Lack of 2′,5′-oligoadenylate-dependent RNase expression in the human hepatoma cell line HepG2

• Published in: Biochimica et biophysica acta 1998-03, Vol.1402 (2), p.139-150
• Main Authors: Tnani, Mehdi, Bayard, Bernard A
• Format: Article
• Language: English
• Subjects: 2',5'-Oligoadenylate Synthetase - drug effects; 2',5'-Oligoadenylate Synthetase - genetics; 2',5'-Oligoadenylate Synthetase - metabolism; 2′,5′-Oligoadenylate; 2′,5′-Oligoadenylate synthetase; 2′,5′-Oligoadenylate-dependent RNAase; Binding Sites; Carcinoma, Hepatocellular - drug therapy; Carcinoma, Hepatocellular - genetics; Carcinoma, Hepatocellular - metabolism; DNA-Binding Proteins - biosynthesis; DNA-Binding Proteins - drug effects; DNA-Binding Proteins - metabolism; Endoribonucleases - drug effects; Endoribonucleases - genetics; Endoribonucleases - metabolism; Gene Expression Regulation, Neoplastic; Humans; Interferon; Interferon Regulatory Factor-1; Interferon Regulatory Factor-2; Interferon-alpha - metabolism; Interferon-alpha - pharmacology; Interferon-beta - metabolism; Interferon-beta - pharmacology; Phosphoproteins - biosynthesis; Phosphoproteins - drug effects; Repressor Proteins; RNA, Messenger; Signal Transduction; Transcription Factors - metabolism; Transcription, Genetic; Tumor Cells, Cultured
• ISSN: 0167-4889; 0006-3002; 1879-2596
• DOI: 10.1016/S0167-4889(97)00158-4

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 ( α/ β). 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 α/ β-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 α/ β. 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 α/ β-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 α/ β signaling pathways.