Molecular Mechanism of Nef-Mediated Inhibition of T Cell Migration in Response to SDF-1α.

Lymphocyte trafficking comprises an intricate multistep process, in which lymphocyte surface integrins, endothelial adhesion molecules, and chemokines produced in the local microenvironment play key roles. We previously reported that HIV-1 nef inhibits T cell chemotaxis in response to the physiological ligand SDF-1αwithout altering CXCR4 expression. Here, we explore the mechanism of this effect. HIV-1 nef significantly reduced the expression of LFA-1, inhibited the adhesion of nef-expressing Jurkat T cells to the HUVEC endothelium, and reduced their transendothelial migration. To gain further insight into how nef mediated these effects, substitution or deletion mutations were introduced into the nef gene, and transwell and transendothelial migration assays were performed. Deletion of the N-terminus proximal basic-rich domain did not change the nef-mediated inhibitory effects on T cell migration, whereas removal of the myristoylation site or the proline-rich amino acid sequence motif of Nef abolished these effects. Similarly, HIV-1 nef blocked the transendothelial migration of Jurkat T cells across the HUVEC monolayer. However, the observed inhibition of transendothelial migration conferred by the wild type nef expression was significantly but not completely reduced by introduction of mutations in the myristoylation site and proline-rich motif, indicating the involvement of other regions in the nef gene. Taken together, these results demonstrate that HIV-1 nef can impair the transendothelial migration of T cells in response to SDF-1αby disturbing different steps in the process, and that the myristoylation site and/or proline-rich motif are key to this effect. These data help to establish the molecular mechanisms of nef-mediated impairment of the T cell migratory response, an essential component of host defense, and provide the basis for targeted therapeutic interventions in patients with AIDS.