Response to cAMP levels of the Epstein-Barr virus EBNA2-inducible LMP1 oncogene and EBNA2 inhibition of a PP1-like activity.
The expression of the Epstein-Barr virus LMP1 oncogene is regulated by viral and non-viral factors in a tissue dependent fashion. The virus encoded transcription factor EBNA2 induces its expression in human B-cells. However, this induction also requires the contribution of cellular and/or other viral factors. In nasopharyngeal carcinoma cells and in cells from Hodgkin's lymphoma, LMP1 gene transcription is independent of viral products. Here we show that the effect of a factor binding to a cAMP responsive-like element (CRE) in the LMP1 gene transcription regulatory sequence (LRS) is essential for efficient promoter activity in the DG75 B-cell line and that elevation of cAMP levels in the cells induces LRS-derived CAT activity in a CRE dependent fashion. Incubation of two EBV-immortalized B-cell lines expressing endogenous EBNA2A with 8-Br cAMP increased the levels of the latency associated 66 kDa LMP1 within 2 h. Interestingly, LMP1 expression in DG75 cells conferred resistance to the inhibitory effect of 8-Br cAMP on cell proliferation. The protein phosphatase 1 and 2A (PP1 and PP2A, respectively) inhibitor okadaic acid also stimulated LRS-CAT activity in DG75 cells. EBNA2A from an EBV-immortalized B-cell line co-immunopurified with a PP1-like protein. An EBNA2A fragment spanning residues 324-436 fused to the GST protein specifically rescued a PP1/PP2A-like component from DG75 cell extracts. This GST-EBNA2A fusion product inhibited a PP1-like activity in nuclear extracts from these cells.
Fåhraeus
R
R
Department of Medical Biochemistry, Göteborg University, Gothenburg, Sweden.
Palmqvist
L
L
Nerdstedt
A
A
Farzad
S
S
Rymo
L
L
Laín
S
S
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000956:Antigens, Viral / Q000235:genetics* / Q000378:metabolism*; D001402:B-Lymphocytes / Q000378:metabolism / Q000821:virology; D001483:Base Sequence; D002051:Burkitt Lymphoma / Q000378:metabolism / Q000821:virology; D002455:Cell Division; D002467:Cell Nucleus / Q000378:metabolism; D000242:Cyclic AMP / Q000494:pharmacology*; D019309:Epstein-Barr Virus Nuclear Antigens; D004988:Ethers, Cyclic / Q000494:pharmacology; D004854:Herpesvirus 4, Human / Q000187:drug effects / Q000235:genetics*; D006801:Humans; D008969:Molecular Sequence Data; D019319:Okadaic Acid; D009857:Oncogenes / Q000235:genetics*; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D054645:Protein Phosphatase 1; D012045:Regulatory Sequences, Nucleic Acid / Q000235:genetics; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured; D014763:Viral Matrix Proteins / Q000235:genetics*; D017735:Virus Latency / Q000235:genetics
D000956:Antigens, Viral; C037662:EBV-associated membrane antigen, Epstein-Barr virus; D019309:Epstein-Barr Virus Nuclear Antigens; D004988:Ethers, Cyclic; D014763:Viral Matrix Proteins; D019319:Okadaic Acid; D015124:8-Bromo Cyclic Adenosine Monophosphate; D000242:Cyclic AMP; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1