Hydroxyurea inhibits the transactivation of the HIV-long-terminal repeat (LTR) promoter

HIV-1 gene expression is regulated by the promoter/enhancer located within the U3 region of the proviral 5' LTR that contains multiple potential cis-a cting regulatory sites. Here we describe that the inhibitor of the cellular ribonucleoside reductase, hydroxyurea (HU), inhibited phorbol myristate ac etate- or tumour necrosis factor-alpha-induced HIV-1-LTR transactivation in both lymphoid and non-lymphoid cells in a dose-dependent manner within the first 6 h of treatment, with a 50% inhibitory concentration of 0.5 mm. Thi s inhibition was found to be specific for the HIV-1-LTR since transactivati on of either an AP-1-dependent promoter or the CD69 gene promoter was not a ffected by the presence of HU. Moreover, gel-shift assays in 5.1 cells show ed that HU prevented the binding of the NF-kappa B to the kappa B sites loc ated in the HIV-1-LTR region, but it did not affect the binding of both the AP-1 and the Sp-1 transcription factors. By Western blots and cell cycle a nalyses we detected that HU induced a rapid dephosphorylation of the pRB, t he product of the retinoblastoma tumour suppressor gene, and the cell cycle arrest was evident after 24 h of treatment. Thus, HU inhibits HIV-1 promot er activity by a novel pathway that implies an inhibition of the NF-kappa B binding to the LTR promoter. The present study suggests that HU may be use ful as a potential therapeutic approach for inhibition of HIV-1 replication through different pathways.