IκB-ζ functionally interacts with the NF-κB subunits p50 and p52. (A) NF-κB reporter activity after co-transfection of individual NF-κB subunits and IκB-ζ measured in 293T cells. IκB-ζ synergizes with p50 and p52, but not with RelA, RelB, or c-Rel. (B) IκB-ζ coimmunoprecipitation assays show a physical interaction of IκB-ζ with p50 and p52 in the ABC DLBCL cell lines OCI-Ly3, OCI-Ly10, and HBL-1. h.c., heavy chain.