HUMAN T-CELL LYMPHOTROPIC VIRUS TYPE-1 TAX(1) ACTIVATION OF NF-KAPPA-B - INVOLVEMENT OF THE PROTEIN-KINASE-C PATHWAY

Human T-cell lymphotropic virus type 1 Tax(1) induces the activation a nd nuclear localization of the cellular transcription factor, NF-kappa B. Treatment of cells with calphostin C, a protein kinase C (PKC) inh ibitor, blocked induction of NF-kappa B DNA binding activity in human T-cell lymphotropic virus type 1-transformed C81 cells and Tax(1)-stim ulated murine pre-B cells, suggesting that PKC was an important interm ediate in the NF-kappa B induction pathway. We further demonstrate tha t Tax(1) associates with, and activates, PKC. PKC was coimmunoprecipit ated with anti-Tax(1) sera from Tax(1)-expressing MT4 extracts and Jur kat extracts in the presence of exogenous Tax(1) protein. In addition, the glutathione-S-transferase-Tax(1) protein bound specifically to th e alpha, delta, and eta PKC isoenzymes synthesized in rabbit reticuloc yte lysates. The addition of Tax(1) to in vitro kinase reaction mixtur es leads to the phosphorylation of Tax(1) and an 18-fold increase in t he autophosphorylation of PKC. Transfection of Jurkat cells with wild- type Tax(1) stimulated membrane translocation of PKC. In contrast, Tax (1) mutant M22, which fails to stimulate NF-kappa B-dependent transcri ption, failed to stimulate membrane translocation of PKC. Tax(1) did n ot directly increase PKC phosphorylation of I kappa B alpha. Our resul ts are consistent with a model in which Tax(1) interacts with PKC and stimulates membrane translocation and triggering of the PKC pathway. S ubsequent steps in the PKC cascade likely stimulate phosphorylation of I kappa B alpha.