IFN-inducible Human Phospholipid Scramblase 1 (PLSCR1) Protein Restricts HIV-1 Infection by Inhibiting Membrane Fusion

Human phospholipid scramblase 1 (PLSCR1) is an interferon-stimulated gene (ISG) that inhibits viral infections through various mechanisms. Here, we identify PLSCR1 as a host restriction factor that inhibits HIV-1 entry by impairing membrane fusion mediated by the envelope glycoprotein (Env). Using multiple cell types including the human SupT1 T cell line and purified CD4 ⁺ T cells, we demonstrate that PLSCR1 inhibits the replication of HIV-1 with diverse tropisms and subtypes, as well as HIV-2 and SIV. Mechanistically, we find that PLSCR1 blocks viral entry and cell-to-cell transmission by restricting HIV-1 virion-cell and cell-cell fusion without affecting CD4 or CXCR4 expression or virus binding to the cell surface. Notably, PLSCR1-mediated restriction of viral entry is independent of type I interferon signaling. Collectively, these findings establish PLSCR1 as a broad-spectrum lentiviral restriction factor that acts at the membrane fusion stage, thereby expanding our understanding of ISG-mediated antiviral defense.