Utilization of signal transduction pathway by the human T-cell leukemia virus type I transcriptional activator tax

Adeno-associated virus (AAV) is a human parvovirus of the genusDependovirus. AAV replication is largely restricted to cells which are coinfected with a helper virus. In the absence of a helper virus, the AAV genome can integrate into a specific chromosomal site where it remains latent until reactivated by superinfection of the host cell with an appropriate helper virus. Replication functions of AAV have been mapped to the Rep68 and Rep78 gene products. Rep proteins demonstrate DNA binding, endonuclease, and helicase activities and are involved in regulation of transcription from both AAV and heterologous promoters. AAV has been associated with suppression of oncogenicity in a range of viral and nonviral tumors. In this study we sought to identify and study cellular protein targets of AAV Rep, in order to develop a better understanding of the various activities of Rep. We used the yeast two-hybrid system to identify HeLa cell proteins that interact with AAV type 2 Rep78. We isolated several strongly interacting clones which were subsequently identified as PRKX (previously named PKX1), a recently described homolog of the protein kinase A (PKA) catalytic subunit (PKAc). The interaction was confirmed in vitro by using pMal-Rep pull-down assays. The region of Rep78 which interacts was mapped to a C-terminal zinc finger-like domain; Rep68, which lacks this domain, did not interact with PRKX. PRKX demonstrated autophosphorylation and kinase activity towards histone H1 and a PKA oligopeptide target. Autophosphorylation was inhibited by interaction with Rep78. In transfection assays, a PRKX expression vector was shown to be capable of activating CREB-dependent transcription. This activation was suppressed by Rep78 but not by Rep68. Since PRKX is a close homolog of PKAc, we investigated whether Rep78 could interact directly with PKAc. pMal-Rep78 was found to associate with purified PKAc and inhibited its kinase activity. Cotransfection experiments demonstrated that Rep78 could block the activation of CREB by a PKAc expression vector. These experiments suggest that AAV may perturb normal cyclic AMP response pathways in infected cells.

Section: Discussionmentioning

confidence: 99%

Adeno-Associated Virus Rep78 Protein Interacts with Protein Kinase A and Its Homolog PRKX and Inhibits CREB-Dependent Transcriptional Activation

Pasquale

Stacey

1998

“…Direct interaction of Tax 1 with each of these transcription factors has been reported (7,15,22,47,78). In vivo studies further suggest that protein kinases, similar to their involvement in human immunodeficiency virus and bovine leukemia virus transcription (1,14,31,33,36,75), are important in Tax 1 transactivation of the HTLV-1 long terminal repeat (27,59,75).…”

mentioning

confidence: 97%

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

Lindholm

Tamami

Makowski

et al. 1996

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.

“…Alternatively, the mechanism exerted by Tax could involve posttranscriptional modifications such as phosphorylation of proteins. Investi-gations of proteins binding to the 21-bp repeats of HTLV-I detected ATF/CREB factors that interact with domain B and two additional proteins, termed HEB1 and HEB2, that interact with domains A and C or domain B, respectively (37,70). A recent study suggested that p40 is able to bind to the 21-bp element, but this interaction was found to be indirect via the HEB1 protein (8).…”

Section: Discussionmentioning

confidence: 99%

“…In contrast to the 21-bp repeat of HTLV-I (46, 58), the HCMV 19-bp motif was found to react efficiently upon Tax cotransfection when the motif was present as a single copy upstream of the minimal IE-1 promoter. The 21-bp motif also does not act as an efficient CRE in Jurkat cells (38,70), whereas the 19-bp repeat does. The constitutive activities of multimerized 19-bp motifs were also higher than those of the 21-bp repeat.…”

Section: Discussionmentioning

confidence: 99%

Strong trans activation of the human cytomegalovirus major immediate-early enhancer by p40tax of human T-cell leukemia virus type I via two repetitive tax-responsive sequence elements

Moch

Lang

Stamminger

1992

The immediate-early 1 and 2 gene locus of human cytomegalovirus (HCMV) that encodes trans-activator proteins with effects on both homologous and heterologous promoters is expressed under control of a complex enhancer/promoter regulatory region. This enhancer contains four types of repetitive sequence elements with 17, 18, 19, and 21 bp that bind cellular transcription factors. Although the HCMV enhancer acts as a powerfil stimulator of transcription in most cell types examined, human T cells do not support strong activity. The present study demonstrates that the tax gene product of human T-cell leukemia virus type I trans activates the major enhancer of HCMV more than 60-fold in the T-cell line Jurkat. When a series of chloramphenicol acetyltransferase expression plasmids containing synthetic oligonucleotides with the 17-, 18-, 19-, or 21-bp motif upstream of a minimal immediate-early 1 and 2 gene promoter was tested, two of the four repeat motifs could be identified as Tax-responsive elements. Both the 18and the 19-bp motifs were able to act as strong Tax-responsive elements even when they were present as single copies. Thus, in addition to interacting with human immunodeficiency virus, HCMV is able to interact with a second retrovirus of clinical importance.