Productive human immunodeficiency virus type 1 (HIV-1) infection causes sustained NF-kappaB DNA-binding activity in chronically infected monocytic cells. A direct temporal correlation exists between HIV infection and the appearance of NF-kappaB DNA-binding activity in myelomonoblastic PLB-985 cells. To examine the molecular basis of constitutive NF-kappaB DNA-binding activity in HIV1 -infected cells, we analyzed the phosphorylation and turnover of IkappaBalpha protein, the activity of the double-stranded RNA-dependent protein kinase (PKR) and the intracellular levels of NF-kappaB subunits in the PLB-985 and U937 myeloid cell models. HIV-1 infection resulted in constitutive, low-level expression of type 1 interferon (IFN) at the mRNA level. Constitutive PKR activity was also detected in HIV-1-infected cells as a result of low-level IFN production, since the addition of anti-IFN-alpha/beta antibody to the cells decreased PKR expression. Furthermore, the analysis of IkappaBalpha turnover demonstrated an increased degradation of IkappaBalpha in HIV-1-infected cells that may account for the constitutive DNA binding activity. A dramatic increase in the intracellular levels of NF-kappaB subunits c-Rel and NF-kappaB2 p100 and a moderate increase in NF-kappaB2 p52 and RelA(p65) were detected in HIV-1-infected cells, whereas NF-kappaB1 p105/p50 levels were not altered relative to the levels in uninfected cells. We suggest that HIV-1 infection of myeloid cells induces IFN production and PKR activity, which in turn contribute to enhanced IkappaBalpha phosphorylation and subsequent degradation. Nuclear translocation of NF-kappaB subunits may ultimately increase the intracellular pool of NF-kappaB/IkappaBalpha by an autoregulatory mechanism. Enhanced turnover of IkappaBalpha and the accumulation of NF-kappaB/Rel proteins may contribute to the chronically activated state of HIV-1-infected cells.