Human T-cell lymphotropic virus type 1 Tax1 activation of NF-kappa B: involvement of the protein kinase C pathway

Abstract

Human T-cell lymphotropic virus type 1 Tax1 induces the activation and nuclear localization of the cellular transcription factor, NF-kappa B. Treatment of cells with calphostin C, a protein kinase C (PKC) inhibitor, blocked induction of NF-kappa B DNA binding activity in human T-cell lymphotropic virus type 1-transformed C81 cells and Tax1-stimulated murine pre-B cells, suggesting that PKC was an important intermediate in the NF-kappa B induction pathway. We further demonstrate that Tax1 associates with, and activates, PKC. PKC was coimmunoprecipitated with anti- Tax1 sera from Tax1-expressing MT4 extracts and Jurkat extracts in the presence of exogenous Tax1 protein. In addition, the glutathione-S-transferase-Tax1 protein bound specifically to the alpha, delta, and eta PKC isoenzymes synthesized in rabbit reticulocyte lysates. The addition of Tax1 to in vitro kinase reaction mixtures leads to the phosphorylation of Tax1 and an 18-fold increase in the autophosphorylation of PKC. Transfection of Jurkat cells with wild-type Tax1 stimulated membrane translocation of PKC. In contrast, Tax1 mutant M22, which fails to stimulate NF-kappa B-dependent transcription, failed to stimulate membrane translocation of PKC. Tax1 did not directly increase PKC phosphorylation of I kappa B alpha. Our results are consistent with a model in which Tax1 interacts with PKC and stimulates membrane translocation and triggering of the PKC pathway. Subsequent steps in the PKC cascade likely stimulate phosphorylation of I kappa B alpha.

Activation of PKC-δ in HTLV-1-infected T cells

“…our studies clearly demonstrate that nuclear import of active PKc-δ is required for tax-mediated nf-κB activation. this conclusion is supported by the findings of previous studies (42), which showed direct interaction of tax with PKc-δ and tax-induced phosphorylation of PKc, and that subsequent steps in the PKc cascade seem to have stimulated iκBα phosphorylation.…”

AP-1-directed human T cell leukemia virus type 1 viral gene expression during monocytic differentiation

“…7). Tax has also been shown to up-regulate PKC activation [71], providing a mechanism to explain how PMA and Tax may be able to synergistically activate HTLV-1 gene expression. Although PKC has been shown to activate NF-B and AP-1, we have clearly demonstrated that AP-1 DNA binding to TRE-1 repeat II was enhanced during induction of differentiation and that inhibition of AP-1 DNA-binding activity abrogated differentiation-induced HTLV-1 LTR activation.…”

“…Differentiation agents such as PMA induce activation of the PKC pathway, resulting in activation of NF-B and AP-1 transcription factors [40,46]. Futhermore, the activation of PKC as well as the DNA-binding activity of NF-B and AP-1 have been shown to be up-regulated by HTLV-1 Tax [58,71]. As NF-B and AP-1 have been shown to interact physically with the viral promoter within TRE-2 and TRE-1 repeat II, respectively [15,52,53,72], it was hypothesized that activation of one or both of these transcriptional regulators may promote up-regulation of HTLV-1 LTR activation during monocytic differentiation.…”

Mechanisms of T-Cell Activation by Human T-Cell Lymphotropic Virus Type I

“…In HTLV-I-infected T cells, Tax physically associates with at least three separate PKC isoforms: PKC-␣, PKC-␦, and PKC- (183). The association results in phosphorylation of Tax and an increase in autophosphorylation of PKC in vitro, indicating that Tax activates PKC activity.…”

“…The NF-B/IB dissociation is thought to occur following phosphorylation of IB, but dephosphorylation of IB may also be involved in NF-B/Rel activation (184). Calphostin C, a PKC inhibitor, prevented both phorbol ester-and Tax-induced NF-B DNA binding activity (183). Moreover, transfection of Jurkat T cells with a Tax mutant (M22) that fails to activate NF-B-dependent transcription failed to induce membrane translocation of PKC (183).…”