Roles of polypyrimidine tract binding proteins in major immediate-early gene expression and viral replication of human cytomegalovirus.
Human cytomegalovirus (HCMV), a member of the beta subgroup of the family Herpesviridae, causes serious health problems worldwide. HCMV gene expression in host cells is a well-defined sequential process: immediate-early (IE) gene expression, early-gene expression, DNA replication, and late-gene expression. The most abundant IE gene, major IE (MIE) gene pre-mRNA, needs to be spliced before being exported to the cytoplasm for translation. In this study, the regulation of MIE gene splicing was investigated; in so doing, we found that polypyrimidine tract binding proteins (PTBs) strongly repressed MIE gene production in cotransfection assays. In addition, we discovered that the repressive effects of PTB could be rescued by splicing factor U2AF. Taken together, the results suggest that PTBs inhibit MIE gene splicing by competing with U2AF65 for binding to the polypyrimidine tract in pre-mRNA. In intron deletion mutation assays and RNA detection experiments (reverse transcription [RT]-PCR and real-time RT-PCR), we further observed that PTBs target all the introns of the MIE gene, especially intron 2, and affect gene splicing, which was reflected in the variation in the ratio of pre-mRNA to mRNA. Using transfection assays, we demonstrated that PTB knockdown cells induce a higher degree of MIE gene splicing/expression. Consistently, HCMV can produce more viral proteins and viral particles in PTB knockdown cells after infection. We conclude that PTB inhibits HCMV replication by interfering with MIE gene splicing through competition with U2AF for binding to the polypyrimidine tract in MIE gene introns.
Cosme
Ruth S Cruz
RS
Department of Microbiology/AIDS Program, Ponce School of Medicine, 395 Zona Industrial, Reparadara-2, Ponce, Puerto Rico 00716.
Yamamura
Yasuhiro
Y
Tang
Qiyi
Q
D002460:Cell Line; D002478:Cells, Cultured; D003587:Cytomegalovirus / Q000502:physiology*; D015967:Gene Expression Regulation, Viral; D055785:Gene Knockdown Techniques; D017781:Genes, Immediate-Early; D006801:Humans; D009687:Nuclear Proteins / Q000378:metabolism; D038941:Polypyrimidine Tract-Binding Protein / Q000378:metabolism*; D011485:Protein Binding; D012322:RNA Precursors / Q000378:metabolism; D012326:RNA Splicing; D012261:Ribonucleoproteins / Q000378:metabolism; D000072668:Splicing Factor U2AF; D014779:Virus Replication
D009687:Nuclear Proteins; D012322:RNA Precursors; D012261:Ribonucleoproteins; D000072668:Splicing Factor U2AF; C000607494:U2AF2 protein, human; D038941:Polypyrimidine Tract-Binding Protein