Inhibition of DNA topoisomerase I activity by 2',5'-oligoadenylates and mismatched double-stranded RNA in uninfected and HIV-1-infected H9 cells.

2',5'-Oligoadenylates (2-5As) inhibit the type I DNA topoisomerase activity both in uninfected and HIV-1-infected human T cell line H9 as well as the purified enzyme (calf thymus). Topoisomerase I activity was determined by measuring the relaxation of negatively supercoiled pBR322 DNA. Inhibition of topoisomerase I by 2-5A depends on the chain length of the oligomer and the presence of 5'-phosphate. The 5'-triphosphate of the 2-5A hexamer was most active (almost total inhibition of DNA relaxation at 10 microM concentration); the 2-5A core trimer (at 100 microM) displayed no significant effect. In crosslinking and immunoprecipitation experiments we present evidence that 2-5A (32P-labelled 2-5A derivative, ppp(A2'p)3 A[32P]pCp) is able to bind to nuclear topoisomerase I. The mismatched dsRNA, poly(I).poly(C12U) (Ampligen), exhibited a strong anti-HIV-1 activity. However, our data show that this antiviral effect is not related to topoisomerase I inhibition. On the other hand, we did observe the production of longer oligomers of 2-5A in cells treated with poly(I).poly(C12U). It remains speculative, whether the in vivo effect could be catalyzed by this activity of poly(I).poly(C12U). In addition we could show that 2-5A also inhibits topoisomerase I activity associated with isolated HIV-1 particles.