Wnt signaling-induced upregulation of TNF-α was antagonized by DKK and Sclerostin (SOST). (A–E) Nucleus pulposus cells were transfected with the TNF-α reporter construct and increasing concentrations of the WT-DKK plasmids (100 to 500 ng) or empty backbone plasmids (A: DKK-1, B: DKK-2, C: DKK-3, D: DKK-4, E: SOST). (F-H) The TNF-α reporter plasmid was transfected into nucleus pulposus cells together with the PGL4.74 vector, and was stimulated with 6-bromoindirubin-3′-oxime (BIO) in the presence or absence of DKK expression plasmids. Luciferase activity was measured 24 h after transfection (F: DKK-3, G: DKK-4, H: SOST). *P <0.05 indicates significant differences between groups. n.s., not significant.