Effect of overexpression of NIK in cell lines with low NF-κB index. (A) Immunoblot of MMCLs after infection with empty vector or NIK gene. Nuclear and cytosol extracts were prepared, and expression of the proteins indicated at right was analyzed on Western blots. (B) Overexpression of NIK and IKK-β activates nuclear NF-κB DNA binding. DNA-binding activity of the indicated NF-κB subunits was quantified by enzyme-linked immunosorbent assay. (C) Activation of NF-κB target gene expression after infection of cells with NIK gene. The Δ NF-κB(3) = increased expression for average of 3 target genes (TNFAIP3, BIRC3, and IL2RG) in MM cells infected with NIK gene versus empty vector. Data are mean ± SE.