Lack of 2',5'-oligoadenylate-dependent RNase expression in the human hepatoma cell line HepG2.
2',5'-adenylate oligonucleotide (2-5A)-dependent RNase and 2-5A-synthetase are two enzymes of the 2-5A system strongly implicated in the basal control of RNA decay of both interferon-treated and untreated cells. RNase is activated by a 2-5A produced by 2-5A-synthetase, both enzymes being overexpressed by type I-interferon (alpha/beta). We described here for the first time a cell line completely deficient in RNase and its mRNA, while p69 2-5A-synthetase was normally interferon alpha/beta-induced. The complete absence of this RNase in human hepatoma cells (HepG2) was shown using three different methods based on the binding of a [32P]-labeled 2-5A probe of high specific activity to its binding site. Negative Western blotting assay with a specific monoclonal antibody correlated the previous findings. RNase-specific mRNA was not detectable even after treatment of cells with 1000 units/ml of interferon alpha/beta. This is not due to a mutation of the gene because an intronless genomic DNA sequence encoding 2-5A-binding site was cloned and expressed. It is likely that the expression of 2-5A-dependent RNase was impaired at the transcriptional level while having the known IFN alpha/beta-transcriptional regulatory factors as revealed by induction of p69 2-5A-synthetase gene. This may account for a differential activation of 2-5A-dependent RNase and 2-5A-synthetase genes by type I-interferon, and suggests that other members of regulatory transcription factors, different from IRF-1 and STAT proteins, may participate in two different interferon alpha/beta signaling pathways.
Tnani
M
M
UMR 5539 Centre National de la Recherche Scientifique, Université de Montpellier II, France.
Bayard
B A
BA
D015088:2',5'-Oligoadenylate Synthetase / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D006528:Carcinoma, Hepatocellular / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000187:drug effects / Q000378:metabolism; D004722:Endoribonucleases / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism*; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D050856:Interferon Regulatory Factor-1; D050836:Interferon Regulatory Factor-2; D016898:Interferon-alpha / Q000378:metabolism / Q000494:pharmacology*; D016899:Interferon-beta / Q000378:metabolism / Q000494:pharmacology; D010750:Phosphoproteins / Q000096:biosynthesis / Q000187:drug effects; D012333:RNA, Messenger; D012097:Repressor Proteins; D015398:Signal Transduction; D014157:Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured
D004268:DNA-Binding Proteins; C494257:IRF1 protein, human; C494229:IRF2 protein, human; D050856:Interferon Regulatory Factor-1; D050836:Interferon Regulatory Factor-2; D016898:Interferon-alpha; D010750:Phosphoproteins; D012333:RNA, Messenger; D012097:Repressor Proteins; D014157:Transcription Factors; D016899:Interferon-beta; D015088:2',5'-Oligoadenylate Synthetase; D004722:Endoribonucleases; C031956:2-5A-dependent ribonuclease