Identification of 2'-phosphodiesterase, which plays a role in the 2-5A system regulated by interferon.

The 2-5A system is one of the major pathways for antiviral and antitumor functions that can be induced by interferons (IFNs). The 2-5A system is modulated by 5'-triphosphorylated, 2',5'-phosphodiester-linked oligoadenylates (2-5A), which are synthesized by 2',5'-oligoadenylate synthetases (2',5'-OASs), inactivated by 5'-phosphatase and completely degraded by 2'-phosphodiesterase (2'-PDE). Generated 2-5A activates 2-5A-dependent endoribonuclease, RNase L, which induces RNA degradation in cells and finally apoptosis. Although 2',5'-OASs and RNase L have been molecularly cloned and studied well, the identification of 2'-PDE has remained elusive. Here, we describe the first identification of 2'-PDE, the third key enzyme of the 2-5A system. We found a putative 2'-PDE band on SDS-PAGE by successive six-step chromatographies from ammonium sulfate precipitates of bovine liver and identified a partial amino acid sequence of the human 2'-PDE by mass spectrometry. Based on the full-length sequence of the human 2'-PDE obtained by in silico expressed sequence tag assembly, the gene was cloned by reverse transcription-PCR. The recombinant human 2'-PDE expressed in mammalian cells certainly cleaved the 2',5'-phosphodiester bond of 2-5A trimer and 2-5A analogs. Because no sequences with high homology to this human 2'-PDE were found, the human 2'-PDE was considered to be a unique enzyme without isoform. Suppression of 2'-PDE by a small interfering RNA and a 2'-PDE inhibitor resulted in significant reduction of viral replication, whereas overexpression of 2'-PDE protected cells from IFN-induced antiproliferative activity. These observations identify 2'-PDE as a key regulator of the 2-5A system and as a potential novel target for antiviral and antitumor treatments.

Bovine 5-oxo-L-prolinase: simple assay method, purification, cDNA cloning, and detection of mRNA in the coronary artery.

RS-7897 is a novel antianginal nitrate containing an L-2-oxothiazolidine-4-carboxylic acid (OTCA) and unlike other organic nitrates does not induce nitrate tolerance. OTCA is known to be converted to L-cysteine (L-Cys) by rat 5-oxo-prolinase (5-OPase) and was detected in the plasma of RS-7897-treated dogs. Nitrate tolerance is considered to develop mainly through sulfhydryl depletion. We hypothesized that RS-7897-derived OTCA was converted into L-Cys by 5-OPase and supplied sulfhydryl groups in vascular smooth muscle cells, the targets of the nitrate. As the initial step for clarifying the presumed role of 5-OPase in RS-7897 metabolism, we established a non-radiochemical assay method highly specific for 5-OPase. Using this assay method, we purified 5-OPase from bovine kidney cytosol until homogeneous results were obtained in sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The catalytic activity of bovine 5-OPase to convert OTCA to L-Cys was confirmed, as was the case for the rat enzyme. Then the cDNA encoding bovine 5-OPase was cloned. The deduced amino acid sequence revealed that bovine 5-OPase was highly homologous to rat 5-OPase. Based on the bovine cDNA sequence, oligonucleotide primers were synthesized and used for RT-PCR. 5-OPase mRNA was significantly detected in the RT-PCR product of the bovine coronary artery, a major target organ of RS-7897. These results suggest that OTCA may be converted to L-Cys by 5-OPase in the mammalian coronary artery when treated with RS-7897, and thus generated L-Cys may reduce sulfhydryl depletion and contribute to the prevention of the development of nitrate tolerance.