The RD1 locus in the Mycobacterium tuberculosis genome contributes to activation of caspase-1 via induction of potassium ion efflux in infected macrophages.
A genomic locus called "region of difference 1" (RD1) in Mycobacterium tuberculosis has been shown to contribute to the generation of host protective immunity as well as to the virulence of the bacterium. To gain insight into the molecular mechanism, we investigated the difference in the cytokine-inducing ability between H37Rv and a mutant strain deficient for RD1 (DeltaRD1). We found that RD1 is implicated in the production of caspase-1-dependent cytokines, interleukin-18 (IL-18) and IL-1beta, from infected macrophages. The expression of these cytokines was similarly induced after infection with H37Rv and DeltaRD1. However, the activation of caspase-1 was observed only in H37Rv-infected macrophages. The cytokine production and caspase-1 activation were induced independently of type I interferon receptor signaling events. We also found that the activation of caspase-1 was markedly inhibited with increasing concentrations of extracellular KCl. Furthermore, the production of IL-18 and IL-1beta and caspase-1 activation were induced independently of a P2X7 purinergic receptor, and the inability of DeltaRD1 in caspase-1 activation was compensated for by nigericin, an agent inducing the potassium ion efflux. Based on these results, we concluded that RD1 participates in caspase-1-dependent cytokine production via induction of the potassium ion efflux in infected macrophages.
Kurenuma
Takeshi
T
Department of Microbiology, Kyoto University Graduate School of Medicine, Kyoto 606-8501, Japan.
Kawamura
Ikuo
I
Hara
Hideki
H
Uchiyama
Ryosuke
R
Daim
Sylvia
S
Dewamitta
Sita Ramyamali
SR
Sakai
Shunsuke
S
Tsuchiya
Kohsuke
K
Nomura
Takamasa
T
Mitsuyama
Masao
M
D000818:Animals; D051017:Apoptosis Regulatory Proteins; D053468:CARD Signaling Adaptor Proteins; D002352:Carrier Proteins / Q000502:physiology; D020170:Caspase 1 / Q000378:metabolism*; D003598:Cytoskeletal Proteins / Q000502:physiology; D004789:Enzyme Activation; D005260:Female; D016680:Genome, Bacterial; D016899:Interferon-beta / Q000502:physiology; D020382:Interleukin-18 / Q000502:physiology; D053583:Interleukin-1beta / Q000502:physiology; D015850:Interleukin-6 / Q000096:biosynthesis; D017136:Ion Transport; D008264:Macrophages / Q000378:metabolism* / Q000382:microbiology; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D009169:Mycobacterium tuberculosis / Q000235:genetics*; D000071199:NLR Family, Pyrin Domain-Containing 3 Protein; D009550:Nigericin / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D018048:Receptors, Purinergic P2 / Q000502:physiology; D058486:Receptors, Purinergic P2X7; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis
D051017:Apoptosis Regulatory Proteins; D053468:CARD Signaling Adaptor Proteins; D002352:Carrier Proteins; D003598:Cytoskeletal Proteins; D020382:Interleukin-18; D053583:Interleukin-1beta; D015850:Interleukin-6; D000071199:NLR Family, Pyrin Domain-Containing 3 Protein; C492716:Nlrp3 protein, mouse; C546469:P2rx7 protein, mouse; C498534:Pycard protein, mouse; D018048:Receptors, Purinergic P2; D058486:Receptors, Purinergic P2X7; D014409:Tumor Necrosis Factor-alpha; D016899:Interferon-beta; D020170:Caspase 1; D009550:Nigericin; D011188:Potassium