Epstein-Barr virus EB2 protein exports unspliced RNA via a Crm-1-independent pathway.
Human herpesviruses encode posttranscriptional activators that are believed to up-regulate viral replication by facilitating early and late gene expression. We have reported previously that the Epstein-Barr virus protein EB2 (also called M or SM) promotes nuclear export of RNAs that are poor substrates for spliceosome assembly, an effect that closely resembles the human immunodeficiency virus type 1 Rev-dependent nuclear export of unspliced viral RNA. Here we present experimental data showing that EB2 efficiently promotes the nuclear export of unspliced RNA expressed from a Rev reporter construct. Site-directed mutagenesis as well as domain swapping experiments indicate that a leucine-rich region found in the EB2 protein, which matches the consensus sequence for the leucine-rich nuclear export signal, is not a nuclear export signal per se. Accordingly, leptomycin B (LMB), a specific Crm-1 inhibitor, impairs Rev- but not EB2-dependent nuclear export of unspliced RNA. Moreover, EB2 nucleocytoplasmic shuttling visualized by a heterokaryon assay is, unlike Rev shuttling, not affected by LMB. We also show that overexpression of an N-terminal deletion mutant of Nup214/can, a major nucleoporin of the nuclear pore complex involved in several aspects of nuclear transport, blocks both Rev- and EB2-dependent nuclear export of RNA. These results strongly suggest that EB2 nuclear export of unspliced RNA is mediated by a Crm-1-independent pathway.
Farjot
G
G
U412 INSERM, ENS-Lyon, France.
Buisson
M
M
Duc Dodon
M
M
Gazzolo
L
L
Sergeant
A
A
Mikaelian
I
I
D016475:3T3 Cells; D000818:Animals; D001692:Biological Transport; D002352:Carrier Proteins / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D004351:Drug Resistance; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology; D015694:Gene Products, rev / Q000235:genetics / Q000378:metabolism; D015497:HIV-1 / Q000378:metabolism; D006367:HeLa Cells; D004854:Herpesvirus 4, Human / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D017874:Immediate-Early Proteins / Q000235:genetics / Q000378:metabolism*; D007438:Introns; D028884:Karyopherins; D007930:Leucine; D051379:Mice; D028861:Nuclear Pore Complex Proteins; D009687:Nuclear Proteins / Q000378:metabolism*; D012326:RNA Splicing; D018160:Receptors, Cytoplasmic and Nuclear; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D014764:Viral Proteins; D054321:rev Gene Products, Human Immunodeficiency Virus; D000097606:Exportin 1 Protein
D002352:Carrier Proteins; D005231:Fatty Acids, Unsaturated; D015694:Gene Products, rev; D017874:Immediate-Early Proteins; D028884:Karyopherins; D007930:Leucine; D028861:Nuclear Pore Complex Proteins; D009687:Nuclear Proteins; D018160:Receptors, Cytoplasmic and Nuclear; D015534:Trans-Activators; D014764:Viral Proteins; D054321:rev Gene Products, Human Immunodeficiency Virus; D000097606:Exportin 1 Protein; C068382:BRLF1 protein, Human herpesvirus 4; C085914:NUP214 protein, human; C490093:Nup214 protein, mouse; C038753:leptomycin B