Dephosphorylation of the HIV-1 restriction factor SAMHD1 is mediated by PP2A-B55 alpha holoenzymes during mitotic exit

SAMHD1 is a critical restriction factor for HIV-1 in non-cycling cells and its antiviral activity is regulated by T592 phosphorylation. Here, we show that SAMHD1 dephosphorylation at T592 is controlled during the cell cycle, occurring during M/G(1) transition in proliferating cells. Using several complementary proteomics and biochemical approaches, we identify the phosphatase PP2A-B55a responsible for rendering SAMHD1 antivirally active. SAMHD1 is specifically targeted by PP2A-B55a holoenzymes during mitotic exit, in line with observations that PP2A-B55a is a key mitotic exit phosphatase in mammalian cells. Strikingly, as HeLa or activated primary CD4(+) T cells enter the G1 phase, pronounced reduction of RT products is observed upon HIV-1 infection dependent on the presence of dephosphorylated SAMHD1. Moreover, PP2A controls SAMHD1 pT592 level in non-cycling monocyte-derived macrophages (MDMs). Thus, the PP2A-B55a holoenzyme is a key regulator to switch on the antiviral activity of SAMHD1.