(A) Examination of the specificity of pTAK1-peptide-specific RaMoAbs. Whole-cell lysates obtained from HeLa cells that were transfected with plasmids containing FLAG-tagged wild type (WT) TAK1 or a phosphorylation site-substituted mutant (T187A) together with HA-tagged TAB1 were separated by SDS-PAGE and immunoblotted with Ra_pTAK01, 04, 05, 06, 14, 19, 21, and 23 antibodies, a commercial antibody specific to phosphorylated TAK1, a TAK1-specific antibody or a TAB1-specific antibody. (B) TNF-α-induced phosphorylation of endogenous TAK1 at Thr187. Whole cell lysates from HeLa cells that had been stimulated with 20 ng ml−1 TNF-α for the indicated time periods were separated by SDS-PAGE and immunoblotted with the Ra_pTAK23 antibody, a commercial pTAK1-pep-specific antibody, or a TAK1-specific antibody.