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

HIV-1 susceptibility of transgenic rat-derived primary macrophage/T cells and a T cell line that express human receptors, CyclinT1 and CRM1 genes

We developed transgenic (Tg) rats that express human CD4, CCR5, CXCR4, CyclinT1, and CRM1 genes. Tg rat macrophages were efficiently infected with HIV-1 and supported production of infectious progeny virus. By contrast, both rat primary CD4+ T cells and established T cell lines expressing human CD4, CCR5, CyclinT1, and CRM1 genes were infected inefficiently, but this was ameliorated by inhibition of cyclophilin A. The infectivity of rat T cell-derived virus was lower than that of human T cell-derived virus.

Both high expression of nucleophosmin/B23 and CRM1 predicts poorer prognosis in human gastric cancer

Nucleophosmin/B23 and CRM1 are molecular markers which play an important role in tumorigenesis and tumor progression in gastric cancer (GC). However, the association between the two remains unclear. This study evaluated the expression and the correlation of B23 and CRM1 in GC. B23 and CRM1 expression in GC and adjacent noncancerous tissues (ANCT) of gastrectomy specimens from 131 GC patients was measured by immunohistochemistry. Positive expression rates of B23 and CRM1 were significantly higher in GC tissues than in ANCT. The high expression rates of B23 and CRM1 were significantly higher in patients with more advanced tumor stages and distant metastasis (all p < 0.05). Only high expression of CRM1was correlated with positive Her2 status (p = 0.01). B23 expression was positively correlated with CRM1expression in GC tissues (p = 0.038). Univariate analysis showed that TNM stage (p = 0.0001), metastasis (p = 0.027), B23 (p = 0.0111), and CRM1 expression (p = 0.0019) were significant risk factors affecting overall survival. Both high expression of B23 and CRM1 in GC patients suggests poor prognosis, co-expression of the two (p = 0.043) even worse. Cox multivariate analysis showed that positive B23 (p = 0.0231) and CRM1 (p = 0.0048) expression were both independent prognostic factors that negatively correlated with survival. We revealed the co-expression of B23 or CRM1 in GC. The expression levels of B23 or CRM1 were closely related to poor prognosis in GC, and both B23 or CRM1 were independent risk factor.

CRM1 is a novel independent prognostic factor for the poor prognosis of gastric carcinomas

Gastric cancer (GC) is a highly aggressive malignant tumor. Its high mortality rate prompts the urgent need for novel therapeutic agents. The aim of this study is to detect the expression of CRM1 in GC, which has not been reported to date. The expression of CRM1 in GC and adjacent noncancerous tissues (ANCT) of gastrectomy specimens from 120 GC patients was measured by immunohistochemistry. In addition, correlations between the CRM1 staining and the clinicopathologic features as well as survival were analyzed. Positive expression rates of CRM1 in GC and ANCT were 57.8 and 6.7%, respectively. High expression of CRM1 was significantly associated with increased serum level of carcinoma embryonic antigen (CEA, P = 0.02) but not associated with that of carbohydrate antigen 19-9 (P = 0.38). CRM1 levels were correlated with more advanced tumor stages (P = 0.01), positive Her2 status (P = 0.01), and distant metastasis (P = 0.02). Univariate analysis showed that CEA (P = 0.0076), TNM stage (P = 0.0001), metastasis (P = 0.027), and CRM1 expression (P = 0.0019) were significant risk factors affecting overall survival of GC patients. The multivariate analysis indicated that the CRM1 was an independent indicator for GC survival (P = 0.0048). The current results indicated that CRM1 expressed in a subpopulation of GC with aggressive behavior and could serve as a prognosis marker for poor outcome.

Role of Nucleocytoplasmic RNA Transport during the Life Cycle of Retroviruses

Retroviruses have evolved mechanisms for transporting their intron-containing RNAs (including genomic and messenger RNAs, which encode virion components) from the nucleus to the cytoplasm of the infected cell. Human retroviruses, such as human immunodeficiency virus (HIV) and human T cell leukemia virus type 1 (HTLV-1), encode the regulatory proteins Rev and Rex, which form a bridge between the viral RNA and the export receptor CRM1. Recent studies show that these transport systems are not only involved in RNA export, but also in the encapsidation of genomic RNA; furthermore, they influence subsequent events in the cytoplasm, including the translation of the cognate mRNA, transport of Gag proteins to the plasma membrane, and the formation of virus particles. Moreover, the mode of interaction between the viral and cellular RNA transport machinery underlies the species-specific propagation of HIV-1 and HTLV-1, forming the basis for constructing animal models of infection. This review article discusses recent progress regarding these issues.

