CRM1, an RNA transporter, is a major species-specific restriction factor of human T cell leukemia virus type 1 (HTLV-1) in rat cells

Abstract

Rat ortholog of human CRM1 has been found to be responsible for the poor activity of viral Rex protein, which is essential for RNA export of human T cell leukemia virus type 1 (HTLV-1). Here, we examined species-specific barrier of HTLV-1 by establishing rat cell lines, including both adherent and CD4 + T cells, which express human CRM1 at physiological levels. We demonstrated that expression of human CRM1 in rat cells is not harmful to cell growth and is sufficient to restore the synthesis of the viral structural proteins, Gag and Env, at levels similar to those in human cells. Gag precursor proteins were efficiently processed to the mature forms in rat cells and released into the culture medium as sedimentable viralparticles. An HTLV-1 pseudovirus infection system suggested that the released virus particles are fully infectious. Our newly developed reporter cell system revealed that Env proteins produced in rat cells are fully fusogenic, which is the basis for cell-cell HTLV-1 infection.Moreover, we show that the early steps in infection, from post-entry uncoating to integration into the host chromosomes, occur efficiently in rat cells. These results, in conjunction with reports describing efficient entry of HTLV-1 into rat cells, may indicate that HTLV-1 is unique in that its major species-specific barrier is determined by CRM1 at a viral RNA export step.These observations will enable us to construct a transgenic rat model expressing human CRM1 that is sensitive to HTLV-1 infection.

Enhanced Replication of Human T-Cell Leukemia Virus Type 1 in T Cells from Transgenic Rats Expressing Human CRM1 That Is Regulated in a Natural Manner

“…We also demonstrated hCRM1 expression in all Tg ratderived cell lines, which will be useful for the functional analysis of hCRM1 in HTLV-1-infected cells. We have previously reported that expression of hCRM1 induced an increase in HTLV-1 Gag production in both rat epithelial and T cells (21,69). Our present study also showed that T-cell lines established from hCRM1-Tg rats produced significantly greater amounts of p19 than cell lines established from Wt rats, further indicating the positive effect of hCRM1 on viral protein synthesis.…”

“…We have previously examined the differences in the pattern of viral gene expression between human and rat T cells infected with HTLV-1 (69). In rat cells, the levels of viral mRNAs encoding the Gag and Env proteins were much lower than those encoding the Tax and Rex proteins (36).…”

“…In rat cells, the levels of viral mRNAs encoding the Gag and Env proteins were much lower than those encoding the Tax and Rex proteins (36). Rex plays an important role in escorting unspliced and incompletely spliced viral mRNAs to the cytoplasm, resulting in enhanced synthesis of viral structural proteins (5,34,69). Human CRM1 (hCRM1) is a critical factor for Rex-dependent viral mRNA export to the cytoplasm, and rat CRM1 (rCRM1) cannot substitute for this function (19,22,69).…”

“…Rex plays an important role in escorting unspliced and incompletely spliced viral mRNAs to the cytoplasm, resulting in enhanced synthesis of viral structural proteins (5,34,69). Human CRM1 (hCRM1) is a critical factor for Rex-dependent viral mRNA export to the cytoplasm, and rat CRM1 (rCRM1) cannot substitute for this function (19,22,69). Thus, it is reasonable to assume that transgenic (Tg) rats carrying the hCRM1 gene should provide a better environment for HTLV-1 replication and that such animals would provide a better animal model of HTLV-1 infection.…”

Functional analysis of Foxp3 and CTLA-4 expressing HTLV-1-infected cells in a rat model

“…Moreover, we identified CRM1, a cellular cofactor of Rex that exports viral mRNA from the nucleus to the cytoplasm, to be a major factor, which restricts efficient replication of HTLV-1 in rats [17][18][19]. Human CRM1 (hCRM1) transgenic (Tg) rat supports replication of HTLV-1 in T cells at the level similar to human T cells ex vivo [20].…”