Stimulation of human Toll-like receptor (TLR) 2 and TLR6 with membrane lipoproteins of Mycoplasma fermentans induces apoptotic cell death after NF-kappa B activation.
Mycoplasmal membrane diacylated lipoproteins not only initiate proinflammatory responses through Toll-like receptor (TLR) 2 and TLR6 via the activation of the transcriptional factor NF-kappaB, but also initiate apoptotic responses. The aim of this study was to clarify the apoptotic machineries. Mycoplasma fermentans lipoproteins and a synthetic lipopeptide, MALP-2, showed cytocidal activity towards HEK293 cells transfected with a TLR2-encoding plasmid. The activity was synergically augmented by co-expression of TLR6, but not by co-expression of other TLRs. Under the condition of co-expression of TLR2 and TLR6, the lipoproteins could induce maximum NF-kappa B activation and apoptotic cell death in the cells 6 h and 24 h after stimulation respectively. Dominant-negative forms of MyD88 and FADD, but not IRAK-4, reduced the cytocidal activity of the lipoproteins. In addition, both dominant-negative forms also downregulated the activation of both NF-kappa B and caspase-8 in the cells. Additionally, the cytocidal activity was sufficiently attenuated by a selective inhibitor of p38 MAPK. These findings suggest that mycoplasmal lipoproteins can trigger TLR2- and TLR6-mediated sequential bifurcate responses: NF-kappa B activation as an early event, which is partially mediated by MyD88 and FADD; and apoptosis as a later event, which is regulated by p38 MAPK as well as by MyD88 and FADD.
Into
Takeshi
T
Department of Oral Pathobiological Science, Hokkaido University Graduate School of Dental Medicine, Nishi 7, Kita 13, Kita-ku, Sapporo 060-8586, Japan.
Kiura
Kazuto
K
Yasuda
Motoaki
M
Kataoka
Hideo
H
Inoue
Nobuo
N
Hasebe
Akira
A
Takeda
Kiyoshi
K
Akira
Shizuo
S
Shibata
Ken-ichiro
K
D017209:Apoptosis / Q000187:drug effects; D053181:Caspase 8; D020169:Caspases / Q000378:metabolism; D002460:Cell Line; D002462:Cell Membrane / Q000737:chemistry; D015536:Down-Regulation; D006801:Humans; D008074:Lipoproteins / Q000494:pharmacology*; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D016858:Mycoplasma fermentans / Q000472:pathogenicity*; D016328:NF-kappa B / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism*; D051195:Toll-Like Receptor 2; D051193:Toll-Like Receptors
D008074:Lipoproteins; D008562:Membrane Glycoproteins; D016328:NF-kappa B; D011956:Receptors, Cell Surface; C495342:TLR2 protein, human; D051195:Toll-Like Receptor 2; D051193:Toll-Like Receptors; C505530:CASP8 protein, human; D053181:Caspase 8; D020169:Caspases