title: Interferon induction by poly(inosinic acid).poly(cytidylic acid) segmented by spin-labels.
abstract: Poly(inosinic acid).poly(cytidylic acid) [(I)n.(C)n] duplexes of which the (C)n strand was modified to various degrees chemically or enzymatically with nitroxide radicals (spin-labels) were evaluated for interferon-inducing activity. Upon annealing of the chemically modified (C)n, (1C,Cx)n (X = 1000 or 16), with (I)n, the interferon-inducing activity was similar to that of (I)n.(C)n in PRK cell cultures. However, to overcome hydrolysis of the spin-label linkage in (1C,Cx)n, and enzymatic approach was taken to synthesize (1S(4)U,Cx)n copolymers with x = 100, 38, 16, and 8. The (1s(4)U,Cx)n copolymers were chemically stable, and upon annealing with (I)n the correlation time of the nitroxide moiety in (I)n. (1s(4)U,Cx)n was determined. A comparison of this correlation time with that measured for (RUGT,U100)n.(A)n, which contains the nitroxide moiety in position 5 of the U moiety, suggests that the 1s(4)U residue is in a nonintrahelical conformation and partitions the duplex into double-helical segments of varying size. The interferon-inducing activity of (I)n. (1s(4)U,Cx)n was evaluated in primary rabbit kidney, human skin fibroblast (strain VGS), and mouse L-929 cell cultures as well as in rabbits. The 1s(4)U residue did not cause a significant change in the interferon induction as compared to (I)n.(C)n in most systems tested unless x less than 16. These findings indicate that double-helical segments of approximately 16 base pairs partitioned by nonintrahelical 1s(4)U residues suffice to trigger the interferon response in all systems studied.
mesh_terms: D000818:Animals; D002460:Cell Line; D004720:Endonucleases / Q000494:pharmacology; D006801:Humans; D007372:Interferons / Q000096:biosynthesis*; D007668:Kidney; D007700:Kinetics; D007739:L Cells / Q000187:drug effects; D051379:Mice; D011070:Poly I-C / Q000494:pharmacology*; D011817:Rabbits; D012259:Ribonuclease, Pancreatic; D012260:Ribonucleases / Q000494:pharmacology; D012867:Skin; D013113:Spin Labels / Q000494:pharmacology*; D013696:Temperature
chemical_list: D013113:Spin Labels; D007372:Interferons; D004720:Endonucleases; D012260:Ribonucleases; D012259:Ribonuclease, Pancreatic; D011070:Poly I-C