HIV-1 Nef Activates STAT3 in Primary Human Monocyte/Macrophages through the Release of Soluble Factors: Involvement of Nef Domains Interacting with the Cell Endocytotic Machinery

Increasing evidence indicates that the expression of the human immunodeficiency virus-1 (HIV-1) Nef protein significantly influences the activation state of the host cell. Here we report that Nef specifically activates STAT3 in primary human monocyte-derived macrophages (MDM). This was demonstrated by both single-cycle infection experiments driven by Vesicular Stomatitis virus glycoprotein (VSV-G) pseudotyped HIV-1 and treatment with exogenous recombinant Nef. The analysis of the effects of Nef mutants revealed that domains of the C-terminal flexible loop interacting with the cell endocytotic machinery are involved in the STAT3 activation. In particular, our data suggest that the Nef-dependent STAT3 activation relies on the targeting of Nef to the late endosome/lysosome compartment. In addition, we found that Nef activates STAT3 through a mechanism mediated by the release of soluble factor(s), including MIP-1alpha, that requires de novo protein synthesis but appears independent from the activation of src tyrosine kinases. The results presented here support the idea that the first intervention of Nef in the intracellular signaling of monocyte-macrophages could generate, by means of the release of soluble factor(s), a secondary wave of activation that could be of a potential pathogenetic significance.