Participation of Rip2 in lipopolysaccharide signaling is independent of its kinase activity.
Rip2 (Rick, Cardiak, CCK2, and CARD3) is a serine/threonine kinase containing a caspase recruitment domain (CARD) at the C terminus. Previous reports have shown that Rip2 is involved in multiple receptor signaling pathways that are important for innate and adaptive immune responses. However, it is not known whether Rip2 kinase activity is required for its function. Here we confirm that Rip2 participates in lipopolysaccharide (LPS)/Toll-like receptor (TLR4) signaling and demonstrate that its kinase activity is not required. Upon LPS stimulation, Rip2 was transiently recruited to the TLR4 receptor complex and associated with key TLR signaling mediators IRAK1 and TRAF6. Furthermore, Rip2 kinase activity was induced by LPS treatment. These data indicate that Rip2 is directly involved in the LPS/TLR4 signaling. Whereas macrophages from Rip2-deficient mice showed impaired NF-kappaB and p38 mitogen-activated protein kinase activation and reduced cytokine production in response to LPS stimulation, LPS signaling was intact in macrophages from mice that express Rip2 kinase-dead mutant. These results demonstrate that Rip2-mediated LPS signaling is independent of its kinase activity. Our findings strongly suggest that Rip2 functions as an adaptor molecule in transducing signals from immune receptors.
Lu
Chafen
C
Millennium Pharmaceuticals, Inc., Cambridge, Massachusetts 02139, USA. chafenlu@berkeley.edu
Wang
Anlai
A
Dorsch
Marion
M
Tian
Jane
J
Nagashima
Kumiko
K
Coyle
Anthony J
AJ
Jaffee
Bruce
B
Ocain
Timothy D
TD
Xu
Yajun
Y
D000818:Animals; D020672:I-kappa B Proteins / Q000378:metabolism; D008070:Lipopolysaccharides / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D000072000:NF-KappaB Inhibitor alpha; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D053475:Receptor-Interacting Protein Serine-Threonine Kinase 2; D053422:Receptor-Interacting Protein Serine-Threonine Kinases; D011971:Receptors, Immunologic / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D051197:Toll-Like Receptor 4; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
D020672:I-kappa B Proteins; D008070:Lipopolysaccharides; C000606205:Nfkbia protein, mouse; D011971:Receptors, Immunologic; C493487:Tlr4 protein, mouse; D051197:Toll-Like Receptor 4; D000072000:NF-KappaB Inhibitor alpha; D017346:Protein Serine-Threonine Kinases; D053475:Receptor-Interacting Protein Serine-Threonine Kinase 2; D053422:Receptor-Interacting Protein Serine-Threonine Kinases; C506255:Ripk2 protein, mouse; D048051:p38 Mitogen-Activated Protein Kinases