Cell phenotype-dependent splicing reflecting differential promoter usage for EBNA transcripts in EBV-carrying cells.
Three types of virus-host cell interactions have been described in cells latently infected with EBV: EBNA 1 expression in type I Burkitt's lymphoma cell lines (BL), EBNA 1, LMP1 and 2 expression in most nasopharyngeal carcinomas (NPC) and EBNA 1-6 with LMP 1 and 2 expression in group III BL-lines as well as lymphoblastoid cell lines (LCL). Two group I BL lines that express only EBNA 1 were found to initiate their EBNA 1 mRNA transcription from a promoter in the Bam HI Q-fragment. They use a sequence at +210 bp relative to the Fp transcription initiation site in group I BL cell lines. The Fp promoter-region seems to be activated in the lytic cycle. LCLs initiate their transcription from one of several upstream sites, usually the Cp promoter or, less frequently, one of several Wp-promoters. Using RNA-reverse transcription polymerase chain reaction (RT-PCR), we have now shown that EBV carrying cells that do not express EBNA 2-6 always splice their EBNA mRNA at the Q-exon, while EBNA 2-6 positive cells use either the Cp or one of the Wp promotors. When EBNA 2-6 are downregulated by somatic cell hybridisation between EBNA 1-6 positive B-cell lines and non B-cells of hematopoetic, epithelial or fibroblastic origin that express the phenotype of the non-B cell parent, the parental usage of Cp/Wp is switched off, and the Q-exon is activated. NPC cells show the same pattern of promoter usage as the hybrids with non-B phenotype. Group III BL cells use both promoter regions. Thus, the virus can use two alternative programs, depending on the cell phenotype. The "EBNA-1 only" program is activated from the Q-promoter. In cells with an immunoblastic (LCL or BL group III) phenotype, the upstream Cp/Wp promoters generate a 100 kb. long pre-mRNA, from which all the EBNAs are spliced. As a rule, only one of the two programs is used for each phenotype, except for the BL group III cells that began as group I but subsequently developed into a more LCL-like cell. Such cells used both promoter regions, with or without activation of the lytic cycle.
Hu
L F
LF
Microbiology and Tumor Biology Center, Karolinska Institutet, Stockholm, Sweden. lifu.hu@mtc.ki.se
Chen
F
F
Altiok
E
E
Winberg
G
G
Klein
G
G
Ernberg
I
I
D000818:Animals; D001402:B-Lymphocytes / Q000821:virology*; D002273:Carcinogens; D002460:Cell Line; D020031:Epstein-Barr Virus Infections / Q000235:genetics / Q000473:pathology; D016679:Genome, Viral; D004854:Herpesvirus 4, Human / Q000737:chemistry*; D006801:Humans; D006822:Hybrid Cells; D051379:Mice; D008819:Mice, Nude; D009856:Oncogene Proteins, Viral; D010641:Phenotype; D012367:RNA, Viral / Q000235:genetics; D011956:Receptors, Cell Surface; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured; D014763:Viral Matrix Proteins / Q000235:genetics; D014764:Viral Proteins / Q000235:genetics
D002273:Carcinogens; C402640:EBNA-LP protein, Human herpesvirus 4; C037662:EBV-associated membrane antigen, Epstein-Barr virus; D009856:Oncogene Proteins, Viral; D012367:RNA, Viral; D011956:Receptors, Cell Surface; D014763:Viral Matrix Proteins; D014764:Viral Proteins