Phosphorylation regulates RNA binding by the human T-cell leukemia virus Rex protein

The human T-cell leukemia virus (HTLV) Rex protein is essential for efficient expression of the viral structural and enzymatic gene products. In this study, we assessed the role of the HTLV-2rex gene in viral RNA expression and Gag protein production. Following transfection of human JM4 T cells with wild-type and rex mutant full-length proviral constructs, PCR was used for semiquantitative analysis of specific viral RNA transcripts. In the presence of Rex, the total amount of steady-state viral RNA was increased fourfold. Rex significantly up-regulated the level of incompletely spliced RNAs by increasing RNA stability and was associated with a twofold down-regulation of the completely splicedtax/rex RNA. PCR analysis of subcellular RNA fractions, isolated from transfected cells, indicated that the level ofgag/pol and env cytoplasmic RNAs were increased 7- to 9-fold in the presence of Rex, whereas Gag protein production was increased 130-fold. These data indicate that HTLV-2 Rex increases the stability and promotes nucleus-to-cytoplasm transport of the incompletely spliced viral RNAs, ultimately resulting in increased structural protein production. Moreover, this model system provides a sensitive approach to further characterize HTLV gene expression from full-length proviral clones following transfection of human T cells.

mentioning

confidence: 99%

Human T-Cell Leukemia Virus Type 2 Rex Protein Increases Stability and Promotes Nuclear to Cytoplasmic Transport of gag/pol and env RNAs

Kusuhara

Anderson

Pettiford

et al. 1999

“…This feature has a precedent in several viral proteins, such as the large T antigen of simian virus 40 (50), the Rex protein of human T-cell leukemia virus types I and II (23), phosphoprotein P of vesicular stomatitis virus (2), the delta antigen of hepatitis delta virus (7, 30), and the core proteins of HBV (51, 58, 75), vaccinia virus (46), and budgerigar fledgling disease virus (26). In most of these cases, phosphorylation affects the nuclear translocation, nucleic acid-binding ability, or transactivation function of the viral proteins (2,23,25,50,58). An interesting question which arises is whether the phosphorylation state of the HCV core protein plays a role in suppression of HBV expression or in other biological functions.…”

Section: Discussionmentioning

confidence: 99%

Suppression of hepatitis B virus expression and replication by hepatitis C virus core protein in HuH-7 cells

Shih

Miyamura

et al. 1993

313

123

Hepatitis B and C viruses (HBV and HCV, respectively) are associated with acute and chronic liver diseases and hepatocellular carcinoma. To elucidate the molecular status of superinfection with these two hepatitis viruses, we cotransfected the full-length or truncated version of HCV structural genes (core and envelope 1) together with the cloned HBV DNA into a human hepatoma cell line (HuH-7). Expression of HBV-specific major transcripts (3.5 and 2.1 kb), as well as HBV antigens (hepatitis B surface antigen and hepatitis B e and core antigens), was reduced about two- to fourfold by the presence of the HCV structural genes. In addition, the secretion of HBV viral particles, including the viral nucleocapsid and mature virion, was drastically suppressed about 20-fold. Analysis of the intracellular HBV core protein-associated nucleic acid indicated that the encapsidated HBV pregenomic RNA was similarly reduced about 14-fold. Deletion analysis of the HCV structural genes demonstrated that the core gene alone or the fragment containing the core protein's N-terminal 122 amino acid residues conferred the same level of suppressive activity as the full-length structural genes. By indirect immunofluorescence, we found that the core protein of HCV was located in the cytoplasm of transfected HuH-7 cells at day 3 posttransfection and was targeted to the nucleus at day 6. Thus, the kinetics of the suppressive effect exerted by HCV constructs matched the timing of core protein entrance into the nucleus. Our results substantiate the clinical finding that HBV markers are suppressed by superinfection with HCV and further imply that this inhibitory effect may occur in the processes of transcription and encapsidation of HBV pregenomic RNA and may be mediated by the core protein of HCV. The deduced amino acid sequence of the HCV core protein has revealed that it is a basic protein which contains a putative DNA-binding motif (SPRG), as well as triplicate nuclear localization signals and several putative protein kinase A and C recognition sites. These characteristics imply that the HCV core protein can also function as a gene-regulatory protein.

“…The regulatory gene tax encodes a transcriptional trans activator that functions through the Tax responsive element (TRE) and transforms lymphocytes (1,14,17,18,32,35,38,39). The second regulatory gene, rex, is a posttranscriptional trans activator that functions through the Rex responsive element (RxRE) that is positioned in long terminal repeat (LTR) RNA (14,19,21,44). Although a specific role for Rex and RxRE in transformation is not documented, asymptomatic human immunodeficiency virus (HIV)-infected patients exhibit a correlation between viral latency and subthreshold availability of the functionally analogous trans activator, Rev (23).…”

mentioning

confidence: 99%

Bovine Leukemia Virus Structural Gene Vectors Are Immunogenic and Lack Pathogenicity in a Rabbit Model

Kučerová

Altanerová

Altaner

et al. 1999

Infection with a replication-competent bovine leukemia virus structural gene vector (BLV SGV) is an innovative vaccination approach to prevent disease by complex retroviruses. Previously we developed BLV SGV that constitutively expresses BLV gag, pol, and env and related cis-acting sequences but lacks tax, rex, RIII, andGIV and most of the BLV long terminal repeat sequences, including the cis-acting Tax and Rex response elements. The novel SGV virus is replication competent and replicates a selectable vector to a titer similar to that of the parental BLV in cell culture. The overall goal of this study was to test the hypothesis that infection with BLV SGV is nonpathogenic in rabbits. BLV infection of rabbits by inoculation of cell-free BLV or cell-associated BLV typically causes an immunodeficiency-like syndrome and death by 1 year postinfection. We sought to evaluate whether in vivo transfection of BLV provirus recapitulates pathogenic BLV infection and to compare BLV and BLV SGV with respect to infection, immunogenicity, and clinical outcome. Three groups of rabbits were subjected to in vivo transfection with BLV, BLV SGV, or negative control DNA. The results of our 20-month study indicate that in vivo transfection of rabbits with BLV recapitulates the fatal BLV infection produced by cell-free or cell-associated BLV. The BLV-infected rabbits exhibited sudden onset of clinical decline and immunodeficiency-like symptoms that culminated in death. BLV and BLV SGV infected peripheral blood mononuclear cells and induced similar levels of seroconversion to BLV structural proteins. However, BLV SGV exhibited a reduced proviral load and did not trigger the immunodeficiency-like syndrome. These results are consistent with the hypothesis that BLV SGV is infectious and immunogenic and lacks BLV pathogenicity in rabbits, and they support the use of this modified proviral vector delivery system for vaccines against complex retroviruses like BLV.