The gp120 Envelope Glycoprotein of HIV-1 Triggers Macropinocytosis in Primary CD4+ T Cells to Promote HIV-1 Infection

Macropinocytosis is a large-scale, actin-driven, fluid-phase form of endocytosis that can be exploited by HIV-1 for entry into primary CD4+ T cells. Herein, we show that HIV-1 actively induces macropinocytosis in resting and activated primary CD4+ T cells. HIV-1-induced T cell macropinocytosis is triggered by the interaction of soluble gp120 Env with cell surface CD4, is clathrin-independent and actin-dependent, and does not require CXCR4 or any other known HIV-1 coreceptors. Notably, Env-induced macropinocytosis requires calcium-independent phospholipase A2 (iPLA2) activity, identifying a role for a lipid-signaling axis downstream of Env-CD4 engagement. Across a gp120 panel, multiple HIV-1 clade B gp120 Envs can induce CD4+ T cell macropinocytosis. However, the magnitude of macropinocytosis does not correlate with CD4-binding strength alone and instead aligns with Env-driven changes in CD4 epitope exposure in CD4 domains distal to the Env-binding domain. Importantly, inhibitors of Env-induced macropinocytosis block HIV-1 infection of resting CD4+ T cells. Therefore, Env-induced macropinocytosis is a functionally important mechanism that promotes HIV-1 infection of this cell type.