29-kDa FN-f activated the NF-κB signaling pathway through the NOD2/RIP2/TAK1 signaling pathway. (A) NOD2 silencing inhibited the 29-kDa FN-f-induced NF-kB activation. Human chondrocytes were transfected with control small interfering RNA (si-con) or si-NOD2, then stimulated with 29-kDa FN-f (300 nM) for 15, 30, and 60 min. The levels of p-ERK/ERK, p-JNK/JNK, p-p38/p38, and p-IκBα/IκBα were determined by immunoblot analyses. Immunoblot data are representative of three independent experiments from different donors. (B) 29-kDa FN-f increased the formation of the NOD2/RIP2/TAK1 complex. 29-kDa FN-f-stimulated chondrocytes were lysed with RIPA buffer and the cell extracts were immunoprecipitated with an antibody against RIP2. The proteins were analyzed by immunoblot analyses using antibodies against NOD2, RIP2, and TAK1. Immunoprecipitation with IgG served as a negative control.
