THE RAS-RAF PATHWAY IS ACTIVATED IN HUMAN IMMUNODEFICIENCY VIRUS-INFECTED MONOCYTES AND PARTICIPATES IN THE ACTIVATION OF NF-KAPPA-B

Persistent human immunodeficiency virus (HIV) infection of human monoc ytes and macrophages increases I kappa B alpha degradation, resulting in the activation of NF-kappa B, a key transcription factor in the reg ulation of the HIV long terminal repeat. The signal transduction pathw ays leading to NF-kappa B activation in cells of the monocytic lineage , especially those regulated by HIV infection, and their relevance in regulating viral persistence remain unknown. Both p21(ras) and its dow nstream Raf-1 kinase participate in the transduction of signals initia ted from a variety of cell surface receptors aid in the regulation of transcription factors. We have studied whether the Ras-Raf pathway is functional and participates in HIV-mediated KF-kappa B activation in m onocytic cells. Constitutively active p21(ras) (v-H-Ras) activates NF- kappa B-dependent transcription and induces the nuclear translocation of a bona fide p65/p50 heterodimer by targeting I kappa B alpha. In ad dition, the constitutively active form of Raf (Raf BXB) also increases the KF-kappa B-dependent transcriptional activity. Because of the sim ilarity between HIV and Ras-Raf-induced NF-kappa B activation in monoc ytic cells, we nest tested whether HIV-induced NF-kappa B activation w as mediated by the Ras-Raf signal transduction pathway. Negative domin ant forms of both Ras (Ras N17) and Raf (Raf 301) decreased the HIV- b ut not lipopolysaccharide-dependent NF-kappa B activation in U937 cell s. Moreover, Raf-1 kinase activity was greater in HIV-infected than un infected monocytic cells in in vitro kinase assays. Altogether, these results indicate that the Ras-Raf pathway is upregulated in HIV monocy tic cells and participates in the virus-induced activation of NF-kappa B.