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

Abstract

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.

Localization and Sub-Cellular Shuttling of HTLV-1 Tax with the miRNA Machinery

“…doi:10.1371/journal.pone.0040662.g004 HTLV-1 gene expression is regulated not only by Tax, but also by the viral protein Rex. Rex induces the expression of HTLV-1 structural proteins post-transcriptionally, by binding to the RxRE (Rex-responsive element) on the U3 region of the HTLV-1 LTR (long-terminal repeat) [81][82][83]. Recently, Rex has been shown to suppress the RNAi pathway by interacting with cellular Dicer, inhibiting the conversion of shRNA to siRNA [15].…”

Interaction of human T‐cell lymphotropic virus type I Rex protein with Dicer suppresses RNAi silencing

“…In addition, by interacting with a number of cellular proteins, Tax influences the survival, cell‐cycle progression and growth of HTLV‐I‐infected T‐cells, and it induces genomic instability [10–12]. In contrast, Rex acts post‐transcriptionally to induce the cytoplasmic expression of incompletely spliced HTLV‐I transcripts that encode the viral structural gene products [13–16]. The cis‐acting RNA target for Rex coincides with a highly structured 254‐nt RNA sequence termed the Rex‐response element (RxRE), which has been mapped to the U3/R region of the HTLV‐I long terminal repeat (Fig.…”

Human T Lymphotropic Virus Type 1 Regulatory and Accessory Gene Transcript Expression and Export Are Not Rex Dependent

“…In HTLV-1, the 27-kDa Rex nuclear phosphoprotein is responsible for this function. [1][2][3][4][5][6][7][8] Two cisacting sequences have been identified in the viral genome that are important for Rex regulation ( Fig. 1): the Rex-response element (RxRE) functionally maps to u3/r sequences and is present at the 3¢ end of all positive sense transcripts; the cisacting repressive sequence (CRS) functionally maps to r/U5 sequences and is present only at the 5¢ end of the full-length gag/pol transcript.…”

“…22 In the context of the entire provirus, Rex has been found to increase the levels of full-length gag/pol and singly spliced env mRNAs, and concomitantly decrease the level of the doubly spliced tax/rex message. 5,11 To date, the role of Rex on the expression and export of alternatively spliced HTLV-1 mRNAs that encode the accessory proteins has been poorly investigated partially due to their complex splicing pattern and low abundance. HTLV-1 accessory proteins, although dispensable in cell culture, have been shown to play an important role in viral replication and persistence in animal models.…”

“…This is consistent with a previous report providing evidence that Rex also facilitates translation of Gag in addition to the regulation of gag/pol mRNA levels. 5 Although Rex has been reported to facilitate the export of the gag/pol and env mRNAs at the expense of the doubly spliced tax/rex mRNA, no studies have evaluated whether Rex mediates the export of the alternatively spliced mRNAs that code for the accessory proteins and the antisense HBZ. To determine whether Rex affects the subcellular distribution of HTLV-1 mRNAs, we quantitated nuclear and cytoplasmic viral mRNAs from wtHTLV-1 or HTLV-1Rexin 293T cells at 48 h posttransfection.…”