Inhibition of CD3/CD28-mediated activation of the MEK/ERK signaling pathway represses replication of X4 but not R5 human immunodeficiency virus type 1 in peripheral blood CD4+ T lymphocytes

Binding of human immunodeficiency virus type 1 (HIV-1) to CD4 receptors ind uces multiple cellular signaling pathways, including the MEK/ERK cascade. W hile the interaction of X4 HIV-1 with CXCR4 does not seem to activate this pathway, viruses using CCR5 for entry efficiently activate MEK/ERK kinases (W. Popik, J. E. Hesselgesser, and P. M. Pitha, J. Virol. 72:6406-6413, 199 8; W. Popik and P. M. Pitha, Virology 252:210-217, 1998). Since the importa nce of MEK/ERK in the initial steps of viral replication is poorly understo od, we have examined the role of MEK/ERK signaling in the CD3- and CD28 (CD 3/CD28)-mediated activation of HIV-1 replication in resting peripheral bloo d CD4(+) T lymphocytes infected with X4 or R5 HIV-1. We have found that the MEK/ERK inhibitor U0126 selectively inhibited CD3/CD28-stimulated replicat ion of X4 HIV-1, while it did not affect the replication of R5 HIV-1. Inhib ition of the CD3/CD28-stimulated MEK/ERK pathway did not affect the formati on of the early proviral transcripts in cells infected with either X4 or R5 HIV-1, indicating that virus reverse transcription is not affected in the absence of MEK/ERK signaling. In contrast, the levels of nuclear provirus i n cells infected with X4 HIV-1, detected by the formation of circular provi ral DNA, was significantly lower in cells stimulated in the presence of MEK /ERK inhibitor than in the absence of the inhibitor. However, in cells infe cted with R5 HIV-1, the inhibition of the MEK/ERK pathway did not affect nu clear localization of the proviral DNA, These data suggest that the nuclear import of X4, but not R5, HIV-1 is dependent on a CD3/CD28-stimulated MEK/ ERK pathway.