Activation of the PAK-related kinase by human immunodeficiency virus type 1 Nef in primary human peripheral blood lymphocytes and macrophages leads to phosphorylation of a PIX-p95 complex

Human immunodeficiency virus type 1 (HIV-1) Nef enhances virus replication in both primary T lymphocytes and monocyte derived macrophages. This enhanc ement phenotype has been linked to the ability of Nef to modulate the activ ity of cellular kinases. We find that despite the reported high-affinity in teraction between Nef and the Src kinase Hck in vitro, a Nef-Hck interactio n in the context of HN-l-infected primary macrophages is not detectable. Ho wever, Nef binding and activation of the PAK-related kinase and phosphoryla tion of its substrate could be readily detected in both infected primary T lymphocytes and macrophages. Furthermore, we show that this substrate is a complex composed of the recently characterized PAK interacting partner PIX (PAK-interacting guanine nucleotide exchange factor) and its tightly associ ated p95 protein. PAK and PIX-p95 appear to be differentially activated and phosphorylated depending on the intracellular environment in which nef is expressed. These results identify the PLY-p95 complex as a novel effector o f Nef in primary cells and suggest that the regulation of the PAK signaling pathway may differ in T cells and macrophages.