enterocolitica. Although triggering initially a weak
NF-kappaB signal, Y. enterocolitica inhibited
NF-kappaB activation in murine J774A.1 and peritoneal macrophages within 60 to 90 min. Simultaneously, Y. enterocolitica prevented prolonged degradation of the inhibitory
proteins IkappaB-alpha and IkappaB-beta observed by treatment with
lipopolysaccharide (LPS) or nonvirulent, plasmid-cured yersiniae. Analysis of different Y. enterocolitica mutants revealed a striking correlation between the abilities of these strains to inhibit
NF-kappaB and to suppress the
tumor necrosis factor alpha (
TNF-alpha) production as well as to trigger macrophage apoptosis. When
NF-kappaB activation was prevented by the
proteasome inhibitor MG-132, nonvirulent yersiniae as well as LPS became able to trigger J774A.1 cell apoptosis and inhibition of the
TNF-alpha secretion. Y. enterocolitica also impaired the activity of
NF-kappaB in epithelial HeLa cells. Although neither Y. enterocolitica nor
TNF-alpha could induce HeLa cell apoptosis alone,
TNF-alpha provoked apoptosis when activation of
NF-kappaB was inhibited by
Yersinia infection or by the
proteasome inhibitor MG-132. Together, these data demonstrate that Y. enterocolitica suppresses cellular activation of
NF-kappaB, which inhibits
TNF-alpha release and triggers apoptosis in macrophages. Our results also suggest that
Yersinia infection confers susceptibility to programmed cell death to other cell types, provided that the appropriate death signal is delivered.