HTLV-1 Tax-associated hTid-1, a Human DnaJ Protein, Is a Repressor of IκB Kinase β Subunit

hTid-1, a human DnaJ protein, is a novel cellular target for HTLV-1 Tax. Here, we show that hTid-1 represses NF-κB activity induced by Tax as well as other activators such as tumor necrosis factor α (TNFα) and Bcl10. hTid-1 specifically suppresses serine phosphorylation of IκBα by activated IκB kinase β (IKKβ), but the activities of other serine kinases including p38, ERK2, and JNK1 are not affected. The suppressive activity of hTid-1 on IKKβ requires a functional J domain that mediates association with heat shock proteins and results in prolonging the half-life of the NF-κB inhibitors IκBα and IκBβ. Collectively, our data suggest that hTid-1, in association with heat shock proteins, exerts a negative regulatory effect on the NF-κB activity induced by various extracellular and intracellular activators including HTLV-1 Tax.