p21 (CDKN1A) Is the Major Driver of Sulforaphane-Mediated Reduction in SAMHD1 T592 Phosphorylation in Macrophages

Sulforaphane (SFN), a natural compound found in cruciferous vegetables, mobilizes the transcription factor NRF2 to protect macrophages from HIV-1. SFN/NRF2 exerts this protective effect by promoting the reduced phosphorylation of the antiviral protein SAMHD1. Phosphorylation at threonine 592 (T592) potently inhibits the capacity of SAMHD1 to restrict HIV-1. How SFN, and other NRF2 mobilizers reduce SAMHD1 T592 phosphorylation is unclear. p21 (CDKN1A) is an NRF2-responsive protein that accumulates in primary macrophages after SFN treatment. p21 blocks SAMHD1 T592 phosphorylation through the inhibition of several cyclin-dependent kinases. We therefore hypothesized that SFN acts through p21 to reduce SAMHD1 T592 phosphorylation in macrophages. Here, we use RNAi, CRISPR-Cas9, and pharmacological inhibition to deplete or delete p21 in macrophages and demonstrate that p21 is necessary for SFN to efficiently reduce SAMHD1 T592 phosphorylation and restrict HIV-1 transduction.