FIG 1.

HIV-1 induces USP18 and USP18 expression enhances HIV-1 infection in PMA-differentiated THP-1 cells. (A) Immunoblot analysis of basal, IFN-β-induced, and stably expressing USP18 levels in THP-1 cells. (B) PMA-differentiated THP-1 cells were mock transduced (media) or HIV-1 transduced with or without copackaged VPX. At 72 h postransduction, cells were harvested and immunoblotted for endogenous total and phosphorylated SAMHD1, USP18, and GAPDH as a loading control. THP-1.USP18 and THP-1.Control cells were treated with different concentrations of IFN-α (C) and IFN-β (D) for 4 h and subsequently transduced with single-round HIV-1 luciferase reporter virus (E). At 72 h postransduction, the luciferase activity was measured. (F) In a related experiment, these cells were PMA differentiated for 48 h and subsequently transduced with HIV-1 luciferase reporter virus with or without the copackaged VPX produced in panel E, which had the ability to deplete SAMHD1. The same experiment was reproduced in the presence of different concentrations of IFN-α (G) and IFN-β (H). Mean differences of three replicates for each group in a single experiment was analyzed and compared between the groups by using a Student t test, with results expressed as means ± the SD. A P value of <0.05 was considered statistically significant (*). The higher the number of asterisks, the lower the P value. Each panel is representative of at least three independent experiments.