Nuclear and cytoplasmic effects of human CRM1 on HIV-1 production in rat cells

The human immunodeficiency virus type 1 (HIV-1) regulatory protein, Rev, mediates the nuclear export of unspliced gag and singly spliced env mRNAs by bridging viral RNA and the export receptor, CRM1. Recently, rat CRM1 was found to be less efficient than human CRM1 in supporting Rev function in rats. In this study, to understand the role of CRM1 in HIV propagation, the mechanism underlying the function of human and rat CRM1 in HIV-1 replication was investigated in rat cells. The production of viral particles, represented by the p24 Gag protein, was greatly enhanced by hCRM1 expression in rat cells; however, this effect was not simply because of the enhanced export of gag mRNA. The translation initiation rate of gag mRNA was not increased, nor was the Gag protein stabilized in the presence of hCRM1. However, the processing of the p55 Gag precursor and the release of viral particles were facilitated. These results indicated that hCRM1 exports gag mRNA to the cytoplasm, not only more efficiently than rCRM1 but also correctly, leading to efficient processing of Gag proteins and particle formation.

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

Human T-cell leukemia virus type 1 (HTLV-1) is the etiologic agent of adult T-cell leukemia (ATL). Some ATL cells express Foxp3, which is known as regulatory T cell (Treg cell) specific transcription factor. It is suggested that Treg cell like suppressive activity of Foxp3 expressing ATL cells is associated to ATL development and related immunodeficiency. To develop an HTLV-1 model system that enables to investigate the association of Treg function in ATL progression, we examined the expression of Foxp3 and CTLA-4, Treg cell-associated factor, in established HTLV-1-infected rat cell lines and their regulatory function. We found the expression of Foxp3 in 10 of 22 and CTLA-4 in 10 of 19 HTLV-1-infected rat cell lines. Moreover, some of the Foxp3 and/or CTLA-4 expressing cell lines suppressed proliferation of naïve T cells that were stimulated with anti-CD3 antibody. Particularly all Foxp3(+) CTLA-4(+) cells showed the suppressive activity. Our data suggest the usefulness of our rat model systems for further analysis of the role of Treg cell-associated factors on the development of ATL and related immunodeficiency in vivo.

Synergistic effect of human CycT1 and CRM1 on HIV-1 propagation in rat T cells and macrophages

BACKGROUND

In vivo studies of HIV-1 pathogenesis and testing of antiviral strategies have been hampered by the lack of an immunocompetent small animal model that is highly susceptible to HIV-1 infection. Although transgenic rats that express the HIV-1 receptor complex hCD4 and hCCR5 are susceptible to infection, HIV-1 replicates very poorly in these animals. To demonstrate the molecular basis for developing a better rat model for HIV-1 infection, we evaluated the effect of human CyclinT1 (hCycT1) and CRM1 (hCRM1) on Gag p24 production in rat T cells and macrophages using both established cell lines and primary cells prepared from hCycT1/hCRM1 transgenic rats.

RESULTS

Expression of hCycT1 augmented Gag production 20-50 fold in rat T cells, but had little effect in macrophages. Expression of hCRM1 enhanced Gag production 10-15 fold in macrophages, but only marginally in T cells. Expression of both factors synergistically enhanced p24 production to levels approximately 10-40% of those detected in human cells. R5 viruses produced in rat T cells and macrophages were fully infectious.

CONCLUSION

The expression of both hCycT1 and hCRM1 appears to be fundamental to developing a rat model that supports robust propagation of HIV-1.

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

Human T-cell leukemia virus type 1 (HTLV-1) is the etiologic agent of adult T-cell leukemia (ATL). To develop a better animal model for the investigation of HTLV-1 infection, we established a transgenic (Tg) rat carrying the human CRM1 (hCRM1) gene, which encodes a viral RNA transporter that is a species-specific restriction factor. At first we found that CRM1 expression is elaborately regulated through a pathway involving protein kinase C during lymphocyte activation, initially by posttranscriptional and subsequently by transcriptional mechanisms. This fact led us to use an hCRM1-containing bacterial artificial chromosome clone, which would harbor the entire regulatory and coding regions of the CRM1 gene. The Tg rats expressed hCRM1 protein in a manner similar to expression of intrinsic rat CRM1 in various organs. HTLV-1-infected T-cell lines derived from these Tg rats produced 100- to 10,000-fold more HTLV-1 than did T cells from wild-type rats, and the absolute levels of HTLV-1 were similar to those produced by human T cells. We also observed enhancement of the dissemination of HTLV-1 to the thymus in the Tg rats after intraperitoneal inoculation, although the proviral loads were low in both wild-type and Tg rats. These results support the essential role of hCRM1 in proper HTLV-1 replication and suggest the importance of this Tg rat as an animal model for HTLV-1.